U.S. patent application number 10/559139 was filed with the patent office on 2006-12-07 for supported catalyst for producing h2 and/or co from low molecular weight hydrocarbons.
Invention is credited to Daniel Gary.
Application Number | 20060275194 10/559139 |
Document ID | / |
Family ID | 33155198 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060275194 |
Kind Code |
A1 |
Gary; Daniel |
December 7, 2006 |
Supported catalyst for producing h2 and/or co from low molecular
weight hydrocarbons
Abstract
Chemical combination (C) between an active solid phase which is
covalently bound to the surface of an inert solid phase,
caracterized in that said solid active phase essentially consists
in a solid solution of a mixture of at least a magnesium oxide type
phase compound and at least a magnesium silicate type phase
compound in which Al, and Rh and/or Ni cations are soluted and
caracterized in that said inert solid phase is either a compound
represented by the general formula (I):
Al.sub.aNi.sub.bRh.sub.cMg.sub.dSi.sub.eO.sub.f (I) wherein a, b,
c, d, and e are integers which are greater than or equal to 0, f is
an integer greater than 0, the sum a+b+c+d.noteq.0, and wherein
(3a+2b+3c+2d+4e)/2=f, or a mixture of compounds represented by the
said general formula (I), provided that at least one of the Si, Al,
Mg, Rh or Ni elements, which is present in the solid active phase,
is also present in the solid inert phase. Use of a catalyst in
chemical reactions involving the conversion hydrocarbonaceous
feedstocks.
Inventors: |
Gary; Daniel;
(2,ALLEED,Anjou, IT) |
Correspondence
Address: |
AIR LIQUIDE
2700 POST OAK BOULEVARD, SUITE 1800
HOUSTON
TX
77056
US
|
Family ID: |
33155198 |
Appl. No.: |
10/559139 |
Filed: |
June 4, 2004 |
PCT Filed: |
June 4, 2004 |
PCT NO: |
PCT/IB04/01821 |
371 Date: |
June 17, 2006 |
Current U.S.
Class: |
423/417 |
Current CPC
Class: |
B01J 23/892 20130101;
B01J 2523/00 20130101; B01J 23/002 20130101; B01J 2523/00 20130101;
C01B 2203/0261 20130101; C01B 2203/0238 20130101; B01J 23/005
20130101; C01B 2203/1052 20130101; C01B 2203/0233 20130101; B01J
2523/00 20130101; C01B 3/386 20130101; C01B 3/40 20130101; C01B
2203/1064 20130101; C01B 2203/1023 20130101; Y02P 20/52 20151101;
B01J 2523/31 20130101; B01J 2523/847 20130101; B01J 2523/22
20130101; B01J 2523/22 20130101; B01J 2523/822 20130101; B01J
2523/22 20130101; B01J 2523/31 20130101; B01J 2523/31 20130101;
B01J 2523/822 20130101; B01J 2523/847 20130101; C01B 2203/1011
20130101; B01J 2523/00 20130101; C01P 2002/72 20130101; B01J 37/08
20130101 |
Class at
Publication: |
423/417 |
International
Class: |
C01G 1/04 20060101
C01G001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2003 |
EP |
03076781.8 |
Claims
1-18. (canceled)
19. A chemical combination (C) between an active solid phase which
is covalently bound to the surface of an inert solid phase,
characterized in that said solid active phase essentially consists
in a solid solution of a mixture of at least a magnesium oxide type
phase compound and at least a magnesium silicate type phase
compound in which Al, and Rh and/or Ni cations are soluted and
characterized in that said inert solid phase is either a compound
represented by the general formula (I):
Al.sub.aNi.sub.bRh.sub.cMg.sub.dSi.sub.eO.sub.f (I) wherein a, b,
c, d, and e are integers which are greater than or equal to 0, f is
an integer greater than 0, the sum a+b+c+d.noteq.0, and wherein
(3a+2b+3c+2d+4e)/2=f, or a mixture of compounds represented by the
said general formula (I), provided that at least one of the Si, Al,
Mg, Rh or Ni elements, which is present in the solid active phase,
is also present in the solid inert phase.
20. The chemical combination according to claim 19, wherein the
amount of active phase on the inert support is in the range from 1%
to 90% weight by weight and preferably between 5% and 60% weight by
weight of the total combination.
21. The chemical combination according to claim 19, wherein the
inert phase is in a form of beads, pellets, disks or monoliths.
22. The chemical combination according to claim 19, wherein the
inert phase is chosen among the compounds represented by the
general formula (I) as defined above, wherein: either a=2,
b=c=d=e=0 and f=3, either a=2,b=c=0, d=1, e=3 and f=10, either e=1
and a=b=c=d=0, f=2 either a=b=c=0, d=2, e=1 and f=4, or a=2,
b=c=d=0, e=2 and f=7, and a mixture thereof.
23. Process for the preparation of the chemical combination (C)
according to claim 19, characterized in that it comprises the
successive following steps: Step (a): An hydrotalcite-type
precursor of the formula (II):
[[Mg.sub.1-aAl.sub.a(OH).sub.2].sup.z+(CO.sub.3.sup.2-.sub.z/2),mH.sub.2O-
] (II), wherein 0<a<1 and z is the total electrical charge of
the cationic element, is calcined to form a mixed oxyde of the
formula (III): [(2-2a)MgO,aAl.sub.2O.sub.3] (III); Step (b): The
mixed oxyde of the formula (III), is mixed with water and put to
react at alkaline pH, with SiO.sub.2.NaOH solution, together with a
Rh.sup.+++ salt, a Ni.sup.++ salt or a mixture of both salts, to
form a chemical combination (C'), between an active solid phase
which is covalently bound to the surface of an inert solid phase,
characterized in that said solid active phase essentially consists
an hydrotalcite active solid phase of the formula (IV):
[Rh.sub.xNi.sub.yMg.sub.pAl.sub.m(OH).sub.2].sup.2+(A.sup.n-.sub.-
z/n)kH.sub.2O, (IV) wherein A.sup.n- is mainly a silicate or a
polysilicate anion; 0.ltoreq.x.ltoreq.0.3, preferably
0.ltoreq.x.ltoreq.0.1; 0.ltoreq.y.ltoreq.0.9, preferably
0.ltoreq.y.ltoreq.0.3; 0.ltoreq.p.ltoreq.0.9, preferably
0.3.ltoreq.p.ltoreq.0.8; 0.ltoreq.m.ltoreq.0.5, preferably
0.1.ltoreq.m.ltoreq.0.4; 0.ltoreq.k.ltoreq.10, preferably
0.ltoreq.k.ltoreq.5; x+y>0; 0.5.ltoreq.y+p.ltoreq.0.9,
preferably 0.6.ltoreq.y+p.ltoreq.0.8; x+y+p+m=1; and z is the total
electrical charge of the cationic element, and characterized in
that said inert solid phase is an hydrotalcite inert solid phase of
the formula (V):
[[Mg.sub.2-2a-pAl.sub.2a-m(OH).sub.2].sup.z'+(A.sup.n'-.sub.z'/n'),k'H.su-
b.2O] (V), wherein A.sup.n'- is mainly a silicate or a polysilicate
anion; 0.ltoreq.2-2a-p.ltoreq.0.9, preferably
0.3.ltoreq.2-2a-p.ltoreq.0.8; 0.ltoreq.2a-m.ltoreq.0.5, preferably
0.1.ltoreq.2a-m.ltoreq.0.4; 0.ltoreq.k'.ltoreq.10, preferably
0.ltoreq.k'.ltoreq.5; p+m=1; and z' is the total electrical charge
of the cationic element; Step (c): The chemical combination (C'),
is calcined to form the chemical combination (C).
