JP2007007531A - Shift reaction catalyst and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for improving the catalytic activity of a shift reaction catalyst, in which a platinum-based catalyst containing platinum being a noble metal is combined with a copper-based catalyst containing copper, under a low temperature condition and keeping the catalytic activity high over a long period of time. <P>SOLUTION: The shift reaction catalyst, which is brought into contact with a gas containing carbon monoxide and water to selectively promote a shift reaction, is manufactured by mixing platinum catalyst powder containing a platinum atom and a cerium atom with copper catalyst powder containing a copper atom. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a shift catalyst. Specifically, the present invention relates to a shift catalyst that promotes the reaction of carbon monoxide and water to hydrogen and carbon dioxide.

  In recent years, various hydrogen-oxygen fuel cells have been developed. Among them, polymer electrolyte fuel cells that can operate at low temperatures (usually below 100 ° C.) have attracted attention, and have been put to practical use as a low-pollution power source for automobiles. It is being considered.

  In the polymer electrolyte fuel cell, it is preferable from the viewpoint of energy efficiency to use pure hydrogen as a fuel source. However, in consideration of safety and the spread of infrastructure, liquids such as alcohol, gasoline, and light oil are used as the fuel source. A method that uses them and converts them to hydrogen-rich reformed gas in a reformer is also a promising candidate.

When hydrocarbon liquid fuel is used as a fuel source, a certain amount of CO may remain in the reformed gas. However, this CO acts as a catalyst poison for the platinum-based catalyst used for the electrode of the fuel cell. For this reason, it is necessary to remove this CO, for example, by converting it to CO ₂ to prevent poisoning of the platinum-based electrode catalyst. Specifically, first, a shift reaction (CO + H ₂ O → CO ₂ + H ₂ ) is used to reduce the CO concentration contained in the reformed gas to about 1% by volume. A method of oxidizing and removing CO (converting to CO ₂ ) using a CO selective oxidation catalyst in which a noble metal is supported on an inorganic carrier has been proposed.

  Conventionally, Cu-based catalysts such as Cu / Zn-based catalysts, Cu / Zn / Al-based catalysts, and Cu / Cr-based catalysts have been known as shift catalysts that promote the shift reaction. However, these Cu-based catalysts do not have sufficient catalytic activity under high space velocity conditions. For this reason, in order to improve the catalyst activity under high space velocity conditions, it was necessary to increase the catalyst volume. As a result, the shift reactor is increased in size, and there is a problem that it is difficult to reduce the space required especially when the vehicle is mounted.

  In the case of a Cu-based catalyst, Cu is maintained in a reduced state when the catalyst is operated. However, when the fuel cell system is stopped, a part thereof is oxidized by contact with air to produce copper oxide, which is restarted at the time of restart. There was also a problem that the catalyst was thermally deteriorated due to heat generated by the reduction.

  In recent years, noble metal catalysts such as Pt / alumina have been proposed for the purpose of solving the above-mentioned problems of Cu-based catalysts. This noble metal-based catalyst is attracting attention as a candidate for a new shift catalyst because of its relatively low decrease in catalytic activity under high space velocity conditions and excellent heat resistance.

Further, in order to utilize the advantages of the Cu-based catalyst and the Pt-based catalyst which is a noble metal-based catalyst, the technologies described in Patent Documents 1 and 2 are known as a technology combining these two types of catalysts. Yes. Specifically, Patent Document 1 discloses a first catalyst body in which a noble metal catalyst containing a noble metal such as platinum is supported on a honeycomb, which is installed upstream of the reformed gas flow direction as a shift catalyst. And a second catalyst body installed downstream of the flow direction of the reformed gas and supporting a copper-based catalyst (copper-zinc catalyst in the embodiment) on a honeycomb is disclosed. Has been. According to such a configuration, thermal deterioration of the catalyst due to the high-temperature reformed gas can be suppressed to a minimum. Patent Document 2 discloses a shift catalyst in which at least one selected from a metal species group containing platinum and at least one selected from a metal species group containing copper are supported on a metal oxide. According to the catalyst having such a configuration, excellent catalytic activity can be obtained even at a high temperature, and the progress of the methanation reaction that is likely to proceed by using a noble metal catalyst under a high temperature condition can be suppressed.
JP 2000-178007 A, claim 3, paragraphs “0036” to “0037”, Example 4, FIG. JP 2003-305364 A, Claim 1

  By the way, the shift reaction described above is strongly subjected to thermodynamic restrictions. That is, the lower the reaction temperature, the more the shift reaction can proceed in the direction in which CO is removed. For this reason, it is preferable that the temperature condition for proceeding the shift reaction using the shift catalyst is lower, but the shift catalysts described in the above-mentioned documents 1 and 2 are said to have sufficient activity under the low temperature condition. hard. Further, when used for a long period of time, the catalyst deteriorates, and there is a problem that sufficient catalytic activity cannot be exhibited.

  Therefore, the present invention improves the catalytic activity under low temperature conditions and maintains high catalytic activity over a long period of time in a shift catalyst that combines a platinum-based catalyst containing platinum, which is a noble metal, and a copper-based catalyst containing copper. It is an object to provide means that can be used.

  The present inventor conducted intensive studies to solve the above-described problems, and searched for a configuration capable of improving the activity of the shift catalyst. As a result, the present inventors have found that the above problems can be solved by incorporating cerium atoms into a powder based on a platinum-based catalyst and mixing this with a powder of a copper-based catalyst, thereby completing the present invention.

