Title of Invention

"A HIGH TEMPERATURE STABLE CATALYST SUPPORT"

Abstract A high temperature stable catalyst support comprising: an alumina phase selected from the group consisting of alpha-alumina, theta-alumina and combinations thereof; and a rare earth aluminate comprising at least one rare earth metal, wherein the rare earth aluminate has a molar ratio of aluminum to rare-earth metal greater than 5, and wherein the catalyst support contains 1 wt% to 50 wt% of rare earth aluminate and not more than 20 wt% alpha-alumina.
Full Text The present invention relates to a high temperature stable catalyst support.
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to catalyst supports having high surface area and
stability in ultra high temperature conditions - and also to the catalytic conversion of light
hydrocarbons (e.g., natural gas) to produce synthesis gas.
BACKGROUND OF THE INVENTION
It is well known that the efficiency of supported catalyst systems is often related to the
surface area on the support. This is especially true for systems using precious metal catalysts or
other expensive catalysts. The greater the surface area, the more catalytic material is exposed to
the reactants and the less time and catalytic material is needed to maintain a high rate of
productivity.
Alumina (A^Os) is a well-known support for many catalyst systems. It is also well
known that alumina has a number of crystalline phases such as alpha-alumina (often noted as aalumina
or a-AlaO3), gamma-alumina (often noted as y-alumina or y-Al2O3) as well as a myriad of
alumina polymorphs. One of the properties of gamma-alumina is that it has a very high surface
area. This is commonly believed to be because the aluminum and oxygen-molecules are in a
crystalline structure or form that is not very densely packed. Gamma-AlaQa is a particularly
important inorganic oxide refractory of widespread technological importance in the field of
catalysis, often serving as a catalyst support. Gamma-A^Oa is an exceptionally good choice for
catalytic applications because of a defect spinel crystal lattice that imparts to it a structure that is
both open and capable of high surface area. Moreover, the defect spinel structure has vacant cation
sites giving the gamma-alumina some unique properties. Gamma-alumina constitutes a part of the
series known as the activated, transition aluminas, so-called because it is one of a series of aluminas
that can undergo transition to different polymorphs. Santos et al. (Materials Research, 2000, vol. 3
(4), pp. 104-114) disclosed the different standard transition aluminas using Electron Microscopy
studies, whereas Zhou et al. (Acta Cryst, 1991, vol. B47, pp. 617-630) and Cai et al. (Phys. Rev.
Lett., 2002, vol. 89, pp. 235501) described the mechanism of the transformation of gamma-alumina
to theta-alumina.
The oxides of aluminum and the corresponding hydrates, can be classified according to
the arrangement of the crystal lattice; y-AkOa being part of the 7 series by virtue of a cubic close
packed (ccp) arrangement of oxygen groups. Some transitions within a series are known; for
example, low-temperature dehydration of an alumina trihydrate (gibbsite> 7-Al(OH)3) at 100°C
provides an alumina monohydrate (boehmite, y-A!O(OH)). Continued dehydration at temperatures
below 450°C in the 7 series leads to the transformation from boehmite to the completely dehydrated
y-AhO.!. Further heating may result in a slow and continuous loss of surface area and a slow
conversion to other polymorphs of alumina having much lower surface areas. Higher temperature
treatment ultimately provides a-A^O.i, a denser, harder oxide of aluminum often used in abrasives
and refractories. Unfortunately, when gamma-alumina is heated to high temperatures, the structure
of the atoms collapses such that the surface area decreases substantially. The most dense crystalline
form of alumina is alpha-alumina. Thus, alpha-alumina has the lowest surface area, but is the most
stable at high temperatures. The structure of alpha-alumina is less well suited to certain catalytic
applications, such as in the Fischer-Tropsch process because of a closed crystal lattice, which
imparts a relatively low surface area to the catalyst particles.
Alumina is ubiquitous as supports and/or catalysts for many heterogeneous catalytic
processes. Some of these catalytic processes occur under conditions of high temperature, high
pressure and/or high water vapor pressure. The prolonged exposure to high temperature typically
exceeding 1,000 "C, combined with a significant amount of oxygen and sometimes steam can result
in catalyst deactivation by support sintering. The sintering of alumina has been widely reported in
the literature (see for example Thevenin et al, Applied Catalysis A: General, 2001, vol. 212, pp.
189-197) and the phase transformation due to an increase in operating temperature is usually
accompanied by a sharp decrease in surface area. In order to prevent this deactivation
phenomenon!, various attempts have been made to stabilize the alumina support against thermal
deactivation (see Beguin et al., Journal of Catalysts, 1991, vol. 127, pp. 595-604; Chen et al.,
Applied Catalysis A: General, 2001, vol. 205, pp. 159-172).
The research focusing on the thermal stabilization of alumina led to the development of
high temperature-resistant materials such as hexaaluminates (Matsuda et al., 8th International
Congress on Catalysis Proceedings, Berlin, 1984, vol. 4, pp. 879-889; Machida et al., Chemistry
Letters, 1987, vol. 5, pp. 767-770) and the investigation of other potential oxide materials such as
perovskites, spinels, and garnets, which have been examined with respect to both the thermal
stability and catalytic performance.
Hexaaluminate structures have been shown to be effective structures for combustion
catalysts because they provide excellent thermal stability and a higher surface area than alphaalumina.
Of particular interest, Arai and coworkers in Japan have developed hexaaluminates and
substituted hexaluminates as combustion catalysts (Arai & Machida, Catalysis Today, 1991, vol.
10, pp. 81-95), and showed that the most promising stabilizer for combustion catalysts was barium
(Arai & Machida, Applied Catalysis A: General, 1996, vol. 138, pp. 161-176). The investigation of
the hexaaluminate material for the use of combustion has been described for example in Machida et
al. (Journal of Catalysis, 1990, vol. 123, pp. 477-485) and in Groppi et al. (Applied Catalysis A:
general, 1993, vol. 104, pp. 101-108). Machida et al. (Journal of American Ceramic Society, 1988,
vol. 71, pp.1142-1147) discovered that the crystal growth of one type of hexaaluminates, betaalumina,
also known as magnetoplumbite, was quite slow and anisotropic, and they proposed that
its anisotropic growth may be the reason why the hexaaluminate can retain a large surface area at
elevated temperatures. Arai and Machida (Catalysis Today, 1991, vol. 10, pp. 81-95) also disclosed
that the thermal resistance of hexaaluminates seems to be quite dependent on the preparation
procedures, primarily due to the difference of formation mechanism of hexaaluminates in various
procedures. Kato et al. (Journal of American Ceramic Society, 1987, vol. 71(7), pp. C157-C159)
disclosed a co-precipitation method to prepare mixtures of lanthanum and aluminum precursors,
which resulted in formation of lanthanum beta-alumina structures with high surface area.
Destabilization of the support is not the sole cause of catalyst deactivation at high
temperature. Stabilizing the catalytically active species on a thermally stable support is also needed.
When an active species is supported on an oxide support, solid state reactions between the active
species and the oxide support can take place at high temperature, creating some instability. That is
why Machida et al. (Journal of Catalysis, 1989, vol. 120, pp. 377-386) proposed the introduction of
cations of active species through direct substitution in the lattice site of hexaaluminates in order to
suppress the deterioration originating from the solid state reaction between the active species and
the oxide support. These cation-substituted hexaaluminates showed excellent surface area retention
and high catalytic activity (see the hexaaluminate examples with Sr, La, Mn combinations in
Machida et al., Journal of Catalysis, 1990, vol. 123, pp. 477-485). Therefore the preparation
procedure for high temperature catalysts is critical for thermal stability and acceptable surface area.
It has long been a desire in the catalyst support arts to have a form of alumina that has
high surface area like gamma-alumina and stability at high temperature like alpha-alumina. Such
a catalyst support would have many uses.
One such use is in the production of synthesis gas in a catalytic partial oxidation reactor.
Synthesis gas is primarily a mixture of hydrogen and carbon monoxide and can be made from the
partial burning of light hydrocarbons with oxygen. The hydrocarbons, such as methane or ethane
are mixed with oxygen or oxygen containing gas and heated. When the mixture comes in contact
with an active catalyst material at a temperature above an initiation temperature, the reactants
quickly react generating synthesis gas and a lot of heat. This very fast reaction requires only
milliseconds of contact of the reactant gases with the catalyst. The combination of high
exothermicity and very fast reaction time causes reactor temperatures to exceed 800 °C, often going
above 1,000 °C and even sometimes going above 1,200 °C. Since catalysts used in the partial
oxidation of hydrocarbons are typically supported, the support should be able to sustain this high
thermal condition during long-term operation. In other words, a stable catalyst support which
retains most of its surface area while enduring very high temperature, is desirable for long catalyst
life.
The reaction pathway for partial oxidation of methane to synthesis gas is still being
debated. Two alternate pathways have been proposed (Dissanayake et al., J. Catal., 1991, vol. 132,
pp. 117; Jin et al., Appl. Catal., 2000, vol. 201, pp. 71; Heitne et al., Catal. Today, 1995, vol. 24, pp.
211).
CH4 + 2 O2 -> CO2 + 2 H2O
CH4 + CO2 -> 2 CO + 2 H2 Scheme 1
CH4 + H2O -> CO + 3 H2
CH4 -> CHX + H
2 H -> H2 Scheme 2
O2 -> 2 O
CHX + O -> CO + Hx
These two pathways have come to be known as the combustion-reforming mechanism (Scheme 1),
and the direct partial oxidation mechanism (Scheme 2). In Scheme 1, methane is completely
oxidized to CO2 and water, and CO is a result of the reforming of water and CO2 with the residual
methane. In Scheme 2, methane is pyrolyzed over the catalyst to produce CO directly without the
pre-formation of CO2.
Weng, et al. (The Chemical Record, 2002, vol. 2, pp. 102-113) reported in situ Fourier
transform infrared (FTIR) studies of the catalytic partial oxidation (CPOX) mechanism of methane
over rhodium and ruthenium based catalysts supported on silica and alumina. They specifically
studied the influence of the catalyst pretreatment conditions, and their relationship with the
concentration of oxygen species on the surface of the catalysts under reaction conditions. They
concluded that a) the CPOX mechanism, whether based on Scheme 2 (i.e., -direct oxidation) or
based on Scheme 1 (combustion/reforming), is determined by the amount of O3" on the catalyst
surface; b) an oxidized catalyst, such as Rh2O.i, promotes the combustion/reforming mechanism
(Scheme 1), whereas rhodium in the reduced state will promote the direct pathway (Scheme 2); c)
rhodium on gamma-alumina under normal feed conditions of methane to molecular oxygen ratio in
the feed will contain mostly oxidized Rh, even if rhodium was pre-reduced; d) the reducibility of
rhodium is greatly affected by the support; and e) a lower reduction peak temperature, as measured
by temperature-programmed reduction (TPR), indicates a weaker Rh-O bond.
A weaker Rh-O bond would lead to easier removal of the surface oxygen, and therefore
the lower TPR temperature peak. During normal operating conditions, a weaker Rh-O bond should
promote reduced rhodium on the surface, which would favor a direct pathway. In turn, this would
lead to lower catalyst surface temperatures, which should slow the alumina phase transformation to
ultimately alpha-A^O^ (also slowing deactivation).
Roh et al. (Chemistry Letters, 2001, vol. 7, pp. 666-667) reported that nickel based partial
oxidation catalyst based on theta-alumina had high activity as well as high stability, and they
ascribed the excellent performance of these catalyst to the combination of the strong interactions
between nickel and theta-alumina and the coexistence of reduced and oxidized nickel species. Liu
et al. (Korean J. Chem. Eng., 2002, vol. 19, pp. 742-748) have also shown that a protective layer
between Ce-ZrO2 and theta-alumina is formed to suppress the formation of nickel-aluminate spinel
structures, which would result in catalyst deactivation. Moreover Miao et al. (Appl. Catal. A, 1997,
vol. 154, pp. 17-27) indicated that the modification with an alkali metal (Li, Na, K) oxide and a rare
earth metal (La, Ce, Y, Sm) oxide improved the ability of a nickel catalyst on alumina to suppress
carbon deposition over the catalyst during partial oxidation of methane. Therefore the type of
support used and the catalytic metal-support interactions are major factors in the catalyst stability
and can have an effect on the reaction mechanism.
In addition to the selection and careful preparation of the support, catalyst composition
also plays an important role in catalyst activity in catalytic partial oxidation of light hydrocarbons
and selectivity towards to the desired products. Noble metals typically serve as the best catalysts
for the partial oxidation of methane. Noble metals are however scarce and expensive, making their
use economically challenging especially when the stability of the catalyst is questionable. One of
the better known noble metal catalysts for catalytic partial oxidation comprises rhodium.
Rhodium-based syngas catalysts deactivate very fast due to sintering of both catalyst support and/or
metal particles. Prevention of any of these undesirable phenomena is well-sought after in the art of
catalytic partial oxidation process, particularly for successful and economical operation at
commercial scale.
It would therefore be highly desirable to create a thermally-stable high surface area
support with a metal from Groups 8, 9, or 10 of the Periodic Table of the Elements (based on the
new IUPAC notation, which is used throughout the present specification), particularly with
rhodium, loaded onto said support for highly productive long lifetime catalysts for the syngas
production, specifically via partial oxidation.
SUMMARY OF THE INVENTION
The current invention addresses the stability and durability of catalyst supports and
catalysts made therefrom for use in reactors operating at very high temperatures. Particularly the
present invention relates to a high surface area aluminum-based support comprising a transition
alumina phase and at least one stabilizing agent. The transition alumina phase preferably comprise
theta-alumina and may contain any other alumina phases comprised between low-temperature
gamma-alumina and high-temperature stable alpha-alumina. The transition alumina phase
preferably comprises mainly a theta-alumina phase. The alumina support preferably may further
comprise alpha-alumina, but is preferably substantially free of gamma-alumina. The stabilizing
agent comprises at least one element from Groups 1-14 of the Periodic Table of Elements, and is
preferably selected from the group consisting of rare earth metals, alkali earth metals and transition
metals. The inventive support also is thermally stable at temperatures above 800 °C.
The present invention also relates to a thermally stable aluminum-based material, which is
suitable as a catalyst support for high temperature reactions. The thermally stable aluminum-based
material includes a rare earth aluminate comprising at least one rare earth metal, wherein the rare
earth aluminate has a molar ratio of aluminum to rare earth metal (Al:Ln) greater than 5:1. The rare
earth aluminate with an Al:Ln greater than 5:1 preferably comprises a lanthanide metal selected
form the group consisting of lanthanum, praseodymium, cerium, neodymium, samarium, and
combinations thereof. In preferred embodiments, the rare earth aluminate comprises a
hexaaluminate-like structure or a beta-alumina-like structure, which comprises an Al:Ln between
11:1 and 14:1.
The present invention further relates to a thermally stable aluminum-based catalyst
support, wherein the thermally stable aluminum-based catalyst support comprises an aluminum
oxide phase selected from the group consisting of alpha-alumina, theta-alumina, or combinations
thereof; and a rare earth aluminate comprising a rare earth metal, wherein the alumina-like rare
earth aluminate has a molar ratio of aluminum to rare earth metal greater than 5:1. The rare earth
aluminate with a high molar ratio of aluminum to rare earth metal comprises from 100 wt% of the
support and more preferably less than 100 wt% down to as little as 1 wt% of the material weight in
the catalyst support. In preferred embodiments, the thermally stable support comprises between
about 1 wt% and about 50 wt% of said rare earth aluminate. In other embodiments, the thermally
stable aluminum-based catalyst support could comprise between 40 wt% and 100 wt% of rare earth
aluminate; and in some cases, the support is a rare earth aluminate or a mixture of rare earth
aluminates with a molar ratio of aluminum to rare earth metal greater than 5:1. The thermally
stable catalyst support could contain between about 1 wt% and about 20 wt% of rare earth metal;
preferably between about 1 wt% and about 10 wt% of rare earth metal. The rare earth aluminate
preferably comprises lanthanum, praseodymium, cerium, neodymium, samarium, or combinations
thereof. In preferred embodiments, the rare earth aluminate comprises a hexaaluminate-like
structure, a beta-alumina like structure, or combinations thereof. In these preferred embodiments,
the thermally stable catalyst support comprises at least one rare earth aluminate with an aluminumto-
rare earth molar ratio between 11:1 and 14:1; and at least one aluminum oxide phase selected
from alpha-alumina, theta-alumina, or combinations thereof. The thermally stable aluminum-based
material may further comprise a transition alumina, such as delta-alumina, eta-alumina, kappaalumina,
chi-alumina, rho-alumina, kappa-alumina, or any combinations thereof, but is preferably
substantially free of gamma-alumina.
The method for making a high surface area aluminum-based support includes applying at
least one stabilizing agent to an aluminum-containing precursor following by heat treatment,
wherein the heat treatment conditions are selected such that a portion of the aluminum-containing
precursor is transformed to a transition alumina and optionally to alpha-alumina, wherein the
transition alumina comprises delta-alumina, eta-alumina, kappa-alumina, chi-alumina, rho-alumina,
kappa-alumina, or any combinations thereof. The heat treatment can be also effective in
transforming another portion of the aluminum-containing precursor to an aluminate comprising at
least a portion of said stabilizing agent, and wherein the resulting support is preferably substantially
free of gamma-alumina. The stabilizing agent preferably comprises a rare earth metal. The
stabilizing agent preferably includes a lanthanide metal selected from the group consisting of
lanthanum, cerium, neodymium, praseodymium, and samarium, but may further include any
element from Groups 1-14 of the Periodic Table (new IUPAC notation) such as an alkali metal, an
alkali earth metal, a second rare earth metal, or a transition metal. The aluminum-containing
precursor comprises at least one material selected from the group consisting of an oxide of
aluminum, a salt of aluminum, an alkoxide of aluminum, a hydroxide of aluminum, and
combinations thereof.
The present invention also includes a method for making a thermally stable aluminumbased
catalyst support suitable for use in a high temperature reaction. This method includes
applying at least one rare earth metal compound to an aluminum-containing precursor; and treating
by heat the applied precursor, wherein the heat treatment conditions are selected such that at least a
portion of the aluminum-containing precursor is transformed to an aluminate comprising at least a
portion of said rare earth metal, and wherein the rare earth aluminate comprises an aluminum-torare
earth metal molar ratio greater than 5:1. The heat treatment is performed in a manner effective
to obtain about 1 wt% and 100 wt% of said rare earth aluminate in the thermally stable catalyst
support. In preferred embodiments, the heat treatment is performed in a manner effective to obtain
between about 1 wt% and about 50 wt% of said rare earth aluminate in the thermally stable support.
In other embodiments, the heat treatment is performed in a manner effective to obtain between 40
wt% and 100 wt% of rare earth aluminate in the thermally stable catalyst support. In some alternate
embodiment, the heat treatment is performed in a manner effective to transform all of the
aluminum-containing precursor to at least one rare earth aluminate with an aluminum-to-rare earth
metal molar ratio greater than 5:1. The application and heating steps preferably employ an
impregnation technique and calcination in an oxidizing atmosphere, respectively. Additionally, the
heat treatment step is effective to transform another portion of said aluminum-containing precursor
to an aluminum oxide phase comprising alpha-alumina, a transition alumina, or combinations
thereof, wherein the transition alumina comprises delta-alumina, eta-alumina, kappa-alumina, chialumina,
rho-alumina, kappa-alumina, theta-alumina, or any combinations thereof. The transition
alumina comprises preferably theta-alumina.
The invention further includes a catalyst comprising a catalytically active metal selected
from the group consisting of rhodium (Rh), ruthenium (Ru), indium (Ir), platinum (Pt), palladium
(Pd), and rhenium (Re), on a thermally stabilized support wherein the thermally stabilized support
comprises theta-alumina, a rare earth aluminate with an aluminum to rare earth metal molar ratio
greater than 5:1, or combinations thereof.
More particularly, the invention includes a catalyst comprising a catalytically active metal
selected from the group consisting of rhodium (Rh), ruthenium (Ru), iridium (Ir), platinum (Pt),
palladium (Pd), and rhenium (Re), on a thermally stabilized support wherein the thermally
stabilized support comprises between about 1 wt% and 100 wt% of a rare earth aluminate with an
aluminum to rare earth metal molar ratio greater than 5:1.
A more specific embodiment of the invention relates to a partial oxidation catalyst with an
active ingredient selected from the group consisting of rhodium, iridium, and ruthenium; and an
optional promoter loaded onto a thermally stable support, wherein said support includes an alumina
phase selected from the group consisting of alpha-alumina, theta-alumina, or any combinations
thereof; and between about 1 wt% and about 50 wt% of a rare earth aluminate with a molar ratio of
aluminum to said rare earth metal greater than 5:1. In other embodiments, the thermally stable
aluminum-based catalyst support could comprise more than 40 wt% of rare earth aluminate and less
than 100 wt% of rare earth aluminate.
The present invention can be more specifically seen as a support, process and catalyst for
a partial oxidation reaction, wherein the support comprises a rare earth aluminate having a molar
ratio of aluminum to rare earth metal greater than 5:7, and wherein the rare earth aluminate
preferably comprises an element selected from the group consisting of lanthanum, cerium,
praseodymium, samarium, and neodymium. The support may comprise between 1 wt% to 100 wt%
of the rare earth aluminate. In preferred embodiments, the thermally stable support comprises
between about 1 wt% and about 50 wt% of said rare earth aluminate. In other embodiments, the
thermally stable aluminum-based catalyst support could comprise between 40 wt% and 100 wt% of
the rare earth aluminate; and in some alternate embodiments, the support is a rare earth aluminate or
a mixture of rare earth aluminates with an aluminum to rare earth metal molar ratio greater than 5:1.
The supported catalyst comprises at least one catalytically active metal selected from the group
consisting of rhodium, ruthenium, iridium, platinum, palladium, and rhenium, preferably selected
from the group consisting of rhodium, iridium, and ruthenium, and optionally the catalyst can also
comprise a promoter.
More particularly, the invention relates to processes for the catalytic partial oxidation of
