WO2015183200A1 - Iridium/cerium-based catalysts for dry reforming methane to syngas - Google Patents

Iridium/cerium-based catalysts for dry reforming methane to syngas Download PDF

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WO2015183200A1
WO2015183200A1 PCT/SG2015/050129 SG2015050129W WO2015183200A1 WO 2015183200 A1 WO2015183200 A1 WO 2015183200A1 SG 2015050129 W SG2015050129 W SG 2015050129W WO 2015183200 A1 WO2015183200 A1 WO 2015183200A1
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compound
zirconium
cerium
lanthanum
nitrate
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PCT/SG2015/050129
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French (fr)
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Fagen WANG
Wei Chen
Guo Qin Xu
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National University Of Singapore Suzhou Research Institute
National University Of Singapore
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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
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • 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
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/46—Ruthenium, rhodium, osmium or iridium
    • B01J23/468—Iridium
    • 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
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/031—Precipitation
    • 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/038—Precipitation; Co-precipitation to form slurries or suspensions, e.g. a washcoat
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • C01B3/40—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts characterised by the catalyst
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0238—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a carbon dioxide reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1041—Composition of the catalyst
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1241—Natural gas or methane
    • 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
    • Y02P20/141—Feedstock
    • 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

  • Transitional metal catalyst Due to the ultra-stability of methane and C0 2 , their activation and transformation requires a high temperature, e.g., 800 °C, during the dry reforming process. Transitional metal catalyst has been used to promote conversion of methane and C0 2 into syngas. At high temperature, the transitional metal catalyst is easily sintered, thus lowering its activity.
  • the present invention relates to a ceria-based transitional metal catalyst for dry reforming methane to syngas.
  • the catalyst exhibits a high activity with an unexpectedly long lifespan.
  • a deposition-precipitation method namely, a deposition-precipitation method, a co-precipitation method, and a sequential precipitation method.
  • the deposition-precipitation method includes the following steps: (a) mixing a cerium compound and/or a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with excess urea in de-ionized water to form a homogeneous solution, a molar ratio of Ce/M (M being La, Pr, Zr, or Ti) being 8.5-9; (b) obtaining a ceria-based solid solution support from the homogeneous solution; (c) mixing the ceria-based solid solution support and an iridium compound in de-ionized water; (d) obtaining a dry powder from the resulting solution; (e) calcining the dry powder at
  • the co-precipitation method includes the following steps: (a) mixing an iridium compound, a cerium compound, and/or a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with excess urea in de-ionized water to form a homogeneous solution, a molar ratio of Ce/M (M being La, Pr, Zr, or Ti) being 8.5-9; (b) obtaining a dry powder from the homogeneous solution; (c) calcining the dry powder at 700- 800 °C; and (d) collecting the transitional metal catalyst thus obtained.
  • the sequential precipitation method includes the following steps: (a) mixing a cerium compound, and/or a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with excess urea in de-ionized water to form a homogeneous solution, a molar ratio of Ce/M (M being La, Pr, Zr, or Ti) being 8.5-9; (b) obtaining a suspension from the homogeneous solution; (c) adding an iridium compound into the suspension; (d) obtaining a dry powder from the mixture thus formed; (e) calcining the dry powder at 700-800 °C; and (f) collecting the transitional metal catalyst thus obtained.
  • the homogeneous solution has a concentration of cerium being
  • Examples of the iridium compound include hydrogen hexachloroiridate, potassium hexachloroiridate, sodium hexachloroiridate, iridium oxide, and iridium chloride.
  • Examples of the cerium compound include cerium nitrate, ammonium cerium nitrate, and cerium chloride.
  • Examples of the praseodymium compound include praseodymium nitrate and praseodymium chloride.
  • Examples of the lanthanum compound include lanthanum nitrate, lanthanum chloride, and lanthanum acetate.
  • Examples of the zirconium compound include zirconium oxynitrate, zirconium nitrate, zirconium chloride, and zirconium acetate.
  • titanium compound examples include titanyl oxalate and titanium nitrate.
  • a transitional metal catalyst containing an active iridium metal in a content of less than 5 wt% and a ceria-based solid solution support in a content of greater than 95 wt%.
  • the ceria-based solid solution includes pure Ce0 2 or includes both Ce0 2 and M x O y , in which M is La, Pr, Zr, or Ti, 1 ⁇ x ⁇ 6, and 2 ⁇ y ⁇ 11.
  • the catalyst contains an active iridium metal in a content of 2-3 wt% and the ceria-based solid solution support in a content of 97-98 wt%.
  • the ceria-based solid solution support can be pure Ce0 2 . It can also include both Ce0 2 and M x O y , e.g., La 2 0 3 , Pr 6 On, Zr0 2 , or Ti0 2 , the molar ratio of Ce/M being 8.5-9.
