U.S. patent application number 14/419658 was filed with the patent office on 2015-07-23 for treating of catalyst support.
The applicant listed for this patent is Velocys Techmologies Limited. Invention is credited to Frank Daly, Laura Richard.
Application Number | 20150202613 14/419658 |
Document ID | / |
Family ID | 46935066 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150202613 |
Kind Code |
A1 |
Richard; Laura ; et
al. |
July 23, 2015 |
TREATING OF CATALYST SUPPORT
Abstract
A method for the preparation of a modified catalyst support
comprising: (a) treating a catalyst support material with an
aqueous solution or dispersion comprising one or more zirconium
metal sources, chromium metal sources, manganese metal sources and
aluminium metal sources, and one or more polar organic compounds;
and (b) drying the treated support, and (c) optionally calcining
the treated support. Also provided are catalyst support materials
obtainable by the methods, and catalysts prepared from such
supports.
Inventors: |
Richard; Laura; (Abingdon,
GB) ; Daly; Frank; (Waldoboro, ME) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Velocys Techmologies Limited |
Abingdon, Oxfordshire |
|
GB |
|
|
Family ID: |
46935066 |
Appl. No.: |
14/419658 |
Filed: |
August 7, 2013 |
PCT Filed: |
August 7, 2013 |
PCT NO: |
PCT/GB2013/052103 |
371 Date: |
February 5, 2015 |
Current U.S.
Class: |
518/712 ;
422/211; 502/300; 502/325; 502/439; 518/714; 518/715 |
Current CPC
Class: |
B01J 37/0203 20130101;
B01J 35/1042 20130101; B01J 37/18 20130101; B01J 23/8986 20130101;
B01J 19/0093 20130101; B01J 21/08 20130101; B01J 37/16 20130101;
B01J 35/1038 20130101; B01J 2219/00873 20130101; B01J 23/26
20130101; B01J 37/0213 20130101; B01J 37/088 20130101; B01J 37/0207
20130101; B01J 35/0053 20130101; B01J 37/0205 20130101; B01J
35/1019 20130101; B01J 23/34 20130101; B01J 2219/00781 20130101;
B01J 35/006 20130101; C10G 2/33 20130101; B01J 8/00 20130101; B01J
35/1061 20130101; B01J 2219/00835 20130101; C07C 1/043 20130101;
C10G 2/34 20130101; C10G 2/333 20130101; B01J 2208/00796 20130101;
B01J 23/8993 20130101; B01J 23/8913 20130101; B01J 37/08 20130101;
B01J 35/0066 20130101; B01J 35/1014 20130101; B01J 35/0046
20130101 |
International
Class: |
B01J 37/08 20060101
B01J037/08; B01J 21/08 20060101 B01J021/08; B01J 23/34 20060101
B01J023/34; C10G 2/00 20060101 C10G002/00; B01J 23/89 20060101
B01J023/89; B01J 37/16 20060101 B01J037/16; B01J 19/00 20060101
B01J019/00; B01J 8/00 20060101 B01J008/00; B01J 37/02 20060101
B01J037/02; B01J 23/26 20060101 B01J023/26 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2012 |
GB |
1214122.2 |
Claims
1. A method for the preparation of a modified catalyst support
comprising: a) treating a catalyst support material with an aqueous
solution or dispersion comprising a metal source and one or more
polar organic compounds, wherein the metal source comprises one or
more of a zirconium metal source, a chromium metal source, a
manganese metal source and an aluminium metal source; and b) drying
the treated support; c) and optionally calcining the treated
support.
2. The method of claim 1, wherein the metal source comprises two or
more different metals.
3. The method of claim 1, further comprising: d) treating the
modified catalyst support obtained in step b), or optionally
obtained in step c), with a further aqueous solution or dispersion
comprising a metal source and one or more polar organic compounds,
wherein the metal source comprises a different metal to the metal
in the metal source comprised in step a); and e) drying the treated
support of step d); f) and optionally calcining the treated
support.
4. The method of claim 1, wherein prior to step a) the catalyst
support material undergoes steps comprising: d) treating the
catalyst support with a further aqueous solution or dispersion
comprising a metal source and one or more polar organic compounds,
wherein the metal source comprises a different metal to the metal
in the metal source comprised in step a); and e) drying the treated
support of step d); f) and optionally calcining the treated
support.
5. The method of claim 3, wherein the metal source in the further
aqueous solution or dispersion used in step d) comprises one or
more of a zirconium metal source, a manganese metal source, a
chromium metal source, an aluminium metal source or a titanium
metal source.
6. The method of claim 1, wherein the method of treating is
impregnating.
7. The method of claim 1, wherein the metal source in step a)
comprises one or both of a zirconium metal source and a chromium
metal source.
8. The method of claim 1, wherein the metal source in step a)
comprises a zirconium metal source.
9. The method of claim 1, wherein the metal source in step a)
comprises a zirconium metal source and a titanium metal source.
10. The method of claim 1, wherein the zirconium metal source in
step a) is zirconium dinitrate oxide hydrate.
11. The method of claim 1, wherein the metal source in step a)
comprises a chromium metal source.
12. The method of claim 11, wherein the chromium metal source in
step a) is chromium (III) nitrate nonahydrate.
13. The method of claim 1, wherein the metal source in step a)
comprises a manganese metal source.
14. The method of claim 13, wherein the manganese metal source is
manganese (II) nitrate tetrahydrate.
15. The method of claim 1, wherein the metal source in step a)
comprises an aluminium metal source.
16. The method of claim 15, wherein the aluminium metal source is
aluminium nitrate.
17. The method of claim 1, wherein the polar organic compound in
step a) is a carboxylic acid.
18. The method of claim 17, wherein the carboxylic acid is citric
acid.
19. The method of claim 17, wherein the carboxylic acid is lactic
acid.
20. The method of claim 1, wherein the polar organic compound in
step d) is a carboxylic acid.
21. The method of claim 20, wherein the carboxylic acid is citric
acid.
22. The method of claim 20, wherein the carboxylic acid is lactic
acid.
23. The method of claim 1, wherein the catalyst support material is
a refractory oxide.
24. The method of claim 23, wherein the refractory oxide is
silica.
25. The method of claim 1, wherein the modified catalyst support is
a modified Fischer-Tropsch catalyst support.
26. A modified catalyst support obtainable by the method of claim
1.
27. A method for preparing a catalyst precursor comprising: a.
depositing a solution or suspension comprising at least one
catalyst metal precursor and a complexing/reducing agent onto the
modified catalyst support of claim 26; b. optionally drying the
modified catalyst support onto which the solution or suspension has
been deposited; and c. calcining the modified catalyst support onto
which the solution or suspension has been deposited.
28. The method of claim 27, wherein the calcination is carried out
in an oxygen-containing atmosphere.
29. The method of claim 27, wherein the complexing/reducing agent
comprises one or more carboxylic acids.
30. The method of claim 27, wherein the catalyst metal precursor is
a cobalt-containing precursor.
31. The method of claim 30, wherein the cobalt-containing precursor
is cobalt nitrate.
32. A catalyst precursor obtainable by the method of claim 27.
33. A catalyst precursor comprising the modified catalyst support
according to claim 26.
34. A catalyst obtained by activation of the catalyst precursor of
claim 32.
35. A microchannel reactor comprising a catalyst according to claim
34.
36. A Fischer-Tropsch catalyst comprising the modified catalyst
support of claim 26.
37. A method for conducting a Fischer-Tropsch reaction comprising
catalyzing reactants in the presence of a catalyst comprising the
modified catalyst support of claim 26.
38. The method according to claim 37, wherein the Fischer-Tropsch
reaction is carried out in a microchannel reactor.
39. A method for making a Fischer-Tropsch catalyst comprising
activting the catalyst precursor of claim 32.
40. A method for conducting a Fischer-Tropsch reaction comprising
catalyzing reactants in the presence of the catalyst of claim
34.
41. The method according to claim 40, wherein the Fischer-Tropsch
reaction is carried out in a microchannel reactor.
42. A method of conducting a Fischer Tropsch reaction comprising
using the catalyst of claim 34 in a microchannel reactor, in which
the performance of the catalyst is substantially maintained over a
reaction period of about 5000 hours or more without regeneration of
the catalyst, such that the contact time is less than 500
milliseconds, the CO conversion is greater than 50% and the methane
selectivity is less than 15%.
43. The method of claim 42, wherein the CO conversion is greater
than 60%.
44. The method of claim 42, wherein the methane selectivity is less
than 10%.
45. A method of conducting a Fischer Tropsch reaction comprising
using the catalyst of claim 34 in a microchannel reactor in a
temperature range of from about 180.degree. C. to about 230.degree.
C., in which the deactivation rate of the catalyst measured as
percent loss of CO conversion per day is 0.29% or less over a
reaction period of about 500 hours or more.
46. The method of claim 42, wherein the reaction period is about
8000 hours or more.
47. The method of claim 42, wherein the microchannel reactor
comprises one or more heat exchange channels adjacent to and/or in
thermal contact with one or more process microchannels.
48. The method of claim 42, wherein the microchannel reactor
comprises process microchannels and the cooling of process
microchannels during the Fischer Tropsch reaction is such that the
temperature of a reactant composition at the entrance to the
process microchannels is within about 200.degree. C. of the
temperature of a product at the exit of the process microchannels.
Description
INTRODUCTORY PARAGRAPH
[0001] The present invention relates to a method for the
preparation of a modified catalyst support and the catalyst
supports formed using this method. The present invention also
relates to catalyst precursors and catalysts formed on the modified
catalyst support.
[0002] The supports, precursors and catalysts of the present
invention are particularly suitable for use in Fischer-Tropsch
reactions.
BACKGROUND
[0003] All documents cited herein are incorporated by reference in
their entirety.
[0004] The modification of catalyst supports has conventionally
been carried out using organic solvents, as described in, for
example, Bouh et al., J. Am. Chem. Soc, 121 (1999) 7201, Bu et al.,
Advanced Materials Research, 194 (2011) 1807 and US patent
application US 2010/0024874 A1. In the modern era, there is a
continual push towards more environmentally friendly, or "greener",
technologies. This push has caused considerable interest in
water-based processes in the catalyst manufacturing industry.
Furthermore, the use of aqueous methods, compared to non-aqueous
methods, often results in a lowering of manufacturing costs.
[0005] Therefore, there is a need for further aqueous methods for
the preparation of modified catalyst supports.
[0006] U.S. Pat. No. 7,510,994 discloses a method of loading an
oxide of titanium onto a support in film form in an amount of from
0.5 to 10% through impregnation with an aqueous solution containing
compounds which act as titanium sources.
[0007] Jeung et al., J. Chem. Soc. Faraday Trans., 91 (1995) 953
discloses modifying silica with chromium using a standard incipient
wetness method. Oh et al., Powder Tech., 204 (2010) 154 discloses
modifying silica with manganese using a standard incipient wetness
method. Meijers et al., Applied Catalysis, 70 (1991) discloses
impregnating a support with zirconium using an alkoxide method.
[0008] An object of the present invention is to provide an improved
method for the preparation of a modified catalyst support.
[0009] A further object of the present invention is to provide
improved modified catalyst supports, catalyst precursors and
catalysts.
STATEMENT OF INVENTION
[0010] The present invention provides a method for the preparation
of a modified catalyst support comprising (a) treating a catalyst
support material with an aqueous solution or dispersion comprising
a metal source and one or more polar organic compounds, wherein the
metal source comprises one or more of a zirconium metal source, a
chromium metal source, a manganese metal source and an aluminium
metal source, and (b) drying the treated support and (c) optionally
calcining the treated support.
[0011] The aqueous solution or dispersion in step (a) may comprise
sources of two or more different metals. Preferably, although a
first metal source is selected from a zirconium metal source, a
chromium metal source, a manganese metal source and an aluminium
metal source, the second or subsequent metal source may be selected
from a zirconium metal source, a manganese metal source, a chromium
metal source, an aluminium metal source and a titanium metal source
as long as the metal in the second metal source is different to the
metal in the first metal source. In this way, the catalyst support
material may undergo simultaneous modification by at least two
different metals.
[0012] In any of the methods described herein, there may be a
further step (d) of treating the modified catalyst support with a
further aqueous solution or dispersion comprising a metal source
and one or more polar organic compounds, wherein the metal source
comprises a different metal to the metal in the metal source
comprised in step (a). Following step (d), there is subsequently a
step (e) of drying the treated support and optionally a step (f) of
calcining the treated support. Further steps (d) and (e) and
optionally step (f) may be carried out either before step (a) or
after step (b), or optionally after step (c). Preferably, the metal
source in the aqueous solution or dispersion in step (d) comprises
a zirconium metal source, a manganese metal source, a chromium
metal source, an aluminium metal source or a titanium metal source.
In this way, the catalyst support material may undergo sequential
modification by at least two different metals.
[0013] The metal source used in step (a) may comprise one or both
of a zirconium metal source and a chromium metal source.
[0014] Preferably, the metal source used in step (a) may comprise a
zirconium metal source. The use of a zirconium metal source may
provide a zirconium oxide-modified catalyst support that can be
used to generate catalysts with particularly good CO conversion
levels and which can thus function well as a Fischer-Tropsch
catalyst. Catalysts based on zirconium oxide-modified catalyst
supports are particularly advantageous because they have good
CH.sub.4 selectivity. Preferably, the zirconium metal source
comprises zirconium dinitrate oxide hydrate.
[0015] One or more zirconium metal sources may be used in the
aqueous solution or dispersion. The aqueous solution or dispersion
may comprise one or more different metal sources in addition to the
zirconium metal source, preferably one or more of a chromium metal
source, manganese metal source, aluminium metal source or titanium
metal source. Alternatively, or in addition, the method comprises
step (d) wherein the aqueous solution or dispersion or step (d)
comprises a chromium metal source, manganese metal source,
aluminium metal source or titanium metal source and one or more
polar organic compounds.
[0016] The metal source used in step (a) may comprise a chromium
metal source. The use of a chromium metal source may provide a
chromium oxide-modified catalyst support that can be used to
generate catalysts with particularly good CO conversion levels and
can thus function well as a Fischer-Tropsch catalyst. Preferably,
the chromium metal source comprises chromium (III) nitrate
nonahydrate.
[0017] One or more chromium metal sources may be used in the
aqueous solution or dispersion. The aqueous solution or dispersion
may comprise one or more different metal sources in addition to the
chromium metal source, preferably one or more of a zirconium metal
source, manganese metal source, aluminium metal source or titanium
metal source. Alternatively, or in addition, the method comprises
step (d) wherein the aqueous solution or dispersion or step (d)
comprises a manganese metal source, zirconium metal source,
aluminium metal source or titanium metal source and one or more
polar organic compounds.
[0018] The one or more metal sources used in step (a) may comprise
a manganese metal source. Preferably, the manganese metal source
comprises manganese (II) nitrate tetrahydrate. One or more
manganese metal sources may be used in the aqueous solution or
dispersion. The aqueous solution or dispersion may comprise one or
more different metal sources in addition to the manganese metal
source, preferably one or more of a zirconium metal source,
chromium metal source, aluminium metal source or titanium metal
source. Alternatively, or in addition, the method comprises step
(d) wherein the aqueous solution or dispersion or step (d)
comprises a chromium metal source, zirconium metal source,
aluminium metal source or titanium metal source and one or more
polar organic compounds.
[0019] The one or more metal sources used in step (a) may comprise
an aluminium metal source. Preferably, the aluminium metal source
comprises aluminium nitrate. One or more aluminium metal sources
may be used in the aqueous solution or dispersion. The aqueous
solution or dispersion may comprise one or more different metal
sources in addition to the aluminium metal source, preferably one
or more of a zirconium metal source, chromium metal source,
manganese metal source or titanium metal source. Alternatively, or
in addition, the method comprises step (d) wherein the aqueous
solution or dispersion of step (d) comprises a chromium metal
source, zirconium metal source, manganese metal source or titanium
metal source and one or more polar organic compounds. The aqueous
solution or dispersion of step (d) may be as defined in the same
way as the corresponding features of the aqueous solution or
dispersion of step (a) described herein.
[0020] This method is advantageous for environmental reasons. In
particular, aqueous methods are more environmentally friendly than
non-aqueous methods because the by-products of aqueous methods are
easier to dispose of safely and are less toxic.
[0021] This method is advantageous because it provides a modified
catalyst support which, when used to manufacture a catalyst,
provides a highly active catalyst as shown in the examples of this
application.
[0022] The present invention also provides a modified catalyst
support obtainable by the methods described herein.
[0023] The modified catalyst support of the present invention is
advantageous because it yields a catalyst that is more stable than
catalysts derived from alternative supports. This is also shown in
the examples of this application.
[0024] The modified catalyst support of the present invention is
advantageous because it can be used to manufacture a more active
catalyst as shown in the examples of this application.
[0025] The present invention also provides a method for preparing a
catalyst precursor comprising (a) depositing a solution or
suspension comprising at least one catalyst metal precursor and a
complexing/reducing agent onto the modified catalyst support
according to the present invention; (b) optionally drying the
modified catalyst support onto which the solution or suspension has
been deposited; and (c) calcining the modified catalyst support
onto which the solution or suspension has been deposited.
[0026] The present invention also provides a catalyst precursor
obtainable by the method according to this aspect of the invention.
The present invention further provides a catalyst precursor
comprising the modified catalyst support according to the
invention.
[0027] A catalyst precursor comprising the modified catalyst
support of the present invention is advantageous because it is more
stable than a catalyst precursor comprising a modified catalyst
support synthesised by alternative methods. This is shown in the
examples of this application.
