US20070092768A1 - Catalyst for oxidizing carbon monoxide and method of manufacturing the same - Google Patents

Catalyst for oxidizing carbon monoxide and method of manufacturing the same Download PDF

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Publication number
US20070092768A1
US20070092768A1 US11/582,974 US58297406A US2007092768A1 US 20070092768 A1 US20070092768 A1 US 20070092768A1 US 58297406 A US58297406 A US 58297406A US 2007092768 A1 US2007092768 A1 US 2007092768A1
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catalyst
platinum
transition metal
carbon monoxide
reaction
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US11/582,974
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Hyun-chul Lee
Soon-ho Kim
Doo-Hwan Lee
Eun-Duck Park
Eun-yong Ko
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Samsung SDI Co Ltd
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Samsung SDI Co Ltd
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Assigned to SAMSUNG SDI CO., LTD. reassignment SAMSUNG SDI CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KIM, SOON-HO, KO, EUN-YONG, LEE, DOO-HWAN, LEE, HYUN-CHUL, PARK, EUN-DUCK
Publication of US20070092768A1 publication Critical patent/US20070092768A1/en
Priority to US11/856,835 priority Critical patent/US8101542B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • 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
    • B01J21/02—Boron or aluminium; Oxides or hydroxides thereof
    • B01J21/04—Alumina
    • 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
    • B01J23/42—Platinum
    • 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
    • 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
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • 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
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8906—Iron and noble metals
    • 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
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8913—Cobalt and noble metals
    • 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
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/892—Nickel and noble metals
    • 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
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8926—Copper and noble metals
    • 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
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • 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
    • B01J37/16—Reducing
    • B01J37/18—Reducing with gases containing free hydrogen
    • 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
    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/56—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids
    • C01B3/58—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction
    • C01B3/583—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction the reaction being the selective oxidation of carbon monoxide
    • 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
    • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
    • 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
    • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
    • B01J2235/30—Scanning electron microscopy; Transmission electron microscopy
    • 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
    • B01J37/16—Reducing
    • 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
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0435—Catalytic purification
    • C01B2203/044—Selective oxidation of carbon monoxide
    • 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
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/047—Composition of the impurity the impurity being carbon monoxide
    • 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
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • 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
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • aspects of the present invention relate to a catalyst for oxidizing carbon monoxide and a method of manufacturing the same. More particularly, aspects of the present invention relate to a catalyst for oxidizing carbon monoxide having high reaction activity and excellent reaction selectivity in which a methanation reaction and reoxidation do not occur, and a method of manufacturing the same.
  • Fuel cells are electricity generation systems that directly convert the chemical energy of oxygen and the hydrogen in hydrocarbons such as methanol, ethanol, and natural gas to electrical energy.
  • Fuel cell systems consist of a fuel cell stack, a fuel processor (FP), a fuel tank, and a fuel pump.
  • the fuel cell stack is the main body of a fuel cell, and includes several to several tens of unit cells, each including a membrane electrode assembly (MEA) and a separator (or bipolar plate).
  • MEA membrane electrode assembly
  • separator or bipolar plate
  • the fuel pump supplies fuel in the fuel tank to the fuel processor.
  • the fuel processor produces hydrogen by reforming and purifying the fuel and supplies the hydrogen to the fuel cell stack.
  • the fuel cell stack receives the hydrogen and generates electrical energy by electrochemical reaction of the hydrogen with oxygen.
  • a reformer of the fuel processor reforms hydrocarbon fuel using a reforming catalyst. Since a hydrocarbon fuel typically contains one or more sulfur compounds, and since the reforming catalyst is easily poisoned by sulfur compounds, it is necessary to subject the hydrocarbon fuel to desulfurization prior to the reforming process in order to remove sulfur compounds prior to reforming the hydrocarbon fuel.
  • FIG. 1 is a schematic flow diagram illustrating fuel processing in a fuel processor used in a conventional fuel cell system.
  • Hydrocarbon reforming produces carbon dioxide (CO 2 ) and a small amount of carbon monoxide (CO) as by-products, together with hydrogen. Since CO acts as a catalyst poison in electrodes of the fuel cell stack, reformed fuel should not be supplied to the fuel cell stack until a CO removal process has been carried out. It is desirable to reduce the CO levels to less than 10 ppm.
  • a high-temperature shift reaction is performed at a temperature of 400 to 500° C. Generally, a high-temperature shift reaction is followed by a low-temperature shift reaction at a temperature of 200 to 300° C. Even after these reactions are performed, it is very difficult to reduce the CO levels to less than 5,000 ppm.
  • a preferential oxidation reaction (referred to as the “PROX” reaction) represented by Reaction Scheme 2 below can be used.
  • PROX catalyst that has a high reaction activity and excellent reaction selectivity, and that does not support a methanation reaction or become reoxidized.
  • aspects of the present invention provide a PROX catalyst having excellent reaction selectivity and a broad operating temperature range in which a methanation reaction and reoxidation do not occur.
  • aspects of the present invention also provide a method of manufacturing the PROX catalyst.
  • aspects of the present invention also provide a fuel processor including the PROX catalyst having excellent reaction selectivity and a broad operating temperature range in which a methanation reaction and reoxidation do not occur.
  • aspects of the present invention also provide a fuel cell system including the PROX catalyst having excellent reaction selectivity and a broad operating temperature range in which a methanation reaction and reoxidation do not occur.
  • a catalyst that oxidizes carbon monoxide including a bimetal consisting of platinum (Pt) and another transition metal in a bimetallic phase, wherein the bimetal is loaded on a ⁇ -alumina ( ⁇ -Al 2 O 3 ) support, and wherein the transition metal of the bimetal is reduced.
  • a method of producing a catalyst for oxidizing carbon monoxide including: adding a platinum precursor, a transition metal precursor, and ⁇ -alumina ( ⁇ -Al 2 O 3 ) to a dispersion medium and uniformly mixing the resultant mixture; drying the mixture; calcining the dried mixture; and reducing the calcined dried mixture.
  • a fuel processor including the catalyst that oxidizes carbon monoxide.
  • a fuel cell system including the catalyst that oxidizes carbon monoxide.
  • the catalyst that oxidizes carbon monoxide according to aspects of the present invention has excellent selectivity for carbon monoxide and a fast reaction rate in a carbon monoxide oxidizing reaction. In addition, efficiency of the entire reaction increases since a methanation reaction and reoxidization do not occur. Thus, the carbon monoxide in the fuel can effectively be eliminated using the catalyst according to aspects of the present invention.