  • a deposition-precipitation method a co-precipitation method
  • a sequential precipitation method a method for preparing a ceria-based transitional metal catalyst of this invention.
  • One embodiment of the deposition precipitation method is performed as follows.
  • a homogeneous aqueous solution formed of a cerium compound and excess urea or formed of a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound, and excess urea, is prepared. Subsequently, the homogeneous solution is heated at 65-90 °C for 4-6 hours to hydrolyze the metal compound(s). The mixture thus formed is filtered and washed to afford a solid material, which is then dried at 100-110 °C to obtain a solid slurry. The solid slurry is calcined at 400- 450 °C for 3.5-4.5 hours to provide a ceria-based solid solution support.
  • the solid solution support is mixed with an iridium compound in de-ionized water and dispersed with vigorous stirring.
  • the resulting solution is stirred at 65-75 °C, followed by slow addition of an aqueous sodium carbonate or sodium bicarbonate solution to adjust its pH to 8-9.
  • a suspension is formed.
  • the suspension is filtered and washed with hot water to provide a slurry.
  • the slurry is then dried at 100-110 °C overnight to obtain a dry powder.
  • the dry powder is calcined at 700-800 °C for 4-5 hours to obtain a transitional metal catalyst.
  • One embodiment of the co -precipitation method is performed as follows.
  • a homogeneous aqueous solution formed of an iridium compound and a cerium compound or formed of an iridium compound, a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound, is prepared.
  • the homogeneous solution is slowly transferred into a sodium carbonate or sodium bicarbonate solution maintained at 65-75 °C.
  • the mixture thus formed is aged for 2-4 hours to form a suspension, which is then filtered to afford a slurry.
  • the slurry is dried at 100-110 °C to afford a dry powder. Finally, the dry powder is calcined at 700-800 °C for 4-5 hours to obtain a transitional metal catalyst.
  • One embodiment of the sequential precipitation method is performed as follows.
  • a homogeneous aqueous solution formed of a cerium compound and excess urea or formed of a cerium compound, and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound, and excess urea, is prepared.
  • the homogeneous solution is heated at 65-90 °C for 4-6 hours to hydrolyze the metal compound(s), followed by addition of an iridium compound.
  • the mixture thus formed is aged for 2-4 hours and then filtered to afford a slurry.
  • the slurry is dried at 100-110 °C to afford a dry powder. Finally, the dry powder is calcined at 700-800 °C for 4-5 hours to obtain a transitional metal catalyst.
  • transitional metal catalyst that can be prepared by one of the methods described above.
  • the catalyst preferably contains less than 5 wt% (e.g., 2-3 wt%) iridium and greater than 95 wt% (e.g., 97-98 wt%) a ceria-based solid solution support.
  • the ceria-based solid solution support can be Ce0 2 , Ce0 2 -La 2 0 3 , Ce0 2 -Pr 6 0n, Ce0 2 -Zr0 2 , or Ce0 2 -Ti0 2 .
  • the Ce0 2 -La 2 0 3 , Ce0 2 -Pr 6 0n, Ce0 2 -Zr0 2 , or Ce0 2 - Ti0 2 solid solution support has a molar ratio of Ce/La, Ce/Pr, Ce/Zr, or Ce/Ti being 8.5-9.
  • the catalyst thus prepared is capable of promoting the conversion of methane and C0 2 into syngas during a dry reforming reaction.
  • the dry reforming reaction features a methane conversion rate of 50-80%, a C0 2 conversion rate of 75-95%, a product molar ratio (i.e., H 2 /CO) of 0.95-1.05, and a space velocity of 6000-36000 mlJ(gh).
  • a catalyst of this invention unexpectedly maintains high activities at 1073 K or 800 °C for as long as 1000 hours in a methane dry reforming reaction at a space velocity of 36000 mlJ(gh).
  • catalyst prepared in each of the following examples is labeled according to its components, e.g., Ir and Ce0 2 -Pr 6 0n, and the preparation method, i.e., deposition- precipitation (DP), co-precipitation (CP), or sequential precipitation (SP).
  • DP deposition- precipitation
  • CP co-precipitation
  • SP sequential precipitation
  • catalyst Ir/CePr-DP refers to a catalyst formed of Ir, Ce, and Pr, and prepared by the deposition-precipitation method.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -Pr 6 0n was prepared following the procedure set forth below.
  • the reaction was conducted in a fixed-bed reactor.
  • the Ir/CePr-DP (A) catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes.
  • a feedstock of methane and CO 2 (methane: 15 mL/min; CO 2 : 15 mL/min) was then passed through the catalyst at a space velocity of 18000 mL/(gh).
  • the products, i.e., 3 ⁇ 4 and CO were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -La 2 0 3 was prepared following the procedure described in Example 1 except that 0.25 g of lanthanum nitrate was used.