24. Process for the preparation of the chemical combination (C)
according to claim 19, characterized in that it comprises the
successive following steps: Step (a): An hydrotalcite-type
precursor of the formula (VI):
[[Mg.sub.1-aAl.sub.a(OH).sub.2].sup.z+(A.sup.n''-.sub.z'/n''),k''H.sub.2O-
] (VI), wherein 0<a<1, A.sup.n''- is mainly a silicate or a
polysilicate anion; and z is the total electrical charge of the
cationic element, is calcined to form a mixed oxyde/silicate of the
formula (VII):
[(2-2a)MgO,aAl.sub.2O.sub.3,a'Al.sub.2Si.sub.2O.sub.7,b'MgSiO.sub.4,d'S-
iO.sub.2] (VII); Step (b): The mixed oxyde/silicate of the formula
(VII), is put to react with a Rh.sup.+++ salt, a Ni.sup.++ salt or
a mixture of both salts, to form a chemical combination (C') as
defined above; Step (c): The chemical combination (C'), is calcined
to form the chemical combination (C).
25. Process for the preparation of the chemical combination (C)
according to claim 19, characterized in that it comprises the
successive following steps: Step (a): A powder mixture of boehmite
(Al.sub.2O.sub.3, w H.sub.2O) and .alpha.-alumina, is added to an
alkaline aqueous silicate solution, to form a dispersion which is
supplemented with at least one inorganic hydrosoluble salt chosen
from hydrosoluble inorganic salts of Al.sup.+++, Rh.sup.+++,
Mg.sup.++ and Ni.sup.++, to form a chemical combination (C'')
between an active solid phase which is covalently bound to the
surface of an inert solid phase, characterized in that said solid
active phase essentially consists an hydrotalcite active solid
phase of the formula (IV) as defined above, and characterized in
that said inert solid phase is a .alpha.-alumina. Step (b): The
chemical combination (C'') obtained in of step (a), is calcined to
form the chemical combination (C).
26. Chemical combination (C'), between an active solid phase which
is covalently bound to the surface of an inert solid phase,
characterized in that said solid active phase essentially consists
an hydrotalcite active solid phase of the formula (IV):
[Rh.sub.xNi.sub.yMg.sub.pAl.sub.m(OH).sub.2].sup.z+(A.sup.n-.sub.z/n)kH.s-
ub.2O, (IV) wherein A.sup.n- is mainly a silicate or a polysilicate
anion; 0.ltoreq.x.ltoreq.0.3, preferably 0.ltoreq.x.ltoreq.0.1;
0.ltoreq.y.ltoreq.0.9, preferably 0.ltoreq.y.ltoreq.0.3;
0.ltoreq.p.ltoreq.0.9, preferably 0.3.ltoreq.p.ltoreq.0.8;
0.ltoreq.m.ltoreq.0.5, preferably 0.1.ltoreq.m.ltoreq.0.4;
0.ltoreq.k.ltoreq.10, preferably 0.ltoreq.k.ltoreq.5; x+y>0;
0.5.ltoreq.y+p.ltoreq.0.9, preferably 0.6.ltoreq.y+p.ltoreq.0.8;
x+y+p+m=1; and z is the total electrical charge of the cationic
element, and characterized in that said inert solid phase is an
hydrotalcite inert solid phase of the formula (V):
[[Mg.sub.2-2a-pAl.sub.2a-m(OH).sub.2].sup.z'+(A.sup.n'-.sub.z'/n'),k'H.su-
b.2O] (V), wherein A.sup.n'- is mainly a silicate or a polysilicate
anion; 0.ltoreq.2-2a-p.ltoreq.0.9, preferably
0.3.ltoreq.2-2a-p.ltoreq.0.8; 0.ltoreq.2a-m.ltoreq.0.5, preferably
0.1.ltoreq.2a-m.ltoreq.0.4; 0.ltoreq.k'.ltoreq.10, preferably
0.ltoreq.k'.ltoreq.5; p+m=1; and z' is the total electrical charge
of the cationic element;
27. Chemical combination (C'') between an active solid phase which
is covalently bound to the surface of an inert solid phase,
characterized in that said solid active phase essentially consists
an hydrotalcite active solid phase of the formula (IV):
[Rh.sub.xNi.sub.yMg.sub.pAl.sub.m(OH).sub.2].sup.z+(A.sup.n-.sub.z/n)kH.s-
ub.2O, (IV) wherein A.sup.n- is mainly a silicate or a polysilicate
anion; 0.ltoreq.x.ltoreq.0.3, preferably 0.ltoreq.x.ltoreq.0.1;
0.ltoreq.y.ltoreq..ltoreq.0.9, preferably 0.ltoreq.y.ltoreq.0.3;
0.ltoreq.p.ltoreq.0.9, preferably 0.3.ltoreq.p.ltoreq.0.8;
0.ltoreq.m.ltoreq.0.5, preferably 0.1.ltoreq.m.ltoreq.0.4;
0.ltoreq.k.ltoreq.10, preferably 0.ltoreq.k.ltoreq.5; x+y>0;
0.5.ltoreq.y+p.ltoreq.0.9, preferably 0.6.ltoreq.y+p.ltoreq.0.8;
x+y+p+m=1; and z is the total electrical charge of the cationic
element, and characterized in that said inert solid phase is a
.alpha.-alumina.
28. Chemical combination according to claim 26, wherein the active
phase is selected from:
[Ni.sub.0.08Mg.sub.0.60Al.sub.0.32(OH).sub.2].sup.0.32+(SiO.sub.3.sup.2-)-
.sub.0.16kH.sub.2O,
[Ni.sub.0.08Rh.sub.0.0015Mg.sub.0.60Al.sub.0.3185(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
[Rh.sub.0.005Mg.sub.0.71Al.sub.0.285(OH).sub.2].sup.0.32+(SiO.sub.3.sup.2-
-).sub.0.16kH.sub.20,
[Ni.sub.0.01Rh.sub.0.0002Mg.sub.0.67Al.sub.0.3198(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
[Ni.sub.0.02Mg.sub.0.63Al.sub.0.35(OH).sub.2].sup.0.35+(SiO.sub.3.sup.2-)-
.sub.0.175kH.sub.20,
[Rh.sub.0.0004Mg.sub.0.65Al.sub.0.3496(OH).sub.2].sup.0.35+(SiO.sub.3.sup-
.2-).sub.0.175kH.sub.20,
[Ni.sub.0.02Mg.sub.0.78Al.sub.0.20(OH).sub.2].sup.0.35+(SiO.sub.3.sup.2-)-
.sub.0.175kH.sub.20,
[Rh.sub.0.0004Mg.sub.0.80Al.sub.0.1996(OH).sub.2].sup.0.20+(SiO.sub.3).su-
b.0.10kH.sub.20, and
[Ni.sub.0.027Rh.sub.0.00085Mg.sub.0.6477Al.sub.0.32445(OH).sub.2].sup.0.3-
253+(SiO.sub.3.sup.2-).sub.0.16265kH.sub.20.