  That is, the present invention provides a shift catalyst capable of selectively promoting a shift reaction by contact with a gas containing carbon monoxide and water, comprising a platinum catalyst powder containing a platinum atom and a cerium atom, and a copper atom. It is a shift catalyst characterized by being mixed with the copper catalyst powder containing.

  ADVANTAGE OF THE INVENTION According to this invention, the shift catalyst which is excellent in the catalyst activity in low temperature conditions, and is excellent also in durability can be provided.

  Embodiments of the present invention will be described below.

The present invention relates to a shift catalyst capable of selectively promoting a shift reaction by contact with a gas containing carbon monoxide and water, a platinum catalyst powder containing a platinum atom and a cerium atom, and a copper containing a copper atom. It is a shift catalyst characterized by being mixed with catalyst powder. In the present application, the “shift catalyst” refers to a catalyst that contacts a gas containing at least CO and H ₂ O to selectively promote a shift reaction in which CO in the gas is converted to CO ₂ . .

[Constitution]
FIG. 1 is a schematic cross-sectional view showing an embodiment of the shift catalyst of the present invention.

  As shown in FIG. 1, the shift catalyst 10 of the present embodiment includes a platinum catalyst powder 20 in which a platinum component 22 is supported on a first inorganic carrier 24 and a copper component 32 supported on a second inorganic carrier 34. The copper catalyst powder 30 is mixed, and the first inorganic carrier 24 contains cerium atoms. For convenience of explanation, the dimensional ratio of each component of the shift catalyst shown in FIG. 1 is exaggerated and may be different from the actual ratio. In many cases, a large number of micropores are formed on the surface of the inorganic carrier (24, 34), but these micropores are omitted in FIG.

  Hereinafter, a preferable configuration of the shift catalyst 10 having the form shown in FIG. 1 will be described in detail in the order of a platinum catalyst powder, a copper catalyst powder, and a shift catalyst obtained by mixing them.

[Platinum catalyst powder]
The platinum catalyst powder 20 has a configuration in which a platinum component 22 is supported on a first inorganic carrier 24. In the present specification, the term “first” and the term “second” placed on the inorganic support for the promoter powder 30 described later refer to the platinum component 22 and the copper component 32. It is used for convenience to show that it is supported on separate inorganic carriers. Therefore, there is no special meaning in the order of “first” and “second”.

The platinum component 22 is a catalyst component containing a platinum atom. In the form shown in FIG. 1, the platinum component 22 is a catalyst component consisting only of platinum atoms. However, the form of the platinum component 22 is not limited to a form composed of only platinum atoms, and may be composed of, for example, platinum oxide (platinum monoxide (PtO), platinum dioxide (PtO ₂ ), etc.) It may consist of a mixture with platinum oxide or a platinum alloy. Examples of the platinum alloy include alloys of other noble metals and transition metals described later and platinum. The shape of the platinum component is not particularly limited, and may be any shape such as a particle shape, a cubic shape, a column shape, a cone shape, or an indefinite shape. However, from the viewpoint of excellent catalytic activity, the platinum component is preferably particulate. The shape of the platinum component can be observed using, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

  The kind of the inorganic carrier (first inorganic carrier 24) on which the platinum component 22 is supported is not particularly limited, and a conventionally known compound can be used as the inorganic carrier for the catalyst. For example, metal oxides such as ceria, alumina (α alumina, θ alumina, γ alumina, δ alumina, β alumina, etc.), titania, silica, silica alumina, zirconia, magnesia, zeolite and the like are exemplified. Among these, ceria is preferably used from the viewpoint of excellent catalytic activity and easy acquisition of raw materials and production and handling of the support. Also in the form shown in FIG. 1, the first inorganic carrier is ceria. In addition, only 1 type of these inorganic support | carriers may be used independently, and these mixtures may be used. Here, the mixture of metal oxides includes not only a form in which two or more inorganic carriers are physically mixed, but also metal oxides having different crystallinity between a part where particles are present and another part.

The specific surface area of the first inorganic carrier 24 is preferably 40 m ² / g or more, more preferably 60 m ² / g or more, and still more preferably 100 m ² / g or more. When the specific surface area of the first inorganic carrier 24 is within such a range, the platinum component 22 is supported on the surface of the first inorganic carrier 24 in a highly dispersed manner, and the catalytic activity is excellent. From such a viewpoint, ceria is preferably used as the first inorganic carrier 24. The “specific surface area” described in the present specification can be calculated, for example, by measuring the BET specific surface area by nitrogen adsorption.

  There is no particular limitation on the average particle size of the first inorganic carrier 24. However, the average particle size of the first inorganic carrier 24 is preferably 1.0 to 50 μm, more preferably 1.0 to 10 μm. If this average particle size is too small, the scattering property may increase and handling may be complicated. On the other hand, if the average particle diameter is too large, the dispersibility of the platinum component is deteriorated as the specific surface area of the inorganic carrier is decreased, and the catalyst performance may be deteriorated. In addition, the moldability of the catalyst is deteriorated, and there is a possibility that the catalyst may be easily peeled off, for example, when the catalyst is applied to a honeycomb carrier. The “average particle diameter” described in the present specification can be measured by a technique such as a laser diffraction method.