light hydrocarbons (e.g., methane or natural gas) to produce primarily synthesis gas and the use of
such supported catalysts to make carbon monoxide and hydrogen under conditions of high gas
hourly space velocity, elevated pressure and high temperature.
The process for making synthesis gas comprises converting a gaseous hydrocarbon stream
and an oxygen-containing stream over a partial oxidation catalyst, to make a product stream
comprising CO and H2, wherein said partial oxidation catalyst includes an active ingredient
comprising rhodium, iridium, platinum, palladium, ruthenium, or combinations thereof; and a
support comprising a rare earth aluminate, said rare earth aluminate having a molar ratio of
aluminum to rare earth metal greater than 5:1. The support could comprise between about 1 wt%
and 100 wt% of said rare earth aluminate, preferably between about 1 wt% and about 50 wt% of
said rare earth aluminate. In other embodiments, the support could comprise between 40 wt% and
100 wt% of the rare earth aluminate; and in some alternate embodiments, the support is a rare earth
aluminate or a mixture of rare earth aluminates with an molar ratio of aluminum to rare earth metal
greater than 5:1. The rare earth metal is selected from the group consisting of lanthanum,
neodymium, praseodymium, cerium, and combinations thereof, and the support could comprise
between about 1 wt% and about 20 wt% of the rare earth metal, but preferably between about 1
wt% and about 10 wt% of the rare earth metal. The support may further comprise an aluminum
oxide such as alpha-alumina, a transition alumina, or combinations thereof, wherein the transition
alumina comprises delta-alumina, eta-alumina, kappa-alumina, chi-alumina, rho-alumina, kappaalumina,
theta-alumina, or any combinations thereof. The transition alumina comprises preferably
theta-alumina. The support may further comprise an oxide of said rare earth metal and/or an
aluminate of said rare earth aluminate with a low aluminum to rare earth metal molar ratio, such as
below 2:1.
The present invention further relates to catalysts and processes for the conversion of
gaseous light hydrocarbons for producing a hydrocarbon product, comprising primarily
hydrocarbons with 5 carbons atoms or more (Cs+).
BRIEF DESCRIPTION OF THE DRAWINGS
For a more detailed understanding of the preferred embodiments, reference is made to the
accompanying drawings, wherein:
Figure 1 represents the temperature programmed reduction (TPR) profile of a catalyst
comprising mainly theta-alumina according to this invention;
Figures 2a, 2b and 2c represent the XRD analysis of materials comprising various
loadings of lanthanum applied to gamma-alumina and calcined at different temperatures;
Figures 3a and 3b represent the effect of lanthanum loadings on the resulting surface area
and pore volume (respectively) of catalyst supports made at two different calcinations temperatures;
and
Figure 4 represents the performance data for synthesis gas production from a catalyst
made according to a preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention is based on the surprising discovery that a supported rhodium-based
catalyst supported on an aluminum-based matrix modified with a lanthanum compound showed
excellent performance with conversion and selectivities above 90%, and a sustainable activity over
more than 300 hours on line while in contact with natural gas and molecular oxygen under suitable
conditions for catalytic partial oxidation, namely at high temperatures and at high pressure. It was
found that this catalyst i n i t i a l ly comprised about 65% theta-alumina phase, some small amount of
alpha-alumina (10%), but was free of gamma-alumina. In addition the catalyst comprised a good
portion of lanthanum aluminum mixed oxide compounds (La-Al-O) with a hexaaluminate-like
structure (18%). This hexaaluminate-like structure comprised the majority of the lanthanum.
Moreover this catalyst showed a low reduction peak temperature in a TPR analysis (shown in
Figure 1), much lower than similar catalysts which comprised supports with less theta-alumina
phase, more gamma-alumina, minimal amount of rare earth aluminates, and substantially almost no
alpha-alumina, or for similar catalysts which comprised supports of mainly alpha-alumina.
As described in Weng et al. (The Chemical Record, 2002, vol. 2, pp. 101-113), it is
believed that a low TPR peak temperature is an indication of a loose Rh-O bond, thereby favoring
the formation of reduced rhodium on the surface of the catalyst, which in turn favors the direct
mechanism of partial oxidation (Scheme 2). The direct mechanism generates a lot less heat (the heat
of CH4+ !/2 Oi reaction is -6.6 kcal/mol) whereas the combustion reaction in Scheme 1 generates
much more heat (as the heat of CH4+ 2 O? is -191.3 kcal/mol). Therefore the direct mechanism
should produce a cooler catalyst surface temperature. Without wishing to be bound to this theory,
the Applicant believes that the presence of a theta-alumina phase might increase oxygen mobility,
increases the fraction of rhodium in reduced state, increases the conversion of methane (and other
light hydrocarbons) via the direct mechanism and thereby reduces the catalyst surface temperature.
It is expected that a cooler catalyst surface temperature prevents or minimizes the formation of
carbonaceous deposit on the catalyst surface, which is one of the source of catalyst deactivation.
Another source of catalyst deactivation is the phase transformation of alumina to ultimately alphaalumina
and concurring support disintegration, surface cracking and/or loss of surface area.
Therefore a cooler catalyst surface temperature should also slow the rate the phase transformation
of alumina, which is thermodynamically favored by increase in temperature.
Modifying alumina (ANO?) with some rare earth metals has been proven to be effective in
stabilizing the surface area of modified ANO}. Doping a gamma-alumina (y-AljO.-O with certain
metal oxides such as for example lanthanum oxide (La2(>0 inhibits or retards the phase
transformation of gamma-alumina phase to theta-alumina (G-AbOj) phase and eventually to alphaalumina
(a-ANO.-O phase and thus stabilizes the surface area and pore structure of the alumina
material even at high calcination temperatures above 1,000 °C. Not only doping the surface of
gamma-alumina (y-AliOj) can stabilize the surface structure of aluminum oxide (AliO.-O and thus
delay the phase transformation to alpha alumina, but also it can slow down the sintering at high
temperatures. The driving force for sintering is the minimization of surface free energy, and thus
thermodynamically, sintering is an irreversible process in which a free energy decrease is brought
about by a decrease in surface area. Sintering is usually initiated on the particle surface at elevated
temperature, in a range where surface atoms become mobile and where diffusional mass transport is
appreciable. The formation of Ln-Al-O mixed oxide compounds could inhibit the surface diffusion
of species responsible for sintering, and thereby may be one of the key stabilization factors on an
alumina surface at high temperatures.
The formation of highly thermal stable La-Al-O mixed oxide compounds such as those of
hexaaluminate-type structure should also ultimately help maintain a relatively high surface area.
However, it is not clear from the literature that the formation of lanthanum aluminates with
hexaaluminate-like or beta-alumina structures from an alumina precursor modified with lanthanum
would explain an improved thermal stability of this catalyst. Beguin et al (1991) in fact disclosed
that the formation of lanthanum beta-alumina structures was associated with the loss of the
stabilizing effect of lanthanum on an alumina-based material; and therefore showed that the
formation of lanthanum beta-alumina structures was detrimental to the stabilization effect
associated with the modification of alumina by lanthanum. Oudet et al (Applied Catalysis, 1991,
vol. 75, pp. 119-132) attributed the stabilization of alumina by lanthanum to the nucleation of a
cubic lanthanum aluminum oxide structure (LaAlO.i) on the surface of the alumina support, which
inhibits the surface diffusion of species responsible for sintering.
As for the method of preparation, Schaper et al. (Applied Catalysis, 1983, vol. 7, pp. 211-
220) who studied the influence of addition of lanthanum (0-5 mol% La^O^) on the thermal stability
of gamma-alumina between 800 and 1,100 °C, did not observed the formation of lanthanum
hexaaluminate even though they observed a retardation in the sintering of gamma-alumina by the
presence of perovskite-type lanthanum aluminate (LaAlOi). The discrepancy between the formation
of lanthanum hexaaluminate structures in Kato et al. (1987) and the absence of lanthanum
hexaaluminate structures in Schaper et al (1983) is most likely attributed to the differences of the
preparation method. Kato et al. mentioned that, with the impregnation technique, the higher
concentration of lanthanum at the surface layer of the alumina phase probably tends to favor the
formation of a lanthanum aluminate with a low aluminum-to-lanthanum ratio. However, according
to this invention, lanthanum aluminates with a high aluminum-to-lanthanum ratio were being
formed using an impregnation technique. It was quite unexpected, first to find that lanthanum
hexaaluminate-like structures were formed in a catalyst support made by an impregnation technique
on a lanthanum precursor on a gamma-alumina, and that, second, the presence of lanthanum
hexaaluminate-like structures in a catalyst support did result in a more stable performance of the
catalyst made therefrom. Therefore, this invention relates to a catalyst support, which comprises a
rare earth aluminate with a high aluminum-to-rare earth molar ratio, and to catalysts made
therefrom used in high temperature environments which show unexpected good thermal stability
and have a greater surface area than those catalysts supported on alpha-alumina under similar
operating conditions.
Herein will be described in detail, specific embodiments of the present invention, with the
understanding that the present disclosure is to be considered an exemplification of the principles of
the invention, and is not intended to limit the invention to that illustrated and described herein. The
present invention is susceptible to embodiments of different forms or order and should not be
interpreted to be limited to the specifically expressed methods or compositions or applications
contained herein. In particular, various embodiments of the present invention provide a number of
different combinations of features to generate high surface area supports for high temperature
applications, which also comprise very good thermal stability.
SUPPORTS
The thermally stable supports according to this invention can have different forms such as
monolith or particulate or have discrete or distinct structures. The term "monolith" as used herein is
any singular piece of material of continuous manufacture such as solid pieces of metal or metal
oxide or foam materials or honeycomb structures. The terms "distinct" or "discrete" structures or
units, as used herein, refer to supports in the form of divided materials such as granules, beads, pills,
pastilles, pellets, cylinders, trilobes, extrudates, spheres or other rounded shapes, or another
manufactured configuration. Alternatively, the divided material may be in the form of irregularly
shaped particles. Preferably at least a majority (i.e., >50%) of the particles or distinct structures
have a maximum characteristic length (i.e., longest dimension) of less than six millimeters,
preferably less than three millimeters. The support is preferably in discrete structures, and
particulates are more preferred.
Thermally stable catalyst support comprising a rare earth aluminate with Al:Ln > 5:1
This invention relates to a thermally stable aluminum-based support comprising a rare
earth aluminate with a high aluminum-to-rare earth molar ratio. The aluminum-to-rare earth molar
ratio (AI:Ln) is greater than 5:1; preferably greater than about 10; and more preferably between
about 11:1 and about 14:1. Preferably the thermally stable aluminum-based contains at least one
rare eaith aluminate selected from a rare earth hexaaluminate-like structure and/or a rare earth betaalumina-
like structure.
The thermally stable aluminum-based support may comprise between 1 wt% to 100 wt%
of the rare earth aluminate with a high Al:Ln ratio. In preferred embodiments, the thermally stable
support comprises between about 1 wt% and about 50 wt% of said rare earth aluminate; more
preferably between about 5 wt% and about 45 wt% of the rare earth aluminate; and still more
preferably between about 10 wt% and about 40 wt% of the rare earth aluminate. In other
embodiments, the thermally stable aluminum-based catalyst support could comprise between 40
wt% and 100 wt% of the rare earth aluminate; and in some alternate embodiments, one or more rare
earth aluminates with high aluminum-to-rare earth molar ratios (greater than 5:1) comprises 100
wt% of the support. The support in the catalyst could comprise between about 1 wt% and 100 wt%
of said rare earth aluminate. In preferred embodiments, the support in the catalyst comprises
between about 1 wt% and about 50 wt% of said rare earth aluminate. In other embodiments, the
support in the catalyst could comprise more than 40 wt% of rare earth aluminate, i.e., between 40
wt% and 100 wt% of rare earth aluminate; and in some cases, the support is a rare earth aluminate
or a mixture of rare earth aluminates with a molar ratio of aluminum to rare earth metal greater than
5:1. It should be readily appreciated that there are preferences within the 1 wt%-100 wt% range for
the rare earth aluminate content of the support depending on the desired properties of the support.
The support should contain between about 1 wt% and about 20 wt% of rare earth metal;
preferably between about 1 wt% and about 10 wt% of rare earth metal. The rare earth aluminate
preferably comprises a hexaaluminate-like structure, a beta-aluminate-like structure, or
combinations thereof, such as a lanthanum hexaaluminate or a lanthanum beta-alumina. The rare
earth aluminate comprises a rare earth metal selected from the group consisting of lanthanum,
neodymium, praseodymium, and combinations thereof. In preferred embodiments, the rare earth
aluminate comprises preferably La, and optionally Sm.
It is envisioned that the rare earth aluminate with a high Al:Ln molar ratio could comprise
different species of aluminates with varying AI:Ln molar ratios, as long as the different ratios are all
greater than 5:1; or that the rare earth aluminate could comprise combinations of different rare earth
aluminates of similar structure but comprising different rare earth metals. It should be appreciated
that the rare earth aluminate could comprise any combinations of these features. For example, the
support could comprise one rare earth aluminate with a Al:Ln ratio of 11:1 and an aluminate of the
same rare earth metal with a higher Al:Ln ratio of 12:1. In another example, the support could
comprise aluminates of two or more rare earth metals all with an AI:Ln ratio of 11:1.
The thermally stable aluminum-based support could comprise between about 1 wt% and
about 20 wt% of the rare earth metal; but preferably between about 1 wt% and about 10 wt%; more
preferably between about 2 wt% and about 8 wt%; and still more preferably between about 4 wt%
and about 8 wt%.
This rare earth metal content corresponds to rare earth oxide loading between about 1.2
wt% and about 23 wt% of the rare earth oxide; preferably between about 1.2 wt% and about 12
wt%; more preferably between about 2.4 wt% and about 9.4 wt%; and still more preferably
between about 4.7 wt% and about 9.4 wt%. This rare earth metal weight content also corresponds to
rare earth oxide molar content between about 0.3 mol% and about 7 mol% of the rare earth oxide;
preferably between about 0.3 mol% and about 3.5 mol% of the rare earth oxide; more preferably
between about 0.6 mol% and about 2.6 mol%; and still more preferably between about 1.2 mol%
and about 2.6 mol%. The rare earth oxide molar content is calculated as the ratio of the number of
moles of rare earth oxide over the total number of moles of rare earth oxide and aluminum oxide.
The selection of the rare earth loading on the support is dependent on the desirable range
of the surface area of the support. There seems to be an optimum range of loadings for which the
surface area is maximized as illustrated in Figures 3a and 3b. Beyond that range, thermal stability
can still be achieved, but the support would have a lower surface area.
The thermally stable aluminum-based support may also comprise an oxide of a rare earth
metal. For example, the rare earth aluminate with a high Al:Ln ratio might comprise only a fraction
of the loaded (or applied) rare earth metal, and the other fraction of the loaded rare earth metal may
form a rare earth metal oxide.
The thermally stable aluminum-based support may also comprise other rare earth
aluminate structures with a low aluminum-to-rare earth metal molar ratio lower than 5:1, such as
perovskite structures, monoclinic structures, or garnet structures with typically Al:Ln ratios less
than 2:1.
According to another embodiment of this invention, the thermally stable catalyst support
further comprises an alumina phase selected from the group consisting of alpha-alumina, thetaalumina
or any combinations thereof. The rare earth aluminate with a high Al:Ln molar ratio and
the alumina phase could be intimately mixed, or the rare earth aluminate could coat the alumina
phase partially or completely. A surface layer comprising said rare earth aluminate with a high
AI:Ln molar ratio preferably covers either partially or completely the alumina phase surface; with a
complete coverage being more preferred. Therefore a person skilled in the art could select a method
of preparation to achieve a well-mixed rare earth aluminate and alumina combination, such as via a
sol-gel method or a co-precipitation method, or to achieve a coating of rare earth aluminate over the
alumina surface, such as via impregnation or chemical vapor deposition. For the later techniques,
which result in a coating of rare earth aluminate over the alumina surface, the rare earth loading
should be selected such that a desired coating is achieved. For example, one can estimate the
necessary amount of rare earth aluminate to completely cover the surface of the support precursor
by one monolayer of said rare earth aluminate.
In preferred embodiments, the thermally stable catalyst support comprises a rare earth
hexaaluminate structure, a rare earth beta-alumina structure, or combinations thereof.
The rare earth aluminate could comprise a chemical formula of LnAlyOz, wherein Al and
O represent aluminum atoms and oxygen atoms respectively; Ln comprises lanthanum,
neodymium, praseodymium, cerium, or combinations thereof; y is between 11 and 14; and z is
between 18 and 23.
The rare earth aluminate could comprise a chemical formula of (LmO^.yCANOrO, where
Ln comprises one rare earth metal chosen from lanthanum, neodymium, praseodymium, cerium, or
combinations thereof; and y is between 11 and 14.
In addition to comprising a rare earth metal, the rare earth aluminate may further comprise
an element from Groups 1-L7 of the Periodic Table; particularly preferred, the rare earth aluminate
may further comprise nickel, magnesium, barium, potassium, sodium, manganese, a second rare
earth metal (such as samarium), or any combinations thereof.
The rare earth aluminate preferably could comprise a chemical formula characterized by
MAlyO,. wherein Al and O represent aluminum atoms and oxygen atoms respectively; y=ll-14;
z=18-23; and wherein M preferably comprises at least one rare earth metal selected from lanthanum
(La), cerium (Ce), praseodymium (Pr), neodymium (Nd), or combinations thereof. M could also
comprise two or more elements from Groups 1-17 of the Periodic Table, with at least one of them
being a rare earth metal. The other element is selected from Groups 1-14, and preferably comprises
nickel, magnesium, barium, potassium, sodium, manganese, a second rare earth metal (such as
samarium), or any combinations thereof. In preferred embodiments, M comprises preferably La,
and optionally Sm. In some embodiments, M comprises both La and Sm.
In more preferred embodiments, the rare earth aluminate comprises a lanthanum
hexaaluminate. The lanthanum hexaaluminates have a chemical formula of (LaiOsXyXAUO.-O,
where La represents lanthanum, and y is between 11 and 14.
The thermally stable support may further comprise an oxide of said rare earth metal, said
rare earth oxide consisting essentially of rare earth metal atoms and oxygen atoms. The oxide of
said rare earth metal (Ln) preferably has a chemical formula of Ln^O.-?. It should be appreciated that
in some cases, the combination of both rare earth aluminates and rare earth oxides in the catalyst
support might be desirable to improve support stability.
In addition, according to one embodiment, there is an expectation that a less acidic surface
layer may encourage the formation of more uniform crystallites of a catalytically active metal
resulting in smaller metal crystallite sizes. The catalysts made from these thermally stable catalyst
supports of the present invention are expected to have excellent stability, high activity and extended
catalyst lifetimes, while maintaining desirable selectivity, pore structure and particle size.
This rare earth modified support with enhanced thermal stability which comprises a rare
earth aluminate with a high Al:Ln molar ratio, has an initial minimum BET surface area of 2 nr/g,
preferably greater than 5 m2/g, more preferably greater than about 7 m2/g, but no more than 30
nr/g.
High surface area catalyst support comprising at least theta-alurnina
In another embodiment, a high surface area catalyst support is obtained by heat treatment
of an alumina precursor with a stabilizing agent. The high surface area alumina support comprises a
transition alumina comprising at least one alumina polymorph between gamma-alumina and alphaalumina,
but excluding gamma-alumina and alpha-alumina. The transition alumina preferably
comprises theta-alumina and is preferably substantially free of gamma-alumina. The high surface
area alumina support may further comprise alpha-alumina and/or an aluminate of said stabilizing
agent. The stabilizing agent comprises at least one element selected from the group consisting of
boron, silicon, gallium, selenium, rare earth metals, transition metals, and alkali earth metals,
preferably selected from the group consisting of boron (B), silicon (Si), gallium (Ga), selenium
(Se), calcium (Ca), zirconium (Zr), iron, (Fe), cobalt (Co), manganese (Mn), magnesium (Mg), and
the rare earth elements, i.e., scandium (Sc), ytrium (Y), lanthanum (La), cerium (Ce),
praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),
gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),
ytterbium (Yb), and lutetium (Lu). More preferably the stabilizing agent comprises La, Sm, Nd, Pr,
Ce, Eu, Yb, Si, Ce, Mg, Ca, Mn, Co, Fe, Zr, or any combinations thereof. Most preferably, the
stabilizing agent comprises La, Sm, Nd, Pr, Ce, Eu, Yb, Si, Mg, Co, or any combinations thereof.
In addition, promoters may be applied to the stabilized support. Such deposited promoters may also
maintain an improved dispersion on active species during catalyst preparation.
According to one embodiment of the present invention, a high surface area alumina
comprising mostly theta-alumina, which is modified with a rare earth metal and/or a rare earth
metal oxide, serves as an improved support for synthesis gas production catalysts used in reactors
operating at high-pressure and high-temperature. The catalyst support thus obtained tends to be
more resistant to phase deterioration under highly thermal conditions than gamma-alumina, and yet
provide greater surface area than alpha-alumina. This thermally stable catalyst support is porous
and is suitable for use in high temperature environments. This surface area is typically higher that
alpha-alumina, and its thermal stability greater than gamma-alumina. It has a surface area greater
than 2 meter square per gram (m2/g), preferably between about 5 nr/g and 100 nr/g, more
preferably between about 20 m2/g and 80 nr/g.
One stabilized alumina support according to one embodiment of this invention preferably
comprises, when fresh, at least 50% theta-alumina phase, preferably between about 60% and 75%
theta-alumina; not more than about 20% alpha-alumina, and is preferably substantially free of
gamma-alumina, i.e., less than about 5% gamma-alumina. In addition the support may comprise
between about 1 wt% and about 50 wt% of a rare earth aluminate with a molar ratio of aluminum to
rare earth metal greater than 5:1.
CATALYSTS
