U.S. patent application number 10/993507 was filed with the patent office on 2005-08-18 for methods of making alkenyl alkanoates.
This patent application is currently assigned to Celanese International Corporation. Invention is credited to Hagemeyer, Alfred, Han, Jun, Kimmich, Barbara, Liu, Yumin, Lowe, David M., Nicolau, Ioan, Sokolovskii, Valery, Wade, Les, Wang, Tao, Wong, Victor.
Application Number | 20050181940 10/993507 |
Document ID | / |
Family ID | 44256615 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050181940 |
Kind Code |
A1 |
Wang, Tao ; et al. |
August 18, 2005 |
Methods of making alkenyl alkanoates
Abstract
The present invention addresses at least four different aspects
relating to catalyst structure, methods of making those catalysts
and methods of using those catalysts for making alkenyl alkanoates.
Separately or together in combination, the various aspects of the
invention are directed at improving the production of alkenyl
alkanoates and VA in particular, including reduction of by-products
and improved production efficiency. A first aspect of the present
invention pertains to a unique palladium/gold catalyst or
pre-catalyst (optionally calcined) that includes rhodium or another
metal. A second aspect pertains to a palladium/gold catalyst or
pre-catalyst that is based on a layered support material where one
layer of the support material is substantially free of catalytic
components. A third aspect pertains to a palladium/gold catalyst or
pre-catalyst on a zirconia containing support material. A fourth
aspect pertains to a palladium/gold catalyst or pre-catalyst that
is produced from substantially chloride free catalytic
components.
Inventors: |
Wang, Tao; (Houston, TX)
; Wade, Les; (Pearland, TX) ; Nicolau, Ioan;
(Corpus Christi, TX) ; Kimmich, Barbara; (League
City, TX) ; Wong, Victor; (San Jose, CA) ;
Liu, Yumin; (Menlo Park, CA) ; Han, Jun;
(Sunnyvale, CA) ; Sokolovskii, Valery; (Sunnyvale,
CA) ; Hagemeyer, Alfred; (Sunnyvale, CA) ;
Lowe, David M.; (Sunnyvale, CA) |
Correspondence
Address: |
DOBRUSIN & THENNISCH PC
29 W LAWRENCE ST
SUITE 210
PONTIAC
MI
48342
US
|
Assignee: |
Celanese International
Corporation
|
Family ID: |
44256615 |
Appl. No.: |
10/993507 |
Filed: |
November 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60531415 |
Dec 19, 2003 |
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60530936 |
Dec 19, 2003 |
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60531486 |
Dec 19, 2003 |
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60530937 |
Dec 19, 2003 |
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Current U.S.
Class: |
502/330 ;
502/339 |
Current CPC
Class: |
B01J 35/1019 20130101;
B01J 23/52 20130101; B01J 35/002 20130101; B01J 35/0026 20130101;
B01J 35/008 20130101; C07C 67/055 20130101; B01J 35/1014 20130101;
B01J 37/16 20130101; B01J 35/1042 20130101; B01J 23/464 20130101;
B01J 37/0244 20130101; B01J 35/0086 20130101; C07C 67/055 20130101;
B01J 35/026 20130101; C07C 69/15 20130101; B01J 23/58 20130101;
B01J 33/00 20130101; B01J 37/0201 20130101 |
Class at
Publication: |
502/330 ;
502/339 |
International
Class: |
B01J 023/66 |
Claims
We claim:
1. A method of producing a catalyst or pre-catalyst suitable for
assisting in the production of alkenyl alkanoates, comprising:
contacting palladium and rhodium precursors to a support material;
and reducing the palladium and rhodium precursors by contacting a
reducing environment to the support material.
2. The method of claim 1, further comprising contacting a gold
precursor to a support material and reducing the gold
precursor.
3. The method of claim 1, calcining the contacted support material
in a non-reducing atmosphere.
4. The method of claim 1, wherein the contacting step comprises
impregnating gold precursor onto the support material after
impregnating with palladium and rhodium precursors.
5. The method of claim 1, wherein the contacting step comprises
co-impregnating palladium and rhodium precursors, followed by
impregnating with the gold precursor.
6. The method of claim 1, wherein the contacting step comprises
co-impregnating palladium, rhodium and gold precursors.
7. The method of claim 1, wherein the calcining step occurs after
the impregnation of the gold precursor.
8. The method of claim 1, wherein the calcining step occurs before
the impregnation of the gold precursor.
9. The method of claim 1, further comprising at least one fixing
step of fixing at least one of the precursors with a fixing
agent.
10. The method of claim 1, wherein the order of method comprises:
impregnating the support material with an aqueous solution of a
water soluble palladium precursor; impregnating the support
material with an aqueous solution of a water soluble rhodium
precursor; fixing the palladium and rhodium precursors with a
fixing agent; calcining the fixed palladium and rhodium precursors;
impregnating the support material with an aqueous solution of a
water soluble gold precursor; and reducing the palladium, gold and
rhodium precursors.
11. The method of claim 1, wherein the order of method comprises:
impregnating the support material with an aqueous solution of a
water soluble palladium precursor; impregnating the support
material with an aqueous solution of a water soluble rhodium
precursor; fixing the palladium and rhodium precursors with a
fixing agent; impregnating the support material with an aqueous
solution of a water soluble gold precursor; and calcining the fixed
palladium, rhodium and gold precursors; and reducing the palladium,
gold and rhodium precursors.
12. The method of claim 1, wherein the order of method comprises:
co-impregnating the support material with an aqueous solution of
water soluble palladium and rhodium precursors; fixing the
palladium and rhodium precursors with a fixing agent; calcining the
fixed palladium and rhodium precursors; impregnating the support
material with an aqueous solution of a water soluble gold
precursor; and reducing the palladium, gold and rhodium
precursors.
13. The method of claim 1, wherein the order of method comprises:
co-impregnating the support material with an aqueous solution of
water soluble palladium and rhodium precursors; fixing the
palladium and rhodium precursors with a fixing agent; calcining the
fixed palladium and rhodium precursors; reducing the palladium and
rhodium precursors; and impregnating the support material with an
aqueous solution of a water soluble gold precursor.
14. The method of claim 1, wherein the order of method comprises:
co-impregnating the support material with an aqueous solution of
water soluble palladium and rhodium precursors; fixing the
palladium and rhodium precursors with a fixing agent; impregnating
the support material with an aqueous solution of a water soluble
gold precursor; and calcining the fixed palladium, rhodium and gold
precursors; and reducing the palladium, gold and rhodium
precursors.
15. The method of claim 1, wherein the order of method comprises:
co-impregnating the support material with an aqueous solution of
water soluble palladium, rhodium and gold precursors; calcining the
palladium, rhodium and gold precursors; and reducing the palladium,
rhodium and gold precursors.
16. The method of claim 1, further comprising contacting potassium
acetate to the support material in an amount of between about 10
and 70 grams per liter of catalyst.
17. The method of claim 1, wherein the contacting step comprises
contacting between about 1 to about 10 grams of palladium, and
about 0.5 to about 10 grams of gold per liter of catalyst, with the
amount of gold being from about 10 to about 125 wt % based on the
weight of palladium.
18. A method of producing a catalyst or pre-catalyst suitable for
assisting in the production of alkenyl alkanoates, comprising:
layering a first support material on to a second support material
to produce a layered support material, wherein catalytic components
of palladium, gold or combinations thereof are contained in the
first support material of the layered support material.
19. The method of claim 18, further comprising contacting the
catalytic components to the first support material before the
layering step.
20. The method of claim 18, further comprising contacting the
catalytic components to the first support material after the
layering step.
21. The method of claim 18, wherein the catalytic components
comprise palladium, gold, or combinations thereof.
22. The method of claim 18, further comprising contacting palladium
to the first support material before the layering step and
contacting gold to the first support material after the layering
step.
23. The method of claim 18, further comprising contacting gold to
the first support material before the layering step and contacting
palladium to the first support material after the layering
step.
24. The method of claim 18, wherein the second support material is
an inner layer and is substantially free of catalytic
components.
25. The method of claim 18, further comprising contacting potassium
acetate to the support material before the layering step.
26. The method of claim 18, further comprising contacting potassium
acetate to the support material after the layering step.
27. The method of claim 18, further comprising impregnating the
first support material with palladium, calcining the first support
material, impregnating the first support material with gold.
28. The method of claim 18, further comprising impregnating the
first support material with palladium, layering the first support
material on to the second support material, calcining the layered
support material, and impregnating the first support material with
gold.
29. The method of claim 18, further comprising calcining the
layered support material before contacting the catalytic components
to the layered support material.
30. The method of claim 18, wherein the second support material is
non-porous.
31. The method of claim 18, wherein the first support material is
selected from the group consisting of alumina, silica/alumina,
zeolites, non-zeolitic molecular sieves, titania, zirconia, niobia,
silica, bentonite, clays, and combinations thereof.
32. The method of claim 18, wherein the second support material is
selected from the group consisting of alumina, silicon carbide,
zirconia, titania, steatite, niobia, silica, bentonite, clays,
metals, glasses, quartz, silicon nitride, alumina-silica, pumice,
non-zeolitic molecular sieves and combinations thereof.
33. The method of claim 18, wherein the layering step comprises
contacting a bonding agent to the first or second support material
to promote adhesion between the materials.
34. The method of claim 18, wherein the bonding agent is selected
from organic and inorganic bonding agents.
35. The method of claim 18, wherein the bonding agent is a zirconia
bonding agent.
36. A method of producing a catalyst or pre-catalyst suitable for
assisting in the production of alkenyl alkanoates, comprising:
contacting palladium and gold precursors to a zirconia containing
support material; and reducing at least the palladium precursor by
contacting a reducing environment to the zirconia containing
support material.
37. The method of claim 36, further comprising calcining the
contacted zirconia containing support material in a non-reducing
atmosphere before the reducing step.
38. The method of claim 36, wherein the contacting step comprises
impregnating the zirconia containing support material with
palladium and gold precursors.
39. The method of claim 36, wherein the impregnating step comprises
sequentially impregnating palladium and gold precursors onto the
zirconia containing support material.
40. The method of claim 36, wherein the calcining step occurs
before the impregnation of the gold precursor.
41. The method of claim 36, wherein the reducing step occurs before
the impregnating of the gold precursor.
42. The method of claims 36, wherein the impregnating step
comprises co-impregnating palladium and gold precursors.
43. The method of claim 36, wherein the impregnating step comprises
impregnating the zirconia containing support material with water
soluble, substantially chloride free precursor solutions.
44. The method of claim 36, wherein the impregnating step comprises
impregnating the zirconia containing support material with chloride
containing precursor solutions and following by a fixing step
comprising fixing with a fixing agent.
45. The method of claim 36, wherein the calcining step comprises
heating the contacted zirconia containing support material at a
temperature between about 200.degree. C. and about 700.degree.
C.
46. The method of claim 36, further comprising contacting potassium
acetate to the zirconia containing support material in an amount of
between about 10 and 70 grams per liter of catalyst.
47. The method of claims 36, wherein the contacting step comprises
contacting between about 1 to about 10 grams of palladium, and
about 0.5 to about 10 grams of gold per liter of catalyst, with the
amount of gold being from about 10 to about 125 wt % based on the
weight of palladium.