  The platinum catalyst powder 20 may contain other components as necessary. For example, it may further contain one or more atoms selected from the group consisting of titanium, zirconium, vanadium, niobium and tantalum (Group 4 or Group 5 atoms). When the platinum catalyst powder 20 further contains at least one of these atoms, further improvement in catalytic activity is expected. In addition, these atoms may be carry | supported by the 1st inorganic support | carrier similarly to the platinum component, and may be contained in the 1st inorganic support | carrier.

  The content of each of the platinum component 22, the first inorganic carrier 24, and other components in the platinum catalyst powder 20 can be appropriately adjusted in consideration of desired catalyst performance, production cost, and the like.

[Copper catalyst powder]
The copper catalyst powder 30 has a configuration in which a copper component 32 is supported on a second inorganic carrier 34.

  In the form shown in FIG. 1, the copper component 32 is a catalyst component consisting only of copper atoms. The copper component 32 may consist only of copper atoms, or may consist of an alloy of copper and other metal atoms. The shape of the copper component is not particularly limited, and may be any shape such as a particle shape, a cubic shape, a column shape, a cone shape, or an indefinite shape. However, from the viewpoint of excellent catalytic activity, the copper component is preferably particulate.

  The kind of the inorganic carrier (second inorganic carrier 34) on which the copper component 32 is supported is not particularly limited, and the above-described form can be similarly adopted as the first inorganic carrier 24 for the platinum catalyst powder 20.

Although there is no restriction | limiting in particular also about the specific surface area of the 2nd inorganic support | carrier 34, Preferably it is 40 m < ² > / g or more, More preferably, it is 60 m < ² > / g or more, More preferably, it is 100 m < ² > / g or more. It is preferable that the specific surface area of the second inorganic carrier 34 be in such a range because the gas-solid contact interface increases and high activity is obtained. From such a viewpoint, as the second inorganic carrier 34, an oxide containing at least one of cerium, aluminum, silicon, zirconium, niobium and the like is preferably used.

  There is no restriction | limiting in particular also about the average particle diameter of the 2nd inorganic support | carrier 34, It is the same as that of the preferable form of said 1st inorganic support | carrier 24. FIG.

  The copper catalyst powder 30 may also contain other components as necessary. For example, it may further contain a rare earth atom. When the copper catalyst powder 30 further contains at least one rare earth atom, further improvement in catalytic activity is expected. In addition, these atoms may be carry | supported by the 2nd inorganic support | carrier similarly to a copper component, and may be contained in the 2nd inorganic support | carrier.

  The contents of the copper component 32, the second inorganic carrier 34, and other components in the copper catalyst powder 30 can be appropriately adjusted in consideration of desired catalyst performance, production cost, and the like.

[Shift catalyst]
The shift catalyst 10 of the present invention has a configuration in which the platinum catalyst powder 20 and the copper catalyst powder 30 are mixed as described above with reference to FIG.

  Since the specific forms of the platinum catalyst powder 20 and the copper catalyst powder 30 included in the shift catalyst 10 are as described above, the description thereof is omitted here.

  According to the present invention, the shift catalyst having the above-described configuration can provide a shift catalyst having excellent catalytic activity under low temperature conditions and excellent durability, but the mechanism is completely clear. It is not. However, a mechanism has been estimated that sintering of platinum atoms and deactivation due to adsorption of generated carbon dioxide can be suppressed. However, such a mechanism is based on estimation, and the technical scope of the present invention is not affected at all even if the effects of the present invention are obtained by other mechanisms.

  Here, the balance of the blending amount of platinum atoms contained in the platinum catalyst powder 20 and the copper atom contained in the copper catalyst powder 30, the balance of the blending amounts of the platinum catalyst powder 20 and the copper catalyst powder 30, etc. were kept good. Can effectively contribute to an improvement in the shift catalytic activity of the catalyst.

  From such a viewpoint, in the shift catalyst of the present invention, the platinum atom content per unit volume of the catalyst is preferably 0.1 to 20 mg / mL, more preferably 1.0 to 20 mg / mL. If the platinum atom content is too low, sufficient shift catalytic activity may not be obtained. On the other hand, if the platinum atom content is too high, the production cost may increase. In the shift catalyst of the present invention, the content of cerium atoms per catalyst unit volume is preferably 50 to 500 mg / mL. If the cerium atom content is too low, sufficient catalytic activity may not be obtained. On the other hand, if the cerium atom content is too high, there may be a problem of deactivation due to adsorption of generated carbon dioxide. Furthermore, in the shift catalyst of the present invention, the content of copper atoms per catalyst unit volume is preferably 0.1 to 80 mg / mL. If the copper atom content is too low, sufficient catalytic activity may not be obtained. On the other hand, if the copper atom content is too high, the copper atom will cover the platinum atom during the reaction, resulting in catalytic activity. May decrease.

  Further, the ratio of the mixing amount of the platinum catalyst powder and the copper catalyst powder is not particularly limited, but in a preferred embodiment, the content of the copper catalyst powder is preferably 1 part by mass of the platinum catalyst powder. It is 0.1-20 mass parts, More preferably, it is 0.1-10 mass parts. Here, when there is too much content of platinum catalyst powder, there exists a possibility that manufacturing cost may rise, and when there is too much content of copper catalyst powder, there exists a possibility that sufficient catalyst activity may not necessarily be acquired.