[0028] A catalyst precursor comprising the modified support of the
present invention is advantageous because it can be activated to
provide a more active catalyst as shown in the examples of this
application.
[0029] The present invention also provides a catalyst obtainable by
activation of the catalyst precursor according to these aspects of
the invention.
[0030] A catalyst comprising the modified catalyst support of the
present invention is advantageous because it is a more active
catalyst as shown in the examples of this application.
[0031] In addition, a catalyst comprising the modified catalyst
support of the present invention is advantageous because it has a
lower deactivation rate (i.e. is more stable) compared to catalysts
comprising alternative modified catalyst supports. This is shown in
the examples of this application.
[0032] The present invention also provides a microchannel reactor
comprising a catalyst according to these aspects of the
invention.
[0033] The present invention also provides the use of the modified
catalyst support according to the present invention as a substrate
in the manufacture of a Fischer-Tropsch catalyst.
[0034] The present invention also provides the use of a catalyst
comprising the modified catalyst support according to the present
invention to catalyse a Fischer-Tropsch reaction.
[0035] The present invention also provides the use of the catalyst
precursor according to the present invention to form a
Fischer-Tropsch catalyst.
[0036] The present invention also provides a catalyst precursor
comprising: [0037] (i) a modified catalyst support obtainable by
the methods described herein; and [0038] (ii) Co.sub.3O.sub.4 on
the catalyst support, wherein the numerical average particle
diameter of the Co.sub.3O.sub.4 is less than 12 nm as determined by
X-ray diffraction (XRD).
[0039] Preferably, the c value of a lognormal particle size
distribution of Co.sub.3O.sub.4 is less than or equal to 0.31. The
c-value is known as "the dimensionless ratio".
[0040] Alternatively or in addition, the D-value of the lognormal
particle size distribution of Co.sub.3O.sub.4 is greater than or
equal to about 19.
[0041] The D-value is a reformulation of the size distribution as
described by the c-value and does not represent any new data.
Therefore, the c- and D-values are mathematically related. A
D-value of 19.2 is equivalent to an average particle size of about
10 nm and a size distribution width of about 0.31. It is preferred
to use the D-value as this number incorporates both the size and
distribution width into a single metric.
[0042] The present invention also provides a catalyst precursor
comprising: [0043] a modified catalyst support obtainable by the
methods described herein comprising silica; and [0044]
Co.sub.3O.sub.4 on the catalyst support, where the catalyst is in
the form of a particulate catalyst with a particle size
distribution of d10 greater than 90 .mu.m and d90 less than 310
.mu.m.
[0045] The present invention also provides a catalyst precursor
comprising: [0046] a zirconium oxide-modified silica catalyst
support obtainable by the methods described herein; [0047] at least
35 wt % Co at least partially in the form of Co.sub.3O.sub.4,
wherein the numerical average particle diameter of the
Co.sub.3O.sub.4 is 8 to 10 nm as determined by XRD; and [0048]
optionally Pt as a promoter; [0049] optionally Re as a promoter;
[0050] wherein one or more of the following conditions is
satisfied: [0051] the mean particle size distribution of the
support is between 180 and 300 .mu.m; [0052] the mean pore volume
is less than 1 ml/g; and [0053] the mean pore diameter is less than
250 .ANG., preferably from 100 to 250 .ANG., more preferably from
125 to 200 .ANG.. The catalyst precursor may comprise at least 40
wt % Co at least partially in the form of Co.sub.3O.sub.4, wherein
the numerical average particle diameter of the Co.sub.3O.sub.4 is 8
to 10 nm as determined by XRD. The catalyst precursor may comprise
Pt as a promoter.
[0054] The present invention also provides a catalyst precursor
comprising: [0055] a chromium oxide-modified silica catalyst
support obtainable by the methods described herein; [0056] at least
35 wt % Co at least partially in the form of Co.sub.3O.sub.4,
wherein the numerical average particle diameter of the
Co.sub.3O.sub.4 is 8 to 10 nm as determined by XRD; and [0057]
optionally Pt as a promoter; [0058] optionally Re as a promoter;
[0059] wherein one or more of the following conditions is satisfied
[0060] the mean particle size distribution of the support is
between 180 and 300 .mu.m; [0061] the mean pore volume is less than
1 ml/g; [0062] the mean pore diameter is less than 175 .ANG.,
preferably from 100 to 175 .ANG.. The catalyst precursor may
comprise at least 40 wt % Co at least partially in the form of
Co.sub.3O.sub.4, wherein the numerical average particle diameter of
the Co.sub.3O.sub.4 is 8 to 10 nm as determined by XRD. The
catalyst precursor may comprise Pt as a promoter.
[0063] The present invention also provides a catalyst precursor
comprising: [0064] a manganese oxide-modified silica catalyst
support obtainable by the methods described herein; [0065] at least
35 wt % Co at least partially in the form of Co.sub.3O.sub.4,
wherein the numerical average particle diameter of the
Co.sub.3O.sub.4 is 8 to 10 nm as determined by XRD; and [0066]
optionally Pt as a promoter; [0067] optionally Re as a promoter;
[0068] wherein one or more of the following conditions is
satisfied: [0069] the mean particle size distribution of the
support is between 180 and 300 .mu.m; [0070] the mean pore volume
is less than 1 ml/g; and [0071] the mean pore diameter is less than
200 .ANG., preferably from 100 to 200 .ANG.. The catalyst precursor
may comprise at least 40 wt % Co at least partially in the form of
Co.sub.3O.sub.4, wherein the numerical average particle diameter of
the Co.sub.3O.sub.4 is 8 to 10 nm as determined by XRD. The
catalyst precursor may comprise Pt as a promoter.
[0072] The present invention also provides a catalyst precursor
comprising: [0073] a zirconium oxide and titanium oxide-modified
silica catalyst support obtainable by the methods described herein;
[0074] at least 35 wt % Co at least partially in the form of
Co.sub.3O.sub.4, wherein the numerical average particle diameter of
the Co.sub.3O.sub.4 is 8 to 10 nm as determined by XRD; and [0075]
optionally Pt as a promoter; [0076] optionally Re as a promoter;
[0077] wherein one or more of the following conditions is
satisfied: [0078] the mean particle size distribution of the
support is between 120 and 300 .mu.m; the mean pore volume is less
than 1 ml/g; and the mean pore diameter is less than 250 .ANG.,
preferably from 100 to 250 .ANG., more preferably from 125 to 200
.ANG.. The catalyst precursor may comprise at least 40 wt % Co at
least partially in the form of Co.sub.3O.sub.4, wherein the
numerical average particle diameter of the Co.sub.3O.sub.4 is 8 to
10 nm as determined by XRD. The catalyst precursor may comprise Pt
as a promoter.
[0079] The present invention also provides the use of the activated
catalyst according to the present invention to catalyse a
Fischer-Tropsch reaction.
[0080] The present invention provides a method of conducting a
Fischer Tropsch reaction comprising using a catalyst as described
herein or using a catalyst derived from a catalyst precursor
described herein in a microchannel reactor, in which the
performance of the catalyst is substantially maintained over a
reaction period of about 5000 hours or more without regeneration of
the catalyst, such that the contact time is less than 500
milliseconds, the CO conversion is greater than 50% and the methane
selectivity is less than 15%. Preferably, the reaction period is
about 8000 hours or more. Preferably, the CO conversion is greater
than 60%. Preferably, the methane selectivity is less than 10%.
[0081] The present invention provides a method of conducting a
Fischer Tropsch reaction comprising using a catalyst as described
herein or using a catalyst derived from a catalyst precursor as
described herein in a microchannel reactor in a temperature range
of from about 180.degree. C. to about 230.degree. C., in which the
deactivation rate of the catalyst measured as percent loss of CO
conversion per day is 0.29% over a reaction period of 500 hours.
Preferably the deactivation rate of the catalyst measured as
percent loss of CO conversion per day is 0.09% or less over a
reaction period of about 5000 hours or more. Preferably, the
reaction period is about 8000 hours or more. Preferably, the
deactivation rate of the catalyst measured as percent loss of CO
conversion per day is 0.085% by day or less.
[0082] The present invention provides a method of conducting a
Fischer Tropsch reaction comprising using a catalyst as described
herein or using a catalyst derived from a catalyst precursor as
described herein in a microchannel reactor in a temperature range
of from about 180.degree. C. to about 230.degree. C., in which the
deactivation rate of the catalyst measured as percent loss of CO
conversion per day is 0.09% or less over a reaction period of about
5000 hours or more.
[0083] As used herein, the term "comprising" encompasses
"including" as well as "consisting" and "consisting essentially of"
e.g. a composition "comprising" X may consist exclusively of X or
may include something additional e.g. X+Y.
Support Modification Method
[0084] As used herein, the term "modified catalyst support" means a
catalyst support material whose structure and/or composition has
been altered by the incorporation of a refractory solid oxide or
mixture of solid oxides in at least a part of the volume of the
support material. By "catalyst support" as used herein encompasses
a catalyst support which is a "bare catalyst support", which refers
to a catalyst support material that is substantially free of
catalytic metals, i.e. platinum group metals, iron, nickel, copper
or cobalt. A suitable catalyst support material is silica or
refractory oxides, for example refractory oxides of Mg, Si, Ti, Zn,
Al, Zr, Hf, Y or Ce or mixtures thereof. Alternatively, the
catalyst support material may comprise or consist essentially of
carbon, a zeolite, a boronitride or silicon carbide. If the
catalyst support material is also a refractory solid oxide, the
refractory solid oxide which modifies the structure or composition
of the catalyst support material will suitably be different to the
catalyst support material. A catalyst may then be affixed to the
modified catalyst support.
[0085] As used herein, the term "treating" when referring to the
treating of a catalyst support material with the aqueous treatment
solution described herein means a method of including a modifying
material on or in the catalyst support material. Treating includes
such methods as impregnating, coating, brushing, spraying, rolling
or spreading. Preferred methods of treating are impregnation, for
example by mixing an impregnation solution and the catalyst support
in order to reach the point or incipient wetness or by
spraying.
[0086] Treating of the catalyst support material with the modifying
material may involve spraying the catalyst support material into
the aqueous treatment solution one or more times (e.g. 1, 2, 3, 4,
5, 6, 7, 8, 9, 10 or more times). Each spraying of the support
material may last from about 5 minutes to about 1 hour, preferably
from about 15 minutes to about 30 minutes. Typically spraying of
the basic support material takes place at a temperature of
30.degree. C. or less. The volume of the solution or dispersion
taken up by the catalyst support in the process may suitably range
from about 0.5 to about 2.50 ml per gram of support material.
[0087] The catalyst support material, may be in the form of a
structured shape, pellets or a powder.
[0088] The refractory solid oxide which modifies the catalyst
support material may comprise or consist of a zirconium metal
oxide, a chromium metal oxide, a manganese metal oxide and/or an
aluminium metal oxide. Preferably, the refractory solid oxide is
zirconium metal oxide or chromium metal oxide.
[0089] The modified catalyst support may be a zirconium
oxide-modified support. Preferably, a zirconium oxide-modified
silica support.
[0090] The modified catalyst support may be a chromium
oxide-modified support. Preferably, a chromium oxide-modified
silica support.
[0091] The modified catalyst support may be a manganese
oxide-modified support. Preferably, a manganese oxide-modified
silica support.
[0092] The modified catalyst support may be an aluminium
oxide-modified support. Preferably, an aluminium oxide-modified
silica support.
[0093] As used herein, the "aqueous treatment solution" is the
aqueous solution or dispersion comprising one or more zirconium,
chromium, manganese and/or aluminium metal sources and one or more
polar organic compounds as described in claim 1.
[0094] The aqueous treatment solution is an aqueous solution or
dispersion comprising one or more zirconium, chromium, manganese
and/or aluminium metal sources and one or more polar organic
compounds, preferably carboxylic acids.
[0095] The aqueous treatment solution may be an aqueous solution or
dispersion comprising one or more zirconium metal sources and one
or more polar organic compounds, preferably carboxylic acids.
[0096] The aqueous treatment solution may be an aqueous solution or
dispersion comprising one or more chromium metal sources and one or
more polar organic compounds, preferably carboxylic acids.
[0097] The aqueous treatment solution may be an aqueous solution or
dispersion comprising one or more manganese metal sources and one
or more polar organic compounds, preferably carboxylic acids.
[0098] The aqueous treatment solution may be an aqueous solution or
dispersion comprising one or more aluminium metal sources and one
or more polar organic compounds, preferably carboxylic acids.
[0099] The term "aqueous" herein refers to solutions or suspensions
of the reagents in a solvent or solvent mixture that is
predominantly (i.e. more than 50%, suitably more than 80%, for
example more than 95%, and most typically about 100%) water. The
aqueous treatment solution may comprise from about 50% w/v to about
95% w/v water, from about 68% w/v to about 88% w/v water, from
about 70% w/v to about 75% w/v water.
[0100] Suitably, the zirconium, chromium, manganese or aluminium
metal source may be present as a water soluble zirconium, chromium,
manganese or aluminium metal ion complex or water soluble compound,
preferably a complex. The metal source may comprise one single
source of one metal or more than one different source of the same
metal. Alternatively, the metal source may comprise different metal
types selected from zirconium, chromium, manganese, aluminium and
titanium.
[0101] The term "water soluble" herein signifies a solubility in
water of at least about 10 g/liter to form a solution that is
stable against precipitation for at least about one hour.
[0102] Suitable zirconium metal sources include ammonium zirconium
carbonate, zirconium acetate and zirconium nitrate, such as
zirconium nitrate pentahydrate, anhydrous zirconyl nitrate and
zirconyl nitrate hydrate. Suitably, the zirconium metal source is
substantially or completely free of sulphur and/or halide, since
these could react adversely with the substrate, catalytic metal
and/or metal promoter. Likewise, the zirconium metal source is
suitably substantially free of metals other than the zirconium
metal (e.g. sodium or potassium counter-ions) since these could
react adversely with the substrate, catalytic metal and/or metal
promoter. The zirconium metal source is preferably zirconyl
nitrate, preferably zirconyl nitrate hydrate (also known as
"zirconium dinitrate oxide hydrate").
[0103] The one or more zirconium metal sources may be present in
the aqueous treatment solution in an amount (defined in terms of
the weight of zirconium metal per volume of solution) of from about
1% w Zr/v to about 22% w Zr/v, preferably about 10% w Zr/v to about
20% w Zr/v.
[0104] Suitable chromium metal sources include chromium formate,
chromium acetate, chromium nitrate such as anhydrous chromium
nitrate and chromium nitrate nonahydrate. Suitably, the chromium
metal source is substantially or completely free of sulphur and/or
halide, since these could react adversely with the substrate,
catalytic metal and/or metal promoter. Likewise, the chromium metal
source is suitably substantially free of metals other than the
chromium metal (e.g. sodium or potassium counter-ions) since these
could react adversely with the substrate, catalytic metal and/or
metal promoter. The chromium metal source is preferably a chromium
nitrate, preferably chromium (III) nitrate nonahydrate.
[0105] The one or more chromium metal sources may be present in the
aqueous treatment solution in an amount (defined in terms of the
weight of chromium metal per volume of solution) of about 2% w Cr/v
to about 15% w Cr/v, preferably about 5% w Cr/v to about 11% w
Cr/v.
[0106] Suitable manganese metal sources include manganese acetate,
manganese nitrate, such as manganese nitrate hexahydrate and
manganese nitrate tetrahydrate. Suitably, the manganese metal
source is substantially or completely free of sulphur and/or
halide, since these could react adversely with the substrate,
catalytic metal and/or metal promoter. Likewise, the soluble
manganese metal source is suitably substantially free of metals
other than the manganese metal (e.g. sodium or potassium
counter-ions) since these could react adversely with the substrate,
catalytic metal and/or metal promoter. The manganese metal source
is preferably a manganese nitrate, preferably manganese (II)
nitrate tetrahydrate.
[0107] The one or more manganese metal sources may be present in
the aqueous treatment solution in an amount (defined in terms of
the weight of manganese metal per volume of solution) of about 2% w
Mn/v to about 15% w Mn/v, preferably about 5% w Mn/v to about 12% w
Mn/v.
[0108] Suitable aluminium metal sources include aluminium nitrate,
aluminium nitrate nonahydrate, aluminium lactate, aluminium
acetate. Suitably, the aluminium metal source is substantially or
completely free of sulphur and/or halide, since these could react
adversely with the substrate, catalytic metal and/or metal
promoter. Likewise, the aluminium metal source is suitably
substantially free of metals other than the aluminium metal (e.g.
sodium or potassium counter-ions) since these could react adversely
with the substrate, catalytic metal and/or metal promoter.
[0109] The one or more aluminium metal sources may be present in
the aqueous treatment solution in an amount (defined in terms of
the weight of aluminium metal per volume of solution) of about 1% w
Al/v to about 12% w Al/v, preferably about 3% w Al/v to about 6% w
Al/v.
[0110] One or more polar organic compounds are present in the
aqueous treatment solution.
[0111] The polar organic compound is preferably liquid at room
temperature (20.degree. C.). However, it is also possible to use
polar organic compounds which become liquid at temperatures above
room temperature. In such cases, the polar organic compound should
preferably be liquid at a temperature below the temperature at
which any of the components of the solution or dispersion
decompose.
[0112] Examples of suitable organic compounds for inclusion in the
solution or dispersion are organic amines, organic carboxylic
acids, alcohols, phenoxides, in particular ammonium phenoxides,
alkoxides, in particular ammonium alkoxides, amino acids, compounds
containing functional groups such as one or more hydroxyl, amine,
amide, carboxylic acid, ester, aldehyde, ketone, imine or imide
groups, such as urea, hydroxyamines, trimethylamine, triethylamine,
and surfactants.
