Use of nickel-manganese olivine and nickel-manganese spinel as bulk metal catalysts for carbon dioxide reforming of methane

Abstract

Disclosed are bulk metal oxide catalysts, and methods for their use, that include at 5 least two or more metals or two or more compounds thereof (M.sup.1, M.sup.2) and having an olivine crystal phase or a spinel crystal phase, or both phases, wherein the bulk metal oxide catalyst is capable of producing the H.sub.2 and CO from the CH.sub.4 and the CO.sub.2 under substantially dry conditions.

Claims

1. A bulk metal oxide catalyst capable of producing hydrogen (H.sub.2) and carbon monoxide (CO) from methane (CH.sub.4) and carbon dioxide (CO.sub.2), wherein the bulk metal oxide catalyst consists of an olivine crystal structure that has discrete SiO.sub.4.sup.4 anions and two metals (M.sup.1, M.sup.2) in the crystal lattice, a discrete spinel structure, or is a mixture thereof, wherein M.sup.1 and M.sup.2 are different; wherein the O.sup. anions of the silicate are coordinated with the metals in the crystal lattice, and wherein the bulk metal oxide catalyst does not include a carrier or a support.

2. The bulk metal oxide of claim 1, wherein M.sup.1 comprises nickel (Ni) or a compound thereof, and M.sup.2 comprises manganese (Mn) or a compound thereof.

3. The bulk metal oxide catalyst of claim 2, wherein the olivine crystal phase comprises a nickel-manganese olivine crystal phase having a structure of (Ni.sub.xMn.sub.1-x).sub.2SiO.sub.4, where x is 0<x0.25 and wherein the catalyst further comprises a spinel crystal phase.

4. The bulk metal oxide catalyst of claim 3, further comprising a metal oxide crystal phase having a structure of MnSiO.sub.3.

5. The bulk metal oxide catalyst of claim 3, wherein the spinel crystal phase comprises a nickel-manganese spinel crystal phase having a structure of (Ni.sub.xMn.sub.3-x)O.sub.4, where x is 0<x1.

6. The bulk metal oxide catalyst of claim 5, further comprising a metal oxide crystal phase having a structure of MnSiO.sub.3.

7. The bulk metal oxide catalyst of claim 1, wherein the olivine crystal phase is represented by the formula of: (M.sup.1.sub.xM.sup.2.sub.1-x).sub.2SiO.sub.4, where x is 0<x0.25, wherein M.sup.1 and M.sup.2 are different.

8. The bulk metal oxide catalyst of claim 1, wherein the catalyst consists of the olivine crystal structure.

9. The bulk metal oxide catalyst of claim 1, wherein the catalyst consists of the spinel structure.

10. The bulk metal oxide catalyst of claim 1, wherein the catalyst consists of a combination of the olivine crystal structure and the spinel structure.

11. A reactant composition comprising the bulk metal oxide catalyst of claim 1, and one or both of CH.sub.4 and CO.sub.2.

12. A method of producing H.sub.2 and CO comprising contacting a reactant gas stream that includes CH.sub.4 and CO.sub.2 with a bulk metal oxide catalyst catalysts of claim 1 under substantially dry reaction conditions and at a temperature of greater than 800 C. sufficient to produce a product gas stream comprising H.sub.2 and CO; wherein the bulk metal oxide catalyst consists of an olivine crystal structure that has discrete SiO.sub.4.sup.4 anions and two metals (M.sup.1, M.sup.2) in the crystal lattice, or a discrete spinel structure, or is a mixture thereof, wherein M.sup.1 and M.sup.2 are different; wherein the O.sup. anions of the silicate are coordinated with the metals in the crystal lattice, and wherein the bulk metal oxide catalyst does not include a carrier or a support.

13. The method of claim 12, wherein a ratio of CO to H.sub.2 ranges from 0.35:1 to 1:1 after 40 hours.

14. The method of claim 12, wherein coke formation on the bulk metal oxide catalyst is substantially or completely inhibited.

15. A method of making the bulk metal oxide of claim 1, the method comprising: (a) obtaining a mixture comprising M.sup.1 oxide particles, silicon dioxide particles, and M.sup.2 oxide particles, and wherein the molar ratio of M.sup.2:Si is 1:1 to 3:1, and the molar ratio of M.sup.1:M.sup.2 is 0.01 to 0.5; and (b) calcining the mixture at a temperature of 1000 C. to 1500 C., for a sufficient period of time to obtain a bulk catalyst having a M-M.sup.2 olivine crystal phase, a spinel phase, or a combination thereof.

16. The method of claim 15, wherein the calcining is conducted at a temperature of about 1100 C. to 1275 C. for about 22 to 48 hours and subsequently cooled to room temperature.

17. A catalyst comprising: a support comprising an olivine mineral having an olivine crystal phase, wherein the olivine mineral is selected from the group consisting of monticelite, calcio-olivine, lienbergite, glaucochroite, and any combination thereof; and two or more additional metals (M.sup.1, M.sup.2) or two or more compounds thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a polyhedral structure of an olivine structure that includes nesosilicate (SiO.sub.4).sup.4 and two metal cations.

(2) FIG. 2 depicts a cubic closed packed array structure of a spinel having the general formula AB.sub.2O.sub.4, where A and B are metal cations.

(3) FIG. 3 shows X-Ray Diffraction (XRD) patterns of various bulk metal oxide catalysts of the present invention and mixed manganese silicon oxides.

(4) FIG. 4 shows the XRD patterns of NiMn olivine: (a) (Ni.sub.0.1Mn.sub.0.9).sub.2SiO.sub.4 (b) (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4, (c) (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 [circle: Mn.sub.2SiO.sub.4 olivine, triangle: NiMn.sub.2O.sub.4 spinel].