  If the action and effect of the present invention are not impaired, the shift catalyst of the present invention may contain other components in addition to the platinum catalyst powder and the copper catalyst powder. As such a form, for example, an inorganic oxide containing one or more atoms selected from the group consisting of silicon, aluminum, titanium, cerium and zirconium is added to the platinum catalyst powder and the copper catalyst powder. Furthermore, the form formed by mixing is illustrated. According to such a form, there is an advantage that the catalytic activity can be further improved. In addition, although there is no restriction | limiting in particular about content of such an inorganic oxide, About 0.1-10 mass% is suitable with respect to the whole quantity of platinum catalyst powder and copper catalyst powder. Here, the content of each component described above and the value of the ratio in the shift catalyst of the present invention can be calculated by, for example, a technique such as ICP analysis or fluorescent X-ray spectroscopy.

[Production method]
2nd of this invention is related with the manufacturing method of a shift catalyst. Specifically, a second aspect of the present invention is a method for producing a shift catalyst capable of selectively promoting a shift reaction by contact with a gas containing carbon monoxide and water, the copper catalyst containing a copper atom. A copper catalyst powder preparation step for preparing a catalyst powder, a platinum catalyst powder preparation step for preparing a platinum catalyst powder by supporting platinum atoms on an inorganic oxide containing cerium atoms, the copper catalyst powder and the platinum catalyst powder And a mixing step of mixing a shift catalyst. The shift catalyst of the present invention shown in FIG. 1 can be produced by this production method. Hereinafter, the case where ceria is employed as the second inorganic carrier will be described as an example, and the second production method of the present invention will be described in the order of steps. However, as described above, other compounds may be used as the second inorganic carrier.

[Copper catalyst powder preparation process]
First, a copper catalyst powder is prepared. The copper catalyst powder prepared in this step is mixed with a platinum catalyst powder (prepared in the following [platinum catalyst powder preparation step]) in a mixing step which will be described later, and used as the shift catalyst of the present invention. In addition, about the preferable structure of the prepared copper catalyst powder, since it is as having already demonstrated in the column of said [structure], description is abbreviate | omitted here.

  As the copper catalyst powder, one prepared by itself may be used, and when the product is commercially available, the product may be purchased and used.

  When the copper catalyst powder is prepared by itself, for example, a copper component is grown on the surface of ceria by supporting copper atoms on an inorganic carrier (second inorganic carrier, for example, ceria) and firing the copper atom. A catalyst powder is preferred. Hereinafter, a specific method for preparing the copper catalyst powder by such a method will be described (see also examples described later). Of course, the copper catalyst powder may be prepared by other methods.

  First, ceria is prepared as an inorganic carrier (second inorganic carrier) for supporting copper atoms.

  As the ceria, one prepared by itself may be used, and when a product is commercially available, the product may be purchased and used. Here, one method for preparing ceria as the second inorganic carrier by itself is described.

  First, ceria raw materials are prepared. The ceria raw material is not particularly limited as long as it is a raw material that can become ceria by firing. Examples of the ceria raw material include cerium nitrate, cerium carbonate, cerium hydroxide, and trisacetylacetonatocerium. Newly developed materials may be used as ceria raw materials.

  In the obtained copper catalyst powder, when desired metal atoms (especially rare earth atoms) are to be contained in ceria (second inorganic support), the desired components are added to the ceria raw material in a desired amount in this step. Good.

  Subsequently, the ceria raw material is fired. Thereby, ceria is obtained.

  There are no particular limitations on the specific method of firing and firing conditions, and conventionally known knowledge can be appropriately referred to in the field of catalyst preparation. Here, the specific surface area and crystal state of the obtained ceria can be controlled by adjusting the firing conditions. For example, ceria having a relatively large specific surface area can be obtained by lowering the firing temperature or shortening the firing time. On the other hand, ceria having a relatively small specific surface area can be obtained by increasing the firing temperature or extending the firing time. As preferable firing conditions, the firing temperature is preferably 200 to 1000 ° C., more preferably 300 to 500 ° C., and the firing time is preferably 0.5 to 8.0 hours, more preferably 0.5 to 4. 0 hours. According to such firing conditions, ceria having a desired specific surface area can be obtained. In some cases, the baking may be performed twice or more at different temperatures. There is no restriction | limiting in particular also about baking atmosphere, For example, baking can be performed under an air atmosphere or nitrogen atmosphere.

  If necessary, only ceria having a desired particle size may be selected by pulverizing and sieving the obtained ceria after firing.

  Next, copper atoms are supported on the ceria (second inorganic support) prepared above.

  First, a solution in which copper ions are dissolved (hereinafter also simply referred to as “copper solution”) is prepared. This copper solution is used in a supporting step described later for the purpose of supporting copper atoms on ceria (second inorganic support).

  In the step of preparing the copper solution, first, a copper compound as a copper atom supply source is prepared. Furthermore, a solvent for dissolving the copper compound is prepared. Then, the copper compound which is a copper raw material is added to the prepared solvent, and it stirs as needed, and prepares a copper solution.

  As a copper compound which is a supply source of a copper atom, the compound of the form of a metal salt is mentioned, For example, copper nitrate, copper carbonate, copper acetate, etc. are mentioned. These compounds are easily available, are widely used as raw materials for catalyst preparation, and are easy to handle when supported on ceria (second inorganic support).

  Examples of the solvent used for the preparation of the copper solution include water and ethanol, but are not limited thereto.

  The concentration of copper atoms in the copper solution is not particularly limited, and is appropriately adjusted in consideration of the amount of ceria (second inorganic support) prepared above, the desired content in the obtained copper catalyst powder, the loading method, and the like. Can be done.