  • FIG. 1 is a schematic flow diagram illustrating fuel processing in a fuel processor used in a conventional fuel cell system
  • FIG. 2 is a flowchart illustrating a method of manufacturing a catalyst for oxidizing carbon monoxide according to an embodiment of the present invention
  • FIGS. 3A, 3B , and 3 C are graphs respectively illustrating the results of a first TPR analysis, a TPO analysis, and a second TPR analysis of the catalyst in which a support is respectively ⁇ -alumina, zirconia, and titania;
  • FIGS. 4A and 4B are graphs illustrating the results of a TPR analysis and a TPO analysis of a Pt/Ni supported catalyst in which platinum is impregnated and then nickel is impregnated;
  • FIGS. 5A and 5B are graphs illustrating the results of a TPR analysis and a TPO analysis of a Pt/Ni supported catalyst in which nickel is impregnated and then platinum is impregnated;
  • FIGS. 6A and 6B are graphs illustrating the results of CO oxidizing tests of the catalysts in which a support is respectively ⁇ -alumina, zirconia, and titania according to temperature;
  • FIGS. 7A and 7B are graphs illustrating the results of CO oxidizing tests of a platinum catalyst loaded on ⁇ -alumina, a Pt/Ni catalyst loaded on ⁇ -alumina, and a bimetallic phase Pt/Ni catalyst loaded on ⁇ -alumina according to temperature;
  • FIGS. 8A and 8B illustrate a TEM photograph image and a graph showing the result of the EDX analysis regarding the Pt-Ni/ ⁇ -Al 2 O 3 according to Example 1;
  • FIGS. 9A and 9B illustrate a TEM photograph image and a graph showing the result of the EDX analysis regarding the Pt-Co/ ⁇ -Al 2 O 3 according to Example 2;
  • FIG. 10 illustrates graph of CO conversion and CO 2 selectivity regarding the supported catalyst of Example 1.
  • a catalyst for oxidizing carbon monoxide includes a bimetal consisting of platinum (Pt) and another transition metal in a bimetallic phase.
  • the other transition metal is referred to herein simply as “the transition metal” and it is to be understood that the term “transition metal” in this context refers to a transition metal other than platinum.
  • the bimetal is loaded onto ⁇ -alumina( ⁇ -Al 2 O 3 ) support, and the transition metal is reduced.
  • the transition metal may be one of Ni, Co, Cu, and Fe.
  • the transition metal may be Ni.
  • bimetallic phase of platinum and the transition metal refers to a correlation between platinum and the transition metal that is created, for example, when platinum and the transition metal are loaded onto the support at the same time.
  • the structural relationship between the platinum and the transition metal in the bimetallic phase is not clearly determined, but the bimetallic phase seems to have its own particular structure since in the bimetallic phase, reoxidization of the transition metal does not occur.
  • the support for the bimetallic phase may be ⁇ -alumina ( ⁇ -Al 2 O 3 ).
  • the bimetallic phase cannot easily be obtained using a support such as zirconia (ZrO 2 ) or titania (TiO 2 ).
  • the catalyst for oxidizing carbon monoxide has a peak of between 130 to 180° C. in a temperature programmed reduction (TPR) analysis and is not reoxidized in a temperature programmed oxidation (TPO) analysis until the temperature reaches 500° C.
  • TPR temperature programmed reduction
  • TPO temperature programmed oxidation
  • the atomic ratio of the transition metal to platinum may be from 0.5 to 20.
  • an effect of the transition metal such as, for example an effect to promote the reaction activity of the catalyst at low temperatures and to widen the operating temperature range cannot be obtained.
  • a promotion effect on the reaction activity of the catalyst may decrease due to an excessive amount of the transition metal.
  • the amount of platinum may be in the range of 0.3 to 5% by weight based on the weight of the catalyst for oxidizing carbon monoxide (including the support). When the amount of platinum is less than 0.3% by weight, the catalyst activity may decrease. When the amount of platinum is greater than 5% by weight, the increase of the catalyst activity may be negligible, which is cost-ineffective.
  • a platinum precursor, a transition metal precursor, and ⁇ -alumina are added to a dispersion medium and uniformly mixed.
  • the platinum precursor may be Pt(NH 3 ) 4 (NO 3 ) 2 and the transition metal precursor may be one of Ni(NO 3 ) 2 .6H 2 O, Co(NO 3 ) 2 .6H 2 O, Cu(NO 3 ) 2 .H 2 O and Fe(NO 3 ) 2 .9H 2 O.
  • a halogen compound such as a chlorine compound is not recommended for the platinum precursor or the transition metal precursor.
  • any method of uniformly mixing the precursors and the support may be used.
  • the mixture may be stirred for 1 to 12 hours at a temperature from 40 to 80° C.
  • the dispersion medium is so named since although the platinum precursor and the transition metal precursor are dissolved in the medium, the ⁇ -alumina support is not dissolved, but rather, is only dispersed.
  • the dispersion medium may be any medium having the property of dissolving the platinum precursor and the transition metal precursor and dispersing the ⁇ -alumina support.
  • the dispersion medium may be water or an alcohol-based solvent.
  • the alcohol-based solvent may be methanol, ethanol, isopropyl alcohol, and butyl alcohol, but is not limited thereto.
  • the weight ratio of the platinum precursor and the transition metal precursor may be adjusted such that the atomic ratio of the transition metal to platinum is from 0.5 to 20.0.
  • the amount of the dispersion medium may be 30 to 95% by weight based on the total weight of the mixture in order to uniformly disperse the platinum precursor, the transition metal precursor, and ⁇ -alumina support, and so that it does not take too long to dry the dispersion medium, but is not limited thereto.
  • the dispersion medium may be removed by drying the mixture.
  • the conditions for drying the mixture are not limited.
  • the mixture may be dried at 30 to 90° C. for 4 to 16 hours in a vacuum or in an oven.
  • the dried resultant is calcined in an airtight container such as an oven.
  • the calcination may be performed at a temperature of 300 to 500° C. for 1 to 12 hours.
  • the calcining temperature is less than 300° C.
  • the catalyst may not be sufficiently crystallized.
  • the temperature is greater than 500° C.
  • the platinum and transition metal particle may grow too large, thereby decreasing the reaction activity of the catalyst.
  • the calcining is performed for less than 1 hour, the catalyst may not be sufficiently crystallized.
  • the calcining may be performed under an air atmosphere, but is not limited thereto.
  • the calcined resultant may be reduced to produce a catalyst having activity for oxidizing carbon monoxide.
  • the reduction may be performed at a temperature of 150 to 500° C. for 1 to 12 hours.
  • the bimetallic phase may not be sufficiently formed.
  • the platinum and transition metal particles loaded on the support may grow too large, thereby decreasing the reaction activity of the catalyst.
