EP1124635A1 - Catalysts and process for reforming of hydrocarbons - Google Patents

Catalysts and process for reforming of hydrocarbons

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Publication number
EP1124635A1
EP1124635A1 EP99948601A EP99948601A EP1124635A1 EP 1124635 A1 EP1124635 A1 EP 1124635A1 EP 99948601 A EP99948601 A EP 99948601A EP 99948601 A EP99948601 A EP 99948601A EP 1124635 A1 EP1124635 A1 EP 1124635A1
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EP
European Patent Office
Prior art keywords
oxide
nickel
catalyst
temperature
synthesis gas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP99948601A
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German (de)
French (fr)
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EP1124635A4 (en
Inventor
Graeme John Millar
Jonathan James Gamman
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University of Queensland UQ
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University of Queensland UQ
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Publication of EP1124635A1 publication Critical patent/EP1124635A1/en
Publication of EP1124635A4 publication Critical patent/EP1124635A4/en
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • This invention relates to catalysts for the production of a mixture of hydrogen and carbon monoxide by carbon dioxide reforming of a hydrocarbon feedstock, and to precursors of such catalysts.
  • the invention also relates to processes for the preparation of such catalysts and precursors, and to a process for the production of a mixture of hydrogen and carbon monoxide by carbon dioxide reforming of a hydrocarbon feedstock.
  • Synthesis gas (commonly termed “ syngas” ) is a mixture of carbon monoxide (CO) and hydrogen (H 2 ) which is used in the manufacture of a wide range of commercially valuable chemicals such as methanol, ammonia, higher alcohols and acetic acid.
  • syngas is primarily produced by steam reforming of a hydrocarbon gas, usually natural gas, in the presence of an appropriate catalyst at high temperature (>700°
  • Choice of product to manufacture is dictated by the ratio of hydrogen to carbon monoxide which is termed the stoichiometric number (SN): For example, methanol synthesis is ideally performed with a value for SN of 2.00
  • the carbon dioxide reforming reaction provides a means of reducing emissions when used in conjunction with the utilization of solar energy.
  • the use of solar energy in this context is via a Chemical Energy Transport System (CETS) known as a heat pipe.
  • CETS Chemical Energy Transport System
  • the thermochemical heat pipe concept is illustrated diagrammatically in Figures 1 & 2. Briefly, in the closed loop configuration illustrated in Figure 1, solar energy is used to supply the process heat for the CO 2 reforming reaction. Subsequently, the reaction products (CO and H 2 ) can be stored and/or transported to a separate site and the reverse methanation reaction may be performed subsequently to release the chemically stored 0 solar energy as required. The methanation products are then returned to the reformer reactor to complete the closed loop. Alternatively, an open loop cycle as illustrated in Figure 2 can be employed.
  • the calorific value of the syngas mixture (CO + H 2 ) is 1137 kJ/mol whereas only 890 kJ/mol would be available if only the original methane was combusted.
  • the present inventors have discovered that certain catalysts obtainable from a composition which includes nickel oxide and a second metal oxide or mixed metal oxide having certain specified properties, are capable of use in a process for reforming hydrocarbons with carbon dioxide to produce a mixture of hydrogen and carbon monoxide, the catalysts having an improved lifetime compared to known catalysts for such a reaction, by virtue of being relatively resistant to deactivation by coking.
  • a catalyst precursor for reforming hydrocarbons to produce synthesis gas at an elevated temperature which catalyst precursor includes a solid solution of nickel oxide in an oxide of cubic structural type which is an oxygen ion conductor at the elevated temperature.
  • a process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300- 1000°C;
  • a process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
  • a catalyst precursor produced by the process of the second or third embodiments.
  • a catalyst for reforming hydrocarbons to produce synthesis gas the catalyst being obtainable by reducing a catalyst precursor of the first or fourth embodiments in a reducing atmosphere at an elevated temperature.
  • a process for producing a catalyst for reforming hydrocarbons to produce synthesis gas including the steps of
  • step (iv) contacting the product of step (iii) with a reducing atmosphere for a time and at a temperature sufficient to reduce at least part of the nickel to nickel metal.
  • a process for reforming a hydrocarbon to produce synthesis gas including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst of the fifth or seventh embodiments at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
  • a catalyst precursor for reforming hydrocarbons to produce synthesis gas at an elevated temperature which catalyst precursor includes a mixture of nickel oxide and an oxide of cubic structural type which is an oxygen ion conductor at the elevated temperature.
  • a process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
  • a catalyst precursor produced by the process of the tenth embodiment.
  • a catalyst for reforming hydrocarbons to produce synthesis gas the catalyst being obtainable by reducing a catalyst precursor of the ninth or eleventh embodiments in a reducing atmosphere at an elevated temperature.
  • a process for reforming a hydrocarbon to produce synthesis gas including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst of the twelfth embodiment at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
  • Fig. 1 is a schematic of the concept of a closed loop thermochemical heat pipe
  • Fig. 2 is a schematic of the concept of an open loop thermochemical heat pipe
  • Figs. 3(a) to 3(c) are XRD traces for nickel oxide/yttrium oxide catalyst precursors including respectively 0, 5 and 30 wt% nickel.
  • Fig. 4 includes XRD traces for nickel oxide/silica catalyst precursors, not in accordance with the present invention, having three different weight loadings of nickel.
  • Figs. 5(a) to 5(c) are XRD traces for nickel oxide/terbium oxide catalyst precursors including respectively 0, 5 and 30 wf% nickel.
  • Figs. 6(a) to 6(c) are XRD traces for nickel oxide/praseodymium oxide catalyst precursors including respectively 0, 5 and 30 wt% nickel.
  • Fig. 7 includes XRD traces for (a) 5 wt% nickel oxide/gadolinium oxide, (b) 5 wt% nickel oxide/praseodymium oxide and (c) 5 wt% nickel oxide/ytterbium oxide
  • Fig. 8 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 wt% nickel/yttrium oxide catalyst.
  • Fig. 9 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 wt% nickel/gadolinium oxide catalyst.
  • Fig. 10 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 : 1 ratio) as a function of temperature in the presence of a 5 wt% nickel/praseodymium oxide catalyst.
  • Fig. 11 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 wt% nickel/ytterbium oxide catalyst.
  • Fig. 12 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 : 1 ratio) as a function of temperature in the presence of a 5 wt% nickel/terbium oxide catalyst.
  • Fig. 13 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 5 wt% nickel/samarium oxide catalyst.
  • Fig. 14 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 : 1 ratio) as a function of temperature in the presence of a 5 wt% nickel/lanthanum-strontium-gallium-magnesium oxide catalyst.
  • Fig. 15 is a transmission electron microscopy (TEM) image of a 5 wt% o nickel/yttrium oxide catalyst after calcination.
  • TEM transmission electron microscopy
  • Fig. 16 is a transmission electron microscopy (TEM) image of a 5 wt% nickel/yttrium oxide catalyst after reaction at 750°C for 50 hours.
  • TEM transmission electron microscopy
  • Fig. 17 shows transmission electron microscopy (TEM) images of (a) 1 wt%, (b) 5 wt , (c) 10 wt% and (d) 30wt % nickel/silica catalyst after calcination.
  • 5 Fig. 18 is a transmission electron microscopy (TEM) image of a 30 wt% nickel/MgO catalyst after calcination.
  • Fig. 19 is a transmission electron microscopy (TEM) image of a 30 wt% nickel/MgO catalyst after reaction at 750°C for 50 h.
  • TEM transmission electron microscopy
  • Fig. 20 shows XRD traces for (a) yttrium oxide, (b) 5 wt% nickel/yttrium oxide o after calcination and (c) 5 wt% nickel/yttrium oxide after reaction with CO 2 /CH 4 at 750° C for 5 Oh.
  • Fig. 21 shows XRD traces for (a) magnesium oxide, (b) 30 wt% nickel/magnesium oxide after calcination and (c) 30 wt% nickel/magnesium oxide after reaction with C0 2 /CH 4 at 750°C for 50h.
  • oxide of cubic structural type means an oxide of a metal or a mixed metal oxide which has an ideal cubic or distorted cubic structure. Examples of such structures includes fluorite, perovskite, pyrochlore, brownmillerite and spinel structures.
  • the oxide of cubic structural type may be any such metal oxide, including an oxide of a single metal or a mixed metal oxide, provided it is also an oxygen ion conductor at a temperature in the range of about 300-1000°C; that is, a temperature range which includes the typical temperatures for the hydrocarbon reforming reaction for which the catalysts of the invention, obtainable from the catalyst precursors of the invention, may be used.
