JP2006181475A - Carbon monoxide selective oxidation catalyst and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for solving the problem of the lowering of catalytic activity caused by the coating of one component on a carrier with another component, in a CO selective oxidation catalyst containing a platinum atom. <P>SOLUTION: The CO selective oxidation catalyst containing the platinum atom is characterized by containing a cobalt atom in a cobalt aluminate form. The manufacturing method of the CO selective oxidation catalyst has a process for preparing an inorganic carrier containing cobalt aluminate and a process for supporting platinum particles on the inorganic carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a CO selective oxidation catalyst for selectively oxidizing carbon monoxide (hereinafter also referred to as “CO”). Specifically, the present invention relates to a CO selective oxidation catalyst that exhibits high CO selective oxidation activity even at low temperatures.

  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 fuel sources. A method that uses them and converts them to hydrogen-rich reformed gas in a reformer is also a promising candidate.

When a hydrocarbon-based liquid fuel is used as a fuel source and converted to reformed gas, a certain amount of CO remains 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 or the like is supported on an inorganic carrier has been proposed.

In this case, in the CO selective oxidation catalyst, the catalyst temperature rises as the oxidation reaction proceeds. As a result, the increase in CO concentration by the reverse shift reaction (CO ₂ + H ₂ → CO + H ₂ O) and the hydrogenation by the methanation reaction (CO + 3H ₂ → CH ₄ + H ₂ O, CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O) The problem of consumption occurs. For this reason, it is common practice to use a heat exchanger or the like to maintain the temperature of the CO selective oxidation catalyst in a relatively low temperature range and to suppress the above undesirable reactions.

  The above unfavorable reactions can be suppressed more effectively at lower temperature conditions. For this reason, a catalyst excellent in low temperature activity is desired. Further, considering a reformer mounted on an automobile, a catalyst that is resistant to atmospheric fluctuations is desired because of frequent start / stop and severe load fluctuations. From the above viewpoints, noble metal-based catalysts, particularly platinum-based catalysts are promising. On the other hand, as a drawback of the platinum-based catalyst, there is a problem that CO removal efficiency decreases due to an adsorption poisoning phenomenon in which CO is strongly adsorbed to platinum atoms under low temperature conditions.

In view of such problems, an attempt has been made to further improve CO selective oxidation activity in a low temperature region by further adding a transition metal atom such as a cobalt atom or a copper atom as a low temperature activation component in addition to a platinum atom ( For example, see Patent Document 1).
JP 2001-149781 A

  Here, in the above-mentioned document 1, a CO selective oxidation catalyst is prepared by simultaneously supporting a low-temperature activation component such as a cobalt atom or a copper atom and a platinum component on a support using means such as impregnation or evaporation to dryness. It is described that it is preferable.

  However, when the catalyst is prepared by such a method, in some cases, either one of the platinum component and the low-temperature activation component may be covered with the other component. As a result, there is a problem that the coated component cannot sufficiently exert its action and the CO selective oxidation activity is not sufficiently improved.

  Accordingly, an object of the present invention is to provide a means capable of sufficiently exerting the action of a low temperature activation component in a CO selective oxidation catalyst containing a platinum atom and sufficiently improving the CO selective oxidation activity under low temperature conditions. .

  The present invention is a CO selective oxidation catalyst containing a platinum atom, which contains a cobalt atom in the form of cobalt aluminate.

  Moreover, this invention is a manufacturing method of the CO selective oxidation catalyst which has the process of preparing the inorganic support | carrier containing a cobalt aluminate, and the process of making a platinum particle carry | support on the said inorganic support | carrier.

  In the CO selective oxidation catalyst of the present invention, the platinum component and the cobalt component are prevented from being coated with each other, so that each component exhibits a sufficient effect, and the CO selective oxidation activity under low temperature conditions is sufficiently improved. Can be done.

  Hereinafter, embodiments of the present invention will be described.

  As described above, conventionally, in a CO selective oxidation catalyst containing a platinum atom which is a noble metal atom, it is known that CO selective oxidation activity in a low temperature region is improved by further adding a transition metal atom such as an iron atom. . The present inventor paid attention to cobalt atoms among these transition metal atoms, and conducted earnest research in order to further improve the catalytic activity of the CO selective oxidation catalyst.

Note that the mechanism by which the CO selective oxidation activity is improved by the addition of cobalt atoms has not yet been clarified. However, the presence of cobalt atoms activates oxygen, water, etc. in the reaction gas to generate some active species, and this active species has some involvement in the oxidation of CO to CO ₂ . Guessed. In addition, it has been estimated that a mechanism in which electrons are attracted from a platinum atom to a cobalt atom due to the presence of a cobalt atom, thereby reducing the CO adsorption power of the platinum atom and facilitating the oxidation of CO to CO ₂ . However, even if other mechanisms are involved, the technical scope of the present invention is not affected at all.

Here, as described in the above-mentioned Document 1 as a preferable preparation method, a CO selective oxidation catalyst containing a platinum atom and a cobalt atom is produced by simultaneously supporting a platinum component and a cobalt component on an inorganic carrier. Think about it. According to such a preparation method, platinum atoms are supported on the surface of the inorganic carrier as platinum metal particles or platinum oxide particles. On the other hand, cobalt atoms are similarly supported on the surface of the inorganic carrier as metal particles of cobalt atoms or particles of oxides (eg, cobalt oxide (Co ₃ O ₄ )). At this time, focusing on one particle of the inorganic carrier, a platinum component and a cobalt component coexist on the surface of the inorganic carrier particle. In many cases, platinum metal particles and cobalt oxide are considered to be simultaneously present on the surface of the inorganic carrier particles.

  Accordingly, in some cases, the platinum component supported on the inorganic carrier may be covered with a cobalt component such as cobalt oxide. Or conversely, the cobalt component supported on the inorganic carrier may be coated with the platinum component. As a result, there is a problem that the coated component cannot sufficiently exhibit the activity and the final CO selective oxidation activity is lowered.

  As an approach for improving the catalytic activity of the CO selective oxidation catalyst, the present inventor has attempted to control the existence state of the platinum component and the cobalt component on the surface of the inorganic carrier. Specifically, by containing cobalt atoms in the form of cobalt aluminate, the platinum component and the cobalt component were prevented from being simultaneously supported on the inorganic carrier, and the above-described problems due to the coating were solved.