  • the bimetallic phase may not be sufficiently formed.
  • the reduction may be performed under a H 2 atmosphere, and the H 2 atmosphere may further optionally include an inert gas such as helium, nitrogen, or neon.
  • an inert gas such as helium, nitrogen, or neon.
  • a fuel processor including the catalyst for oxidizing carbon monoxide is provided.
  • the fuel processor will be described.
  • the fuel processor may include a desulfurizer, a reformer, a high-temperature shift reaction device, a low-temperature shift reaction device, and a PROX reaction device.
  • the desulfurizer is a device that removes sulfur compounds that can poison catalysts downstream from the desulfurizer.
  • An absorbent that is well known in the art may be used for the desulfurizer, and a hydrodesulfurization (HDS) process may also be used.
  • HDS hydrodesulfurization
  • the reformer is a device that reforms hydrocarbons to produce hydrogen. Any catalyst such as platinum, ruthenium, and nickel that is well known in the art may be used for the reforming catalyst.
  • the high-temperature shift reaction device and the low-temperature shift reaction device are devices that remove carbon monoxide, which can poison the catalyst layer of a fuel cell.
  • the high-temperature shift reaction device and the low-temperature shift reaction device reduce the carbon monoxide concentration to less than 1%.
  • the PROX reaction device further reduces the carbon monoxide concentration to less than 10 ppm.
  • the PROX reaction device may include the catalyst for oxidizing carbon monoxide as described herein.
  • the catalyst for oxidizing carbon monoxide may be charged in the PROX reaction device as a fixed bed.
  • a fuel cell system including the catalyst for oxidizing carbon monoxide is provided.
  • the fuel cell system includes a fuel processor and a fuel cell stack.
  • the fuel cell processor may include a desulfurizer, a reformer, a high-temperature shift reaction device, a low-temperature shift reaction device, and a PROX reaction device as described above.
  • the fuel cell stack may be formed by stacking or arranging a plurality of unit cells. Each of the unit cells may include a cathode, an anode, and an electrolyte membrane, and may further include a separator.
  • the catalyst for oxidizing carbon monoxide may be included in the fuel cell processor, and more specifically, in the PROX reaction device.
  • Pt—Co/ ⁇ -Al 2 O 3 was prepared in the same manner as in Example 1, except that 1.554 g of Co(NO 3 ) 2 .6H 2 O was used instead of Ni(NO 3 ) 2 .6H 2 O.
  • Pt—Cu/ ⁇ -Al 2 O 3 was prepared in the same manner as in Example 1, except that 1.004 g of Cu(NO 3 ) 2 .H 2 O was used instead of Ni(NO 3 ) 2 .6H 2 O.
  • Pt—Fe/ ⁇ -Al 2 O 3 was prepared in the same manner as in Example 1, except that 2.154 g of Fe(NO 3 ) 2 .9H 2 O was used instead of Ni(NO 3 ) 2 .6H 2 O.
  • Pt/ ⁇ -Al 2 O 3 was prepared in the same manner as in Example 1, except that Ni(NO 3 ) 2 .6H 2 O was not added.
  • Pt—Ce/ ⁇ -Al 2 O 3 was prepared in the same manner as in Example 1, except that 2.424 g of Ce(NO 3 ) 2 .6H 2 O was used instead of Ni(NO 3 ) 2 .6H 2 O.
  • Example 4 As shown in Table 1, the CO conversions of the catalysts in Examples 1 through 3, 100%, were far better than those of Comparative Examples 1 and 2. In Example 4, the CO conversion was relatively low, but the O 2 selectivity was excellent.
  • Pt—Ni/ ⁇ -Al2O 3 and Pt—Co/ ⁇ -Al2O 3 prepared according to Examples 1 and 2 were analyzed using a transmission electron microscope (TEM) and an energy dispersive X-ray micro analyzer (EDX) to identify whether a bimetallic phase of platinum and the transition metal was formed. The results are shown in FIGS. 8A, 8B , 9 A and 9 B.
  • TEM transmission electron microscope
  • EDX energy dispersive X-ray micro analyzer
  • the results of the EDX analysis confirmed the presence of the bimetallic phase in the catalyst according to Example 1 since the ratio of nickel to platinum was 0.92, as illustrated in FIG. 8A .
  • the results of the EDX analysis shown in FIG. 8B also confirmed the presence of the bimetallic phase.
  • the EDX analysis confirmed the presence of the bimetallic phase in the catalyst according to Example 2 since a ratio of cobalt to platinum was 0.54, as illustrated in FIG. 9A .
  • the results of the EDX analysis shown in FIG. 9B also confirmed presence of the bimetallic phase.
  • Activity tests of the supported catalyst prepared according to Example 1 were performed at 120° C. to identify whether the activity and selectivity were constantly maintained with respect to time.
  • a gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 50 vol % of hydrogen, 20 vol % of carbon dioxide, 2 vol % of water vapor, and the remaining percentage of helium was flowed at a rate of 1000 ml/(min.gcat), and the resultants were analyzed. The results are presented in FIG. 10 .
  • the CO conversion of the catalyst was high and was almost constantly maintained with respect to time.
  • the CO 2 selectivity of the catalyst was almost constantly maintained as well.
  • the supported catalyst according to an embodiment of the present invention is highly stable with respect to time.
  • Pt—Ni/ZrO 2 was prepared in the same manner as in Example 1, except that 10 g of zirconia was used instead of ⁇ -alumina.
  • Pt—Ni/TiO 2 was prepared in the same manner as in Example 1, except that 10 g of titania was used instead of ⁇ -alumina.
  • the catalysts prepared according to Example 1, and Comparative Examples 3 and 4 were analyzed using a first temperature programmed reduction (TPR), a temperature programmed oxidation (TPO), and a second TPR to identify whether the catalysts were subject to reoxidation.
  • TPR temperature programmed reduction
  • TPO temperature programmed oxidation
  • FIGS. 3A through 3C The results are presented in FIGS. 3A through 3C .
  • FIGS. 3A two peaks were observed in the first TPR (shown in FIG. 3A ) of Comparative Examples 3 and 4, but only one peak was observed (around 410 K) in the first TPR of Example 1.
  • FIG. 3B oxygen consumption was observed in the TPO with respect to catalysts of Comparative Examples 3 and 4, indicating that the catalysts of Comparative Examples 3 and 4 were reoxidized in the TPO, but it was observed that the catalyst of Example 1 showed only the base line, which indicates that the catalyst of Example 1 was not reoxidized. Since the catalyst of Example 1 was not reoxidized, hydrogen was not consumed in the second TPR (shown in FIG. 3C ) with respect to the catalyst of Example 1. On the other hand, as shown in FIG. 3C , hydrogen was consumed in the second TPR with respect to the catalysts of Comparative Examples 3 and 4, since the catalysts of Comparative Examples 3 and 4 were reoxidized in the TPO.