  • the thusly prepared catalyst Ir/CeLa-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor. More specifically, the Ir/CeLa-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and CO 2 (methane: 15 mL/min; CO 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mlJ(gh). The products, i.e., 3 ⁇ 4 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce ZrC ⁇ was prepared following the procedure described in Example 1 except that 0.14 g of zirconium oxynitrate was used.
  • the thusly prepared catalyst Ir/CeZr-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CeZr-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and CO 2 (methane: 15 mL/min; CO 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., 3 ⁇ 4 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 3 wt% Ir and 97 wt% Ce0 2 -Pr 6 0n was prepared following the procedure described in Example 1 except that 0.27 g of praseodymium nitrate, 0.97 g of solid solution support Ce0 2 -Pr 6 0n, and hydrogen hexachloroiridate (containing Ir 0.03 g) were used.
  • the thusly prepared catalyst Ir/CePr-DP (B) was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CePr-DP (B) catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and CO 2 (methane: 15 mL/min; CO 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -Ti0 2 was prepared following the procedure described in Example 1 except that 0.18 g of titanium nitrate was used.
  • the thusly prepared catalyst Ir/CeTi-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CeTi-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C0 2 (methane: 15 mL/min; C0 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mlJ(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -Pr 6 0n was prepared following the procedure set forth below.
  • hexachloroiridate (containing Ir 0.02 g) were dissolved in 500 mL of de-ionized water to form a homogeneous solution.
  • the homogeneous solution was slowly added to an aqueous sodium carbonate solution (0.1 mol/L) at 65-75 °C and its pH was maintained at 8-9.
  • the mixture thus formed was aged for 2 hours. After filtration and washing, the resulting solid material was dried at 100 °C overnight to provide a dry powder. Finally, the dry powder was then calcined at 750 °C for 4 hours.
  • the catalyst Ir/CePr-CP thus obtained was collected.
  • the thusly prepared catalyst Ir/CePr-CP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CePr-CP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C0 2 (methane: 15 mL/min; C0 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mlJ(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -La 2 0 3 was prepared following the procedure described in Example 6 except that 0.25 g of lanthanum nitrate was used.
  • the thusly prepared catalyst Ir/CeLa-CP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CeLa-CP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C0 2 (methane: 15 mL/min; C0 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.
  • the same catalyst was evaluated in a similar experiment when the space velocity was 6000 mL/(gh). It was found that the conversion rates of methane and C0 2 were 75% and 97%, respectively.
  • the molar ratio of H 2 /CO was about 1.03. The catalytic activity persisted for at least 200 h.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -Zr0 2 was prepared following the procedure described in Example 6 except that 0.14 g of zirconium oxynitrate was used.
  • the thusly prepared catalyst Ir/CeZr-CP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CeZr-CP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C0 2 (methane: 15 mL/min; C0 2 : 15 mL/min) was passed through the catalyst at a space velocity of 6000 mL/(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 -Pr 6 0n was prepared following the procedure set forth below.
  • the thusly prepared catalyst Ir/CePr-SP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/CePr-SP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C0 2 (methane: 15 mL/min; C0 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.
  • a catalyst composed of 2 wt% Ir and 98 wt% Ce0 2 was prepared following the procedure set forth below.
  • the thusly prepared catalyst Ir/Ce-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
  • the Ir/Ce-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H 2 /N 2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C0 2 (methane: 15 mL/min; C0 2 : 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H 2 and CO, were analyzed by an online GC7890A gas chromatography.

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Abstract

A transitional metal catalyst containing an active iridium metal in a content of less 5 than 5 wt% and a ceria-based solid solution support in a content of greater than 95 wt%. The ceria-based solid solution support includes pure CeO2 or includes both CeO2 and MxOy, in which M is lanthanum (La), praseodymium (Pr), zirconium (Zr), or titanium (Ti), 1 ≤ x ≤ 6, and 2 ≤ y ≤ 11. Also disclosed are a deposition-precipitation method, a co-precipitation method, and a sequential precipitation method for preparing such a catalyst.

Description

IRIDIUM/CERIUM-BASED CATALYSTS
FOR DRY REFORMING METHANE TO SYNGAS
BACKGROUND OF THE INVENTION
Conversion of methane, which is naturally abundant, to energy chemicals, e.g., syngas, has gained great attention. Dry reforming methane in the presence of C02, a main component of greenhouse gas, to produce syngas is an approach that both protects and improves the environment.
Due to the ultra-stability of methane and C02, their activation and transformation requires a high temperature, e.g., 800 °C, during the dry reforming process. Transitional metal catalyst has been used to promote conversion of methane and C02 into syngas. At high temperature, the transitional metal catalyst is easily sintered, thus lowering its activity.