That is, the first of the present invention is a carbon monoxide selective oxidation catalyst containing platinum atoms, which is a CO selective oxidation catalyst characterized by containing cobalt atoms in the form of cobalt aluminate. In the present application, the “CO selective oxidation catalyst” refers to a catalyst that selectively promotes an oxidation reaction of CO in the gas to CO ₂ by contacting with a gas containing at least CO and O ₂ . Moreover, in this application, "low temperature" refers to the temperature of about 200 degreeC or less, for example, and points out the temperature of about 100-180 degreeC in detail.

  The CO selective oxidation catalyst of the present invention contains a platinum atom. And it has the characteristics in the point in which a cobalt atom is contained with the form of cobalt aluminate. Hereinafter, preferred embodiments of the CO selective oxidation catalyst of the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to only the forms described below.

(First form)
[Constitution]
FIG. 1 is a schematic cross-sectional view showing a preferred embodiment (also referred to as “first embodiment” in the present specification) of the CO selective oxidation catalyst of the present invention.

  As shown in FIG. 1, the first embodiment of the CO selective oxidation catalyst 10 has a configuration in which platinum particles 30 are supported on the surface of an inorganic carrier 20. The inorganic carrier 20 contains alumina 22 as a main component. Furthermore, the inorganic support | carrier 20 has the cobalt aluminate layer 24 which consists of cobalt aluminate in the surface layer. For convenience of explanation, the dimensional ratio of each component of the CO selective oxidation 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 20, but these micropores are omitted in FIG.

The platinum particle 30 is a particle composed of only platinum atoms. However, the platinum particles 30 are not limited to particles composed only of platinum atoms, and for example, from particles composed of platinum oxide (platinum monoxide (PtO), platinum dioxide (PtO ₂ ), etc.), a mixture of platinum and platinum oxide. Or a particle made of a platinum alloy. Examples of the platinum alloy include alloys of other noble metal atoms and transition metal atoms described later and platinum.

  In the first embodiment, the inorganic carrier 20 is mainly composed of alumina 22 as described above, and has a cobalt aluminate layer 24 on its surface layer. It is preferable to use alumina 22 as the main component of the inorganic carrier 20 because the catalytic activity is improved and it is easy to obtain raw materials and to produce and handle the carrier.

“Cobalt aluminate” is a composite oxide of aluminum and cobalt, and its composition is represented by Al ₂ CoO ₄ . The presence of cobalt aluminate in the catalyst can be confirmed by X-ray diffraction, but since it exhibits a light blue color tone, it can also be judged visually.

  In the form shown in FIG. 1, the cobalt aluminate layer 24 is formed on the entire surface of the inorganic carrier 20. However, the form is not limited to such a form. For example, a form in which the cobalt aluminate layer 24 is formed on a part of the surface layer of the inorganic carrier 20 and a part of the surface of the alumina 22 is exposed can also be adopted.

  The kind in particular of alumina 22 is not restrict | limited, A conventionally well-known thing can be used as an inorganic support | carrier for catalysts. Examples of the alumina 22 include α alumina, θ alumina, γ alumina, δ alumina, β alumina, and the like. In addition, these may be used individually by 1 type and these mixtures may be used. Here, the mixture of alumina includes not only a form in which two or more kinds of alumina are physically mixed, but also alumina having different crystallinity between a portion having a crystal structure and another portion. As such a form, for example, alumina in which a part is α-type and the other part is θ-type can be mentioned.

Although there is no restriction | limiting in particular also about the specific surface area of the inorganic support | carrier 20, Preferably it is 35-150 m < ² > / g, More preferably, it is 50-110 m < ² > / g. If the specific surface area of the inorganic carrier 20 is too small, the dispersibility of the platinum particles 30 and the cobalt aluminate during the production of the catalyst may deteriorate, and the catalytic activity may decrease. On the other hand, if the specific surface area of the inorganic carrier 20 is too large, the platinum particles 30 may not be sufficiently supported on the cobalt aluminate layer 24 present on the surface layer of the inorganic carrier 20 in some cases, and the catalytic activity may similarly decrease. . The “specific surface area” described in the present specification can be calculated, for example, by measuring the BET specific surface area by nitrogen adsorption.

  The average particle size of the inorganic carrier 20 is not particularly limited. However, it is preferably about 0.8 to 3.5 μm, more preferably 1.5 to 2.5 μm. If the average particle size of the inorganic carrier 20 is too small, the scattering property may be increased and the handling may be complicated. On the other hand, if the average particle diameter of the inorganic carrier 20 is too large, the moldability of the catalyst is deteriorated, and there is a possibility that it will be easily peeled off when applied to a honeycomb carrier, for example. Further, the specific surface area of the catalyst is relatively reduced, and the catalyst performance may be deteriorated.

  The thickness of the cobalt aluminate layer 24 formed on the surface layer of the inorganic carrier 20 is not particularly limited, but is preferably about several nm to 0.5 μm. The thickness of the cobalt aluminate layer 24 can be appropriately controlled by adjusting the cobalt atom content, the concentration and pH of the cobalt aqueous solution, and the like.

  In the form shown in FIG. 1, cobalt aluminate exists only on the surface layer of the inorganic carrier 20. However, it is not limited only to such a form, and in some cases, cobalt aluminate may be present in the alumina 22 inside the inorganic carrier 20.

  The area ratio of the site where the cobalt aluminate layer 24 is formed, which occupies the surface area of the inorganic carrier 20, is, for example, about 50 to 100%. In addition, in the form (1st form) shown in FIG. 1, since the cobalt aluminate layer 24 is formed in the whole surface of the inorganic support | carrier 20, this area ratio will be 100%. Here, when this area ratio is too small, there is a possibility that the effect due to the inclusion of cobalt atoms cannot be sufficiently obtained.

