Use of lanthanide oxides to reduce sintering of catalysts

Abstract

Disclosed is a lanthanide oxide coated catalyst, and methods for its use, that includes a supported catalyst comprising a support material, a catalytic material, and a lanthanide oxide, wherein the lanthanide oxide is attached to at least a portion of the surface of the supported catalyst.

Claims

1. A lanthanide oxide coated catalyst comprising: (a) a supported catalyst comprising a support material and a catalytic material; and (b) a lanthanide oxide coating that coats at least a portion of the supported catalyst, wherein the lanthanide oxide coating includes at least 2 wt. % lanthanide oxide; wherein the catalytic material comprises at least one catalytic metal selected from the group consisting of Pt, Pd, Ru and Ir.

2. The lanthanide oxide coated catalyst of claim 1, wherein a weight ratio of the lanthanide oxide to the catalytic material is 5:1 to 10:1.

3. The lanthanide oxide coated catalyst of claim 2, wherein the weight ratio of the lanthanide oxide to the catalytic material is 6:1 to 8:1.

4. The lanthanide oxide coated catalyst of claim 1, comprising 0.1 wt. % to 20 wt. % catalytic material.

5. The lanthanide oxide coated catalyst of claim 1, wherein the weight ratio of the lanthanide oxide to the supported catalyst is from 5:100 to 20:100.

6. The lanthanide oxide coated catalyst of claim 1, comprising 99 to 50 wt. % of the support material.

7. The lanthanide oxide coated catalyst of claim 1, wherein the lanthanide oxide coating includes 2 to 50 wt. % lanthanide oxide.

8. The lanthanide oxide coated catalyst of claim 1, wherein the catalytic material comprises at least one catalytic metal selected from the group consisting of Pd and Ir.

9. The lanthanide oxide coated catalyst of claim 8, wherein the catalytic metal is Pt.

10. The lanthanide oxide coated catalyst of claim 1, wherein the lanthanide oxide is CeO.sub.2, La.sub.2O.sub.3, Gd.sub.2O.sub.3, or any combination thereof.

11. The lanthanide oxide coated catalyst of claim 1, wherein the support material comprises at least one member selected from the group consisting of Al.sub.2O.sub.3, MgAl.sub.2O.sub.3, kaolinite, TiO.sub.2, ZrO.sub.2 and SiO.sub.2, or any combination thereof.

12. The lanthanide oxide coated catalyst of claim 11, wherein the support material is kaolinite.

13. The lanthanide oxide coated catalyst of claim 11, wherein the catalytic metal is Pt and the lanthanide oxide is CeO.sub.2.

14. The lanthanide oxide coated catalyst of claim 1, wherein the catalytic material is a catalytic metal.

15. The lanthanide oxide coated catalyst of claim 1, wherein the support material is Al.sub.2O.sub.3.

16. A method of producing a gaseous mixture comprising contacting a reactant gas mixture comprising a hydrocarbon and an oxidant with the lanthanide oxide coated catalyst of claim 1 at a reaction temperature of 700° C. to 1100° C. to produce a gaseous mixture comprising hydrogen and carbon monoxide.

17. The method of claim 16, wherein the reaction temperature is 800° C. to 1000° C.

18. The method of claim 16, wherein the lanthanide oxide coating reduces sintering of the catalytic material.

19. The method of claim 16, wherein the hydrocarbon is methane and the oxidant is carbon dioxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Scanning electron micrographs of (A) 2 wt % Pt/Al.sub.2O.sub.3 250° C. reduced, (B) 2 wt % Pt/Al.sub.2O.sub.3 800° C. reduced for 4 hours, and (C) 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3 reduced at 800° C. for 4 hours.

(2) FIG. 2: Carbon dioxide reforming of methane (CDRM) with 10 wt % CeO.sub.2/2 wt % Pt/Kaolin catalysts at 800° C. and 1 bara.

DETAILED DESCRIPTION OF THE INVENTION

(3) The currently available catalysts used to reform hydrocarbons into syngas are prone to sintering, which can lead to inefficient catalyst performance and ultimately failure of the catalyst after relatively short periods of use. This can lead to inefficient syngas production as well increased costs associated with its production.