29. Chemical combination (C) characterized in that it is obtained
by calcination of the combination (C') or of the combination (C'')
as defined in claim 27.
30. Use of the chemical combination (C) as defined in claim 27, a
catalyst in chemical reactions involving the conversion
hydrocarbonaceous feedstocks.
31. Production of Synthesis gas, by catalytic partial oxidation of
methane or of low-boiling liquid hydrocarbons characterized in that
the worked catalyst is the chemical combination as defined in claim
27.
32. Production of Synthesis gas, by steam reforming of methane or
of low-boiling liquid hydrocarbons, characterized in that the
worked catalyst is the chemical combination as defined in claim
27.
33. Production of Synthesis gas, by dry reforming (CO.sub.2) of
methane or of low-boiling liquid hydrocarbons, characterized in
that the worked catalyst is the chemical combination as defined in
claim 27.
34. The said inert solid phase can be others classical catalytic
supports such as zirconia or magnesium oxide or silicon or silicon
carbide, molybdenum carbide, refractory alloys available in several
forms (beads, pellets, monoliths, disks, . . . ).
35. Use of a composition according to claim 19 which the operating
catalyst conditions one in the range of 500 to 1300.degree. C. and
preferably between 600 to 1100.degree. C.
36. Use of a composition according to claim 19 which the operating
catalyst conditions one in the range of 10.sup.5 Pa to 510.sup.6 Pa
and preferably between 10.sup.5 Pa to 310.sup.6 Pa.
Description
[0001] The present invention relates to a new catalyst for the
partial oxidation of hydrocarbons.
[0002] The catalytic partial oxidation of hydrocarbons, natural gas
or methane to synthesis gas has been processed for many years.
While currently limited as an industrial process, the partial
oxidation is of interest for the significant released heat and for
the use of smaller reactors.
[0003] European patent application EP 0 725 038, discloses
materials having a layered structure of Hydrocalcite type, in which
rhodium is inside the interior of said structure, which can be
represented by the general formula:
[Rh.sub.aRu.sub.bX.sub.cY.sub.d(OH).sub.2].sup.Z+(A.sup.n-.sub.z/n)mH.sub-
.2O wherein X and Y are divalent or trivalent metal cations,
0.ltoreq.a.ltoreq.0.5; 0.ltoreq.b.ltoreq.0.5;
0.5.ltoreq.c.ltoreq.0.9; 0.ltoreq.d.ltoreq.0.5 and a+b+c+d=1, m is
0 or a positive integer, A is a hydroxyl or any anion or anionic
complex having n electrical charge. z is the total electrical
charge of the cationic component.
[0004] International application WO 01/25142, discloses a catalyst
which is obtained from an Hydrotalcite-type precursor containing
Ni, which is worked in a reforming process using steam and/or
CO.sub.2.
[0005] International application WO 01/53196, discloses a catalyst
which consists in a refractory fibrous structure comprising a
plurality of ceramic oxide fibres and at least one active catalyst
element, chosen among Rh, Ni and Cr, supported on said fibrous
structure. Such a catalyst is claimed to better resist to a thermal
shock, than the conventional supported catalysts do.
[0006] International application WO 01/28679 discloses a catalyst
which consists in a mixture of at least two differents metal
carbides (especially Mo, W, Cr), which optionally include an
additional promoter and/or a catalyst support. It is claimed that
no appreciable coking occurs, that the catalyst deactivation is
avoided or at least delayed, and that this catalyst can be
industrially worked under better economical conditions than the
conventional catalysts do.
[0007] International application WO 03/000398, discloses a catalyst
which consists on a classical catalytic active phase such as a
metal transition element (Ni, Mo, Rh, Pt, . . . ), which is
supported on a silicon carbide having a high specific surface area
less or equal to 100 m.sup.2 g. The contact time between the
gaseous hydrocarbon, the oxidizing gas, optionally in the presence
of a small amount of water, and the silicon carbide catalytic
support, is greater than 0.05 s, the temperature greater than
800.degree. C. and the pressure inside the reactor greater than the
atmospheric pressure. The avantages of these invention is the use
of a new silicon carbide support having a high surface area,
typically between 10 and 50 m.sup.2/g, with classical active
phases.
[0008] U.S. Pat. No. 6,458,334 B1 discloses a catalytic partial
oxidation process involving the use of a classical metal catalyst
(Ni, Co, Ir, Pt, . . . ) or a combinaison of them thereof which is
supported on or in a ceria monolith. The pressure is between
10.sup.5 Pa and 20.10.sup.5 Pa (1 to 20 bar), the Gas Hourly Space
Velocity (GHSV) is of about 50,000 to 500,000 hr.sup.-1.
[0009] However, none of the known existing catalytic partial
oxidation processes are able to reach a sufficient high conversion
rate of reactant gas. Moreover a high selectivity of CO and H.sub.2
reaction products can only be reached with the using of a large
amount of rare and costly catalysts, or with taking the risk of an
excessive coking or of a premature failure due to a lack of heat
resistance and a mechanical instability of cheaper catalysts on the
support structure.
[0010] There is indeed a continuing need for new catalysts that are
mechanically stable, with high surface area, preferably from 10 to
300 m.sup.2/g, and that retain a high level of activity and
selectivity to CO and H.sub.2 products under conditions of high
temperature, without excessive coking.
[0011] In the International application PCT/IB03/01673 filed on
Apr. 30, 2003, the inventors claimed a composition overcome the
above-mentioned drawbacks, which may thus be used as a catalyst for
partial oxidation of hydrocarbons and which essentially consists in
a solid solution of a mixture of at least a magnesium oxide type
phase compound and at least a magnesium silicate type phase
compound in which Al, and Rh and/or Ni cations are soluted.
[0012] The precursor of this composition is a hydrotalcite-type
structure. After calcination at 900.degree. C., two main phases are
present: magnesium oxide type phase, a magnesium silicate type
phase (forsterite-type), in which Al and the cation of the active
phase (Rh and/or Ni) are soluted.
[0013] The composition claimed in PCT/IB03/01673 can be prepared
from a precursor containing active metals of VIII group (Ni and/or
Rh) and silicates as anions having a structure that is referred to
as "hydrotalcite-like" (HT). Hydrotalcite-like compounds are
anionic clays, that have a sheet-like structure. The sheets are
separated by anions which balance the net positive charge of the
sheets. In the context of the present invention, the anions of the
anionic sheets are silicates or polysilicates and in the cationic
sheets are present Ni or Rh, or a combination of those. The
materials obtained by calcination of said Hydrotalcite-like
compounds have high thermal resistance and are very stable. After
an activation procedure, they are very active and do not show any
carbon formation in the catalytic partial oxidation process.