(5) FIG. 5 shows the XRD pattern of NiMn olivine: (a) (Ag.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (b) (Ru.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (c), (Ir.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (d) (Pt.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (e) (Rh.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (f) Pd.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4 [circle: Mn.sub.2SiO.sub.4 olivine, triangle: NiMn.sub.2O.sub.4 spinel].

(6) FIG. 6 are graphical depictions of % methane conversion versus time, in hours, for the various bulk metal oxide catalysts of the present invention and manganese silicon oxides.

(7) FIG. 7 are graphical depictions of carbon dioxide conversion versus, time in hours, for the various bulk metal oxide catalysts of the present invention and manganese silicon oxides.

(8) FIG. 8 are graphical depictions of ratio of hydrogen to carbon monoxide conversion versus time, in hours, for the various bulk metal oxide catalysts of the present invention and manganese silicon oxides.

(9) FIG. 9 are X-Ray Diffraction (XRD) patterns of a spent bulk metal oxide catalyst of the present invention and manganese silicon oxide.

(10) FIG. 10 graphical depictions of % methane conversion versus time, in hours, for the (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 (.square-solid.), (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 (), (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 (.box-tangle-solidup.) catalysts the present invention and comparative pyrochlore catalyst (.Math.).

(11) FIG. 11 are graphical depictions of carbon dioxide conversion versus, time in hours, for the (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 (.square-solid.), (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 (), (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 (.box-tangle-solidup.) catalysts of the present invention and comparative pyrochlore catalyst (.Math.).

(12) FIG. 12 are graphical depictions of ratio of hydrogen to carbon monoxide conversion versus time, in hours, for the (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 (.square-solid.), (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 (.circle-solid.), (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 (.box-tangle-solidup.) catalysts of the present invention and comparative pyrochlore catalyst (.Math.).

(13) FIG. 13 shows the XRD patterns of the olivine (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 before (top) and after the CDRM reaction (bottom pattern).

(14) FIG. 14 are graphical depictions of % methane conversion versus time, in hours, for the Ag.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.square-solid.), Ru.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (), Ir.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.box-tangle-solidup.), Pt.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.Math.) and Rh.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.diamond-solid.) catalysts of the present invention.

(15) FIG. 15 are graphical depictions of % methane conversion versus time, in hours, for the Ag.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.square-solid.), Ru.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (), Ir.sub.0.02(Ni.sub.0.28Mh.sub.1.7)SiO.sub.4 (.box-tangle-solidup.), Pt.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.Math.) and Rh.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.diamond-solid.) catalysts of the present invention.

(16) FIG. 16 are graphical depictions of ratio of hydrogen to carbon monoxide conversion versus time, in hours, Ag.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.square-solid.), Ru.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (), Ir.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.box-tangle-solidup.), Pt.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.Math.) and Rh.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.diamond-solid.) catalysts of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(17) The currently available catalysts used to reform hydrocarbons into syngas are prone to sintering and coking, 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 as increased costs associated with its production.

(18) A discovery has been made that avoids the sintering issues. The discovery is based on the use of bulk metal oxide catalysts having an olivine crystal phase, a spinel crystal phase, or both phases. Without wishing to be bound by theory, it is believed that the solid state synthesis method and special calcination conditions to produce a catalyst having an olivine phase can reduce or prevent agglomeration of the catalytic material, thereby reducing or preventing sintering of the materials.

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

(20) A. Crystal Phases

(21) 1. Olivine Phases

(22) The bulk metal catalysts of the present invention can have an olivine crystal phase. In the olivine crystal phase, the counter ions (cationic metals) can be coordinated by the four oxygen ions of the silicate anions ((SiO.sub.4).sup.4). The coordination with the cationic metals with the four oxygen atoms provides the olivine crystal phase. In the olivine crystal structure, the SiO.sub.4.sup.4 anions can be isolated from each other (i.e., the Si cations do not share oxygen atoms). The olivine structure can be characterized by hexagonal close packed arrays of O.sup. anions in that one-half of the octahedral interstices are occupied by the cations of the metals of the invention, and one-eighth of the tetrahedral interstices are occupied by Si cations. FIG. 1 depicts a polyhedral structure of an olivine structure that includes nesosilicate ((SiO.sub.4).sup.4) and two metal cations. Bulk metal oxide catalyst of the present invention can be prepared by heating silicon dioxide at high temperatures in the presence of other metal oxides to produce nesosilicate phases (i.e., olivine phases). A non-limiting structure of the olivine phase is provided below in Formulas (I) and (II).

(23) 2. Spinel Phases

(24) The bulk metal catalysts of the present invention can have a spinel crystal phase. Spinel structures can be characterized as having a cubic close packing (ccp) array of oxide ions. In the spinel structure, oxygen (O.sup.) anions form a the ccp array (lattice) and the metals (e.g., M.sup.1, M.sup.2 of the present invention) sit in tetrahedral ( occupied) and octahedral ( occupied) sites in the lattice. FIG. 2 depicts a structure of a spinel having the general structure AB.sub.2O.sub.4, where A and B are metal cations. Spinels of the present invention can be prepared by heating M.sup.1 (e.g., nickel oxide) and M.sup.2 (e.g., manganese oxide) at high temperatures in the solid phase. A non-limiting structure of the spinel phase is provided below in Formulas (III) and (IV).

(25) B. Metals

(26) The metals that can be used in the context of the present invention to create bulk metal oxides or supported catalysts include: (1) manganese or a compound thereof (e.g., manganese oxide such as MnO), with manganese oxide being preferred; and (2) nickel or a compound thereof (e.g., nickel oxide such as Ni.sub.2O.sub.3), with nickel oxide being preferred. These metals or metal compounds can be purchased from any chemical supplier such as Sigma-Aldrich (St. Louis, Mo., USA), Alfa-Aeaser (Ward Hill, Mass., USA), Strem Chemicals (Newburyport, Mass., USA).