(4) A discovery has been made that avoids the sintering issues described above. The discovery is based on the use of lanthanide oxides to reduce or prevent sintering—the lanthanide oxides can be used to create sinter resistant catalysts when such catalysts are used at elevated temperatures. Without wishing to be bound by theory, it is believed that the lanthanide oxides can reduce or prevent agglomeration of the support material and the catalytic material at elevated temperatures, thereby reducing or preventing sintering of said materials. Further, the use of lanthanide oxides as a coating on particular supported catalysts (such as the clay mineral or alkaline earth metal/metal oxide supported catalysts disclosed in U.S. Provisional Applications 61/821,514, filed May 9, 2013, and 61/821,522, filed May 9, 2013, both of which are incorporated into the present application by reference), further reduces the occurrence of sintering at elevated temperatures.

(5) These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

(6) A. Lanthanide Oxides

(7) Lanthanides that can be used in the context of the present invention to create lanthanide oxides include lanthanum (La), cerium (Ce), gadolinium (Gd), neodymium (Nd), praseodymium (Pr), and Europium (Eu), or combinations of such lanthanides. Non-limiting examples of lanthanide oxides include CeO.sub.2, Pr.sub.2O.sub.3, Eu.sub.2O.sub.3, Nd.sub.2O.sub.3, Gd.sub.2O.sub.3, or La.sub.2O.sub.3, or any combination thereof. Salts of lanthanide (e.g., chlorides, nitrates, sulphates, etc.) can be obtained from commercial sources such as Sigma-Aldrich, Alfa-Aeaser, Strem, etc. Lanthanide oxides can be produced by methods known in the art such as by high temperature (e.g., >500° C.) decomposition of lanthanide salts or by precipitation of salts into respective hydroxides followed by calcination to the oxide form.

(8) B. Support Material

(9) A variety of support materials can be used in the context of the present invention. For instance, the support material can be a metal oxide, an alkaline earth metal/metal oxide compound, a clay mineral, a pervoskite, or a zeolite based support. With respect to metal oxide supports, non-limiting examples that can be used include silica, aluminum oxide, zirconium oxide, titanium dioxide, or cerium oxide, or combinations thereof.

(10) For clay mineral supports, non-limiting examples of such materials are provided below. In particular instances, however, clay minerals having a 1:1 silicate layer structural format can be used (e.g., kaolinite). Typically, a clay mineral includes silica, alumina or magnesia or both, and water. Some clay minerals may be expressed using ideal chemical formulas as the following: 2SiO.sub.2 Al.sub.2O.sub.3 2H.sub.2O (kaolinite), 4SiO.sub.2 Al.sub.2O.sub.3 H.sub.2O (pyrophyllite), 4SiO.sub.2 3MgO H.sub.2O (talc), and 3 SiO.sub.2 Al.sub.2O.sub.3 5FeO 4H.sub.2O (chamosite). The SiO.sub.2 ratio is a key factor for determining clay mineral types. Clay minerals can be classified on the basis of variations of chemical composition and atomic structure into nine groups: (1) kaolin-serpentine (kaolinite, halloysite, lizardite, chrysotile), (2) pyrophyllite-talc, (3) mica (illite, glauconite, celadonite), (4) vermiculite, (5) smectite (montmorillonite, nontronite, saponite), (6) chlorite (sudoite, clinochlore, chamosite), (7) sepiolite-palygorskite, (8) interstratified clay minerals (e.g., rectorite, corrensite, tosudite), and (9) allophane-imogolite.

(11) The prevalent structural feature of clay minerals is the presence of hydrous-layer silicates. These features are continuous two-dimensional tetrahedral sheets of Si.sub.2O.sub.5, with SiO.sub.4 tetrahedrons linked by the sharing of three corners of each tetrahedron to form a hexagonal mesh pattern. The apical oxygen at the fourth corner of the tetrahedrons, which is usually directed normal to the sheet, forms part of an adjacent octahedral sheet in which octahedrons are linked by sharing edges. There are two major types for the structural “backbones” of clay minerals called silicate layers. The unit silicate layer formed by aligning one octahedral sheet to one tetrahedral sheet is referred to as a 1:1 silicate layer, and the exposed surface of the octahedral sheet consists of hydroxyls. In another type, the unit silicate layer consists of one octahedral sheet sandwiched by two tetrahedral sheets that are oriented in opposite directions and is termed a 2:1 silicate layer. Therefore, a clay mineral comprising a 1:1 silicate layer is one in which an octahedral sheep is aligned with a tetrahedral sheet. By comparison, a clay mineral comprising a 2:1 silicate layer is one in which an octahedral sheet is aligned with a tetrahedral sheet on one side and a second tetrahedral sheet on the opposing side.