[0014] More specifically, this composition is prepared from an HT
precursor represented by the general formula (I):
[Rh.sub.xNi.sub.yMg.sub.lAl.sub.m(OH).sub.2].sup.z+(A.sup.n-.sub.z/n)kH.s-
ub.2O, (I) wherein A.sup.- is mainly a silicate or a polysilicate
anion; [0015] 0.ltoreq.x.ltoreq.0.3 [0016] 0.ltoreq.y.ltoreq.0.9;
[0017] 0.ltoreq.l.ltoreq.0.9; [0018] 0.ltoreq.m.ltoreq.0.5; [0019]
0.ltoreq.k.ltoreq.10; [0020] x+y>0; [0021]
0.5.ltoreq.y+1.ltoreq.0.9; [0022] x+y+l+m=1; and z is the total
electrical charge of the cationic element.
[0023] In a preferred embodiment of this composition, [0024]
0.ltoreq.x.ltoreq.0.1; [0025] 0.ltoreq.y.ltoreq.0.3; [0026]
0.3.ltoreq.l.ltoreq.0.8; [0027] 0.1.ltoreq.m.ltoreq.0.4; [0028]
0.ltoreq.k.ltoreq.5l [0029] x+y>0; [0030]
0.6.ltoreq.y+1.ltoreq.0.8; [0031] x+y+l+m=1.
[0032] Among these above mentioned HT precursor, the following
compounds are the most preferred:
[Ni.sub.0.08Mg.sub.0.60Al.sub.0.32(OH).sub.2].sup.0.32+(SiO.sub.3.sup.2-)-
.sub.0.16kH.sub.20,
[Ni.sub.0.08Rh.sub.0.0015Mg.sub.0.60Al.sub.0.3185(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
[Rh.sub.0.005Mg.sub.0.71Al.sub.0.285(OH).sub.2].sup.0.32+(SiO.sub.3.sup.2-
-).sub.0.16kH.sub.20,
[Ni.sub.0.01Rh.sub.0.0002Mg.sub.0.67Al.sub.0.3198(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
[Ni.sub.0.02Mg.sub.0.63Al.sub.0.35(OH).sub.2].sup.0.35+(SiO.sub.3.sup.2-)-
.sub.0.175kH.sub.20,
[Rh.sub.0.0004Mg.sub.0.65Al.sub.0.3496(OH).sub.2].sup.0.35+(SiO.sub.3.sup-
.2-).sub.0.175kH.sub.20,
[Ni.sub.0.02Mg.sub.0.78Al.sub.0.20(OH).sub.2].sup.0.35+(SiO.sub.3.sup.2-)-
.sub.0.175kH.sub.20, and
[Rh.sub.0.0004Mg.sub.0.80Al.sub.0.1996(OH).sub.2].sup.0.20+(SiO.sub.3).su-
b.0.10kH.sub.20.
[0033] In order to improve the stability of this composition and to
improve its selectivity, the inventors have tried to develop a
process to support the above-mentioned composition (the active
phase) on an inert support.
[0034] They however found that working a classical deposition
process on standard catalytic supports, such as alumina, zirconia,
silicon carbide or magnesium oxide, was not efficient. In fact the
deposition of the hydrotalcite precursor on .alpha.-alumina beads
did not tie with the support, the active phase being separated from
the beads, the same occured with commercial silicon carbide which
have an average specific area os less than 5 m.sup.2/g, and the
tentative with ZrO.sub.2 pellets resulted in the crash of the
pellets during the preparation.
[0035] That is why they develop a new process on the "form memory"
concept, to increase the interaction between the support and the
active phase in order to improve the stability of the resulting to
high temperature. This concept involves the use one raw material
(O), which owns one or several chemical elements (for example A),
which is still present in the final product after synthesis. This
raw material, which can have several geometric forms (pellets,
beads, honeycomb, filter, tube, . . . ) and several
architecture/microstructures (high surface area, porosity, pore
size, . . . ) is attacked by chemical reactions (solid-liquid
and/or solid-gas and/or solid-solid reactions) with precursors (B,
C for example), which must also be present in the final product.
The final product is a new material (ABC for example), which is
supported on the initial raw material (O).
[0036] In the best case, one or several layers of the new material
(ABC) are developed around a core of the raw material.
[0037] Such a concept was first disclosed in U.S. Pat. No.
4,914,070 and related to the production of silicon carbide with
high surface area for catalyst applications. This patent disclosed
a process for the production of fine grains of silicon carbon,
which are formed by reacting SiO vapour on carbon. SiO vapour is
obtained by heating a mixture of SiO.sub.2 and Si at a temperature
between 1100 to 1400.degree. C. This vapour attacks reactive carbon
with a high specific surface area (more than 200 m.sup.2/g) in a
second zone at temperature between 1100 to 1400.degree. C. The
final product issued of the reaction between SiO.sub.gas and
C.sub.solide is silicon carbide with high surface area (more than
100 m.sup.2/g) with or without a carbon core. The main advantages
of this process are the production of silicon carbide with high
surface-area while keeping the initial geometry and the
architecture/microstructure of the raw carbon.
[0038] The ideas of "dissolution/precipitation" method similar to
that described new section are developed to build hydrotalcites of
two Congresses ICC (6.sup.th and 11.sup.th International Congresses
on Catalysis) in Baltimore (1976, 1996).
[0039] Papers of van Dillen J. A., Geus J. W., Hermans L. A. and
van der Meijden J. (1976, 6.sup.th ICC) described a method of
production of supported copper or nickel catalysts by
"deposition-precipitation". The support, which reacted with the
nickel and the cobalt precursor in solution to form an
hydrotalcite, was SiO.sub.2. Penetration of nickel ions into the
silica support or migration of the silica, lead to thicker nickel
hydrotalcite layers. Conversion of an appreciable fraction of the
support into a compound having a layer structure profoundly
affected the texture of the support.
[0040] Papers of Espinose J. B. and Clause O. (1996, 11.sup.th ICC,
p1321-1329) described the promotion of .gamma.-alumina dissolution
by metal ions during impregnation and the thermal stability of the
formed coprecipitates. The metallic elements were nickel and
cobalt. The method developed was the "deposition-precipitation" and
the support was .gamma.-alumina. As described in the 6.sup.th ICC
the Al can reacted in solution with the Ni(II) ions or Co(II) to
form an hydrotalcite structure. The experiments allow to separate
the secondary phase--hydrotalcite--from the mother oxide support,
alumina. However, the authors suggested that, the supported
hydrotalcites were, in fact, weakly bound to the surface and free
to move away from alumina once formed. In both papers, no chemical
reaction was studied using this new type of "active support".
[0041] That is why the inventors developped a new combination which
overcome the above mentioned drawbacks.
[0042] Aaccording to a first embodiment, the invention relates to a
chemical combination (C) between an active solid phase which is
covalently bound to the surface of an inert solid phase,
caracterized in that said solid active phase essentially consists
in a solid solution of a mixture of at least a magnesium oxide type
phase compound and at least a magnesium silicate type phase
compound in which Al, and Rh and/or Ni cations are soluted and
caracterized in that said inert solid phase is either a compound
represented by the general formula (I):
Al.sub.aNi.sub.bRh.sub.cMg.sub.dSi.sub.eO.sub.f wherein a, b, c, d,
and e are integers which are greater than or equal to 0, f is an
integer greater than 0, the sum a+b+c+d: 0, and wherein
(3a+2b+3c+2d+4e)/2=f, or a mixture of compounds represented by the
said general formula (I),
[0043] provided that at least one of the Si, Al, Mg, Rh or Ni
elements, which is present in the solid active phase, is also
present in the solid inert phase.