Further, severe carbon deposition often occurs at elevated temperature. Both catalyst sintering and carbon deposition lead to catalyst deactivation, which results in a short lifespan of the catalyst.
There is a need to develop a robust catalyst that has a long lifespan for dry reforming methane to syngas.
SUMMARY OF THE INVENTION
The present invention relates to a ceria-based transitional metal catalyst for dry reforming methane to syngas. The catalyst exhibits a high activity with an unexpectedly long lifespan.
Disclosed herein are three methods for preparing a transitional metal catalyst of this invention, namely, a deposition-precipitation method, a co-precipitation method, and a sequential precipitation method.
The deposition-precipitation method includes the following steps: (a) mixing a cerium compound and/or a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with excess urea in de-ionized water to form a homogeneous solution, a molar ratio of Ce/M (M being La, Pr, Zr, or Ti) being 8.5-9; (b) obtaining a ceria-based solid solution support from the homogeneous solution; (c) mixing the ceria-based solid solution support and an iridium compound in de-ionized water; (d) obtaining a dry powder from the resulting solution; (e) calcining the dry powder at
700-800 °C; and (f) collecting the transitional metal catalyst thus obtained.
The co-precipitation method includes the following steps: (a) mixing an iridium compound, a cerium compound, and/or a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with excess urea in de-ionized water to form a homogeneous solution, a molar ratio of Ce/M (M being La, Pr, Zr, or Ti) being 8.5-9; (b) obtaining a dry powder from the homogeneous solution; (c) calcining the dry powder at 700- 800 °C; and (d) collecting the transitional metal catalyst thus obtained.
The sequential precipitation method includes the following steps: (a) mixing a cerium compound, and/or a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with excess urea in de-ionized water to form a homogeneous solution, a molar ratio of Ce/M (M being La, Pr, Zr, or Ti) being 8.5-9; (b) obtaining a suspension from the homogeneous solution; (c) adding an iridium compound into the suspension; (d) obtaining a dry powder from the mixture thus formed; (e) calcining the dry powder at 700-800 °C; and (f) collecting the transitional metal catalyst thus obtained.
Typically, the homogeneous solution has a concentration of cerium being
0.01-1.0 mol/L and a concentration of lanthanum, praseodymium, zirconium, or titanium being 0.0012-0.12 mol/L.
Examples of the iridium compound include hydrogen hexachloroiridate, potassium hexachloroiridate, sodium hexachloroiridate, iridium oxide, and iridium chloride. Examples of the cerium compound include cerium nitrate, ammonium cerium nitrate, and cerium chloride. Examples of the praseodymium compound include praseodymium nitrate and praseodymium chloride. Examples of the lanthanum compound include lanthanum nitrate, lanthanum chloride, and lanthanum acetate. Examples of the zirconium compound include zirconium oxynitrate, zirconium nitrate, zirconium chloride, and zirconium acetate.
Examples of the titanium compound include titanyl oxalate and titanium nitrate.
Also within the scope of this invention is a transitional metal catalyst containing an active iridium metal in a content of less than 5 wt% and a ceria-based solid solution support in a content of greater than 95 wt%. The ceria-based solid solution includes pure Ce02 or includes both Ce02 and MxOy, in which M is La, Pr, Zr, or Ti, 1 < x < 6, and 2 < y < 11.
Preferably, the catalyst contains an active iridium metal in a content of 2-3 wt% and the ceria-based solid solution support in a content of 97-98 wt%. The ceria-based solid solution support can be pure Ce02. It can also include both Ce02 and MxOy, e.g., La203, Pr6On, Zr02, or Ti02, the molar ratio of Ce/M being 8.5-9.
The details of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the following detailed description of several embodiments, and also from the appending claims.
DETAILED DESCRIPTION
Described in detail below are three methods for preparing a ceria-based transitional metal catalyst of this invention, i.e., a deposition-precipitation method, a co-precipitation method, and a sequential precipitation method.
One embodiment of the deposition precipitation method is performed as follows.
A homogeneous aqueous solution, formed of a cerium compound and excess urea or formed of a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound, and excess urea, is prepared. Subsequently, the homogeneous solution is heated at 65-90 °C for 4-6 hours to hydrolyze the metal compound(s). The mixture thus formed is filtered and washed to afford a solid material, which is then dried at 100-110 °C to obtain a solid slurry. The solid slurry is calcined at 400- 450 °C for 3.5-4.5 hours to provide a ceria-based solid solution support. The solid solution support is mixed with an iridium compound in de-ionized water and dispersed with vigorous stirring. The resulting solution is stirred at 65-75 °C, followed by slow addition of an aqueous sodium carbonate or sodium bicarbonate solution to adjust its pH to 8-9. After standing for 2-4 hours, a suspension is formed. The suspension is filtered and washed with hot water to provide a slurry. The slurry is then dried at 100-110 °C overnight to obtain a dry powder. Finally, the dry powder is calcined at 700-800 °C for 4-5 hours to obtain a transitional metal catalyst.