  • suitable oxides include but are not limited to Z ⁇ - ] _ x Y x O 2 _ x/2 , Ce ⁇ _ ⁇ Gd x° 2 -x /2> La Ci"i- ⁇ Mg x O 3 . x/2 , La 1 .
  • the oxide of cubic structural type is an oxide of an element selected from the group consisting of yttrium, gadolinium, praseodymium, samarium, ytterbium and terbium.
  • the amount of nickel in the catalysts and catalyst precursors of the invention is in the range of from about 1% to 50% by weight, more typically from about 5%> to about 40% by weight, or from about 6% to about 40%> by weight, or from about 7% to about 40%) by weight, or from about 8% to about 40% by weight, or from about 9% to about 40%) by weight, still more typically from about 10% to about 40% by weight, even more typically from about 10% to about 30% by weight, based on the total weight of the catalyst or catalyst precursor.
  • Modifiers to enhance the activity of the catalyst and catalyst precursor formulations described above may be added.
  • these can be included in the catalyst by any convenient method, the precise choice may depend on the identity of the additive.
  • promoting species may simply be added to the initial impregnating solution of nickel precursor, or they be incorporated as part of a co-precipitation procedure.
  • a catalyst of the invention may further include one or more additives selected from the group consisting of:
  • noble metals selected from the group consisting of Pt, Ir, Rl , Ru, Os, Pd and Re
  • oxides selected from the group consisting of TiO 2 , Mo0 3 . WO 3 , ZrO 2 , V 2 O 5 ,
  • elements selected from the group consisting of Ag, Cu, Au and Zn elements selected from the group consisting of P, Sb, As, Sn and Ge.
  • the amounts included are typically in the range of:
  • V 2 0 , Nb 2 0 5 , Sc 2 O 5 and Ta 2 O 5 from 0.01% to 20%;
  • the active catalyst components can be dispersed on the surface of a conventional oxide carrier of which silica, alumina, zirconia, thoria, silica-alumina, zeolites, clay minerals and derivatives of clay minerals are common examples.
  • a conventional oxide carrier of which silica, alumina, zirconia, thoria, silica-alumina, zeolites, clay minerals and derivatives of clay minerals are common examples.
  • the support material employed although it is desirable that the catalyst display good attrition resistance and high crush strength for industrial usage. Formation of a supported catalyst of this kind may readily be achieved by impregnation of soluble precursors of the nickel oxide and the oxide of cubic structural type on the support of choice, followed by drying and calcination.
  • step (i) is a step of wet impregnation of the oxide of cubic structural type by an aqueous solution of a soluble nickel compound.
  • a suitable soluble nickel compound is nickel nitrate.
  • any other metal salt which is soluble in an aqueous solution can alternatively be used, such as nickel bromide, nickel chloride, nickel iodide and nickel sulfate.
  • use may also be made of an organic solvent and a nickel compound which is soluble in the organic solvent.
  • Catalyst precursors of the invention may be prepared using methods other than wet impregnation techniques, however.
  • Alternative synthesis routes known to those skilled in the art can also be employed, examples of which include coprecipitation and solid state reaction.
  • the heating temperature in step (ii) is typically carried out in an oxygen containing atmosphere. More typically the atmosphere is air or oxygen gas.
  • the heating o temperature in step (ii) is typically in the range of from 250°C to 1500°C, more typically in the range selected from the group consisting of 250°C to 1400°C, 250°C to 1300°C, 250°C to 1200°C, 250°C to 1100°C, 250°C to 1000°C, 250°C to 950°C, 250°C to 900°C, 250°C to 850°C, 250°C to 800°C, 300°C to 800°C, more typically 350°C to 600°C.
  • Calcination temperatures for nickel salts that is, temperatures at which nickel salts may be converted to nickel oxide, are generally known to persons of ordinary skill in the art, as are appropriate calcination times.
  • Step (iii) of the process of the second, third, sixth or tenth embodiments may also be carried out a temperature typically in the range of from 250°C to 1500°C, more typically in the range selected from the group consisting of 250°C to 1400°C, 250°C to 1300°C, 250°C to 1200°C, 250°C to 1100°C, 250°C to 1000°C, 250°C to 950°C, 250°C to 900°C, 250°C to 850°C, 250°C to 800°C, 300°C to 800°C, more typically 350°C to 600°C.
  • the temperature for step (ii) may be the same or different to the temperature for step (iii).
  • the time required in step (iii) of the process of the second, third or tenth embodiments to heat the mixture of the nickel oxide and support material to form the catalyst precursor is in the range selected from the group consisting of about 15 to about 30 minutes, about 30 to about 40 minutes, about 40 to about 50 minutes, about 50 to about 60 minutes, about 60 minutes to about 70 minutes, about 70 minutes to about 80 minutes, about 80 minutes to about 90 minutes. It is also usual that the time required in step (iii) of the process may take at least 100 minutes or more, or at least 2 hours or more. It will be appreciated, however, that the time required is dependent on the temperature of process step (iii).
  • Conditions for step (iii) of the process of the second embodiment may be determined readily by monitoring the heated composition for the formation of a solid solution.
  • the identification of the formation of the catalyst precursor which in one embodiment of the invention entails the identification of the formation of a solid solution is readily made by inspection of an X-ray powder diffraction profile for the material, as illustrated in accompanying Figures 3 to 7. There is shown in Figure 3, X-ray diffraction (XRD) patterns for yttrium oxide, 10 wt % nickel oxide-yttrium oxide and 30 wt % nickel oxide-yttrium oxide. Notably, the XRD trace for pure yttrium oxide is very sharp and intense which is indicative, to those of ordinary skill, of a highly crystalline material.
  • the XRD pattern becomes less intense and the lines become broader in character as the nickel is added.
  • the 30 wt % nickel oxide-yttrium oxide catalyst exhibits extremely broad lines due to the yttrium oxide component which is recognised by those skilled in the art to be representative of an amorphous or nanocrystallme oxide material.
  • the presence of very wide reflections attributable to nickel oxide which again not only indicates the presence of amorphous or nanocrystallme nickel oxide but also the weak intensity of these latter features can be interpreted as meaning that there may exist a fraction of the nickel species in a solid solution with the yttrium oxide.
  • FIG. 4 illustrates XRD profiles recorded for a series of calcined nickel/silica catalysts.
  • the silica support is characterized by an amorphous "lump" at low values of 2 ⁇ . whereas sharp, intense peaks are apparent for nickel oxide at 37, 43 and 63 degrees 20. As the loading of nickel becomes higher, the XRD peaks become narrower, thus indicating that the nickel particles were becoming larger and more crystalline in character. o Electron microscopy observations are consistent with this interpretation. Importantly, the silica support of the nickel/silica catalyst does not have the ability to form a solid solution with nickel.
  • Nickel particles are neither as well dispersed as in those catalysts described in this invention or as small and amorphous or nanocrystalline in structure.
  • Figures 5 and 6 which display XRD patterns for a nickel oxide/terbium oxide and nickel oxide/praseodymium catalysts, respectively.
  • the features for the terbium oxide component diminish in intensity as the nickel loading is increased, again indicative of a o more amorphous or nanocrystalline material.
  • the reflections characteristic for nickel oxide are extremely weak in intensity.
  • the nickel component may at least in part be forming a solid solution with the rare earth material or at least the rare earth material has the ability to disperse the nickel component to a greater extent, than that for a silica support.
  • the XRD trace clearly illustrates that the reflections assigned to praseodymium oxide become very broad and weak in intensity as the nickel loading increases.
  • Another feature of the catalysts of the present invention is the general observation that the catalyst surface area increases as the nickel loading increases.
  • Table 1 illustrates the surface areas as calculated by the standard BET method for several of the catalysts revealed in this disclosure, and for comparison purposes, surface areas of silica and nickel oxide/silica catalysts are shown.
  • the precursors of catalysts of the invention require reduction to produce the catalysts.
  • Reduction of the catalyst precursor can be achieved by pre-reducing the catalyst at a temperature of 300°C or greater with a gas stream comprising of hydrogen or any other readily available reductant, such as carbon monoxide or a hydrocarbon, such as methane.
  • a gas stream comprising of hydrogen or any other readily available reductant, such as carbon monoxide or a hydrocarbon, such as methane.
  • Other catalyst precursor compositions may require reduction at still higher temperatures, such as up to about 900° C.