[0044] In the context of the present invention, active phase must
be understood as a catalytically active phase for various organic
reactions, whereas inert phase correspond to the non reactive part
of the above mentioned chemical combination under the reaction
conditions wherein the active phase is active.
[0045] In the context of the present invention, chemical
combination means that more than 0% of the surface of the inert
phase is coated with the active phase.
[0046] In the context of the present invention, the inert phase can
be in various forms, such as beads, pellets, or monoliths.
[0047] In a preferred aspect of the present invention, the amount
of active phase on the inert support is in the range from 5% to 60%
weight by weight and preferably between 5% and 20% weigh by weight
of the the total combination.
[0048] The subject matter of the present invention is more
specifically, the above-mentioned chemical combination (C), wherein
the inert phase is chosen among the compounds represented by the
general formula (I) as defined above, wherein:
[0049] either a=2, b=c=d=e=0 and f=3, and in this case, the inert
phase is Al.sub.2O.sub.3,
[0050] either a=2, b=c=0, d=1, e=3 and f=10, and in this case, the
inert phase is a mixed oxyde (3SiO.sub.2, Al.sub.2O.sub.3,
MgO),
[0051] either e=1 and a=b=c=d=0 and f=2 and n in this case, the
inert phase is SiO.sub.2,
[0052] either a b=c=0, d=2, e=1 and f=4, and in this case, the
inert phase is Mg.sub.2SiO.sub.4,
[0053] or a=2, b=c=d=0, e=2 and f=7, and in this case, the inert
phase is Al.sub.2Si.sub.2O.sub.7.
[0054] According to a second embodiment, the invention relates to a
process for the preparation of the chemical combination (C), as
defined above, characterized in that it comprises the successive
following steps:
[0055] Step (a): An hydrotalcite-type precursor of the formula
(II):
[[Mg.sub.1-aAl.sub.a(OH).sub.2].sup.z+(CO.sub.3.sup.2-.sub.z/2),mH.sub.2O-
] (II), wherein 0<a<1 and z is the total electrical charge of
the cationic element, is calcined to form a mixed oxyde of the
formula (III): [(2-2a)MgO,aAl.sub.2O.sub.3] (III);
[0056] Step (b): The mixed oxyde of the formula (III), is mixed
with water and put to react at alkaline pH, with a SiO.sub.2.NaOH
solution, together with a Rh.sup.+++ salt, a Ni.sup.++ salt or a
mixture of both salts, to form a chemical combination (C'), between
an active solid phase which is covalently bound to the surface of
an inert solid phase, caracterized in that said solid active phase
essentially consists in an hydrotalcite active solid phase of the
formula (IV)
[Rh.sub.xNi.sub.yMg.sub.pAl.sub.m(OH).sub.2].sup.z+(A.sup.n-.sub.z/n)kH.s-
ub.2O, (IV) wherein A.sup.n- is mainly a silicate or a polysilicate
anion; [0057] 0.ltoreq.x.ltoreq.0.3, preferably
0.ltoreq.x.ltoreq.0.1; [0058] 0.ltoreq.y.ltoreq.0.9, preferably
0.ltoreq.y.ltoreq.0.3; [0059] 0.ltoreq.p.ltoreq.0.9, preferably
0.3.ltoreq.p.ltoreq.0.8; [0060] 0.ltoreq.m.ltoreq.0.5, preferably
0.1.ltoreq.m.ltoreq.0.4; [0061] 0.ltoreq.k.ltoreq.10,preferably
0.ltoreq.k.ltoreq.5; [0062] x+y>0; [0063]
0.5.ltoreq.y+p.ltoreq.0.9, preferably 0.6.ltoreq.y+p.ltoreq.0.8;
[0064] x+y+p+m=1; and z is the total electrical charge of the
cationic element, and caracterized in that said inert solid phase
is an hydrotalcite inert solid phase of the formula (V):
[[Mg.sub.2-2a-pAl.sub.2a-m(OH).sub.2].sup.z'+(A.sup.n'-.sub.z'/n'),k'H.su-
b.2O] (V), wherein A.sup.n'- is mainly a silicate or a polysilicate
anion; [0065] 0.ltoreq.2-2a-p.ltoreq.0.9, preferably
0.3.ltoreq.2-2a-p.ltoreq.0.8; [0066]
0.ltoreq.2a-m.ltoreq.0.5,preferably 0.1.ltoreq.2a-m.ltoreq.0.4;
[0067] 0.ltoreq.k'.ltoreq.10, preferably 0.ltoreq.k'.ltoreq.5;
[0068] p+m=1; and z' is the total electrical charge of the cationic
element;
[0069] Step (c): The chemical combination (C'), is calcined to form
the chemical combination (C).
[0070] The above mentioned process includes the migration of the
elements at short range in relatively mild conditions, that is at a
temperature <1000.degree. C.; it is favoured by the proximity
among the phases and by the analogies of the lattice structure of
both the inert phase precursor and the active-phase precursor. The
reaction forms a surface layer of the precursors of mixed oxide and
mixed silicate, containing Rh, Ni, Mg and/or Al, which are strongly
bonded to the support. Without being ling by the theory, the
inventors however believe that the silicates reconstruct the
hydrotalcite structure of the inert phase, while the mixed oxide is
partially solved and re-precipitated as an hydrotalcite structure,
which includes the metallic Rh and Ni in the lattice. Thus, after
the calcination, mixed oxides and silicates with high Rh and Ni
concentration on the surface can be obtained. The presence of a
common oxide and silicate structure guarantees a good
interconnection among the phases. This concept is illustrated on
FIG. 1a.
[0071] According to a third embodiment, the invention relates to a
process for the preparation of the chemical combination (C), as
defined above, characterized in that it comprises the successive
following steps:
[0072] Step (a): An hydrotalcite-type precursor of the formula
(VI):
[[Mg.sub.1-aAl.sub.a(OH).sub.2].sup.z+(A.sup.n''-.sub.z'/n''),k''H.sub.2O-
] (VI), wherein 0<a<1, A.sup.n''- is mainly a silicate or a
polysilicate anion and z is the total electrical charge of the
cationic element, is calcined to form a mixed oxyde/silicate of the
formula (VII):
[(2-2a)MgO,aAl.sub.2O.sub.3,a'Al.sub.2Si.sub.2O.sub.7,b'MgSiO.sub.4,d'Si-
O.sub.2] (VII);
[0073] Step (b): The mixed oxyde/silicate of the formula (VII), is
put to react with a Rh.sup.+++ salt, a Ni.sup.++ salt or a mixture
of both salts, to form a chemical combination (C') as defined
above;
[0074] Step (c): The chemical combination (C'), is calcined to form
the chemical combination (C).