  As described above, the case where the main component of the inorganic carrier 20 is the alumina 22 has been described as an example. However, if the cobalt aluminate layer 24 can be formed on the surface, a compound other than alumina is the main component of the inorganic carrier 20. It may be used as a component. Examples of components other than alumina that can be used as the inorganic carrier 20 include metal oxides such as titania, silica, silica alumina, zirconia, magnesia, and zeolite. Only one of these may be used alone, or a mixture thereof may be used. Furthermore, it goes without saying that a mixture of these metal oxides and alumina may be used. Note that, even when a metal oxide other than alumina is used as the main component of the inorganic carrier 20, the specific surface area, average particle diameter, and other preferred modes of the inorganic carrier 20 are described above by taking alumina as an example. Can be adopted as well.

The CO selective oxidation catalyst of the present invention contains a platinum atom for adsorbing CO and a cobalt atom that promotes the oxidation of CO adsorbed on the platinum atom to CO ₂ . If the amount balance is kept good, it can contribute to the improvement of the CO selective oxidation activity of the catalyst. From such a viewpoint, in the CO selective oxidation catalyst of the present invention, the mass ratio of the cobalt atom to the total amount of the platinum atom and the cobalt atom is preferably more than 70% by mass and less than 100% by mass, more preferably. It is 80-90 mass%, More preferably, it is 80-85 mass%. In other words, in the CO selective oxidation catalyst of the present invention, the molar ratio of the cobalt atom content to the platinum atom content (Co / Pt) is preferably 8 to 65, more preferably. Is 11-20. When these values are within the above range, the balance between the CO adsorption effect by the platinum atoms and the CO oxidation promoting effect by the cobalt atoms can be maintained well, and as a result, the CO removal performance of the catalyst can be improved. Further, since the platinum atom content is relatively smaller than that of the conventional CO selective oxidation catalyst, it is advantageous in terms of cost.

  Similarly to the above, the content of each of the platinum atom and the cobalt atom in the CO selective oxidation catalyst of the present invention is not particularly limited, but the content of the platinum atom is preferably 0.2 with respect to the total amount of the catalyst. It is about -2.5 mass%, More preferably, it is 0.4-2.0 mass%. Similarly, the cobalt atom content is preferably about 0.6 to 12.0 mass%, more preferably 1.5 to 10 mass%, based on the total amount of the catalyst. If the content of these atoms is too small, the catalyst activity may not be sufficiently obtained. On the other hand, if the content of these atoms is too large, catalyst activity commensurate with the increase in content cannot be obtained, and the production cost of the catalyst may increase.

Here, depending on the space velocity condition when the CO selective oxidation catalyst of the present invention is used, the required content of platinum atoms and cobalt atoms may vary. The preferred value of the above content has a certain range. For example, the preferred content when used under high space velocity conditions exceeding 100,000 h ⁻¹ as in the case of being mounted on an automobile is the catalyst. The platinum atom is about 0.4 to 2.0% by mass and the cobalt atom is about 1.5 to 10.0% by mass with respect to the total amount. On the other hand, a preferable content when used under a space velocity condition that is not so high as less than 10000 h ⁻¹ as in a consumer device is 0.08 platinum atoms relative to the total amount of the catalyst. It is sufficient that about -1.0 mass% and cobalt atoms are about 0.5-5.0 mass%. In addition, in this application, content of a platinum atom and a cobalt atom means the quantity converted into a metal atom unless there is particular notice. The various values described above relating to the platinum and cobalt contents are calculated from the amounts of the platinum raw material and the cobalt raw material used in producing the catalyst, and can be controlled by adjusting the amounts of these raw materials. .

  Here, a metal atom other than a platinum atom and a cobalt atom may be contained as a catalyst metal as long as the function and effect of the present invention are not impaired. For example, in addition to platinum atoms, other noble metal atoms such as ruthenium, rhodium and palladium can be contained. These noble metal atoms can be supported on the inorganic carrier 20 as particles similar to the platinum particles 30 shown in FIG. 1 or particles of an alloy with platinum. Furthermore, rare earth atoms such as lanthanum, cerium, praseodymium, and neodymium, and transition metal atoms such as manganese, nickel, copper, and iron may be contained. These atoms are preferably contained in a form that does not cover the platinum particles 30. Further, for example, it may be supported on the inorganic carrier 20 as particles of an alloy with platinum, or may be contained in the form of a complex oxide such as perovskite. The amount of metal atoms other than platinum atoms and cobalt atoms supported on the inorganic carrier 20 is not particularly limited, but about 0.05 to 3.0% by mass in terms of metal atoms is appropriate.

[Action and effect]
In the CO selective oxidation catalyst of the first embodiment shown in FIG. 1, platinum particles 30 are supported on the cobalt aluminate layer 24 formed on the surface layer of the inorganic carrier 20 as described above. According to such a configuration, the platinum particles 30 are not covered with other components. For this reason, the platinum particles 30 can sufficiently adsorb CO. Further, cobalt atoms are present on the surface of the inorganic carrier 20 as cobalt aluminate constituting the cobalt aluminate layer 24. For this reason, the oxidation of CO adsorbed by platinum atoms to CO ₂ can be sufficiently promoted.

  Therefore, according to the first embodiment of the CO selective oxidation catalyst, both the mechanism of CO adsorption by platinum atoms and the promotion of CO oxidation by cobalt atoms can proceed efficiently. As a result, a CO selective oxidation catalyst having excellent catalytic activity can be provided.

[Production method]
The second of the present invention relates to a method for producing a CO selective oxidation catalyst. Specifically, the second of the present invention is a method for producing a carbon monoxide selective oxidation catalyst, comprising the steps of preparing an inorganic support containing cobalt aluminate and supporting the platinum particles on the inorganic support. is there. The CO selective oxidation catalyst of the form shown in FIG. 1 (first form) can be produced by this production method. Hereinafter, it demonstrates in order of a process.

[Inorganic carrier preparation step]
First, an inorganic carrier containing cobalt aluminate is prepared. Since the preferable form of the inorganic carrier prepared in this step is as already described, the description is omitted here.

  As the inorganic carrier containing cobalt aluminate, one prepared by itself may be used, and when a product is commercially available, the product may be purchased and used.

  When an inorganic carrier containing cobalt aluminate is prepared by itself, for example, it is preferable to obtain alumina having cobalt aluminate formed on the surface by supporting cobalt atoms on an alumina raw material and firing. Hereinafter, a specific method for preparing the inorganic carrier by such a method will be described (see also Example 1 described later). However, it is of course possible to prepare the inorganic carrier by other methods.