(12) Kaolin-serpentine groups of clay minerals are 1:1 layer silicates. Their basic unit of structure includes tetrahedral and octahedral sheets in which the anions at the exposed surface of the octahedral sheet are hydroxyls. Therefore, their general structure can be expressed as: Y.sub.2-3Z.sub.2O.sub.5(OH).sub.4, where Y are cations in the octahedral sheet such as Al.sup.3+ and Fe.sup.3+ for dioctahedral species and Mg.sup.2+, Fe.sup.2+, Mn.sup.2+, and Ni.sup.2+ for trioctahedral species, and Z are cations in the tetrahedral sheet, largely Si and, to a lesser extent, Al and Fe.sup.3+. Kaolinite has a structural formula of Al.sub.2Si.sub.2O.sub.5(OH).sub.4. Kaolinite is electrostatically neutral and has triclinic symmetry. Dickite and nacrite are polytypic varieties of kaolinite, both of which include a double 1:1 layer and have monoclinic symmetry, but have different stacking sequences of the two 1:1 silicate layers. Halloysite also has a composition close to that of kaolinite and is characterized by its tubular nature in contrast to the platy nature of kaolinite particles. Halloysite has a hydrated form with a composition of Al.sub.2Si.sub.2O.sub.5(OH).sub.4 2H.sub.2O. This hydrated form irreversibly changes to a dehydrated variety at relatively low temperatures (60° C.) or upon being exposed to conditions of low relative humidity. Trioctahedral magnesium species, chrysotile, antigorite, and lizardite, have a formula of Mg.sub.3Si.sub.2O.sub.5(OH).sub.4. Chrysotile crystals have a cylindrical roll morphology. Antigorite crystals exhibit an alternating wave structure. Lizardite crystals are platy and can include a small amount of substitution of aluminum or ferric iron for both silicon and magnesium.

(13) With respect to the pyrophyllite-talc group of clay minerals, they have a 2:1 layer form with a unit thickness of approximately 9.2 to 9.6 Å. The structure is an octahedral sheet sandwiched by two tetrahedral sheets. Pyrophyllite and talc represent the dioctahedral and trioctahedral members, respectively, of the group. The structural formulas are Al.sub.2Si.sub.4O.sub.10(OH).sub.2 for pyrophyllite and Mg.sub.3Si.sub.4O.sub.10(OH).sub.2 for talc. Therefore, the 2:1 layers of these minerals are electrostatically neutral and are held together with van der Waals bonding.

(14) Mica clay minerals also have a basic structural unit of the 2:1 layer type like pyrophyllite and talc. Examples include muscovite (KAl.sub.2(Si.sub.3Al)O.sub.10(OH).sub.2), phlogopite (KMg.sub.3(Si.sub.3Al)O.sub.10(OH).sub.2), biotite (K(Mg, Fe).sub.3(Si.sub.3Al)O.sub.10(OH).sub.2), celadonite (K(Mg, Fe.sub.3+)(Si.sub.4−xAl.sub.x)O.sub.10(OH).sub.2, where x=0-0.2), and Glauconite.

(15) The vermiculite clay mineral includes sheets of trioctahedral mica or talc separated by layers of water molecules.