  • the reduction procedure employed should preferably be at a temperature which will facilitate reduction of a fraction of the nickel ions to nickel metal.
  • the catalyst precursor may be prereduced in situ by exposure to the reactant mixture itself, and optionally raising the temperature above the desired reaction temperature for the reforming reaction.
  • a process of the eighth or thirteenth embodiments of the invention may be carried out using a catalyst in accordance with the invention under conditions generally known in the art for carbon dioxide reforming reactions.
  • typically conditions for carrying out the process of the fourth embodiment of the present invention include a temperature range of from about 300-1100°C, more typically from about 400°C to 850°C, at a pressure of from about lOkPa to about 10,000kPa, more typically from about lOOkPa to about 5,000kPa, still more typically from about lOOkPa to about 3,000kPa. at an apparent space velocity in the range of from about 1000 to lOOOOOOlr' ., more typically from about 10000 to 500000h- ] .
  • the hydrocarbon in a reactant mixture for the process of the eighth or thirteenth embodiments is typically methane but may also be a mixture of one or more hydrocarbons selected from methane and higher hydrocarbons such as ethane, ethene, ethyne, propane, propene, butane(s), butene(s), butyne(s), etc.
  • Typical reactant mixture compositions in the process of the eighth or thirteenth embodiments may contain, in addition to the hydrocarbon and carbon dioxide, other gases such as hydrogen, carbon monoxide, substantially inert gases such as nitrogen, helium and/or argon, and/or small amounts of oxygen.
  • the proportion of hydrocarbon relative to carbon dioxide will be in the range of from 20:1 to 1 :20, more typically 9: 1 to 1 :9, even more typically 4: 1 to 1 :4.
  • Example 1 Commercially available yttrium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(N0 3 ) 2 .6H 2 O (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 1 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species.
  • yttrium oxide Pi-KEM, UK
  • Ni(NO 3 ) 2 .6H 2 O Aldrich, 99.999 %
  • the impregnated catalyst consisting of 5 wt%> nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species.
  • the catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature.
  • TPRxn temperature programmed reaction
  • Example 3 Commercially available gadolinium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO 3 ) 2 .6H 2 0 (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours.
  • the impregnated catalyst consisting of 5 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature.
  • Example 7 Commercially available terbium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO 3 ) 2 .6H 2 O (Aldrich, 99.999 %) and the resulting slurry dried at
  • a portion of the oxygen ion conductor lanthanum-strontium-gallium-magnesium oxide (La 0.9 Sro .
  • the impregnated catalyst consisting of 5 wt % nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature.
  • Example 9 The calcined 5% Ni/yttrium oxide precursor, prepared as described in Example 2, after calcining, was pelleted, crushed and sieved to a particle size between 0.7 and 1.0 mm before placement into a microreactor facility for catalyst activity evaluation. Approximately 0.2 g of catalyst was loaded into a 12 mm diameter quartz reactor tube situated in an electrically heated furnace which was capable of operation between 25 and 1000°C. Samples were pre-reduced in a 20% hydrogen/helium mixture at 500°C for lh. Subsequently, an equimolar mixture of carbon dioxide and methane (total flow rate 200 mL/min) was contacted with the catalyst resulting in an apparent space velocity (GHSV) of 35,000h"' .
  • GHSV apparent space velocity
  • Example 10 The unique behaviour of the catalysts described in this invention is also revealed by inspection of transmission electron microscopy (TEM) obtained before after 50 hours of C0 2 /CH 4 reaction at 750°C.
  • Fig. 15 displays TEM images of a 5 wt % Ni/yttrium oxide catalyst following calcination of the sample. Notably, the images reveal the presence of only nanocrystalline yttrium oxide with no evidence for large nickel grain (>5 nm) detected. Even after reaction at 750°C for 50 h (Fig. 16) no nickel crystallites were discerned: indeed the only significant feature was the growth of yttrium oxide tubules. Comparative Example 2
  • Fig. 17 displays TEM images of a range of nickel/silica catalysts following the calcination procedure.
  • nickel particles were readily detected which illustrated that silica was not an effective support for dispersing nickel. Consequently, those skilled in the art would realise that silica supported catalysts would not only deactivate due to significant coking on the large nickel crystallites but also nickel sintering would occur during reaction conditions leading to disastrous loss of surface area.
  • Fig. 18 provides an image of a 30 wt % Ni/MgO catalyst following calcination. The nickel species appeared to be well dispersed due to the formation of a solid solution
  • Example 1 1 The efficiency of the catalysts disclosed in this invention for dispersion and stabilization of nickel species is further shown by inspection of the relevant X-ray diffraction (XRD) patterns for the catalyst before and after reaction at 750°C for 50 hours.
  • Figure 20 shows XRD traces for yttrium oxide, calcined 5 wt % nickel/yttrium oxide and 5 wt % nickel/yttrium oxide after reaction. Significantly, no evidence for nickel crystallite growth is detected.
  • XRD X-ray diffraction
  • Table 1 BET surface areas of a representative sample of catalysts for this invention.

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Abstract

The present invention is directed to catalysts for the production of a mixture of hydrogen and carbon monoxide by carbon dioxide reforming as well as to the precursors of such catalysts. The catalyst precursors include a mixture of nickel oxide and an oxide of cubic structural type which is an oxygen ion conductor at elevated temperatures. Processes for the preparation of such catalyst precursors and catalysts are also disclosed as are processes for producing a mixture of hydrogen and carbon monoxide by carbon dioxide reforming of a hydrocarbon feedstock.

Description

Catalysts and process for reforming of hydrocarbons
Field of the Invention
This invention relates to catalysts for the production of a mixture of hydrogen and carbon monoxide by carbon dioxide reforming of a hydrocarbon feedstock, and to precursors of such catalysts. The invention also relates to processes for the preparation of such catalysts and precursors, and to a process for the production of a mixture of hydrogen and carbon monoxide by carbon dioxide reforming of a hydrocarbon feedstock.
Background of the Invention
Synthesis gas (commonly termed " syngas" ) is a mixture of carbon monoxide (CO) and hydrogen (H2) which is used in the manufacture of a wide range of commercially valuable chemicals such as methanol, ammonia, higher alcohols and acetic acid.
Industrially, syngas is primarily produced by steam reforming of a hydrocarbon gas, usually natural gas, in the presence of an appropriate catalyst at high temperature (>700°
C) and high pressure (1-30 atm). For example, with methane as the hydrocarbon source the theoretical reaction can be described as follows:
CH4 + H2O → CO + 3H2 (ΔH298 = +206.4 kJ/mole)
Choice of product to manufacture is dictated by the ratio of hydrogen to carbon monoxide which is termed the stoichiometric number (SN): For example, methanol synthesis is ideally performed with a value for SN of 2.00
CO + 2H2 → CH3OH However, SN from steam reforming is usually in the range 2.8-2.6 and thus it must be adjusted by the addition of CO2:
3CH4 + CO2 + 2H2O → 4CH3OH There is a growing desire to make syngas with SN values of 1.0 or lower as a number of significant chemicals are more favoured by those latter ratios. For instance, acetic acid is manufactured by the carbonylation of methanol in the presence of a homogeneous catalyst:
CO+CH3OH → CH3COOH Catalytic reforming of methane with carbon dioxide produces syngas with a low hydrogen to carbon monoxide ratio (SN=1):
CO2 + CH4→ 2CO + 2H2 This latter reaction is also of considerable interest in terms of present environmental concerns regarding global warming by the so called " greenhouse effect" . Carbon dioxide is the main greenhouse gas by volume emitted from anthropogenic sources, and in addition methane is also of concern due to its high global warming potential (21 times that for CO ) even though significantly less by volume of methane is emitted to the atmosphere compared to carbon dioxide.
5 The consumption of two greenhouse gases in the CO2/CH reforming reaction makes it a potential candidate for achieving substantial reductions in emissions of these gases. Furthermore there exist several large sources of carbon dioxide and methane which are not exploited to their full potential as yet. Such sources include landfill gas which is a mixture of about 50% methane and 50%o carbon dioxide (plus trace impurities), o coal bed methane which typically contains from 10 to 70% carbon dioxide, and natural gas fields which may contain from 1 to 70% carbon dioxide.