The present invention pertains to catalysts comprising one catalytically active metal on
high surface area alumina supports or thermally stabilized aluminum-based supports, wherein the
catalysts are active for the conversion of light hydrocarbons to synthesis gas. In particular, the
current invention addresses the stability and durability of catalyst supports and catalysts made
therefrom for use in catalytic partial oxidation reactors operating at high temperatures and
pressures.
Catalysts based on high surface area supports comprising at least theta-alumina
According to one embodiment of the present invention, an alumina support comprising
mostly theta-alumina, which is modified with one rare earth oxide, serves as an improved support
for synthesis gas production catalysts used in reactors operating at high-pressure and hightemperature.
The catalyst support thus obtained tends to be more resistant to phase deterioration
under highly thermal conditions than gamma-alumina. The presence of mostly theta-alumina may
result in a weaker R-O bond, where R is the catalytically active metal. The weaker R-O bond
should lead to easier removal of the surface oxygen, and therefore a lower TPR temperature peak.
During normal operating conditions, a weaker R-O bond would promote reduced active metal on
the surface, which would favor a direct oxidation pathway (Scheme 2). In turn, this would lead to
lower catalyst surface temperatures, which will slow the phase transformation of alumina to alphaalumina
(also slows deactivation).
Moreover, interactions between catalytically active metal and the alumina support are
affected by the presence of the rare earth oxide. Without wishing to be bound to a particular theory,
it is believed that the active metal-support interaction in catalysts supported on rare earth modified
alumina, for example La^Orrnodified AhO^ is stronger than that in the similar catalysts supported
on unmodified AbO^, and that this strong metal-support interaction in La2Ormodified A12O^
supported catalysts might be another reason for the unusually high catalyst stability.
The present invention also relates to improved catalyst compositions using a stabilized
alumina support, as well as methods of making and using them, wherein the stabilized comprises a
transition alumina phase (excluding gamma-alumina) between the low-temperature transition
gamma-alumina and the high-temperature stable alpha-alumina, wherein the transition alumina is
preferably theta-alumina, but could comprise low amounts of other transition alumina phases. In
addition the stabilized alumina may comprise rare earth aluminates. The catalyst is supported on a
stabilized alumina with an initial minimum BET surface area of 2 m2/g, preferably greater than 5
m2/g, more preferably greater than 10 nr/g, but no more than 30 m2/g, after high temperature
treatment or calcination. Preferably the stabilized alumina is modified with compounds of
lanthanide metals, such as for example, compounds of lanthanum, samarium, praseodymium,
cerium, or neodymium. Without wishing to be bound to a particular theory, it is believed that the
metal-support interaction in catalysts supported on for example La^CVmodified AbO} is stronger
than that in the catalyst supported on unmodified AbO}, and that this strong metal-support
interaction in La^O.i-modified Al^Oi supported catalysts might be responsible for the unusually high
catalyst stability.
Catalysts based on supports comprising a rare earth aluminate with a Al:Ln >5:1
According to another embodiment of the present invention, an alumina-containing support
comprising a rare earth aluminate with an aluminum-to-rare earth metal molar ratio greater than 5:1,
serves as an improved support for synthesis gas production catalysts used in reactors operating at
high-pressure and high-temperature. The catalyst support thus obtained tends to be more resistant
to phase deterioration under highly thermal conditions than gamma-alumina, and offers greater
surface area than alpha-alumina. In addition to the presence of an alumina phase (either thetaalumina,
alpha-alumina, or both), the presence of rare earth hexaaluminate structures is an
indication that a distinct ordered aluminum structure comprising at least one rare earth metal is
being formed during the preparation of the catalyst support. The formation of hexaaluminates
comprising a rare earth metal during the preparation of the support described herein is believed to
be another potential source of stabilization of the support, as the presence of rare earth aluminates
most likely also affect the active metal-support interactions.
Catalysts based on high surface area thermally stable supports
This invention also relates to a partial oxidation catalyst comprising an active ingredient
selected from the group consisting of rhodium, iridium, platinum, palladium, and ruthenium; an
optional promoter; and a support comprising a rare earth aluminate with a molar ratio of aluminum
to rare earth metal greater than 5:1. The support in the catalyst could comprise between about 1
wt% and 100 wt% of said rare earth aluminate. In preferred embodiments, the support in the
catalyst comprises between about 1 wt% and about 50 wt% of said rare earth aluminate. In other
embodiments, the support in the catalyst could comprise more than 50 wt% of rare earth aluminate,
i.e., between 40 wt% and 100 wt% of rare earth aluminate; and in some cases, the support is a rare
earth aluminate or a mixture of rare earth aluminates with a molar ratio of aluminum to rare earth
metal greater than 5:1, such as a lanthanum hexaaluminate or a lanthanum beta-alumina. The
support should contain between about 1 wt% and about 20 wt% of rare earth metal; preferably
between about 1 wt% and about 10 wt% of rare earth metal. The rare earth aluminate preferably
comprises a hexaaluminate structure, a beta-aluminate structure, or combinations thereof. The rare
earth aluminate comprises a rare earth metal selected from the group consisting of lanthanum,
neodymium, praseodymium, and combinations thereof. In preferred embodiments, the rare earth
aluminate comprises preferably La, and optionally Sin.
A particularly preferred embodiment discloses a partial oxidation catalyst comprising an
active ingredient selected from the group consisting of rhodium, iridium, platinum, palladium, and
ruthenium; an optional promoter; and a support comprising an alumina phase selected from the
group consisting of alpha-alumina, theta-alumina, or any combinations thereof; and a rare earth
aluminate with a molar ratio of aluminum to rare earth metal greater than 5:1, and wherein the
support comprises between about 1 wt% and about 50 wt% of said rare earth aluminate. The rare
earth aluminate preferably comprises a hexaaluminate-like structure, a beta-aluminate-like
structure, or any combinations thereof. The rare earth aluminate comprises a rare earth metal
selected from the group consisting of lanthanum, neodymium, cerium, praseodymium, and
combinations thereof. In preferred embodiments, the rare earth aluminate comprises preferably La,
and optionally Sm.
Another embodiment discloses a partial oxidation catalyst comprising an active ingredient
selected from the group consisting of rhodium, iridium, and ruthenium; an optional promoter; and a
rare earth aluminate, wherein the rare earth aluminate comprises an Al:Ln molar ratio between 11:1
and 14:1. The rare earth aluminate preferably has a hexaaluminate like structure, a beta-aluminate
like structure, or combinations thereof. The rare earth aluminate preferably comprises a rare earth
metal selected from the group consisting of lanthanum, neodymium, cerium, praseodymium, and
combinations thereof. In preferred embodiments, the rare earth aluminate comprises preferably La,
and optionally Sm. The active ingredient and the optional promoter are preferably supported on said
rare earth aluminate with a high Al:Ln molar ratio.
All catalysts according to this invention can be used for producing synthesis gas, and
therefore should comprise an active metal selected from the group consisting of metals from Groups
8, 9, or 10 of the Periodic Table, rhenium, tungsten, molybdenum, and any mixtures thereof.
Preferably the catalyst used for producing synthesis gas comprises rhodium, ruthenium, iridium,
platinum, palladium, rhenium, or any combinations thereof. More preferably the catalyst used for
producing synthesis gas comprises rhodium, ruthenium, iridium, or any combinations thereof.
In some embodiments, the active metal may be comprised in an alloy form, preferably a
rhodium alloy. Although not wishing the scope of this application to be limited to this particular
theory, the Applicants believe that alloying rhodium with other metals appears to sustain the
resistance of rhodium catalysts to sintering, and therefore to allow the Rh alloy catalysts to
deactivate at a slower rate than syngas catalysts containing only rhodium. Suitable metals for the
rhodium alloy generally include but are not limited to metals from Groups 8, 9, or 10 of the
Periodic Table, as well as rhenium, tantalum, niobium, molybdenum, tungsten, zirconium and
mixtures thereof. The preferred metals for alloying with rhodium are ruthenium, iridium, platinum,
palladium, tantalum, niobium, molybdenum, rhenium, tungsten, cobalt, and zirconium, more
preferably ruthenium, rhenium, and iridium. In accordance with the present invention, the loading
of the active metal in the catalyst is preferably between 0.1 and 50 weight percent of the total
catalyst weight (herein wt%).
In a preferred embodiment of the invention, the catalyst comprises rhodium as the active
metal. The rhodium content in the catalyst is between about 0.1 wt% to about 20 wt%, preferably
from about 0.5 wt% to about 10 wt %, and more preferably from about 0.5 wt% to about 6 wt%.
When a rhodium alloy is used, the other metal in the rhodium alloy preferably comprises from
about 0.1 wt% to about 20 wt % of the catalyst, preferably from about 0.5 wt% to about 10 wt %,
and more preferably from about 0.5 wt% to about 5 wt%. The other metal in the rhodium alloy
could be iridium, ruthenium, or rhenium.
In another embodiment of the invention, the catalyst comprises ruthenium as the active
metal. The ruthenium content in the catalyst is between about 0.1 to 15 wt %, preferably from about
1 to about 8 wt %, and more preferably from about 2 to about 5 wt %.
The catalyst structure employed is characterized by having a metal surface area of at least
0.5 square meters of metal per gram of catalyst structure, preferably at least 0.8 nr/g. Preferably
the metal is rhodium and the rhodium surface area at least 0.5 square meters of rhodium per gram of
supported catalyst, preferably at least 0.8 rrr/g.
Catalyst compositions may also contain one or more promoters. In some embodiments
when one active metal is rhodium, rhenium, ruthenium, palladium, platinum, or iridium, the
promoter comprises an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, preferably Sm, Eu, Pr and Yb. The introduction of a
lanthanide oxide, especially StrbO.i, on the stabilized alumina support surface before deposition of
active metal is believed to further enhance the metal-support interaction, and that the active metal
also disperses better on the surface of A12O3 modified with La^O} and/or SirbO;,. According to some
embodiments with the use of a rhodium alloy, the presence of a promoter metal can be omitted
without detriment to the catalyst activity and/or selectivity. It is foreseeable however that, in some
alternate embodiments, a promoter could be added to a catalyst material comprising a rhodium
alloy.
In one embodiment of the present invention is more preferably directed towards syngas
catalysts used in partial oxidation reactions and even more preferably used in syngas catalysts that
contain solely rhodium or rhodium alloys. However, it should be appreciated that the catalyst
compositions according to the present invention are useful for other partial oxidation reactions,
which are intended to be within the scope of the present invention.
A preferred embodiment of this invention relates to a partial oxidation catalyst
composition. The partial oxidation catalyst comprises an active ingredient selected from the group
consisting of rhodium, iridium, platinum, palladium, and ruthenium; an optional promoter; and a
support comprising an alumina phase selected from the group consisting of alpha-alumina, thetaalumina
or any combinations thereof; and a rare earth aluminate comprising a rare earth metal,
wherein the rare earth aluminate has a molar ratio of aluminum to rare earth metal greater than 5:1,
and wherein the support comprises between about 1 wt% and about 50 wt% of said rare earth
aluminate. The optional promoter comprises an element selected from the group consisting of La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, preferably Sm, Eu, Pr and Yb. The
preferred promoter comprises samarium.
METHODS OF SUPPORT PREPARATION
This invention covers several embodiments of means for making catalyst supports
disclosed earlier. All method embodiments comprise an application step of at least one stabilizing
agent followed by a high temperature treatment.
Preferably the stabilizing agent comprises a rare earth metal. The rare earth metal is
selected from lanthanum, cerium, praseodymium, neodymium, samarium, or combinations. The
aluminum-containing precursor may comprise at least one material selected from the group
consisting of an oxide of aluminum, an aluminum salt, a salt of aluminum, an alkoxide of
aluminum, a hydroxide of aluminum and any combination thereof. The aluminum-containing
precursor comprises an aluminum structure selected from the group consisting of bayerite, gibbsite,
boehmite, pseudo-boehmite, bauxite, gamma-alumina, delta-alumina, chi-alumina, rho-alumina,
kappa-alumina, eta-alumina, theta-alumina, and any combinations thereof. The aluminumcontaining
precursor preferably comprises a transition alumina selected from the group consisting
of gamma-alumina, delta-alumina, chi-alumina, rho-alumina, kappa-alumina, eta-alumina, thetaalumina,
and combinations thereof. In a preferred embodiment, the aluminum-containing precursor
comprises mostly gamma-alumina.
The gamma-alumina used as the aluminum-containing precursor in the present method of
preparation of the catalyst support possesses a desired profile of physical characteristics with
respect to, say, morphology and pore structure. Preferably, the gamma-alumina of the present
method possesses a surface area between about 100 m2/g and about 300 m2/g; more preferably
between about 120 m2/g and about 300 nr/g, but most preferably between about 120 nr/g and
about 220 m2/g. The gamma-alumina as used in the present method further possesses a pore
volume of at least about 0.2 ml/g. Any aluminum oxide, which meets these requirements in surface
area and pore dimension, is called for the purpose of this patent gamma-alumina.
It should be understood that the aluminum-containing precursor could be pre-treated prior
to calcination or application of the stabilizing agent. The pre-treatment could be heating, spraydrying
to for example adjust particle sizes, dehydrating, drying, steaming or calcining. When the
aluminum-containing precursor comprises an aluminum oxide such as gamma-alumina, steaming
can be done at conditions sufficient to transform the aluminum oxide into a hydrated form of said
aluminum oxide, such as boehmite or pseudo-boehmite or gibbsite.
The present process for preparing a stabilized alumina support may further comprise
steaming the aluminum-containing precursor at conditions sufficient to at least partially transform
the aluminum-containing precursor into a boehmite or pseudo-boehmite wherein steaming is
defined as subjecting a given material, within the confines of an autoclave or other suitable device,
to an atmosphere comprising a saturated or under-saturated water vapor at conditions of elevated
temperature and elevated water partial pressure.
In one aspect, the steaming of the modified alumina precursor is preferably performed at a
temperature ranging from 150 °C to 500 °C, more preferably ranging from 180 °C to 300 °C, and
most preferably ranging from 200 °C to 250 °C; a water vapor partial pressure preferably ranging
from 1 bar to 40 bars, more preferably ranging from 4 bars to 20 bars, and most preferably from 10
bars to 20 bars; and an interval of time preferably from 0.5 hour to 10 hours, and most preferably
0.5 hour to 4 hours. Preferably, under these steaming conditions, the deposited aluminumcontaining
precursor is at least partially transformed to at least one phase selected from the group
boehmite, pseudo-boehmite and the combination thereof. A pseudo-boehmite refers to a
monohydrate of alumina having a crystal structure corresponding to that of boehmite but having
low crystallinity or ultrafine particle size. Alternatively, the optional steaming of the modified
aluminum-containing precursor may comprise same conditions of temperature and time as above,
but with a reduced water vapor partial pressure preferably ranging from 1 bar to 5 bar, and more
preferably ranging from 2 bars to 4 bars.
The compound or precursor of a stabilizing agent can be in the form of salt, acid, oxide,
hydroxide, oxyhydroxide, carbide, and the like. Preferably the compound or precursor of a
stabilizing agent is an oxide or a salt (such as carbonate, acetate, nitrate, chloride, or oxalate). The
stabilizing agent comprises at least one element selected from the group consisting of aluminum,
boron, silicon, gallium, selenium, rare earth metals, transition metals, alkali earth metals, their
corresponding oxides or ions, preferably at least one element selected from the group consisting of
B, Si, Ga, Se, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and their
corresponding oxides or ions. More preferably, the stabilizing agent comprises La, Pr, Ce, Eu, Yb,
Sm, their corresponding oxides, their corresponding ions, or any combinations thereof. Preferably
the compound or precursor of the stabilizing agent comprises a nitrate salt or a chloride salt, as for
example only La(NO.O?, or AI(NO3). It should be understood that more than one stabilizing agent or
more than one compound or precursor of a stabilizing agent can be used.
The stabilizing agent can be applied to the aluminum-containing precursor by means of
different techniques. For example only, application methods can be spray-drying, impregnation,
co-precipitation, chemical vapor deposition, and the like. It should also be understood that any
combination of techniques or multiple steps of the same technique could be used to applying a
stabilizing agent.
One preferred technique for applying the stabilizing agent is impregnation, particularly
incipient wetness impregnation. When the application is done via impregnation, a drying step at
temperatures between 80 °C and 150 "C is performed on the modified aluminum-containing
precursor prior to calcination.
In another embodiment, the modified aluminum-containing precursor is derived from the
aluminum-containing precursor by contacting the aluminum-containing precursor with the
stabilizing agent so as to form a support material and treating the support material so as to form a
hydrothermally stable support. Contacting the modified aluminum-containing precursor with the
stabilizing agent preferably includes dispersing the aluminum-containing precursor in a solvent so as
to form a sol, adding a compound of the stabilizing agent to the sol, and spraydrying the sol so as to
form the support material. It should be understood that more than one stabilizing agents or more
than one compound or precursors of a stabilizing agent can be added to the sol. Alternatively, one
stabilizing agent can be incorporated into the support by means of the aforementioned techniques.
Alternatively, two or more stabilizing agents can be incorporated into the support by means of the
aforementioned techniques. The preferred stabilizing agent comprises at least one rare earth selected
from the group consisting of lanthanum, cerium, praseodymium, and neodymium.
In another embodiment, a method of making a stabilized alumina support further
comprises applying at least one promoter to the stabilized alumina support. In some embodiments,
the promoter comprises an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, preferably Sm, ,Eu, Pr and Yb. It is believed that the
introduction of a lanthanide oxide, especially SirbO.i, on the stabilized alumina support surface
before deposition of active metal seems to further enhance the metal-support interaction, and that
the active metal also disperses better on the surface of stabilized support comprising an aluminum
oxide and a rare earth aluminate.
Methods of preparation of high surface area catalyst support comprising theta-alumina
Jn particular, the present invention discloses, in one aspect, a method of making a catalyst
support comprising calcining an aluminum-comprising precursor in a manner effective for
converting at least a portion of the aluminum-comprising precursor to an alumina support
comprising a majority of theta-alumina, and substantially free of gamma-alumina. The calcination
is preferably performed after an application of a stabilizing agent to the aluminum-comprising
precursor, wherein the stabilizing agent preferably comprises a rare earth metal.
The calcination is done at a high temperature greater than 800 °C, preferably not greater
than 1,300 "C. The calcination temperature could be selected based on the highest temperature the
catalyst would likely experience in operation, i.e. the catalytic reactor.
When the aluminum-comprising precursor comprises mainly gamma-alumina, the
calcination temperature is preferably selected such that it is above the minimum temperature
necessary to start the phase transformation from gamma-alumina to another transition alumina
phase between the low-temperature metastable transition gamma-alumina and the high-temperature
thermodynamically stable alpha-alumina, but below about the minimum temperature necessary to
start the phase transformation from said transition alumina to alpha-alumina. The other transition
alumina (i.e., which excludes gamma-alumina) is preferably theta-alumina, but could comprise low
amounts of other transition alumina phases. The calcination temperature is preferably selected such
that substantially all of the gamma-alumina phase is transformed into other alumina phases,
particularly to theta-alumina or a combination of theta-alumina and alpha-alumina. For example, if
a good portion of theta-alumina is desired in the support, the calcination following the application
step of a rare earth compound to a gamma-alumina, should be performed at a temperature
preferably between 800 °C and 1,100 °C, more preferably between 900 °C and 1,000 °C. Under
these conditions of calcination temperatures, it is most likely that the formation of rare earth
hexaaluminates would be minimized. The heat treatment is preferably performed, for a time period
between 3 to 24 hours.
The calcination can be performed under an oxidizing atmosphere, either statically or
under a flow of gas, preferably in static air or under a flow of a gas comprising diatomic oxygen.
Steam, either by itself or in combination with air, can also be used.
The calcination can be done at a pressure between 0 and 500 psia; preferably under
atmospheric pressure (about 101 psia), or under a subatmospheric pressure such as in a vacuum, or
at slightly above atmospheric pressure (J 01-200 psia).
Preparation of thermally stable catalyst support comprising a rare earth aluminate with an AI:Ln>5:
An alternate preferred method comprises applying a compound of a stabilizing agent to an
alumina support precursor; drying the modified alumina precursor; and treating the dried modified
alumina precursor with heat in a manner effective for converting at least a portion of the aluminumcomprising
material and a portion of said stabilizing agent to an aluminum-containing precursor to
an aluminate of said stabilizing agent. The stabilizing agent comprises preferably a rare earth metal.
When the stabilizing agent comprises preferably a rare earth metal, the heat treatment
conditions such as temperature and time are preferably selected such that at least a portion of the
aluminum-comprising material is transformed to the aluminate of said rare earth metal. This rare
earth aluminate could comprise a hexaaluminate structure, a beta-alumina structure, a monoclinic
structure, a perovskite-type structure, or combinations thereof, but preferably, the rare earth
aluminate comprises a beta-alumina structure, an hexaaluminate structure, or any combinations
thereof.
In a specific example, when the aluminum-comprising precursor comprises mainly a
gamma-alumina material, if the formation of rare earth aluminate with a high Al:Ln ratio (i.e.,
greater than 5:1) is desired in the support, the heat treatment step following the application step of a