[0113] Preferred alcohols are those containing from 1 to 30 carbon
atoms, preferably 1 to 15 carbon atoms. Examples of suitable
alcohols include methanol, ethanol and glycol and sugar alcohols,
such as sorbitol.
[0114] Preferably, the polar organic compound is a carboxylic acid.
The carboxylic acids are organic acids that are soluble in
water.
[0115] Suitable carboxylic acids may be branched, linear or
unbranched, saturated, unsaturated, aliphatic and/or aromatic,
and/or derivatives thereof. Suitably, the carboxylic acid comprises
or consists essentially of one or more dicarboxylic or
tricarboxylic acids. Alternatively or in addition, the carboxylic
acid may comprise one or more alpha- or beta-hydroxyl carboxylic
acids. Examples of suitable carboxylic acids include acetic acid,
citric acid, tartaric acid, malic acid, maleic acid, lactic acid,
glycolic acid, propionic acid, succinic acid, oxalic acid and
combinations thereof.
[0116] Mixtures or one of more different carboxylic acids may be
used. In one embodiment, the mixture of one or more different
carboxylic acids includes a tricarboxylic acid, preferably citric
acid. In an alternative embodiment, the mixture of one or more
different carboxylic acids includes an alpha hydroxyl carboxylic
acid, such as lactic acid. In a further alternative embodiment, the
mixture of one or more different carboxylic acids includes a
tricarboxylic acid, preferably citric acid, and an alpha hydroxyl
carboxylic acid, preferably lactic acid.
[0117] Preferred carboxylic acids are acetic acid, lactic acid,
citric acid and mixtures thereof. More preferably, citric acid is
present in the aqueous treatment solution.
[0118] Without wishing to be bound by theory, the inventors believe
that the one or more carboxylic acids, particularly citric acid, in
the aqueous treatment solution act as ligands to the zirconium,
chromium, manganese or aluminium metal source thereby changing the
coordination sphere around the metal. The carboxylic acid is also
thought to replace OH groups on the catalyst support material (e.g.
silica) forming dimeric and oligomeric zirconium, chromium,
manganese or aluminium metal species on the surface of the catalyst
support material leading to a higher dispersion of the metal
species over the catalyst support material surface. This is thought
to lead to the increased stability of a catalyst manufactured with
the modified catalyst support.
[0119] The one or more carboxylic acids may be present in the
aqueous treatment solution in an amount of about 1% w/v to about
30% w/v, preferably 2% w/v to about 25% w/v, preferably about 4%
w/v to about 24% w/v, preferably about 5% w/v to about 20% w/v,
preferably from about 18% w/v to about 20% w/v, more preferably
from about 18% w/v to about 19% w/v.
[0120] Preferably, the aqueous treatment solution consists of a
metal source precursor, a carboxylic acid and water, wherein the
metal source precursor is selected from a zirconium, chromium,
aluminium and manganese precursor.
[0121] A particularly preferred aqueous treatment solution for
preparing a zirconium oxide-modified catalyst support has from
about 10% w Zr/v to about 20% w Zr/v, from about 15% w/v to about
27% w/v of citric acid, preferably 18% w/v to about 20% w/v of
citric acid.
[0122] A particularly preferred aqueous treatment solution for
preparing a chromium oxide-modified catalyst support has from about
5% w Cr/v to about 11% w Cr/v, from about 12% w/v to about 25% w/v
of citric acid, preferably from about 18% w/v to about 20% w/v of
citric acid.
[0123] A particularly preferred aqueous treatment solution for
preparing a manganese oxide-modified catalyst support has from
about 5% w Mn/v to about 12% w Mn/v, from about 12% w/v to about
25% w/v of citric acid, preferably from about 18% w/v to about 20%
w/v of citric acid.
[0124] A particularly preferred aqueous treatment solution for
preparing an aluminium oxide-modified catalyst support has from
about 3% w Al/v to about 6% w Al/v, from about 12% w/v to about 25%
w/v of citric acid, preferably from about 18% w/v to about 20% w/v
of citric acid.
[0125] The treated support is dried and optionally calcined
following treatment. The purpose of the drying step and optional
calcining step includes driving off water, which has an effect of
increasing the support pore volume as compared to the
just-impregnated state. Additionally, the metal oxide precursor and
the polar organic compound may be partially decomposed during the
heat treatment (although ideally not fully converted to the metal
oxide). Without wishing to be bound by theory, the inventors feel
that the presence of residual organic species on the catalyst
support assists in the later dispersion of cobalt and thus may help
improve the stability of the resulting catalyst.
[0126] One way of measuring the amount of residual organic species
on the modified support is by determining the weight of the
modified support after the drying and optional calcining steps and
comparing this to the nominal weight of the support after full
conversion to the metal oxide and removal of all water and
precursor and polar organic compound species. The weight after
drying/calcining should be higher than the nominal fully oxidised
weight, indicating the presence of some additional species
(presumed residual organic moieties). Suitable ranges for the
weight ratio (weight after drying/calcining:nominal fully oxidised
weight) may be 1.01 to 1.50, preferably 1.05 to 1.30, more
preferably 1.10 to 1.25.
[0127] A suitable temperature for the drying step and optional
calcining step is determined by identifying the temperature of
decomposition of the metal oxide precursor plus polar organic
compound mixture and selecting a temperature less than this.
Suitably, the drying step and optional calcining step are carried
out at a temperature from 100 to 500.degree. C., from 100 to
350.degree. C., from 150 to 300.degree. C., or from 225 to
275.degree. C.
[0128] The drying step may take place in a box furnace or muffle
furnace. For example, where a box furnace or muffle furnace is
used, drying may take place by heating at a temperature that
increases at a rate (known as a "ramp rate") of 2.degree. C./min up
to a temperature of 100.degree. C. and the temperature is then held
at 100.degree. C. for about 5 hours. Alternatively, drying may take
place in other equipment, such as in a cone blender or in a rotary
calciner. Where a rotary calciner is used, preferably the ramp rate
is higher than 2.degree. C./min and the holding time is shorter
than 5 hours.
[0129] The treated support may be calcined following treatment.
Calcining may further increase stability of a catalyst manufactured
with the modified catalyst support. Calcination may use a
programmed heating regime which increases the temperature gradually
so as to control gas and heat generation from the treated support
and the other components of the treatment solution. Suitably,
calcination is carried out at a temperature from 100 to 500.degree.
C., from 100 to 350.degree. C., preferably from 150 to 300.degree.
C., more preferably from 225 to 275.degree. C. A preferred heating
regime has a final temperature of up to 250.degree. C. Preferably,
the temperature ramp rate is 2.degree. C./min. The final
temperature should not exceed about 350.degree. C. because
calcining at higher temperatures reduces the amount of carbon and
nitrogen retained on the modified support after drying and
calcination, which has the effect of reducing catalyst stability.
During calcination of the treated support, the final temperature is
preferably held for about 5 hours.
[0130] The modified catalyst support of the present invention is
preferably a modified Fischer-Tropsch catalyst support.
Modified Catalyst Support
[0131] The present invention further provides a catalyst support
obtainable by the method of the present invention.
Method of Preparation of Catalyst Precursor
[0132] A method for preparing a catalyst precursor may comprise (a)
depositing a solution or suspension comprising at least one
catalyst metal precursor and a complexing/reducing agent onto the
modified catalyst support of the present invention; (b) optionally
drying the modified catalyst support onto which the solution or
suspension has been deposited; and (c) calcining the modified
catalyst support onto which the solution or suspension has been
deposited.
[0133] Other methods for the preparation of catalyst precursors may
be found in WO 2008/104793.
[0134] The catalyst metal precursor may be a cobalt-containing
precursor or an iron-containing precursor. In one embodiment, the
catalyst metal precursor is a cobalt-containing precursor.
[0135] Suitable cobalt-containing precursors include cobalt
benzoylacetonate, cobalt carbonate, cobalt cyanide, cobalt
hydroxide, cobalt oxalate, cobalt oxide, cobalt nitrate, cobalt
acetate, cobalt acetylacetonate and cobalt citrate. These cobalt
precursors can be used individually or in combination. These cobalt
precursors may be in the form of hydrates or in anhydrous form. In
some cases, where the cobalt precursor is not soluble in water,
such as cobalt carbonate or cobalt hydroxide, a small amount of
nitric acid or a carboxylic acid may be added to enable the
precursor to fully dissolve in an aqueous solution or
suspension.
[0136] The catalyst metal precursor may be cobalt nitrate. Cobalt
nitrate may react with a complexing/reducing agent, such as citric
acid, during calcination to produce Co.sub.3O.sub.4. The citric
acid may act as a complexing/reducing agent and/or as a fuel (i.e.
reducing agent for cobalt nitrate) in the calcination reaction.
[0137] Preferably, the catalyst precursor comprises cobalt on the
modified catalyst support. More preferably, the catalyst precursor
comprises Co.sub.3O.sub.4 on the modified catalyst support.
[0138] Without wishing to be bound by theory, the inventors believe
that the activity and the selectivity of cobalt-based catalysts are
principally influenced by the density of active sites, favouring
very small particle sizes. However, the deactivation mechanisms of
cobalt catalysts follow in general the reverse trend, where the
largest particles are the most stable.
[0139] The inventors have found that a numerical average particle
diameter of Co.sub.3O.sub.4 of less than 12 nm (determined by
powder X-ray diffraction, preferably using a Siemens D5000
theta/theta powder diffractometer and Cu K.sub..alpha. radiation)
gives a catalyst having optimum Fischer-Tropsch synthesis
performance. The inventors have further found that the cobalt oxide
particle size distribution influences the catalyst's activity and
stability, such that, a particle size distribution as narrow as
possible is preferred. The width of the particle size distribution
can be measured by the c value of the lognormal particle size
distribution. Preferably, the c value of the lognormal particle
size distribution of Co.sub.3O.sub.4 particles is less than 0.31.
The average particle diameter of Co.sub.3O.sub.4 may be below 11
nm, or between 8 and 10 nm. The c value may be between 0.19 and
0.31, or below 0.25, or between 0.19 and 0.25. Preferably, where
the numerical average particle diameter of the Co.sub.3O.sub.4 is
in the range 8 to 10 nm, c is less than 0.31.
[0140] Preferably, where the numerical average particle diameter is
in the range 8 to 10 nm, the c-value may be 0.31 or less, e.g. 0.29
or less, 0.26 or less or 0.25 or less. Alternatively or in
addition, the c-value may be 0.19 or more, e.g. 0.20 or more or
0.235 or more. It is within the scope of the present application to
combine any of these upper and lower limits such that the c-value
may be 0.19.ltoreq.c.ltoreq.0.31; 0.19.ltoreq.c.ltoreq.0.29;
0.19.ltoreq.c.ltoreq.0.26; 0.19.ltoreq.c.ltoreq.0.25;
0.20.ltoreq.c.ltoreq.0.31; 0.20.ltoreq.c.ltoreq.0.29;
0.20.ltoreq.c.ltoreq.0.26; 0.20.ltoreq.c.ltoreq.0.25;
0.235.ltoreq.c.ltoreq.0.31; 0.235.ltoreq.c.ltoreq.0.29;
0.235.ltoreq.c.ltoreq.0.26; or 0.235.ltoreq.c.ltoreq.0.25.
[0141] c is known as the dimensionless ratio, and characterises the
width of the size distribution. In a sample of calcined catalyst
(assuming spherical particles equivalent to crystallites or
crystallites with a lognormal monomodal distribution) the form of
the particle size distribution may be written as:
f ( R ) = 1 R 2 .pi. ln ( 1 + c ) - [ ln ( R R O 1 + c ) ] 2 2 ln (
1 + c ) where c = .sigma. 2 R O 2 Equation 1 ##EQU00001##
where R.sub.O is the numeric average particle radius and c, which
is known as the dimensionless ratio, characterises the width of the
size distribution. Multiplication of R.sub.O by 2 yields the
numerical average particle diameter.
[0142] An alternative way to characterise the relationship between
the Co.sub.3O.sub.4 particle size distribution and the catalyst's
activity and stability is through the D-value. It is important to
note that the D-value is simply a reformulation of the size
distribution as described by the c-value and does not represent any
new data. Therefore, the c- and D-values are mathematically
related, but an improved correlation is seen between the D-value
and the catalyst's activity and stability.
[0143] The D-value is calculated from parameters of the particle
size distribution of Co.sub.3O.sub.4 particles in a fresh,
unreduced catalyst, i.e. in a catalyst precursor
[0144] Trends between the c-value and the deactivation rate can be
seen for Co.sub.3O.sub.4 particles of substantially the same
numerical average particle diameter. The D-value is an improvement
on the c-value because, while it still takes into account both the
width of the Co.sub.3O.sub.4 particle size distribution and the
numerical average particle diameter, it places a larger weighting
on the numerical average Co.sub.3O.sub.4 particle diameter, which
removes the need to maintain substantially the same numerical
average particle diameter in order to observe trends in the data.
This enables a single metric (D-value) to be reported and compared,
rather than two metrics (c-value and numerical average particle
diameter).
[0145] The D-value may be calculated by plotting the lognormal
particle size distribution using Equation 1. The frequency at the
mode of this lognormal distribution (f.sub.mode) may be considered
to be a measure of the width of the distribution. In order to
account for the dependence of the FTS catalyst stability on
numerical average particle diameter, the inventors have developed a
formula in which f.sub.mode is weighted by the size distribution
median to create a "size-weighted distributed breadth", or D-value,
using the formula:
D=f.sub.mode.sup.y.times.R.sub.O.times.2 Equation 2
wherein f.sub.mode is the frequency at the mode of the lognormal
distribution, R.sub.O is the numeric average particle radius, and y
is an empirical value based on experimental observation. The value
of y is determined via comparison of the stability of a selection
of catalysts (at least about 5 to 10) with substantially similar
compositions but small variations in Co.sub.3O.sub.4 particle size
and size distribution width. These variations may be achieved via
minor modifications of the synthesis method eg. increasing the
dilution of the impregnation solution (which is shown in an example
to cause subtle changes to the particle size distribution). FTS
stability data on these catalysts under the same testing conditions
is then collected. Within this set of similar catalysts, y is then
manually adjusted to create a spread of D-values such that the
difference in the stability of the FTS catalysts can be
distinguished.
[0146] Therefore, an increase in the D-value represents either a
narrowing of the particle size distribution or an increase in the
numerical average particle diameter.
[0147] The inventors have further found that the Co.sub.3O.sub.4
particle size distribution influences catalyst's FTS activity and
stability, such that, preferably, the D-value of the lognormal
particle size distribution of Co.sub.3O.sub.4 particles is about 19
or more. A D-value of 19.2 corresponds to a size distribution with
a c-value of about 0.31 and numerical average particle diameter of
about 10 nm. A D-value of 19.8 corresponds to a size distribution
with a c-value of about 0.31 and an average particle size of about
8 nm. In either of these cases, a decrease in c (eg. narrowing of
the size distribution) would result in an increase in D. Therefore
the specification of c.ltoreq.0.31 over the average particle size
range 8-10 nm corresponds to particle distributions defined by
having D-values greater than or equal to about 19.
[0148] The D-value may be about 19 or more, e.g. 19.2 or more, 20.4
or more, 21.0 or more or 21.35 or more, or 21.4 or more.
Alternatively or in addition, the D-value may be 23.5 or less, e.g.
22.2 or less. It is within the scope of the present application to
combine any of these upper and lower limits such that the D-value
may be 19.ltoreq.D.ltoreq.23.5; 19.ltoreq.D.ltoreq.22.2;
19.2.ltoreq.D.ltoreq.23.5; 19.2.ltoreq.D.ltoreq.22.2;
20.4.ltoreq.D.ltoreq.23.5; 20.4.ltoreq.D.ltoreq.22.2;
21.0.ltoreq.D.ltoreq.23.5; 21.0.ltoreq.Dc.ltoreq.22.2;
21.35.ltoreq.D.ltoreq.23.5; or 21.35.ltoreq.D.ltoreq.22.2.
[0149] The solution or suspension used in the method for preparing
a catalyst precursor may contain a mixture of the primary catalyst
metal precursor (i.e. a cobalt-containing precursors or an
iron-containing precursor) and at least one secondary catalyst
metal precursor. Such secondary catalyst metal precursor(s) may be
present to provide a promoter and/or modifier in the catalyst.
Suitable secondary catalyst metals include noble metals, such as
Pd, Pt, Rh, Ru, Ir, Au, Ag and Os, transition metals, such as Zr,
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Tc, Cd, Hf, Ta, W, Re,
Hg and Ti and the 4f-block lanthanides, such as La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
[0150] In particular, the secondary catalyst metals may be one or
more of Pd, Pt, Ru, Ni, Co (if not the primary catalyst metal), Fe
(if not the primary catalyst metal), Cu, Mn, Mo, Re and W.
[0151] Suitable complexing/reducing agents for use in the method of
making the catalyst precursor of the present invention are the
polar organic compounds as hereinbefore described. Preferred
complexing/reducing agents are urea, carboxylic acids such as
acetic acid, citric acid, glycolic acid, malic acid, propionic
acid, succinic acid, lactic acid and oxalic acid. Mixtures of
complexing/reducing agents may also be used.