The carbon dioxide reforming reaction provides a means of reducing emissions when used in conjunction with the utilization of solar energy. The use of solar energy in this context is via a Chemical Energy Transport System (CETS) known as a heat pipe. The thermochemical heat pipe concept is illustrated diagrammatically in Figures 1 & 2. Briefly, in the closed loop configuration illustrated in Figure 1, solar energy is used to supply the process heat for the CO2 reforming reaction. Subsequently, the reaction products (CO and H2) can be stored and/or transported to a separate site and the reverse methanation reaction may be performed subsequently to release the chemically stored 0 solar energy as required. The methanation products are then returned to the reformer reactor to complete the closed loop. Alternatively, an open loop cycle as illustrated in Figure 2 can be employed. In this configuration the product syngas is combusted to produce heat and power (typically in a gas turbine system integrated to an IGCC power plant). The advantage of this process is that the calorific value (relative to the combustion 5 of methane alone) of the fuel is "boosted" by about 28% as can be seen by inspection of the thermodynamics of the reactions involved: Conventional Combustion
CH4 + 2O2 → CO2 + 2H2O ΔH = -890kJ/mol
Solar boosted reforming followed by combustion C02 + CH4→ 2CO + 2H2 ΔH = +247kJ/mol
2CO + O2 - 2CO2 ΔH = -566 kJ/mol
2H2 + O2 → 2H2O ΔH = - 571 kJ/mol
Thus, the calorific value of the syngas mixture (CO + H2) is 1137 kJ/mol whereas only 890 kJ/mol would be available if only the original methane was combusted. To date, there is no established industrial technology for carbon dioxide reforming of methane due primarily to excessive carbon deposition on the catalysts used hitherto, causing catalyst deactivation. Therefore, there is a need for novel catalysts which are not only active for the carbon dioxide reforming reaction, but also of high resistance to deactivation by coking and therefore of long lifetime. Desirably, such catalysts will also be of relatively low cost.
Surprisingly, the present inventors have discovered that certain catalysts obtainable from a composition which includes nickel oxide and a second metal oxide or mixed metal oxide having certain specified properties, are capable of use in a process for reforming hydrocarbons with carbon dioxide to produce a mixture of hydrogen and carbon monoxide, the catalysts having an improved lifetime compared to known catalysts for such a reaction, by virtue of being relatively resistant to deactivation by coking.
Summary of the Invention In accordance with a first embodiment of this invention, there is provided a catalyst precursor for reforming hydrocarbons to produce synthesis gas at an elevated temperature, which catalyst precursor includes a solid solution of nickel oxide in an oxide of cubic structural type which is an oxygen ion conductor at the elevated temperature.
In accordance with a second embodiment of the invention, there is provided a process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300- 1000°C;
(ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide; and (iii) heating the resulting mixture of nickel oxide and support material for a time and at a temperature sufficient to form a solid solution of at least part of the nickel oxide in the support material.
In accordance with a third embodiment of the invention, there is provided a process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
(ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide; and (iii) heating the resulting mixture of nickel oxide and support material at a temperature of from 250°C to 1500°C for a time sufficient to form the catalyst precursor.
In accordance with a fourth embodiment of the invention, there is provided a catalyst precursor produced by the process of the second or third embodiments. In accordance with a fifth embodiment of the invention, there is provided a catalyst for reforming hydrocarbons to produce synthesis gas, the catalyst being obtainable by reducing a catalyst precursor of the first or fourth embodiments in a reducing atmosphere at an elevated temperature.
In accordance with a sixth embodiment of the invention, there is provided a process for producing a catalyst for reforming hydrocarbons to produce synthesis gas including the steps of
(i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C; (ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide;
(iii) heating the resulting mixture of nickel oxide and support material for at least about 15 minutes at a temperature of from 250°C to 1500°C; and
(iv) contacting the product of step (iii) with a reducing atmosphere for a time and at a temperature sufficient to reduce at least part of the nickel to nickel metal.
In accordance with a seventh embodiment of the invention, there is provided a catalyst produced by the process of the sixth embodiment.
In accordance with an eighth embodiment of the invention, there is provided a process for reforming a hydrocarbon to produce synthesis gas, including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst of the fifth or seventh embodiments at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
In accordance with a ninth embodiment of this invention, there is provided a catalyst precursor for reforming hydrocarbons to produce synthesis gas at an elevated temperature, which catalyst precursor includes a mixture of nickel oxide and an oxide of cubic structural type which is an oxygen ion conductor at the elevated temperature.
In accordance with a tenth embodiment of the invention, there is provided a process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
(ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide; and
(iii) heating the resulting mixture of nickel oxide and support material for a time and at a temperature sufficient to form the catalyst precursor.
In accordance with an eleventh embodiment of the invention, there is provided a catalyst precursor produced by the process of the tenth embodiment. In accordance with a twelfth embodiment of the invention, there is provided a catalyst for reforming hydrocarbons to produce synthesis gas, the catalyst being obtainable by reducing a catalyst precursor of the ninth or eleventh embodiments in a reducing atmosphere at an elevated temperature.
In accordance with a thirteenth embodiment of the invention, there is provided a process for reforming a hydrocarbon to produce synthesis gas, including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst of the twelfth embodiment at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
Brief Description of the Drawings Fig. 1 is a schematic of the concept of a closed loop thermochemical heat pipe
Fig. 2 is a schematic of the concept of an open loop thermochemical heat pipe Figs. 3(a) to 3(c) are XRD traces for nickel oxide/yttrium oxide catalyst precursors including respectively 0, 5 and 30 wt% nickel.
Fig. 4 includes XRD traces for nickel oxide/silica catalyst precursors, not in accordance with the present invention, having three different weight loadings of nickel.
Figs. 5(a) to 5(c) are XRD traces for nickel oxide/terbium oxide catalyst precursors including respectively 0, 5 and 30 wf% nickel.
Figs. 6(a) to 6(c) are XRD traces for nickel oxide/praseodymium oxide catalyst precursors including respectively 0, 5 and 30 wt% nickel. Fig. 7 includes XRD traces for (a) 5 wt% nickel oxide/gadolinium oxide, (b) 5 wt% nickel oxide/praseodymium oxide and (c) 5 wt% nickel oxide/ytterbium oxide
Fig. 8 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 wt% nickel/yttrium oxide catalyst. Fig. 9 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 wt% nickel/gadolinium oxide catalyst.
Fig. 10 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 : 1 ratio) as a function of temperature in the presence of a 5 wt% nickel/praseodymium oxide catalyst.
Fig. 11 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 wt% nickel/ytterbium oxide catalyst. o Fig. 12 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 : 1 ratio) as a function of temperature in the presence of a 5 wt% nickel/terbium oxide catalyst.
Fig. 13 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 :1 ratio) as a function of temperature in the presence of a 5 5 wt% nickel/samarium oxide catalyst.
Fig. 14 is a temperature programmed reaction profile of the interaction between carbon dioxide and methane (1 : 1 ratio) as a function of temperature in the presence of a 5 wt% nickel/lanthanum-strontium-gallium-magnesium oxide catalyst.
Fig. 15 is a transmission electron microscopy (TEM) image of a 5 wt% o nickel/yttrium oxide catalyst after calcination.
Fig. 16 is a transmission electron microscopy (TEM) image of a 5 wt% nickel/yttrium oxide catalyst after reaction at 750°C for 50 hours.
Fig. 17 shows transmission electron microscopy (TEM) images of (a) 1 wt%, (b) 5 wt , (c) 10 wt% and (d) 30wt % nickel/silica catalyst after calcination. 5 Fig. 18 is a transmission electron microscopy (TEM) image of a 30 wt% nickel/MgO catalyst after calcination.
Fig. 19 is a transmission electron microscopy (TEM) image of a 30 wt% nickel/MgO catalyst after reaction at 750°C for 50 h.
Fig. 20 shows XRD traces for (a) yttrium oxide, (b) 5 wt% nickel/yttrium oxide o after calcination and (c) 5 wt% nickel/yttrium oxide after reaction with CO2/CH4 at 750° C for 5 Oh.
Fig. 21 shows XRD traces for (a) magnesium oxide, (b) 30 wt% nickel/magnesium oxide after calcination and (c) 30 wt% nickel/magnesium oxide after reaction with C02/CH4 at 750°C for 50h. Detailed Description of the Preferred Embodiments
In this invention, a novel family of nickel based catalysts characterised by excellent activity and stability for carbon dioxide reforming of methane (or other hydrocarbons) to produce syngas is described. As used herein, the expression "oxide of cubic structural type" means an oxide of a metal or a mixed metal oxide which has an ideal cubic or distorted cubic structure. Examples of such structures includes fluorite, perovskite, pyrochlore, brownmillerite and spinel structures.