rare earth compound to said gamma-alumina material and the drying step, should be performed at a
temperature preferably between 1,000 °C and 1,600 °C, more preferably between 1,100 °C and
1,400 °C. The heat treatment is preferably performed, for a time period between 3 to 24 hours.
The heat treatment can be performed under an oxidizing atmosphere (and in this case is
called calcination), either statically or under a flow of gas, preferably in static air or under a flow of
a gas comprising diatomic oxygen. Steam, either by itself or in combination with air, can also be
used, as Nair et al. (Journal of American Ceramic Society, 2000, vol. 83, pp. 1942-1946) indicated
that no difference in surface area was observed when the lanthanum hexaaluminate,
(LaiO.-O.l 1(A1:O;0, was calcined in air or steam.
The holding time at high calcination temperatures is expected to be greater than a
calcination time necessary for a typical phase transformation from gamma-alumina to theta-alumina
to alpha-alumina, as the growth of rare earth hexaaluminates or beta-alumina structures is quite
slow. Therefore one person skilled in the art should select a time period for heat treatment long
enough to transform most of the rare earth compound to a rare earth hexaaluminate.
Calcining conditions can be also selected such that calcination is effective to convert a
portion of the rare earth metal solution into a second rare earth aluminate but which comprises a
low aluminum to rare earth metal molar ratio, such as a perovskite structure. It is possible that if the
rare earth metal is not completely transformed to hexaaluminate, it could be converted in the
formation of rare earth oxides and/or other rare earth aluminates, such as a pervoskite type, which
do not generate a higher surface area than the hexaaluminate structures are known to do. However it
should be appreciated that in some cases, the combination of rare earth aluminates with high
aluminum to rare earth molar ratio (i.e., between 11:1 and 14:1 for hexaaluminate-like structure or
beta-alumina structures) and rare earth aluminates with low aluminum to rare earth molar ratios
(i.e., 5:3 for garnet structure, 1:1 for perovskite structure, and 1:2 for monoclinic structure) might
be desirable as the former species are known to increase the surface area and the later species are
known to inhibit the surface diffusion of species responsible for sintering.
Calcining can be also effective to convert a portion of the rare earth metal solution into an
oxide of said rare earth metal, said rare earth oxide consisting essentially of rare earth metal atoms
and oxygen atoms.
The amount of a compound of a stabilizing agent applied to an aluminum-containing
precursor is sufficient so as to obtain a stabilizing agent content in the support between about 1 wt%
and about 20 wt%. When the stabilizing agent comprises a rare earth metal, the amount of a
compound of a rare earth compound applied to the aluminum-containing precursor is sufficient so
as to obtain a rare earth content in the support between about 1 wt% and about 20 wt%, preferably
between about 1 wt% and about 10 wt%, more preferably between about 3 wt% and about 8 wt%,
and still more preferably between about 4 wt% and about 8 wt%.
More specifically, a method for making a thermally stable aluminum-based support with a
high surface area comprises impregnating a solution of a rare earth metal onto an aluminumcontaining
precursor; drying impregnated aluminum-containing precursor; and calcining in a
manner effective to convert one portion of said aluminum-containing precursor to an aluminum
oxide phase comprising alpha-alumina, theta-alumina, or combinations thereof; and to convert
another portion of said aluminum-containing precursor with at least a fraction of said rare earth
metal to a rare earth aluminate with a molar ratio of aluminum to rare earth metal greater than 5:1.
After calcining, the material comprises between about 1 wt% and 100 wt% of said rare earth
aluminate, preferably between about 1 wt% and about 50 wt% of said rare earth aluminate, more
preferably between about 5 wt% and about 45 wt% of the rare earth aluminate, and still more
preferably between about 10 wt% and about 40 wt% of the rare earth aluminate. The solution of
rare earth metal comprises more than one rare earth metal. Drying is preferably performed at a
temperature above 75 °C, preferably between 75 °C and 150 °C.
The calcination temperature is preferably selected such that at least a portion of the
aluminum-containing precursor is converted to another alumina phase, so as to obtain at least a
theta-alumina phase and/or alpha-alumina phase, whereas another portion of the aluminumcontaining
precursor is transformed with a stabilizing agent to an aluminate of said stabilizing
agent.
When the stabilizing agent comprises a rare earth metal, preferably the calcination
temperature is chosen to favor the formation of a solid solution of aluminum comprising rare earth
aluminates. For this particular embodiment, the temperature is greater than about 1,100°C. The
calcination temperature is preferably between 1,100 °C and 1,400 °C; more preferably between
about 1,200 °C and about 1,300 °C. The calcination time will depend greatly on the type of
equipment used, whether commercial or lab-scale. It is preferred in the laboratory scale for 10-g to
50-g samples to use a calcination time of at least about 3 hours to achieve at least a content of 5
wt% by weight of rare earth hexaaluminates.
Calcining can be also effective to convert a portion of the rare earth metal solution into an
oxide of said rare earth metal, said rare earth oxide consisting essentially of rare earth metal atoms
and oxygen atoms.
Calcining can be also effective to convert a portion of the rare earth metal solution into a
second rare earth aluminate but which comprises a low aluminum to rare earth metal molar ratio,
such as a perovskite structure.
METHOD OF CATALYST PREPARATION
The present invention further presents a method of making a partial oxidation catalyst
wherein said method comprises optionally applying a compound of one or more promoters to a
stabilized support of this invention and calcining the applied stabilized support at temperatures
greater than 600 °C, preferably between about 800 "C and about 1,400 °C, more preferably between
about 900 °C and about 1,300 °C to form a catalyst precursor; depositing a compound of at least one
active metals to the catalyst precursor; calcining the deposited catalyst precursor at temperatures
between about 300 °C and about 1,200 °C, preferably between about 500 °C and about 1,100 °C.
The stabilized support can be any of the supports disclosed earlier. A preferred support at least
comprises a rare earth hexaaluminate with a Al:Ln ratio greater than 5:1. The stabilized support
may further include an aluminum oxide phase such as comprising theta-alumina, alpha-alumina, or
combinations thereof. The stabilized support preferably include between about 1 wt% and 50 wt%
of said rare earth aluminate with a Al:Ln ratio greater than 5:1.
The compound of the promoter can be in the form of salt, acid, oxide, hydroxide,
oxyhydroxide, carbide, and the like. Preferably the compound of the promoter is a salt. The
promoter comprises at least one element selected from the group consisting of La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tin, Yb, Lu, and their corresponding oxides or ions. Preferably the
promoter comprises either Pr, Yb, Eu, Sm, their corresponding oxides or ions, or any combinations
thereof. Preferably the compound of the promoter comprises a nitrate salt, as for example only
Sm(NO;0.i or La(NO;0. It should be understood that more than one promoter or more than one
compound or precursor of a promoter can be used.
The promoter can be deposited into the modified alumina by means of different
techniques. For example only, deposition methods can be impregnation, co-precipitation, chemical
vapor deposition, and the like. The preferred technique for depositing the promoter is impregnation.
When the deposition of the promoter is done via impregnation, optionally a drying step at
temperatures between 75 °C and 150 "C is performed on the deposited modified alumina prior to
calcination.
The compound of the active metal can be in the form of salt, acid, oxide, hydroxide,
oxyhydroxide, carbide, and the like. Preferably the compound of the active metal is a salt. The
active metal comprises one element selected from the group consisting of metals from Groups 8, 9,
and 10 of the Periodic Table, rhenium, tungsten, and any combinations thereof. Preferably the
active metal for syngas catalyst comprises rhodium, indium, ruthenium, rhenium, or any
combinations thereof. Preferably the compound of the active metal is a nitrate or a chloride salt, as
for example only Rh(NO.-03 or RhCl> It should be understood that more than one active metal or
more than one compound of an active metal can be used. When two active metals are used in the
syngas catalyst, it is preferred that at least rhodium is selected as one metal, that the other metal is
selected from the active metal list above for syngas catalyst, and that the loading of both metals is
such so as to form a rhodium alloy.
The active metal can be deposited on the catalyst precursor (on promoted or unpromoted
stabilized alumina support) by means of different techniques. For example only, deposition methods
can be impregnation, co-precipitation, chemical vapor deposition, and the like. The preferred
technique for depositing the active metal is impregnation.
When the deposition of the active metal is done via impregnation, optionally a drying step
at temperatures between 75 °C and 150 °C is performed on the deposited catalyst precursor prior to
calcination.
Even though the applications of both promoter and active metal to the stabilized supports
are descfibed as separate steps, the application of both promoter(s) and active metal can be done
simultaneously.
Finally, after the application, drying, calcination steps to incoiporate at least one active
metal and an optional promoter into the support to make a catalyst, an activation step may be
necessary. In some embodiments, the activation step is not required; therefore the activation step
can be viewed as an optional step. The activation could comprise contacting the catalyst to a
reducing atmosphere so as to convert at least a portion of the active metal to a zero-valent state. The
reducing atmosphere preferably comprises hydrogen, but could also contain other gases (such as
nitrogen, methane, carbon monoxide), which are preferably not poisons to the catalyst and/or do not
chemically react with it.
METHOD OF PRODUCTING SYNTHESIS GAS
According to the present invention, a syngas reactor can comprise any of the synthesis gas
technology and/or methods known in the art. The hydrocarbon-containing feed is almost
exclusively obtained as natural gas. However, the most important component is generally methane.
Natural gas comprise at least 50% methane and as much as 10% or more ethane. Methane or other
suitable hydrocarbon feedstocks (hydrocarbons with four carbons or less) are also readily available
from a variety of other sources such as higher chain hydrocarbon liquids, coal, coke, hydrocarbon
gases, etc., all of which are clearly known in the art. Preferably, the feed comprises at least about
50% by volume methane, more preferably at least 80% by volume, and most preferably at least
90% by volume methane. The feed can also comprise as much as 10% ethane. Similarly, the
oxygen-containing gas may come from a variety of sources and will be somewhat dependent upon
the nature of the reaction being used. For example, a partial oxidation reaction requires diatomic
oxygen as a feedstock, while steam reforming requires only steam. According to the preferred
embodiment of the present invention, partial oxidation is assumed for at least part of the syngas
production reaction.
Regardless of the source, the hydrocarbon-containing feed and the oxygen-containing feed
are reacted under catalytic conditions. Improved catalyst compositions in accordance with the
present invention are described herein. They generally are comprised of a catalytic metal, some
alloyed, that has been reduced to its active form and with one or more optional promoters on a
stabilized aluminum-based support.
It has been discovered that the stabilization of an aluminum-based support by the presence
of at least one rare earth aluminate with a molar ratio of aluminum-to-rare earth metal greater than
5:1 results in obtaining a catalytic support suitable for high-temperature reactions such as syngas
production via partial oxidation.
Thus this invention relates to a method for making synthesis gas comprising converting a
gaseous hydrocarbon stream and an oxygen-containing stream over a partial oxidation catalyst, to
make a product stream comprising CO and H2, wherein said partial oxidation catalyst includes an
active ingredient comprising rhodium, iridium, platinum, palladium, ruthenium, or combinations
thereof; and a support comprising a rare earth aluminate, said rare earth aluminate having a molar
ratio of aluminum to rare earth metal greater than 5:1. The rare earth aluminate preferably has a
molar ratio of aluminum to rare earth metal between 11:1 and 14:1. The rare earth aluminate
preferably has a hexaaluminate-like structure, a beta-alumina like structure, or combinations
thereof. The catalytic support can contain from about 1 wt% to 100 wt% of the rare earth aluminate.
In some preferred embodiments, the catalytic support contains from about 1 wt% to about 50 wt%
of the rare earth aluminate. In other embodiments, the thermally stable aluminum-based catalyst
support could comprise between 40 wt% and 100 wt% of the rare earth aluminate. In some alternate
embodiments, the support is a rare earth aluminate or a mixture of rare earth aluminates with an
aluminum-to-rare earth metal molar ratio greater than 5:1, such as a lanthanum hexaaluminate-like
material or a lanthanum beta-alumina-like material.
In addition, it has been discovered that the stabilization of an aluminum-based support by
the addition of at least one stabilizing agent to a transition alumina between gamma-alumina and
alpha-alumina (but excluding gamma-alumina) results in a high-surface area catalytic support
suitable for high-temperature reactions.
This invention also relates to a method for making synthesis gas comprising converting a
gaseous hydrocarbon stream and an oxygen-containing stream over a partial oxidation catalyst, to
make a product stream comprising CO and H2, wherein said partial oxidation catalyst includes an
active ingredient comprising rhodium, iridium, platinum, palladium, ruthenium, or combinations
thereof; and a support comprising a transition alumina excluding gamma-alumina, and at least one
stabilizing agent. The transition alumina in the support preferably comprises theta-alumina. The
support may also comprise alpha-alumina. The stabilizing agent is preferably a rare earth metal.
The stabilizing agent more preferably includes a lanthanide metal selected from the group
consisting of lanthanum, cerium, neodymium, praseodymium, samarium, and combinations thereof,
but may further include any element from Groups 1-14 of the Periodic Table (new IUPAC notation)
such as an alkali metal, an alkali earth metal, an additional rare earth metal, or a transition metal.
The syngas catalyst compositions according to the present invention comprise an active
metal selected from the group consisting of metals from Group 8, 9, and 10 of the Periodic Table,
rhenium, tungsten, and any combinations thereof, preferably a metal from Group 8, 9, and 10 of the
Periodic Table and any combinations thereof, more preferably rhodium, iridium, ruthenium, or
combinations thereof.
In some embodiments when the active metal is rhodium, rhodium is comprised in a high
melting point alloy with another metal. It has been discovered that in addition to the enhanced
thermal stability of the support, the high melting point rhodium alloys used in some of these syngas
catalysts confer additional thermally stability than non-alloy rhodium catalysts, which leads to
enhanced ability of the catalyst to resist various deactivation phenomena.
It is well known that during syngas reactions, several undesired processes, such as coking
(carbon deposition), metal migration, and sintering of metal and/or the support, can occur and
severely deteriorate catalytic performance. The catalyst compositions of the present invention are
better able to resist at least one of these phenomena over longer periods of time than prior art
catalysts. As a consequence, these novel rhodium-containing catalysts on stabilized alumina
comprising mainly theta alumina can maintain high methane conversion as well as high CO and t^
selectivity over extended periods of time with little to no deactivation of the syngas catalyst.
The support structure of these catalysts can be in the form of a monolith or can be in the
form of divided or discrete structures or particulates. Particulates are preferred. Small support
particles tend to be more useful in fluidized beds. Preferably at least a majority (i.e., >50%) of the
particles or distinct structures have a maximum characteristic length (i.e., longest dimension) of less
than six millimeters, preferably less than three millimeters. According to some embodiments, the
divided catalyst structures have a diameter or longest characteristic dimension of about 0.25 mm to
about 6.4 mm (about 1/100" to about 1/4"), preferably between about 0.5 mm and about 4.0 mm. In
other embodiments they are in the range of about 50 microns to 6 mm.
The hydrocarbon feedstock and the oxygen-containing gas may be passed over the
catalyst at any of a variety of space velocities. Space velocities for the process, stated as gas hourly
space velocity (GHSV), are in the range of about 20,000 hr"1 to about 100,000,000 hr"1, more
preferably of about 100,000 hr"1 to about 10,000,000 hr"1, most preferably of about 400,000 hr"1 to
about 1,000,000 hr"1. Although for ease in comparison with prior art systems space velocities at
standard conditions have been used to describe the present invention, it is well recognized in the art
that residence time is the inverse of space velocity and that the disclosure of high space velocities
corresponds to low residence times on the catalyst. "Space velocity," as that term is customarily
used in chemical process descriptions, is typically expressed as volumetric gas hourly space
velocity in units of hr"1. Under these operating conditions a flow rate of reactant gases is maintained
sufficient to ensure a residence or dwell time of each portion of reactant gas mixture in contact with
the catalyst of no more than 200 milliseconds, preferably less than 50 milliseconds, and still more
preferably less than 20 milliseconds. A contact time less than 10 milliseconds is highly preferred.
The duration or degree of contact is preferably regulated so as to produce a favorable balance
between competing reactions and to produce sufficient heat to maintain the catalyst at the desired
temperature.
In order to obtain the desired high space velocities, the process is operated at atmospheric
or superatmospheric pressures. The pressures may be in the range of about 100 kPa to about 4,000
kPa (about 1-40 atm), preferably from about 200 kPa to about 3,200 kPa (about 2-32 atm).
The process is preferably operated at a temperature in the range of about 350 °C to about
2,000 °C. More preferably, the temperature is maintained in the range 400 °C - 1,600 °C, as
measured at the reactor outlet.
The catalysts of the present invention should maintain hydrocarbon conversion of equal to
or greater than about 85%, preferably equal to or greater than about 90% after 100 hours of
operation when operating at pressures of greater than 2 atmospheres. Likewise, the catalysts of the
present invention should maintain CO and t^ selectivity of equal to or greater than about 85%,
preferably equal to or greater than about 90% after 100 hours of operation when operating at
pressures of greater than 2 atmospheres.
The synthesis gas product contains primarily hydrogen and carbon monoxide, however,
many other minor components may be present including steam, nitrogen, carbon dioxide, ammonia,
hydrogen cyanide, etc., as well as unreacted feedstock, such as methane and/or oxygen. The
synthesis gas product, i.e. syngas, is then ready to be used, treated, or directed to its intended
purpose. The product gas mixture emerging from the syngas reactor may be routed directly into
any of a variety of applications, preferably at pressure. For example, in the instant case some or all
of the syngas can be used as a feedstock in subsequent synthesis processes, such as Fischer-Tropsch
synthesis, alcohol (particularly methanol) synthesis, hydrogen production, hydroformylation, or any
other use for syngas. One preferred such application for the CO and H: product stream is for
producing via the Fischer-Tropsch reaction synthesis higher molecular weight hydrocarbons, such
as Cj+hydrocarbons.
Syngas is typically at a temperature of about 600 °C-l,500 °C when leaving a syngas
reactor. The syngas must be transitioned to be useable in a Fischer-Tropsch or other synthesis
reactors, which operate at lower temperatures of about 160 °C to 400 °C. The syngas is typically
cooled, dehydrated (i.e., taken below 100 °C to knock out water) and compressed during the
transition phase. Thus, in the transition of syngas from the syngas reactor to for example a Fischer-
Tropsch reactor, the syngas stream may experience a temperature window of 50 °C to 1,500 °C.
In addition, the present invention contemplates an improved method for converting
hydrocarbon gas to liquid hydrocarbons using the novel catalyst compositions described herein for
synthesis gas production from light hydrocarbons. Thus, the invention also relates to processes for
converting hydrocarbon-containing gas to liquid products via an integrated syngas to Fischer-
Tropsch, methanol or other process.
HYDROCARBON SYNTHESIS FROM SYNTHESIS GAS
The synthesis gas (a mixture of hydrogen and carbon monoxide) produced by the use of
catalysts as described above is assumed to comprise at least a portion of the feed to a Fischer-
Tropsch reactor. The Fischer-Tropsch reactor can comprise any of the Fischer-Tropsch technology
and/or methods known in the art. The feed to the Fischer-Tropsch comprises a synthesis gas (or
syngas) with a hydrogen to carbon monoxide molar ratio between 0.67:1 and 5:1 but is generally
deliberately adjusted to a desired ratio of between about 1:4:1 to 2.3:1, preferably approximately
1.7:1 to 2.2:1. The syngas is then contacted with a Fischer-Tropsch catalyst. Fischer-Tropsch
catalysts are well known in the art and generally comprise a catalytically active metal and a
promoter. The most common catalytic metals are metals from Groups 8, 9, 10 of the Periodic Table,
such as cobalt, nickel, ruthenium, and iron or mixtures thereof. They may also comprise a support
structure. The support is generally alumina, titania, zirconia, silica, or mixtures thereof. In some
embodiments, it is envisioned that the Fischer-Tropsch catalyst may be supported on a stabilized
alumina as described in this invention. Fischer-Tropsch reactors use fixed and fluid type
conventional catalyst beds as well as slurry bubble columns. The literature is replete with particular
embodiments of Fischer-Tropsch reactors and Fischer-Tropsch catalyst compositions. As the
syngas feedstock contacts the catalyst, the hydrocarbon synthesis reaction takes place. The Fischer-
Tropsch product contains a wide distribution of hydrocarbon products from C. The Fischer-Tropsch process is typically run in a continuous mode. In this mode, the gas hourly
space velocity through the reaction zone typically may range from about 50 hr"1 to about 10,000 hr"
', preferably from about 300 hr"1 to about 2,000 hr"1. The gas hourly space velocity is defined as the
volume of reactants per time per reaction zone volume (the volume of reactant gases is at standard
pressure of 1 atm or 101 kPa and standard temperature of 0 °C; the reaction zone volume is defined
by the portion of the reaction vessel volume where reaction takes place and which is occupied by a
gaseous phase comprising reactants, products and/or inerts; a liquid phase comprising liquid/wax
products and/or other liquids; and a solid phase comprising catalyst). The reaction zone temperature
is typically in the range from about 160 °C to about 300 °C. Preferably, the reaction zone is
operated at conversion promoting conditions at temperatures from about 190 °C to about 260 °C,
more preferably between about 200 °C and about 230 °C. The reaction zone pressure is typically in
the range of about 80 psia (552 kPa) to about 1,000 psia (6895 kPa), more preferably from 80 psia
(552 kPa) to about 800 psia (5515 kPa), and still more preferably, from about 140 psia (965 kPa) to