[0152] If a catalyst metal precursor which is a hydrate is used,
the solution or suspension will necessarily contain some water of
hydration. This water may be sufficient to dissolve some of the
components of the solution or suspension, such as the
complexing/reducing agent (if solid at room temperature). However,
in some cases, it may be necessary to add some water to the
solution or suspension in order to ensure that the catalyst metal
precursor(s) and the other components are able to dissolve or
become suspended. In such cases, the amount of water used is
usually the minimum required to allow the catalyst metal
precursor(s) and the other components to dissolve or be
suspended.
[0153] As will be clear to the skilled person, the choice of
complexing/reducing agent will be partly dictated by the
aqueous/non-aqueous nature of the solution or suspension. For
example, if the solution or suspension is aqueous, a citric acid
complexing/reducing agent is preferred because it provides a highly
stable catalyst compared to other organic complexing/reducing
agents such as polyols and sugars. The use of citric acid is also
preferred because it provides a catalyst which is selective and
stable at CO conversion levels greater than 70%.
[0154] The use of an aqueous method for the preparation of a
modified catalyst support in combination with an aqueous method for
the preparation of the catalyst precursor is advantageous for
environmental reasons. In particular, aqueous methods are more
environmentally friendly than non-aqueous methods because the
by-products of aqueous methods are easier to dispose of safely and
are less toxic. For example, most organic solvents are highly
flammable and have low boiling points. As such, the vapours of
these organic solvents tend to escape through the exhaust without
decomposing. An effect of this is that manufacturing plants need to
have extra safety measures in addition to COx and NOx
scrubbers.
[0155] Optionally, the modified catalyst support onto which the
solution or suspension has been deposited may be dried. Drying may
take place at a temperature in the range from about 100.degree. C.
to about 130.degree. C., preferably from about 100.degree. C. to
about 120.degree. C. Drying may take place in a box oven, furnace
or rotary calciner. Preferably drying takes place by heating at a
temperature that increases at a ramp rate of 2.degree. C./min up to
a temperature of 100.degree. C. and the temperature is then held at
100.degree. C. for about 5 hours.
[0156] The modified catalyst support onto which the solution or
suspension has been deposited may be calcined at a temperature in
the range from about 200.degree. C. to about 350.degree. C.,
preferably from about 200.degree. C. to about 250.degree. C.
Calcining may take place in a box oven, furnace or rotary calciner.
Preferably, calcining takes place by heating at a temperature that
increases at a ramp rate of 2.degree. C./min up to a final
temperature of 250.degree. C. The temperature is held at
250.degree. C. for about 3 hours. Alternatively, calcining
preferably takes place by heating at a temperature that increases
at a ramp rate of 2.degree. C./min up to a temperature of
200.degree. C. The temperature is held at 200.degree. C. for about
3 hours before being increased again at a ramp rate of 1.degree.
C./min up to a temperature of 250.degree. C. and then held at that
temperature for a further 3 hours. The final temperature should not
exceed about 250.degree. C. because calcining at higher
temperatures reduces the amount of carbon and nitrogen retained on
the modified support after drying and calcination, which has the
effect of reducing catalyst stability.
[0157] The deposition, drying and calcination steps may be repeated
one or more times. For each repeat, the solution or suspension used
in the deposition step may be the same or different. If the
solution or suspension in each repetition is the same, the
repetition of the steps allows the amount of catalyst metal(s) to
be brought up to the desired level on the modified catalyst support
stepwise in each repetition. If the solution or suspension in each
repetition is different, the repetition of the steps allows schemes
for bringing the amounts of different catalyst metals up to the
desired level in a series of steps to be executed.
[0158] A programmed heating regime may be used during drying and
calcination which increases the temperature gradually so as to
control gas and heat generation from the catalyst metal precursors
and the other components of the solution or suspension.
[0159] During the heating processes, the catalyst support may reach
a maximum temperature of no more than 500.degree. C., or no more
than 375.degree. C., or no more than 250.degree. C. at atmospheric
pressure. The temperature may be ramped up at a rate of from 0.0001
to 10.degree. C. per minute, or from 0.1 to 5.degree. C. per
minute.
[0160] An illustrative programmed heating regime may comprise:
[0161] (a) heating the catalyst support onto which the solution or
suspension has been deposited at a rate of 1 to 10, or about 1 to
5, or about 2.degree. C. per minute to a temperature of 80 to
120.degree. C., or about 100.degree. C. and maintaining it at this
temperature for 0.25 to 10, or about 1 to 10, or about 5 hours;
[0162] (b) heating it at a rate of 1 to 10, or about 1 to 5, or
about 2.degree. C. per minute to a temperature of 150 to
400.degree. C., or 200 to 350.degree. C., or about 250.degree. C.
and maintaining it at this temperature for 0.25 to 6, or about 1 to
6, or about 3 hours.
[0163] The heating steps can be carried out in a rotating kiln, in
a static oven or in a fluidised bed. Preferably, the heating steps
are carried out in a rotating kiln because generally this has a
more even temperature profile than a static oven.
[0164] Once the calcination step has been completed, either after
the steps are first carried out or at the end of a repetition,
further catalyst metals may optionally be loaded onto the catalyst
support.
[0165] The calcination step may be carried out in an
oxygen-containing atmosphere (e.g. air), in particular if metal
catalyst oxides are to be formed.
Catalyst Precursor
[0166] A catalyst precursor is a material that may be activated to
form a catalyst. The terms "catalyst" and "catalyst precursor" are
used herein interchangeably and will be understood accordingly to
their specific context.
[0167] A catalyst precursor comprises at least one catalyst metal,
such as cobalt or iron, which may be present in oxide form, as
elemental metal or as a mixture of any of these. In particular, the
catalyst precursor may comprise from 10 to 60% cobalt and/or iron
(based on the weight of the metal as a percentage of the total
weight of the catalyst precursor), or from 35 to 50% of cobalt
and/or iron, or from 40 to 44% of cobalt and/or iron or about 42%
of cobalt and/or iron. The catalyst precursor may comprise both
cobalt and iron, or it may not comprise iron. The cobalt may be
present as Co.sub.3O.sub.4.
[0168] The catalyst precursor may comprise a noble metal on the
support that may be one or more of Pd, Pt, Rh, Re, Ru, Ir, Au, Ag
and Os. In particular, the noble metal may be selected from the
group consisting of Ru, Re or Pt, and mostsuitably it comprises Pt.
The catalyst precursor may suitably comprise from about 0.01 to
about 1% in total of noble metal(s) (based on the total weight of
all noble metals present as a percentage of the total weight of the
catalyst precursor), or from about 0.015 to about 0.5% in total of
noble metal(s), or from about 0.02 to about 0.3% in total of noble
metal(s).
[0169] If desired, the catalyst precursor may include one or more
other metal-based components as promoters or modifiers. These
metal-based components may also be present in the catalyst
precursor at least partially as oxides or elemental metals. A
suitable metal for the one or more other metal-based components is
one or more of Zr, Ti, V, Cr, Mn, Ni, Cu, Zn, Nb, Mo, Tc, Cd, Hf,
Ta, W, Re, Hg, Tl and the 4f-block lanthanides. Suitable 4f-block
lanthanides are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb and Lu. In particular, the metal for the one or more other
metal-based components may be one or more of Zn, Cu, Mn, Mo and W.
Alternatively, the metal for the one or more other metal-based
components may be one or more of Re and Pt. The catalyst precursor
may comprise from 0.01 to 10% in total of other metal(s) (based on
the total weight of all the other metals as a percentage of the
total weight of the catalyst precursor), or from 0.1 to 5% in total
of other metals, or about 3% in total of other metals.
[0170] The catalyst precursor may contain up to 10% carbon (based
on the weight of the carbon, in whatever form, in the catalyst as
percentage of the total weight of the catalyst precursor), or from
0.001 to 5% of carbon, or about 0.01% of carbon. Alternatively, the
catalyst precursor may comprise no carbon.
[0171] Optionally, the catalyst precursor may contain a
nitrogen-containing organic compound such as urea, or an organic
ligand such as an amine or a carboxylic acid, such as citric acid
or acetic acid, which may be in the form of a salt or an ester.
[0172] The precursor may be activated to produce a Fischer-Tropsch
catalyst, for instance by heating the catalyst precursor in
hydrogen and/or a hydrocarbon gas, or in a hydrogen gas diluted
with another gas, such as nitrogen and/or methane, to convert at
least some of the oxides to elemental metal. In the active
catalyst, the cobalt or iron may optionally be at least partially
in the form of its oxide.
Catalyst Activation
[0173] The catalyst precursor may be activated by any of the
conventional activation processes. For instance, the catalyst
precursor may be activated using a reducing gas, such as hydrogen,
a gaseous hydrocarbon, a mixture of hydrogen and a gaseous
hydrocarbon (e.g. methane), a mixture of gaseous hydrocarbons, a
mixture of hydrogen and gaseous hydrocarbons, a mixture of hydrogen
and nitrogen, syngas, or a mixture of syngas and hydrogen.
[0174] The gas may be at a pressure of from 1 bar (atmospheric
pressure) to 100 bar, or at a pressure of less than 30 bar.
[0175] The catalyst precursor may be heated to its activation
temperature at a rate of from 0.01 to 20.degree. C. per minute. The
activation temperature may be no more than 600.degree. C., or no
more than 400.degree. C.
[0176] The catalyst precursor may be held at the activation
temperature for from 2 to 24 hours, or from 8 to 12 hours.
[0177] After activation, the catalyst may be cooled to a desired
reaction temperature.
[0178] The catalyst, after activation, may be used in a
Fischer-Tropsch process. This process may be carried out in a fixed
bed reactor, a continuous stirred tank reactor, a slurry bubble
column reactor or a circulating fluidized bed reactor. This process
may be carried out in a microchannel reactor (or
"microreactor").
[0179] The Fischer-Tropsch process is well known and the reaction
conditions can be any of those known to the person skilled in the
art, for instance the conditions discussed in WO 2008/104793. For
example the Fischer-Tropsch process may be carried out at a
temperature of from 150 to 300.degree. C., or from 200 to
260.degree. C., a pressure of from 1 to 100 bar, or from 15 to 25
bar, a H.sub.2 to CO molar ratio of from 1.2 to 2.2 or 1.5 to 2.0
or about 1.8, and a gaseous hourly space velocity of from 200 to
5000, or from 1000 to 2000. In a microchannel reactor, the gaseous
hourly space velocity may be from 5000 to 30000.
[0180] As used herein the term "microchannel reactor" refers to an
apparatus comprising one or more process microchannels wherein a
reaction process is conducted. The process may comprise any
chemical reaction such as a Fischer-Tropsch Synthesis (FTS)
process. When two or more process microchannels are used, the
process microchannels may be operated in parallel. The microchannel
reactor may include a manifold for providing for the flow of
reactants into the one or more process microchannels, and a
manifold providing for the flow of product out of the one or more
process microchannels. The microchannel reactor may further
comprise one or more heat exchange channels adjacent to and/or in
thermal contact with the one or more process microchannels. The
heat exchange channels may provide heating and/or cooling for the
fluids in the process microchannels. The heat exchange channels may
be microchannels. The microchannel reactor may include a manifold
for providing for the flow of heat exchange fluid into the heat
exchange channels, and a manifold providing for the flow of heat
exchange fluid out of the heat exchange channels. Examples of
microchannel reactors are as described in WO 2009/126769, WO
2008/030467, WO 2005/075606 and U.S. Pat. No. 7,084,180 B2.
[0181] The depth of each microchannel may be in the range of about
0.05 to about 10 mm, or from about 0.05 to about 5 mm, or from
about 0.05 to about 2 mm, or from about 0.1 to about 2 mm, or from
about 0.5 to about 2 mm, or from about 0.5 to about 1.5 mm, or from
about 0.08 to about 1.2 mm. The width of each microchannel may be
up to about 10 cm, or from about 0.1 to about 10 cm, or from about
0.5 to about 10 cm, or from about 0.5 to about 5 cm.
[0182] As used herein in relation to microchannel reactors, the
term "contact time" refers to the volume of the reaction zone
within the microchannel reactor divided by the volumetric feed flow
rate of the reactant composition at a temperature of 0.degree. C.
and a pressure of one atmosphere.
[0183] Preferably, the microchannel reactor used for the FTS
process is capable of high heat flux for cooling of the process
microchannels during the reaction, which may be achieved by
incorporating heat exchange channels as described above. The
microchannel reactor for FTS may be designed to achieve a heat flux
greater than 1 W/cm.sup.2. The heat flux for convective heat
exchange in the microchannel reactor may range from about 1 to
about 25 watts per square centimetre of surface area of the process
microchannels (W/cm.sup.2) in the microchannel reactor, suitably
from about 1 to about 10 W/cm.sup.2. The heat flux for phase change
or simultaneous endothermic reaction heat exchange may range from
about 1 to about 250 W/cm.sup.2, from about 1 to about 100
W/cm.sup.2, from about 1 to about 50 W/cm.sup.2, from about 1 to
about 25 W/cm.sup.2, and from about 1 to about 10 W/cm.sup.2.
[0184] The cooling of the process microchannels during the reaction
is advantageous for controlling selectivity towards the main or
desired product due to the fact that such added cooling reduces or
eliminates the formation of undesired by-products from undesired
parallel reactions with higher activation energies. As a result of
this cooling, the temperature of the reactant composition at the
entrance to the process microchannels may be within about
200.degree. C., within about 150.degree. C., within about
100.degree. C., within about 50.degree. C., within about 25.degree.
C., within about 10.degree. C., of the temperature of the product
(or mixture of product and unreacted reactants) at the exit of the
process microchannels.
[0185] It will be recognised that features related to one aspect of
the invention are also, where applicable, features of other aspects
of the invention. It will further be recognised that features
specified herein in one embodiment of the invention may be combined
with other features specified herein to provide further
embodiments.
DETAILED DESCRIPTION
[0186] The present invention is now described, by way of
illustration only, with reference to the accompanying drawings, in
which:
[0187] FIG. 1 shows variation in turnover frequency with average
Co.sub.3O.sub.4 particle size.
[0188] FIG. 2 shows variation in methane selectivity with average
pore size of the catalyst.
[0189] The invention is further illustrated by the following
examples. It will be appreciated that the examples are for
illustrative purposes only and are not intended to limit the
invention as described above. Modification of detail may be made
without departing from the scope of the invention.
EXAMPLES
[0190] The precursor materials used in the preparation of the
supports and catalysts of the following Examples are listed in
Table 1.
TABLE-US-00001 TABLE 1 Raw Material Supplier Other details Citric
acid monohydrate Fischer Purity 99.5% Zirconium dinitrate oxide
hydrate Alfa Aesar Purity 99.90% Silica, SG432 (LC150) (silica A)
Grace Davison Particle size 180-300 .mu.m Silica, AGC D-60/80-200A
(silica B) AGC Silica Particle size 120-300 .mu.m Manganese (II)
nitrate tetrahydrate Alfa Aesar Purity 98% Chromium (III) nitrate
nonahydrate Sigma Aldrich Purity 99% Cobalt nitrate hexahydrate
Sigma Aldrich Purity 98% Tetraammine platinum hydroxide Alfa Aesar
9.3% Pt w/w Perrhenic acid Sigma Aldrich 70 wt % in water TALH
Sigma Aldrich 50% solution (Titanium(IV) bis(ammonium in water
lactato) dihydroxide)
Preparation of Modified Catalyst Supports
[0191] Examples 1 to 8, relate to the preparation of silica
catalyst supports modified with one of zirconium oxide, chromium
oxide, and manganese oxide and to catalysts prepared from the
catalyst supports. The amounts of the metal precursor used were
chosen to give 4 metal atoms per nm.sup.2 over the resulting
support, except in the case of the 17% ZrO.sub.2 support where
there are 3 metal atoms per nm.sup.2. For each metal, two modified
supports were prepared, one using Method A (the "aqueous method")
and the other using Method B (the "standard incipient wetness
impregnation method"). In Method A, catalyst supports were prepared
in which the metal precursor was mixed with an aqueous solution of
citric acid (molar ratio of metal atoms to citric acid 1:0.6) and
then used to impregnate the support. In Method B, catalyst supports
were prepared in which an aqueous solution of only the metal
precursor was used to impregnate the support. Two different silica
supports have been have been used: a lower pore volume silica
(silica A with a BJH pore volume of 1.30 cm.sup.3/g) and a higher
pore volume silica (silica B, with a BJH pore volume of 1.80
cm.sup.3/g).
Example 1
Synthesis of ZrO.sub.2-Modified Silica Catalyst Support (22%
ZrO.sub.2/SiO.sub.2) Using Method a (Supports A1 to A3)
[0192] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 31.4 g of silica was weighed and
allowed to cool to room temperature. 8.82 g citric acid was mixed
with 12 ml H.sub.2O and heated to about 50.degree. C. with stirring
until fully dissolved. The solution was then allowed to cool to
room temperature. 16.22 g zirconium dinitrate oxide hydrate (also
known as "zirconyl nitrate") was mixed with 15 ml H.sub.2O and
stirred using a magnetic stirbar, without heat, for 20 minutes to
obtain a translucent solution. The zirconyl nitrate solution and
citric acid solution were mixed together to form the impregnation
solution. The impregnation solution was used immediately after
preparation to impregnate the silica support. The support was
impregnated by mixing the impregnation solution and the silica in
order to reach the point of incipient wetness.
[0193] Following impregnation, a portion of the modified catalyst
support was dried in a muffle furnace at a temperature that
increased at a ramp rate of 2.degree. C./min up to 100.degree. C.
The temperature was held at 100.degree. C. for 10 hours (support
A1, code 1112-13-005-3).