48. A method of producing a catalyst or pre-catalyst suitable for
assisting in the production of alkenyl alkanoates, comprising:
contacting at least one catalytic precursor solution comprising
palladium and gold to a support material wherein the at least one
catalytic precursor solution is an aqueous solution that is
substantially free of chloride; and reducing the palladium or gold
by contacting a reducing environment to the support material.
49. The method of claim 48, wherein the palladium catalytic
precursor solution comprises Pd(NH.sub.3).sub.2(NO.sub.2).sub.2,
Pd(NH.sub.3).sub.4(OH).sub.2, Pd(NH.sub.3).sub.4(NO.sub.3).sub.2,
Pd(NO.sub.3).sub.2, Pd(NH.sub.3).sub.4(OAc).sub.2,
Pd(NH.sub.3).sub.2(OAc).sub.2, Pd(OAc).sub.2 in KOH or NMe.sub.4OH
or NaOH, Pd(NH.sub.3).sub.4(HCO.sub.3).sub.2, palladium oxalate or
combinations thereof.
50. The method of claim 48, wherein the gold catalytic precursor
solution comprises KAuO.sub.2, NaAuO.sub.2, NMe.sub.4AuO.sub.2,
Au(OAc).sub.3 in KOH or NMe.sub.4OH, HAu(NO.sub.3).sub.4 in nitric
acid or combinations thereof.
51. The method of claim 48, wherein the support material comprises
silica, alumina, silica-alumina, titania, zirconia, niobia,
silicates, aluminosilicates, titanates, spinel, silicon carbide,
silicon nitride, carbon, steatite, bentonite, clays, metals,
glasses, quartz, pumice, zeolites, non-zeolitic molecular sieves,
or combinations thereof.
52. The method of claim 48, wherein the support material comprises
a layered support material.
53. The method of claim 48, wherein the layered support material
comprises an inner layer and an outer layer, wherein the inner
layer is substantially free of palladium and gold.
54. The method of claim 48, wherein the contacting step comprises
contacting between about 1 to about 10 grams of palladium, and
about 0.5 to about 10 grams of gold per liter of catalyst to the
support material, with the amount of gold being from about 10 to
about 125 wt % based on the weight of palladium.
55. The method of claim 48, wherein the contacting step comprises
separately impregnating palladium and gold on to the support
material.
56. The method of claim 48, further comprising a calcining step in
a non-reducing atmosphere after impregnation of palladium and
before impregnation of gold.
57. The method of claim 48, wherein the contacting step comprises
co-impregnating palladium and gold on to the support material.
58. The method of claim 48, further comprising a calcining step in
a non-reducing atmosphere before the reducing step.
59. The method of claim 48, further comprising contacting potassium
acetate to the support material in an amount of between about 10
and 70 grams per liter of catalyst.
Description
CLAIM OF PRIORITY
[0001] The present application claims the benefit of U.S.
provisional application 60/531,415; 60/530,936; 60/531,486; and
60/530,937, all filed on Dec. 19, 2003 and claims the benefit of
international applications PCT/U.S.2004/______ (Atty. No
1197.001WO); PCT/U.S. 2004/______ (Atty. No 1197.002WO);
PCT/U.S.2004/______ (Atty. No 1197.003WO); and PCT/U.S.2004/______
(Atty. No 11197.004WO), all filed on Nov. 19, 2004, all of which
are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to catalysts, methods of
making the catalysts, and methods of making alkenyl alkanoates.
More particularly, the invention relates to methods of making vinyl
acetate.
BACKGROUND OF THE INVENTION
[0003] Certain alkenyl alkanoates, such as vinyl acetate (VA), are
commodity chemicals in high demand in their monomer form. For
example, VA is used to make polyvinyl acetate (PVAc), which is used
commonly for adhesives, and accounts for a large portion of VA use.
Other uses for VA included polyvinyl alcohol (PVOH), ethylene vinyl
acetate (EVA), vinyl acetate ethylene (VAE), polyvinyl butyral
(PVB), ethylene vinyl alcohol (EVOH), polyvinyl formal (PVF), and
vinyl chloride-vinyl acetate copolymer. PVOH is typically used for
textiles, films, adhesives, and photosensitive coatings. Films and
wire and cable insulation often employ EVA in some proportion.
Major applications for vinyl chloride-vinyl acetate copolymer
include coatings, paints, and adhesives often employ VAE having VA
in some proportion. VAE, which contains more than 50 percent VA, is
primarily used as cement additives, paints, and adhesives. PVB is
mainly used for under layer in laminated screens, coatings, and
inks. EVOH is used for barrier films and engineering polymers. PVF
is used for wire enamel and magnetic tape.
[0004] Because VA is the basis for so many commercially significant
materials and products, the demand for VA is large, and VA
production is frequently done on a relatively large scale, e.g.
50,000 metric tons or more per year. This large scale production
means that significant economies of scale are possible and
relatively subtle changes in the process, process conditions or
catalyst characteristics can have a significant economic impact on
the cost of the production of VA.
[0005] Many techniques have been reported for the production of
alkenyl alkanoates. For example, in making VA, a widely used
technique includes a catalyzed gas phase reaction of ethylene with
acetic acid and oxygen, as seen in the following reaction:
C.sub.2H.sub.4+CH.sub.3COOH+0.5O.sub.2CH.sub.3COOCH.dbd.CH.sub.2+H.sub.2O
[0006] Several side reactions may take place, including, such as,
the formation of CO.sub.2. The results of this reaction are
discussed in terms of the space-time yield (STY) of the reaction
system, where the STY is the grams of VA produced per liter of
catalyst per hour of reaction time (g/l*h).
[0007] The composition of the starting material feed can be varied
within wide limits. Typically, the starting material feed includes
30-70% ethylene, 10-30% acetic acid and 4-16% oxygen. The feed may
also include inert materials such as CO.sub.2, nitrogen, methane,
ethane, propane, argon and/or helium. The primary restriction on
feed composition is the oxygen level in the effluent stream exiting
the reactor must be sufficiently low such that the stream is
outside the flammability zone. The oxygen level in the effluent is
affected by the oxygen level in the starting material stream,
O.sub.2 conversion rate of the reaction and the amount of any inert
material in the effluent.
[0008] The gas phase reaction has been carried out where a feed of
the starting materials is passed over or through fixed bed
reactors. Successful results have been obtained through the use of
reaction temperatures in the range of -125.degree. C. to
200.degree. C., while reaction pressures of 1-15 atmospheres are
typical.
[0009] While these systems have provided adequate yields, there
continues to be a need for reduced production of by-products,
higher rates of VA output, and lower energy use during production.
One approach is to improve catalyst characteristics, particularly
as to CO.sub.2 selectivity and/or activity of the catalyst. Another
approach is to modify reaction conditions, such as the ratio of
starting materials to each other, the O.sub.2 conversion of the
reaction, the space velocity (SV) of the starting material feed,
and operating temperatures and pressures.
[0010] The formation of CO.sub.2 is one aspect which may be reduced
through the use of improved catalysts. The CO.sub.2 selectivity is
the percentage of the ethylene converted that goes to CO.sub.2.
Decreasing the CO.sub.2 selectivity permits a larger amount of VA
per unit volume and unit time in existing plants, even retaining
all other reaction conditions.
[0011] VA output of a particular reaction system is affected by
several other factors including the activity of the catalyst, the
ratio of starting materials to each other, the O.sub.2 conversion
of the reaction, the space velocity (SV) of the starting material
feed, and operating temperatures and pressures. All these factors
cooperate to determine the space-time yield (STY) of the reaction
system, where the STY is discussed in terms of grams of VA produced
per liter of catalyst per hour of reaction time or g/l*h.
[0012] Generally, activity is a significant factor in determining
the STY, but other factors may still have a significant impact on
the STY. Typically, the higher the activity of a catalyst, the
higher the STY the catalyst is able to produce.
[0013] The O.sub.2 conversion is a measure of how much oxygen
reacts in the presence of the catalyst. The O.sub.2 conversion rate
is temperature dependent such that the conversion rate generally
climbs with the reaction temperature. However, the amount of
CO.sub.2 produced also increases along with the O.sub.2 conversion.
Thus, the O.sub.2 conversion rate is selected to give the desired
VA output balanced against the amount of CO.sub.2 produced. A
catalyst with a higher activity means that the overall reaction
temperature can be lowered while maintaining the same O.sub.2
conversion. Alternatively, a catalyst with a higher activity will
give a higher O.sub.2 conversion rate at a given temperature and
space velocity.
[0014] It is common that catalysts employ one or more catalytic
components carried on a relatively inert support material. In the
case of VA catalysts, the catalytic components are typically a
mixture of metals that may be distributed uniformly throughout the
support material ("all through-out catalysts"), just on the surface
of the support material ("shell catalysts"), just below a shell of
support material ("egg white catalysts") or in the core of the
support material ("egg yolk catalysts").
[0015] Numerous different types of support materials have been
suggested for use in VA catalyst including silica, cerium doped
silica, alumina, titania, zirconia and oxide mixtures. But very
little investigation of the differences between the support
materials has been done. For the most part, only silica and alumina
have actually been commercialized as support materials.
[0016] One useful combination of metals for VA catalysis is
palladium and gold. Pd/Au catalysts provide adequate CO.sub.2
selectivity and activity, but there continues to be a need for
improved catalysts given the economies of scale that are possible
in the production of VA.
[0017] One process for making Pd/Au catalysts typically includes
the steps of impregnating the support with aqueous solutions of
water-soluble salts of palladium and gold; reacting the impregnated
water-soluble salts with an appropriate alkaline compound e.g.,
sodium hydroxide, to precipitate (often called fixing) the metallic
elements as water-insoluble compounds, e.g. the hydroxides; washing
the fixed support material to remove un-fixed compounds and to
otherwise cleanse the catalyst of any potential poisons, e.g.
chloride; reducing the water insoluble compounds with a typical
reductant such as hydrogen, ethylene or hydrazine, and adding an
alkali metal compound such as potassium or sodium acetate.
[0018] Various modifications to this basic process have been
suggested. For example, in U.S. Pat. No. 5,990,344, it is suggested
that sintering of the palladium be undertaken after the reduction
to its free metal form. In U.S. Pat. No. 6,022,823, it suggested
that calcining the support in a non-reducing atmosphere after
impregnation with both palladium and gold salts might be
advantageous. In WO94/21374, it is suggested that after reduction
and activation, but before its first use, the catalyst may be
pretreated by successive heating in oxidizing, inert, and reducing
atmospheres.
[0019] In U.S. Pat. No. 5,466,652, it is suggested that salts of
palladium and gold that are hydroxyl-, halide- and barium-free and
soluble in acetic acid may be useful to impregnate the support
material. A similar suggestion is made in U.S. Pat. No. 4,902,823,
i.e. use of halide- and sulfur-free salts and complexes of
palladium soluble in unsubstituted carboxylic acids having two to
ten carbons.
[0020] In U.S. Pat. No. 6,486,370, it suggested that a layered
catalyst may be used in a dehydrogenation process where the inner
layer support material differs from the outer layer support
material. Similarly, U.S. Pat. No. 5,935,889 suggests that a
layered catalyst may useful as acid catalysts. But neither suggests
the use of layered catalysts in the production of alkenyl
alkanoates.
[0021] Taken together, the inventors have recognized and addressed
the need for continued improvements in the field of VA catalysts to
provide improved VA production at lower costs.