  • the catalyst since the bimetallic phase of platinum and nickel was not formed when zirconia or titania was used, the catalyst was reoxidized in the temperature programmed oxidation (TPO). On the other hand, when ⁇ -alumina was used, the bimetallic phase of platinum and nickel was formed, and thus the catalyst was not reoxidized in the presence of oxygen.
  • TPO temperature programmed oxidation
  • the catalysts prepared according to Comparative Examples 5 and 6 were analyzed using temperature programmed reduction and temperature programmed oxidation to determine whether the catalysts were reoxidized. The results are shown in FIGS. 4A, 4B , 5 A and 5 B.
  • the properties of the bimetallic phase catalyst of Example 1 are different from those of the Pt/Ni catalysts supported on a carrier prepared according to Comparative Examples 5 and 6.
  • Pt/Ni supported catalysts prepared according to Comparative Examples 5 and 6 are not in the bimetallic phase, they can be reoxidized in the presence of oxygen.
  • the catalyst of Example 1 is not reoxidized in the presence of oxygen due to its bimetallic phase.
  • Carbon monoxide oxidizing tests were performed using the catalysts prepared according to Example 1, and Comparative Examples 3 and 4.
  • a gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 10 vol % of hydrogen, 2 vol % of water vapor, and the remaining percentage of helium is flowed at a GHSV of 60,000 hr-1.
  • the results are presented in FIGS. 6A and 6B .
  • Example 1 when zirconia or titania was used, the operating temperature range was limited since the CO conversion sharply decreased as temperature increased even though the CO conversion was high in a low temperature range.
  • Example 1 the CO conversion was the highest and was constantly maintained at a level close to 100% at temperatures over about 400 K. Further, a methanation reaction did not occur at all in Example 1, but the methanation reaction increasingly occurred as temperature increased in Comparative Examples 3 and 4.
  • Carbon monoxide oxidizing tests were performed using the catalysts prepared according to Example 1, and Comparative Examples 1 and 5.
  • a gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 80 vol % of hydrogen, 2 vol % of water vapor, and the remaining percentage of helium was flowed at a GHSV of 60,000 hr-1.
  • the results are presented in FIGS. 7A and 7B .
  • the catalyst of Example 1 had a higher CO conversion than either the catalyst of Comparative Example 1 in which only platinum was loaded or the catalyst of Comparative Example 5 in which platinum was loaded and then nickel was loaded. In addition, methanation reaction did not occur despite the high hydrogen partial pressure.
  • the catalyst of Example 1 had a high O 2 conversion and excellent CO 2 selectivity.
  • the catalysts of Comparative Examples 1 and 5 had a low O 2 conversion and poor CO 2 selectivity.
  • the catalyst for oxidizing carbon monoxide has a high reaction activity even at low temperatures and an excellent reaction selectivity, and since the methanation reaction and reoxidization do not occur, the catalyst can effectively eliminate carbon monoxide in the fuel.

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Abstract

A catalyst that oxidizes carbon monoxide includes a bimetal consisting of platinum and a transition metal in a bimetallic phase that is loaded on γ-alumina support. The catalyst is manufactured by uniformly mixing a platinum precursor, a transition metal precursor, and γ-alumina (γ-Al2O3) in a dispersion medium to provide a mixture; drying the mixture; calcining the dried mixture; and reducing the calcined dried mixture. Since the catalyst that oxidizes carbon monoxide has high reaction activity even at low temperature and excellent reaction selectivity, and a methanation reaction and reoxidization do not occur, and the catalyst can effectively eliminate carbon monoxide in the fuel.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • This application claims the benefit of Korean Application No. 2005-99620, filed Oct. 21, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
    • BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • Aspects of the present invention relate to a catalyst for oxidizing carbon monoxide and a method of manufacturing the same. More particularly, aspects of the present invention relate to a catalyst for oxidizing carbon monoxide having high reaction activity and excellent reaction selectivity in which a methanation reaction and reoxidation do not occur, and a method of manufacturing the same.
  • 2. Description of the Related Art
  • Fuel cells are electricity generation systems that directly convert the chemical energy of oxygen and the hydrogen in hydrocarbons such as methanol, ethanol, and natural gas to electrical energy.
  • Fuel cell systems consist of a fuel cell stack, a fuel processor (FP), a fuel tank, and a fuel pump. The fuel cell stack is the main body of a fuel cell, and includes several to several tens of unit cells, each including a membrane electrode assembly (MEA) and a separator (or bipolar plate).
  • The fuel pump supplies fuel in the fuel tank to the fuel processor. The fuel processor produces hydrogen by reforming and purifying the fuel and supplies the hydrogen to the fuel cell stack. The fuel cell stack receives the hydrogen and generates electrical energy by electrochemical reaction of the hydrogen with oxygen.
  • A reformer of the fuel processor reforms hydrocarbon fuel using a reforming catalyst. Since a hydrocarbon fuel typically contains one or more sulfur compounds, and since the reforming catalyst is easily poisoned by sulfur compounds, it is necessary to subject the hydrocarbon fuel to desulfurization prior to the reforming process in order to remove sulfur compounds prior to reforming the hydrocarbon fuel.
  • FIG. 1 is a schematic flow diagram illustrating fuel processing in a fuel processor used in a conventional fuel cell system.
  • Hydrocarbon reforming produces carbon dioxide (CO2) and a small amount of carbon monoxide (CO) as by-products, together with hydrogen. Since CO acts as a catalyst poison in electrodes of the fuel cell stack, reformed fuel should not be supplied to the fuel cell stack until a CO removal process has been carried out. It is desirable to reduce the CO levels to less than 10 ppm.
  • CO can be removed using a high-temperature shift reaction represented by Reaction Scheme 1 below.
  • <Reaction Scheme 1>
    CO+H2O→CO2+H2
  • A high-temperature shift reaction is performed at a temperature of 400 to 500° C. Generally, a high-temperature shift reaction is followed by a low-temperature shift reaction at a temperature of 200 to 300° C. Even after these reactions are performed, it is very difficult to reduce the CO levels to less than 5,000 ppm.
  • To solve this problem, a preferential oxidation reaction (referred to as the “PROX” reaction) represented by Reaction Scheme 2 below can be used.
  • <Reaction Scheme 2>
    CO+½O2→CO2
  • However, a side reaction represented by Reaction Scheme 3 occurs together with the PROX reaction.