(16) Smectite clay minerals are derived from the structures of pyrophyllite and talc. Unlike pyrophyllite and talc, the 2:1 silicate layers of smectite have a slight negative charge due to ionic substitutions in the octahedral and tetrahedral sheets. The structural formula of smectites include (Al.sub.2−yMg.sup.2+/.sub.y)(Si.sub.4−xAl.sub.x)O.sub.10(OH).sub.2M.sup.+/.sub.x+y nH.sub.2O, where M.sup.+ is the interlayer exchangeable cation expressed as a monovalent cation and where x and y are the amounts of tetrahedral and octahedral substitutions, respectively (0.2≦x+y≦0.6). The smectites with y>x are called montmorillonite and those with x>y are known as beidellite. Nontronites are those in which ferric iron is a dominant cation in the octahedral sheet instead of aluminum and magnesium. Beidellites are those where chromium (Cr.sup.3+) and vanadium (V.sup.3+) also are found as dominant cations in the octahedral sheets. Trioctahedral ferromagnesian smectites have the following formula (Mg, Fe.sup.2+).sub.3(Si.sub.4−xAl.sub.x)O.sub.10(OH).sub.2M.sup.+/x nH.sub.2O.

(17) Chlorite clay minerals include: clinochlore (Mg.sub.5Al)(Si.sub.3Al)O.sub.10(OH).sub.8; chamosite (Fe.sub.5.sup.2+Al)(Si.sub.3Al)O.sub.10(OH).sub.8; pennantite (Mn.sub.5Al)(Si.sub.3Al)O.sub.10(OH).sub.8; and (nimite) (Ni.sub.5Al)(Si.sub.3Al)O.sub.10(OH).sub.8.

(18) Sepiolite and palygorskite are papyrus-like or fibrous hydrated magnesium silicate minerals. They include two-dimensional tetrahedral sheet of composition Si.sub.2O.sub.5 and are regarded as having narrow strips or ribbons of 2:1 layers that are linked stepwise at the corners. The structure of sepiolite is Mg.sub.8Si.sub.12O.sub.30(OH).sub.4(OH.sub.2).sub.4(H.sub.2O).sub.8, and the structure of palygorskite is and (Mg, Al).sub.5Si.sub.8O.sub.20(OH).sub.2(OH.sub.2).sub.4(H.sub.2O).sub.4.

(19) Interstratified clay minerals include mixtures of various clay minerals. Examples include rectorite (dioctahedral mica/montmorillonite), tosudite (dioctahedral chlorite/smectite), corrensite (trioctahedral vermiculite/chlorite), hydrobiotite (trioctahedral mica/vermiculite), aliettite (talc/saponite), and kulkeite (talc/chlorite). Other examples include illite/smectite, glauconite/smectite, dioctahedral mica/chlorite, dioctahedral mica/vermiculite, and kaolinite/smectite.

(20) Imogolite clay mineral is an aluminosilicate with an approximate composition of SiO.sub.2 Al.sub.2O.sub.3 2.5H.sub.2O. Allophane is a hydrous aluminosilicate mineral dominated by Si—O—Al bonds—i.e., the majority of aluminum atoms are tetrahedrally coordinated. Unlike imogolite, the morphology of allophane varies from fine, rounded particles through ring-shaped particles to irregular aggregates.

(21) Any of the above noted clay minerals can be used in the context of the present invention. Further, while it is contemplated that natural/non-purified or non-isolated or non-synthetic forms can be used, in certain aspects, the clay minerals can be isolated or purified or synthetically produced. One of the reasons for using isolated or purified or synthetically produced clay minerals is to reduce or remove impurities that may cause or lead to sintering of the minerals or coking on the surface of the minerals when used as a support for a catalyst in reforming reactions. Such impurities that may induce sintering or coking during syngas production include iron, nickel, manganese, sodium, potassium, chloride, calcium, lithium, rubidium, berylium, barium, SiO.sub.2, and/or organic impurities. By way of example, when clay minerals are heated at elevated temperatures such as those used in carbon dioxide reformation of hydrocarbons to produce syngas, such impurities (e.g., iron or potassium) within the clay mineral could fuse together. Removal or reducing the amounts of such impurities can therefore help reduce or avoid sintering and/or coking.