SUMMARY OF THE INVENTION
[0022] The present invention addresses at least four different
aspects relating to catalyst structure, methods of making those
catalysts and methods of using those catalysts for making alkenyl
alkanoates. Separately or together in combination, the various
aspects of the invention are directed at improving the production
of alkenyl alkanoates and VA in particular, including reduction of
by-products and improved production efficiency. A first aspect of
the present invention pertains to a unique palladium/gold catalyst
or pre-catalyst (optionally calcined) that includes rhodium or
another metal. A second aspect pertains to a palladium/gold
catalyst or pre-catalyst that is based on a layered support
material where one layer of the support material is substantially
free of catalytic components. A third aspect pertains to a
palladium/gold catalyst or pre-catalyst on a zirconia containing
support material. A fourth aspect pertains to a palladium/gold
catalyst or pre-catalyst that is produced from substantially
chloride free catalytic components.
DETAILED DESCRIPTION
[0023] Catalysts
[0024] For present purposes, a catalyst is any support material
that contains at least one catalytic component and that is capable
of catalyzing a reaction, whereas a pre-catalyst is any material
that results from any of the catalyst preparation steps discussed
herein.
[0025] Catalysts and pre-catalysts of the present invention may
include those having at least one of the following attributes: 1)
the catalyst will be a palladium and gold containing catalyst that
includes at least another catalytic component, e.g. rhodium where
the one or more of the catalytic components have been calcined; 2)
the catalyst will be carried on a layered support, 3) the catalyst
will be carried on a zirconia containing support material; 4) the
catalyst will be produced with chloride free precursors or any
combination of the foregoing. Effective use of the catalyst
accordingly should help improve CO.sub.2 selectivity, activity or
both, particularly as pertaining to VA production.
[0026] It should be appreciated that the present invention is
described in the context of certain illustrative embodiments, but
may be varied in any of a number of aspects depending on the needs
of a particular application. By way of example, without limitation,
the catalysts may have the catalytic components uniformly
distributed throughout the support material or they may be shell
catalysts where the catalytic components are found in a relatively
thin shell around a support material core. Egg white catalysts may
also be suitable, where the catalytic components reside
substantially away from the center of support material. Egg yolk
catalysts may also be suitable.
[0027] Catalytic Components
[0028] In general, the catalysts and pre-catalysts of the present
invention include metals and particularly include a combination of
at least two metals. In particular, the combination of metals
includes at least one from Group VIIIB and at least one from Group
IB. It will be appreciated that "catalytic component" is used to
signify the metal that ultimately provides catalytic functionally
to the catalyst, but also includes the metal in a variety of
states, such as salt, solution, sol-gel, suspensions, colloidal
suspensions, free metal, alloy, or combinations thereof. Preferred
catalysts include palladium and gold as the catalytic
components.
[0029] One embodiment of the catalyst includes a combination of
catalytic components having palladium and gold combined with a
third catalytic component. The third catalytic component is
preferably selected from Group VIIIB, with Rh being the most
preferred. Other preferred catalysts include those where the third
catalytic component is selected from W, Ni, Nb, Ta, Ti, Zr, Y, Re,
Os, Fe, Cu, Co, Zn, In, Sn, Ce, Ge, Ga and combinations
thereof.
[0030] Another embodiment of the catalyst includes a combination of
catalytic components including proportions of palladium, gold, and
rhodium. Optionally a third catalytic component (as listed above)
may also be included in this embodiment in place of Rh. In another
embodiment, two or more catalytic components from the above list
may be employed.
[0031] In one example, palladium and gold may be combined with Rh
to form a catalyst that shows improved CO.sub.2 selectively (i.e.
decreased formation of CO.sub.2) compared to Pd/Au catalysts that
lack Rh. Also, the addition of Rh does not appear to adversely
affect the activity of the catalyst. The CO.sub.2 selectivity of
the palladium, gold, rhodium catalyst may also be improved through
calcining during the catalyst preparation and/or through the use of
water-soluble halide free precursors (both discussed below),
although these are not necessary to observe the Rh effect.
[0032] The atomic ratio of the third catalytic component to
palladium may be in the range of about 0.005 to about 1.0, more
preferably about 0.01 to about 1.0. In one embodiment, the catalyst
contains between about 0.01 and about 5.0 g of the third catalytic
component per liter of catalyst.
[0033] Another preferred embodiment of the catalyst includes
between about 1 to about 10 grams of palladium, and about 0.5 to
about 10 grams of gold per liter of catalyst. The amount of gold is
preferably from about 10 to about 125 wt % based on the weight of
palladium.
[0034] In one embodiment for ground catalysts, Au to Pd atomic
ratios between about 0.5 and about 1.00 may be preferred for ground
catalysts. The atomic ratio can be adjusted to balance the activity
and CO.sub.2 selectivity. Employment of higher Au/Pd weight or
atomic ratios tends to favor more active, more selective catalysts.
Stated alternatively, a catalyst with an atomic ratio of about 0.6
is less selective for CO.sub.2, but also has less activity than a
catalyst with a ratio of about 0.8. The effect of the high Au/Pd
atomic ratio on ground support material may also be enhanced
through the use of relatively high excess of hydroxide ion, as
discussed below with respect to the fixing step. A ground catalyst
may be one where the catalytic components are contacted to the
support material followed by a reduction in the particle size (e.g.
by grinding or ball milling) or one where the catalytic components
are contacted to the support material after the support material
has been reduced in size.
[0035] For shell catalysts, the thickness of the shell of catalytic
components on the support material ranges from about 5 .mu.m to
about 500 .mu.m. More preferred ranges include from about 5 .mu.m
to about 300 .mu.m.
[0036] Support Materials
[0037] As indicated, in one aspect of the invention, the catalytic
components of the present invention generally will be carried by a
support material. Suitable support materials typically include
materials that are substantially uniform in identity or a mixture
of materials. Overall, the support materials are typically inert in
the reaction being performed. Support materials may be composed of
any suitable substance preferably selected so that the support
materials have a relatively high surface area per unit mass or
volume, such as a porous structure, a molecular sieve structure, a
honeycomb structure, or other suitable structure. For example, the
support material may contain silica, alumina, silica-alumina,
titania, zirconia, niobia, silicates, aluminosilicates, titanates,
spinel, silicon carbide, silicon nitride, carbon, cordierite,
steatite, bentonite, clays, metals, glasses, quartz, pumice,
zeolites, non-zeolitic molecular sieves combinations thereof and
the like. Any of the different crystalline form of the materials
may also be suitable, e.g. alpha or gamma alumina. Silica and
zirconia containing support materials are the most preferred. In
addition, multilayer support materials are also suitable for use in
the present invention.
[0038] The support material in the catalyst of this invention may
be composed of particles having any of various regular or irregular
shapes, such as spheres, tablets, cylinders, discs, rings, stars,
or other shapes. The support material may have dimensions such as
diameter, length or width of about 1 to about 10 mm, preferably
about 3 to about 9 mm. In particular having a regular shape (e.g.
spherical) will have as its preferred largest dimension of about 4
mm to about 8 mm. In addition, a ground or powder support material
may be suitable such that the support material has a regular or
irregular shape with a diameter of between about 10 microns and
about 1000 micron, with preferred sizes being between about 10 and
about 700 microns, with most preferred sizes being between about
180 microns and about 450 microns. Larger or smaller sizes may be
employed, as well as polydisperse collections of particles sizes.
For example, for a fluid bed catalyst a preferred size range would
include 10 to 150 microns. For precursors used in layered
catalysts, a size range of 10 to 250 microns is preferred.
[0039] Surface areas available for supporting catalytic components,
as measured by the BET (Brunauer, Emmett, and Teller) method, may
generally be between about 1 m.sup.2/g and about 500 m.sup.2/g,
preferably about 100 m.sup.2/g to about 200 m.sup.2/g. For example,
for a porous support, the pore volume of the support material may
generally be about 0.1 to about 2 ml/g, and preferably about 0.4 to
about 1.2 ml/g. An average pore size in the range, for example, of
about 50 to about 2000 angstroms is desirable, but not
required.
[0040] Examples of suitable silica containing support materials
include KA160 from Sud Chemie, Aerolyst350 from Degussa and other
pyrogenic or microporous-free silicas with a particle size of about
1 mm to about 10 mm.
[0041] Examples of suitable zirconia containing support materials
include those from N or Pro, Zirconia Sales (America), Inc., Daichi
Kigenso Kagaku Kogyo, and Magnesium Elektron Inc (MEI). Suitable
zirconia support materials have a wide range of surface areas from
less than about 5 m.sup.2/g to more than 300 m.sup.2/g. Preferred
zirconia support materials have surface areas from about 10
m.sup.2/g to about 135 m.sup.2/g. Support materials may have their
surfaces treated through a calcining step in which the virgin
support material is heated. The heating reduces the surface area of
the support material (e.g. calcining). This provides a method of
creating support materials with specific surface areas that may not
otherwise be readily available from suppliers.
[0042] In another embodiment, it is contemplated to employ at least
a plural combination of support materials, each with a different
characteristic. For example, at least two support materials (e.g.
zirconia) with different characteristics may exhibit different
activities and CO.sub.2 selectivities, thus permitting preparation
of catalysts with a desired set of characteristics, i.e. activity
of a catalyst may be balanced against the CO.sub.2 selectivity of
the catalyst.
[0043] In one embodiment, plural different supports are employed in
a layered configuration. Layering may be achieved in any of a
number of different approaches, such as a plurality of lamella that
are generally flat, undulated or a combination thereof. One
particular approach is to utilize successively enveloping layers
relative to an initial core layer. In general, herein, layered
support materials typically include at least an inner layer and an
outer layer at least partially surrounding the inner layer. The
outer layer preferably contains substantially more of catalytic
components than the inner layer. In one embodiment, the inner and
outer layers are made of different materials; but the materials may
be the same. While the inner layer may be non-porous, other
embodiments include an inner layer that is porous.
[0044] The layered support material preferably results in a form of
a shell catalyst. But the layered support material offers a well
defined boundary between the areas of the support material that
have catalytic components and the areas that do not. Also, the
outer layer can be constructed consistently with a desired
thickness. Together the boundary and the uniform thickness of the
outer layer result in a shell catalyst that is a shell of catalytic
components that is of a uniform and known thickness.
[0045] Several techniques are known for creating layered support
materials includes those described in U.S. Pat. Nos. 6,486,370;
5,935,889; and 5,200,382, each of which is incorporated by
reference. In one embodiment, the materials of the inner layer are
also not substantially penetrated by liquids, e.g., metals
including but not limited to aluminum, titanium and zirconium.
Examples of other materials for the inner layer include, but are
not limited to, alumina, silica, silica-alumina, titania, zirconia,
niobia, silicates, aluminosilicates, titanates, spinel, silicon
carbide, silicon nitride, carbon, cordierite, steatite, bentonite,
clays, metals, glasses, quartz, pumice, zeolites, non-zeolitic
molecular sieves and combinations thereof. A preferred inner layer
is silica and KA160, in particular.
[0046] These materials which make up the inner layer may be in a
variety of forms such as regularly shaped particulates, irregularly
shaped particulates, pellets, discs, rings, stars, wagon wheels,
honeycombs or other shaped bodies. A spherical particulate inner
layer is preferred. The inner layer, whether spherical or not, has
an effective diameter of about 0.02 mm to about 10.0 mm and
preferably from about 0.04 mm to about 8.0 mm.