  In the obtained copper catalyst powder, when metal atoms other than copper atoms (particularly rare earth atoms) are to be supported on ceria (second inorganic support), in this step, desired components are added to the copper solution. It is good to add only the amount. At this time, the desired component may be added to the solvent in the form of a metal salt and dissolved by stirring as necessary.

  Thereafter, the copper atoms dissolved in the copper solution prepared above are supported on the ceria (second inorganic carrier) prepared above.

  As a specific method for supporting, a conventionally known method in the field of catalyst preparation such as an impregnation method, a coprecipitation method, and a competitive adsorption method can be employed. The treatment conditions can be appropriately selected according to the method employed, but usually, the ceria (second inorganic carrier) is contacted with the copper solution at a temperature of about 60 to about 60 ° C. for about 0.5 to 8.0 hours. You can do it.

  After supporting copper atoms on ceria (second inorganic support), it is dried as necessary. As a specific method for drying, for example, natural drying, evaporation to dryness, drying using a rotary evaporator, an air dryer, or the like can be employed. The drying time can be appropriately set according to the method employed. In some cases, this drying step may be omitted, and drying may be performed in a baking step described later.

  Subsequently, ceria (second inorganic support) on which copper atoms are supported is fired. Thereby, a copper component grows on the surface of ceria (second inorganic carrier), and a copper catalyst powder is obtained.

  There are no particular limitations on the specific method of firing and firing conditions, and conventionally known knowledge can be appropriately referred to in the field of catalyst preparation. As an example of the firing conditions, the firing temperature is preferably 200 to 1000 ° C., more preferably 300 to 500 ° C., and the firing time is preferably 0.5 to 8.0 hours, more preferably 0.5. ~ 4.0 hours. In some cases, the baking may be performed twice or more at different temperatures. There is no restriction | limiting in particular also about baking atmosphere, For example, baking can be performed under an air atmosphere or nitrogen atmosphere.

  If necessary, after firing, the obtained copper catalyst powder may be pulverized and sieved to select only the powder having a desired particle size.

[Platinum catalyst powder preparation process]
Meanwhile, a platinum catalyst powder is prepared. The platinum catalyst powder prepared in this step is mixed with a copper catalyst powder (prepared in the above [copper catalyst powder preparation step]) in the mixing step described later, and used as the shift catalyst of the present invention. In addition, about the preferable structure of the platinum catalyst powder prepared, since it is as having already demonstrated in the column of said [structure], description is abbreviate | omitted here.

  As the platinum catalyst powder, one prepared by itself may be used, and when a product is commercially available, the product may be purchased and used.

  When the platinum catalyst powder is prepared by itself, for example, the platinum component is grown on the surface of the inorganic support by supporting the platinum atom on the inorganic support (first inorganic support) and firing the platinum catalyst powder. Good. Hereinafter, a specific method for preparing the platinum catalyst powder by such a method will be described (see also examples described later). Of course, the platinum catalyst powder may be prepared by other methods.

  First, an inorganic carrier (first inorganic carrier) for supporting platinum atoms is prepared. In the production method of the present invention, the first inorganic carrier is an inorganic oxide containing a cerium atom. Here, ceria is illustrated as a preferred form of the first inorganic carrier to be prepared. Moreover, as the preparation method thereof, the method described in the above-mentioned “copper catalyst powder preparation step” for ceria as the second inorganic carrier can be similarly employed.

  Next, platinum atoms are supported on the ceria (first inorganic carrier) prepared above.

  First, a solution in which ions of platinum atoms are dissolved (hereinafter also simply referred to as “platinum solution”) is prepared. This platinum solution is used in a supporting step described later for the purpose of supporting platinum atoms on ceria (first inorganic support).

  In the step of preparing the platinum solution, first, a platinum compound is prepared as a supply source of platinum atoms. Furthermore, a solvent for dissolving the platinum compound is prepared. Thereafter, a platinum compound is added to the prepared solvent, and stirred as necessary to prepare a platinum solution.

  Examples of the promoter compound that is a supply source of platinum atoms include compounds in the form of metal salts, such as dinitrodiamine platinum, chloroplatinic acid, and acetylacetonatoplatinum. These compounds are easily available, are widely used as raw materials for catalyst preparation, and are easy to handle when supported on ceria (first inorganic support).

  Examples of the solvent used for preparing the platinum solution include water and ethanol, but are not limited thereto.

  The concentration of platinum atoms in the platinum solution is not particularly limited, and is appropriately adjusted in consideration of the amount of ceria (first inorganic carrier) prepared above, the desired content in the resulting platinum catalyst powder, the loading method, and the like. Can be done.

  In the obtained platinum catalyst powder, when it is desired to support metal atoms other than platinum atoms (for example, Group 4 or Group 5 atoms) on ceria (first inorganic support), in this step, The desired component may be added in the desired amount. At this time, the desired component may be added to the solvent in the form of a metal salt and dissolved by stirring as necessary.

  Thereafter, platinum atoms dissolved in the platinum solution prepared above are supported on the ceria (first inorganic carrier) prepared above and dried as necessary. There are no particular limitations on the specific methods and conditions for supporting and drying, and the form described in the above section of “Copper Catalyst Powder Preparation Step” for the copper catalyst powder can be similarly employed. For this reason, explanation is omitted here.