(22) For alkaline earth metal/metal oxide supports that can be used in the context of the present invention, such supports have the following general structure: D-E, where D is a M.sub.1 or M.sub.1M.sub.2, and M.sub.1 and M.sub.2 are each individually an alkaline earth metal selected from the group consisting of Mg, Ca, Ba, and Sr, and E is a metal oxide selected from the group consisting of Al.sub.2O.sub.4, SiO.sub.2, ZrO.sub.2, TiO.sub.2, and CeO.sub.2. Specific compounds are disclosed above and throughout this specification. These compounds are commercially available from a wide range of sources (e.g., Sigma-Aldrich® Co. LLC (St. Louis, Mo., USA); Alfa Aesar GmbH & Co KG, A Johnson Matthey Company (Germany)).

(23) All of the support materials can be made by the process used in the examples section of this specification or by processes known to those of ordinary skill in the art (e.g., precipication/co-precipitation, sol-gel, templates/surface derivatized metal oxides synthesis, solid-state synthesis, of mixed metal oxides, microemulsion technique, solvothermal, sonochemical, combustion synthesis, etc.).

(24) C. Catalytic Materials

(25) It is contemplated that any of the known catalytic materials that are currently used in reaction processes that are run at elevated temperatures can be used. The reason for this is that the lanthanide oxide coating reduces sintering, which can make it applicable for a wide variety of catalytic materials. For instance, the catalytic material can be a catalytic metal, such as Pt, Pd, Au, Ag, Ni, Co, Fe, Mn, Cu, Zn, Mo, Rh, Ru, or Ir, or any combination thereof. In some instances, the catalytic material can be a combination of a noble metal and a base metal. Such non-limiting combinations can include PtX, PdX, AuX, AgX, RhX, RuX, or IrX, where X═Ni, Co, Fe, Mn, Cu, Zn, or Mo.

(26) In particular reactions, such as the production of syngas from hydrocarbons, metal catalysts (e.g., Pt, Pd, Au, Ag, Ir, Ni, Co, Rh, Ru, La, Mg, Ca, Sr, Ba, Li, Na, K, Fe, Sn, Cu, Zn, Zr, Mo, Nb, Bi, or Mn, or any combination thereof), metal oxide catalysts (e.g., La.sub.2O.sub.3, Ru.sub.2O.sub.3, CeO.sub.2, ZrO.sub.2, ZnO, MoO.sub.3, WO.sub.3, Nb.sub.2O.sub.5, and/or Ta.sub.2O), pyrochlore catalysts, and other known catalysts used in the production of syngas from hydrocarbons (e.g., perovskites type solid solutions, various metals like Pt, Pd, Ir, Ni, Co, Rh, Ru, La, Mg, Ca, Sr, Ba, Fe, Sn, Cu, or Zn supported on various metal oxides such as Al.sub.2O.sub.3, SiO.sub.2, SBA-15, MCM-40, TiO.sub.2, ZrO.sub.2, CeO.sub.2, etc.) can be used. Non-limiting examples of pyrochlore catalysts include those having the following structure:
A.sub.xB.sub.y−zC.sub.zO.sub.7
wherein, A is a trivalent ion of an element of La, Ce, Nd, Bi, Sc, or Y, where 0<x<2, B is a tetravalent ion of an element of Zr, Pt, Pd, Ni, Mo, Rh, Ru, or Ir, where 0<y−z<2, C is a bivalent, trivalent or tetravalent ion of Ba, Ca, Cu, Mg, Ru, Rh, Pt, Pd, Ni, Co, or Mo, where 0<z<2.
D. Methods of Making Lanthanide Oxide Coated Catalysts

(27) The lanthanide oxide coated catalyst of the present invention can be made by processes known in the art that provide attachment of the lanthanide oxide to the surface of the support material and/or the catalytic material. The attachment can be through chemical bonds or physical bonds or both. In particular instances, the bonds can be M1-M2 bonds (where M1 is a metal from the lanthanide oxide and M2 is a metal from the support or catalytic material) or M1-O bonds (where M1 is a metal from the lanthanide and O is oxygen from the support or catalytic material) or O-M1 bonds (where O is a metal from the lanthanide oxide and M1 is a metal from the support or catalytic material)