In the catalyst precursors, catalysts and processes of the invention, the oxide of cubic structural type may be any such metal oxide, including an oxide of a single metal or a mixed metal oxide, provided it is also an oxygen ion conductor at a temperature in the range of about 300-1000°C; that is, a temperature range which includes the typical temperatures for the hydrocarbon reforming reaction for which the catalysts of the invention, obtainable from the catalyst precursors of the invention, may be used. Examples of suitable oxides include but are not limited to Zι-]_xYxO2_x/2, Ceι_ χGdx°2-x/2> LaCi"i-χMgxO3.x/2, La1.xSrxGa0 8Mg0 2O2 85, SrFeCo0 5Ox, La^S^Co^ yFey03.z, Bi2V,.xCuxO5 35, LaCoO3, SrCoO0 25, Sc203, Y2O3, Nd203, Sm2O3, Gd2O3, Yb2O3, Pr6On , Tb2O3, CaO-La2O3, Sc2O3-ZrO2, La0 8Sr0.2MnO3+x, La0 <5Ca0 4Coo, Feo 8O3_x and Sm0 6Cao.4CoO3_x, BaCeO3, BaTbo.9Ino.1O3, BaZr0 3lno.7θ3-x, BaTho.9Gdo.1O3, BaTb0 9I1 0.1O3, CaCe0 9E10 1O3. CaCe0.9Gd0 ]O3, Ba8In6O17, Ba3InxZrxO8, Ba3In2ZrO8, Ba3Y2ZrO8, Ba3Gd2Ce08, Ba2GdIn1.xGaxO5, BaBi4Ti3InO14 5, BaBi4Ti3ScO14 5, Sr2Gd2O5, Sr2Dy2O5, Sr6Nb2On , SrBa6Ta2On, Sr3Ti207, Sr3Zr2O7, Ba3Ti2O7, NdA103, Nd0 9Ca0.1AIO3, Ba3Sc2ZrO8, SrIn2HfO8, Ba3In2TiO8, Ba3Y4O9, Ba8In6O17, BaCe,.xGdxO3.x, Sr3Ti , 9Mg0.ιO6 9, BaCe03(Gd,Yb,Nd), CaTiO3(Mg), SrZrO3(Yb), BiV^, ^Cu-Ni), Ba2In2O5, Ba3In2CeO8, Ba3In2HfO8, LaGa03(Ca), Nd2Zr2O7, Nd2Ce2O7, Nd2CeZrO7, Gd2(ZrxTix)207, Gd2Ti2O7, Gd2Zr2O7, Gd2(Zr,Ti)2O7(Ca), Sm2Zr2O7. Y2(ZryTi2.y)2O7, Gd2Zr2O7, Nd2Zr2O7, Sm2Zr2O7, Gd2Zr2O7 (P), Gd2Zr2O7 (F), Tb2Zr2O7+x, Er2T2O7, Y2Ti2O7, Gd2Zr207(Ru), Sm2Ti2O7(Sr,Ca,Mg), PbWO4, Pb8La2WO4 Λ, BiVO4, Bi(Ca)VO4, Bi(Ca,Ce)VO4, PbMoO4(Na), Ca12Al14O33, Sr6Nb2On , Sr6Ta2Oπ, Ba6Nb20 H , Ba6Ta2On , Y3Al5O12, α-Ta2O5, Yo.75Nbo.15Ce,, .,0, 7. δ-Bi2O3, Bi203- SrO. Bi2O3-BaO, Bi2VxPbxOx, Bi2°3-Pr 6°l b Bi 2°3> PbO, Sb20, BiCuVOx, Bi2O3- Y2O3(0.25), SrCeO3(Y), SrCe(Yb)O3, SrZrO3(Y,Sc,Yb), Sr2(ScNb)06.d, Ba3(CaNb)O9- d, H2Ln2Ti3O,0 (Ln = La, Nd, Sm, Gd) and HCa2Nb3O10. Typically, the oxide of cubic structural type is an oxide of an element selected from the group consisting of yttrium, gadolinium, praseodymium, samarium, ytterbium and terbium.
Typically, the amount of nickel in the catalysts and catalyst precursors of the invention is in the range of from about 1% to 50% by weight, more typically from about 5%> to about 40% by weight, or from about 6% to about 40%> by weight, or from about 7% to about 40%) by weight, or from about 8% to about 40% by weight, or from about 9% to about 40%) by weight, still more typically from about 10% to about 40% by weight, even more typically from about 10% to about 30% by weight, based on the total weight of the catalyst or catalyst precursor.
Modifiers to enhance the activity of the catalyst and catalyst precursor formulations described above may be added. In general, these can be included in the catalyst by any convenient method, the precise choice may depend on the identity of the additive. For example, promoting species may simply be added to the initial impregnating solution of nickel precursor, or they be incorporated as part of a co-precipitation procedure.
In particular, a catalyst of the invention may further include one or more additives selected from the group consisting of:
(a) noble metals selected from the group consisting of Pt, Ir, Rl , Ru, Os, Pd and Re; (b) oxides selected from the group consisting of TiO2, Mo03. WO3, ZrO2, V2O5,
Nb20,. Sc2O5 and Ta2O5;
(c) oxides of elements selected from the group consisting of boron, aluminium, gallium and indium;
(d) elements selected from the group consisting of Ag, Cu, Au and Zn; and (e) elements selected from the group consisting of P, Sb, As, Sn and Ge.
Where an additive is included in the catalyst precursor or the catalyst, the amounts included are typically in the range of:
(a) for noble metals selected from the group consisting of Pt, Ir, Rh, Ru, Os, Pd and Re, from 0.01% % to 20%; (b) for oxides selected from the group consisting of Ti02. MoO3, WO , ZrO2,
V20 , Nb205, Sc2O5 and Ta2O5, from 0.01% to 20%;
(c) for oxides of elements selected from the group consisting of boron, aluminium, gallium and indium, from 0.01% to 20%; (d) for elements selected from the group consisting of Ag, Cu, Au and Zn, from 0.01% to 20%; and
(e) for elements selected from the group consisting of P, Sb, As, Sn and Ge, from 0.01% to 20%; wherein the percentages are expressed as percentages by weight based on the total weight of the catalyst.
If desired the active catalyst components can be dispersed on the surface of a conventional oxide carrier of which silica, alumina, zirconia, thoria, silica-alumina, zeolites, clay minerals and derivatives of clay minerals are common examples. There is no specific limitation on the support material employed although it is desirable that the catalyst display good attrition resistance and high crush strength for industrial usage. Formation of a supported catalyst of this kind may readily be achieved by impregnation of soluble precursors of the nickel oxide and the oxide of cubic structural type on the support of choice, followed by drying and calcination. In a process of the second, third, sixth or tenth embodiments, step (i) is a step of wet impregnation of the oxide of cubic structural type by an aqueous solution of a soluble nickel compound. A suitable soluble nickel compound is nickel nitrate. Naturally, any other metal salt which is soluble in an aqueous solution can alternatively be used, such as nickel bromide, nickel chloride, nickel iodide and nickel sulfate. If desired, use may also be made of an organic solvent and a nickel compound which is soluble in the organic solvent.
Catalyst precursors of the invention may be prepared using methods other than wet impregnation techniques, however. Alternative synthesis routes known to those skilled in the art can also be employed, examples of which include coprecipitation and solid state reaction.
In the process of the second, third, sixth or tenth embodiments, the heating temperature in step (ii) is typically carried out in an oxygen containing atmosphere. More typically the atmosphere is air or oxygen gas.
In the process of the second, third, sixth or tenth embodiments, the heating o temperature in step (ii) is typically in the range of from 250°C to 1500°C, more typically in the range selected from the group consisting of 250°C to 1400°C, 250°C to 1300°C, 250°C to 1200°C, 250°C to 1100°C, 250°C to 1000°C, 250°C to 950°C, 250°C to 900°C, 250°C to 850°C, 250°C to 800°C, 300°C to 800°C, more typically 350°C to 600°C. Calcination temperatures for nickel salts; that is, temperatures at which nickel salts may be converted to nickel oxide, are generally known to persons of ordinary skill in the art, as are appropriate calcination times.
Step (iii) of the process of the second, third, sixth or tenth embodiments may also be carried out a temperature typically in the range of from 250°C to 1500°C, more typically in the range selected from the group consisting of 250°C to 1400°C, 250°C to 1300°C, 250°C to 1200°C, 250°C to 1100°C, 250°C to 1000°C, 250°C to 950°C, 250°C to 900°C, 250°C to 850°C, 250°C to 800°C, 300°C to 800°C, more typically 350°C to 600°C. The temperature for step (ii) may be the same or different to the temperature for step (iii).