  According to such a form, in addition to platinum atoms, metal atoms other than platinum atoms are simultaneously supported on ceria (first inorganic carrier). Thereby, the effect that a platinum-ceria interface is obtained largely is acquired. However, it is not limited only to such a form. For example, a platinum atom may be supported after a metal atom other than a platinum atom (for example, a Group 4 or Group 5 atom) is supported.

  Subsequently, ceria (first inorganic support) on which platinum atoms are supported is fired. Thereby, a platinum component grows on the surface of ceria (first inorganic support), and a platinum catalyst powder is obtained.

  There is no restriction | limiting in particular also about the specific method and baking conditions of baking, The form demonstrated in the column of said [copper catalyst powder preparation process] can be employ | adopted similarly. For this reason, explanation is omitted here.

  If necessary, after the calcination, the obtained platinum catalyst powder may be pulverized and sieved to select only the powder having a desired particle diameter.

[Mixing process]
Subsequently, the copper catalyst powder prepared above and the platinum catalyst powder are mixed. Thereby, the shift catalyst of the present invention is completed.

  In this step, first, the copper catalyst particles prepared above and a platinum catalyst powder are prepared. The preferred configurations of the prepared copper catalyst powder and platinum catalyst powder are the same as those already described in the above [Configuration] section, and thus the description thereof is omitted here.

  The specific method of mixing is not particularly limited, and conventionally known knowledge can be appropriately referred to regarding powder mixing. At this time, the amounts of the copper catalyst powder and the platinum catalyst powder to be mixed can be appropriately adjusted by considering the final content of copper atoms and platinum atoms (and further cerium atoms) in the obtained catalyst. . Hereinafter, as an example of the mixing method, for example, a method in which each catalyst powder is charged in a pot mill containing φ5 mm alumina balls at a mass ratio of 1: 1 and mixed by vibration is exemplified.

  As described above, a copper catalyst powder is prepared by supporting the copper component on the second inorganic carrier, and a platinum catalyst powder is prepared by supporting the platinum component on the first inorganic carrier containing cerium atoms. Although the method for producing the shift catalyst of the present invention by mixing the above has been described in detail, the present invention is not limited to such a form, and it may of course be produced by other methods.

  As a manufacturing method other than the method described above, for example, a form in which an inorganic oxide containing a copper atom is employed as the copper catalyst powder is exemplified. Here, the method described in detail above can be similarly used except that “inorganic oxide containing a copper atom” is employed as the copper catalyst powder.

[Shift reactor]
The shift catalyst of this invention is arrange | positioned at a shift reaction apparatus, for example. The shift reaction apparatus in which the shift catalyst of the present invention is disposed can be used, for example, to selectively oxidize and remove CO in a hydrogen-rich gas supplied to a polymer electrolyte fuel cell. Therefore, the present application provides a shift reactor for a polymer electrolyte fuel cell in which the shift catalyst of the present invention described above is disposed. In addition, the form in particular when the shift catalyst of this invention is arrange | positioned in a shift reaction apparatus is not restrict | limited, A conventionally well-known technique and its improvement technique can be employ | adopted suitably. For example, the form obtained by preparing a slurry containing the shift catalyst of the present invention and applying the slurry to, for example, a honeycomb carrier is exemplified. The specific form of the honeycomb carrier is not particularly limited, and a conventionally known form can be adopted. For example, a ceramic honeycomb, a metal honeycomb, a ceramic foam, a metal foam, or the like can be employed. For example, when the shift reaction apparatus is integrated with the heat exchanger, the shift catalyst of the present invention may be applied to the fins of the heat exchanger.

  Hereinafter, the shift reaction apparatus of the present invention will be described in detail with reference to the drawings. FIG. 2 is a schematic diagram of a fuel cell system 100 in which a shift reaction apparatus in which the shift catalyst of the present invention is disposed is used.

  First, a fuel such as hydrocarbon is supplied to the fuel reformer 110 in which the fuel reforming catalyst is arranged. In the fuel reformer 110, the fuel is reformed into a hydrogen-rich reformed gas, usually by steam reforming using steam. A hydrogen-rich reformed gas can also be obtained by autothermal reforming in which a gas containing oxygen is simultaneously supplied in addition to water vapor and a partial oxidation reaction is simultaneously performed.

  Next, the reformed gas obtained in the fuel reformer 110 is sent to the shift reactor 120 in which the shift catalyst 10 of the present invention is arranged, and the CO concentration in the reformed gas is reduced to about 1% by volume. The reformed gas whose CO concentration is reduced to about 1% by volume is sent to the CO selective oxidation reactor 130 in which the CO selective oxidation catalyst is arranged, and the CO concentration is reduced to the ppm order.

  The power generation reaction proceeds in the polymer electrolyte fuel cell 140 using the reformed gas whose CO concentration is reduced to the ppm order in the CO selective oxidation reactor 130 and the oxidizing agent (usually air). From the polymer electrolyte fuel cell 140, spent fuel and oxidant are discharged. The combustion system 150 is provided to burn the spent fuel and oxidant, and the evaporation system 160 uses the heat of combustion to evaporate water, thereby generating water vapor used in the fuel reformer 110, thereby generating the entire system. Energy efficiency can be improved. You may supply a hydrocarbon etc. to the combustion apparatus 150 and the evaporator 160 as needed.