One embodiment of the co -precipitation method is performed as follows.
A homogeneous aqueous solution, formed of an iridium compound and a cerium compound or formed of an iridium compound, a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound, is prepared. The homogeneous solution is slowly transferred into a sodium carbonate or sodium bicarbonate solution maintained at 65-75 °C. The mixture thus formed is aged for 2-4 hours to form a suspension, which is then filtered to afford a slurry. The slurry is dried at 100-110 °C to afford a dry powder. Finally, the dry powder is calcined at 700-800 °C for 4-5 hours to obtain a transitional metal catalyst.
One embodiment of the sequential precipitation method is performed as follows.
A homogeneous aqueous solution, formed of a cerium compound and excess urea or formed of a cerium compound, and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound, and excess urea, is prepared. The homogeneous solution is heated at 65-90 °C for 4-6 hours to hydrolyze the metal compound(s), followed by addition of an iridium compound. The mixture thus formed is aged for 2-4 hours and then filtered to afford a slurry. The slurry is dried at 100-110 °C to afford a dry powder. Finally, the dry powder is calcined at 700-800 °C for 4-5 hours to obtain a transitional metal catalyst.
Also within this invention is a transitional metal catalyst that can be prepared by one of the methods described above.
The catalyst preferably contains less than 5 wt% (e.g., 2-3 wt%) iridium and greater than 95 wt% (e.g., 97-98 wt%) a ceria-based solid solution support.
The ceria-based solid solution support can be Ce02, Ce02-La203, Ce02-Pr60n, Ce02-Zr02, or Ce02-Ti02. Preferably, the Ce02-La203, Ce02-Pr60n, Ce02-Zr02, or Ce02- Ti02 solid solution support has a molar ratio of Ce/La, Ce/Pr, Ce/Zr, or Ce/Ti being 8.5-9.
The catalyst thus prepared is capable of promoting the conversion of methane and C02 into syngas during a dry reforming reaction.
More specifically, when using a catalyst of this invention, the dry reforming reaction features a methane conversion rate of 50-80%, a C02 conversion rate of 75-95%, a product molar ratio (i.e., H2/CO) of 0.95-1.05, and a space velocity of 6000-36000 mlJ(gh).
In one example, a catalyst of this invention unexpectedly maintains high activities at 1073 K or 800 °C for as long as 1000 hours in a methane dry reforming reaction at a space velocity of 36000 mlJ(gh).
Without further elaboration, it is believed that one skilled in the art can, based on the above description, utilize the present invention to its fullest extent. The specific examples below are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
The catalyst prepared in each of the following examples is labeled according to its components, e.g., Ir and Ce02-Pr60n, and the preparation method, i.e., deposition- precipitation (DP), co-precipitation (CP), or sequential precipitation (SP). For instance, catalyst Ir/CePr-DP refers to a catalyst formed of Ir, Ce, and Pr, and prepared by the deposition-precipitation method.
EXAMPLE 1: Catalyst Ir/CePr-DP (A) preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-Pr60n was prepared following the procedure set forth below.
2.42 g of cerium nitrate, 0.27 g of praseodymium nitrate, and 50 g of urea were dissolved in 500 mL of de-ionized water to form a homogeneous solution. The homogeneous solution was heated at 90 °C for 5 hours to hydrolyze the metal compounds. The resulting slurry, after filtration and washing, was dried at 100 °C overnight and calcined at 400 °C for 4 hours to obtain a Ce02-Pr60n solid solution support. The solid solution support
Ce02-Pr60ii (0.98 g) and hydrogen hexachloroiridate (containing Ir 0.02 g) were mixed in 400 mL of de-ionized water. The solution was heated at 65-75 °C. Subsequently, an aqueous sodium carbonate solution (0.1 mol/L) was slowly added until the pH reached 8-9. The resulting suspension was aged for 2-4 hours. After filtration and washing, the resulting solid material was dried at 100 °C overnight to provide a dry powder, which was then calcined at 750 °C for 4 hours. The catalyst Ir/CePr-DP (A) thus obtained was collected.
The thusly prepared catalyst Ir/CePr-DP (A) was evaluated in a methane dry reforming reaction as follows.
The reaction was conducted in a fixed-bed reactor. The Ir/CePr-DP (A) catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. A feedstock of methane and CO2 (methane: 15 mL/min; CO2: 15 mL/min) was then passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., ¾ and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and CO2 were 60% and 90%, respectively. The molar ratio of H2/CO was about 1.05. The catalytic activity persisted for at least 200 h.