Usually, the time required in step (iii) of the process of the second, third or tenth embodiments to heat the mixture of the nickel oxide and support material to form the catalyst precursor is in the range selected from the group consisting of about 15 to about 30 minutes, about 30 to about 40 minutes, about 40 to about 50 minutes, about 50 to about 60 minutes, about 60 minutes to about 70 minutes, about 70 minutes to about 80 minutes, about 80 minutes to about 90 minutes. It is also usual that the time required in step (iii) of the process may take at least 100 minutes or more, or at least 2 hours or more. It will be appreciated, however, that the time required is dependent on the temperature of process step (iii). Conditions for step (iii) of the process of the second embodiment may be determined readily by monitoring the heated composition for the formation of a solid solution. The identification of the formation of the catalyst precursor which in one embodiment of the invention entails the identification of the formation of a solid solution is readily made by inspection of an X-ray powder diffraction profile for the material, as illustrated in accompanying Figures 3 to 7. There is shown in Figure 3, X-ray diffraction (XRD) patterns for yttrium oxide, 10 wt % nickel oxide-yttrium oxide and 30 wt % nickel oxide-yttrium oxide. Notably, the XRD trace for pure yttrium oxide is very sharp and intense which is indicative, to those of ordinary skill, of a highly crystalline material. Significantly, the XRD pattern becomes less intense and the lines become broader in character as the nickel is added. Indeed the 30 wt % nickel oxide-yttrium oxide catalyst exhibits extremely broad lines due to the yttrium oxide component which is recognised by those skilled in the art to be representative of an amorphous or nanocrystallme oxide material. In harmony, with this observation is the presence of very wide reflections attributable to nickel oxide which again not only indicates the presence of amorphous or nanocrystallme nickel oxide but also the weak intensity of these latter features can be interpreted as meaning that there may exist a fraction of the nickel species in a solid solution with the yttrium oxide.
Inspection of comparative XRD profiles for known nickel/silica catalysts provides a clear indication of the novel and surprising behaviour of the catalysts disclosed in this invention. Figure 4 illustrates XRD profiles recorded for a series of calcined nickel/silica catalysts. The silica support is characterized by an amorphous "lump" at low values of 2Θ . whereas sharp, intense peaks are apparent for nickel oxide at 37, 43 and 63 degrees 20. As the loading of nickel becomes higher, the XRD peaks become narrower, thus indicating that the nickel particles were becoming larger and more crystalline in character. o Electron microscopy observations are consistent with this interpretation. Importantly, the silica support of the nickel/silica catalyst does not have the ability to form a solid solution with nickel. Consequently, the nickel particles are neither as well dispersed as in those catalysts described in this invention or as small and amorphous or nanocrystalline in structure. 5 Further illustration of the behaviour of the novel catalysts of the present invention can be seen by inspection of Figures 5 and 6 which display XRD patterns for a nickel oxide/terbium oxide and nickel oxide/praseodymium catalysts, respectively. As in the case of the nickel oxide-yttrium oxide catalyst the features for the terbium oxide component diminish in intensity as the nickel loading is increased, again indicative of a o more amorphous or nanocrystalline material. Furthermore, the reflections characteristic for nickel oxide are extremely weak in intensity. Therefore, without wishing to be bound by theory, it appears that the nickel component may at least in part be forming a solid solution with the rare earth material or at least the rare earth material has the ability to disperse the nickel component to a greater extent, than that for a silica support. Similarly, 5 for the nickel oxide/praseodymium oxide system (Figure 6), the XRD trace clearly illustrates that the reflections assigned to praseodymium oxide become very broad and weak in intensity as the nickel loading increases. Furthermore, there is very little evidence for the presence of nickel crystallites, thus again indicating that either a solid solution has formed or that the praseodymium has a surprising ability to disperse nickel o oxide particles extremely well, that is to an extent where the nickel oxide particles become amorphous or nanocrystalline. Other examples are provided in Fig. 7 which show similar behaviour for nickel/gadolinium oxide and nickel/ytterbium oxide catalysts.
Another feature of the catalysts of the present invention is the general observation that the catalyst surface area increases as the nickel loading increases. For example, Table 1 illustrates the surface areas as calculated by the standard BET method for several of the catalysts revealed in this disclosure, and for comparison purposes, surface areas of silica and nickel oxide/silica catalysts are shown.
The precursors of catalysts of the invention require reduction to produce the catalysts. Reduction of the catalyst precursor, such as in step (iv) of the process of the sixth embodiment, can be achieved by pre-reducing the catalyst at a temperature of 300°C or greater with a gas stream comprising of hydrogen or any other readily available reductant, such as carbon monoxide or a hydrocarbon, such as methane. For some catalyst compositions, it is sufficient to reduce the sample at a temperature as low as 300° C. although a temperature in excess of 500°C is more typical. Other catalyst precursor compositions may require reduction at still higher temperatures, such as up to about 900° C.
Without wishing to be bound by theory, it appears that it is necessary to partially reduce a fraction of the nickel ions present in the solid solution or amorphous or nanocrystalline form to produce small metal crystallites which participate in the catalytic reaction. Therefore, the reduction procedure employed should preferably be at a temperature which will facilitate reduction of a fraction of the nickel ions to nickel metal. Given the teaching herein, it is a matter of no more than routine experimentation to establish appropriate reduction conditions to achieve this objective for any given catalyst precursor of the invention.
Alternatively, where a catalyst precursor is to be used to generate a catalyst to be used directly in a reforming process of the invention, the catalyst precursor may be prereduced in situ by exposure to the reactant mixture itself, and optionally raising the temperature above the desired reaction temperature for the reforming reaction. A process of the eighth or thirteenth embodiments of the invention may be carried out using a catalyst in accordance with the invention under conditions generally known in the art for carbon dioxide reforming reactions. That is, typically conditions for carrying out the process of the fourth embodiment of the present invention include a temperature range of from about 300-1100°C, more typically from about 400°C to 850°C, at a pressure of from about lOkPa to about 10,000kPa, more typically from about lOOkPa to about 5,000kPa, still more typically from about lOOkPa to about 3,000kPa. at an apparent space velocity in the range of from about 1000 to lOOOOOOlr' ., more typically from about 10000 to 500000h-] . The hydrocarbon in a reactant mixture for the process of the eighth or thirteenth embodiments is typically methane but may also be a mixture of one or more hydrocarbons selected from methane and higher hydrocarbons such as ethane, ethene, ethyne, propane, propene, butane(s), butene(s), butyne(s), etc. Typical reactant mixture compositions in the process of the eighth or thirteenth embodiments may contain, in addition to the hydrocarbon and carbon dioxide, other gases such as hydrogen, carbon monoxide, substantially inert gases such as nitrogen, helium and/or argon, and/or small amounts of oxygen.
Generally, the proportion of hydrocarbon relative to carbon dioxide will be in the range of from 20:1 to 1 :20, more typically 9: 1 to 1 :9, even more typically 4: 1 to 1 :4.
EXAMPLES Example 1 Commercially available yttrium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(N03)2.6H2O (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 1 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species.
Example 2
Commercially available yttrium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO3)2.6H2O (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 5 wt%> nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature. Catalyst activity for the C02 reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 : 1 mixture of CO2 and CH4 to a temperature of 1073K, with all gas products continuously monitored by on-line mass spectrometry. This technique is known to those of average skill in the art as temperature programmed reaction (TPRxn). The resultant TPRxn profile is shown in Figure 8.
Example 3 Commercially available gadolinium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO3)2.6H20 (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 5 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature. Catalyst activity for the CO2 reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 :1 mixture of CO2 and CH4 to a temperature of 1073K, with all gas products continuously monitored by on-line mass spectrometry. The resultant TPRxn profile is shown in Figure 9.
Example 4
5 Commercially available praseodymium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO3)2.6H2O (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 5 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient
I D temperature. Catalyst activity for the CO? reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 :1 mixture of CO2 and CH4 to a temperature of 1073K, with all gas products continuously monitored by on-line mass spectrometry. The resultant TPRxn profile is shown in Figure 10.
Example 5
15 Commercially available samarium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO3)2.6H2O (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 5 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient
2o temperature. Catalyst activity for the CO2 reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 :1 mixture of CO2 and CH4 to a temperature of 1073K, with all gas products continuously monitored by on-line mass spectrometry. The resultant TPRxn profile is shown in Figure 13.