  As described above, the shift catalyst of the present invention exhibits excellent CO removal performance even in a low temperature region, and is also excellent in durability. By oxidizing and removing a small amount of CO in the reformed gas using such a catalyst, the CO concentration in the fuel gas supplied to the fuel cell can be efficiently reduced. As a result, the lifetime of the platinum electrode used in the fuel cell can be extended, which can greatly contribute to the practical application of the fuel cell vehicle.

  As described above, as a preferred application of the shift catalyst of the present invention, the case where it is used in a fuel cell system by being disposed in a shift reactor for a polymer electrolyte fuel cell has been described as an example. However, the present invention is not limited to this, and can be applied to any use for oxidizing and removing trace amounts of CO by promoting a shift reaction. Applications other than those described above for the shift catalyst of the present invention include, for example, CO removal in a closed space such as a tunnel, CO removal in exhaust from an engine or a combustor, and the like.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

<Example>
A dinitrodiamine platinum complex salt containing 8.451% by mass of platinum was prepared as a source of platinum atoms. Moreover, copper nitrate was prepared as a supply source of copper atoms which are promoter atoms. A predetermined amount of each of these was added to water as a solvent to prepare a platinum solution and a copper solution, respectively.

On the other hand, cerium oxide (BET specific surface area: 100 m ² / g) was prepared as an inorganic carrier.

  The platinum solution and the copper solution prepared above were impregnated in the inorganic carrier similarly prepared above, and platinum atoms and copper atoms were supported on the inorganic carrier, respectively. At this time, the supported amounts of platinum atoms and copper atoms were adjusted to 10% by mass (respectively in terms of metals) with respect to the total amount of the shift catalyst powder obtained. Each inorganic support carrying each catalyst atom was dried at 150 ° C. for 10 hours and then calcined in an electric furnace at 400 ° C. for 1 hour to prepare a platinum catalyst powder and a copper catalyst powder, respectively.

  The platinum catalyst powder and copper catalyst powder prepared above were mixed by the same mass to prepare a mixed catalyst powder.

  To the obtained mixed catalyst powder (200 g), alumina sol (4 g in terms of alumina) as a coating aid and water (200 mL) were added and dispersed in a ball mill for 1 hour to prepare a mixed catalyst powder slurry.

120 mL of cordierite honeycomb monolith support (400 cells / inch ² ) is coated with the mixed catalyst powder slurry prepared above, dried at 150 ° C. for 10 hours, and then fired in air at 500 ° C. for 1 hour. Thus, the monolith-supported shift catalyst of the example was completed. The coating amount of the catalyst powder slurry on the monolith support was 24 g (200 g / L) in terms of mixed catalyst powder.

<Comparative Example 1>
A monolith-supported shift catalyst of Comparative Example 1 was completed in the same manner as in Example 1 except that the honeycomb catalyst was coated with the platinum catalyst powder obtained in Example 1 above instead of the mixed catalyst powder. I let you.

<Comparative example 2>
Instead of preparing the mixed catalyst powder, a dinitrodiamine platinum complex salt and copper nitrate are simultaneously dissolved in water as a solvent to prepare a platinum-copper solution. This solution is impregnated into an inorganic support, and the inorganic support is subjected to platinum atoms. And a co-impregnation catalyst was obtained by simultaneously supporting copper atoms. At this time, the supported amounts of platinum raw material and copper atoms were adjusted to 5% by mass (respectively in metal conversion) with respect to the total amount of the shift catalyst powder obtained. Then, the monolith-supported shift catalyst of Comparative Example 3 was completed by the same method as in Example 1 except that the co-impregnated catalyst was coated on the honeycomb monolith support instead of the mixed catalyst powder.

<Comparative Example 3>
The platinum catalyst-coated monolith-supported shift catalyst (18 mL) obtained in Comparative Example 1 was placed upstream with respect to the flow direction of the reformed gas, and the copper catalyst powder obtained in Example 1 was used as the above The monolith-supported shift catalyst (18 mL) obtained by coating the honeycomb monolith support by the same method as in Example 1 of the above was arranged with respect to the flow direction of the reformed gas so as to be adjacent to the catalyst arranged on the upstream side. Arranged downstream, the monolith-supported shift catalyst of Comparative Example 4 was completed.

<Comparative example 4>
The copper catalyst-coated monolith-supported shift catalyst (18 mL) obtained in the above Comparative Example 3 is disposed upstream with respect to the flow direction of the reformed gas, and the platinum catalyst-coated monolith supported in the above Comparative Example 1 is supported. The shift catalyst (18 mL) was arranged downstream with respect to the flow direction of the reformed gas so as to be adjacent to the catalyst arranged on the upstream side, and the monolith-supported shift catalyst of Comparative Example 5 was completed.

<Catalyst performance evaluation test>
Using the monolith-supported shift catalysts obtained in the above Examples and Comparative Examples 1 to 4, the catalyst performance for the shift reaction was evaluated by the following method.

  As pre-reaction treatment, each shift catalyst (36 mL) was subjected to an activation treatment at 400 ° C. for 1 hour in a nitrogen atmosphere containing 2% hydrogen.

Next, each shift catalyst was cooled to 200 ° C. under a nitrogen atmosphere, and the outlet gas was analyzed by gas chromatography while raising the temperature. In all the evaluation tests, the input gas composition was CO / H ₂ O / H ₂ / CO ₂ / N ₂ = 2.5 / 24/35/15 / 23.5% by volume, and the flow rate of the reaction gas Was 30 L / min. Therefore, the gas space velocity (GHSV) for the catalyst sample in this test was 50000 h ⁻¹ .