  First, an alumina raw material for supporting cobalt atoms is prepared. The alumina raw material is not particularly limited as long as it is a raw material that can become alumina by firing. Examples of the alumina raw material include γ-alumina in addition to aluminum hydroxide such as boehmite alumina and gibbsite. A newly developed material may be used as the alumina raw material.

  Subsequently, a solution in which cobalt ions are dissolved (hereinafter also simply referred to as “cobalt solution”) is prepared. This cobalt solution is used in a supporting process described later for the purpose of supporting cobalt atoms on the alumina raw material prepared above.

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

  Examples of the cobalt compound that is a cobalt raw material include compounds in the form of metal salts, and examples include compounds in the form of nitrates, acetates, carbonates, ammonium salts, chlorides, and the like. These compounds are easily available, are widely used as raw materials for preparing catalysts, and are easy to handle when supported on alumina raw materials.

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

  The concentration of cobalt in the cobalt solution is not particularly limited, and can be appropriately adjusted in consideration of the amount of the alumina raw material prepared above, the desired content of cobalt atoms in the resulting catalyst, the loading method, and the like.

  In the obtained catalyst, when it is desired to contain a metal atom other than cobalt atom in the inorganic support, a desired component may be added to the cobalt solution in a desired amount in this step. 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, cobalt atoms dissolved in the cobalt solution prepared above are supported on the alumina raw material 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 alumina raw material and the cobalt solution may be brought into contact at room temperature to 80 ° C. for about 0.5 to 8 hours.

  After cobalt atoms are supported on the alumina raw material, 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, the alumina raw material carrying cobalt atoms is fired. Thereby, the inorganic support | carrier containing a cobalt aluminate, specifically the alumina which the cobalt aluminate produced | generated on the surface 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. Taking an example of the firing conditions, the firing temperature is preferably 700 to 900 ° C., more preferably 750 to 800 ° C., and the firing time is preferably 1 to 6 hours, more preferably 2 to 4 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. By adjusting the firing conditions, the specific surface area and crystal state of the resulting inorganic carrier can be controlled. For example, an inorganic carrier having a relatively large specific surface area can be obtained by lowering the firing temperature or shortening the firing time. On the other hand, an inorganic carrier having a relatively small specific surface area can be obtained by raising the firing temperature or lengthening the firing time.

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

[Platinum loading process]
Next, platinum particles are supported on the inorganic carrier prepared in the above-described inorganic carrier preparing step. As a result, the CO selective oxidation catalyst according to the first embodiment of the present invention shown in FIG. 1 is obtained.

  First, a solution in which platinum ions 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 particles on an inorganic carrier.

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

  Examples of platinum compounds that are platinum raw materials include compounds in the form of metal salts, such as dinitrodiammine platinum and chloroplatinic acid. These compounds are easy to obtain, are widely used as raw materials for catalyst preparation, and are easy to handle when supported on an inorganic carrier.

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

  The concentration of platinum in the platinum solution is not particularly limited, and can be appropriately adjusted in consideration of the amount of the inorganic carrier prepared above, the desired content in the resulting catalyst, the loading method, and the like.

  In the obtained catalyst, when it is desired to support a metal atom (particularly a noble metal atom) other than a platinum atom on an inorganic support, a desired amount of a desired component may be added to the platinum solution in this step. 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 platinum atoms dissolved in the platinum solution prepared above are supported on the inorganic carrier prepared above. As for the specific method and conditions for loading, the above-described embodiment for loading cobalt atoms on the alumina raw material can be similarly adopted. In addition, the amount of the platinum solution and the inorganic carrier used at this time can be appropriately adjusted in consideration of the final content of platinum atoms and cobalt atoms in the obtained catalyst.

  After carrying | supporting a platinum atom on an inorganic support | carrier, this is dried as needed. The form mentioned above can be similarly adopted also about the specific method of drying.

  Subsequently, the inorganic carrier carrying platinum atoms is baked. Thereby, platinum particles grow on the surface of the inorganic carrier, and the CO selective oxidation catalyst according to the first embodiment of the present invention is completed.

  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 400 to 600 ° C., more preferably 450 to 550 ° C., and the firing time is preferably 0.5 to 4 hours, more preferably 1 to 3 hours. is there. 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 the calcination, the obtained catalyst powder may be pulverized and sieved to select only the catalyst powder having a desired particle size.

  The preferred form of the CO selective oxidation catalyst of the form shown in FIG. 1 (first form) has been described above, but other forms shown below can also be adopted.

(Second form)
[Constitution]
FIG. 2 is a schematic cross-sectional view showing another preferred embodiment of the CO selective oxidation catalyst of the present invention (also referred to as “second embodiment” in the present specification). The 2nd form differs in the containing form of a platinum atom and a cobalt atom (cobalt aluminate) compared with said 1st form.

  As shown in FIG. 2, in the CO selective oxidation catalyst 10 of the second embodiment, cobalt aluminate particles 40 are supported on the surface of the inorganic carrier 20, and further, platinum particles 30 are supported on the surface of the cobalt aluminate particles 40. Have a configuration. For convenience of explanation, the dimensional ratio of each component of the CO selective oxidation catalyst shown in FIG. 2 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 20, but these micropores are omitted in FIG. Furthermore, when the form similar to the form described in the description column of the first form is adopted, a duplicate description is omitted.

  The preferable form of the platinum particles 30 in the second embodiment of the present invention is the same as that described in the description of the first embodiment.

As described above, in the second embodiment, the platinum particles 30 are supported on the surface of the cobalt aluminate particles 40. The cobalt aluminate particles 40 are particles made of cobalt aluminate (Al ₂ CoO ₄ ). However, in some cases, other materials such as Co ₃ O ₄ may be included in the cobalt aluminate particles 40 in an amount of about 1 to 10% by mass.

  There is no particular limitation on the average particle size of the cobalt aluminate particles 40. However, it is usually about 0.1 to 2 μm, preferably 0.1 to 1 μm, and more preferably 0.5 to 1 μm. If the average particle size of the cobalt aluminate particles 40 is too small, the cobalt aluminate particles 40 may be easily aggregated, which may cause a decrease in the dispersibility of platinum. On the other hand, if the average particle size of the cobalt aluminate particles 40 is too large, the dispersibility is deteriorated, and similarly, the platinum aggregates and there is a possibility that sufficient performance may not be exhibited.