[0075] The above mentioned process includes the impregnation of Rh
and Ni on a hydrotalcite-like mixed Magnesium, Aluminium silicate
and oxide of the formula (VII), which generates by calcination, a
mixed oxide and silicate phase, with a high Rh and Ni concentration
near the surface. The ratio between the oxide phase and the
silicate phase is controlled by the amount of silicates during the
precipitation of the Hydrotalcite precursors. In fact, this
structure is supposed to be intercalated by silicate or
polysilicate anions with variable Si composition, which are
represented by the general formula (Si.sub.nO.sub.2n+1).sup.2-. The
concept is illustrated on FIG. 1b.
[0076] According to a fourth embodiment, the invention relates to a
process for the preparation of the chemical combination (C), as
defined above, characterized in that it comprises the successive
following steps:
[0077] Step: A powder mixture of boehrite (Al.sub.2O.sub.3, w
H.sub.2O) and .alpha.-alumina, is added to an alkaline aqueous
silicate solution, to form a dispersion which is supplemented with
at least one inorganic hydrosoluble salt chosen from hydrosoluble
inorganic salts of Al.sup.+++, Rh.sup.+++, Mg.sup.++ and Ni.sup.++,
to form a chemical combination (C'') between an active solid phase
which is covalently bound to the surface of an inert solid phase,
caracterized in that said solid active phase essentially consists
an hydrotalcite active solid phase of the formula (IV) as defined
above, and caracterized in that said inert solid phase is a
.alpha.-alumina.
[0078] Step (b): The chemical combination (C'') obtained in of step
(a), is calcined to form the chemical combination (C).
[0079] According to this process, the chemical combination (C'')
also generates by calcination, a mixed oxide and silicate phase,
with a high Rh and Ni concentration near the surface. This concept
is illustrated on FIG. 1c.
[0080] According to a fifth embodiment, the invention relates to
the chemical combinations (C') and (C''), as defined above.
[0081] According to this last embodiment, the invention more
specifically relates to combinations (C') and (C'') as defined
above, wherein the active phase is selected from:
[Ni.sub.0.08Mg.sub.0.60Al.sub.0.32(OH).sub.2].sup.0.32+(SiO.sub.3.sup.2-)-
.sub.0.16kH.sub.20,
[Ni.sub.0.08Rh.sub.0.0015Mg.sub.0.60Al.sub.0.3185(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
[Rh.sub.0.005Mg.sub.0.71Al.sub.0.285(OH).sub.2].sup.0.32+(SiO.sub.3.sup.2-
-).sub.0.16kH.sub.20,
[Ni.sub.0.01Rh.sub.0.0002Mg.sub.0.67Al.sub.0.3198(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
[Ni.sub.0.02Mg.sub.0.63Al.sub.0.35(OH).sub.2].sup.0.35+(SiO.sub.3.sup.2-)-
.sub.0.175kH.sub.20,
[Rh.sub.0.0004Mg.sub.0.65Al.sub.0.3496(OH).sub.2].sup.0.35+(SiO.sub.3.sup-
.2-).sub.0.175kH.sub.20,
[Ni.sub.0.02Mg.sub.0.78Al.sub.0.20(OH).sub.2].sup.0.35+(SiO.sub.3.sup.2-)-
.sub.0.175kH.sub.20,
[Rh.sub.0.0004Mg.sub.0.80Al.sub.0.1996(OH).sub.2].sup.0.20+(SiO.sub.3).su-
b.0.10kH.sub.20, and
[Ni.sub.0.027Rh.sub.0.00085Mg.sub.0.6477Al.sub.0.32445(OH).sub.2].sup.0.3-
253+(SiO.sub.3.sup.2-).sub.0.16265kH.sub.20.
[0082] According a sixth embodiment the present invention relates
to the chemical combination (C) as defined above, characterized in
that it is obtained by calcination of the combination (C') or of
the combination (C'') as defined above.
[0083] The above mentioned chemical combination according to the
first embodiment of the present invention is used as a catalyst in
chemical reactions involving the conversion hydrocarbonaceous
feedstocks. It is preferably used as a catalyst in the conversion,
of natural gas or of low-boiling liquid hydrocarbons
(C.sub.2-C.sub.4 hydrocarbons) into Synthesis gas either by
catalytic partial oxydation, or by steam reforming.
[0084] The composition according to the present invention is also
used in the reactions of reduction of nitrogen oxides, of
hydroformulation, of hydrogenation of CO, CO.sub.2 and mixtures
thereof or as a catalyst of dehydrogenated oxydative reactions.
[0085] The chemical combination according the first embodiment of
the invention is generally used in temperature operating conditions
within the range of 500.degree. C. to 1300.degree. C., preferably
between 600.degree. C. to 1100.degree. C., and in pressure
operating conditions within the range of 10.sup.5 Pa to 60 10.sup.5
Pa, preferably between 10 10.sup.5 Pa to 35 10.sup.5 Pa.
[0086] The supported catalysts are generally used under temperature
and pressure in operating conditions which are reductive atmosphere
(natural gaz) mixed with an oxydant feed preferably pure oxygen,
oxygen and an inert gas mixture, such as nitrogen or argon, steam,
carbon dioxide or a mixture of part or/and all of them.
[0087] The chemical combination according to the first embodiment
of the invention, is generally activated before use, by an "in
site" reduction, giving rise to very active and stable Rh and Ni
metal particles.
[0088] The following examples illustrate the present invention
without limiting it.
Catalyst Preparation
EXAMPLE 1
Illustration of the Concept of FIG. 1a
[0089] A slurry containing 5.00 g of a Mg/Al hydrotalcite with a
atomic ratio 69:31, previously calcined at 650.degree. C. (HT650),
4.97 g of a 27 wt % solution of SiO.sub.2.NaOH and 1200 ml of
H.sub.2O was prepared under magnetic stirring. An aqueous solution
of the nitrates of the metals [0.0977 g of a 10 wt % solution of
Rh(NO.sub.3).sub.3 and 0.8857 g of Ni(NO.sub.3).sub.2.6H.sub.2O
(99%)] was dropped into the slurry, maintaining the pH and the
temperature constant (pH=10-11, T=80.degree. C.). The slurry was
kept under stirring for 1 h and then filtered and washed with hot
water (60.degree. C.). The obtained hydrotalcite was dried
overnight at 100.degree. C. and than calcined at 900.degree. C. for
12 h.
[0090] The surface area before calcination was 85 m.sup.2/g and
after calcination was 117 m.sup.2/g. The XRD analysis of FIG. 2,
shows the peaks of Mg.sub.2SiO.sub.4, Mg.sub.2AlO.sub.4 and MgO
phases (FIG. 2). The hydrotalcite active phase of the intermediate
chemical combination (C'') can be represented by the following
formula:
[Ni.sub.0.027Rh.sub.0.00085Mg.sub.0.6477Al.sub.0.32445(OH).sub.2].sup.0.3-
253+(SiO.sub.3.sup.2-).sub.0.16265kH.sub.20.