[0047] The outermost layer of any multilayer structure is one which
is porous, has a surface area in the range of about 5 m.sup.2/g to
about 300 m.sup.2/g. The material of the outer layer is a metal,
ceramic, or a combination thereof, and in one embodiment it is
selected from alumina, silica, silica-alumina, titania, zirconia,
niobia, silicates, aluminosilicates, titanates, spinel, silicon
carbide, silicon nitride, carbon, cordierite, steatite, bentonite,
clays, metals, glasses, quartz, pumice, zeolites, non-zeolitic
molecular sieves and combinations thereof and preferably include
alumina, silica, silica/alumina, zeolites, non-zeolite molecular
sieves (NZMS), titania, zirconia and mixtures thereof. Specific
examples include zirconia, silica and alumina or combinations
thereof.
[0048] While the outer layer typically surrounds substantially the
entire inner layer, this is not necessarily the case and a
selective coating on the inner layer by the outer layer may be
employed.
[0049] The outer layer may be coated on to the underlying layer in
a suitable manner. In one embodiment, a slurry of the outer layer
material is employed. Coating of the inner layer with the slurry
may be accomplished by methods such as rolling, dipping, spraying,
wash coating, other slurry coating techniques, combinations thereof
or the like. One preferred technique involves using a fixed or
fluidized bed of inner layer particles and spraying the slurry into
the bed to coat the particles evenly. The slurry may be applied
repeatedly in small amounts, with intervening drying, to provide an
outer layer that is highly uniform in thickness.
[0050] The slurry utilized to coat the inner layer may also include
any of a number of additives such as a surfactant, an organic or
inorganic bonding agent that aids in the adhesion of the outer
layer to an underlying layer, or combinations thereof. Examples of
this organic bonding agent include but are not limited to PVA,
hydroxypropylcellulose, methyl cellulose, and
carboxymethylcellulose. The amount of organic bonding agent which
is added to the slurry may vary, such as from about 1 wt % to about
15 wt % of the combination of outer layer and the bonding agent.
Examples of inorganic bonding agents are selected from an alumina
bonding agent (e.g. Bohmite), a silica bonding agent (e.g. Ludox,
Teos), zirconia bonding agent (e.g. zirconia acetate or colloidal
zirconia) or combinations thereof. Examples of silica bonding
agents include silica sol and silica gel, while examples of alumina
bonding agents include alumina sol, bentonite, Bohmite, and
aluminum nitrate. The amount of inorganic bonding agent may range
from about 2 wt % to about 15 wt % of the combination of the outer
layer and the bonding agent. The thickness of the outer layer may
range from about 5 microns to about 500 microns and preferably
between about 20 microns and about 250 microns.
[0051] Once the inner layer is coated with the outer layer, the
resultant layered support will be dried, such as by heating at a
temperature of about 100.degree. C. to about 320.degree. C. (e.g.
for a time of about 1 to about 24 hours) and then may optionally be
calcined at a temperature of about 300.degree. C. to about
900.degree. C. (e.g. for a time of about 0.5 to about 10 hours) to
enhance bonding the outer layer to it underlying layer over a least
a portion of its surface and provide a layered catalyst support.
The drying and calcining steps can be combined into one step. The
resultant layered support material may be contacted with catalytic
components just as any other support material in the production of
catalysts, as described below. Alternately, the outer layer support
material is contacted to catalytic components before it is coated
onto the underlying layer.
[0052] In another embodiment of the layered support, a second outer
layer is added to surround the initial outer layer to form at least
three layers. The material for the second outer layer may be the
same or different than the first outer layer. Suitable materials
include those discussed with respect to the first outer layer. The
method for applying the second outer layer may be the same or
different than the method used to apply the middle layer and
suitable methods include those discussed with respect to the first
outer layer. Organic or inorganic bonding agents as described may
suitably used in the formation of the second outer layer.
[0053] The initial outer layer may or may not contain catalytic
components. Similarly, the second outer layer may or may not
contain catalytic components. If both outer layers contain
catalytic component, then preferably different catalytic components
are used in each layer, although this is not necessarily the case.
In one preferred embodiment, the initial outer layer does not
contain a catalytic component. Contacting catalytic component to
the outer layers may be accomplished by impregnation or spray
coating, as described below.
[0054] In embodiments where the initial outer layer contains
catalytic component, one method of achieving this is to contact the
catalytic component to the material of the initial outer layer
before the material is applied to the inner layer. The second outer
layer may be applied to the initial outer layer neat or containing
catalytic component.
[0055] Other suitable techniques may be used to achieve a three
layered support material in which one or more of the outer layers
contain catalytic components. Indeed, the layered support material
is not limited to three layers, but may include four, five or more
layers, some or all of which may contain catalytic components.
[0056] In addition, the number and type of catalytic components
that vary between the layers of the layered support material, other
characteristics (e.g. porosity, particle size, surface area, pore
volume, or the like) of the support material may vary between the
layers.
[0057] Methods of Making Catalysts
[0058] In general the method includes contacting support material
catalytic components and reducing the catalytic components.
Preferred methods of the present invention include impregnating the
catalytic components into the support material, calcining the
catalytic component containing support material, reducing the
catalytic components and modifying the reduced catalytic components
on the support material. Additional steps such as fixing the
catalytic components on the support material and washing the fixed
catalytic components may also be included in the method of making
the catalyst or pre-catalyst. Some of the steps listed above are
optional and others may be eliminated (e.g. the washing and/fixing
steps). In addition, some steps may be repeated (e.g. multiple
impregnation or fix steps) and the order of the steps may be
different from that listed above (e.g. the reducing step precedes
the calcining step). To a certain extent, the contacting step will
determine what later steps are needed for the formation of the
catalyst.
[0059] Contacting Step
[0060] One particular approach to contacting is one pursuant to
which an egg yolk catalyst or pre-catalyst is formed, an egg white
catalyst or pre-catalyst is formed, an all throughout catalyst or
pre-catalyst is formed or a shell catalyst or pre-catalyst is
formed, or a combination thereof. In one embodiment, techniques
that form shell catalysts are preferred.
[0061] The contacting step may be carried out using any of the
support materials described above, with silica, zirconia and
layered support materials containing zirconia being the most
favored. The contacting step is preferably carried out at ambient
temperature and pressure conditions; however, reduced or elevated
temperatures or pressures may be employed.
[0062] In one preferred contacting step, a support material is
impregnated with one or more aqueous solutions of the catalytic
components (referred to as precursor solutions). The physical state
of the support material during the contacting step may be a dry
solid, a slurry, a sol-gel, a colloidal suspension or the like.
[0063] In one embodiment, the catalytic components contained in the
precursor solution are water soluble salts made of the catalytic
components, including but not limited to, chlorides, other halides,
nitrates, nitrites, hydroxides, oxides, oxalates, acetates (OAc),
and amines, with halide free salts being preferred and chloride
free salts being more preferred. Examples of palladium salts
suitable for use in precursor solutions include PdCl.sub.2,
Na.sub.2PdCl.sub.4, Pd(NH.sub.3).sub.2(NO.sub.2).sub.2,
Pd(NH.sub.3).sub.4(OH).sub.2, Pd(NH.sub.3).sub.4(NO.sub.3).sub.2,
Pd(NO.sub.3).sub.2, Pd(NH.sub.3).sub.4(OAc).sub.2,
Pd(NH.sub.3).sub.2(OAc).sub.2, Pd(OAc).sub.2 in KOH and/or
NMe.sub.4OH and/or NaOH, Pd(NH.sub.3).sub.4(HCO.sub.3).sub.2 and
palladium oxalate. Of the chloride-containing palladium precursors,
Na.sub.2PdCl.sub.4 is most preferred. Of the chloride free
palladium precursor salts, the following four are the most
preferred: Pd(NH.sub.3).sub.4(NO.sub.3).sub.2, Pd(NO.sub.3).sub.2,
Pd(NH.sub.3).sub.2(NO.sub.2).sub.2, Pd(NH.sub.3).sub.4(OH).sub.2.
Examples of gold salts suitable for use in precursor solution
include AuCl.sub.3, HAuCl.sub.4, NaAuCl.sub.4, KAuO.sub.2,
NaAuO.sub.2, NMe.sub.4AuO.sub.2, Au(OAc).sub.3 in KOH and/or
NMe.sub.4OH as well as HAu(NO.sub.3).sub.4 in nitric acid, with
KAuO.sub.2 being the most preferred of the chloride free gold
precursors. Examples of rhodium salts suitable for use in precursor
solutions include RhCl.sub.3, Rh(OAc).sub.3, and
Rh(NO.sub.3).sub.2. Similar salts of the above described third
catalytic components may also be selected.
[0064] Furthermore, more than one salt may be used in a given
precursor solution. For example, a palladium salt may be combined
with a gold salt or two different palladium salts may be combined
together in a single precursor solution. Precursor solutions
typically may be made by dissolving the selected salt or salts in
water, with or without solubility modifiers such as acids, bases or
other solvents. Other non-aqueous solvents may also be
suitable.
[0065] The precursor solutions may be impregnated onto the support
material simultaneously (e.g. co-impregnation) or sequentially and
may be impregnated through the use of one or multiple precursor
solutions. With three or more catalytic components, a combination
of simultaneous and sequential impregnation may be used. For
example, palladium and rhodium may be impregnated through the use
of a single precursor solution (referred to as a co-impregnation),
followed by impregnation with a precursor solution of the gold. In
addition, a catalytic component may be impregnated on to support
material in multiple steps, such that a portion of the catalytic
component is contacted each time. For example, one suitable
protocol may include impregnating with Pd, followed by impregnating
with Au, followed by impregnating again with Au.
[0066] The order of impregnating the support material with the
precursor solutions is not critical; although there may be some
advantages to certain orders, as discussed below, with respect to
the calcining step. Preferably, the palladium catalytic component
is impregnated onto the support material first, with gold being
impregnated after palladium, or last. Rhodium or other third
catalytic component, when used, may be impregnated with the
palladium, with the gold or by itself. Also, the support material
may be impregnated multiple times with the same catalytic
component. For example, a portion of the overall gold contained in
the catalyst may be first contacted, followed by contacting of a
second portion of the gold. One more other steps may intervene
between the steps in which gold is contacted to the support
material, e.g. calcining, reducing, and/or fixing.
[0067] The acid-base profile of the precursor solutions may
influence whether a co-impregnation or a sequential impregnation is
utilized. Thus, only precursor solutions with similar acid-base
profile should be used together in a co-impregnating step; this
eliminates any acid-base reactions that may foul the precursor
solutions.
[0068] For the impregnating step, the volume of precursor solution
is selected so that it corresponds to between about 85% and about
110% of the pore volume of the support material. Volumes between
about 95% and about 100% of the pore volume of the support material
are preferred, and more preferably between about 98% and about 99%
of the pore volume.
[0069] Typically, the precursor solution is added to the support
material and the support material is allowed absorb the precursor
solution. This may be done drop wise until incipient wetness of the
support material is substantially achieved. Alternatively, the
support material may be placed by aliquots or batch wise into the
precursor solution. A roto-immersion or other assistive apparatus
may be used to achieve thorough contact between the support
material and the precursor solution. Further, a spray device may be
used such that the precursor solution is sprayed through a nozzle
onto the support material, where it absorbed. Optionally,
decanting, heat or reduced pressure may be used to remove any
excess liquid not absorbed by the support material or to dry the
support material after impregnation.