  • <Reaction Scheme 3>
    H2+½O2→H2O
  • Thus, in order to maintain a high level of H2 while reducing CO, it is important to increase the rate of the PROX reaction represented by Reaction Scheme 2 and enhance the reaction selectivity for the PROX reaction by minimizing the side reaction represented by Reaction Scheme 3 as well.
  • Another serious potential problem is that a methanation reaction may occur between CO to be removed and reformed hydrogen, as represented by Reaction Scheme 4 below. It is important to inhibit this reaction since even limited methanation reactions can lead to a significant decrease in the hydrogen concentration and can affect the efficiency of the entire reforming process.
  • <Reaction Scheme 4>
    CO+3H2→CH4+H2O
  • Conventional catalysts for oxidizing carbon monoxide in the PROX reaction have low reaction selectivity. Further, when conventional catalysts are used, the methanation reaction partially occurs and the conventional catalysts lose reactivity by becoming reoxidized by oxygen in the reaction device during the catalytic operations or during intervals between operations.
  • Therefore, it is necessary to develop a PROX catalyst that has a high reaction activity and excellent reaction selectivity, and that does not support a methanation reaction or become reoxidized.
    • SUMMARY OF THE INVENTION
  • Aspects of the present invention provide a PROX catalyst having excellent reaction selectivity and a broad operating temperature range in which a methanation reaction and reoxidation do not occur.
  • Aspects of the present invention also provide a method of manufacturing the PROX catalyst.
  • Aspects of the present invention also provide a fuel processor including the PROX catalyst having excellent reaction selectivity and a broad operating temperature range in which a methanation reaction and reoxidation do not occur.
  • Aspects of the present invention also provide a fuel cell system including the PROX catalyst having excellent reaction selectivity and a broad operating temperature range in which a methanation reaction and reoxidation do not occur.
  • According to an aspect of the present invention, there is provided a catalyst that oxidizes carbon monoxide, including a bimetal consisting of platinum (Pt) and another transition metal in a bimetallic phase, wherein the bimetal is loaded on a γ-alumina (γ-Al2O3) support, and wherein the transition metal of the bimetal is reduced.
  • According to another aspect of the present invention, there is provided a method of producing a catalyst for oxidizing carbon monoxide including: adding a platinum precursor, a transition metal precursor, and γ-alumina (γ-Al2O3) to a dispersion medium and uniformly mixing the resultant mixture; drying the mixture; calcining the dried mixture; and reducing the calcined dried mixture.
  • According to another aspect of the present invention, there is provided a fuel processor including the catalyst that oxidizes carbon monoxide.
  • According to another aspect of the present invention, there is provided a fuel cell system including the catalyst that oxidizes carbon monoxide.
  • The catalyst that oxidizes carbon monoxide according to aspects of the present invention has excellent selectivity for carbon monoxide and a fast reaction rate in a carbon monoxide oxidizing reaction. In addition, efficiency of the entire reaction increases since a methanation reaction and reoxidization do not occur. Thus, the carbon monoxide in the fuel can effectively be eliminated using the catalyst according to aspects of the present invention.
  • Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
  • FIG. 1 is a schematic flow diagram illustrating fuel processing in a fuel processor used in a conventional fuel cell system;
  • FIG. 2 is a flowchart illustrating a method of manufacturing a catalyst for oxidizing carbon monoxide according to an embodiment of the present invention;
  • FIGS. 3A, 3B, and 3C are graphs respectively illustrating the results of a first TPR analysis, a TPO analysis, and a second TPR analysis of the catalyst in which a support is respectively γ-alumina, zirconia, and titania;
  • FIGS. 4A and 4B are graphs illustrating the results of a TPR analysis and a TPO analysis of a Pt/Ni supported catalyst in which platinum is impregnated and then nickel is impregnated;
  • FIGS. 5A and 5B are graphs illustrating the results of a TPR analysis and a TPO analysis of a Pt/Ni supported catalyst in which nickel is impregnated and then platinum is impregnated;
  • FIGS. 6A and 6B are graphs illustrating the results of CO oxidizing tests of the catalysts in which a support is respectively γ-alumina, zirconia, and titania according to temperature;
  • FIGS. 7A and 7B are graphs illustrating the results of CO oxidizing tests of a platinum catalyst loaded on γ-alumina, a Pt/Ni catalyst loaded on γ-alumina, and a bimetallic phase Pt/Ni catalyst loaded on γ-alumina according to temperature;
  • FIGS. 8A and 8B illustrate a TEM photograph image and a graph showing the result of the EDX analysis regarding the Pt-Ni/γ-Al2O3 according to Example 1;
  • FIGS. 9A and 9B illustrate a TEM photograph image and a graph showing the result of the EDX analysis regarding the Pt-Co/γ-Al2O3 according to Example 2; and
  • FIG. 10 illustrates graph of CO conversion and CO2 selectivity regarding the supported catalyst of Example 1.
    • DETAILED DESCRIPTION OF THE EMBODIMENTS
  • Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
  • According to an embodiment of the present invention, a catalyst for oxidizing carbon monoxide includes a bimetal consisting of platinum (Pt) and another transition metal in a bimetallic phase. (For convenience, the other transition metal is referred to herein simply as “the transition metal” and it is to be understood that the term “transition metal” in this context refers to a transition metal other than platinum.) The bimetal is loaded onto γ-alumina(γ-Al2O3) support, and the transition metal is reduced.
  • The transition metal may be one of Ni, Co, Cu, and Fe. For example, the transition metal may be Ni.
  • The term “bimetallic phase of platinum and the transition metal” refers to a correlation between platinum and the transition metal that is created, for example, when platinum and the transition metal are loaded onto the support at the same time. The structural relationship between the platinum and the transition metal in the bimetallic phase is not clearly determined, but the bimetallic phase seems to have its own particular structure since in the bimetallic phase, reoxidization of the transition metal does not occur.
  • The support for the bimetallic phase may be γ-alumina (γ-Al2O3). The bimetallic phase cannot easily be obtained using a support such as zirconia (ZrO2) or titania (TiO2).
  • The catalyst for oxidizing carbon monoxide has a peak of between 130 to 180° C. in a temperature programmed reduction (TPR) analysis and is not reoxidized in a temperature programmed oxidation (TPO) analysis until the temperature reaches 500° C.
  • The atomic ratio of the transition metal to platinum may be from 0.5 to 20. When the atomic ratio is too low, an effect of the transition metal, such as, for example an effect to promote the reaction activity of the catalyst at low temperatures and to widen the operating temperature range cannot be obtained. When the atomic ratio is too high, a promotion effect on the reaction activity of the catalyst may decrease due to an excessive amount of the transition metal.