about 750 psia (5170 kPa). Most preferably, the reaction zone pressure is from about 140 psia (965
kPa) to about 500 psia (3447 kPa).
DEFINITIONS
For purposes of the present disclosure, certain terms are intended to have the following
meanings.
"Active metal" refers to any metal that is present on a catalyst that is active for catalyzing
a particular reaction. Active metals may also be referred to as catalytic metals.
A "promoter" is one or more substances, such as a metal or a metal oxide or metal ion that
enhances an active metal's catalytic activity in a particular process, such as a CPOX process (e.g.,
increase conversion of the reactant and/or selectivity for the desired product). In some instances a
particular promoter may additionally provide another function, such as aiding in dispersion of
active metal or aiding in stabilizing a support structure or aiding in reduction of the active metal.
A "stabilizing agent" is one or more substances, comprising an element from the Periodic
Table of Elements, or an oxide or ion of such element, that modifies at least one physical property
of the support material that it is deposited onto, such as for example structure of crystal lattice,
mechanical strength, and/or morphology.
A rare earth "aluminate" refers to a compounds or related materials in the system Ln-Al-
O, where Ln, Al and O represent the rare earth metal, aluminum, oxygen, respectively.
With respect to the catalytic reaction such as partial oxidation of light hydrocarbons such
as methane or natural gas to produce synthesis gas or conversion of synthesis gas to hydrocarbons,
references to "catalyst stability" refer to maintenance of at least one of the following criteria: level
of conversion of the reactants, productivity, selectivity for the desired products, physical and
chemical stability of the catalyst, lifetime of the catalyst on stream, and resistance of the catalyst to
deactivation.
A compound of an element is a chemical entity that contains the atoms of said element
(whether the element is a catalytically active metal, a promoter, or a stabilizing agent).
A transition alumina is typically defined as any crystalline aluminun oxide phase which is
obtained by dehydration from an aluminum hydrate precursor such as boehmite or pseudoboehmite,
gibbsite, or bayerite, to ultimately the thermodynamically stable phase of alumina, alphaalumina.
Transition aluminas comprise gamma-alumina, theta-alumina, delta-alumina, eta-alumina,
rho-alumina, chi-alumina, and kappa-alumina.
Gamma-alumina and theta-alumina are two metastable phases of aluminum oxide
observed along the dehydration sequence of boehmite upon thermal treatment before conversion to
the final product alpha-alumina (see for example, Transformation of gamma-alumina to thetaalumina'
by Cai, Physical Review Letters, 2002, vol. 89, pp. 235501).
Theta-alumina is a metastable phase of alumina with aluminum atoms both octahedrally
and tetrahedrally coordinated. The local cation coordinations in theta-alumina are close to those in
gamma-alumina but different from alpha-alumina. Theta-alumina has an indirect energy band gap,
which is 1.6 eV smaller than that of alumina. The linear optical properties of theta-alumina are very
close to those of alpha-alumina. [Mo and Ching (1998), Session W19, 1998 March Meeting of The
American Physical Society, March 16-20, 1998, Los Angeles, CAJ.
EXAMPLES
The invention having been generally described, the following examples are given as
particular embodiments of the invention and to demonstrate the practice and advantages hereof. It
is understood that the examples are given by way of illustration and are not intended to limit the
specification or the claims to follow in any manner.
An aluminum-containing precursor was obtained as gamma-ANO} spheres from Davison,
with the following characteristics: a size in the range of 1.2 to 1.4 mm (average diameter of 1.3
mm.), a bulk density of 0.44 g/ml, a surface area and pore volume measure with N2 adsorption of
143 m2/g and 0.75 ml/g respectively. For a control, supports using Y-A^O^ spheres were formed
using no modifier by calcination at different calcination temperatures between 600 and 1,300 °C for
3 hours. For generating lanthanum-modified supports, A^Os spheres were impregnated with a
lanthanum nitrate (La(NO.i)i) solution, dried in an oven at 120 °C overnight, and then calcined at
different calcination temperatures between 600 and 1,300 °C for 3 hours. The y-AbOs spheres were
impregnated with an aqueous solution containing desired amount of La(NO.-?)3 so that the lanthanum
oxide (La2O.i) amount in the final material after drying and calcinations is approximately 3 wt% or
10 wt% lanthanum oxide by weight of the total support (this corresponds to a weight content of
about 2.56 wt% and 8.53 wt% La and a molar content of 0.94 mol% and 3.1 mol% of La2O3,
respectively).
Figures 2a, 2b and 2c represent the X-Ray Diffraction patterns of several support
materials comprising respectively no lanthanum, 3 wt% La2O3 and 10 wt% La^O^, all obtained after
an impregnation and a 3-hour calcination at different temperatures. When one compares the XRD
traces of undoped alumina (Figure 2a) and the 3 wt% LaiO.i on alumina in (Figure 2b) that were
calcined at 1,100 °C or 1,200 °C, it is noted that a-ANOj phase was present in higher percentage in
undoped alumina (Al^Oi) than in 3 wt% La on alumina (3 wt% La^Oj/AliOj). The a-AhO.i phase
was detected already in the undoped A^O^ calcined at 1,100 °C while a-Al^O.^ peaks in the 1,100
°C calcined 3 wt% La2O.VA2O3 were negligible. The difference in AliO.i phase compositions of
those two samples is more obvious for the 1,200 °C calcinated samples — a phase is the
predominant phase in undoped A]2Oj while O-Al^O^ is the main phase in 3 wt% La2O?,/A2Qj
sample, suggesting a lanthanum dopant with 3 wt% La^Oi loading is effective in preventing 9 phase
from transforming into a phase at 1,200 °C. Nevertheless, the thermodynamically stable a phase
becomes the dominant phase in both undoped and 3 wt% L^Oj/AiO? after calcination at 1,300 °C.
In order to further retard the a-AbO} phase formation and to maintain a relatively high surface area
after 1,300 °C calcination, the La2O3 doping level needs to be increased. The XRD results obtained
with 10% La2O3/Al2O3 samples calcined at different temperatures indicate that La-Al-O mixed
oxide compounds were formed upon calcination at high temperatures (Figure 2c). The presence of
perovskite -structured LaAlO} compound was detected in the 1,100 °C calcined sample. A
hexaluminate-type La-Al-O compound, LaAlnOig emerged after 1,200 °C calcination at the
expense of LaAlO^, which completely disappeared in the 1,300 °C calcined 10% La^CVAbOs.
Based on the XRD results in Figure 2c, we conclude that the sequences of La^O? + ANO^ reaction
at high temperatures follow:
~1100°C ~1200°C
La2O3 + Al2O3 > LaAlO3 > LaAl,,O,8
For the 1,200 °C-calcined 10% La2O3/Al2O3 sample, the intensities of XRD diffraction
peaks from a-ANOj are much lower than those in the 1,200 °C-calcined 3% I^CVAbOj sample,
suggesting the retardation of a-A^O.i formation is more effective at higher La^O.-? doping levels.
Moreover, when comparing the XRD traces of 1,300 °C-calcined sample in Figure 2b and Figure
2c, one may notice that the a-A!2O3 phase in the 10% La2O3/Al2O3 sample is not as predominant as
in 3% La2O3/Al2O3 (Figure 2c). It seems that there is an absence of dominant a-AloO} phase and
the present of more thermal stable LaAlnO|8 in the 1,300 °C calcined samples (Figure 2c) in the
10% La2O3/Al2O3 support than those of unmodified AliOj and 3% La2O3/Al2O3.
In order to find the optimum La^Oj doping level to stabilize the AhO^ structure, La2O3
doping level was varied from 3 wt% to 10 wt%. The BET surface area and pore volume of
La^CVAbO.i of different La2Os doping levels were shown in Figures 3a and 3b respectively.
Doping A12O3 with 3 wt% La2O.-? dopant retards A12O.3 phase transition to a phase upon thermal
treatment with limited success in retaining the surface area and pore volume after calcination at
1,200 °C or higher. Thermal sintering, formation of a phase and the consequent dramatic decrease
in surface area and pore structure, are inevitable under extremely severe condition (e.g., at 1,300 °C,
Figure 2a and Figure 2b). Increasing the La2O3 dopant level above 3 wt% further helps to stabilize
A12O3 structure. The results in Figures 3a and 3b indicate that the optimum La loadings to achieve
the highest surface area and pore volume of La2O.3 modified A12O3 are dependent of calcination
temperature. For 1,200 °C calcined samples, the largest surface area and pore volume was found to
be that of 5 wt% La2O3/Al2O3 (Figure 3a). Optimum surface area/pore volume was achieved with 8
wt% La2O3 loading with 1,300 °C calcined La2O3/Al2O3 samples (Figure 3b). With a La2O3 doping
level higher than those optimum values, the surface area and pore volume decrease.
Thus, support formulation comprising 6-8 wt% I^C^ (corresponding respectively to ca.
5.1-6.8 wt% La and ca. 1.88-2.5 mol% La2O?) in the aluminum oxide matrix and calcined at 1,300
°C seemed to provide higher surface area than the unmodified alumina structure or those modified
with higher or lower La loadings.
Catalyst Example
The y-AhOj spheres described above were impregnated with an aqueous solution
containing desired amount of lanthanum nitrate fLaCNOj)^] so that the lanthanum oxide [La2O3l
amount in the final material after drying and calcinations is approximately 3% by weight. The
ANOj spheres impregnated with the La(NO.-03 solution were dried in oven at 120 °C overnight and
then calcined at 1,200 °C for 3 hours to form a La2O3-modified AKOj support material. The La^O^-
AliOj spheres (Support Example S) were then subjected to samarium addition.
The La^CVmodified AhO.-? support material obtained as EXAMPLE 1 was impregnated
with a samarium nitrate [Sm(NO;0.i] solution. The material was dried in oven for overnight at 120
°C and then calcined at 1,100 °C for 3 hours to form a samarium-promoted catalyst support
(Promoted Support Example PS). The Sm content in the catalyst was 4 wt% SiTbOi in the final
material after drying and calcinations.
The promoted catalyst support calcined was then impregnated with a rhodium chloride
[RhCl.i] solution and the catalyst precursor was dried in oven for overnight at 120 °C, calcined at
900 °C for 3 hours, and then reduced in Hi at 600 °C for 3 hours to generate some metallic rhodium
form before being charged into the reactor to as to form a catalyst (Catalyst Example C). The Rh
metal content in the catalyst was 4% by weight again determined by mass balance.
Table 1 lists the alumina phase content, the rare earth aluminate content, BET surface
areas, pore volume, average pore diameter, average pore volume and average pore diameter both
measured by the BJH desorption method using N2 as the adsorptive of the modified alumina
catalyst support, the promoted modified support and the catalyst made therefrom.
The characterization of the transition alumina support was done by Rietveld X-Ray
Diffraction. Rietveld XRD uses a modeling tool which can extrapolate the percentage of different
alumina phases based on crystalline raw data from XRD. The Rietveld neutron profile refinement
method is disclosed by Rietveld (J. Appl. Cryst.. 1969, vol. 2, pp. 65-71) and the quantitative
analysis of minerals using the full powder diffraction profile using the Rietveld modeling are
described in Bish & Howard (J. Appl. Cryst.. 1988, vol. 21, pp. 86-91). The Rietveld neutron
profile of gamma-alumina and theta-alumina disclosed in Zhou et al. (Acta Cryst., 1991, vol. B47,
pp. 617-630) were used as a reference for the determination of the alumina phase content in the
samples.
Surface area and pore size distribution are obtained on a Micromeritics TriStar 3000
analyzer after degassing the sample at 190°C in flowing nitrogen for five hours. Surface area is
determined from ten points in the nitrogen adsorption isotherm between 0.05 and 0.3 relative
pressure and calculating the surface area by the standard BET procedure. Pore size distribution is
determined from a minimum of 30 points in the nitrogen desorption isotherm and calculated using
the BJH model for cylindrical pores. The instrument control and calculations are performed using
the TriStar software and are consistent with ASTM D3663-99 "Surface Area of Catalysts and
Catalyst Carriers", ASTM D4222-98 "Determination of Nitrogen Adsorption and Desorption
Isotherms of Catalysts by Static Volumetric Measurements", and ASTM D4641-94 "Calculation of
Pore Size Distributions of Catalysts from Nitrogen Desorption Isotherms". The initial surface area
(A) of the catalyst is the surface area of the catalyst structure prior to contact of reactant gas. The
pore volume (V) of the catalyst (N2 as adsorptive) is measured and calculated using the method
described above. Average pore size (diameter) based on N2 adsorptive is calculated as 4V/A.
For the alumina material modified with La (Example S), calcinations at 1,200 °C resulted
in a mixture of gamma-ANO;, (24 wt%), theta-Al2O3 (66 wt %) and alpha-Al2O3 (10 wt %).
Addition of samarium to Example S and calcination at 900 °C (Example PS) produced a mixture of
theta-ANO.i (88wt %) and alpha-AljO.-? (12 wt %), as the gamma-alumina phase seemed to be no
longer present. The addition of rhodium to Example PS and subsequent calcination at 600°C
(Example C) consisted of theta- Al2Oi (87 wt %) and alpha-AI2(>? (13 wt %). Therefore Examples
PS and C had similar alumina phase composition.
From Table 1, it is noted that calcination at 1,200 °C completely transformed gamm.a-
A12O3 to theta-A!2Oi or alpha-ANO.v One also anticipates that a longer calcination time at a given
temperature would also result in transforming more gamma-Al2O3 to theta-ANO.-).
TABLE 1: Surface area, pore volume, average pore diameter, and alumina phase content of support
and catalyst examples after different calcination temperatures of the support.
Ex
S
aPS
hc
Composition
La2OrAl2C>3
4% Sm/
La2OrAl2O3
4%Rh/4%Sm/
La2OrAl2O3
Support
Calc.
Temp.,
°C
1,200
1,200
1,200
BET
SA,
nr/g
56
-
39
Pore
vol.,
ml/g
0.42
-
0.35
Avg.
pore
size,
nm
23
-
30
d
LnAlyOz
With
(wt%)
7%
20%
18%
Estimated alumina
(A12O3) content0
(wt%)
Y
21
0
0
e
63
68
66
a
9
10
10
this sample also contained 2% of samarium oxide.
b this sample also contained 2% of samarium oxide and 4% rhodium.
c Y> 6' and a re^er to gamma-alumina, theta-alumina, and alpha-alumina respectively
d LnAlyOz represents a rare earth hexaaluminate-like structure with y=l 1-12 and z= 18-19,
and Ln represents lanthanum, or samarium, or combinations thereof.
As the phase transformations of ANOi follow gamma —> theta—* alpha with progressive
heating, the calcination temperature also has a great impact on the porous structure and support
characteristics. A significant difference in surface area (143 nr/g vs. 56 m2/g) and pore volume
(0.75 ml/g vs. 0.44 ml/g) in unmodified untreated alumina material and Example S was observed,
concurrently to the appearance of a good portion of theta-alumina phase and some alpha-alumina
phase.
It is worth mentioning that additional XRD data using Rietvel modeling (Rietveld, J.
Appl. Cryst., 1969, vol. 2, pp. 65-71; Bish & Howard, J. Appl. Cryst., 1988, vol. 21, pp. 86-91;
Taylor, Powder Diffraction, 1991, vol. 6, pp. 2-9) indicated that there was no distinguished phase of
LaiO.i found in any of the samples, instead, two forms of rare earth alumina solid solution were
found matching the spectrum. One is a random form, alumina maintained gamma or theta structures
with some of aluminum atoms in the lattices randomly replaced by rare earth metal atoms. All
gamma-AloOj and theta-AliOj mentioned above actually existed as such a random solid solution
form of alumina and LaiO^. Another one is an ordered form, a distinguished new crystallite phase
formulated as LnAl^OiQ, which was found a significant amount in promoted support Example PS
(20 wt % based on the sample weight) and catalyst Example C (18 wt % based on the sample
weight), much more than support Example S (7 wt % based on the sample weight). This may
suggest that addition of more rare earth element such as samarium might help form more solid
solution of LnAlnOio.
Catalyst composition, metal surface area, and metal dispersion are summarized in the
Table 2 below for Example C (4%Rh-4%Srn/La2OrAl2O:0.
TABLE 2: Catalyst Compositions for Example C, metal surface area, and rhodium dispersion.
EX.
C
Active metal
loading, wt%
4 %Rh
Promoter
loading, wt%
4% Sm
Metal Surface Area,
-m2/g rhodium
0.53
Metal dispersion -
rhodium, %
3.0
The metal surface area of the catalyst is determined by measuring the dissociative
chemical adsorption of Hi on the surface of the metal. A Micromeritics ASAP 2010 automatic
analyzer system is used, employing H2 as a probe molecule. The ASAP 2010 system uses a
flowing gas technique for sample preparation to ensure complete reduction of reducible oxides on
the surface of the sample. A gas such as hydrogen flows through the heated sample bed, reducing
the oxides on the sample (such as platinum oxide) to the active metal (pure platinum). Since only
the active metal phase responds to the chemisorbate (hydrogen in the present case), it is possible to
measure the active surface area and metal dispersion independently of the substrate or inactive
components. The analyzer uses the static volumetric technique to attain precise dosing of the
chemisorbate and rigorously equilibrates the sample. The first analysis measures both strong and
weak sorption data in combination. A repeat analysis measures only the weak (reversible) uptake of
the probe molecule by the sample supports and the active metal. As many as 1,000 data points can
be collected with each point being fully equilibrated. Prior to the measurement of the metal surface
area the sample is pre-treated. The first step is to pretreat the sample in He for 1 hr at 100 °C. The
sample is then heated to 350 °C in He for 1 hr. These steps clean the surface prior to measurement.
Next the sample is evacuated to sub-atmospheric pressure to remove all previously adsorbed or
chemisorbed species. The sample is then oxidized in a 10% oxygen/helium gas at 350 °C for 30
minutes to remove any possible organics that are on the surface. The sample is then reduced at 400
°C for 3 hours in pure hydrogen gas. This reduces any reducible metal oxide to the active metal
phase. The sample is then evacuated using a vacuum pump at 400 °C for 2 hours. The sample is
then cooled to 35 °C prior to the measurement. The sample is then ready for measurement of the
metal surface. From the measurement of the volume of H2 uptake during the measurement step, it is
possible to determine the metal surface area per gram of catalyst structure by the following
equation.
MSA = (V)(A)(S)(a)/22400/m
where MSA is the metal surface are in m2 /gram of catalyst structure;
V is the volume of adsorbed gas at Standard Temperature and Pressure in ml.;
A is the Avogadro constant;
S is the stoichiometric factor (2 for H2 chemisorption on rhodium);
m is the sample weight in grams; and
a is the metal cross sectional area.
A temperature-programmed reduction (TPR) was also performed for catalyst Example 3.
TPR was used to analyze the metal oxide reducibility and metal-to-support interactions. A 0.05-g
sample was pretreated with flowing Argon at temperature of 200 °C for 0.5 hour and cooled down
to ambient, then heated up to 800 °C in flowing 20% of H2/Ar (50 cc/min) at the ramp rate of 10
°C/min. The number of reduction peaks can be used to determine the number of environments
where metals reside and the temperatures can be used as indicators for metal-to-support
interactions, higher temperature stronger metal-to-support interaction. The TPR profile, its peak
temperatures and total H2 consumption, of as-calcined Example C are shown in Figure 1. Example
C had three reduction peaks at temperatures of 122 °C, 156 °C and 200 °C, respectively, with total
H: consumption of 9.2 ml/g. The three peaks in the TPR of Example most likely indicated that the
support calcined at 1,200 °C resulted in three different kinds of support environments for rhodium
to exist, which probably mean that the metal-to-support interactions are non-uniform across the
catalyst surface. The lower reduction peak temperature of Example 3 indicates a weaker Rh-O bond
on the surface of the catalyst, thereby most likely increasing the amount of metallic rhodium on the
surface of the reaction and favoring the direct oxidation mechanism (Scheme 2) as discussed earlier.
FIXED BED REACTIVITY TESTING
The catalyst Example C was tested with molecular oxygen and natural gas as the
hydrocarbon feed. The natural gas had a typical composition of about 93.1% methane, 3.7 %
ethane, 1.34% propane, 0.25 % butane, 0.007% pentane, 0.01% C,+, 0.31% carbon dioxide, 1.26%
nitrogen (with % meaning volume percent). The hydrocarbon feed was pre-heated at 300 °C and
then mixed with CK The reactants were fed into a fixed bed reactor at a carbon to O2 molar ratio of
1.87 or a Oimatural gas mass ratio of 1.05 at gas weight hourly space velocities (GHSV) of about
675,000 hr'. The gas hourly space velocity is defined by the volume of reactant feed per volume of
catalyst per hour. The partial oxidation reaction was carried out in a conventional flow apparatus
using a 12.7 mm I.D. quartz insert embedded inside a refractory-lined steel vessel. The quartz
insert contained a catalyst bed (comprising of 2.0 g of catalyst particles) held between two inert 80-
ppi alumina foams. The reaction took place for several days at a pressure of about 90 psig (722 kPa)
and at temperatures at the exit of reactor between about 930 °C and about 1010 °C. All the flows
were controlled by mass flow controllers. The reactor effluent as well as feedstock was analyzed
using a gas chromatograph equipped with a thermal conductivity detector. Pressures at the inlet and
outlet on the reactor were measured by a differential pressure transmitter, which gives the overall
pressure drop across the catalytic bed by subtracting the pressure at the outlet from the pressure at
the inlet.
The data analyzed include catalyst performance as determined by conversion and
selectivity, and deactivation rate measured for some over a period of over 300 hours. The catalyst
performances (CH4 conversion, Hi and CO selectivity) at 2 hours after reaction ignition are listed in
the following Table 3 and the observed deactivation rate are listed in Table 4.
Table 3: Test data for Catalyst Example C with initial CH4 conversion, CO and H2 selectivity at
about24 hours of reaction.
Catalyst
Example
C
GHSV,
hr-'
675,000
CH4
conversion,
94
CO
selectivity,
96
H2
selectivity,
96
Table 4: Deactivation for Catalyst Example C measured over a time period for about 300+ hours at
a GHSV of about 675,000 hr'1.
Catalyst
Example
C
TOS,
hrs
321
CH4
conv. loss,
% /day
0.48
CO
sel. loss,
% /day
0.14
H2
sel. loss,
% /day
0.48
As shown in Table 3, Example C has very good overall catalytic performance, towards
synthesis gas production. The oxygen conversion (not shown) was also measured for all tests, and
was above 99%. As seen in Table 4, Example C appears to deactivate at a slow rate, showing
remarkable stability in conversion and selectivity over time.
Figure 4 shows the plots of the methane conversion and product (H? and CO) selectivity
for the test run of catalyst Example C, demonstrating the great stability in partial oxidation of
natural gas, with only 0.48_% loss per day in methane conversion and 0.48_% loss per day in
hydrogen selectivity for the duration of the run (about 300 hours).
The examples and testing data show that the catalyst compositions of the present
invention represent an improvement over prior art partial oxidation catalysts in their ability to resist
deactivation over sustained time periods while maintaining high methane conversion and hydrogen
and carbon monoxide selectivity values. While the preferred embodiments of the invention have
been shown and described, modifications thereof can be made by one skilled in the art without
departing from the spirit and teachings of the invention. The embodiments described herein are
exemplary only, and are not intended to be limiting. Many variations and modifications of the
invention disclosed herein are possible and are within the scope of the invention. Accordingly, the
scope of protection is not limited by the description set out above, but is only limited by the claims
which follow, that scope including all equivalents of the subject matter of the claims. The
disclosures of all issued patents, patent applications and publications cited herein are incorporated
by reference. The discussion of certain references in the Description of Related Art, above, is not an
admission that they are prior art to the present invention, especially any references that may have a
publication date after the priority date of this application.