(27) Metal catalysts for the production of hydrogen and carbon monoxide from hydrocarbons and carbon dioxide include two or more of the above described metal or metals compounds in combination with nesosilicate. Catalytic material can be mixed with the nesosilicate or with a nesosilicate precursor. Catalytic material includes a catalytic metal, such as MnO and NiO. The catalyst can have an olivine crystal phase, a spinel crystal phase, or both phases. The olivine crystal phase can have an overall formula of:
(M.sup.1.sub.xM.sup.2.sub.1x).sub.2SiO.sub.4(I)

(28) where 0<x0.25, preferably 0.1<x0.25, and M.sup.1 and M.sup.2 are different;

(29) or
(M.sup.1.sub.x,M.sup.2.sub.1xy,M.sup.3.sub.y).sub.2SiO.sub.4(II)

(30) where 0<x0.25, 0y0.05 and 0<(x+y)0.25, preferably 0.1<x0.25, 0y0.05 and 0.1<(x+y)0.25, and M.sup.1, M.sup.2, and M.sup.3 are different. M.sup.1 can be nickel (Ni) or a compound thereof, and M.sup.2 can be manganese (Mn) or a compound thereof. As shown in formula (II), the ratio of M.sup.1, M.sup.2, to M.sup.3 is adjusted to compensate for the third metal. The third metal (M.sup.3) can be a noble metal. In preferred embodiments, M.sup.1 is nickel, M.sup.2 is manganese, and M.sup.3 is a noble metal (e.g., Ru, Rh, Ir Pd, Pt, Ag, or Au). It should be understood, that the number of metals can be varied as long as the empirical formula for the olivine structure (AB).sub.2SiO.sub.4, where A and B are metals, is preserved.

(31) The spinel crystal phase can have an overall formula of:
M.sup.1.sub.xM.sup.2.sub.3xO.sub.4(III)

(32) where x is 0<x1, preferable 0.01<x1, and M.sup.1, M.sup.2, and M.sup.3 are different,

(33) or
(M.sup.1.sub.x,M.sup.2.sub.3xy,M.sup.3.sub.y)O.sub.4(IV) where 0<x1, 0y0.05 and 0<(x+y)1, preferably 0.01x1, 0y0.05 and 0<(x+y)1, and M.sup.1, M.sup.2, and M.sup.3 are different.
As shown in formula (IV), the ratio of M.sup.1, M.sup.2, to M.sup.3 is adjusted to compensate for the third metal. The third metal can be a noble metal. In preferred embodiments, M.sup.1 is nickel, M.sup.2 is manganese, and M.sup.3 is a noble metal (e.g., Ru, Rh, Ir Pd, Pt, Ag, or Au). It should be understood, that the number of metals can be varied as long as the empirical formula for the spinel structure AB.sub.2O.sub.4, where A and B are metals, is preserved. In some instances, the catalyst includes some M.sup.2SiO.sub.3, which has little to no catalytic activity.
C. Preparation of Catalysts

(34) The bulk metal oxide catalyst of the present invention can be made by processes that provide an olivine lattice structure, for example, a solid state reaction with catalytic and/or base metals, and silicon oxide. A non-limiting example includes, mixing a 1:1 to 3:1 molar ratio, preferably, a 2:1 molar ratio, of M.sup.2 and Si oxides (for example, MnO and SiO.sub.2) until a homogeneous powder is formed. The M.sup.1 metal oxide can be added after mixing the M.sup.2 and silicon dioxide, or to a master batch of the powdered mixture of M.sup.2 oxide and silicon dioxide. In some embodiments (for example, when a high (greater than 8, preferably greater than 9) olivine/spinel ratio is desired), M.sup.1, M.sup.2 and Si oxides are dried at an average temperature of 90 to 110 C., or 95 to 105 C., or 100 C. The amount of M.sup.1 is based on the molar amount of silicon (Si) and the amount of M.sup.2 is adjusted so that the overall molar ratio of catalytic metal (M.sup.1+M.sup.2) to Si is from 1:1 to 2:1. In some aspects of the invention, a molar ratio of M.sup.1 to M.sup.2 can range from 0.01 to 0.5, or 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5. Said another way, the molar ratio of M.sup.2 to M.sup.1 ranges from 3 to <50, or 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or any value there between. In a particular instance, the M.sup.2 to M.sup.1 (e.g., Mn/Ni) molar ratio is from 3 to 9, 4 to 8, or 5 to 7. For example, nickel oxide is added to the powdered mixture based on the molar amount of manganese in the mixture and the overall molar ratio of the catalytic metals to silicon. In embodiments when a noble metal is added as a third metal, the amount of at least one other catalytic material (for example, M.sup.2) is adjusted such that the overall molar ratio of catalytic metal (M.sup.1+M.sup.2) to Si is from 1:1 to 3:1 (i.e., (M.sup.1+M.sup.2+M.sup.3) to Si molar ratio). For example, the amount of noble metal can be adjusted such that to meet the formula for the olivine crystal phase of the catalyst is M.sup.1.sub.x,M.sup.2.sub.1xy,M.sup.3.sub.y).sub.2SiO.sub.4 where 0<x0.25, 0y0.05 and 0<(x+y)0.25, and M.sup.1, M.sup.2, and M.sup.3 are different. The powdered homogeneous mixture can be dried at temperatures at about 115 C. to about 125 C. for 8 to 12 hours. The dried mixture can be mixed with force (for example, grinding, milling, or crushing), and then molded under a pressure of about 8 Tons-force/sq.inch to about 12 Tons-force/sq.inch (110 MPa to 185 MPa) to form pellets. The pellets may be any shape or size (for example, cylindrical, rods, round, elliptical, etc.). The pellets can be calcined by heating the pellets to a temperature between 1200 C. and 1500 C., with 1200 C. and 1300 C. being preferred, at a rate of 1 C. per minute and holding at between 1200 C. and 1500 C. for 24 hours, and then cooled at a rate of about 1 C. per minute to ambient temperature (about 72 C.). In a preferred aspect of the invention, the calcining temperature is 1250 C. The calcining and cooling treatment can be repeated 2, 3, 4, 5 or multiple times. The calcined pellets are then powdered using force (for example, crushed and ground). The resulting catalyst has an olivine structure that has discrete SiO.sub.4.sup.4 anions in the crystal lattice, where the 0 anions of the silicate are coordinated with the metals of the invention, or a discrete spinel structure, or is a mixture of both. In a preferred aspect of the invention, the catalyst is substantially olivine in structure.