  • Further, the amount of platinum may be in the range of 0.3 to 5% by weight based on the weight of the catalyst for oxidizing carbon monoxide (including the support). When the amount of platinum is less than 0.3% by weight, the catalyst activity may decrease. When the amount of platinum is greater than 5% by weight, the increase of the catalyst activity may be negligible, which is cost-ineffective.
  • Hereinafter, a method of manufacturing a catalyst for oxidizing carbon monoxide according to an embodiment of the present invention will be described more specifically with reference to FIG. 2.
  • First, a platinum precursor, a transition metal precursor, and γ-alumina (γ-Al2O3) are added to a dispersion medium and uniformly mixed. As examples, the platinum precursor may be Pt(NH3)4(NO3)2 and the transition metal precursor may be one of Ni(NO3)2.6H2O, Co(NO3)2.6H2O, Cu(NO3)2.H2O and Fe(NO3)2.9H2O. In particular, a halogen compound such as a chlorine compound is not recommended for the platinum precursor or the transition metal precursor.
  • Any method of uniformly mixing the precursors and the support may be used. For example, the mixture may be stirred for 1 to 12 hours at a temperature from 40 to 80° C.
  • The dispersion medium is so named since although the platinum precursor and the transition metal precursor are dissolved in the medium, the γ-alumina support is not dissolved, but rather, is only dispersed.
  • The dispersion medium may be any medium having the property of dissolving the platinum precursor and the transition metal precursor and dispersing the γ-alumina support. For example, the dispersion medium may be water or an alcohol-based solvent. The alcohol-based solvent may be methanol, ethanol, isopropyl alcohol, and butyl alcohol, but is not limited thereto.
  • As described above, the weight ratio of the platinum precursor and the transition metal precursor may be adjusted such that the atomic ratio of the transition metal to platinum is from 0.5 to 20.0.
  • The amount of the dispersion medium may be 30 to 95% by weight based on the total weight of the mixture in order to uniformly disperse the platinum precursor, the transition metal precursor, and γ-alumina support, and so that it does not take too long to dry the dispersion medium, but is not limited thereto.
  • The dispersion medium may be removed by drying the mixture. The conditions for drying the mixture are not limited. For example, the mixture may be dried at 30 to 90° C. for 4 to 16 hours in a vacuum or in an oven.
  • After the dispersion medium is removed by drying, the dried resultant is calcined in an airtight container such as an oven.
  • The calcination may be performed at a temperature of 300 to 500° C. for 1 to 12 hours. When the calcining temperature is less than 300° C., the catalyst may not be sufficiently crystallized. When the temperature is greater than 500° C., the platinum and transition metal particle may grow too large, thereby decreasing the reaction activity of the catalyst. When the calcining is performed for less than 1 hour, the catalyst may not be sufficiently crystallized. On the other hand, it generally is not cost-effective to perform calcining for longer than 12 hours.
  • The calcining may be performed under an air atmosphere, but is not limited thereto.
  • The calcined resultant may be reduced to produce a catalyst having activity for oxidizing carbon monoxide.
  • The reduction may be performed at a temperature of 150 to 500° C. for 1 to 12 hours. When the reduction temperature is less than 150° C., the bimetallic phase may not be sufficiently formed. When the temperature of the reduction is higher than 500° C., the platinum and transition metal particles loaded on the support may grow too large, thereby decreasing the reaction activity of the catalyst. In addition, when the reduction is performed for less than 1 hour, the bimetallic phase may not be sufficiently formed. On the other hand, it generally is not cost-effective to perform a reduction for longer than 12 hours.
  • The reduction may be performed under a H2 atmosphere, and the H2 atmosphere may further optionally include an inert gas such as helium, nitrogen, or neon.
  • According to an embodiment of the present invention, a fuel processor including the catalyst for oxidizing carbon monoxide is provided. Hereinafter, the fuel processor will be described.
  • The fuel processor may include a desulfurizer, a reformer, a high-temperature shift reaction device, a low-temperature shift reaction device, and a PROX reaction device.
  • The desulfurizer is a device that removes sulfur compounds that can poison catalysts downstream from the desulfurizer. An absorbent that is well known in the art may be used for the desulfurizer, and a hydrodesulfurization (HDS) process may also be used.
  • The reformer is a device that reforms hydrocarbons to produce hydrogen. Any catalyst such as platinum, ruthenium, and nickel that is well known in the art may be used for the reforming catalyst.
  • The high-temperature shift reaction device and the low-temperature shift reaction device are devices that remove carbon monoxide, which can poison the catalyst layer of a fuel cell. Typically, the high-temperature shift reaction device and the low-temperature shift reaction device reduce the carbon monoxide concentration to less than 1%.
  • The PROX reaction device further reduces the carbon monoxide concentration to less than 10 ppm. According to an embodiment of the present invention, the PROX reaction device may include the catalyst for oxidizing carbon monoxide as described herein. For example, the catalyst for oxidizing carbon monoxide may be charged in the PROX reaction device as a fixed bed.
  • According to an embodiment of the present invention, a fuel cell system including the catalyst for oxidizing carbon monoxide is provided.
  • The fuel cell system according to the an embodiment of the present invention includes a fuel processor and a fuel cell stack. The fuel cell processor may include a desulfurizer, a reformer, a high-temperature shift reaction device, a low-temperature shift reaction device, and a PROX reaction device as described above. The fuel cell stack may be formed by stacking or arranging a plurality of unit cells. Each of the unit cells may include a cathode, an anode, and an electrolyte membrane, and may further include a separator.
  • The catalyst for oxidizing carbon monoxide may be included in the fuel cell processor, and more specifically, in the PROX reaction device.
  • Hereinafter, the constitution and effects of aspects of the present invention will be described more specifically with reference to the following Examples and Comparative Examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.
    • EXAMPLE 1
  • 0.207 g of Pt(NH3)4(NO3)2, 1.553 g of Ni(NO3)2.6H2O, and 10 g of γ-alumina were added to 50 ml of water and the mixture was stirred for 6 hours to prepare a uniform mixture. The mixture was dried at 60° C. in a vacuum to remove the solvent, and dried at 110° C. for 12 hours in an oven. Then, the dried resultant was calcined at 350° C. for 2 hours under an air atmosphere. The calcined resultant was reduced at 300° C. for 2 hours in an oven under a H2 atmosphere to prepare Pt—Ni/γ-Al2O3.
    • EXAMPLE 2
  • Pt—Co/γ-Al2O3 was prepared in the same manner as in Example 1, except that 1.554 g of Co(NO3)2.6H2O was used instead of Ni(NO3)2.6H2O.