  In the first embodiment, the case where the main component of the inorganic carrier is alumina has been described as an example. However, in the second embodiment, the form of the inorganic carrier 20 is not particularly limited, and is conventionally known in the catalyst preparation field. An inorganic carrier is preferably used. Examples of the inorganic carrier 20 include metal oxides such as titania, silica, silica alumina, zirconia, magnesia, and zeolite in addition to the various aluminas described above. Only one of these may be used alone, or a mixture thereof may be used. Among these, from the viewpoint of catalyst activity, availability of raw materials, ease of production and handling of the support, the main component of the inorganic support 20 is preferably alumina. In addition, the specific surface area, average particle diameter, and other preferable forms of the inorganic carrier 20 are the same as the forms described in the description of the first form.

  The preferable form of each content of platinum atom and cobalt atom and the ratio of these contents is the same as the form described in the column of the explanation of the first form.

  Also in the second form, similarly to the first form, metal atoms other than platinum atoms and cobalt atoms can be contained as catalyst metals. The types and amounts of metal atoms contained in addition to platinum atoms and cobalt atoms are the same as those described in the description of the first embodiment. These metal atoms may be supported on the cobalt aluminate particles 40 in the form of an alloy with platinum, or may be included in the cobalt aluminate particles 40.

  In some cases, the platinum-supported cobalt aluminate particles may be directly used as a CO selective oxidation catalyst without being supported on an inorganic carrier.

[Action and effect]
In the CO selective oxidation catalyst of the second form shown in FIG. 2, platinum particles 30 are further supported on the cobalt aluminate particles 40 supported on the surface of the inorganic carrier 20 as described above. With such a configuration, the platinum particles 30 are not covered with other components. For this reason, the platinum particles 30 can sufficiently adsorb CO. Further, cobalt atoms are present on the surface of the inorganic carrier 20 as cobalt aluminate particles 40. For this reason, the oxidation of CO adsorbed by platinum atoms to CO ₂ can be sufficiently promoted.

  Therefore, both the mechanisms of CO adsorption by platinum atoms and promotion of CO oxidation by cobalt atoms can proceed efficiently even by the second form of the CO selective oxidation catalyst. As a result, a CO selective oxidation catalyst having excellent catalytic activity can be provided.

[Production method]
The CO selective oxidation catalyst of the second form can be produced, for example, by supporting platinum particles on the surface of cobalt aluminate particles and dispersing the obtained platinum-supported cobalt aluminate particles on the surface of an inorganic support. Hereinafter, such a manufacturing method will be described in the order of steps.

[Cobalt aluminate particle preparation process]
First, cobalt aluminate particles are prepared. Since the preferable form of the cobalt aluminate particles prepared in this step is as already described, the description is omitted here.

  As the cobalt aluminate particles, those prepared by themselves may be used, and when the product is commercially available, the product may be purchased and used.

  When cobalt aluminate particles are prepared by themselves, for example, a coprecipitation method can be used. Hereinafter, a specific method for preparing cobalt aluminate particles by a coprecipitation method will be described (see also Example 2 described later). Of course, cobalt aluminate particles may be prepared by other methods.

  First, a cobalt compound that is a cobalt raw material and an aluminum compound that is an aluminum raw material are prepared. Furthermore, a solvent for dissolving these compounds is prepared. Thereafter, the cobalt compound and the aluminum compound are added to the prepared solvent and stirred as necessary to prepare a cobalt-aluminum solution.

  As a cobalt compound which is a cobalt raw material, the compound mentioned above in the column of preparation of the inorganic support | carrier containing cobalt aluminate can be used similarly. Moreover, the aluminum compound which is an aluminum raw material also includes a compound in the form of a metal salt similarly to the cobalt raw material, and examples thereof include aluminum nitrate, aluminum sulfate, and aluminum chloride.

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

The concentration of cobalt and aluminum in the cobalt-aluminum solution is not particularly limited, but can be appropriately adjusted by taking into consideration the amount of inorganic carrier and platinum particles used for preparing the catalyst and the loading method. In consideration of the composition of cobalt aluminate (Al ₂ CoO ₄ ), it is possible to adjust the molar ratio of cobalt atoms to aluminum atoms in the cobalt-aluminum solution to about 1: 2, from the viewpoint of manufacturing cost and the like. preferable.

  Here, when it is desired to contain a metal atom other than cobalt atom as a catalyst metal in the cobalt aluminate particles, a desired component may be added to the cobalt-aluminum solution in a desired amount in this step. At this time, the desired component may be added to the solvent in the form of a metal salt.

  Next, a suitable precipitant is added to the cobalt-aluminum solution prepared above to obtain a precipitate containing cobalt and aluminum.

  Examples of the precipitating agent include basic compounds. Examples of the basic compound include ammonia, urea, sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate and the like. These may be used alone or in combination of two or more.

  The precipitant may be added to the cobalt-aluminum solution in the form of a granular or powdery solid, but if added in the form of an aqueous solution, the operation is simple. When the precipitant is added in the form of an aqueous solution, the concentration of the basic compound in the aqueous precipitant solution is not particularly limited. Moreover, there is no restriction | limiting in particular also about the addition amount of the precipitant to a cobalt-aluminum solution, According to the quantity of the desired deposit, it can adjust suitably. If necessary, the precipitate may be purified by filtration and washing. Furthermore, you may dry the obtained precipitate as needed. As a specific method of drying, the above-described form can be similarly adopted.

  Thereafter, the precipitate obtained above is fired. Thereby, cobalt aluminate particles are obtained.

  There is no restriction | limiting in particular about the specific method and baking conditions of baking, A conventionally well-known knowledge can be referred suitably. Taking an example of the firing conditions, the firing temperature is preferably 700 to 900 ° C., more preferably 750 to 800 ° C., and the firing time is preferably 1 to 6 hours, more preferably 2 to 4 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 cobalt aluminate particles may be pulverized and sieved to select only particles having a desired particle diameter.

[Platinum loading process]
Next, platinum particles are supported on the surface of the cobalt aluminate particles prepared in the above [Cobalt aluminate particle preparation step]. Thereby, the platinum carrying | support cobalt aluminate particle by which the platinum particle was carry | supported on the surface of the cobalt aluminate particle is obtained.