[0070] For the impregnating step, the volume of precursor solution
is selected so that it corresponds to between about 85% and about
110% of the pore volume of the support material. Volumes between
about 95% and about 100% of the pore volume of the support material
are preferred, and more preferably between about 98% and about 99%
of the pore volume.
[0071] Typically, the precursor solution is added to the support
material and the support material is allowed absorb the precursor
solution. This may be done drop wise until incipient wetness of the
support material is substantially achieved. Alternatively, the
support material may be placed by aliquots or batch wise into the
precursor solution. A roto-immersion or other assistive apparatus
may be used to achieve thorough contact between the support
material and the precursor solution. Further, a spray device may be
used such that the precursor solution is sprayed through a nozzle
onto the support material, where it absorbed. Optionally,
decanting, heat or reduced pressure may be used to remove any
excess liquid not absorbed by the support material or to dry the
support material after impregnation.
[0072] Other contacting techniques may be used to avoid a fixing
step while still achieving a shell catalyst. For example, catalytic
components may be contacted to a support material through a
chemical vapor deposition process, such as described in U.S.
2001/0048970, which is incorporated by reference. Also, spray
coating or otherwise layering a uniformly pre-impregnated support
material, as an outer layer, on to an inner layer effectively forms
shell catalyst that may also be described as a layered support
material. In another technique, organometallic precursors of
catalytic components, particularly with respect to gold, may be
used to form shell catalysts, as described in U.S. Pat. No.
5,700,753, which is incorporated by reference.
[0073] A physical shell formation technique may also be suitable
for the production of shell catalysts. Here, the precursor solution
may be sprayed onto a heated support material or a layered support
material, where the solvent of the precursor solution evaporates
upon contact with the heated support material, thus depositing the
catalytic components in a shell on the support material.
Preferably, temperatures between about 40 and 140.degree. C. may be
used. The thickness of the shell may be controlled by selecting the
temperature of the support material and the flow rate of the
solution through the spray nozzle. For example, with temperatures
above about 100.degree. C., a relatively thin shell is formed. This
embodiment may be particularly useful when chloride free precursors
are utilized to help enhance the shell formation on the support
material.
[0074] One skilled in the art will understand that a combination of
the contacting steps may be an appropriate method of forming a
contacted support material.
[0075] Fixing Step
[0076] It may be desirable to transform at least a portion of the
catalytic components on the contacted support material from a
water-soluble form to a water-insoluble form. Such a step may be
referred to as a fixing step. This may be accomplished by applying
a fixing agent (e.g. dispersion in a liquid, such as a solution) to
the impregnated support material which causes at least a portion of
the catalytic components to precipitate. This fixing step helps to
form a shell catalyst, but is not required to form shell
catalysts.
[0077] Any suitable fixing agent may be used, with hydroxides (e.g.
alkali metal hydroxides), silicates, borates, carbonates and
bicarbonates in aqueous solutions being preferred. The preferred
fixing agent is NaOH. Fixing may be accomplished by adding the
fixing agent to the support material before, during or after the
precursor solutions are impregnated on the support material.
Typically, the fixing agent is used subsequent to the contacting
step such that the contacted support material is allowed to soak in
the fixing agent solution for about 1 to about 24 hours. The
specific time depends upon the combination of the precursor
solution and the fixing agent. Like the impregnating step, an
assistive device, such as a roto immersion apparatus as described
in U.S. Pat. No. 5,332,710, which is incorporated herein by
reference, may advantageously be used in the fixing step.
[0078] The fixing step may be accomplished in one or multiple
steps, referred as a co-fix or a separate fix. In a co-fix, one or
more volumes of a fixing agent solution is applied to the contacted
support material after all the relevant precursor solutions have
been contacted to the support material, whether the contact was
accomplished through the use of one or multiple precursor
solutions. For example, fixing after sequential impregnation with a
palladium precursor solution, a gold precursor solution and a
rhodium precursor solution would be a co-fix, as would fixing after
a co-impregnation with a palladium/rhodium precursor solution
followed by impregnation with a gold precursor solution. An example
of co-fixing may be found in U.S. Pat. No. 5,314,888, which is
incorporated by reference.
[0079] A separate fix, on the other hand, would include applying a
fixing agent solution during or after each impregnation with a
precursor solution. For example, the following protocols would be a
separate fix: a) impregnating palladium followed by fixing followed
by impregnating with gold followed by fixing; or b) co-impregnating
with palladium and rhodium followed by fixing followed by
impregnating with gold followed by fixing. Between a fix and
subsequent impregnation, any excess liquid may be removed and the
support material dried, although this is not necessarily the case.
An example of separate fixing may be found in U.S. Pat. No.
6,034,030, which is incorporated by reference.
[0080] In another embodiment, the fixing step and the contacting
step are conducted simultaneously, one example of which is
described in U.S. Pat. No. 4,048,096, which is incorporated by
reference. For example, a simultaneous fix might be: impregnating
with palladium followed by fixing followed by impregnating with
gold and fixing agent. In a variation on this embodiment, the fix
may be conducted twice for a catalytic component. A catalytic
component may be partially fixed when it is contacted to the
support material (called a "pre-fix"), followed an additional,
final fix. For example: impregnating with palladium followed by
impregnating with gold and a pre-fixing agent followed by fixing
with a final fixing agent. This technique may be used to help
insure the formation of shell type catalyst as opposed to an all
throughout catalyst.
[0081] In another embodiment, particularly suitable for use with
chloride free precursors, the support material is pre-treated with
a fixing agent to adjust the properties of the support material. In
this embodiment, the support material is first impregnated with
either an acid or base solution, typically free of metals. After
drying, the support material is impregnated with a precursor
solution that has the opposite acidity/alkalinity as the dried
support material. The ensuing acid-base reaction forms a shell of
catalytic components on the support material. For example, nitric
acid may be used to pre-treat a support material that in turn is
impregnated with a basic precursor solution such as Pd(OH).sub.2 or
Au(OH).sub.3. This formation technique may be considered as using a
fixing step followed by a contacting step.
[0082] The concentration of fixing agent in the solution is
typically a molar excess of the amount of catalytic components
impregnated on the support material. The amount of fixing agent
should be between about 1.0 to about 2.0, preferably about 1.1 to
about 1.8 times the amount necessary to react with the
catalytically active cations present in the water-soluble salt. In
one embodiment using a high Au/Pd atomic or weight ratio, an
increased molar excess of hydroxide ion enhances the CO.sub.2
selectivity and activity of the resultant catalyst.
[0083] The volume of fixing agent solution supplied generally
should be an amount sufficient to cover the available free surfaces
of the impregnated support material This may be accomplished by
introducing, for example, a volume that is greater than the pore
volume of the contacted support material.
[0084] The combination of impregnating and fixing steps can form a
shell type catalyst. But, the use of halide free precursor
solutions also permits the formation of a shell catalyst while
optionally eliminating the fixing step. In the absence of a
chloride precursor, a washing step, as discussed below, may be
obviated. Further, the process can be free of a step of fixing
catalytic components that would otherwise be needed to survive the
washing step. Because no washing step is needed, the catalytic
components need not be fixed to survive the washing step.
Subsequent steps in the method making the catalyst do not require
the catalytic components be fixed and thus the remainder of the
step maybe carried out without additional preparatory steps.
Overall, the use of chloride free precursors permits a catalyst or
pre-catalyst production method that is free of a step of washing,
thus reducing the number of steps needed to produce the catalyst
and eliminating the need to dispose of chloride containing
waste.
[0085] Washing Step
[0086] Particularly, when halide containing precursor solutions are
utilized and in other applications as desired, after the fixing
step, the fixed support material may be washed to remove any halide
residue on the support or otherwise treated to eliminate the
potential negative effect of a contaminant on the support material.
The washing step included rinsing the fixed support material in
water, preferably deionized water. Washing may be done in a batch
or a continuous mode. Washing at room temperature should continue
until the effluent wash water has a halide ion content of less than
about 1000 ppm, and more preferably until the final effluent gives
a negative result to a silver nitrate test. The washing step may be
carried out after or simultaneously with the reducing step,
discussed below, but preferably is carried out before. As discussed
above, the use of halide free precursor solutions permits the
elimination of the washing step.
[0087] Calcining Step
[0088] After at least one catalytic component has been contacted to
the support material, a calcining step may be employed. The
calcining step typically is before the reducing step and after the
fixing step (if such a step is used) but may take place elsewhere
in the process. In another embodiment, the calcining step is
carried out after the reducing step. The calcining step includes
heating the support material in a non-reducing atmosphere (i.e.
oxidizing or inert). During calcination, the catalytic components
on the support material are at least partially decomposed from
their salts to a mixture of their oxide and free metal form.
[0089] For example, the calcining step is carried out at a
temperature in the range of about 100.degree. C. to about
700.degree. C., preferably between about 200.degree. C. and about
500.degree. C. Non-reducing gases used for the calcination may
included one or more inert or oxidizing gases such as helium,
nitrogen, argon, neon, nitrogen oxides, oxygen, air, carbon
dioxide, combinations thereof or the like. In one embodiment, the
calcining step is carried out in an atmosphere of substantially
pure nitrogen, oxygen, air or combinations thereof. Calcination
times may vary but preferably are between about 1 and 5 hours. The
degree of decomposition of the catalytic component salts depends on
the temperature used and length of time the impregnated catalyst is
calcined and can be followed by monitoring volatile decomposition
products.
[0090] One or more calcining steps may be used, such that at any
point after at least one catalytic component is contacted to the
support material, it may be calcined. Preferably, the last
calcining step occurs before contact of the gold catalytic
component to a zirconia support material. Alternately, calcining of
a zirconia support material containing gold is conducted at
temperatures below about 300.degree. C. By avoiding calcining the
gold containing zirconia support material at temperatures above
about 300.degree. C., the risk that the CO.sub.2 selectivity of the
resultant catalyst will be detrimentally affected is reduced.
[0091] Exemplary protocols including a calcining step include: a)
impregnating with palladium followed by calcining followed by
impregnating with gold; b) co-impregnating palladium and rhodium
followed by calcining followed by impregnating with Au; c)
impregnating with palladium followed by calcining followed by
impregnating with rhodium followed by calcining followed by
impregnating with gold; or d) impregnating with palladium and
rhodium, followed by impregnating with gold, followed by
calcination.
[0092] Reducing Step
[0093] Another step employed generally herein to at least partially
transform any remaining catalytic components from a salt or oxide
form to a catalytically active state, such as by a reducing step.
Typically this is done by exposure of salts or oxides to a reducing
agent, examples of which include ammonia, carbon monoxide,
hydrogen, hydrocarbons, olefins, aldehydes, alcohols, hydrazine,
primary amines, carboxylic acids, carboxylic acid salts, carboxylic
acid esters and combinations thereof. Hydrogen, ethylene,
propylene, alkaline hydrazine and alkaline formaldehyde and
combinations thereof are preferred reducing agents with ethylene
and hydrogen blended with inert gases particularly preferred.