We Claim:
1. A high temperature stable catalyst support comprising: an alumina
phase selected from the group consisting of alpha-alumina, theta-
alumina and combinations thereof; and a rare earth aluminate
comprising at least one rare earth metal, wherein the rare earth
aluminate has a molar ratio of aluminum to rare-earth metal greater
than 5, and wherein the catalyst support contains 1 wt% to 50 wt% of
rare earth aluminate and not more than 20 wt% alpha-alumina.
2. The catalyst support as claimed in claim 1 wherein the catalyst support
comprises 5 wt% to 50 wt% of rare earth aluminate based on the total
weight of the catalyst support.
3. The catalyst support as claimed in claim 1 wherein the rare earth metal
is selected from the group consisting of lanthanum, neodymium,
praseodymium, cerium, samarium, and combinations thereof.
4. The catalyst support as claimed in claim 1 wherein the rare earth
aluminate comprises lanthanum.
5. The catalyst support as claimed in claim 1 wherein the catalyst support
comprises 1 wt% to 10 wt% of lanthanum.
6. The catalyst support as claimed in claim 1 wherein the rare earth
aluminate optionally comprises an element from Groups 1-14 of the
Periodic Table of Elements.
7. The catalyst support as claimed in claim 1 wherein the rare earth
aluminate optionally comprises one or more metals selected from the
group consisting of nickel, magnesium, barium, potassium, sodium,
manganese, rare earth metals, and combinations thereof.