[0194] Further portions of the impregnated support were calcined to
different temperatures in order to examine the effect of
calcination temperature.
[0195] One portion of the impregnated support was calcined at a
temperature that increased at a ramp rate of 2.degree. C./min up to
100.degree. C. The temperature was held at 100.degree. C. for 5
hours. The temperature was then increased at a ramp rate of
2.degree. C./min up to 250.degree. C. The temperature was held at
250.degree. C. for 5 hours (support A2, code 1203-21-005-2).
[0196] Another portion of the impregnated support was calcined at a
temperature that increased at a ramp rate of 2.degree. C./min up to
100.degree. C. The temperature was held at 100.degree. C. for 5
hours. The temperature was then increased at a ramp rate of
2.degree. C./min up to 350.degree. C. The temperature was held at
350.degree. C. for 8 hours (support A3, code 1112-13-005-1).
[0197] The resulting catalyst supports A1 to A3 had ZrO.sub.2 bound
to the silica surface at an amount equivalent to 22% ZrO.sub.2 on
silica support.
Example 2 (Reference)
Synthesis of ZrO.sub.2-Modified Silica Catalyst Support (22%
ZrO.sub.2/SiO.sub.2) Using Method B (Support B)
[0198] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 31.4 g of silica was weighed and
allowed to cool to room temperature. The impregnation solution was
prepared by mixing 16.22 g zirconyl nitrate with 30 ml H.sub.2O and
stirring using a magnetic stirbar, without heat, for 20 minutes to
obtain a translucent solution with a total volume of 33 ml. The
impregnation solution was used immediately after preparation to
impregnate the silica support. The support was impregnated by
mixing the impregnation solution and the silica in order to reach
the point of incipient wetness.
[0199] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support B, code
1112-13-005-4).
[0200] The resulting catalyst support B had ZrO.sub.2 bound to the
silica surface at an amount equivalent to 22% ZrO.sub.2 on the
silica support.
Example 3
Synthesis of Mn.sub.2O.sub.3-modified Silica Catalyst Support (15%
Mn.sub.2O.sub.3/SiO.sub.2) Using Method a (Support C)
[0201] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 16.8 g of silica was weighed and
allowed to cool to room temperature. 4.71 g citric acid was mixed
with 8 ml H.sub.2O and heated to about 50.degree. C. with stirring
until fully dissolved. The solution was cooled to about 35.degree.
C., then 9.57 g of manganese nitrate was added and the solution was
stirred until fully dissolved. The volume of the solution was
adjusted to 19 ml with H.sub.2O to form the impregnation solution
and then allowed to cool to room temperature. The impregnation
solution was used to impregnate the silica support by mixing the
impregnation solution and the silica in order to reach the point of
incipient wetness.
[0202] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support C, code
1112-14-005-3).
[0203] The resulting modified catalyst support C had
Mn.sub.2O.sub.3 bound to the silica surface at an amount equivalent
to 15% Mn.sub.2O.sub.3 on silica support.
Example 4 (Reference)
Synthesis of Mn.sub.2O.sub.3-Modified Silica Catalyst Support (15%
Mn.sub.2O.sub.3/SiO.sub.2) Using Method B (Support D)
[0204] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 16.8 g of silica was weighed and
allowed to cool to room temperature. 9.57 g of manganese nitrate
was added to 8 ml H.sub.2O and heated to about 35.degree. C. with
stirring until fully dissolved. The volume of the solution was
adjusted to 19 ml with H.sub.2O to form the impregnation solution
and then allowed to cool to room temperature. The impregnation
solution was used to impregnate the silica support by mixing the
impregnation solution and the silica in order to reach the point of
incipient wetness.
[0205] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support D, code
1112-14-005-4).
[0206] The resulting modified catalyst support C had
Mn.sub.2O.sub.3 bound to the silica surface at an amount equivalent
to 15% Mn.sub.2O.sub.3 on silica support.
Example 5
Synthesis of Cr.sub.2O.sub.3-Modified Silica Catalyst Support (15%
Cr.sub.2O.sub.3/SiO.sub.2) Using Method A (Support E)
[0207] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 17.1 g of silica was weighed and
allowed to cool to room temperature. 4.81 g citric acid was mixed
with 5 ml H.sub.2O and heated to about 50.degree. C. with stirring
until fully dissolved. The citric acid solution was cooled to room
temperature and then 15.42 g of chromium nitrate was added and the
solution heated gently until fully dissolved. The solution was
cooled, thereby forming the impregnation solution. The impregnation
solution was used to impregnate the silica support by mixing the
impregnation solution and the silica in order to reach the point of
incipient wetness.
[0208] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support E, code
1203-09-005-3).
[0209] The resulting modified catalyst support E had
Cr.sub.2O.sub.3 bound to the silica surface at an amount equivalent
to 15% Cr.sub.2O.sub.3 on silica support.
Example 6 (Reference)
Synthesis of Cr.sub.2O.sub.3-Modified Silica Catalyst Support (15%
Cr.sub.2O.sub.3/SiO.sub.2) Using Method B (Support F)
[0210] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 17.1 g of silica was weighed and
allowed to cool to room temperature. 15.42 g of chromium nitrate
was added to 5 ml H.sub.2O and the solution heated gently until
fully dissolved. The solution was cooled. The volume of the
solution was adjusted with H.sub.2O to 19 ml to form the
impregnation solution. The impregnation solution was used to
impregnate the silica support by mixing the impregnation solution
and the silica in order to reach the point of incipient
wetness.
[0211] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support H, code
1203-09-005-4).
[0212] The resulting modified catalyst support F had
Cr.sub.2O.sub.3 bound to the silica surface at an amount equivalent
to 15% Cr.sub.2O.sub.3 on silica support.
Example 7
Synthesis of ZrO.sub.2-Modified Silica Catalyst Support (17%
ZrO.sub.2/SiO.sub.2) Using Method A (Support G)
[0213] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 16.6 g of silica was weighed and
allowed to cool to room temperature. 3.5 g citric acid was mixed
with 5 ml H.sub.2O and heated to about 50.degree. C. with stirring
until fully dissolved. The solution was then allowed to cool to
room temperature. 6.42 g zirconium dinitrate oxide hydrate (also
known as "zirconyl nitrate") was mixed with 9 ml H.sub.2O and
stirred using a magnetic stirbar, without heat, for 20 minutes to
obtain a translucent solution. The zirconyl nitrate solution and
citric acid solution were mixed together to form the impregnation
solution of total volume about 19 ml. The impregnation solution was
used immediately after preparation to impregnate the silica
support. The support was impregnated by mixing the impregnation
solution and the silica in order to reach the point of incipient
wetness.
[0214] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support G, code
1203-06-005-7).
[0215] The resulting catalyst support G had ZrO.sub.2 bound to the
silica surface at an amount equivalent to 17% ZrO.sub.2 on silica
support.
Example 8 (Reference)
Synthesis of ZrO.sub.2-Modified Silica Catalyst Support (17%
ZrO.sub.2/SiO.sub.2) Using Method B (Support H)
[0216] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 16.6 g of silica was weighed and
allowed to cool to room temperature. The impregnation solution was
prepared by mixing 6.42 g zirconyl nitrate with 16 ml H.sub.2O and
stirring using a magnetic stirbar, without heat, for 20 minutes to
obtain a translucent solution with a total volume of 19 ml. The
impregnation solution was used immediately after preparation to
impregnate the silica support. The support was impregnated by
mixing the impregnation solution and the silica in order to reach
the point of incipient wetness.
[0217] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 10 hours (support H, code
1203-06-005-8).
[0218] The resulting catalyst support H had ZrO.sub.2 bound to the
silica surface at an amount equivalent to 17% ZrO.sub.2 on the
silica support.
Synthesis of Catalysts from Modified Supports
Example 9
[0219] A catalyst was prepared from each of the modified catalyst
supports made using Method A (Examples 1, 3, 5 and 7, except for
support A3).
[0220] For each modified support, an impregnation solution was
prepared by dissolving 12.75 g cobalt nitrate hexahydrate in 3 ml
H.sub.2O and heating to about 50.degree. C. with stirring until
fully dissolved. The solution was cooled to room temperature and
0.024 g perrhenic acid was added. H.sub.2O was added to make the
volume of the solution 11 ml.
[0221] A first impregnation of each support was carried out by
using the 11 ml of impregnation solution to impregnate about 11.7 g
of the support (support purity estimated at 85% to give a final
support weight of 10 g). The impregnated modified catalyst support
was then dried at a temperature that increased at a ramp rate of
2.degree. C./min up to 100.degree. C. The temperature was held at
100.degree. C. for 5 hours. The modified catalyst support was
subsequently calcined by increasing the temperature to 250.degree.
C. using a ramp rate of 2.degree. C./min and holding the
temperature at 250.degree. C. for 3 hours.
[0222] Second, third and fourth impregnation steps of each modified
catalyst support were carried out by preparing, for each modified
catalyst support, a stock impregnation solution of 5.78 g citric
acid mixed with 4 ml H.sub.2O and heating to about 50.degree. C.
with stirring until fully dissolved. This solution was added to
40.71 g cobalt nitrate hexahydrate and heated to about 50.degree.
C. with stirring until fully dissolved. To this was added 0.077 g
perrhenic acid and the solution was cooled to room temperature. The
resulting stock impregnation solution was divided over impregnation
steps 2 to 4, as shown in Table 2, which summarises the four
impregnation steps. After each impregnation step, the modified
catalyst support was calcined at a temperature that increased at a
ramp rate of 2.degree. C./min up to 100.degree. C. The temperature
was held at 100.degree. C. for 5 hours. The modified support
catalyst was subsequently calcined by increasing the temperature to
250.degree. C. using a ramp rate of 2.degree. C./min and holding
the temperature at 250.degree. C. for 3 hours.
TABLE-US-00002 TABLE 2 Co(NO.sub.3).sub.2 Co(NO.sub.3).sub.2
6H.sub.2O (g) 6H.sub.2O (g) Citric Perrhenic Solution Calc. Support
Purity *Purity Co.sub.3O.sub.4 Co acid acid Re H.sub.2O volume Wt %
Step wt (g) 98% 100% (g) (g) (g) (g) (g) (ml) (ml) (g) Co 1 10
12.75 12.49 3.44 2.53 0.00 0.0242 0.0117 min. 11.0 13.5 18.8 2 --
13.57 13.3 3.67 2.69 1.93 0.0258 0.0124 min. 10.0 17.1 30.5 3 --
13.57 13.3 3.67 2.69 1.93 0.0258 0.0124 min. 9.5 20.8 38.0 4 --
13.57 13.3 3.67 2.69 1.93 0.0258 0.0124 min. 8.0 24.5 43.3 *This is
a calculated value to show how much Co(No.sub.3).sub.2. 6H.sub.2O
is actually added.
[0223] After the impregnation step 4 and the last calcination, each
resulting catalyst precursor was subjected to a promoter addition
step. 0.048 g of tetraammine platinum hydroxide (9.3% Pt w/w) was
diluted to 3.4 ml with water to make a dilute solution and this
solution was used to further impregnate 15 g of the catalyst
precursor. After impregnation, the catalyst was then dried at a
temperature that increased at a ramp rate of 2.degree. C./min up to
100.degree. C. The temperature was held at 100.degree. C. for 5
hours. The catalyst was subsequently calcined by increasing the
temperature to 250.degree. C. using a ramp rate of 2.degree. C./min
and holding the temperature at 250.degree. C. for 3 hours.
[0224] Each of the resulting catalysts made from a Method A support
had 0.03% Pt and is suitable for use as, for example, a
Fischer-Tropsch catalyst.
Example 10
[0225] A catalyst was prepared from each of the modified catalyst
supports made using Method B (Examples 2, 4, 6 and 8) and the
modified catalyst support made from Method A but calcined to
350.degree. C. (Support A3).
[0226] For each modified support, a stock impregnation solution was
prepared by mixing 7.24 g citric acid with 6 ml H.sub.2O and
heating to about 50.degree. C. with stirring until fully dissolved.
This solution was added to 50.98 g cobalt nitrate hexahydrate and
heated to about 50.degree. C. with stirring until fully dissolved.
0.099 g perrhenic acid was added and the solution was cooled to
room temperature
[0227] For each modified catalyst support, the stock impregnation
solution was dived over each of four impregnation steps, as
summarised in Table 3. For the first impregnation step 11.7 g of
the support (support purity estimated at 85% to give a final
support weight of 10 g) was used. After each of impregnation steps
1 to 4, the impregnated modified catalyst support was dried at a
temperature that increased at a ramp rate of 2.degree. C./min up to
100.degree. C. The temperature was held at 100.degree. C. for 5
hours. The modified catalyst support was subsequently calcined by
increasing the temperature to 250.degree. C. using a ramp rate of
2.degree. C./min and holding the temperature at 250.degree. C. for
3 hours.
TABLE-US-00003 TABLE 3 Co(NO.sub.3).sub.2 Co(NO.sub.3).sub.2
6H.sub.2O (g) 6H.sub.2O (g) Citric Perrhenic Solution Calc. Support
Purity Purity Co.sub.3O.sub.4 Co acid acid Re H.sub.2O volume Wt %
Step wt (g) 98% 100% (g) (g) (g) (g) (g) (ml) (ml) (g) Co 1 10
12.75 12.49 3.44 2.53 1.81 0.0247 0.0119 min. 10.0 13.5 18.8 2 --
12.75 12.49 3.44 2.53 1.81 0.0247 0.0119 min. 10.0 16.9 39.9 3 --
12.75 12.49 3.44 2.53 1.81 0.0247 0.0119 min. 9.0 20.4 37.2 4 --
12.75 12.49 3.44 2.53 1.81 0.0247 0.0119 min. 9.0 23.8 42.4
[0228] After the impregnation step 4 and the last calcination, each
resulting catalyst precursor was subjected to a promoter addition
step. 0.048 g of tetraammine platinum hydroxide (9.3% Pt w/w) was
diluted to 3.4 ml with water to make a dilute solution and this
solution was used to further impregnate 15 g of the catalyst
precursor. After impregnation, the catalyst was then dried at a
temperature that increased at a ramp rate of 2.degree. C./min up to
100.degree. C. The temperature was held at 100.degree. C. for 5
hours. The catalyst was subsequently calcined by increasing the
temperature to 250.degree. C. using a ramp rate of 2.degree. C./min
and holding the temperature at 250.degree. C. for 3 hours.
[0229] Each of the resulting catalysts made from a Method B support
had 0.03% Pt and is suitable for use as, for example, a
Fischer-Tropsch catalyst.
Comparison of Catalysts Made from a Method a Support and a Method B
Support
Example 11
Fischer-Tropsch Reaction Tests
[0230] Catalysts obtained in Examples 9 and 10 were tested for
Fischer Tropsch synthesis (FTS) performance. The catalysts were
diluted with SiC at a 1:18 ratio and then loaded in a fixed-bed
combinatorial reactor (L/D 31 cm, Volume catalytic bed: 0.1285
cm.sup.3) and reduced using pure hydrogen at 400.degree. C. for 120
minutes at Gas Hourly Space Velocity (GHSV)=15 000 per hour. The
temperature was increased from room temperature to 400.degree. C.
at 1.degree. C./min. After the reduction, the reactor was cooled to
165.degree. C. and the gas was switched from hydrogen to synthesis
gas. The operating conditions were kept constant for 1 hour. The
pressure was then increased to 20 bar at the flow rate of the
reaction and held for 1 hour. The temperature was then increased
from 165.degree. C. to 190.degree. C. at a ramp rate of 4.degree.
C./hour, from 190 to 210.degree. C. (GHSV=12 400 per hour) at
2.degree. C./hour and then kept at the FTS reaction temperature
(between 203.degree. C. and 210.degree. C. in these examples)
(GHSV=12 400 per hour) for about 120 hours. The Fischer Tropsch
reaction was carried out for a total of 160 hours.
[0231] The liquid products from the reaction were condensed with a
hot (temperature=80.degree. C.) and cold (temperature=5.degree. C.)
trap downstream of the FT reactor, and the gas products were
injected online into a Clarus 600 gas chromatograph. Hydrogen,
carbon monoxide and nitrogen were detected with a thermal
conductivity detector and hydrocarbons (from C1 to C4) with a flame
ionization detector. CO conversion and product selectivity were
calculated by using nitrogen as a tracer and employing a carbon
mass balance.
[0232] The % C.sub.5+ selectivity (S.sub.C5+) of the catalyst was
calculated at 24 hours time on stream via
S.sub.C5+=100-(S.sub.CH4+S.sub.C2+S.sub.C2=+S.sub.C3+S.sub.C3=+S.sub.C4+-
S.sub.C4=+S.sub.CO2);
where S.sub.CH4; S.sub.C2, S.sub.C2=, S.sub.C3, S.sub.C3=,
S.sub.C4, S.sub.C4= and S.sub.CO2 are the calculated % of
selectivity of methane, ethane, ethene, propane, propene, butane,
butene and carbon dioxide, respectively. These are calculated
via
S x = 100 ( X out CO in - CO out ) ##EQU00002##
Where S.sub.X is either S.sub.CH4, S.sub.C2, S.sub.C2=, S.sub.C3,
S.sub.C3=, S.sub.C4, S.sub.C4= or S.sub.CO2; X.sub.out is the
amount (expressed in grams per hour, g hr.sup.-1) of the species X
measured at the rector outlet and CO.sub.in and CO.sub.out are the
amount (expressed in grams per hour, g hr.sup.-1) of carbon
monoxide measured at the inlet and outlet of the reactor,
respectively.