Although reduction employing a gaseous environment is preferred, a
reducing step carried with a liquid environment may also be used
(e.g. employing a reducing solution). The temperature selected for
the reduction can range from ambient up to about 550.degree. C.
Reduction times will typically vary from about 1 to about 5
hours.
[0094] Since the process used to reduce the catalytic components
may influences the characteristics of the final catalyst,
conditions employed for the reduction may be varied depending on
whether high activity, high selectivity or some balance of these
properties is desired.
[0095] In one embodiment, palladium is contacted to the support
material, fixed and reduced before gold is contacted and reduced,
as described in U.S. Pat. Nos. 6,486,093, 6,015,769 and related
patents, all of which are incorporated by reference.
[0096] Exemplary protocols including a reducing step include: a)
impregnating with palladium followed by optionally calcining
followed by impregnating with gold followed by reducing; b)
co-impregnating with palladium and gold followed by optionally
calcining followed by reducing; or c) impregnating with palladium
followed by optionally calcining followed by reducing followed by
impregnating with gold.
[0097] Modifying Step
[0098] Usually after the reducing step and before the catalyst is
used, a modifying step is desirable. While the catalyst may be used
with the modifying step, the step has several beneficial results,
including lengthening the operational life time of the catalyst.
The modifying step is sometimes called an activating step and may
be accomplished in accordance with conventional practice. Namely,
the reduced support material is contacted with a modifying agent,
such as an alkali metal carboxylate and/or alkali metal hydroxide,
prior to use. Conventional alkali metal carboxylates such as the
sodium, potassium, lithium and cesium salts of C.sub.2-4 aliphatic
carboxylic acids are employed for this purpose. A preferred
activating agent in the production of VA is an alkali acetate, with
potassium acetate (KOAc) being the most preferred.
[0099] The support material may optionally be impregnated with a
solution of the modifying agent. After drying, the catalyst may
contain, for example, about 10 to about 70, preferably about 20 to
about 60 grams of modifying agent per liter of catalyst.
[0100] Methods of Making Alkenyl Alkanoates
[0101] The present invention may be utilized to produce alkenyl
alkanoates from an alkene, alkanoic acid and an oxygen containing
gas in the presence of a catalyst. Preferred alkene starting
materials contain from two to four carbon atoms (e.g. ethylene,
propylene and n-butene). Preferred alkanoic acid starting materials
used in the process of this invention for producing alkenyl
alkanoates contain from two to four carbon atoms (e.g., acetic,
propionic and butyric acid). Preferred products of the process are
VA, vinyl propionate, vinyl butyrate, and allyl acetate. The most
preferred starting materials are ethylene and acetic acid with the
VA being the most preferred product. Thus, the present invention is
useful in the production of olefinically unsaturated carboxylic
esters from an olefinically unsaturated compound, a carboxylic acid
and oxygen in the presence of a catalyst. Although the rest of the
specification discusses VA exclusively, it should be understood
that the catalysts, method of making the catalysts and production
methods are equally applicable to other alkenyl alkanoates, and the
description is not intended as limiting the application of the
invention to VA.
[0102] When VA is produced using the catalyst of the present
invention, a stream of gas, which contains ethylene, oxygen or air,
and acetic acid is passed over the catalyst. The composition of the
gas stream can be varied within wide limits, taking in account the
zone of flammability of the effluent. For example, the molar ratio
of ethylene to oxygen can be about 80:20 to about 98:2, the molar
ratio of acetic acid to ethylene can be about 100:1 to about 1:100,
preferably about 10:1 to 1:10, and most preferably about 1:1 to
about 1:8. The gas stream may also contain gaseous alkali metal
acetate and/or inert gases, such as nitrogen, carbon dioxide and/or
saturated hydrocarbons. Reaction temperatures which can be used are
elevated temperatures, preferably those in the range of about
125-220.degree. C. The pressure employed can be a somewhat reduced
pressure, normal pressure or elevated pressure, preferably a
pressure of up to about 20 atmospheres gauge.
[0103] In addition to fixed bed reactors, the methods of producing
alkenyl alkanoates and the catalyst of the present invention may
also be suitably employed in other types of reaction, for example,
fluidized bed reactors.
EXAMPLES
[0104] The following examples are provided for illustration only
and not intended to be limiting. The amounts solvents and reactants
are approximate. The Au/Pd atomic ratio may be converted to the
Au/Pd weight ratio and vice versa by the following equations: Au/Pd
atomic ratio=0.54*(Au/Pd weight ratio) and Au/Pd weight
ratio=1.85(Au/Pd atomic ratio. Reduction may be abbreviated `R`
followed by the temperature in .degree. C. at which the reduction
was carried out. Likewise, calcination may be abbreviated `C`
followed by the temperature in .degree. C. at which the calcination
was carried out, whereas a drying step may be abbreviated as
`dry`.
[0105] The catalyst of examples 1-11 may be prepared as described
in the example and tested according to the following procedure,
where catalyst from Examples 1-7 may be compared to each other and
catalyst from 8-11 may be compared to each other. Results are
provided where available.
[0106] The catalysts of the examples were tested for their activity
and selectivity to various by-products in the production of vinyl
acetate by reaction of ethylene, oxygen and acetic acid. To
accomplish this, about 60 ml of the catalyst prepared as described
were placed in a stainless steel basket with the temperature
capable of being measured by a thermocouple at both the top and
bottom of the basket. The basket was placed in a Berty continuously
stirred tank reactor of the recirculating type and was maintained
at a temperature which provided about 45% oxygen conversion with an
electric heating mantle. A gas mixture of about 50 normal liters
(measured at N.T.P.) of ethylene, about 10 normal liters of oxygen,
about 49 normal liters of nitrogen, about 50 g of acetic acid, and
about 4 mg of potassium acetate, was caused to travel under
pressure at about 12 atmospheres through the basket, and the
catalyst was aged under these reaction conditions for at least 16
hours prior to a two hour run, after which the reaction was
terminated. Analysis of the products was accomplished by on-line
gas chromatographic analysis combined with off-line liquid product
analysis by condensing the product stream at about 10.degree. C. to
obtain optimum analysis of the end products carbon dioxide
(CO.sub.2), heavy ends (HE) and ethyl acetate (EtOAc), the results
of which may be used to calculate the percent selectivities
(CO.sub.2 Selectivity) of these materials for each example. The
relative activity of the reaction expressed as an activity factor
(Activity) may be computer calculated using a series of equations
that correlates the activity factor with the catalyst temperature
(during the reaction), oxygen conversion, and a series of kinetic
parameters for the reactions that take place during VA synthesis.
More generally, the activity factor typically is inversely related
to the temperature required to achieve constant oxygen
conversion.
[0107] Rhodium Catalyst Examples
Example 1
[0108] A support material containing palladium and rhodium metal
was prepared as follows: The support material in an amount of 250
ml consisting of Sud Chemie KA-160 silica spheres having a nominal
diameter of 7 mm., a density of about 0.569 g/ml, in absorptivity
of about 0.568 g H.sub.2O/g support, a surface area of about 160 to
175 m.sup.2/g, and a pore volume of about 0.68 ml/g., was first
impregnated by incipient wetness with 82.5 ml of an aqueous
solution of sodium tetrachloropalladium (II) (Na.sub.2PdCl.sub.4)
and rhodium chloride trihydrite (RhCl.sub.3.3H.sub.2O) sufficient
to provide about 7 grams of elemental palladium and about 0.29
grams of elemental rhodium per liter of catalyst. The support was
shaken in the solution for 5 minutes to ensure complete absorption
of the solution. The palladium and rhodium were then fixed to the
support as palladium (II) and rhodium (III) hydroxides by
contacting the treated support by roto-immersion for 2.5 hours at
approximately 5 rpm with 283 ml of an aqueous sodium hydroxide
solution prepared from 50% w/w NaOH/H.sub.2O in an amount of 120%
of that needed to convert the palladium and rhodium to their
hydroxides. The solution was drained from the treated support and
the support was then rinsed with deionized water and dried at
100.degree. C. in a fluid bed drier for 1.2 hours. The support
material containing palladium and rhodium hydroxides was then
impregnated with an aqueous solution (81 ml) containing 1.24 g Au
from NaAuCl.sub.4 and 2.71 g 50% NaOH solution (1.8 equivalents
with respect to Au) using the incipient wetness method. The NaOH
treated pills were allowed to stand overnight to ensure
precipitation of the Au salt to the insoluble hydroxide. The pills
were thoroughly washed with deionized water (.about.5 hours) to
remove chloride ions and subsequently dried at 100.degree. C. in a
fluid bed drier for 1.2 hours. The palladium, rhodium, and gold
containing support was then calcined at 400.degree. C. for 2 hours
under air and then allowed to naturally cool to room temperature.
The palladium, rhodium, and gold were reduced by contacting the
support with C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at
150.degree. C. for 5 hours. Finally the catalyst was impregnated by
incipient wetness with an aqueous solution of 10 g of potassium
acetate in 81 ml H.sub.2O and dried in a fluid bed drier at
100.degree. C. for 1.2 hours.
Example 2
[0109] A support material utilizing palladium and rhodium
hydroxides was prepared as described in Example 1. The palladium
and rhodium containing support was then calcined at 400.degree. C.
for 2 hours under air and then allowed to naturally cool to room
temperature. The calcined support material containing palladium and
rhodium hydroxides was then impregnated with an aqueous solution
(81 ml) containing 1.24 g Au from NaAuCl.sub.4 and 2.71 g 50% NaOH
solution (1.8 equivalents with respect to Au) using the incipient
wetness method. The NaOH treated pills were allowed to stand
overnight to ensure precipitation of the Au salt to the insoluble
hydroxide. The pills were thoroughly washed with deionized water
(.about.5 hours) to remove chloride ions and subsequently dried at
100.degree. C. in a fluid bed drier for 1.2 hours. The palladium,
rhodium, and gold were then reduced by contacting the support with
C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at 150.degree.
C. for 5 hours. Finally the catalyst was impregnated by incipient
wetness with an aqueous solution of 10 g of potassium acetate in 81
ml H.sub.2O and dried in a fluid bed drier at 100.degree. C. for
1.2 hours.
Example 3
[0110] A support material containing palladium and rhodium
hydroxides was prepared as described in Example 1. The palladium
and rhodium containing support was then calcined at 400.degree. C.
for 2 hours under air and then allowed to naturally cool to room
temperature. The calcined support material containing palladium and
rhodium hydroxides was then reduced by contacting the support with
C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at 150.degree.
C. for 5 hours. The support containing palladium and rhodium metal
was subsequently impregnated with an aqueous solution (81 ml)
containing 1.24 g Au from NaAuCl.sub.4 and 2.71 g 50% NaOH solution
(1.8 equivalents with respect to Au) using the incipient wetness
method. The NaOH treated pills were allowed to stand overnight to
ensure precipitation of the Au salt to the insoluble hydroxide. The
pills were thoroughly washed with deionized water (.about.5 hours)
to remove chloride ions and subsequently dried at 100.degree. C. in
a fluid bed drier for 1.2 hours. The palladium, rhodium, and gold
were then reduced by contacting the support with C.sub.2H.sub.4 (1%
in nitrogen) in the vapor phase at 150.degree. C. for 5 hours.
Finally the catalyst was impregnated by incipient wetness with an
aqueous solution of 10 g of potassium acetate in 81 ml H.sub.2O and
dried in a fluid bed drier at 100.degree. C. for 1.2 hours.