8. The catalyst support as claimed in claim 1 wherein the rare earth
aluminate has a chemical formula of LnAlyOz, where y is between 11 and
14; and z is between 18 and 23, and where Ln comprises lanthanum,
neodymium, praseodymium, samarium, cerium, or combinations thereof.
9. The catalyst support as claimed in claim 1 wherein the rare earth
aluminate has a chemical formula of MAlyOz, where y is between 11 and
12; z is between 18 and 19; and M comprises a combination of
lanthanum and samarium.
10. A method for making the thermally stable aluminum-based catalyst
support as claimed in claim 1, the method comprising:
(a) impregnating a solution of a rare earth metal onto an aluminum-containing precursor; (b) drying the impregnated aluminum-containing precursor; and (c) calcining at a temperature greater than 1000°C and a pressure of between 0 psia and 500 psia in a manner effective to convert a portion of said aluminum-containing precursor to an aluminum oxide phase comprising alpha-alumina, theta-alumina, or combinations thereof, and to convert another portion of said aluminum-containing precursor with at least a fraction of said rare earth metal to a rare earth aluminate with a molar ratio of aluminum to rare earth metal greater than 5, such that the catalyst support comprises 1 wt% to 50 wt% of said rare earth aluminate.
11. The method as claimed in claim 10 wherein the aluminum-containing
precursor comprises an aluminum structure selected from the group
consisting of bayerite, gibbsite, boehmite, pseudoboehmite, bauxite,
gamma-alumina, delta-alumina, chi-alumina, rho-alumina, kappa-
alumina, eta- alumina, theta-alumina, and combinations thereof.