(28) In addition to known methods, it has been discovered that the following process could be used to prepare the lanthanide oxide coated catalysts of the present invention: Step 1: Catalytic material is dissolved in pore volume equivalent of water and impregnated with support material. Subsequently, the impregnated support material is subject to a drying step (from 100 to 150° C.) for 1 to 3 hours followed by calcination at 150 to 250° C. for 3 to 5 hours. Step 2: Lanthanide oxide salt is dissolved in pore volume equivalent of water. The material from step 1 is then impregnated with the dissolved lanthanoxide. Step 3: The mixture from step 2 is dried at 100 to 200° C. for 1 to 3 hours followed by calcination at 800 to 1000° C. for 7 to 9 hours.
The amounts of ingredients can be varied to obtain a desired weight ratio of lanthanide oxide to the catalytic material, to the support material, or to the supported catalyst. Further, the materials can vary to create a desired lanthanide oxide coated catalyst in the context of the present invention. Specific examples of this process are provided in the Examples section.

(29) As illustrated in the Examples section, the produced lanthanide oxide coated catalysts are sinter resistant materials at elevated temperatures, such as those typically used in syngas production or methane reformation reactions (i.e., 700° C. to 1100° C. or a range from 725° C., 750° C., 775° C., or 800° C. to 900° C., 1000° C., or 1100° C.). Further, the produced catalysts can be used effectively in carbon dioxide reforming of methane reactions at a temperature range from 800° C. to 1000° C. or from 800° C. to 1100° C., a pressure range from 1 bara to 30 bara, and/or at a gas hourly space velocity (GHSV) range from 500 to 10000 h.sup.−1.

(30) In instances when the produced catalytic material is used in carbon dioxide reformation reactions, the carbon dioxide in the gaseous feed mixture can be obtained from various sources. In one non-limiting instance, the carbon dioxide can be obtained from a waste or recycle gas stream (e.g. from a plant on the same site, like for example from ammonia synthesis) or after recovering the carbon dioxide from a gas stream. A benefit of recycling such carbon dioxide as starting material in the process of the invention is that it can reduce the amount of carbon dioxide emitted to the atmosphere (e.g., from a chemical production site). The hydrogen in the feed may also originate from various sources, including streams coming from other chemical processes, like ethane cracking, methanol synthesis, or conversion of methane to aromatics. The gaseous feed mixture comprising carbon dioxide and hydrogen used in the process of the invention may further contain other gases, provided that these do not negatively affect the reaction. Examples of such other gases include steam or oxygen. The hydrocarbon material used in the reaction can be methane. The resulting syngas can then be used in additional downstream reaction schemes to create additional products. Such examples include chemical products such as methanol production, olefin synthesis (e.g., via Fischer-Tropsch reaction), aromatics production, carbonylation of methanol, carbonylation of olefins, the reduction of iron oxide in steel production, etc.

EXAMPLES

(31) The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Synthesis of CeO2 Coated Catalysts

(32) The following two-step process was used to synthesize a 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3 catalyst. In the first step 0.17 g of tetrammine platinum chloride hydrate salt was dissolved in pore volume equivalent of water and impregnated with dried 4.9 g of Al.sub.2O.sub.3. The resultant product was first dried at 125° C. for 2 hours followed by calcination at 200° C. for 4 hours. In a second step, 0.5 g of cerium ammonium nitrate salt was dissolved in pore volume equivalent of water and impregnated with Pt/Al.sub.2O.sub.3 sample. The resultant mixture was first dried at 150° C. for 2 hours followed by calcination at 900° C. for 8 hours. Additional catalysts were prepared by this method to modify the weight percentage of CeO.sub.2 to be 2, 5, and 8 wt %, respectively (i.e., 2 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3; 5 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3; and 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3).

(33) The following two-step procedure was used to synthesize a 10 wt % CeO.sub.2/2 wt % Pt catalyst grafted on Kaolin support. In the first step 0.17 g of tetrammine platinum chloride hydrate salt was dissolved in pore volume equivalent of water and impregnated with dried 4.9 g of Kaolin. The resultant product was first dried at 125° C. for 2 hours followed by calcination at 200° C. for 4 hours. In a second step 0.5 g of cerium ammonium nitrate salt was dissolved in pore volume equivalent of water and impregnated with Pt/Kaolin sample. The resultant mixture was first dried at 150° C. for 2 hours followed by calcination at 900° C. for 8 hours. Different weight percentages and catalysts can be obtained by adjusting the amount of and types of ingredients as desired.