Example 6
25 Commercially available ytterbium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO3)2.6H2O (Aldrich, 99.999 %) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 5 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient
30 temperature. Catalyst activity for the C02 reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 : 1 mixture of CO2 and CH4 to a temperature of 1073 K, with all gas products continuously monitored by on-line mass spectrometry. The resultant TPRxn profile is shown in Figure 11.
Example 7 Commercially available terbium oxide (Pi-KEM, UK) was impregnated with an aqueous solution of Ni(NO3)2.6H2O (Aldrich, 99.999 %) and the resulting slurry dried at
100°C for several hours. The impregnated catalyst consisting of 5 wt% nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature. Catalyst activity for the CO2 reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 :1 mixture of CO2 and CH4 to a temperature of 1073K, with all gas products continuously monitored by on-line mass spectrometry. The resultant TPRxn profile is shown in Figure 12. Example 8
A portion of the oxygen ion conductor lanthanum-strontium-gallium-magnesium oxide (La0.9Sro.|Gao.8Mg0.2O3-x) was impregnated with an aqueous solution of Ni(N03)2 6H2O (Aldrich, 99.999%) and the resulting slurry dried at 100°C for several hours. The impregnated catalyst consisting of 5 wt % nickel was then calcined in flowing air at 500°C for 2 h to decompose the nitrate species. The catalyst was subsequently reduced in hydrogen at 500°C for 2 hours and then cooled to ambient temperature. Catalyst activity for the CO2 reforming reaction was demonstrated by heating the catalyst at a rate of 20K/min in the presence of a 1 : 1 mixture of CO2 and CH4 to a temperature of 1073K, with all gas products continuously monitored by on-line mass spectrometry. The resultant TPRxn profile is shown in Figure 14.
Example 9 The calcined 5% Ni/yttrium oxide precursor, prepared as described in Example 2, after calcining, was pelleted, crushed and sieved to a particle size between 0.7 and 1.0 mm before placement into a microreactor facility for catalyst activity evaluation. Approximately 0.2 g of catalyst was loaded into a 12 mm diameter quartz reactor tube situated in an electrically heated furnace which was capable of operation between 25 and 1000°C. Samples were pre-reduced in a 20% hydrogen/helium mixture at 500°C for lh. Subsequently, an equimolar mixture of carbon dioxide and methane (total flow rate 200 mL/min) was contacted with the catalyst resulting in an apparent space velocity (GHSV) of 35,000h"' . The catalyst activity and selectivity was then monitored as a function of reaction time for a period of 50h at 750°C. The conversion of carbon dioxide was stable over this period at a value of 98.5%. Notably, the testing conditions employed were such that coking of the catalyst surface was thermodynamically favoured, but no coking was observed. Comparative Example 1
The activity of a 5wf% nickel on silica catalyst was evaluated using the conditions outlined in example 8. This catalyst exhibited deactivation over the 50 h testing period the conversion of carbon dioxide falling from an initial value of 96% to 93 %> and according to the criteria described above this catalyst is not part of the current invention.
Example 10 The unique behaviour of the catalysts described in this invention is also revealed by inspection of transmission electron microscopy (TEM) obtained before after 50 hours of C02/CH4 reaction at 750°C. Fig. 15 displays TEM images of a 5 wt % Ni/yttrium oxide catalyst following calcination of the sample. Notably, the images reveal the presence of only nanocrystalline yttrium oxide with no evidence for large nickel grain (>5 nm) detected. Even after reaction at 750°C for 50 h (Fig. 16) no nickel crystallites were discerned: indeed the only significant feature was the growth of yttrium oxide tubules. Comparative Example 2
Fig. 17 displays TEM images of a range of nickel/silica catalysts following the calcination procedure. In contrast to the catalysts of the present invention, nickel particles were readily detected which illustrated that silica was not an effective support for dispersing nickel. Consequently, those skilled in the art would realise that silica supported catalysts would not only deactivate due to significant coking on the large nickel crystallites but also nickel sintering would occur during reaction conditions leading to disastrous loss of surface area.
Comparative Example 3
Fig. 18 provides an image of a 30 wt % Ni/MgO catalyst following calcination. The nickel species appeared to be well dispersed due to the formation of a solid solution
(as evidenced by XRD analysis). However, after CO2/CH4 reaction at 750°C for 50h the
TEM images revealed (Fig. 19) the growth of large (>10nm) nickel crystallites (dark, angular features in image) which suggests that MgO was not as efficient at minimising the growth of nickel grains relative to those catalysts disclosed in this invention. Consequently, the reduced nickel dispersion will lead to poorer industrial performance compared to the catalysts of this invention.
Example 1 1 The efficiency of the catalysts disclosed in this invention for dispersion and stabilization of nickel species is further shown by inspection of the relevant X-ray diffraction (XRD) patterns for the catalyst before and after reaction at 750°C for 50 hours. Figure 20 shows XRD traces for yttrium oxide, calcined 5 wt % nickel/yttrium oxide and 5 wt % nickel/yttrium oxide after reaction. Significantly, no evidence for nickel crystallite growth is detected.
Comparative Example 4 The XRD pattern for 30 wt % nickel/magnesium oxide catalyst after the carbon dioxide reforming reaction (Figure 21) shows dramatic changes in the catalyst structure. In particular, a reflection at 43 degrees 20 characteristic of large nickel crystallites (>10nm) appears after reaction which is in harmony with the observation of crystallite growth by TEM. Thus, this known catalyst system is less effective than those described in this invention.
Table 1 ; BET surface areas of a representative sample of catalysts for this invention.

Claims

Claims
1. A catalyst precursor for reforming hydrocarbons to produce synthesis gas at an elevated temperature, which catalyst precursor includes a mixture of nickel oxide and an oxide of cubic structural type which is an oxygen ion conductor at the elevated
5 temperature.
2. A catalyst precursor for reforming hydrocarbons to produce synthesis gas at an elevated temperature, which catalyst precursor includes a solid solution of nickel oxide in an oxide of cubic structural type which is an oxygen ion conductor at the elevated temperature. o
3. A catalyst precursor according to claim 1 or claim 2 wherein the oxide of cubic structural type is a metal oxide including a single metal oxide or mixed metal oxide.
4. A catalyst precursor according to claim 1 or claim 2 wherein the oxide of cubic structural type is an oxide of an element selected from the group consisting of yttrium, gadolinium, praseodymium, samarium, ytterbium and terbium. 5 5. A catalyst precursor according to claim 1 or claim 2 wherein the oxide of cubic structural type is selected from the group consisting of Zrj.xYxO2.x/ , Ce].xGdxO2.x/2, LaCr,.xMgxO3.x^, La].xSrxGa0.8Mg0 2O2 85, SrFeCo0.5Ox, La1.xSrxCo,.yFeyO3.z, Bi2V,.xCuxO5 35, LaCoO3, SrCoO0 25, Sc2O3, Y2O3, Nd2O3, Sm203, Gd2O3, Yb2O3, Pr6O] ] , Tb O3, CaO-La2O3, Sc2O3-ZrO2, Lao,8Sr0 2MnO3+x, La0 6Ca0 4Co0 2Feo.8O3_x o and Sm0 gCao 4CoO3.x, BaCe03, BaTbo 9I110.1O3, BaZrø ,3ln0 7O3.x, BaTliQ gGdø 1O3, BaTb0 9lno. ιθ3, CaCe0 9Er0 ]O3, CaCe0 9Gd0 1O3, Ba8In6O] 7, Ba3inxZrxO8, Ba3In2ZrO8, Ba3Y2ZrO8, Ba3Gd2CeO8, Ba2GdIn,.xGaxO5, BaBi4Ti3InO14 5, BaBi4Ti3ScO14 5, Sr2Gd2O5, Sr2Dy2O5, Sr6Nb2On , SrBa6Ta2Oπ, Sr3Ti2O7, Sr3Zr2O7, Ba3Ti207, NdAlO3, Nd0 9Cao.1AlO3, Ba3Sc2ZrO8, SrIn2HfO8, Ba3In2TiO8, Ba3Y4O9,
5 Ba8In6017, BaCe,.xGdxO3.x, Sr3Ti1 9Mgo O6 9, BaCeO3(Gd,Yb,Nd), CaTi03(Mg), SrZrO3(Yb), BiV2On(Cu,Ni), Ba2In2O5, Ba3In2CeO8, Ba3In2HfO8, LaGaO3(Ca), Nd2Zr207, Nd2Ce2O7, Nd2CeZrO7, Gd2(ZrxTix)2O7, Gd2Ti207, Gd2Zr2O7, Gd2(Zr,Ti)207(Ca), Sm2Zr2O7, Y2(Zr i2_y)207, Gd2Zr207, Nd2Zr207, Sm2Zr207, Gd2Zr207 (P). Gd2Zr207 (F), Tb2Zr2O7+x, Er2T207, Y2Ti207, Gd2Zr2O7(Ru), 0 Sm2Ti2O7(Sr,Ca,Mg), PbWO4, Pb8La2WO4 ,, BiVO4, Bi(Ca)V04, Bi(Ca,Ce)VO4, PbMo04(Na), Ca12Al] 4O33, Sr6Nb2Oπ, Sr6Ta2O , Ba6Nb2On , Ba6Ta2On, Y3Al5O12, α-Ta2O5, Y0.75Nb0.ι5Ce0 ^i .y, δ-Bi2O3, Bi203-SrO, Bi203-BaO, Bi2VxPb O , Bi^-P^O, ,, Bi203, PbO, Sb2O, BiCuVOx, Bi2O3-Y2O3(0.25), SrCeO3(Y), SrCe(Yb)O3, SrZrO3(Y,Sc,Yb), Sr2(ScNb)O6.d, Ba3(CaNb)O9.d, H2Ln2Ti3O10 (Ln = La, Nd, Sm, Gd) and HCa2Nb3O10.