EXAMPLE 2
Illustration of the Concept of FIG. 1b
[0091] A Mg/Al hydrotalcite (atomic ratio=68/32) with silicate as
anions was prepared by co-precipitation. 5.29 g of a 27 wt %
solution of SiO.sub.2.NaOH were first added to 120 ml of H.sub.2O,
and kept under magnetic stirring at 50-60.degree. C. An aqueous
solution 0.2M of the nitrates of the metals [20.14 g of
Mg(NO.sub.3).sub.2.6H.sub.2O (99%), 14.00 g of
Al(NO.sub.3).sub.3.9H.sub.2O (98%)], was dropped into the previous
solution, maintaining the pH constant (=10.5) with the addition of
NaOH 3M and the temperature at 50-60.degree. C. Finally the
solution was kept under magnetic stirring for 45 minutes and then
filtered and washed with hot water (60.degree. C.). The
hydrotalcite obtained was dried overnight at 100.degree. C. and
then calcined at 900.degree. C. for 12 h. 5.00 g of the sample
obtained were impregnated, by incipient wetness method, using a
nitrate solution prepared with 0.227 g of
Ni(NO.sub.3).sub.2.6H.sub.2O (99%) and 0.0149 g of a 10 wt %
solution of Rh(NO.sub.3).sub.3. Then it was calcined at 900.degree.
C. for 12 h.
EXAMPLE 3
Illustration of the Concept of FIG. 1c
[0092] A boehmite primer was prepared by dispersing 0.50 g of
Disperal.TM. (boehmite sold by Condea Chemie GmBH) in 5 ml of
H.sub.2O and 0.031 g of 65 wt % solution of HNO.sub.3. 5.00 g of
the support, powder of sub-micronic .alpha.-Al.sub.2O.sub.3 (0.4
.mu.m), was added slowly to the boehmite dispersion and then kept
under stirring for 30 min at room temperature. The slurry obtained
was dried at room temperature overnight. 0.50 g of silicate
solution (SiO.sub.2.NaOH 27 wt %) were added to 112 ml of H.sub.2O
with a small amount of NaOH sufficient to bring the pH=10-11. The
powder of .alpha.-Al.sub.2O.sub.3/Disperal was added to this
aqueous solution and kept under stirring at 50-60.degree. C.,
forming a homogeneous dispersion. 1.67 g of
Mg(NO.sub.3).sub.2.6H.sub.2O (99%), 1.31 g of
Al(NO.sub.3).sub.3.9H.sub.2O (98%), 0.25 g of
Ni(NO.sub.3).sub.2.6H.sub.2O (99%) and 0.017 g of a solution 10 wt
% of Rh(NO.sub.3).sub.3 were dissolved in 55 ml of H.sub.2O. The
aqueous solution (0.2M) of the nitrates of the metals was dropped
into the silicates/.alpha.-Al.sub.2O.sub.3/Disperal dispersion,
maintaining the pH constant (=10-11) by the addition of NaOH 3 M
and the temperature at 50-60.degree. C. The dispersion was kept
under stirring for 45 minutes and then filtered and washed with hot
water (60.degree. C.). The supported hydrotalcite was dried at
100.degree. C. overnight and calcined at 900.degree. C. for 12
h.
[0093] The XRD analysis of FIG. 3, shows the reflection of the
.alpha.-Al.sub.2O.sub.3 and Mg.sub.2SiO.sub.4 phases. The surface
area after calcination was 25 m.sup.2/g.
[0094] The hydrotalcite active phase of the intermediate chemical
combination (C') can be represented by the following formula:
[Ni.sub.0.08Rh.sub.0.0015Mg.sub.0.60Al.sub.0.3185(OH).sub.2].sup.0.32+(Si-
O.sub.3.sup.2-).sub.0.16kH.sub.20,
EXAMPLE 4
Illustration of the Concept of FIG. 1c
[0095] The .alpha.-Al.sub.2O.sub.3/Disperal support was prepared as
in Example 3.
[0096] 0.50 g of the silicate solution (SiO.sub.2. NaOH 27 wt %)
were added to 112 ml of distilled water with a small amount of NaOH
sufficient to bring the pH=10-11. The powder of
.alpha.-Al.sub.2O.sub.3/Disperal was added to this aqueous solution
and kept under stirring at 50-60.degree. C., forming a homogeneous
dispersion. 1.67 g of Mg(NO.sub.3).sub.2.6H.sub.2O (99%), 0.25 g of
Ni(NO.sub.3).sub.2.6H.sub.2O (99%) and 0.017 g of a solution 10 wt
% of Rh(NO.sub.3).sub.3 were dissolved in 55 ml of H.sub.2O. The
aqueous solution (0.2M) of the metal nitrates, was dropped into the
silicates/.alpha.-Al.sub.2O.sub.3/Disperal dispersion, maintaining
the pH constant (=10-11) by addition of NaOH 3 M and the
temperature at 50-60.degree. C. At the end of the dropping, the
solution was left under stirring for 45 minutes and then filtered
and washed with hot water (60.degree. C.). The hydrotalcite so
obtained was dried at 100.degree. C. overnight and then calcined at
900.degree. C. for 12 h.
[0097] In this example, the hydrotalcite supported on
Disperal/.alpha.-Al.sub.2O.sub.3 was prepared assuming that part of
the boehmite-.alpha.-Al.sub.2O.sub.3 support may be dissolved to
deliver Al.sup.3+ ions.
[0098] The XRD analysis of FIG. 3, shows the reflection of the
.alpha.-Al.sub.2O.sub.3 and M92SiO.sub.4 phases. The surface area
after calcination was 22 m.sup.2/g.
EXAMPLE 4
Illustration of the Concept of FIG. 1c
[0099] 0.50 g of a 27 wt % solution of SiO.sub.2.NaOH were first
added to 112 ml of H.sub.2O together with an amount of NaOH
sufficient to maintain the pH=10-11. Then 5.00 g of beads of
.alpha.-Al.sub.2O.sub.3 were added to the aqueous solution and kept
under stirring at 50-60.degree. C. 1.67 g of
Mg(NO.sub.3).sub.2.6H.sub.2O (99%), 1.31 g of
Al(NO.sub.3).sub.3.9H.sub.2O (98%), 0.25 g of
Ni(NO.sub.3).sub.2.6H.sub.2O (99%) and 0.017 g of a 10 wt %
solution of Rh(NO3).sub.3 were dissolved in 55 ml of H.sub.2O. The
aqueous solution 0.2M of the nitrates of the metals was dropped
into the silicates/support, maintaining the pH constant (=10-11) by
addition of NaOH 3 M and the temperature at 50-60.degree. C.
Finally the solution was kept under stirring for 45 minutes and
then filtered, washed with hot water (60.degree. C.) and dried at
100.degree. C. overnight.
[0100] Using the beads of .alpha.-Al.sub.2O.sub.3, the hydrotalcite
precursor does not tied together with the support. The result was
that the beads remained intact, but separated from the active
phase.
EXAMPLE 6
Illustration of Classical Coating-Deposition on Beads of .alpha.
Alumina/Disperal
[0101] In this example, the technical way of supporting the active
phase (ex-HT-sil Ni.sub.8Rh.sub.0.15Mg.sub.60Al.sub.31.85) on beads
of .alpha.-Al.sub.2O.sub.3/Disperal, is the classical method using
the formation of ink containing the active phase.
[0102] 0.50 g of ex-HT-sil Ni.sub.8Rh.sub.0.15Mg.sub.60Al.sub.31.85
calcined at 900.degree. C. was dispersed in 5.0 g of H.sub.2O and
0.031 g of 65 wt % solution of HNO.sub.3 and mixed for some hours.