(34) The following procedure was used to synthesize 10 wt % CeO.sub.2/2 wt % Pt catalyst supported on a MgAl.sub.2O.sub.4 support. The catalyst was synthesized by a two-step incipient wetness impregnation technique. First, the 10 wt % CeO.sub.2/2 wt % Pt catalytic material was synthesized in a two-step process. In the first step 0.17 g of tetrammine platinum chloride hydrate salt was dissolved in pore volume equivalent of water and impregnated with dried 4.9 g of MgAl.sub.2O.sub.4. The resultant product was first dried at 125° C. for 2 hours followed by calcination at 200° C. for 4 hours. In a second step, 0.5 g of cerium ammonium nitrate salt was dissolved in pore volume equivalent of water and impregnated with Pt/MgAl.sub.2O.sub.4 sample. The resultant mixture was first dried at 150° C. for 2 hours followed by calcination at 900° C. for 8 hours.

(35) The amounts and types of materials can be modified to create a desired catalytic material that is coated with a lanthanide oxide and which has improved sintering (anti-sintering) characteristics.

Example 2

Sintering Effects of CeO2

(36) A 2 wt % Pt/Al.sub.2O.sub.3 and 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3 were each analyzed by Scanning transmission electron microscopy (STEM). FIG. 1 gives STEM images of 2 wt % Pt/Al.sub.2O.sub.3 reduced at 250° C. (A), 2 wt % Pt/Al.sub.2O.sub.3 reduced at 800° C. for 4 hours (B) and 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3 reduced at 800° C. for 4 hours (C). The 2 wt % Pt/Al.sub.2O.sub.3 reduced at 250° C. results in particle of size≈2 nm and homogeneously dispersed (A). FIG. 1(B) is derived from catalyst 2 wt % Pt/Al.sub.2O.sub.3 but reduced at 800° C. It is evident that Pt particles have grown in size and particle size ranges from≈2-20 nm. By comparison, the Pt particles in the catalyst 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3 catalyst have completely segregated in the presence of CeO.sub.2 and could not be seen in STEM images (FIG. 1(C)).

(37) Additional experiments were also performed on the 2 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3, 5 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3, and 10 wt % CeO.sub.2/2 wt % Pt/Al.sub.2O.sub.3 catalysts. The 2, 5 and 8 wt % CeO.sub.2 was not enough to segregate all the Pt particles in the 2 wt % Pt/Al.sub.2O.sub.3 catalyst. The minimum amount of CeO.sub.2 needed to fully segregate Pt particles in 2 wt % Pt/Al.sub.2O.sub.3 was therefore 10 wt %.

(38) The presence of CeO.sub.2 overcomes aggregation of Pt metallic particles by segregating them on an atomic scale, which allows for their use as catalysts at elevated temperatures and to avoid catalyst deactivation of catalyst due to sintering effect.

Example 3

CDRM Reaction With 10 wt % CeO2/2 wt % Pt/Kaolin Catalyst

(39) A carbon dioxide reforming of methane (CDRM) reaction was performed a with 10 wt % CeO.sub.2/2 wt % Pt/Kaolin catalyst at 800° C. and 1 bara for 20 hours. Prior to the reaction, the catalyst was first reduced in 10% H.sub.2 atmosphere at 900° C. for 4 hours. Subsequently, the CDRM reaction was each initiated by changing the gas mixture to 10% CH.sub.4+10% CO.sub.2+80% N.sub.2. Both GC and Mass spectrometer were used to monitor gas composition. The 200-500 mesh size catalyst powder was used for testing, and the GHSV applied was 5000 h.sup.−1.

(40) The CO/H.sub.2 ratio obtained from the reaction was about 1:1 (see FIG. 2). Further, the catalyst was found to be stable without any deactivation for 20 hours of duration. Notably, no sintering nor coke formation was not observed (no appearance of dark black color on catalysts) in any of these catalysts at temperatures above 800° C. The lack of coking was confirmed by performing a loss on ignition test of the used catalysts in an open atmosphere at 800° C. By comparison, coke formation was observed (catalyst turned dark black in color) at a temperature of 700° C. However, no sintering was observed at this reduced temperature.