6. A catalyst precursor according to claim 1 or claim 2 wherein the elevated temperature is a temperature in the range of about 300-1000°C.
7. A process for producing a catalyst precursor including the steps of
(i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
(ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide; and
(iii) heating the resulting mixture of nickel oxide and support material for a time and at a temperature sufficient to form the catalyst precursor.
8. A process for producing a catalyst precursor including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
(ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide; and
(iii) heating the resulting mixture of nickel oxide and support material for a time and at a temperature sufficient to form a solid solution of at least part of the nickel oxide in the support material.
9. A process according to claim 7 wherein in step (iii) the heating is at a temperature of from 250°C to l500°C.
10. A process according to claim 7 wherein the support material is a metal oxide including a single metal oxide or mixed metal oxide.
1 1. A process according to claim 7 wherein the oxide of cubic structural type is an oxide of an element selected from the group consisting of yttrium, gadolinium, praseodymium, samarium, ytterbium and terbium.
12. A process according to claim 7 wherein the oxide of cubic structural type is selected from the group consisting of Zr].xYxO2.x/2, Ceι_xGdxO2_x/2, LaCrι_xMgxO3_x/2. La1.xSrxGa0.8Mgo.2O2 85, SrFeCo0.5Ox, Laι_xSrxCo,_yFeyO3.z, Bi2V ,.xCux05 35, LaCo03, SrCoO0.25, Sc203, Y2O3, Nd203, Sm203, Gd203, Yb203, Pr6On , Tb2O3, CaO-La2O3, Sc203-ZrO2, La0.8Sro.2Mn03+x, La0 6Ca0 4Co0 2Fe0 8O3_x and Smo.6Cao.4CoO3.x, BaCeO3, BaTb0 9I1 0.1O3, BaZr0.3 no.7θ3-x, BaTh0 gGdo.^, BaTbo.9Ino.1O3, CaCeo 9Er0.ιO3, CaCe0 9Gd0.ιO , Ba8In6O17, Ba3InxZrxO8, Ba3In2ZrO8, Ba3Y2ZrO8, Ba3Gd2CeO8, Ba2GdIn1.xGaxO5, BaBi4Ti3InO14 5, BaBi4Ti3ScO14 5, Sr2Gd2O5, Sr2Dy2O5, Sr6Nb2Oπ, SrBa6Ta2O] , , Sr3Ti2O7, Sr3Zr2O7, Ba3Ti2O7, NdAlO3, Nd0.9Cao.1AlO3, Ba3Sc2ZrO8, SrIn2HfO8, Ba3In2TiO8, Ba3Y4O9, Ba8In6Ol 7, BaCe!.xGdxO3.x, Sr3Ti1 9Mg0.ιO6 9, BaCeO3(Gd,Yb,Nd), CaTiO3(Mg), SrZr03(Yb), BiV2O] ι(Cu,Ni), Ba2In2O5, Ba3In2CeO8, Ba3In2HfO8, LaGaO3(Ca), Nd2Zr2O7, Nd2Ce2O7, Nd2CeZrO7, Gd2(Zr Ti )2O7, Gd2Ti2O7, Gd2Zr2O7, Gd2(Zr,Ti)2O7(Ca), Sm2Zr2O7, Y2(Zr i2.y)2O7, Gd2Zr2O7, Nd2Zr2O7, Sm2Zr2O7, Gd2Zr207 (P), Gd2Zr2O7 (F), Tb2Zr2O7+x, Er2T2O7, Y2Ti2O7, Gd2Zr2O7(Ru), Sm2Ti2O7(Sr.Ca,Mg), PbWO4, Pb8La2WO4 ,, BiVO4, Bi(Ca)VO4, Bi(Ca,Ce)VO4, PbMoO4(Na). Ca] 2Al14O33, Sr6Nb2O, ι , Sr6Ta2Oπ, Ba6Nb2On, Ba6Ta2O , Y3A15012, α-Ta2O5, Y0 75Nb0. l 5Ce0 ,01 7, δ-Bi2O3, Bi2O3-SrO, Bi2O3-BaO, Bi2V PbxO , Bi2O3-Pr6On, Bi2O3, PbO, Sb2O, BiCuVOx, Bi2O3-Y2O3(0.25), SrCeO3(Y), SrCe(Yb)O3, SrZrO3(Y,Sc,Yb), Sr2(ScNb)O6.d, Ba3(CaNb)O9.d, H2Ln2Ti3O10 (Ln = La, Nd, Sm, Gd) and HCa2Nb3O] 0.
13. A catalyst precursor produced by the process of any one of claims 7-12.
14. A catalyst for reforming hydrocarbons to produce synthesis gas, the catalyst being obtainable by reducing a catalyst precursor according to claim 1 or claim 2 in a reducing atmosphere at an elevated temperature.
15. A catalyst for reforming hydrocarbons to produce synthesis gas, the catalyst being obtainable by reducing a catalyst precursor according to claim 13 in a reducing atmosphere at an elevated temperature.
16. A catalyst according to claim 14, further including one or more additives selected from the group consisting of: ^ (a) noble metals selected from the group consisting of Pt, Ir, Rh, Ru, Os, Pd and Re;
(b) oxides selected from the group consisting of TiO?, M0O3, W03, Zr02, V2O5, Nb2O , Sc20, and Ta2O5;
(c) oxides of elements selected from the group consisting of boron, aluminium, gallium and indium; 0 (d) elements selected from the group consisting of Ag, Cu, Au and Zn; and (e) elements selected from the group consisting of P, Sb, As, Sn and Ge.
17. A process for producing a catalyst for reforming hydrocarbons to produce synthesis gas including the steps of (i) impregnating a support material with a solution of a nickel compound, the support material being an oxide of cubic structural type which is an oxygen ion conductor at a temperature in the range 300-1000°C;
(ii) if necessary heating the mixture in an atmosphere at a temperature and for a time sufficient to calcine the nickel containing compound to nickel oxide;
(iii) heating the resulting mixture of nickel oxide and support material for at least about 15 minutes at a temperature of from 250°C to 1500°C; and
(iv) contacting the product of step (iii) with a reducing atmosphere for a time and at a temperature sufficient to reduce at least part of the nickel to nickel metal.
18. A catalyst produced by the process of claim 17.
19. A process for reforming a hydrocarbon to produce synthesis gas, including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst according to claim 14 at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
20. A process for reforming a hydrocarbon to produce synthesis gas, including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst according to claim 15 at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
21. A process for reforming a hydrocarbon to produce synthesis gas, including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst according to claim 16 at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
22. A process for reforming a hydrocarbon to produce synthesis gas, including the step of contacting a reactant mixture of carbon dioxide and the hydrocarbon with a catalyst according to claim 18 at a temperature and pressure, and for a time sufficient to convert at least part of the reactant mixture to synthesis gas.
EP99948601A 1998-09-21 1999-09-21 CATALYSTS AND PROCESS FOR REFORMING HYDROCARBONS Withdrawn EP1124635A4 (en)

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