    • EXAMPLE 3
  • Pt—Cu/γ-Al2O3 was prepared in the same manner as in Example 1, except that 1.004 g of Cu(NO3)2.H2O was used instead of Ni(NO3)2.6H2O.
    • EXAMPLE 4
  • Pt—Fe/γ-Al2O3 was prepared in the same manner as in Example 1, except that 2.154 g of Fe(NO3)2.9H2O was used instead of Ni(NO3)2.6H2O.
    • COMPARATIVE EXAMPLE 1
  • Pt/γ-Al2O3 was prepared in the same manner as in Example 1, except that Ni(NO3)2.6H2O was not added.
    • COMPARATIVE EXAMPLE 2
  • Pt—Ce/γ-Al2O3 was prepared in the same manner as in Example 1, except that 2.424 g of Ce(NO3)2.6H2O was used instead of Ni(NO3)2.6H2O.
  • Carbon monoxide oxidizing tests were performed using the catalysts prepared according to Examples 1 through 4 and Comparative Examples 1 and 2. A gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 10 vol % of hydrogen, 2 vol % of water vapor, and the remaining percentage of helium was flowed at a gas hourly space velocity (GHSV) of 60,000 hr-1. The results are presented in Table 1 below.
    TABLE 1
    Temperature (K) CO conversion (%) O2 selectivity (%)
    Example 1 393 100 50
    Example 2 393 100 50
    Example 3 353 100 50
    Example 4 313 61 100
    333 80 90
    Comparative 433 95 51
    Example 1
    Comparative 353 93 47
    Example 2
  • As shown in Table 1, the CO conversions of the catalysts in Examples 1 through 3, 100%, were far better than those of Comparative Examples 1 and 2. In Example 4, the CO conversion was relatively low, but the O2 selectivity was excellent.
  • Pt—Ni/γ-Al2O3 and Pt—Co/γ-Al2O3 prepared according to Examples 1 and 2 were analyzed using a transmission electron microscope (TEM) and an energy dispersive X-ray micro analyzer (EDX) to identify whether a bimetallic phase of platinum and the transition metal was formed. The results are shown in FIGS. 8A, 8B, 9A and 9B.
  • The results of the EDX analysis confirmed the presence of the bimetallic phase in the catalyst according to Example 1 since the ratio of nickel to platinum was 0.92, as illustrated in FIG. 8A. The results of the EDX analysis shown in FIG. 8B also confirmed the presence of the bimetallic phase.
  • In addition, the EDX analysis confirmed the presence of the bimetallic phase in the catalyst according to Example 2 since a ratio of cobalt to platinum was 0.54, as illustrated in FIG. 9A. The results of the EDX analysis shown in FIG. 9B also confirmed presence of the bimetallic phase.
  • Activity tests of the supported catalyst prepared according to Example 1 were performed at 120° C. to identify whether the activity and selectivity were constantly maintained with respect to time. A gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 50 vol % of hydrogen, 20 vol % of carbon dioxide, 2 vol % of water vapor, and the remaining percentage of helium was flowed at a rate of 1000 ml/(min.gcat), and the resultants were analyzed. The results are presented in FIG. 10.
  • As illustrated in FIG. 10, the CO conversion of the catalyst was high and was almost constantly maintained with respect to time. The CO2 selectivity of the catalyst was almost constantly maintained as well. Thus, the supported catalyst according to an embodiment of the present invention is highly stable with respect to time.
    • COMPARATIVE EXAMPLE 3
  • Pt—Ni/ZrO2 was prepared in the same manner as in Example 1, except that 10 g of zirconia was used instead of γ-alumina.
    • COMPARATIVE EXAMPLE 4
  • Pt—Ni/TiO2 was prepared in the same manner as in Example 1, except that 10 g of titania was used instead of γ-alumina.
  • The catalysts prepared according to Example 1, and Comparative Examples 3 and 4 were analyzed using a first temperature programmed reduction (TPR), a temperature programmed oxidation (TPO), and a second TPR to identify whether the catalysts were subject to reoxidation. The results are presented in FIGS. 3A through 3C.
  • As illustrated in FIGS. 3A, two peaks were observed in the first TPR (shown in FIG. 3A) of Comparative Examples 3 and 4, but only one peak was observed (around 410 K) in the first TPR of Example 1. As shown in FIG. 3B, oxygen consumption was observed in the TPO with respect to catalysts of Comparative Examples 3 and 4, indicating that the catalysts of Comparative Examples 3 and 4 were reoxidized in the TPO, but it was observed that the catalyst of Example 1 showed only the base line, which indicates that the catalyst of Example 1 was not reoxidized. Since the catalyst of Example 1 was not reoxidized, hydrogen was not consumed in the second TPR (shown in FIG. 3C) with respect to the catalyst of Example 1. On the other hand, as shown in FIG. 3C, hydrogen was consumed in the second TPR with respect to the catalysts of Comparative Examples 3 and 4, since the catalysts of Comparative Examples 3 and 4 were reoxidized in the TPO.
  • That is, since the bimetallic phase of platinum and nickel was not formed when zirconia or titania was used, the catalyst was reoxidized in the temperature programmed oxidation (TPO). On the other hand, when γ-alumina was used, the bimetallic phase of platinum and nickel was formed, and thus the catalyst was not reoxidized in the presence of oxygen.
    • COMPARATIVE EXAMPLE 5
  • 0.207 g of Pt(NH3)4(NO3)2 and 10 g of γ-alumina were added to 50 ml of water and the mixture was stirred for 4 hours to prepare a uniform mixture. The mixture was dried at 60° C. in a vacuum to remove the solvent, and dried at 110° C. for 12 hours in an oven. Then, the dried resultant was calcined at 500° C. for 4 hours under an air atmosphere.
  • Meanwhile, 1.553 g of Ni(NO3)2.6H2O was dissolved in 5 ml of water and the dissolved solution was dropped into the calcined resultant while uniformly mixing. Then, the resultant was dried at 110° C. for 12 hours in the oven, and calcined at 300° C. for 4 hours in the oven under an air atmosphere.
    • COMPARATIVE EXAMPLE 6
  • 1.553 g of Ni(NO3)2.6H2O and 10 g of γ-alumina were added to 50 ml of water and the mixture was stirred for 4 hours to prepare a uniform mixture. The mixture was dried at 110° C. for 12 hours in an oven and calcined at 500° C. for 4 hours under an air atmosphere.
  • Meanwhile, 0.207 g of Pt(NH3)4(NO3)2 was dissolved in 5 ml of water and the dissolved solution dropped into the calcined resultant and uniformly mixed. Then, the resultant was dried at 110° C. for 12 hours in the oven, and calcined at 300° C. for 4 hours in the oven under air atmosphere.