(35) The bulk metal catalysts of the present invention can be put on a support. Supported metal catalyst of the present invention can be made by generally known catalyst preparation techniques. In some embodiments, the support may be combined with the catalytic metal to form a catalyst.

(36) In one instance, naturally occurring olivine minerals can be used as supports for the metals of the invention. Examples of olivine minerals that can be used as supports include, but are not limited to, the minerals of forsterite (Mg.sub.2SiO.sub.4), monticelite (CaMgSiO.sub.4), calcio-olivine (Ca.sub.2SiO.sub.4), lienbergite (NiMgSiO.sub.4), glaucochroite (CaMn.sup.2+SiO.sub.4), and any combination thereof. In a particular aspect of the invention, the support does not include iron or iron compounds. In some aspects of the invention, the support can be heat-treated at temperatures prior to combining with a metal of the invention. In some embodiments, impregnation aids may be used during preparation of the catalyst. In certain embodiments, the support may be combined with a metal solution. The metal solution may be mixed with the support and/or sprayed on the support. The metal solution can include Group VIII metals or Group VIII metal compounds, for example, Ni. In some aspects, the metal solution includes Group VIII metals or metal compounds in combination with noble metals, such as Pt and/or Pd. In certain aspects, the metal solution includes Ni, Pt, Pd, Sc, Zr, Mo, Cr, Ru, Os, Rh, Ir, La, Ce, Dy, Tm, Yb, Lu, Co, or any combination thereof. The amount of metal or metal precursor is chosen such that supported catalyst has a total metal content of from 5-15 wt. %. In a non-limiting example, the catalyst is prepared using an incipient impregnation technique. The metal impregnated support can be dried at 80 to 120 C. for about 1 to 3 hours. The dried catalyst can be heat treated (e.g., calcined) at a temperature ranging from 800 C. to about 900 C. for about 3 hours or a time determined to be sufficient to oxide the metals impregnated on the support.

(37) As illustrated in the Examples section, the produced bulk metal oxide catalyst of the invention are sinter and coke resistant materials at elevated temperatures, such as those typically used in syngas production or methane reformation reactions (e.g., 700 C. to 950 C. or a range from 725 C., 750 C., 775 C., 800 C., 900 C., to 950 C.). Further, the produced catalysts can be used effectively in carbon dioxide reforming of methane reactions at a temperature range from 700 C. to 950 C. or from 800 C. to 900 C., a pressure range of 1 bara, and/or at a gas hourly space velocity (GHSV) range from 500 to 10000 h.sup.1, preferably a temperature of 800 C., a pressure of 1 bara, and a GHSV of 75,000 h.sup.1.

(38) D. Carbon Dioxide Reforming of Methane

(39) Also disclosed is a method of producing hydrogen and carbon monoxide from methane and carbon dioxide. The method includes contacting a reactant gas mixture of a hydrocarbon and oxidant with any one of the bulk metal oxide catalysts and/or or supported metal oxide catalysts discussed above and/or throughout this specification under sufficient conditions to produce hydrogen and carbon monoxide at a ratio of 0.35 or greater, from 0.35 to 0.95, or from 0.6 to 0.9. Such conditions sufficient to produce the gaseous mixture can include a temperature range of 700 C. to 950 C. or a range from 725 C., 750 C., 775 C., 800 C., to 900 C., or from 700 C. to 950 C. or from 750 C. to 900 C., a pressure range of about 1 bara, and/or a gas hourly space velocity (GHSV) ranging from 500 to 100,000 h.sup.1 or a range from 500 h.sup.1, 1000 h.sup.1, 5000 h.sup.1, 10,000 h.sup.1, 20,000 h.sup.1, 30,000 h.sup.1, 40,000 h.sup.1, 50,000 h.sup.1, 60,000 h.sup.1, 70,000 h.sup.1, 80,000 h.sup.1, 90,000 h.sup.1, to 100,000 h.sup.1. In a particular instance, a temperature of 800 C., a pressure of 1 bara, and a GHSV of 75,000 h.sup.1 is used. In particular instances, the hydrocarbon includes methane and the oxidant is carbon dioxide. In other aspects, the oxidant is a mixture of carbon dioxide and oxygen. In certain aspects, the carbon formation or coking is reduced or does not occur on the bulk metal oxide catalyst or the supported catalyst and/or sintering is reduced or does not occur on the bulk metal oxide catalyst or the supported catalyst. In particular instances, carbon formation or coking and/or sintering is reduced or does not occur when the bulk metal oxide catalyst is subjected to temperatures at a range of greater than 700 C. or 800 C. or a range from 725 C., 750 C., 775 C., 800 C., 900 C., to 950 C. In particular instances, the range can be from 700 C. to 950 C. or from 750 C. to 900 C. at a pressure of 1 bara. Without wishing to be bound by theory it is believed that no or substantially little sintering occurs because the active sites are incorporated into the framework (bulk catalyst) and there is no metallic particle deposition.

(40) In instances when the produced catalytic material is used in dry reforming methane 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 oxygen and nitrogen. The gaseous feed mixture has is substantially devoid of water or steam. In a particular aspect of the invention the gaseous feed contains 0.1 wt. % or less of water, or 0.0001 wt. % to 0.1 wt. % water. 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.