EXAMPLE 2: Catalyst Ir/CeLa-DP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-La203 was prepared following the procedure described in Example 1 except that 0.25 g of lanthanum nitrate was used.
The thusly prepared catalyst Ir/CeLa-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor. More specifically, the Ir/CeLa-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and CO2 (methane: 15 mL/min; CO2: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mlJ(gh). The products, i.e., ¾ and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and CO2 were 72% and 92%, respectively. The molar ratio of H2/CO was about 1.05. The catalytic activity persisted for at least 200 h.
EXAMPLE 3: Catalyst Ir/CeZr-DP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce ZrC^ was prepared following the procedure described in Example 1 except that 0.14 g of zirconium oxynitrate was used.
The thusly prepared catalyst Ir/CeZr-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CeZr-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and CO2 (methane: 15 mL/min; CO2: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., ¾ and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and CO2 were 56% and 83%, respectively. The molar ratio of ¾/CO was about 1.05. The catalytic activity persisted for at least 200 h.
EXAMPLE 4: Catalyst Ir/CePr-DP (B) preparation and evaluation
A catalyst composed of 3 wt% Ir and 97 wt% Ce02-Pr60n was prepared following the procedure described in Example 1 except that 0.27 g of praseodymium nitrate, 0.97 g of solid solution support Ce02-Pr60n, and hydrogen hexachloroiridate (containing Ir 0.03 g) were used.
The thusly prepared catalyst Ir/CePr-DP (B) was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CePr-DP (B) catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and CO2 (methane: 15 mL/min; CO2: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that conversions of methane and C02 were 75% and 95%, respectively. A molar ratio of H2/CO was about 1.02. The catalyst's activity sustained for at least 200 h.
EXAMPLE 5: Catalyst Ir/CeTi-DP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-Ti02 was prepared following the procedure described in Example 1 except that 0.18 g of titanium nitrate was used.
The thusly prepared catalyst Ir/CeTi-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CeTi-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C02 (methane: 15 mL/min; C02: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mlJ(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and C02 were 50% and 80%, respectively. The molar ratio of H2/CO was about 1.02. The catalytic activity persisted for at least 200 h. EXAMPLE 6: Catalyst Ir/CePr-CP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-Pr60n was prepared following the procedure set forth below.
2.42 g of cerium nitrate, 0.18 g of praseodymium nitrate, and hydrogen
hexachloroiridate (containing Ir 0.02 g) were dissolved in 500 mL of de-ionized water to form a homogeneous solution. The homogeneous solution was slowly added to an aqueous sodium carbonate solution (0.1 mol/L) at 65-75 °C and its pH was maintained at 8-9. The mixture thus formed was aged for 2 hours. After filtration and washing, the resulting solid material was dried at 100 °C overnight to provide a dry powder. Finally, the dry powder was then calcined at 750 °C for 4 hours. The catalyst Ir/CePr-CP thus obtained was collected.
The thusly prepared catalyst Ir/CePr-CP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CePr-CP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C02 (methane: 15 mL/min; C02: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mlJ(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and C02 were 55% and 80%, respectively. The molar ratio of H2/CO was about 1.05. The catalytic activity persisted for at least 200 h.
EXAMPLE 7: Catalyst Ir/CeLa-CP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-La203 was prepared following the procedure described in Example 6 except that 0.25 g of lanthanum nitrate was used.
The thusly prepared catalyst Ir/CeLa-CP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CeLa-CP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C02 (methane: 15 mL/min; C02: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and C02 were 60% and 95%, respectively. The molar ratio of H2/CO was about 1.03. The catalytic activity persisted for at least 200 h.
The same catalyst was evaluated in a similar experiment when the space velocity was 6000 mL/(gh). It was found that the conversion rates of methane and C02 were 75% and 97%, respectively. The molar ratio of H2/CO was about 1.03. The catalytic activity persisted for at least 200 h.
EXAMPLE 8: Catalyst Ir/CeZr-CP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-Zr02 was prepared following the procedure described in Example 6 except that 0.14 g of zirconium oxynitrate was used.
The thusly prepared catalyst Ir/CeZr-CP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CeZr-CP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C02 (methane: 15 mL/min; C02: 15 mL/min) was passed through the catalyst at a space velocity of 6000 mL/(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and C02 were 73% and 95%, respectively. The molar ratio of H2/CO was about 1.02. The catalytic activity persisted for at least 200 h.
EXAMPLE 9: Catalyst Ir/CePr-SP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02-Pr60n was prepared following the procedure set forth below.