[0233] The deactivation rate of the catalyst was calculated via a
linear regression analysis of the percent of CO converted during
the reaction between a time on stream of 24 hours until the end of
the run (160 hours). The activity of the catalyst, in mol CO
hr.sup.-1 g.sub.Co.sup.-1, at 24 hours time on stream was
calculated via
activity = CO % conversion 100 % CO flow rate in mL min 60 min hr
22400 mL mol CO 1 catalyst weight in g 0.42 ##EQU00003##
[0234] The temperature at which the FT reaction test was carried
out varied depending on the activity of the catalyst. Catalysts
were tested initially at 210.degree. C. Catalysts displaying high
activity were also tested at 203.degree. C. in order to compare FTS
performance of catalysts with differing activities at similar
conversion levels.
[0235] A summary of the FTS performance of the catalysts is shown
in Table 4 and compared to a reference titania-modified silica made
using the aqueous method.
TABLE-US-00004 TABLE 4 Activity .DELTA. % CO Selectivity mol % CO
conversion (%) CO/hr/g Run .rho. T Support used conversion (%/day)
C.sub.5+ CH.sub.4 Co # (g/ml) (.degree. C.) Titania-modified 73.6
-1.12 86.4 9.3 0.273 69 1.12 210 silica A, example 16 (reference)
Support A1 80.7 -1.41 86.2 9.2 0.266 69 1.26 210 (22% ZrO.sub.2,
method A, dried 100.degree. C.) Support A1 74.6 -0.83 86.1 9.2
0.222 76 1.39 203 (22% ZrO.sub.2, method A, dried 100.degree. C.,
repeat preparation) Support A1 65.8 -1.08 87.5 7.7 0.216 76 1.26
203 (22% ZrO.sub.2, method A, dried 100.degree. C.) Support A2 83.2
-1.43 87.3 8.8 0.278 69 1.24 210 (22% ZrO.sub.2, method A, calcined
250.degree. C.) Support A2 69.1 -1.01 87.4 8.3 0.231 76 1.24 203
(22% ZrO.sub.2, method A, calcined 250.degree. C.) Support A3 77.1
-1.54 87.8 8.8 0.281 69 1.14 210 (22% ZrO.sub.2, method A, calcined
350.degree. C.) Support B 74.3 -1.74 87.8 8.7 0.266 65 1.16 210
(22% ZrO.sub.2, method B) Support C 12.7 -0.42 55.0 11.3 0.043 65
1.21 210 (15% Mn.sub.2O.sub.3, method A, dried 100.degree. C.)
Support E 71.3 -2.22 85.0 10.1 0.238 69 1.24 210 (15%
Cr.sub.2O.sub.3, method A, dried 100.degree. C.) Support F 76.9
-2.10 85.6 10.3 0.242 72 1.32 210 (15% Cr.sub.2O.sub.3, method B)
Support G 66.7 -0.94 85.2 7.9 0.208 76 1.33 203 (17% ZrO.sub.2,
method A, dried 100.degree. C.) Support H 63.5 -0.99 86.5 7.9 0.221
76 1.19 203 (17% ZrO.sub.2, method B)
[0236] The results show that catalysts made using the
zirconia-modified supports display particularly good FTS
performance, comparable to a reference catalyst made using a
titania-modified silica catalyst support.
[0237] The catalyst made on a support modified with 22% ZrO.sub.2
via Method A shows an improvement in stability over the reference
catalyst made using a titania-modified silica support. The
stability of the catalyst on zirconium oxide-modified silica is
shown to vary depending on the temperature at which the support was
pretreated. The stability of the catalyst is highest when the
support is either dried only or treated to 250.degree. C.; a
significant decrease in stability is observed when the support is
calcined to 350.degree. C. However, even the support treated to
350.degree. C. is more stable than the catalyst made on silica
modified with 22% ZrO.sub.2 via Method B. The catalyst made on the
Method B 22% ZrO.sub.2/SiO.sub.2 support has a deactivation rate
that is approximately twice as fast as the catalyst on the Method A
support. Additionally, the catalysts on the Method A supports which
were either dried or calcined to just 250.degree. C. are more
active than either the reference catalyst on titania-modified
silica or the Method B 22% ZrO.sub.2/SiO.sub.2 supports. The
increased activity of the catalysts on the supports modified using
Method A is shown by the lower temperature used during FTS to reach
similar conversion levels. Without being bound by theory, the
inventors believe that the residual organic species on the modified
support are a factor in making the catalysts derived from Method A
supports more stable. The higher the pretreatment temperature, the
fewer organic species remain on the surface of the support, which
results in a decrease in stability.
[0238] In addition to the increase in stability and activity of the
catalysts on 22% ZrO.sub.2/SiO.sub.2, there is an unexpected
decrease in the methane selectivity of these catalysts as compared
to the reference catalyst made using a titania-modified silica
support. All the catalysts on a 22% ZrO.sub.2/SiO.sub.2 support
have a methane selectivity that is lower than the reference
catalyst on titania-modified silica.
[0239] The catalysts on 17% ZrO.sub.2 modified silica made by
Method A is more stable than the catalyst on the Method B support
but the magnitude of the difference is much less than was observed
for 22% ZrO.sub.2. This indicates that a minimum level of metal
oxide modifier may be required to observe a substantial increase in
stability. However, the 17% ZrO.sub.2 catalyst is more active than
the reference titania-modified silica catalyst, as shown by the
decreased temperature used during FTS testing.
[0240] The catalysts on supports modified with 15% Cr.sub.2O.sub.3
made using Method A and Method B are both more unstable during FTS
than the zirconium oxide-modified support.
[0241] In summary, catalysts made using ZrO.sub.2-modified silica
supports prepared using Method A are more stable than those
prepared using Method B. Furthermore, comparison of the catalysts
made using ZrO.sub.2-modified silica supports shows that calcining
at 250.degree. C. is advantageous compared to calcining at
350.degree. C. or to simply drying at 100.degree. C. and leads to
more stable catalysts.
Example 12
Comparison of Porosity and Acidity of Modified Supports Prepared in
Examples 1 to 6
[0242] The BET surface areas of the modified supports prepared in
Examples 1 to 6 were determined using nitrogen physisorption at 77K
in a Micromeritics Tristar II instrument. All supports were
calcined to 400.degree. C. before measurement. Prior to
measurement, all samples were degassed in nitrogen at 100.degree.
C. for 3 hours. The pore size distribution, average pore size and
total pore volume were determined using a density functional theory
(DFT) calculation method, with adsorption isotherm pressure points
over the range 0.25 to 0.99 p/po. A Micromeritics built-in
cylindrical model based on oxide surfaces was chosen, and a high
degree of regularisation applied. The results of this analysis are
shown in Table 5.
[0243] To determine the acidity of the modified support surface of
the modified supports prepared in Examples 1 to 6, temperature
programmed desorption (TPD) experiments were carried out using an
Altamira AMI200 instrument. All modified supports were calcined to
400.degree. C. before measurement. About 50 mg of the modified
support sample was loaded into a U-shaped quartz tube, with a small
wad of quartz wool above and below the sample. The samples were
first degassed in argon at 150.degree. C. for 30 minutes, before
decreasing the temperature to 100.degree. C. and changing the flow
to 10% NH.sub.3 in helium. This gas mixture was passed over the
sample of modified catalyst support at 100.degree. C. for 30
minutes (analysis of the TCD signal indicated gas absorption was
complete within a few minutes), before switching back to argon.
Inert gas flow was maintained for 1 hour to remove physisorbed
species after which the temperature was then reduced to 70.degree.
C. The desorption was carried out under flowing argon from 70 to
400.degree. C. at 5.degree. C./min, followed by a hold at
400.degree. C. for 30 minutes. A moisture trap was not used.
Quantification of the amount of gas released was carried out by
calibration of a 10% NH.sub.3 in a stream of helium. The results of
this analysis are shown in Table 5.
TABLE-US-00005 TABLE 5 Method A supports Method B supports
(reference) 22% 15% 15% 15% ZrO.sub.2 Mn.sub.2O.sub.3
Cr.sub.2O.sub.3 22% ZrO.sub.2 Mn.sub.2O.sub.3 15% Cr.sub.2O.sub.3
BET As (m.sup.2/g) 299.65 291.18 274.74 292.58 278.51 273.70 DFT
pore volume 0.9183 0.9444 0.9748 0.9316 0.9802 1.018 (cm.sup.3/g)
DFT Av pore 171.1 183.73 174.78 193.2 189.85 183.82 diameter
(.ANG.) Surface acidity 0.120 0.251 0.282 -- -- -- (.mu.mol
NH.sub.3/m.sup.2)
[0244] The results summarised in Table 5 show that when Method A is
used to modify silica, the resulting catalyst supports have higher
surface areas and smaller average pore diameters than supports
modified using Method B. It is believed that the use of an aqueous
metal precursor and citric acid is more effective at dispersing the
metal oxides over the support than the use of the standard
incipient wetness impregnation method (Method B).
[0245] The results also show that the porosity and the surface
acidity of the supports vary significantly as the metal used to
modify the support is varied. This shows that modifying silica with
a metal oxide offers a way to alter the porosity and acidity of the
support and, as such, specific surface acidity and/or porosity
properties of silica can be obtained by selecting the metal species
used to modify the catalyst support.
Example 13
Comparison of Porosity of Catalysts Made from the Modified
Supports
[0246] The BET surface area of catalysts obtained in Examples 9 and
10 was determined using nitrogen physisorption at 77 K in a
Micromeritics Tristar II instrument. Prior to measurement, all
samples were degassed in nitrogen at 100.degree. C. for 3 hours.
The pore size distribution, average pore size and total pore volume
were determined using a DFT calculation method, with adsorption
isotherm pressure points over the range 0.25-0.99 p/po. A
Micromeritics built-in cylindrical model based on oxide surfaces
was chosen, and a high degree of regularisation applied. The
porosities of catalysts made from the modified silica supports are
shown in Table 6.
TABLE-US-00006 TABLE 6 Method A supports 22% Method B supports
ZrO.sub.2, (reference) 22% calc 17% 15% 22% 17% 15% ZrO.sub.2
250.degree. C. ZrO.sub.2 Cr.sub.2O.sub.3 ZrO.sub.2 ZrO.sub.2
Cr.sub.2O.sub.3 (support (Support (Support (Support (Support
(Support (Support A1) A2) G) E) B) H) F) BET As (m.sup.2/g) 104 111
95.7 114 111 116 107 DFT pore volume 0.219 0.233 0.226 0.223 0.251
0.286 0.214 (cm.sup.3/g) DFT Av pore 136 144 149 127 158 157 140
diameter (.ANG.)
[0247] The results show that the method of modifying the support
has a significant effect on the porosity of the resulting
catalysts. The catalyst supported on 22% ZrO.sub.2/SiO.sub.2,
Method A, has a lower pore volume and a smaller average pore
diameter than the catalyst supported on the 22% ZrO.sub.2/SiO.sub.2
support made via Method B. The same trend is observed for the
catalysts supported on 17% ZrO.sub.2/SiO.sub.2. Although the
catalysts on 15% Cr.sub.2O.sub.3/SiO.sub.2 supports have very
similar pore volumes, the catalyst on the Method B support has a
larger average pore diameter than the catalyst on the Method A
support.
[0248] For all three comparisons, the catalyst on the Method B
support has a larger pore diameter than the catalyst on the Method
A support. This indicates that the dispersion through the Method A
supported catalysts differs from the Method B supported
catalysts.
[0249] When Method B is used to prepare the modified catalyst
support, the resulting catalysts have larger pore diameters and the
catalyst components are less well dispersed through the particle
pores than when Method A is used. Without being bound by theory,
the inventors believe that a better dispersion of the metal oxide
through the catalyst support material results in a more effective
coverage of hydroxyl groups on the silica surface, thus resulting
in a more stable catalyst.
Example 14
Comparison of Co.sub.3O.sub.4 Particle Size of Catalysts Made from
the Modified Supports
[0250] X-ray diffraction patterns of fresh catalysts obtained in
Examples 9 and 10 were collected on a fully automated Siemens D5000
theta/theta powder diffractometer using Cu K.sub..alpha. radiation.
Each sample was ground thoroughly before loading into a spinner
carousel in air. Data were collected over the range 10-80.degree.
2.theta., with a step size of 0.05.degree. and a step length of 12
s, and were analysed using the Rietveld method via the program
GSAS. Likely crystalline phases were included until all peaks were
indexed. The average Co.sub.3O.sub.4 crystallite size (D.sub.O),
the c value and the D value of the Co.sub.3O.sub.4 crystallites
were determined as described below.
[0251] The lattice parameters and phase fractions of all phases
were refined first along with the background, which was fitted with
a 16 term shifted Chebyshev polynomial. The sample shift and
transparency were freely refined. As Co.sub.3O.sub.4 was the major
phase in all calcined catalysts studied, this phase was analysed in
detail. The oxygen atom position of the Co.sub.3O.sub.4 phase was
first refined, along with the thermal parameters of all positions
in this phase. The profile shape of the Co.sub.3O.sub.4 phase was
then fitted with a Caglioti instrumental function (previously
determined using a corundum standard) and a Lorentzian X and Y term
were refined along with a Gaussian U and P contribution. The X, Y,
U and P profile parameters of the Co.sub.3O.sub.4 phase were
deconvoluted into their size and strain components using the
methods described in Balzar et al. Journal of Applied
Crystallography (2004), 37, 911-924 and Krill et al, Philosophical
Magazine A (1998) 77, 620-640.
[0252] Explicitly, the X and P profile shape terms were used to
determine the average crystallite size and the width of the
distribution (assuming a lognormal, monomodal size distribution of
spherical crystallites). First, the profile parameters were
converted into integral breadths via
.beta. G , S = 2 .pi. 3 P 18000 ##EQU00004## .beta. L , S = .pi. 2
X 2 18000 ##EQU00004.2##
[0253] The Lorentzian and Gaussian intergral breadths are then
combined for the size (S) part:
.beta. S = .beta. G , S - k s 2 1 - erf ( k S ) where k S = .beta.
L , S .pi. .beta. G , S ##EQU00005##
[0254] Once the separate peak shapes have been deconvoluted into
the size component via this method, the volume-weighted (L.sub.V,
size distribution function weighted by the volume of the domains)
and area-weighted (L.sub.A, size distribution function weighted by
the cross-sectional area of the domains) domain sizes may be
determined through
L V = .lamda. .beta. S and L A = .lamda. 2 .beta. L , S
##EQU00006##
[0255] If the crystallites are assumed to be spheres, the area- and
volume-weighted domain sizes can be related to the sphere diameters
via
D V = 4 3 L V and D A = 3 2 L A ##EQU00007##
[0256] Finally, the volume and area weighted domain sizes are
related to the dimensionless ratio c of the lognormal distribution
and the numeric average particle radii R.sub.O by
c = 8 L V 9 L A - 1 and R O = 2 L V 3 ( 1 + c ) 3 ##EQU00008##
[0257] This explicitly assumes that the real particles are
equivalent to the crystallites. The numeric average particle
diameter)(D.sub.O=2R.sub.O) is thus related to the volume- and
area-weighed diameters through
D.sub.V=D.sub.0(1+c).sup.3 and D.sub.A=D.sub.0(1+c).sup.2
[0258] The form of the distribution is:
f ( R ) = 1 R 2 .pi. ln ( 1 + c ) - [ ln ( R R O 1 + c ) ] 2 2 ln (
1 + c ) where c = .sigma. 2 R O 2 Equation 1 ##EQU00009##
Where R.sub.O is the numeric average particle radius and c, which
is known as the dimensionless ratio, characterises the width of the
size distribution.
[0259] The frequency at the mode of this lognormal distribution
(f.sub.mode) modelled using Equation 1 was weighted by the size
distribution median to create a "size-weighted distributed
breadth", or D-value, using the formula:
D=f.sub.mode.sup.y.times.R.sub.O.times.2 Equation 2
wherein f.sub.mode is the frequency at the mode of the lognormal
distribution; y is an exponential factor which is determined
experimentally to obtain the best degree of fit with the FTS
stability data, as described above, and R.sub.O is the numeric
average particle radius.
[0260] The D-value provides a characterisation of the width of the
size distribution.
TABLE-US-00007 TABLE 7 Catalysts on Method A supports Catalysts on
Method B Catalyst on 22% ZrO.sub.2, supports (reference) titania
modified calc 250.degree. C. 15% Cr.sub.2O.sub.3 22% ZrO.sub.2 15%
Cr.sub.2O.sub.3 silica A support (Support A2) (Support E) (Support
B) (Support F) (reference) Average particle 8.8(8) 4.7(9) 9.3(9)
5.8(6) 7.1(4) size (nm) c value 0.23(2) 0.29(3) 0.23(3) 0.22(2)
0.33(2) D value 21.8 .sup. 21.9 .sup. 21.8 .sup. 23.9 .sup. 19.7
.sup.
[0261] It is clear from Table 7 that there is significant scatter
in the D-value of the modified silica supports and, in conjunction
with Table 4, this value does not appear to correlate readily with
deactivation rate. The catalyst on 22% ZrO.sub.2/SiO.sub.2 (method
A, dried to 100.degree. C.) and the catalyst on 15%
Cr.sub.2O.sub.3/SiO.sub.2 (method A, dried to 100.degree. C.) have
very similar D-values but their deactivation rates, as shown in
Table 4, are very different. This may indicate that the correlation
developed between D-value and deactivation rate may be sensitive to
the nature of the catalyst support.