Example 4
[0111] A support material containing palladium and rhodium
hydroxides was prepared as described in Example 1. The palladium
and rhodium containing support was then calcined at 400.degree. C.
for 2 hours under air and then allowed to naturally cool to room
temperature. The calcined support material containing palladium and
rhodium hydroxides was then reduced by contacting the support with
C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at 150.degree.
C. for 5 hours. The support containing palladium and rhodium metal
was subsequently impregnated with an aqueous solution (81 ml)
containing 1.1 g Au from KAuO.sub.2 using the incipient wetness
method. The pills were subsequently dried at 100.degree. C. in a
fluid bed drier for 1.2 hours. The palladium, rhodium, and gold
were then reduced by contacting the support with C.sub.2H.sub.4 (1%
in nitrogen) in the vapor phase at 150.degree. C. for 5 hours.
Finally the catalyst was impregnated by incipient wetness with an
aqueous solution of 10 g of potassium acetate in 81 ml H.sub.2O and
dried in a fluid bed drier at 100.degree. C. for 1.2 hours.
Example 5
[0112] A support material containing palladium and rhodium
hydroxides was prepared as described in Example 1. The palladium
and rhodium containing support was then calcined at 400.degree. C.
for 2 hours under air and then allowed to naturally cool to room
temperature. The calcined support containing palladium and rhodium
hydroxides was subsequently impregnated with an aqueous solution
(81 ml) containing 1.1 g Au from KAuO.sub.2 using the incipient
wetness method. The pills were then dried at 100.degree. C. in a
fluid bed drier for 1.2 hours. The palladium, rhodium, and gold
were then reduced by contacting the support with C.sub.2H.sub.4 (1%
in nitrogen) in the vapor phase at 150.degree. C. for 5 hours.
Finally the catalyst was impregnated by incipient wetness with an
aqueous solution of 10 g of potassium acetate in 81 ml H.sub.2O and
dried in a fluid bed drier at 100.degree. C. for 1.2 hours.
Example 6
[0113] A support material containing palladium and rhodium
hydroxides was prepared as described in Example 1. The palladium
and rhodium containing support was then calcined at 400.degree. C.
for 2 hours under air and then allowed to naturally cool to room
temperature. The calcined support material containing palladium and
rhodium hydroxides was then reduced by contacting the support with
C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at 150.degree.
C. for 5 hours. The support containing palladium and rhodium metal
was subsequently impregnated with an aqueous solution (81 ml)
containing 1.1 g Au from KAuO.sub.2 and 10 g potassium acetate
using the incipient wetness method. The pills were subsequently
dried at 100.degree. C. in a fluid bed drier for 1.2 hours.
Example 7
Reference Catalyst
[0114] A support material containing palladium metal was prepared
as follows: The support material in an amount of 250 ml consisting
of Sud Chemie KA-160 silica spheres having a nominal diameter of 7
mm., a density of about 0.569 g/ml, in absorptivity of about 0.568
g H.sub.2O/g support, a surface area of about 160 to 175 m.sup.2/g,
and a pore volume of about 0.68 ml/g., was first impregnated by
incipient wetness with 82.5 ml of an aqueous solution of sodium
tetrachloropalladium (II) (Na.sub.2PdCl.sub.4) sufficient to
provide about 7 grams of elemental palladium per liter of catalyst.
The support was shaken in the solution for 5 minutes to ensure
complete absorption of the solution. The palladium was then fixed
to the support as palladium (II) hydroxides by contacting the
treated support by roto-immersion for 2.5 hours at approximately 5
rpm with 283 ml of an aqueous sodium hydroxide solution prepared
from 50% w/w NaOH/H.sub.2O in an amount of 110% of that needed to
convert the palladium to its hydroxide. The solution was drained
from the treated support and the support was then rinsed with
deionized water and dried at 100.degree. C. in a fluid bed drier
for 1.2 hours. The support material containing palladium hydroxide
was then impregnated with an aqueous solution (81 ml) containing
1.24 g Au from NaAuCl.sub.4 and 2.71 g 50% NaOH solution (1.8
equivalents with respect to Au) using the incipient wetness method.
The NaOH treated pills were allowed to stand overnight to ensure
precipitation of the Au salt to the insoluble hydroxide. The pills
were thoroughly washed with deionized water (.about.5 hours) to
remove chloride ions and subsequently dried at 100.degree. C. in a
fluid bed drier for 1.2 hours. The palladium and gold containing
support was then reduced by contacting the support with
C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at 150.degree.
C. for 5 hours. Finally the catalyst was impregnated by incipient
wetness with an aqueous solution of 10 g of potassium acetate in 81
ml H.sub.2O and dried in a fluid bed drier at 100.degree. C. for
1.2 hours. Table 1 shows comparison CO.sub.2 selectivity and
activity for the catalyst of Examples 1 and 7.
1 TABLE 1 CO.sub.2 Selectivity Activity Example 1 9.89 2.32 Example
7 (Reference Catalyst) 11.13 2.36
[0115] Layered Support Examples
Example 8
[0116] 40 g of ZrO.sub.2 (RC-100, supplied by DKK) was calcined at
650.degree. C. for 3 h. Resulting material has a BET surface area
38 m.sup.2/g. The material was ball milled with 120 ml of DI water
for 6 h. The sol was mixed with 22.5 g of the binder zirconium
acetate supplied by DKK (ZA-20) and sprayed onto 55 g of spheres of
bentonite KA-160 with OD.about.7.5 mm. Coated beads were calcined
for 3 h at 600.degree. C. Examination under microscope has shown
uniform shell formation with thickness of 250 .mu.m.
Example 9
[0117] 20 g of ZrO.sub.2 (XZ16075, BET surface area 55 m.sup.2/g)
were impregnated with Pd(NO.sub.3).sub.2 solution (Aldrich) to give
Pd loading of 39 mg/g of ZrO2. Impregnated material was dried and
calcined at 450.degree. C. for 4 h. The material was ball milled
with 60 ml of DI water for 4 h, mixed with 11 g of a binder (ZA-20)
and sprayed onto 30 g of bentonite KA-160 spheres. The beads were
calcined at 450.degree. C. for 3 h. This procedure results in
formation of a strong uniform shell with 160 .mu.m thickness.
Example 10
[0118] The beads from Example 8 were impregnated with solution of
potassium acetate to give loading of 40 mg KOAc/ml of KA-160, dried
and calcined at 300.degree. C. for 4 h. After that the solution,
containing 9.4 mM of Pd(from Pd(NH.sub.3).sub.4(OH).sub.2 supplied
by Heraeus) and 4.7 mM of Au (from a 1 M solution, Au(OH).sub.3
"Alfa" dissolved in 1.6 M KOH) was sprayed onto these beads.
Material was reduced with the mixture: 5% H.sub.2, 95% N.sub.2 at
200.degree. C. for 4 h. The beads were crushed and tested in fix
bed micro reactor under conditions described in the experimental
section. CO.sub.2 selectivity of 6% at 45% oxygen conversion was
achieved.
Example 11
Reference Catalyst
[0119] The same catalyst prepared in Example 7 was used as a
reference catalyst here. Table 2 shows comparison CO.sub.2
selectivity and activity for the catalyst of Examples 9-11.
2 TABLE 2 CO.sub.2 Selectivity Activity Example 9 9.33 2.08 Example
10 9.03 1.69 Example 11 (Reference Catalyst) 11.13 2.36
[0120] Zirconia Support Material and Chloride Free Precursor
Examples
[0121] The following general procedure was used for this set of
examples. Zirconia support material catalysts were made as follows:
various shaped catalyst carriers were crushed and sieved. Zirconia
support materials were supplied by N or Pro (XZ16052 and XZ16075),
DKK and MEI. Silica support materials were supplied by Degussa and
Sud Chemie. The sieve fraction of 180-425 um was impregnated
(either simultaneously or sequentially with an intermediate drying
step at 110.degree. C. and optionally with an intermediate
calcination step) to incipient wetness with a Pd and Au precursor
solution, optionally calcined in air, reduced with 5%
H.sub.2/N.sub.2 formation gas, post-impregnated with KOAc solution,
dried at 100.degree. C. under N.sub.2, and screened in a 8.times.6
multi channel fixed bed reactor. A solution of Au(OH).sub.3 in KOH
was used as the Au precursor. Aqueous solutions of
Pd(NH.sub.3).sub.4(OH).sub.2, Pd(NH.sub.3).sub.2(NO.sub.2).sub.2,
Pd(NH.sub.3).sub.4(NO.sub.3).sub.2 and Pd(NO.sub.3).sub.2 were used
as the Pd precursors.
[0122] A silica support material catalyst reference was made as
follows: A support material containing palladium and rhodium metal
was prepared as follows: The support material in an amount of 250
ml consisting of Sud Chemie KA-160 silica spheres having a nominal
diameter of 7 mm, a density of about 0.569 g/ml, an absorptivity of
about 0.568 g H.sub.2O/g support, a surface area of about 160 to
175 m.sup.2/g, and a pore volume of about 0.68 ml/g., was first
impregnated by incipient wetness with 82.5 ml of an aqueous
solution of sodium tetrachloropalladium (II) (Na.sub.2PdCl.sub.4)
sufficient to provide about 7 grams of elemental palladium per
liter of catalyst. The support was shaken in the solution for 5
minutes to ensure complete absorption of the solution. The
palladium was then fixed to the support as palladium(II) hydroxides
by contacting the treated support by roto-immersion for 2.5 hours
at approximately 5 rpm with 283 ml of an aqueous sodium hydroxide
solution prepared from 50% w/w NaOH/H.sub.2O in an amount of 110%
of that needed to convert the palladium to its hydroxide. The
solution was drained from the treated support and the support was
then rinsed with deionized water and dried at 100.degree. C. in a
fluid bed drier for 1.2 hours. The support material containing
palladium hydroxide was then impregnated with an aqueous solution
(81 ml) containing 1.24 g Au from NaAuCl.sub.4 and 2.71 g 50% NaOH
solution (1.8 equivalents with respect to Au) using the incipient
wetness method. The NaOH treated pills were allowed to stand
overnight to ensure precipitation of the Au salt to the insoluble
hydroxide. The pills were thoroughly washed with deionized water
(.about.5 hours) to remove chloride ions and subsequently dried at
100.degree. C. in a fluid bed drier for 1.2 hours. The palladium
and gold containing support was then reduced by contacting the
support with C.sub.2H.sub.4 (1% in nitrogen) in the vapor phase at
150.degree. C. for 5 hours. Finally the catalyst was impregnated by
incipient wetness with an aqueous solution of 10 g of potassium
acetate in 81 ml H.sub.2O and dried in a fluid bed drier at
100.degree. C. for 1.2 hours. Before testing, the catalyst was
crushed and sieved. The sieved fraction in the size range of
180-425 um was used.
[0123] Catalyst libraries of arrays of 8 rows.times.6 columns in
glass vials were designed and a rack of 36 glass vials was mounted
on a vortexer and agitated while dispensing metal precursor
solutions using Cavro.TM. liquid dispensing robots. 0.4 ml of
support was used for each library element, for the glass vial
synthesis as well as loaded to each reactor vessel.