  About the detail of this process, it replaces with an inorganic support | carrier, and the cobalt aluminate particle prepared above is used, In the column of [Platinum support process] of the manufacturing method of the CO selective oxidation catalyst of 1st form of this invention. It is the same as that of the form demonstrated.

[Platinum-supported cobalt aluminate particle dispersion process]
Subsequently, the platinum-supported cobalt aluminate particles obtained in the above [Platinum support step] are dispersed on the surface of the inorganic support. Thereby, the CO selective oxidation catalyst of the second embodiment of the present invention is completed.

  In this step, the platinum-supported cobalt aluminate particles and inorganic support obtained above are prepared. Since the preferable form of the prepared inorganic carrier is as already described, the description is omitted here.

  A specific method of dispersion is not particularly limited, and a conventionally known method can be appropriately employed. Under the present circumstances, the quantity of the platinum carrying | support cobalt aluminate particle and inorganic support | carrier used can be suitably adjusted by considering the final content of the platinum atom and cobalt atom in the catalyst obtained. As an example of the dispersion method, for example, platinum-supported cobalt aluminate particles and inorganic carrier particles are mixed, dry or added with water and wetted with an alumina ball having a diameter of about 5 mm in a pot mill container, and pulverized and mixed by vibration The technique to do is illustrated.

(Third form)
[Constitution]
FIG. 3 is a schematic cross-sectional view showing still another preferred form (also referred to as “third form” in the present specification) of the CO selective oxidation catalyst of the present invention. The 3rd form also differs in the containing form of a platinum atom and a cobalt atom (cobalt aluminate) compared with said 1st form and 2nd form.

  As shown in FIG. 3, the CO selective oxidation catalyst 10 of the third embodiment has a configuration in which platinum catalyst particles 50 in which platinum particles 30 are supported on the surface of an inorganic carrier 20 and cobalt aluminate particles 40 are mixed. . For convenience of explanation, the dimensional ratio of each component of the CO selective oxidation catalyst shown in FIG. 3 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 20, but these micropores are omitted in FIG. Furthermore, when the form similar to the form described in the description column of the first form and the second form is adopted, the overlapping explanation is omitted.

  The preferable form of the platinum particles 30 in the third form of the present invention is also the same as the form described in the description of the first form.

  As shown in FIG. 3, in the third embodiment, platinum particles 30 are supported on the surface of the inorganic carrier 20 to constitute platinum catalyst particles 50. A preferred form of the inorganic carrier 20 on which the platinum particles 30 are supported is the same as the form described in the description of the second form. However, in the third embodiment, the average particle size of the inorganic carrier 20 is preferably 1 to 4 μm, more preferably 2 to 3 μm.

  In some cases, an inorganic carrier having a cobalt aluminate layer on the surface as described in the description of the first embodiment may be used as the inorganic carrier 20 of the third embodiment. In other words, such a form can be said to be a form in which the CO selective oxidation catalyst of the first aspect of the present invention is further mixed with cobalt aluminate particles.

  In the third form, the preferred form of the cobalt aluminate particles 40 mixed with the platinum catalyst particles 50 is the same as the form described in the description of the second form. Here, in the third embodiment, in consideration of the mixing properties of the platinum catalyst particles 50 and the cobalt aluminate particles 40, the average particle diameter of the cobalt aluminate particles 40 may be made smaller than that of the second embodiment, preferably It is 0.1-1.5 micrometers, More preferably, it is 0.1-1 micrometer, More preferably, it is 0.5-1 micrometer. However, the technical scope of the present invention is not limited only to the form having such a particle size.

  The preferable form of each content of platinum atom and cobalt atom and the ratio of these contents is the same as the form described in the column of the explanation of the first form.

  In the third form, similarly to the first form, metal atoms other than platinum atoms and cobalt atoms may be contained. The types and amounts of metal atoms contained in addition to platinum and cobalt are the same as those described in the description of the first embodiment. These metal atoms may be supported on the inorganic carrier 20 in the form of an alloy with platinum or may be included in the cobalt aluminate particles 40.

[Action and effect]
In the third embodiment of the CO selective oxidation catalyst shown in FIG. 3, the platinum particles 30 are supported on the surface of the inorganic carrier 20 separately from the cobalt component to constitute the platinum catalyst particles 50 as described above. With such a configuration, the platinum particles 30 are not covered with other components. For this reason, the platinum particles 30 can sufficiently adsorb CO. Cobalt atoms are also present separately from the platinum catalyst particles 50 in the form of cobalt aluminate particles 40. For this reason, the oxidation of CO adsorbed by platinum atoms to CO ₂ can be sufficiently promoted.

  Therefore, both the mechanisms of CO adsorption by platinum atoms and promotion of CO oxidation by cobalt atoms can proceed efficiently even by the third embodiment of the CO selective oxidation catalyst. As a result, a CO selective oxidation catalyst having excellent catalytic activity can be provided.

[Production method]
The CO selective oxidation catalyst of the third form is produced by, for example, preparing platinum catalyst particles by supporting platinum particles on the surface of an inorganic carrier, and mixing the obtained platinum catalyst particles and cobalt aluminate particles. sell. Hereinafter, such a manufacturing method will be described in the order of steps.

[Platinum loading process]
First, platinum particles are supported on the surface of an inorganic carrier. Thereby, platinum catalyst particles are prepared.

  The details of this step are those of [Platinum supporting step] of the method for producing a CO selective oxidation catalyst according to the first embodiment of the present invention, except that the inorganic carrier is the one described in the above [Configuration] column. This is the same as the form described in the column.

[Mixing process]
Subsequently, the platinum catalyst particles prepared above and cobalt aluminate particles are mixed. Thereby, the CO selective oxidation catalyst according to the third embodiment of the present invention is completed.

  In this step, first, the platinum catalyst particles prepared above and cobalt aluminate particles are prepared.

  The preferred form of the cobalt aluminate particles prepared in this step is the same as the form described in [Cobalt aluminate particle preparation step] in [Manufacturing method] of the second aspect of the present invention.