[0262] The results show that the method of modifying the catalyst
support has only a small effect on the resulting Co.sub.3O.sub.4
particle size of the catalyst. For the catalyst supported on 22%
ZrO.sub.2/SiO.sub.2, using Method A to deposit zirconia results in
a catalyst with slightly smaller Co.sub.3O.sub.4 particles than
using Method B. The same trend is observed for the catalyst
supported on 15% Cr.sub.2O.sub.3/SiO.sub.2. However, in both cases,
the difference between the Co.sub.3O.sub.4 size on the catalysts
made with Method A and Method B supports is within the error of the
measurement. This suggests that using Method A (aqueous precursor
with citric acid) to deposit the support modifier may result in
slightly smaller cobalt oxide crystallites in the resulting
catalyst as compared to the use of Method B.
Example 15
Co.sup.0 Dispersion of Catalysts Made from the Modified
Supports
[0263] The Co.sup.0 surface area was determined via H.sub.2
chemisorption on the Micromeritics ASAP 2020c instrument.
Approximately 300 mg of samples obtained from Examples 9 and 10
were loaded into a U-shaped quartz tube, with a small wad of quartz
wool above and below the sample. The samples were first degassed in
helium at 70.degree. C. for 10 minutes, and then evacuated for 1.5
hours. The flow was then changed to H.sub.2, and the temperature
increased to 400.degree. C. at 1.degree. C./min, and held at that
temperature for six hours. After this reduction, the sample was
flushed with helium for 1 hour, evacuated, and hydrogen
chemisorption was performed at 100.degree. C. A repeat analysis was
carried out, and the quantity of gas adsorbed was determined from
the difference between the two chemisorptions. The percentage
dispersion of Co.sup.0 and the metal surface area were determined
assuming a total cobalt concentration of 42 wt. %
TABLE-US-00008 TABLE 8 Method A supports Method B supports
(reference) 22% 17% 15% 22% 17% 15% ZrO.sub.2 ZrO.sub.2
Cr.sub.2O.sub.3 ZrO.sub.2 ZrO.sub.2 Cr.sub.2O.sub.3 (Support
(Support (Support (Support (Support (Support A2) G) E) B) H) F) %
Co.sup.0 dispersion 2.93 2.91 1.26 2.27 2.27 2.14 Co.sup.0 surface
area (m.sup.2/g 8.33 8.26 3.58 6.45 6.46 6.08 sample)
[0264] The results show that the dispersion of Co.sup.0 on the
catalysts is affected by the method used to modify the support.
Comparing the catalysts made using a 22% ZrO.sub.2/SiO.sub.2
support, the catalyst made on the support modified via Method A has
a higher dispersion of cobalt than the catalyst made on the support
modified via Method B. At a lower zirconia loading (17%), the same
trend is observed. The results suggest that for both support
modification Methods A and B, the change in zirconia loading from
22% to 17% does not have a significant impact on Co.sup.0
dispersion.
[0265] For the catalyst support on 15% Cr.sub.2O.sub.3/SiO.sub.2,
there is also a difference in the cobalt dispersion between the
catalysts on the support modified using Methods A and B. The
catalyst on the Method A support has a lower cobalt dispersion than
the catalyst on the Method B support.
[0266] These results suggest that both the method of support
modification (Method A or B) and the nature of the oxide modifier
(ZrO.sub.2 or Cr.sub.2O.sub.3) has an effect on the dispersion of
Co.sup.0 metal. The catalysts made from zirconia-modified supports
have particularly high % Co.sup.0 dispersion.
Preparation of Reference Catalysts and Catalysts on Silica B
Supports
Example 16
Preparation of Catalyst Using Titania-Modified Silica a Support,
16% TiO.sub.2/SiO.sub.2 Support (Reference)
[0267] Silica A bare catalyst support material was dried at
100.degree. C. for 2 hours. 84 g of silica was weighed and allowed
to cool to room temperature. The impregnation solution was made by
dissolving 25 g of citric acid in minimum water at about 50.degree.
C. with stirring until fully dissolved. The solution was cooled
down to less than 30.degree. C. and the citric acid solution was
then added to 118 g (97 ml) of titanium (IV) bis(ammonium
lactate)dihydroxide solution (TALH) and made up to the required
volume of impregnation, which was about 130 ml, with water. The
impregnation solution was allowed to cool.
[0268] 84 g of silica (weight determined after drying) was
impregnated via incipient wetness impregnation with the
impregnation solution. Following impregnation, the modified
catalyst support was dried at a temperature that increased at a
ramp rate of 2.degree. C./min up to 100.degree. C. The temperature
was held at 100.degree. C. for 5 hours. The modified support
catalyst was subsequently calcined by increasing the temperature to
250.degree. C. using a ramp rate of 2.degree. C./min and holding
the temperature at 250.degree. C. for 5 hours.
[0269] To prepare the catalyst using the silica A modified support,
25 g of cobalt nitrate was dissolved in a minimum amount of water
to achieve dissolution over heat at about 50.degree. C. 0.048 g
perrhenic acid was added and the solution cooled to room
temperature. The volume was adjusted to 19 ml and used to
impregnate 23-24 g of titania modified silica. This was calcined in
a muffle furnace according to the following program: ramp at
2.degree. C./min to 100.degree. C. and dwell for 5 hours, ramp at
2.degree. C./min to 200.degree. C. and dwell for 3 hours, then ramp
at 1.degree. C./min to 250.degree. C. and dwell for 3 hours.
[0270] For impregnation steps 2 to 4, a stock solution was
prepared. 12 g citric acid was mixed with H.sub.2O (minimum amount
to obtain a clear solution) and heated to about 50.degree. C. with
stirring until fully dissolved. This was added to 8.14 g cobalt
nitrate and heated to about 50.degree. C. with stirring until fully
dissolved. 0.14 g of perrhenic acid was added and the solution
cooled to room temperature. The stock impregnation solution was
made up to 67 ml and divided over the impregnation steps as shown
in Table 9, and calcined after each step using the following
program: ramp at 2.degree. C./min to 100.degree. C. and dwell for 5
hours, then ramp at 2.degree. C./min to 250.degree. C. and dwell
for 3 hours. After the last impregnation and calcination, the
catalyst was promoted with 0.03% Pt. 0.06 g of the tetraamine
platinum hydroxide solution was diluted to 9 ml with water and used
to impregnate 20 g of catalyst then calcined using the same program
as above.
TABLE-US-00009 TABLE 9 Co(NO.sub.3).sub.2 Co(NO.sub.3).sub.2
6H.sub.2O (g) 6H.sub.2O (g) Citic Solution Calc Purity Purity
Co.sub.3O.sub.4 Co acid Perrhenic Re volume wt % Co Step Base (g)
98% 100% (g) (g) (g) acid (g) (g) (ml) (g) (approx.) 1 20 24.49 24
6.62 4.86 0.00 0.0480 0.05 19 26.6 18.2 2 27.2 27.14 26.6 7.33 5.38
3.84 0.0480 0.05 22 34.5 29.7 3 34.4 27.14 26.6 7.33 5.38 3.84
0.0480 0.05 22 41.7 37.4 4 41.6 27.14 26.6 7.33 5.38 3.84 0.0480
0.05 22 48.9 42.9
Example 17
Preparation of a Mixed TiO.sub.2/ZrO.sub.2-Modified Silica Catalyst
Support (10% TiO.sub.2-4% ZrO.sub.2/SiO.sub.2) Using Method a
(Support I)
[0271] Silica B bare catalyst support material was dried at
100.degree. C. for 2 hours. 25.8 g of silica was weighed and
allowed to cool to room temperature. 6.0 g citric acid was mixed
with 6 ml H.sub.2O and heated to about 50.degree. C. with stirring
until fully dissolved. The solution was then allowed to cool to
room temperature. 2.3 g zirconium dinitrate oxide hydrate (also
known as "zirconyl nitrate") was mixed with 8 ml H.sub.2O and
stirred using a magnetic stirbar, without heat, for 20 minutes to
obtain a translucent solution. The zirconyl nitrate solution and
citric acid solution were mixed together, and then 22.1 g of
titanium bis(ammonium lactato)dihydroxide was added to form the
impregnation solution of total volume about 42 ml. The impregnation
solution was used immediately after preparation to impregnate the
silica support. The support was impregnated by mixing the
impregnation solution and the silica in order to reach the point of
incipient wetness.
[0272] Following impregnation, the modified catalyst support was
dried in a muffle furnace at a temperature that increased at a ramp
rate of 2.degree. C./min up to 100.degree. C. The temperature was
held at 100.degree. C. for 5 hours. The temperature was held at
100.degree. C. for 5 hours. The temperature was then increased to
180.degree. C. at a ramp rate of 2.degree. C./min, and held at that
temperature for 0.5 hours. The temperature was then increased to
220.degree. C. at a ramp rate of 1.degree. C./min, and held at that
temperature for 5 hours (support I).
[0273] The resulting catalyst support K had TiO.sub.2 and ZrO.sub.2
bound to the silica surface at an amount equivalent to 4% ZrO.sub.2
and 10% TiO.sub.2 on silica support.
Example 18
Preparation of a Titania-Modified Silica B Support, 16%
TiO.sub.2/SiO.sub.2 Support (Reference) (Support J)
[0274] Silica B bare catalyst support material was dried at
100.degree. C. for 2 hours. 84 g of silica was weighed and allowed
to cool to room temperature. The impregnation solution was made by
dissolving 25 g of citric acid in minimum water at about 50.degree.
C. with stirring until fully dissolved. The solution was cooled
down to less than 30.degree. C. and the citric acid solution was
then added to 118 g (97 ml) of titanium (IV) bis(ammonium
lactate)dihydroxide solution (TALH) and made up to the required
volume of impregnation, which was about 150 ml, with water. The
impregnation solution was allowed to cool.
[0275] 84 g of silica B (weight determined after drying) was
impregnated via incipient wetness impregnation with the
impregnation solution. Following impregnation, the modified
catalyst support was dried at a temperature that increased at a
ramp rate of 2.degree. C./min up to 100.degree. C. The temperature
was held at 100.degree. C. for 5 hours. The modified support
catalyst was subsequently calcined by increasing the temperature to
250.degree. C. using a ramp rate of 2.degree. C./min and holding
the temperature at 250.degree. C. for 5 hours (support J).
Example 19
Preparation of a Titania-Modified Silica B Support, 10%
TiO.sub.2/SiO.sub.2 Support (Reference) (Support K)
[0276] Silica B bare catalyst support material was dried at
100.degree. C. for 2 hours. 27 g of silica was weighed and allowed
to cool to room temperature. The impregnation solution was made by
dissolving 4.74 g of citric acid in minimum water at about
50.degree. C. with stirring until fully dissolved. The solution was
cooled down to less than 30.degree. C. and the citric acid solution
was then added to 22.1 g of titanium (IV) bis(ammonium
lactate)dihydroxide solution (TALH) and made up to the required
volume of impregnation, which was about 44 ml, with water. The
impregnation solution was allowed to cool.
[0277] 27 g of silica B (weight determined after drying) was
impregnated via incipient wetness impregnation with the
impregnation solution. Following impregnation, the modified
catalyst support was dried at a temperature that increased at a
ramp rate of 2.degree. C./min up to 100.degree. C. The temperature
was held at 100.degree. C. for 5 hours. The modified support
catalyst was subsequently calcined by increasing the temperature to
250.degree. C. using a ramp rate of 2.degree. C./min and holding
the temperature at 250.degree. C. for 5 hours (support K).
Example 20
Preparation of Catalyst Using Silica B Modified Supports I, J and
K
[0278] A catalyst was prepared from the modified catalyst supports
made using titanium and a mixture of titanium and zirconium
(examples 17 and 18, supports I and J).
[0279] The first impregnation solution was prepared by mixing 16.10
g cobalt nitrate hexahydrate with 4 mL H.sub.2O and heated to about
50.degree. C. with stirring until fully dissolved. The solution,
total volume 14 mL, was cooled to room temperature. For the first
impregnation step 11.7 g of the support (support purity estimated
at 85% to give a final support weight of 10 g) was used. After
impregnation with the cobalt nitrate solution, the impregnated
modified catalyst support was dried at a temperature that increased
at a ramp rate of 2.degree. C./min up to 100.degree. C. The
temperature was held at 100.degree. C. for 5 hours. The modified
catalyst support was subsequently calcined by increasing the
temperature to 200.degree. C. using a ramp rate of 2.degree. C./min
and holding the temperature at 200.degree. C. for 3 hours, and then
increasing the temperature to 250.degree. C. using a ramp rate of
1.degree. C./min and holding the temperature at 250.degree. C. for
3 hours.
TABLE-US-00010 TABLE Co(NO.sub.3).sub.2 Co(NO.sub.3).sub.2
Tetraammine 6H.sub.2O (g) 6H.sub.2O (g) Citric Perrhenic platinum
Solution Calc. Support Purity Purity Co.sub.3O.sub.4 Co acid acid
hydroxide H.sub.2O volume Wt % Step wt (g) 98% 100% (g) (g) (g) (g)
(g) (ml) (ml) (g) Co 1 10 16.10 15.78 4.35 3.19 0.00 0.00 0.00 min.
14 14.4 22.3 2 -- 17.25 16.91 4.66 3.42 2.46 0.00 0.00 min. 15 19.0
34.8 3 -- 16.10 15.78 4.35 3.19 2.30 0.090 0.075 min. 14 23.4
42.0
[0280] The impregnation solution for the second impregnation step
was prepared by mixing 2.46 g citric acid with 4 ml H.sub.2O and
heating to about 50.degree. C. with stirring until fully dissolved.
This solution was added to 17.25 g cobalt nitrate hexahydrate and
heated to about 50.degree. C. with stirring until fully dissolved.
The solution, total volume 15 mL, was cooled to room temperature
and used to impregnate the calcined material after the first
impregnation step. The impregnated modified catalyst support was
dried at a temperature that increased at a ramp rate of 2.degree.
C./min up to 100.degree. C. The temperature was held at 100.degree.
C. for 5 hours. The catalyst was subsequently calcined by
increasing the temperature to 250.degree. C. using a ramp rate of
2.degree. C./min and holding the temperature at 250.degree. C. for
3 hours.
[0281] The impregnation solution for the third impregnation step
was prepared by mixing 2.30 g citric acid with 3 ml H.sub.2O and
heating to about 50.degree. C. with stirring until fully dissolved.
This solution was added to 16.10 g cobalt nitrate hexahydrate and
heated to about 50.degree. C. with stirring until fully dissolved.
0.075 g of tetraammine platinum hydroxide (9.3% Pt w/w) was added
to the solution, with stirring, and then 0.090 g perrhenic acid was
added, with stirring. This was heated to about 50.degree. C. with
stirring until fully dissolved. The solution, total volume 14 mL,
was cooled to room temperature and used to impregnate the calcined
material after the first impregnation step. The impregnated
modified catalyst support was dried at a temperature that increased
at a ramp rate of 2.degree. C./min up to 100.degree. C. The
temperature was held at 100.degree. C. for 5 hours. The catalyst
was subsequently calcined by increasing the temperature to
250.degree. C. using a ramp rate of 2.degree. C./min and holding
the temperature at 250.degree. C. for 3 hours.
[0282] The resulting catalysts made from the modified silica
supports I and J had 0.03% Pt and 0.2% Re and were suitable for use
as, for example, a Fischer-Tropsch catalyst.
[0283] A catalyst was prepared from the modified catalyst supports
made using titanium (example 19, support K) using the procedure
outlined above except that no Re was included. The resulting
catalyst made from the modified silica support K had 0.03% Pt and
was suitable for use as, for example, a Fischer-Tropsch
catalyst.
Example 21
Preparation of Catalyst Using Unmodified Silica Support
(Reference)
[0284] A catalyst was made on a support that was not modified with
a metal oxide (eg. bare silica A), labelled 1101-06-016-4. The
catalyst was prepared by dissolving 15.01 g of citric acid in
H.sub.2O (minimum amount to achieve clear solution) and heating to
about 50.degree. C. with stirring until fully dissolved. The
resulting solution was added to 106.12 g cobalt nitrate hexahydrate
and heated to about 50.degree. C. with stirring until fully
dissolved. 0.19 g of perrhenic acid was added and the solution
cooled to room temperature. This stock solution was divided over 4
impregnation steps as shown in Table 10, and calcined after each
step: ramp at 2.degree. C./min to 100.degree. C. and dwell for 5
hours, then ramp at 2.degree. C./min to 250.degree. C. and dwell
for 3 hours. After the last impregnation and calcination, the
catalyst was promoted with 0.03% Pt using tetraamine platinum
hydroxide solution diluted with H.sub.2O, then calcined using the
same program.
TABLE-US-00011 TABLE 10 Co(NO.sub.3).sub.2 Co(NO.sub.3).sub.2
6H.sub.2O (g) 6H.sub.2O (g) Citic Solution Calc Purity Purity
Co.sub.3O.sub.4 Co acid Perrhenic Re volume wt % Co Step Base (g)
98% 100% (g) (g) (g) acid (g) (g) (ml) (g) (approx.) 1 20 26.53 26
7.17 5.26 3.75 0.0480 0.0231 26.6 27.2 19.4 2 26.53 26 7.17 5.26
3.75 0.0480 0.0231 25.8 34.4 30.6 3 26.53 26 7.17 5.26 3.75 0.0480
0.0231 26.1 41.6 38.0 4 26.53 26 7.17 5.26 3.75 0.0480 0.0231 24.2
48.8 43.2
Example 22
Preparation of Catalysts Using Titania-Modified Silica Support,
Alkoxide Method (Reference)
[0285] Catalyst precursors having the composition 42% Co-0.2%
Re-0.03% Pt/TiO.sub.2--SiO.sub.2 were made using the reagents in
Table 11.