  • The catalysts prepared according to Comparative Examples 5 and 6 were analyzed using temperature programmed reduction and temperature programmed oxidation to determine whether the catalysts were reoxidized. The results are shown in FIGS. 4A, 4B, 5A and 5B.
  • As illustrated in FIGS. 4A and 4B, when platinum was impregnated into γ-alumina, and then nickel was impregnated the calcined platinum-impregnated γ-alumina, reoxidization occurred in the catalyst product (FIG. 4B). As illustrated in FIGS. 5A and 5B, reoxidization also occurred (FIG. 5B) when nickel was impregnated, and then platinum was impregnated into the nickel-impregnated calcined product. However, as illustrated in FIGS. 3A through 3C reoxidization did not occur in Example 1 (in which platinum and nickel were impregnated into the γ-alumina at the same time).
  • Thus, the properties of the bimetallic phase catalyst of Example 1 are different from those of the Pt/Ni catalysts supported on a carrier prepared according to Comparative Examples 5 and 6.
  • That is, since Pt/Ni supported catalysts prepared according to Comparative Examples 5 and 6 are not in the bimetallic phase, they can be reoxidized in the presence of oxygen. On the other hand, without being bound to a particular theory, it is believed that the catalyst of Example 1 is not reoxidized in the presence of oxygen due to its bimetallic phase.
  • Carbon monoxide oxidizing tests were performed using the catalysts prepared according to Example 1, and Comparative Examples 3 and 4. A gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 10 vol % of hydrogen, 2 vol % of water vapor, and the remaining percentage of helium is flowed at a GHSV of 60,000 hr-1. The results are presented in FIGS. 6A and 6B.
  • As illustrated in FIG. 6A, when zirconia or titania was used, the operating temperature range was limited since the CO conversion sharply decreased as temperature increased even though the CO conversion was high in a low temperature range. On the other hand, in Example 1, the CO conversion was the highest and was constantly maintained at a level close to 100% at temperatures over about 400 K. Further, a methanation reaction did not occur at all in Example 1, but the methanation reaction increasingly occurred as temperature increased in Comparative Examples 3 and 4.
  • As illustrated in FIG. 6B, the reaction selectivity was constantly maintained in Example 1. On the other hand, the reaction selectivity was low and decreased as to temperature increased in Comparative Examples 3 and 4.
  • Carbon monoxide oxidizing tests were performed using the catalysts prepared according to Example 1, and Comparative Examples 1 and 5. In order to observe the behavior of the catalysts under conditions similar to the hydrogen-rich atmosphere of a fuel cell, a gas including 1 vol % of carbon monoxide, 1 vol % of oxygen, 80 vol % of hydrogen, 2 vol % of water vapor, and the remaining percentage of helium was flowed at a GHSV of 60,000 hr-1. The results are presented in FIGS. 7A and 7B.
  • As illustrated in FIG. 7A, the catalyst of Example 1 had a higher CO conversion than either the catalyst of Comparative Example 1 in which only platinum was loaded or the catalyst of Comparative Example 5 in which platinum was loaded and then nickel was loaded. In addition, methanation reaction did not occur despite the high hydrogen partial pressure.
  • As illustrated in FIG. 7B, the catalyst of Example 1 had a high O2 conversion and excellent CO2 selectivity. On the contrary, the catalysts of Comparative Examples 1 and 5 had a low O2 conversion and poor CO2 selectivity.
  • Since the catalyst for oxidizing carbon monoxide according to aspects of the present invention has a high reaction activity even at low temperatures and an excellent reaction selectivity, and since the methanation reaction and reoxidization do not occur, the catalyst can effectively eliminate carbon monoxide in the fuel.
  • Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims (18)

1. A catalyst that oxidizes carbon monoxide, comprising a bimetal consisting of platinum (Pt) and a transition metal other than platinum in a bimetallic phase, wherein the bimetal is loaded on a γ-alumina (γ-Al2O3) support, and wherein the transition metal of the bimetal is reduced.
2. The catalyst of claim 1, wherein the catalyst has a peak between 130 to 180° C. in a temperature programmed reduction (TPR) analysis and is not reoxidized until the temperature reaches 500° C. in a temperature programmed oxidation (TPO) analysis.
3. The catalyst of claim 1, wherein the transition metal is selected from the group consisting of Ni, Co, Cu, and Fe.
4. The catalyst of claim 1, wherein the atomic ratio of the transition metal to platinum is from 0.5 to 20.
5. The catalyst of claim 1, wherein the amount of platinum is in the range of 0.3 to 5% by weight based on the weight of the catalyst.
6. The catalyst of claim 1, wherein the catalyst has a reaction selectivity such that when the catalyst oxidizes carbon monoxide, a methanation reaction does not occur.
7. A method of manufacturing a catalyst that oxidizes carbon monoxide, the method comprising:
uniformly mixing a platinum precursor, a transition metal precursor, and γ-alumina (γ-Al2O3) in a dispersion medium to provide a mixture;
drying the mixture;
calcining the dried mixture; and
reducing the calcined dried mixture.
8. The method of claim 7, wherein the weight ratio of the platinum precursor and the transition metal precursor is adjusted such that the atomic ratio of the transition metal to platinum is from 0.5 to 20.0.
9. The method of claim 7, wherein the calcining is performed at a temperature of 300 to 500° C. for 1 to 12 hours.
10. The method of claim 7, wherein the reducing is performed at a temperature of 150 to 500° C. for 1 to 12 hours.
11. The method of claim 7 wherein the platinum precursor and the transition metal precursor are compounds that do not contain a halogen.
12. The method of claim 7, wherein the platinum precursor is Pt(NH3)4(NO3)2.
13. The method of claim 7, wherein the transition metal precursor is selected from the group consisting of Ni(NO3)2.6H2O, Co(NO3)2.6H2O, Cu(NO3)2.H2O and Fe(NO3)2.9H2O.
14. A fuel processor comprising the catalyst of claim 1.
15. A fuel processor of claim 14, comprising a desulfurization device, at least one shift reaction device, and a PROX reaction device, wherein the catalyst is included in the PROX reaction device.
16. A fuel cell system comprising the catalyst of claim 1.
17. A fuel cell system of claim 16, comprising a fuel cell stack and a fuel processor, wherein the catalyst is included in the fuel processor.
18. A fuel cell system of claim 17, wherein the fuel processor comprises a desulfurization device, at least one shift reaction device, and a PROX reaction device, and wherein the catalyst is included in the PROX reaction device.
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