5.00 g of the support, beads of .alpha.-Al.sub.2O.sub.3/Disperal,
was added to the dispersion and kept under stirring for some hours
at room temperature, dried at room temperature overnight and then
calcined at 900.degree. C. for 12 h.
Catalytic Tests
[0103] The sample of example 5 was not tested, because the
hydrotalcite precursor does not tied together with the support made
by beads of .alpha.-Al.sub.2O.sub.3. The result was that the beads
remained intact, but separated from the active phase.
[0104] No interaction is developed between the active phase
(HT-silicate material) and the support (.alpha.-alumina) prepared
in these conditions.
[0105] After reduction of the catalysts under a mixture of N.sub.2
and H.sub.2 at 750.degree. C. (v/v) for 12 h, the materials were
tested in Catalytic Partial Oxidation reactions (called hereafter:
CPO test).
[0106] The preliminary reduction is useful to obtain a maximum
catalytic activity without induction time for activation and
stabilisation and to avoid the partial oxidation of the catalyst.
This activation could also be obtained under reaction conditions
with the methane/oxygen/helium mixture.
[0107] The tests were carried out in a fixed bed quartz
microreactor of 8 mm of diameter, loaded with 0.50 g of catalyst
(20-40 mesh). The tests were carried out at atmospheric pressure,
with different feeds and two different oven temperatures:
[0108] methane/oxygen/helium 2/1/20 at 500.degree. C. and
750.degree. C. (residence time=0.065 s),
[0109] methane/oxygen/helium 2/1/4 at 750.degree. C. (residence
time=0.065 s)
[0110] methane/oxygen/helium 2/1/1 at 750.degree. C. (residence
time=0.111 s) and
[0111] methane/oxygen/helium 4/2/2 at 750.degree. C. (residence
time=0.056 s).
[0112] The reaction products were analysed by gas chromatography.
All the catalysts showed in all conditions total oxygen
conversion.
[0113] The oven temperature is the temperature of the gas mixture
just before the catalytic bed. The temperature maximal (T.sub.max)
is the maximum temperature measured moving the thermocouple through
the catalytic bed.
CPO Tests with the Catalyst of Example 1
[0114] CPO tests were carried out using:
[0115] methane/oxygen/helium 2/1/20 at 500.degree. C. and
750.degree. C. (residence time=0.065 s),
[0116] methane/oxygen/helium 2/1/4 at 750.degree. C. (residence
time=0.065 s)
[0117] methane/oxygen/helium 2/1/1 at 750.degree. C. (residence
time=0.111 s) and
[0118] methane/oxygen/helium 4/2/2 at 750.degree. C. (residence
time=0.056 s).
[0119] The methane conversion and CO and H.sub.2 selectivity were
high both at low (500.degree. C.) and high oven temperature.
[0120] The catalytic performances of this catalyst reached the
maximum with the methane/oxygen/helium 2/1/20 mixture at
750.degree. C., showing very high value. Using the harder reaction
conditions the CH.sub.4 conversion and the CO and H.sub.2
selectivities were about constant and maintained high values.
[0121] No deactivation of the catalyst was observed coming back to
initial conditions (500.degree. C. and 2/1/20 feed) after several
days.
[0122] The results of the tests are consolidated in Table 1.
TABLE-US-00001 TABLE 1 Oven Gas mixture temperature CH.sub.4 CO
H.sub.2 T.sub.max (CH.sub.4/O.sub.2/He) (.degree. C.) conversion
selectivity selectivity (.degree. C.) 2/1/20 500.degree. C. 57.1
53.4 75.6 604 2/1/20 750.degree. C. 96.3 95.7 93.4 785 2/1/4
750.degree. C. 85.0 96.3 89.9 841 2/1/1 750.degree. C. 81.8 96.0
89.8 839 4/2/2 750.degree. C. 79.8 96.8 89.8 886 2/1/20**(RET)
500.degree. C. 56.0 53.5 74.8 601 *: initial test conditions
**(RET): return to initial test conditions after several
experimental conditions (temperature, . . . )
CPO Tests with the Catalyst of Example 3
[0123] The catalyst showed an increase of activity in respect to
that prepared as in example 1, both at low and high temperature.
This was due to the better dispersion of the active phase in the
bulk of the support.
[0124] The results of the tests are consolidated in Table 2.
TABLE-US-00002 TABLE 2 Oven Gas mixture temperature CH.sub.4 CO
H.sub.2 T.sub.max (CH.sub.4/O.sub.2/He) (.degree. C.) conversion
selectivity selectivity (.degree. C.) 2/1/20* 500.degree. C. 67.1
67.4 82.7 600 2/1/20 750.degree. C. 98.8 92.9 95.7 786 2/1/4
750.degree. C. 88.5 96.2 94.3 840 2/1/1 750.degree. C. 87.0. 95.8
92.2 845 4/2/2 750.degree. C. 85.6 95.7 94.6 905 2/1/20**(RET)
500.degree. C. 64.5 62.3 80.0 599 *initial test conditions **(RET):
return to initial conditions after several experimental tests
conditions (temperature, . . . )
CPO Tests with the Catalyst of Example 6
[0125] The catalyst showed lower methane conversion in comparison
to the sample prepared as in example 1 feeding the 2/1/20 gas
mixture at 500.degree. C. Using harder reaction conditions the
catalytic performances are close to those of the sample of the
example 1. No deactivation of the catalyst was observed coming back
to initial conditions (500.degree. C. and 2/1/20 feed).
[0126] The results of the tests are consolidated in Table 3.
TABLE-US-00003 TABLE 3 Oven Gas mixture temperature CH.sub.4 CO
H.sub.2 T.sub.max (CH.sub.4/O.sub.2/He) (.degree. C.) conversion
selectivity selectivity (.degree. C.) 2/1/20* 500.degree. C. 67.1
76.4 75.7 502 2/1/20 750.degree. C. 98.8 94.0 93.6 813 2/1/4
750.degree. C. 88.5 93.4 93.2 905 2/1/1 750.degree. C. 87.0. 91.4
90.5 924 2/1/20**(RET) 500.degree. C. 52.2 40.9 75.7 556 *initial
test conditions **(RET): return to initial test conditions after
several experimental conditions (temperature, . . .)
These results demonstrate that a catalyst made by a classical
coating (example 6) is less efficient in terms of methane
conversion than the same catalyst made by the process according to
the concept of FIG. 1c. Time-On-Stream CPO Tests of the Catalyst of
Example 3
[0127] The objective is to prove the stability of the supported
catalyst prepared by "reactive-impregnation" method during time on
stream.
[0128] In all reaction conditions no deactivation was observed with
time-on-stream. At 750.degree. C. the methane conversion was around
84%. CO and H.sub.2 selectivities respectively 96 and 91%.
[0129] These values are equal to the conversion and the
selectivities obtained under the same operating conditions (contact
time, temperature, gas feed ratio) on the bulk unsupported catalyst
Ex-HT-sil Ni.sub.8Rh.sub.0.15Mg.sub.60Al.sub.31.85; see patent
demand S5922). The results are given on FIG. 4.
* * * * *