(41) The reactant gas mixture can include natural gas, liquefied petroleum gas comprising C.sub.2-C.sub.5 hydrocarbons, C.sub.6+ heavy hydrocarbons (e.g., C.sub.6 to C.sub.24 hydrocarbons such as diesel fuel, jet fuel, gasoline, tars, kerosene, etc.), oxygenated hydrocarbons, and/or biodiesel, alcohols, or dimethyl ether. In particular instances, the reactant gas mixture has an overall oxygen to carbon atomic ratio equal to or greater than 0.9.

(42) The method can further include isolating and/or storing the produced gaseous mixture. The method can also include separating hydrogen from the produced gaseous mixture (such as by passing the produced gaseous mixture through a hydrogen selective membrane to produce a hydrogen permeate). The method can include separating carbon monoxide from the produced gaseous mixture (such as passing the produced gaseous mixture through a carbon monoxide selective membrane to produce a carbon monoxide permeate).

EXAMPLES

(43) 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 Olivine/Spinel Catalysts

(44) All chemical precursors used for the olivine based catalyst were obtained from Sigma Aldrich, USA. Manganese oxide and silicon dioxide in the molar ratios shown below in Table 1 were mixed together to form a homogeneous powder of MnO and SiO.sub.2. Nickel oxide was added in amounts sufficient to prepare a mixture of nickel oxide, manganese oxide, and silicon dioxide as shown in Table 1. The amount of nickel and manganese was based on the moles of silicon and the amount of manganese was adjusted such that the overall molar ratio of catalytic metal (Mn+Ni) to Si was 2:1. The homogeneous powder was dried at 120 C. for 10 hours. The dried material was ground to a fine powder, and then pelletized (i.e., molded) with an infrared press at a pressure of about 10 tons to form cylindrical pellets. The formed pellets were calcined at 1250 C. at a ramp rate of 1 C. per minute, held at 1250 C. for 24 hours, and then cooled slowly to room temperature. The calcining and cooling cycle was repeated. The calcined pellets were crushed and ground to form a fine crystalline powder of the NiMn catalyst. FIG. 3 are X-Ray Diffraction (XRD) patterns 31-36 of various bulk metal oxide catalysts of the invention and MnSi or MnO phases. Pattern 31 is for sample 1, pattern 32 is for sample 2, pattern 33 is for sample 3, pattern 34 is for sample 4, pattern 35 is for sample 5, and pattern 36 is for sample 6. The peaks identified with circles are Mn.sub.2SiO.sub.4, the peaks identified with triangles are NiMn.sub.2O.sub.4 (spinel phase), and the peaks identified with stars are MnSiO.sub.3. Patterns 31 and 32 show the phase's determination of the n.sub.mn in.sub.m ratio of infinity (sample 1) and 19 (sample 2), respectively. All the peaks in patterns 31 and 32 can be attributed to the 2 phases, which are Mn.sub.3O.sub.4 (spinel) and MnSiO.sub.3. Pattern 31 (sample 1) had a composition of 25 wt. % Mn.sub.3O.sub.4 and 75 wt. % MnSiO.sub.3. Pattern 31 (sample 2) had composition of 15 wt. % of (Ni.sub.xMn.sub.1x).sub.2SiO.sub.4 and 85 wt. % MnSiO.sub.3. The addition of nickel modified the intensity of several peaks, but did not change the crystalline phases. Patterns 33-36 (samples 3, 4, 5, and 6) all include (Ni.sub.xMn.sub.1x)2SiO.sub.4 and as shown in FIG. 3, which is exactly similar to an XRD pattern of natural olivine mineral.

(45) TABLE-US-00001 TABLE 1 Sample Material SiO.sub.2 MnO NiO n.sub.Mn/n.sub.Ni Crystal No. Name Moles Moles Moles (Molar Ratio) Phases 1 Mn.sub.2Si 1 2 0 Mn.sub.3O.sub.4 MnSiO.sub.3 2 Mn.sub.1.9SiNi.sub.0.1 1 1.9 0.1 19 MnSiO.sub.3 Ni.sub.xMn.sub.3xO.sub.4 3 Mn.sub.1.8SiNi.sub.0.2 1 1.8 0.2 9 MnSiO.sub.3 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4 4 Mn.sub.1.7SiNi.sub.0.3 1 1.7 0.3 5.7 MnSiO.sub.3 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4 5 Mn.sub.1.6SiNi.sub.0.4 1 1.6 0.4 4 MnSiO.sub.3 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4 6 Mn.sub.1.5SiNi.sub.0.5 1 1.5 0.5 3 MnSiO.sub.3 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4

Example 2

Synthesis of Olivine Catalysts

(46) Chemical precursors used for the olivine based catalyst were, NiO (from Alfa Aesar, USA), MnO (from Sigma Aldrich, USA) and SiO.sub.2 (40-63 m from SilicAR, Barranquilla, Colombia). Noble metal precursors of silver oxide (AgO), ruthenium chloride hydrate (RuCl.sub.3.xH.sub.2O), iridium chloride hydrate (IrCl.sub.3.xH.sub.2O), sodiumhexachloroplatinate hydrate (Na.sub.2PtCl.sub.6.6H.sub.2O), ruthenium chloride (RhCl.sub.3) and palladium chloride (PdCl.sub.2) were obtained from Sigma Aldrich, USA.

(47) 1. Olivine Catalysts ((Ni.sub.xMn.sub.y)SiO.sub.4, with x+y=1)

(48) General Procedure. All the reactants were dried at 110 C. under air overnight. Then, the mixtures of Mn:Si in a molar ratio of 2:1 were prepared. Manganese oxide (MnO, 2.3 g) and silicon dioxide (SiO.sub.2, 1.2 g) were mixed together thoroughly in a mortar to form a homogeneous powder. NiO was added with different molar ratio, ranging from 0 to 0.5 mole, with respect to the mole of manganese. Then the mixture was transferred to a crucible and dried at 120 C. for 10 h. After this, the material was grounded to fine powder in a mortar, and finally pelletized with a hydraulic press at an operating pressure of 8 tons-force/(sq.inch) to form cylindrical pellets. The formed pellets were then transferred into a crucible and calcined to 1250 C. at a ramp rate of 1 C. per minute, held at that temperature for 24 h and finally cooled down slowly to room temperature. The grinding and calcination procedure were repeated twice.