2.42 g of cerium nitrate, 0.27 g of praseodymium nitrate, and 50 g of urea were dissolved in 500 mL of de-ionized water to form a homogeneous solution. The homogeneous solution was heated at 90 °C for 5 hours to hydrolyze the metal compounds, followed by addition of hydrogen hexachloroiridate (containing Ir 0.02 g). The resulting mixture was aged for 3 hours. After filtration and washing, the resulting solid material was then dried at 100 °C overnight to provide a dry powder, which was calcined at 750 °C for 4 hours. The catalyst Ir/CePr-SP thus obtained was collected.
The thusly prepared catalyst Ir/CePr-SP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/CePr-SP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C02 (methane: 15 mL/min; C02: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and C02 were 60% and 75%, respectively. The molar ratio of H2/CO was about 0.95. The catalytic activity persisted for at least 200 h.
EXAMPLE 10: Catalyst Ir/Ce-DP preparation and evaluation
A catalyst composed of 2 wt% Ir and 98 wt% Ce02 was prepared following the procedure set forth below.
5 g of cerium nitrate and 50 g of urea were dissolved in 500 mL of de-ionized water to form a homogeneous solution. The homogeneous solution was heated at 90 °C for 5 hours to hydrolyze the metal compound. After filtration and washing, the slurry thus received was dried at 100 °C overnight and then calcined at 400 °C for 4 hours to obtain a Ce02 solid solution support. The solid solution support Ce02 (0.98 g) and hydrogen hexachloroiridate (containing Ir 0.02 g) were mixed in 400 mL of de-ionized water. The solution was heated at 65-75 °C. Then an aqueous sodium carbonate solution (0.1 mol/L) was slowly added until its pH reached 8-9. The suspension thus formed was aged for 2-4 hours. After filtration and washing, the resulting solid material was dried at 100 °C overnight to provide a dry powder, which was calcined at 750 °C for 4 hours. The catalyst Ir/Ce-DP thus obtained was collected.
The thusly prepared catalyst Ir/Ce-DP was evaluated in a methane dry reforming reaction conducted in a fixed-bed reactor.
More specifically, the Ir/Ce-DP catalyst (100 mg) was loaded into the reactor and reduced by 25% H2/N2 at 750 °C for 30 minutes. Subsequently, a feedstock of methane and C02 (methane: 15 mL/min; C02: 15 mL/min) was passed through the catalyst at a space velocity of 18000 mL/(gh). The products, i.e., H2 and CO, were analyzed by an online GC7890A gas chromatography.
It was found that the conversion rates of methane and C02 were 40% and 70%, respectively. The molar ratio of H2/CO was about 1.05. The catalytic activity persisted for at least 200 h.
OTHER EMBODIMENTS
All of the features disclosed in this specification may be combined in any
combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.
Further, from the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the claims.

Claims

What is claimed is:
1. A transitional metal catalyst comprising a mixture of an iridium metal and a ceria- based solid solution, wherein the iridium metal is present at less than 5 wt% and the ceria- based solid solution is present at greater than 95 wt%, the ceria-based solid solution including pure Ce02 or including both Ce02 and MxOy, in which M is lanthanum (La), praseodymium (Pr), zirconium (Zr), or titanium (Ti), 1 < x < 6, and 2 < y < 11.
2. The transitional metal catalyst of claim 1, wherein the iridium metal is present at 2-3 wt% and the ceria-based solid solution is present at 97-98 wt%.
3. The transitional metal catalyst of claim 2, wherein the ceria-based solid solution is pure Ce02.
4. The transitional metal catalyst of claim 2, wherein the ceria-based solid solution includes both Ce02 and MxOy.
5. The transitional metal catalyst of claim 4, wherein MxOy is La203, Pr6On, Zr02, or Ti02.
6. The transitional metal catalyst of claim 5, wherein the catalyst has a Ce/M molar ratio of 8.5-9.
7. The transitional metal catalyst of claim 1, wherein the ceria-based solid solution is pure Ce02.
8. The transitional metal catalyst of claim 1, wherein the ceria-based solid solution includes both Ce02 and MxOy.
9. The transitional metal catalyst of claim 8, wherein MxOy is La203, Pr6On, Zr02, or Ti02.
10. The transitional metal catalyst of claim 9, wherein the catalyst has a Ce/M molar ratio of 8.5-9.
11. A deposition-precipitation method of preparing a transitional metal catalyst, the method comprising the following steps:
(a) mixing a cerium compound alone or mixing a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with urea in water to form a first homogeneous solution, a Ce/M molar ratio being 8.5-9, in which M is La, Pr, Zr, or Ti;
(b) obtaining a ceria-based solid solution from the first homogeneous solution;
(c) mixing the ceria-based solid solution and an iridium compound in water to form a second homogeneous solution;
(d) obtaining a dry powder from the second homogeneous solution;
(e) calcining the dry powder at 700-800 °C; and
(f) collecting the transitional metal catalyst thus obtained.