  During the test, the CO conversion was calculated by the following formula 1 by analyzing the outlet gas. That is, it can be said that the higher the CO conversion rate, the better the shift catalyst.

Here, in this test, the maximum CO conversion rate exhibited by each shift catalyst was measured. Here, the temperature at which the shift catalyst exhibits the maximum CO conversion is also referred to as “T _max (° C.)”. In order to evaluate low-temperature activity, the CO conversion rate at a temperature 25 ° C. lower than T _max (hereinafter also referred to as “T _max −25 (° C.)”) was also measured.

Further, in order to evaluate the durability of each shift catalyst, the above performance evaluation test was continuously performed for 30 hours, and the CO conversion rate at T _max (° C.) and T _max −25 (° C.) was measured. Further, as a specific activity at T _max -25 (° C.), the ratio (%) of the CO conversion rate after 30 hours from the initial CO conversion rate was calculated. The obtained results are shown in Table 1 below.

  From the results shown in Table 1, the shift catalyst of the present invention is not only superior in catalytic activity under low temperature conditions but also has a high specific activity as compared with conventional shift catalysts, and thus after a long period of use. It is also shown that the catalytic activity is difficult to decrease.

  Therefore, since the catalyst of the present invention can be used under a lower temperature condition, the shift reaction governed by thermodynamic equilibrium can efficiently proceed. In addition, since it is excellent in durability, it can be preferably used as a CO shift reaction device in a fuel cell system or the like mounted on an automobile or the like that is expected to have a certain period of use after mounting. As a result, it is expected that the present invention can greatly contribute to the practical application of the fuel cell system in the end.

It is a schematic cross section showing one embodiment of the shift catalyst of the present invention. 1 is a schematic view of a fuel cell system in which a shift reaction apparatus in which a shift catalyst of the present invention is arranged is used.

Explanation of symbols

10 shift catalyst,
20 platinum catalyst powder,
22 Platinum component,
24 first inorganic carrier,
30 Copper catalyst powder,
32 Copper component,
34 second inorganic carrier,
100 fuel cell system,
110 Fuel reformer,
120 shift reactor,
130 CO selective oxidation reactor,
140 polymer electrolyte fuel cell,
150 combustion equipment,
160 Evaporator.

Claims (15)

A shift catalyst capable of selectively promoting a shift reaction by contact with a gas containing carbon monoxide and water,
A shift catalyst comprising a platinum catalyst powder containing a platinum atom and a cerium atom and a copper catalyst powder containing a copper atom.   The shift catalyst according to claim 1, wherein the platinum catalyst powder has a structure in which a platinum component is supported on an inorganic carrier containing a cerium atom.   The shift catalyst according to claim 1 or 2, wherein the platinum catalyst powder further contains one or more atoms selected from the group consisting of titanium, zirconium, vanadium, niobium, and tantalum.   The shift catalyst according to any one of claims 1 to 3, wherein the copper catalyst powder further contains a rare earth atom.   The shift catalyst according to any one of claims 1 to 4, wherein the platinum atom content per catalyst unit volume is 0.1 to 20 mg / mL.   The shift catalyst according to any one of claims 1 to 5, wherein a content of the cerium atom per catalyst unit volume is 50 to 500 mg / mL.   The shift catalyst according to any one of claims 1 to 6, wherein a content of the copper atom per catalyst unit volume is 0.1 to 80 mg / mL.   The shift catalyst according to any one of claims 1 to 7, wherein the content of the copper catalyst powder is 0.1 to 10 parts by mass with respect to 1 part by mass of the platinum catalyst powder.   The shift according to any one of claims 1 to 8, wherein an inorganic oxide containing one or more atoms selected from the group consisting of silicon, aluminum, titanium, cerium and zirconium is further mixed. catalyst. A method for producing a shift catalyst, which can selectively promote a shift reaction by contact with a gas containing carbon monoxide and water,
A copper catalyst powder preparation step of preparing a copper catalyst powder containing copper atoms;
A platinum catalyst powder preparation step of preparing a platinum catalyst powder by supporting platinum atoms on an inorganic oxide containing cerium atoms;
A mixing step of mixing the copper catalyst powder and the platinum catalyst powder;
A process for producing a shift catalyst.   In the platinum catalyst powder preparation step, simultaneously with supporting platinum atoms on the inorganic oxide, one or more atoms selected from the group consisting of titanium, zirconium, vanadium, niobium and tantalum are further supported. The manufacturing method according to claim 10.   The step of preparing the platinum catalyst powder further comprises supporting one or more atoms selected from the group consisting of titanium, zirconium, vanadium, niobium and tantalum after the inorganic oxide supports the platinum atom. The manufacturing method according to claim 10 or 11, further comprising:   The step of preparing the platinum catalyst powder comprises supporting one or more atoms selected from the group consisting of titanium, zirconium, vanadium, niobium and tantalum before the inorganic oxide supports platinum atoms. Furthermore, the manufacturing method of any one of Claims 10-12 which has.   The manufacturing method of any one of Claims 10-13 in which the said copper catalyst powder preparation process includes the process of carry | supporting a copper atom on the inorganic oxide which does not contain a copper atom substantially.   The manufacturing method of any one of Claims 10-13 whose said copper catalyst powder is an inorganic oxide containing a copper atom.

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