(49) All the olivine based catalysts were prepared by following the same method. Table 2 lists the catalyst, catalyst composition and Ni/Mn ratio of the Ni/Mn olivine catalyst. FIG. 4 shows the XRD patterns of NiMn olivine: (a) (Ni.sub.0.1Mn.sub.0.9).sub.2SiO.sub.4 (b) (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4, (c) (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 [circle: Mn.sub.2SiO.sub.4 olivine, triangle: NiMn.sub.2O.sub.4 spinel]. By using the protocol described above, the NiMn olivine yield was increased over NiMn spinel in Example 1. Indeed, the ratio of the relative area for the 2 first peaks, at 2=16.7 (refers to olivine phase) and 2=18.7 (refers to spinel phase), increase by two comparing to the previously reported data. In this work, the wt % of Ni varied from 0.01 to 14.45 wt %. Even at high Ni content, NiO was not detected. Without wishing to be bound by theory, it is believed that the Ni completely incorporated into the olivine lattice. At low n.sub.Mn/n.sub.Ni ratio, peaks at high 2(50-90) start to shift on the right. One possible explanation could be the incorporation of the Ni into the olivine structure.

(50) TABLE-US-00002 TABLE 2 Ni/Mn Catalyst Composition ratio NiMn Olivine (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 High Olivine/Spinel 0.17 ratio NiMn Olivine (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 High Olivine/Spinel 0.25 ratio NiMn Olivine (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 High Olivine/Spinel 0.33 ratio

(51) 2. Nobel Metal Olivine's Catalyst (M-Ni/Mn-olivine, where M=Pt, Pd, Ag, Ru, Ir and Rh)

(52) From the above olivine catalysts, the olivine catalyst with the best Ni/Mn ratio (Ni/Mn=0.17), which gave the highest crystalline NiMn olivine phase, was selected to be doped with noble metals. Six different materials were synthesized with 6 different noble metal precursors.

(53) General Procedure, exemplified with RuNiMn Olivine. All the reactants were dried at 110 C. under air over night. Then, the mixtures of (noble metal: Ni:Mn:Si) in a molar ratio of (0.02:0.28:1.7:1) were prepared. Manganese oxide (MnO, 2.93 g), silicon dioxide (SiO.sub.2, 1.46 g), NiO (0.5 g) and of RuCl.sub.3.xH.sub.2O (0.1 g) were mixed together thoroughly in a mortar to form a homogeneous powder. Then, the mixture was transferred to a crucible and dried at 120 C. for 10 h. After drying, the material was grounded to fine powder with the help of a mortar and pressed by hydraulic press to form cylindrical pellets with an operating pressure of 8 tons-force/(sq. inch). The shaped catalyst was transferred into a crucible and calcined at 1250 C. with a ramp rate of 1 C. per minute, held at that temperature for 24 h and cooled down to room temperature. This procedure was repeated twice.

(54) All the noble metal olivine based catalysts were prepared by following the same method except the amount and the kind of noble metal precursor. Table 3 lists the catalyst, catalyst composition and Ni/Mn ratio of the noble metal olivine catalyst. FIG. 5 shows the XRD pattern of NiMn olivine: (a) (Ag.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (b) (Ru.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (c), (Ir.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (d) (Pt.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (e) (Rh.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4, (f) Pd.sub.0.02Ni.sub.0.28Mn.sub.01.7)SiO.sub.4 [circle: Mn.sub.2SiO.sub.4 olivine, triangle: NiMn.sub.2O.sub.4 spinel]. It can be noticed that a low amount of spinel was obtained in all cases. The intensity ratio between the olivine's peak at 2=16.7 and the spinel peak at 2=18.7 vary from 2 to 5. Moreover, neither NiO nor noble metal oxide, except for the Pt, was detected, suggesting a complete incorporation of these metals into the olivine lattice. XRD pattern (d), PtNi/Mn olivine, shows two peaks at 2=39.8 and 2=48.6 inferring segregation of Pt on the olivine surface.

(55) TABLE-US-00003 TABLE 3 Ni/Mn Catalyst Composition ratio AgNi/Mn Olivine Ag.sub.0.02(Mn.sub.1.7Ni.sub.0.28)SiO.sub.4 0.16 RuNi/Mn Olivine Ru.sub.0.02(Mn.sub.1.7Ni.sub.0.28)SiO.sub.4 0.16 IrNi/Mn Olivine Ir.sub.0.02(Mn.sub.1.7Ni.sub.0.28)SiO.sub.4 0.16 PtNi/Mn Olivine Pt.sub.0.02(Mn.sub.1.7Ni.sub.0.28)SiO.sub.4 0.16 RhNi/Mn Olivine Rh.sub.0.02(Mn.sub.1.7Ni.sub.0.28)SiO.sub.4 0.16 PdNi/Mn Olivine Pd.sub.0.02(Mn.sub.1.7Ni.sub.0.28)SiO.sub.4 0.16

Example 3

Dry Reforming of Methane with Olivine/Spinel Bulk Metal Catalysts of the Invention