  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 platinum catalyst particles and cobalt aluminate particles to be mixed can be appropriately adjusted by considering the final content of platinum atoms and cobalt atoms in the obtained catalyst. As an example of the mixing method, a method similar to the example of the second embodiment is illustrated, and thus detailed description thereof is omitted here.

(CO concentration reduction device)
The CO selective oxidation catalyst of the present invention is disposed, for example, in a CO concentration reduction device. The CO concentration reduction apparatus in which the CO selective oxidation 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 solid polymer fuel cell. Therefore, the present application provides a CO concentration reduction device for a polymer electrolyte fuel cell, in which the CO selective oxidation catalyst of the present invention described above is disposed. In addition, the form in particular at the time of arrange | positioning the CO selective oxidation catalyst of this invention in a CO concentration reduction 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 CO selective oxidation 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 CO concentration reduction apparatus is integrated with the heat exchanger, the CO selective oxidation catalyst of the present invention may be applied to the fins of the heat exchanger.

  Hereinafter, the CO concentration reducing apparatus of the present invention will be described in detail with reference to the drawings. FIG. 4 is a schematic diagram of a fuel cell system 100 in which a CO concentration reducing device in which the CO selective oxidation catalyst of the present invention is disposed is used.

  First, a fuel such as a hydrocarbon is supplied to the reforming unit 110. In the reforming unit 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 reforming unit 110 is sent to the shift reaction unit 120 to reduce the CO concentration in the reformed gas to about 1% by volume. The reformed gas whose CO concentration has been reduced to about 1% by volume is then sent to the CO concentration reducing device 130 for a polymer electrolyte fuel cell of the present invention, in which the CO selective oxidation catalyst 10 of the present invention is disposed. , CO concentration is reduced to the order of ppm.

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

  As described above, the CO selective oxidation catalyst of the present invention exhibits excellent CO removal performance even in a low temperature region. 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, the preferred use of the CO selective oxidation catalyst of the present invention has been described by taking as an example the case where the CO selective oxidation catalyst of the present invention is used in a fuel cell system arranged in a CO concentration reducing device for a polymer electrolyte fuel cell. The use of the oxidation catalyst is not limited to this, and can be applied to any use for oxidizing and removing trace amounts of CO. Applications other than those described above for the CO selective oxidation catalyst of the present invention include, for example, CO removal in a sealed 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 by the following examples.

(Example 1: 1st form)
A CO selective oxidation catalyst having the form shown in FIG. 1 (first form) was prepared by the following method.

[Inorganic carrier preparation step]
An unfired powder of boehmite alumina was prepared as an alumina raw material. Further, a predetermined amount of cobalt nitrate as a cobalt raw material was added to distilled water as a solvent and stirred to prepare a cobalt solution. Next, the prepared boehmite alumina powder was impregnated in the cobalt solution, and cobalt atoms were supported on the boehmite alumina. Further, after boehmite alumina supporting cobalt atoms was dried at 120 ° C. for 24 hours or more, it was baked at 800 ° C. for 5 hours in an electric furnace to form an inorganic carrier (alumina with cobalt aluminate formed on the surface). Prepared. The average particle size of the obtained inorganic carrier was about 5 μm. Moreover, the production | generation of cobalt aluminate was confirmed by the surface of the obtained inorganic support | carrier exhibiting the light blue color tone.

[Platinum loading process]
Dinitrodiammine platinum was prepared as a platinum raw material, and a predetermined amount thereof was added to distilled water as a solvent and stirred to prepare a platinum solution. Next, the inorganic carrier powder prepared above was impregnated in the platinum solution, and platinum atoms were supported on the inorganic carrier. Further, after drying an inorganic carrier carrying platinum atoms at 120 ° C. for 24 hours or more, it is fired in an electric furnace at 460 ° C. for 2 hours to grow platinum particles on the surface of the inorganic carrier, and the present invention Thus, a CO selective oxidation catalyst of the first form was obtained. In addition, content of the platinum atom and cobalt atom with respect to the whole quantity of the catalyst obtained was controlled by adjusting the quantity of a platinum raw material and a cobalt raw material. The specific surface area of the obtained catalyst was measured by the BET method.

  The values of the specific surface area of the catalyst measured above are shown in Table 1 below together with the content values of the platinum atoms and cobalt atoms. Further, the value of the mass ratio of cobalt atoms (Co / Pt + Co) to the total amount of platinum atoms and cobalt atoms, calculated from these values, and the mole of cobalt atom content to the platinum atom content The value of the ratio (Co / Pt) is similarly shown in Table 1 below.

(Example 2: Second embodiment)
A CO selective oxidation catalyst having the form shown in FIG. 2 (second form) was prepared by the following method.

[Cobalt aluminate particle preparation process]
Cobalt aluminate particles were prepared by a coprecipitation method. First, as raw materials for cobalt aluminate, cobalt nitrate as a cobalt raw material and aluminum nitrate as an aluminum raw material were prepared. These predetermined amounts were simultaneously added to distilled water as a solvent and stirred to prepare a cobalt-aluminum solution. Next, a 2.5% aqueous ammonia solution was gradually added dropwise to the cobalt-aluminum solution to form a precipitate. The resulting precipitate was filtered and washed with distilled water. The precipitate was dried at 120 ° C. for 24 hours or more and then baked in an electric furnace at 780 ° C. for 5 hours to prepare cobalt aluminate exhibiting a light blue color tone. In addition, the average particle diameter of the obtained cobalt aluminate was 2.3 μm.

[Platinum loading process]
A platinum solution was prepared in the same manner as in Example 1. Next, the cobalt aluminate powder prepared above was impregnated in the platinum solution, and platinum atoms were supported on the cobalt aluminate. Furthermore, after the cobalt aluminate supporting platinum atoms was dried at 120 ° C. for 8 hours, the cobalt aluminate was baked in an electric furnace at 460 ° C. for 2 hours to grow platinum particles on the surface of the cobalt aluminate particles, A platinum-supported cobalt aluminate was obtained.

[Platinum-supported cobalt aluminate particle dispersion process]
As an inorganic carrier material, an unfired boehmite alumina powder similar to that in Example 1 was prepared. This inorganic carrier raw material was fired by the same method as in Example 1 except that no cobalt atom was supported, to prepare an inorganic carrier (alumina). The average particle size of the obtained inorganic carrier was 4.4 μm.