12. The deposition-precipitation method of claim 11, wherein
step (b) is conducted by heating the first homogeneous solution at 65-90 °C, filtering the resulting mixture to obtain a filtrate, washing and drying the filtrate at 100-110 °C, and calcining the solid slurry thus obtained at 400-450 °C to provide the ceria-based solid solution; and
step (d) is conducted by heating the second homogeneous solution at 65-75 °C, adjusting the pH thereof to 8-9, aging the resulting solution to form a suspension, filtering the suspension to obtain a slurry, and drying the slurry at 100-110 °C to provide the dry powder.
13. The deposition-precipitation method of claim 11, wherein the iridium compound is hydrogen hexachloroiridate, potassium hexachloroiridate, sodium hexachloroiridate, iridium oxide, or iridium chloride; the cerium compound is cerium nitrate, ammonium cerium nitrate, or cerium chloride; the praseodymium compound is praseodymium nitrate or praseodymium chloride; the lanthanum compound is lanthanum nitrate, lanthanum chloride, or lanthanum acetate; the zirconium compound is zirconium oxynitrate, zirconium nitrate, zirconium chloride, or zirconium acetate; and the titanium compound is titanyl oxalate or titanium nitrate.
14. The deposition-precipitation method of claim 11, wherein the first homogeneous solution has a concentration of cerium being 0.01-1.0 mol/L and a concentration of lanthanum, praseodymium, zirconium, or titanium being 0.0012-0.12 mol/L.
15. A co-precipitation method of preparing a transitional metal catalyst, the method comprising the following steps:
(a) mixing a cerium compound alone or mixing a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with an iridium compound and urea in water to form a homogeneous solution, a Ce/M molar ratio being 8.5-9, in which M is La, Pr, Zr, or Ti;
(b) obtaining a dry powder from the homogeneous solution;
(c) calcining the dry powder at 700-800 °C; and
(d) collecting the transitional metal catalyst thus obtained.
16. The co-precipitation method of claim 15, wherein step (b) is conducted by
transferring the homogeneous solution into a sodium carbonate or sodium bicarbonate solution maintained at 65-75 °C, aging the resulting mixture to form a suspension, filtering the suspension to afford a slurry, and drying the slurry at 100-110 °C to obtain the dry powder.
17. The deposition-precipitation method of claim 15, wherein the iridium compound is hydrogen hexachloroiridate, potassium hexachloroiridate, sodium hexachloroiridate, iridium oxide, or iridium chloride; the cerium compound is cerium nitrate, ammonium cerium nitrate, or cerium chloride; the praseodymium compound is praseodymium nitrate or praseodymium chloride; the lanthanum compound is lanthanum nitrate, lanthanum chloride, or lanthanum acetate; the zirconium compound is zirconium oxynitrate, zirconium nitrate, zirconium chloride, or zirconium acetate; and the titanium compound is titanyl oxalate or titanium nitrate.
18. The deposition-precipitation method of claim 15, wherein the homogeneous solution has a concentration of cerium being 0.01-1.0 mol/L and a concentration of lanthanum, praseodymium, zirconium, or titanium being 0.0012-0.12 mol/L.
19. A sequential precipitation method of preparing a transitional metal catalyst, the method comprising the following steps:
(a) mixing a cerium compound alone or mixing a cerium compound and a lanthanum compound, a praseodymium compound, a zirconium compound, or a titanium compound with urea in water to form a homogeneous solution, a Ce/M molar ratio being 8.5-9, in which M is La, Pr, Zr, or Ti;
(b) treating the homogeneous solution with an iridium compound to obtain a dry powder;
(c) calcining the dry powder at 700-800 °C; and
(d) collecting the transitional metal catalyst thus obtained.
20. The sequential precipitation method of claim 19, wherein step (b) is conducted by heating the homogeneous solution at 65-90 °C, adding an iridium compound thereto, aging the resulting solution to form a suspension, filtering the suspension, and drying the resulting slurry at 100-110 °C to obtain the powder.
21. The deposition-precipitation method of claim 19, wherein the iridium compound is hydrogen hexachloroiridate, potassium hexachloroiridate, sodium hexachloroiridate, iridium oxide, or iridium chloride; the cerium compound is cerium nitrate, ammonium cerium nitrate, or cerium chloride; the praseodymium compound is praseodymium nitrate or praseodymium chloride; the lanthanum compound is lanthanum nitrate, lanthanum chloride, or lanthanum acetate; the zirconium compound is zirconium oxynitrate, zirconium nitrate, zirconium chloride, or zirconium acetate; and the titanium compound is titanyl oxalate or titanium nitrate.
22. The deposition-precipitation method of claim 19, wherein the homogeneous solution has a concentration of cerium being 0.01-1.0 mol/L and a concentration of lanthanum, praseodymium, zirconium, or titanium being 0.0012-0.12 mol/L.
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