(56) General testing procedure. The effectiveness of catalysts of the invention towards carbon dioxide reforming of methane (CDRM, dry reforming of methane) were tested using a high throughput reactor system (hte, GmbH, Heidelberg, Germany). The reactors were of a plug flow design and constructed of steel with ceramic liners. The ceramic liner was 5 mm in diameter and 60 cm in length. The ceramic liner is considered to be inert and used to inhibit steel catalyzed cracking of methane. Catalyst pellets were crushed and sieved to a particle size of 300-500 micrometers. A required amount of catalyst sieve fraction was placed on top of inert material inside the ceramic liner. The catalyst in its oxidized state was heated to about 800 C. in the presence of 90% nitrogen (N.sub.2) and 10% Ar. A mixture of 45% CO.sub.2+45% CH.sub.4+10% Argon (Ar) was used as feed. The mixture was provided to the reactor in 4 steps with 5 minute intervals, replacing the feed with equivalent amounts of nitrogen during the interludes. The reaction conditions are specified in the individual Examples. Gas chromatography was used for gas analysis with Ar being the internal standard. Methane and CO.sub.2 conversion was calculated as follows:

(57) ${\mathrm{CH}}_4\mathrm{conversion}=\frac{\mathrm{moles}\mathrm{of}\mathrm{methane}\mathrm{converted}}{\mathrm{moles}\mathrm{of}\mathrm{methane}\mathrm{in}\mathrm{feed}}100$${\mathrm{CO}}_2\mathrm{conversion}=\frac{\mathrm{moles}\mathrm{of}\mathrm{carbon}\mathrm{dioxide}\mathrm{converted}}{\mathrm{moles}\mathrm{of}\mathrm{carbon}\mathrm{dioxide}\mathrm{in}\mathrm{feed}}100$
The ratio of hydrogen (H.sub.2) to carbon monoxide (CO) was calculated as follows

(58) $H_2/\mathrm{CO}\mathrm{ratio}=\frac{\mathrm{moles}\mathrm{of}{H}_2\mathrm{in}\mathrm{product}}{\mathrm{moles}\mathrm{of}\mathrm{CO}\mathrm{in}\mathrm{product}}100$

(59) CDRM using bulk NiMn catalysts of the present invention. The bulk NiMn catalysts of Table 1 and Table 4 were tested at 700 C. to 800 C. at 1 bara, and a gas hourly space velocity (GSHV) of 75,500 h.sup.1 for 100 hours of operation. The initial temperature was 700 C. and was increased to 750 C. after 15 hours, and then increased to 800 C. after about 30 hours. After 40 hours of operation, the percent conversion of methane was between 10% and 50%, the percent conversion of carbon dioxide was greater than 10% and 70%, and the H.sub.2/CO ratio was between 0.35 and 0.60 for the catalysts. The catalyst that had a non-detectable olivine crystal phase had a percent conversion of methane of about 10%, a percent conversion of carbon dioxide of about 20%, and the H.sub.2/CO ratio of about 0.35 after about 40 hours time on stream and 800 C. For catalysts that contained olivine crystal phases, the percent conversion of methane was greater than 30%, the percent conversion of carbon dioxide was greater than 40%, and the H.sub.2/CO ratio was greater than 0.45 after 40 hours time on stream and 800 C. Table 4 lists the percent methane conversion for the catalysts of the present invention (samples 2-6) and inert manganese silicon oxides (sample 1) at 100 hours of run time. FIGS. 6-8 are graphical depictions of % methane (FIG. 6), % carbon dioxide conversion (FIG. 7), and the ratio of hydrogen to carbon monoxide versus time, in hours (FIG. 8) for the samples listed in Tables 1 and 2. In FIGS. 6-8, the data using the inactive sample 1 as the catalyst is represented by square blocks, the data for novel catalyst Sample #2 is represented by circles, the data for novel catalyst Sample #3 is represented by upright triangles, the data for novel catalyst Sample #4 is represented by upside down triangles, the data for novel catalyst Sample #5 is represented by turned squares, and the data for novel catalyst Sample #6 is represented by turned triangles. Further, the catalyst was found to be stable without any deactivation for 100 hours of duration as shown by the XRD pattern in FIG. 9. FIG. 9 shows XRD patterns of spent catalyst (top pattern, sample 3) of the present invention and inert material steatite a kind of mineral talc, magnesium silicate (bottom pattern). The circles on the peaks in the top pattern represent the peaks for both crystalline phases Ni.sub.xMn.sub.3xO.sub.4 and (Ni.sub.xMn.sub.1x).sub.2SiO.sub.4. Since both crystalline phases were still present in the spent catalyst, the activity of the catalyst had not changed after 100 hours time on stream. No sintering was observed.

(60) TABLE-US-00004 TABLE 4 CH.sub.4 n.sub.Mn/n.sub.Ni conver- Sample Material (Molar Crystal sion TOS No. Name Ratio) Phases (%) (hours) 1 Mn.sub.2Si Mn.sub.3O.sub.4 0 100 MnSiO.sub.3 2 Mn.sub.1.9SiNi.sub.0.1 19 MnSiO.sub.3 20 100 Ni.sub.xMn.sub.3xO.sub.4 3 Mn.sub.1.8SiNi.sub.0.2 9 MnSiO.sub.3 40 100 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4 4 Mn.sub.1.7SiNi.sub.0.3 5.7 MnSiO.sub.3 40 100 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4 5 Mn.sub.1.6SiNi.sub.0.4 4 MnSiO.sub.3 40 100 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4 6 Mn.sub.1.5SiNi.sub.0.5 3 MnSiO.sub.3 40 100 Ni.sub.xMn.sub.3xO.sub.4 (Ni.sub.xMn.sub.1x)2SiO.sub.4

(61) CDRM using bulk MnSi catalysts of the present invention. The MnSi catalyst listed in Table 1 having Mn.sub.3O.sub.4 and MnSiO3 phases were tested at the same conditions the NiMn were tested. No methane conversion were observed for this catalyst after 100 hours (see FIGS. 6-8). Thus, the Mn.sub.3O.sub.4 and MnSiO.sub.3 phases were considered inactive towards carbon dioxide reforming of methane.