12. The method as claimed in claim 10 wherein the aluminum-containing
precursor comprises a transition alumina selected from the group
consisting of gamma-alumina, delta-alumina, chi-alumina, rho-alumina,
kappa-alumina, eta-alumina, theta-alumina, and combinations thereof.
13. The method as claimed in claim 10 wherein the aluminum-containing
precursor comprises mostly gamma-alumina.
14. The method as claimed in claim 13 wherein calcining is done at a
temperature between 1,000 °C and 1,600°C.
15. The method as claimed in claim 13 wherein calcining is done at a
temperature between 1,100 °C and 1,400 °C.
16. The method as claimed in claim 10 wherein the rare earth metal is
selected from the group consisting of lanthanum, neodymium,
praseodymium, cerium and combinations thereof.
17. The method as claimed in claim 10 wherein the rare earth aluminate
comprises lanthanum.
18. The method as claimed in claim 10 wherein the solution of rare earth
metal comprises more than one rare-earth metal.

Documents:

1881-delnp-2005-abstract-05-05-2008.pdf

1881-delnp-2005-abstract.pdf

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1881-DELNP-2005-Correspondence-Others-(04-12-2007).pdf

1881-delnp-2005-correspondence-others-05-05-2008.pdf

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1881-delnp-2005-description (complete)-05-05-2008.pdf

1881-delnp-2005-description (complete).pdf

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1881-DELNP-2005-Form-1-(04-12-2007).pdf

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1881-DELNP-2005-Form-2-(04-12-2007).pdf

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1881-delnp-2005-form-5.pdf

1881-DELNP-2005-GPA-(04-12-2007).pdf

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1881-delnp-2005-pct-220.pdf

1881-delnp-2005-pct-306.pdf

1881-delnp-2005-pct-notification.pdf

1881-delnp-2005-pct-search report.pdf

1881-DELNP-2005-Petition-137-(04-12-2007).pdf

1881-DELNP-2005-Petition-138-(04-12-2007).pdf


Patent Number 220867
Indian Patent Application Number 1881/DELNP/2005
PG Journal Number 30/2008
Publication Date 25-Jul-2008
Grant Date 09-Jun-2008
Date of Filing 05-May-2005
Name of Patentee CONOCOPHILLIPS COMPANY
Applicant Address
Inventors:
# Inventor's Name Inventor's Address
1 SHUIBO XIE
2 CHARLES R. RAPIER
3 DAVID E. SIMON
4 DAVID M, MINAHAN
5 CEMAL ERCAN
6 BAILI HU
7 BEATRICE C. ORTEGO
PCT International Classification Number C01B 3/26
PCT International Application Number PCT/US2003/036051
PCT International Filing date 2003-11-12
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/425,381 2002-11-11 U.S.A.
2 60/425,383 2002-11-11 U.S.A.
3 60/501,185 2003-09-08 U.S.A.