TABLE-US-00012 TABLE 11 Supplier Code Purity Titanium(IV)
Sigma-Aldrich 205273 97% isopropoxide Cobalt nitrate Alfa Aesar --
98% hexahydrate Tetraammine platinum Alfa Aesar 38201-97-7 9.3%
hydroxide Pt w/w Silica A, Grace Davison (180-300 .mu.m) SG432
(LC150) Citric acid Sigma Aldrich C1909 ACS monohydrate (CA)
Reagent Perrhenic acid Sigma Aldrich 65-70 wt % solution 99.99% in
water
[0286] Sieved silica A, of size 180 to 300 .mu.m, was dried in an
oven at 100.degree. C. for 1 hour. Once cool, 21.0 g of the support
was impregnated with a titanium isopropoxide solution: 15.5 ml of
titanium isopropoxide was diluted to a volume of 29 ml with
isopropanol. This solution was added gradually to the support, with
stirring. The impregnated yet still free-flowing support was
calcined in a muffle furnace at 100.degree. C. for 10 hours via a
ramp of 2.degree. C. per minute. The resulting catalyst support was
16% TiO.sub.2-modified silica (expressed as a weight percentage of
the catalyst support).
[0287] Portions of the titania-modified catalyst support (of a
variety of scales of batch size) were impregnated via 4 to 8
impregnation steps with a solution of cobalt nitrate hexahydrate
and perrhenic acid and a variety of polar organic compounds as the
combustion fuel (either citric acid (citric acid: Co ratio of 0.2),
acetic acid (acetic acid: Co ratio of 0.45), malic acid (malic
acid: Co ratio of 0.26), glutaric acid (glutaric acid: Co ratio of
0.16) or no polar organic compound). The catalysts were promoted
with platinum to achieve a final composition of 42% Co-0.2%
Re-0.03% Pt/TiO.sub.2--SiO.sub.2.
Example 23
Fischer-Tropsch Reaction Tests
[0288] The catalysts obtained in Examples 9, 10, 16, 20, 21 and 22
were tested for Fischer Tropsch synthesis (FTS) performance. The
catalysts were diluted with SiC at a 1:18 ratio and then loaded in
a fixed-bed combinatorial reactor (L/D 31 cm) and reduced using
pure hydrogen at 400.degree. C. for 120 minutes at Gas Hourly Space
Velocity (GHSV)=15 000 per hour. The temperature was increased from
room temperature to 400.degree. C. at 1.degree. C./min. After the
reduction, the reactor was cooled to 165.degree. C. and the gas was
switched from hydrogen to synthesis gas. The operating conditions
were kept constant for 1 hour. The pressure was then increased to
20 bar at the flow rate of the reaction and held for 1 hour. The
temperature was then increased from 165.degree. C. to 190.degree.
C. at a ramp rate of 4.degree. C./hour, from 190 to 210.degree. C.
(GHSV=12 400 per hour) at 2.degree. C./hour and then kept at
210.degree. C. (GHSV=12 400 per hour) for about 120 hours. The
Fischer Tropsch reaction was carried out for a total of 160
hours.
[0289] The deactivation rate of the catalyst was calculated via a
linear regression analysis of the percent of CO converted during
the reaction between a time on stream of 24 hours until the end of
the run (160 hours).
[0290] The liquid products from the reaction were condensed with a
hot (temperature=80.degree. C.) and cold (temperature=5.degree. C.)
trap downstream of the FT reactor, and the gas products were
injected online into a Clarus 600 gas chromatograph. Hydrogen,
carbon monoxide and nitrogen were detected with a thermal
conductivity detector and hydrocarbons (from C1 to C4) with a flame
ionization detector. CO conversion and product selectivity were
calculated by using nitrogen as a tracer and employing a carbon
mass balance.
[0291] The % C.sub.5+ selectivity (S.sub.C5+) of the catalyst was
calculated at 24 hours time on stream via
S.sub.C5+=100-(S.sub.CH4+S.sub.C2+S.sub.C2=+S.sub.C3+S.sub.C3=+S.sub.C4+-
S.sub.C4=+S.sub.CO2);
where S.sub.CH4, S.sub.C2, S.sub.C2=, S.sub.C3, S.sub.C3=,
S.sub.C4, S.sub.C4= and S.sub.CO2 are the calculated % of
selectivity of methane, ethane, ethene, propane, propene, butane,
butane and carbon dioxide, respectively. These are calculated
via
S x = 100 ( X out CO in - CO out ) ##EQU00010##
Where S.sub.X is either S.sub.CH4, S.sub.C2, S.sub.C2=, S.sub.C3,
S.sub.C3=, S.sub.C4, S.sub.C4= or S.sub.CO2; X.sub.out is the
amount (expressed in grams per hour, g hr.sup.-1) of the species X
measured at the rector outlet and CO.sub.in and CO.sub.out are the
amount (expressed in grams per hour, g hr.sup.-1) of carbon
monoxide measured at the inlet and outlet of the reactor,
respectively.
[0292] The activity of the catalyst, in mol CO hr.sup.-1
g.sub.Co.sup.-1, at 24 hours time on stream was calculated via
activity = CO % conversion 100 % CO flow rate in mL min 60 min hr
22400 mL mol CO 1 catalyst weight in g 0.42 ##EQU00011##
[0293] The intrinsic activity, or turnover frequency (TOF) in mol
CO converted per second, was calculated using:
TOF = activity 58.93 g CO mol % dispersion DOR 3600
##EQU00012##
[0294] The FTS performance of the catalysts made from the modified
silica supports of Examples 1, 5, 17-19 and from a bare silica
support of reference Example 21 and a reference titania-modified
support (aqueous method, example 16) are shown in Table 12. The FTS
performance of catalysts made from the titania-modified silica
supports prepared by the alkoxide method of reference Example 22
are shown in Table 13.
[0295] The results show that catalysts made using the
zirconia-modified supports and the chromium oxide-modified supports
display particularly good FTS performance, comparable to a
reference catalyst made using a titania-modified silica catalyst
support.
Example 24
Silica and Catalyst Porosity
Silica Porosity
[0296] The BET surface area of silica A and silica B was determined
using nitrogen physisorption at 77 K in a Micromeritics Tristar II
instrument. Prior to measurement, all samples were degassed in
nitrogen at 100.degree. C. for 3 hours. The pore size distribution,
average pore size and total pore volume were determined using a BET
calculation method, wherein the BJH pore size distribution was
determined with 63 pressure data points, using the Halsey: Faas
correction. In all cases, the reported average pore diameter and
total pore volume is taken from adsorption measurements. The
results are shown in the following table:
TABLE-US-00013 BET surface area BJH average pore BJH pore volume
(m.sup.2/g) size (.ANG.) (cm.sup.3/g) Silica A 349 138 1.30 Silica
B 407 173 1.80
Catalyst Porosity
[0297] The BET surface area of catalysts obtained in Examples 9,
16, 20, 21 and 22 was determined using nitrogen physisorption at 77
K in a Micromeritics Tristar II instrument. Prior to measurement,
all samples were degassed in nitrogen at 100.degree. C. for 3
hours. The pore size distribution, average pore size and total pore
volume were determined using a DFT or BJH calculation method. For
the DFT method, with adsorption isotherm pressure points over the
range 0.25-0.99 p/po, a Micromeritics built-in cylindrical model
based on oxide surfaces was chosen, and a high degree of
regularisation applied. For the BJH method, the BJH pore size
distribution was determined with 63 pressure data points, using the
Halsey: Faas correction. In all cases, the reported average pore
diameter is taken from adsorption measurements.
[0298] The average pore diameter, calculated using the DFT method
described above, of catalysts made from the modified silica
supports of Examples 1, 5, 17, 18, 19 and from a reference bare
silica support (example 21) and a reference titania-modified
support (aqueous method, example 16) are shown in Table 12. The
average pore diameter, calculated using the BJH method described
above, of catalysts made from the reference titania-modified silica
supports prepared by the alkoxide method of Example 22 are shown in
Table 13.
Example 25
Comparison of Co.sub.3O.sub.4 Particle Size (D.sub.0) of
Catalysts
[0299] The diffraction patterns of fresh catalysts obtained in
Example 9 (made from supports A2 and E), in example 20 (made with
supports I, J and K) and fresh catalysts obtained using bare silica
(Example 21), reference titania-modified supports using the aqueous
method (Example 16) and reference titania-modified supports using
the alkoxide method (Example 22) were collected on a fully
automated Siemens D5000 theta/theta powder diffractometer using Cu
K.alpha. radiation at BegbrokeNano, Oxford University and compared.
Each sample was ground thoroughly before loading into a spinner
carousel in air. Data were collected over the range 10-80.degree.
2.theta., with a step size of 0.05.degree. and a step length of 12
s. The average Co.sub.3O.sub.4 crystallite size (D.sub.O), and the
theoretical % dispersion of the Co.sub.3O.sub.4 crystallites were
determined via the method hereinbefore described in relation to
Example 14. The Co.sup.0 metal size was estimated by multiplying
the Co.sub.3O.sub.4 particle size by 75%.
[0300] The results for catalysts made from the modified silica
supports of Examples 1, 5, 17, 18, 19 and from a reference bare
silica support (example 21) and a reference titania-modified
support (aqueous method, example 16) are shown in Table 12. The
results for catalysts made from the reference titania-modified
silica supports prepared by the alkoxide method of Example 22 are
shown in Table 13.
Example 26
Comparison of the Degree of Reduction (DOR)
[0301] TPR experiments were carried out using the Altamira AMI200
instrument. About 50 mg of the sample of catalyst (the catalysts of
Example 9 (made from supports A2 and E), the catalyst of example 20
(made from support J) and catalysts obtained using bare silica
(Example 21), reference titania-modified supports using the aqueous
method (Example 16) and reference titania-modified supports using
the alkoxide method (Example 22)) was loaded into a U-shaped quartz
tube, with a small wad of quartz wool above and below the sample.
The samples were first degassed in argon at 150.degree. C. for 30
minutes, before decreasing the temperature to 50.degree. C. and
changing the flow to 5% H.sub.2 in Ar. The temperature was then
ramped to 800.degree. C. at 5.degree. C./min, and held for one
hour, whilst the TCD signal was monitored. A moisture trap was not
used. Quantification of the amount of hydrogen consumed was carried
out by calibration of a 5% H.sub.2 in Ar stream.
[0302] The reduction experiment was carried out using the same
instrument using a fresh sample of catalyst. The samples were
degassed in argon at 100.degree. C. for 60 minutes. The flow was
then changed to 5% H.sub.2 in Ar and ramped to 400.degree. C. at
2.degree. C./min, and held for two hours, whilst the TCD signal was
monitored. Calibration and quantification of the gas stream was
carried out as above.
[0303] DOR was calculated by comparing the hydrogen consumed in two
experiments using the following formula:
DOR = mol H 2 / g catalyst consumed up to 400 .degree. C . mol H 2
/ g catalyst consumed up to 800 .degree. C . .times. 100 %
##EQU00013##
[0304] The results for catalysts made from the modified silica
supports of Examples 1, 5 and 18 and from a reference bare silica
support (Example 21) and a reference titania-modified support
(aqueous method, Example 16) are shown in Table 12. The results for
various catalysts made from the reference titania-modified silica
supports prepared by the alkoxide method of Example 22 are shown in
Table 13.
TABLE-US-00014 TABLE 12 Activity Ave. .DELTA. % CO Selectivity mol
pore % CO conversion (%) CO/hr/g Run D.sub.0 size* DOR Support used
conversion (%/day) C.sub.5+ CH.sub.4 Co # (nm) (.ANG.) (%) 16%
TiO.sub.2, 73.6 -1.12 86.4 9.3 0.273 69 7.1(4) 125.1 83.6 silica A
(reference Example 16) Support A2 83.2 -1.43 87.3 8.8 0.278 69
8.8(8) 143.5 95.6 (22% ZrO.sub.2, method A, calcined 250.degree.
C.) Support E 71.3 -2.22 85.0 10.1 0.238 69 4.7(9) 127.2 67.0 (15%
Cr.sub.2O.sub.3, method A, dried 100.degree. C.) Bare SiO.sub.2 A
78.9 -1.63 87.8 8.2 0.352 46 5.1(2) 169.6 77.6 (reference Example
21) Support J 81.8 -1.16 89.6 7.8 0.295 73 7.5(2) 130.6 87.7 (16%
TiO.sub.2, silica B, example 18 and 20) Support K 81.5 -1.33 90.9
7.2 0.310 78 -- 148.6 -- (10% TiO.sub.2, silica B, example 19 and
20) Support I 79.5 -1.39 90.4 7.0 0.314 86 8.9(9) 158.8 -- (10%
TiO.sub.2/4% ZrO.sub.2, silica B, example 17 and 20 *Pore size
calculated by DFT method
TABLE-US-00015 TABLE 13 Activity Ave. .DELTA. % CO Selectivity mol
pore % CO conversion (%) CO/hr/g Run size* DOR Catalyst code
conversion (%/day) C.sub.5+ CH.sub.4 Co # D.sub.0 (nm) (.ANG.) (%)
Citric acid, 75.7 -0.69 87.9 8.2 0.243 61 7.8(2) 93.4 82.6 diluted
labscale [1011-02- 005-2] Citric acid, 66.8 -0.61 86.5 9.1 0.250 44
9.0(5) 83.5 80.0 standard labscale [1011-26- 003-2] Citric acid,
72.4 -1.37 86.5 9.6 0.242 46 9.6(3) 93.2 94.7 150 kg [1101-05-
003-1] Citric acid, 73.4 -1.96 89.0 8.0 0.279 53 12.9(5) -- 84.9
labscale [1104-01- 003-1] No polar 73.6 -1.11 87.1 8.7 0.280 46
10.8(9) 101.7 87.2 organic compound [1012-09- 016-2] Citric acid,
73.9 -0.91 88.2 8.5 0.273 61 10.6(9) 93.6 88.2 100 kg [1108-26-
003-1] Acetic acid 82.4 -1.12 88.1 8.0 0.267 61 6.7(3) 108.1 87.3
[1107-25- 005-1] Malic acid 75.5 -0.98 87.6 8.5 0.263 61 6.6(3)
108.3 80.9 [1108-03- 005-1] Glutaric acid 78.7 -0.80 86.9 8.6 0.281
61 5.1(2) 108.5 87.7 [1108-03- 005-7] *Pore size calculated by BJH
method
[0305] The FTS performance set of reference catalysts prepared on
titania-modified silica A (via the alkoxide method) is given in
Table 13. The Co.sub.3O.sub.4 crystallite size of this set of
catalysts has been varied through a selection of methods, e.g.
dilution of the impregnation solution, use of a different organic
fuel (polar organic compound). It is clear from this data that the
FTS activity of the set of reference catalysts varies as the
particle size varies, although all catalysts maintain a % CO
conversion that is greater than 60%. As there is a significant
difference in the degree of reduction (DOR) of the catalyst at
standard conditions, this must be considered in determining the
intrinsic activity of the cobalt sites.
[0306] A plot of the turnover frequency of those catalysts
described in tables 12 and 13 that are formed on silica A supports
against the average Co.sub.3O.sub.4 particle size is shown in FIG.
1. This data set has been fit with a linear trend line (r=0.978),
showing that the intrinsic activity of the Co.sup.0 site increases
linearly as the particle size increases over this whole size range
(estimated Co.sup.0 size 3.8-9.7 nm).
[0307] The CH.sub.4 selectivity of the set of reference
titania-modified silica A catalysts given in Table 13 varies
between 8.0 and 9.6% (the estimated error on the measurement is
0.5%). The apparent variation in CH.sub.4 selectivity of this set
of catalysts may be a factor of the concomitant variation in the %
CO conversion, as the selectivities do not correlate to changes in
the pore size or any other factor measured here. This suggests that
the intrinsic selectivities of these catalysts may not be
significantly different.
[0308] The FTS performance of the catalysts made from the
ZrO.sub.2-, Cr.sub.2O.sub.3- and TiO.sub.2/ZrO.sub.2-modified
supports shown in Table 12, along with the reference bare silica
catalyst (example 21) and reference titania-modified (aqueous
method) catalyst show that silica modified with ZrO.sub.2,
Cr.sub.2O.sub.3 or TiO.sub.2 via an aqueous method leads to a
catalyst with CO conversion levels between 70 and 85%. Therefore,
catalysts made from ZrO.sub.2-, Cr.sub.2O.sub.3- and
TiO.sub.2/ZrO.sub.2-modified supports have been shown to function
well as Fischer-Tropsch catalysts. The catalyst supported on bare
silica also has a conversion level in this range. However, a
significant difference in the methane selectivities of these
catalysts is observed. FIG. 2 shows the variation in methane
selectivity with pore size for this set of catalysts and shows that
CH.sub.4 selectivity tends to increase as the average pore size
decreases. FIG. 2 also shows that variations in methane selectivity
appear not to be solely down to changes in pore size but is also
affected by the catalyst support modifier. In particular, although
chromium oxide-modified support catalysts and titanium
oxide-modified support catalysts have similar pore size, they have
a difference in methane selectivity of about 1%.
[0309] The results in Table 12 highlight that catalysts made from
ZrO.sub.2-modified supports are particularly advantageous as they
perform well as a Fischer-Tropsch catalyst and have good CH.sub.4
selectivity compared to reference catalyst based on
titania-modified supports.
* * * * *