Example 4

Dry Reforming of Methane with Olivine Bulk Metal Catalysts of the Present Invention

(62) Testing of the olivine bulk metal catalysts was performed using the general procedure described in Example 4, with exceptions described in the specific sections below.

(63) CDRM using bulk NiMn olivine of the present invention at a pressure of 10 bar. CDRM reaction was carried out at T=800 C. and P.sub.tot=10 bar. The space velocity was 60,000 h.sup.1 for a gas composition of 10% Ar/45% CO.sub.2/45% CH.sub.4, with 40 mg of catalyst. The feed rate used was 50 cc.Math.min.sup.1. FIGS. 10 and 11 show the CH.sub.4 conversion and CO.sub.2 conversion respectively. The tested catalysts were (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4, (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4, (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 and comparative catalyst pyrochlore LRZ. FIG. 10: CH.sub.4 conversion of (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 (.square-solid.), (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 (), (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 (.box-tangle-solidup.) and comparative pyrochlore catalyst (.Math.). FIG. 11 CO.sub.2 conversion of (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 (.square-solid.), (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 (), (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 (.box-tangle-solidup.) and comparative pyrochlore catalyst (.Math.). Under these experimental conditions, the comparative pyrochlore catalyst exhibited the highest CH.sub.4 conversion and CO.sub.2 conversion with 60% and 70% respectively. However, the competitive pyrochlore catalyst deactivated after 200 h of run time. After 80 h, olivine catalysts of the present invention, with a Ni/Mn ratio of 0.17 and 0.33, exhibited the same CH.sub.4 and CO.sub.2 conversion, 45% and 55% respectively. The olivine catalysts of the present invention with Ni/Mn ratio=0.25 exhibited a CH.sub.4 conversion of 35% and a CO.sub.2 conversion of 45%. After 80 h of run, olivine catalysts of the present invention did not show any deactivation behavior. FIG. 12 shows graphs of H.sub.2/CO ratio of (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 (.square-solid.), (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 (), (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 (.box-tangle-solidup.) and comparative pyrochlore catalyst (.Math.). The H.sub.2/CO of (Ni.sub.0.15Mn.sub.0.85).sub.2SiO.sub.4 and (Ni.sub.0.25Mn.sub.0.75).sub.2SiO.sub.4 are stable and equal to 0.6, however, the H.sub.2/CO ratio of (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 is slightly lower than the other and decreases from 0.6 to 0.55 after 80 h. From these results is was determined that the different reactions involved in the CDRM, (dry reforming, RWGS and steam reforming) are not in a steady state and the active site of the catalyst is still evolving.

(64) FIG. 13 shows the XRD pattern of the olivine (Ni.sub.0.2Mn.sub.0.8).sub.2SiO.sub.4 before (top) and after the CDRM reaction (bottom pattern). Under these experimental reactions, no modification of the olivine structure was detected. Thus, Ni/Mn olivine of the present invention is a stable catalyst for the CDRM. It was noted that the spinel XRD pattern was not detected after the CDRM reaction, which was determined to result in a modification of the spinel phase during the experiment. Without wishing to be bound by theory, it is believed that the change in the spinel phase explains the modification of the reactivity of the catalyst over the time. The XRD pattern of the spent catalyst (after the CDRM reaction) shows a broad peak at 2=26.3. This peak was attributed to the coke formation during the reaction and 30 wt % of coke was determined by using the Vegard's law.

(65) CDRM using the M-Ni/Mn olivine of the present invention at a pressure of 5 bar. CDRM reaction is carried out at T=800 C. and P.sub.tot=5 bar. The space velocity is 60,000 h.sup.1 for a gas composition of 10% Ar/45% CO.sub.2/45% CH.sub.4, with 40 mg of catalyst. The feed flow was 50 cc.Math.min.sup.1.

(66) FIGS. 14 and 15 show the CH.sub.4 conversion and CO.sub.2 conversion respectively of AgNi/Mn olivine, RuNi/Mn olivine, IrNi/Mn olivine, PtNi/Mn olivine, and RhNi/Mn olivine. FIG. 14: CH.sub.4 conversion of Ag.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.square-solid.), Ru.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (), Ir.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.box-tangle-solidup.), Pt.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.Math.) and Rh.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.diamond-solid.). FIG. 15 CO.sub.2 conversion of Ag.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.square-solid.), Ru.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (), Ir.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.box-tangle-solidup.), Pt.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.Math.) and Rh.sub.0.02(Ni.sub.0.28Mm.sub.1.7)SiO.sub.4 (.diamond-solid.). After few hours of run, the PdNi/Mn olivine deactivated because of the coke formation. Consequently, the catalyst results were not shown on these figures. The others olivine catalyst of the present invention show a very good stability and after 180 h of run no trend of deactivation was detected. The CH.sub.4 conversion of the AgNi/Mn, RuNi/Mn, IrNi/Mn and PtNi/Mn based olivine catalysts of the present invention were around 35-40% while RhNi/Mn shows a conversion of 50%. FIG. 16 shows the H.sub.2/CO ratio of AgNi/Mn olivine, RuNi/Mn olivine, IrNi/Mn olivine, PtNi/Mn olivine, and RhNi/Mn olivine. FIG. 16: H.sub.2/CO ratio of Ag.sub.0.02(Ni.sub.0.28Mn.sub.1.7SiO.sub.4 (.square-solid.), Ru.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (), Ir.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.box-tangle-solidup.), Pt.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.Math.) and Rh.sub.0.02(Ni.sub.0.28Mn.sub.1.7)SiO.sub.4 (.diamond-solid.). All of these catalysts were stable over 180 h. The lowest ratio was around 0.75 while the RhNi/Mn was 0.95. By comparing this result with the H.sub.2/CO ratio obtained without noble metal doping, it was determined that the H.sub.2/CO ratio were increased by 10 to 15%. This improvement was attributed to the noble metal doping.