[0124] KOAc loading is reported as grams KOAc per liter catalyst
volume or as .mu.mol KOAc on 0.4 ml support. For the specification
of Au loading, the relative atomic ratio of Au to Pd is reported as
Au/Pd. Pd loading is specified as mg Pd per 0.4 ml support volume
(i.e. absolute amount of Pd in reactor vessel).
[0125] The screening protocol used a temperature ramp from
145.degree. C. to 165.degree. C. in 5.degree. C. increments, at a
fixed space velocity of 175% (with 1.5 mg Pd on 0.4 ml support).
100% space velocity is defined as the following flows: 5.75 sccm of
Nitrogen, 0.94 sccm of Oxygen, 5.94 sccm of Ethylene, and 5.38
microliters per minute of Acetic Acid through each of the 48
catalyst vessels (all of which had an inner diameter of
approximately 4 mm). CO.sub.2 selectivity was plotted versus oxygen
conversion, a linear fit performed, and the calculated
(interpolated in most cases) CO.sub.2 selectivity at 45% oxygen
conversion reported in the performance summary tables below. The
temperature at 45% oxygen conversion calculated from the T ramp
(linear fits of CO.sub.2 selectivity and oxygen conversion versus
reaction temperature is also reported). The lower this calculated
temperature the higher the activity of the catalyst. The space time
yield (STY; g VA produced per ml catalyst volume per h) at 45%
oxygen conversion is a measure of the productivity of the
catalyst.
Example 12
[0126] 400 ul of ZrO.sub.2 carriers XZ16075 (55 m.sup.2/g as
supplied) and XZ16052 (precalcined at 650.degree. C./2 h to lower
the surface area to 42 m.sup.2/g) were impregnated with 3 different
Pd solutions to incipient wetness, dried at 110.degree. C. for 5 h,
impregnated with KAuO.sub.2 (0.97M Au stock solution) to incipient
wetness, dried at 110.degree. C. for 5 h, reduced at 350.degree. C.
for 4 h in 5% H.sub.2/N.sub.2 formation gas, post-impregnated with
KOAc and dried at 110.degree. C. for 5 h. The Pd/Au/ZrO.sub.2
samples (shells) were then diluted 1/9.3 with KA160 diluter
(preloaded with 40 g/l KOAc), i.e. 43 ul Pd/Au/ZrO.sub.2 shell and
357 ul diluter (400 ul total fixed bed volume) were charged to the
reactor vessels. The Pd loading was 14 mg Pd in 400 ul ZrO.sub.2
shell (or 14*43/400=14/9.3=1.5 mg Pd in reactor vessel for all
library elements. The Pd precursors were
Pd(NH.sub.3).sub.2(NO.sub.2).sub.2 in columns 1 and 4,
Pd(NH.sub.3).sub.4(OH).sub.2 in columns 2 and 5,
Pd(NH.sub.3).sub.4(NO.sub.3).sub.2 in columns 3 and 6. Au/Pd=0.3 in
row 2 and row 5, Au/Pd=0.6 in row 3, Au/Pd=0.9 in row 4, row 6 and
row 7. The KOAc loading was 114 mmol in rows 2, 3, 5 and 147 mmol
in rows 4, 6, 7. The silica reference catalyst was loaded into Row
1. The library was screened using the T ramp screening protocol at
fixed SV. Screening results are summarized in Table 3
3 TABLE 3 CO.sub.2 Selectivity Temp at STY Cl Precursors on
SiO.sub.2 7.37 156.6 729 Pd(NH.sub.4).sub.2(OH).sub.2 on ZrO.sub.2
5.79 152.4 787 Pd(NH.sub.3).sub.4(NO.sub.3).sub.2 on ZrO.sub.2 5.90
152.3 783 Pd(NH.sub.3).sub.2(NO.sub.2).sub.2 on ZrO.sub.2 5.57
150.7 795 *Data shown is taken from average of two Au/Pd atomic
ratios(namely 0.3 and 0.6) and two different ZrO.sub.2
supports.
Example 13
[0127] 400 ul of ZrO.sub.2 carriers XZ16075 (55 m.sup.2/g as
supplied) and XZ16052 (precalcined at 650.degree. C./2 h to lower
the surface area to 42 m.sup.2/g) were impregnated with
Pd(NH.sub.3).sub.4(OH).sub.2 (1.117M Pd stock solution) to
incipient wetness, calcined at 350.degree. C. for 4 h in air,
impregnated with KAuO.sub.2 (0.97M Au stock solution) to incipient
wetness, dried at 110.degree. C. for 5 h, reduced at 350.degree. C.
for 4 h in 5% H.sub.2/N.sub.2 formation gas, post-impregnated with
KOAc and dried at 110.degree. C. for 5 h. The Pd/Au/ZrO.sub.2
samples (shells) were then diluted 1/12 with KA160 diluter
(preloaded with 40 g/l KOAc), i.e. 33.3 ul Pd/Au/ZrO.sub.2 catalyst
and 366.7 ul diluter (400 ul total fixed bed volume) were charged
to the reactor vessels. The library design and library element
compositions were as follows: ZrO.sub.2 XZ16075 in columns 1-3
(left half of library) and ZrO.sub.2 XZ16052 (650.degree. C.) in
columns 4-6 (right half of library). The Pd loading was 18 mg Pd in
400 ul ZrO.sub.2 shell (or 18*33/400=18/12 mg Pd in reactor vessel)
in cell G2, column 3 (cells B3-G3), cell G5, column 6 (cells
B6-G6); 10 mg Pd in 400 ul ZrO.sub.2 shell (or 10*33/400=10/12 mg
Pd in reactor vessel) in column 1 (cells A1-G1) and column 4 (cells
A4-G4); 14 mg Pd in 400 ul ZrO.sub.2 shell (or 14*33/400=14/12 mg
Pd in reactor vessel) in column 2 (cells B2-F2) and column 5 (cells
B5-F5). Au/Pd=0.3 in row 2 and row 5, Au/Pd=0.5 in row 3 and row 6,
Au/Pd=0.7 in row 4 and row 7 (except cells A1, A4, G2, G5 where
Au/Pd was 0.3). The KOAc loading was 114 mmol (except cells D3, G3,
D6, G6 where KOAc loading was 147 mmol). The silica reference
catalyst was loaded into Row 1. The library was screened using the
T ramp screening protocol at fixed SV. Screening results are
summarized in Table 4.
4 TABLE 4 CO.sub.2 Selectivity Temp at 45% Conv STY Au/Pd Atomic
Ratio 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 Cl Precursors on
SiO.sub.2 6.98 -- -- 154.8 -- -- 742.8 -- -- ZrO.sub.2: XZ16052
6.06 5.31 5.38 153.7 152.3 154.9 776.8 806.0 803.0 ZrO.sub.2:
XZ16075 6.18 5.62 5.71 147.5 151.0 154.4 773.8 791.6 790.3
Example 14
[0128] ZrO2 carrier (supplied by N or Pro, XZ16075, sieve fraction
180-425 um, density 1.15 g/ml, pore volume 475 ul/g, BET surface
area 55 m2/g) was impregnated with Pd(NO3)2 precursor solution to
incipient wetness, dried at 110.degree. C., calcined at 250.degree.
C. (columns 1-2), 350.degree. C. (columns 3-4), 450.degree. C.
(columns 5-6) in air, impregnated with KAuO.sub.2 solution
(prepared by dissolution of Au(OH).sub.3 in KOH), dried at
110.degree. C., reduced with 5% H.sub.2/N.sub.2 formation gas at
350.degree. C. for 4 h, and post-impregnated with KOAc solution.
The library has a KOAc gradient from 25 to 50 g/l in row 2 to row
7. The Pd loading amounts to 1.5 mg Pd on 0.4 ml support. Two
different Au loadings were chosen (Au/Pd=0.5 in columns 1, 3, 5 and
Au/Pd=0.7 in columns 2, 4, 6). The silica reference catalyst was
loaded in row 1. The library was screened using the T ramp
screening protocol in MCFB48 VA reactor at fixed SV. Screening
results are summarized in Table 5.
5 TABLE 5 CO.sub.2 Selectivity Temp at 45% Conv STY Cl Precursors
on SiO.sub.2 7.21 154.7 734 Pd(NO3)2 on ZrO2 6.10 145.3 775 *Data
shown is taken from average of two Au/Pd atomic ratios (namely 0.5
and 0.7) at 40 g/L KOAc, calcination at 450.degree. C., and
reduction at 350.degree. C.
Example 15
[0129] ZrO.sub.2 carrier (supplied by N or Pro, XZ16075, sieve
fraction 180-425 um, density 1.15 g/ml, pore volume 575 ul/g, BET
surface area 55 m2/g) was impregnated with Pd(NO3)2 precursor
solution to incipient wetness, dried at 110.degree. C., calcined at
450.degree. C. in air, impregnated with KAuO.sub.2 solution
(prepared by dissolution of Au(OH).sub.3 in KOH), dried at
110.degree. C., reduced with 5% H.sub.2/N.sub.2 formation gas at
200.degree. C. (columns 1-2), 300.degree. C. (columns 3-4), or
400.degree. C. (columns 5-6), and post-impregnated with KOAc
solution. The library has a KOAc gradient from 15 to 40 g/l in row
2 to row 7. The Pd loading amounts to 1.5 mg Pd on 0.4 ml support.
Two different Au loadings were chosen (Au/Pd=0.5 in columns 1, 3, 5
and Au/Pd=0.7 in columns 2, 4, 6). The silica reference catalyst
was loaded in row 1. The library was screened in MCFB48 VA reactor
using the T ramp screening protocol at fixed SV. Screening results
are summarized in Table 6.
6TABLE 6 CO.sub.2 Selectivity Temp at 45% Conv STY Cl Precursors on
SiO.sub.2 7.11 154.2 738 Pd(NO3)2 on ZrO2 5.51 145.4 797 *Data
shown is taken from average of two Au/Pd atomic ratios (namely 0.5
and 0.7) at 40 g/L KOAc, calcination at 450.degree. C., and
reduction at 400.degree. C.
[0130] It will be further appreciated that functions or structures
of a plurality of components or steps may be combined into a single
component or step, or the functions or structures of one step or
component may be split among plural steps or components. The
present invention contemplates all of these combinations. Unless
stated otherwise, dimensions and geometries of the various
structures depicted herein are not intended to be restrictive of
the invention, and other dimensions or geometries are possible.
Plural structural components or steps can be provided by a single
integrated structure or step. Alternatively, a single integrated
structure or step might be divided into separate plural components
or steps. In addition, while a feature of the present invention may
have been described in the context of only one of the illustrated
embodiments, such feature may be combined with one or more other
features of other embodiments, for any given application. It will
also be appreciated from the above that the fabrication of the
unique structures herein and the operation thereof also constitute
methods in accordance with the present invention.
[0131] The explanations and illustrations presented herein are
intended to acquaint others skilled in the art with the invention,
its principles, and its practical application. Those skilled in the
art may adapt and apply the invention in its numerous forms, as may
be best suited to the requirements of a particular use.
Accordingly, the specific embodiments of the present invention as
set forth are not intended as being exhaustive or limiting of the
invention. The scope of the invention should, therefore, be
determined not with reference to the above description, but should
instead be determined with reference to the appended claims, along
with the full scope of equivalents to which such claims are
entitled. The disclosures of all articles and references, including
patent applications and publications, are incorporated by reference
for all purposes.
* * * * *