  The platinum-supported cobalt aluminate prepared above was dispersed on the surface of the inorganic support prepared as above to prepare a CO selective oxidation catalyst. Specifically, it was dispersed by wet pulverization mixing using an alumina ball mill having a diameter of 5 mm to obtain a CO selective oxidation catalyst according to the second embodiment of the present invention. In addition, the platinum and cobalt content with respect to the total amount of the obtained catalyst was controlled by adjusting the amount of the platinum raw material and the cobalt raw material. The specific surface area of the obtained catalyst was measured by the BET method. Along with these values, parameters calculated in the same manner as in Example 1 are shown in Table 1 below.

(Examples 3-7: 1st form)
The first method of the present invention was performed using the same method as in Example 1 except that the firing temperature at the time of preparing the inorganic support and the contents of platinum atoms and cobalt atoms were set to the values shown in Table 1 below. A form of CO selective oxidation catalyst was prepared. Further, as in Example 1, the specific surface area was measured by the BET method. In addition to these values, parameters calculated in the same manner as in Example 1 are shown in Table 1 below.

(Comparative Example 1)
A CO selective oxidation catalyst was prepared in the same manner as in Example 1 except that the inorganic carrier (alumina) prepared in Example 2 was used as the inorganic carrier. Further, as in Example 1, the specific surface area was measured by the BET method. The parameters that can be calculated are shown in Table 1 below.

(Comparative Example 2)
A CO selective oxidation catalyst was prepared by supporting cobalt atoms and platinum atoms on an inorganic support by a sequential impregnation method.

  Specifically, first, boehmite alumina, which is an alumina raw material, was impregnated in the same cobalt solution as in Example 1, and dried at 120 ° C. for 24 hours or more to support cobalt atoms on boehmite alumina. Next, the obtained cobalt-supported boehmite alumina was impregnated with the same platinum solution as in Example 1 and dried at 120 ° C. for 24 hours or more to further support platinum atoms on the cobalt-supported boehmite alumina. Then, it baked at 500 degreeC for 2 hours in the electric furnace, and obtained the CO selective oxidation catalyst. In addition, since the obtained catalyst did not exhibit light blue color tone, it was confirmed that no cobalt aluminate was produced in this comparative example. Moreover, the platinum and cobalt content with respect to the total amount of the obtained catalyst was controlled by adjusting the amount of the platinum raw material and the cobalt raw material. Furthermore, the specific surface area of the obtained catalyst was measured by the BET method. Along with these values, parameters calculated in the same manner as in Example 1 are shown in Table 1 below.

(Test example)
The powder of the CO selective oxidation catalyst prepared in Example 1 was sieved using a 30 to 45 ASTM mesh, and 0.04 g thereof was weighed. On the other hand, silica sand was sieved using 18-35 ASTM mesh, and 0.21 g thereof was weighed.

  The catalyst powder and silica sand sieved and weighed above were mixed and filled in a quartz reaction tube (inner diameter: 4 mm) to obtain a catalyst sample.

To catalyst sample obtained above, the model gas _(H 2: 32 vol%, _CO 2: 15 _vol%, H 2 O: 33 vol%, CO: 0.9 _vol%, O 2: 1.0 vol %, He: remaining) was supplied so that the gas space velocity (total gas flow rate (cm ³ / h) / catalyst sample volume (cm ³ )) was 100,000 h ^−1, and a CO removal test was performed. The reaction temperature was maintained at 170 ° C., and the CO concentration in the outlet gas of the catalyst sample was measured. Based on this, the CO conversion was calculated by the following formula 1.

  That is, it can be said that the higher the CO conversion rate, the better the CO removal performance.

  In this embodiment, the catalyst powder is diluted with silica sand for the purpose of preventing clogging of the catalyst powder in the reaction tube.

  For the CO selective oxidation catalysts prepared in Examples 2 to 7 and Comparative Examples 1 and 2, a catalyst sample was prepared in the same manner as described above, a CO removal test was performed, and the CO conversion rate was calculated. The values of CO conversion calculated for each example and each comparative example are shown in Table 2 below.

  From the results in Table 2, it is shown that the CO conversion can be improved by adding cobalt atoms in the form of cobalt aluminate in addition to platinum atoms. It can also be seen that an excellent CO conversion rate can be exhibited by the CO selective oxidation catalyst of any of the first form shown in FIG. 1 and the second form shown in FIG.

It is a schematic cross section which shows one preferable form (1st form) of the CO selective oxidation catalyst of this invention. It is a schematic cross section which shows another preferable form (2nd form) of the CO selective oxidation catalyst of this invention. It is a schematic cross section which shows another preferable one form (3rd form) of the CO selective oxidation catalyst of this invention. 1 is a schematic view of a fuel cell system in which a CO concentration reduction device in which a CO selective oxidation catalyst of the present invention is arranged is used.

Explanation of symbols

10 CO selective oxidation catalyst,
20 inorganic carrier,
22 Alumina,
24 cobalt aluminate layer,
30 platinum particles,
40 cobalt aluminate particles,
50 platinum catalyst particles,
100 fuel cell system,
110 reforming section,
120 shift reaction part,
130 CO concentration reduction device for polymer electrolyte fuel cell,
140 polymer electrolyte fuel cell,
150 combustion section,
160 Evaporation part.

Claims (9)

A carbon monoxide selective oxidation catalyst containing a platinum atom,
A carbon monoxide selective oxidation catalyst comprising cobalt atoms in the form of cobalt aluminate.   The carbon monoxide selective oxidation catalyst according to claim 1, wherein the cobalt aluminate is contained in an inorganic carrier on which platinum particles made of the platinum atoms are supported.   The carbon monoxide selective oxidation catalyst according to claim 2, wherein the inorganic carrier has a cobalt aluminate layer made of cobalt aluminate on a surface layer thereof.   The carbon monoxide selective oxidation catalyst according to any one of claims 1 to 3, wherein a mass ratio of the cobalt atom to a total amount of the platinum atom and the cobalt atom is more than 70% by mass and less than 100% by mass. .   The carbon monoxide selective oxidation catalyst according to any one of claims 1 to 4, wherein a molar ratio of the cobalt atom content to the platinum atom content is 8 to 65.   The carbon monoxide selective oxidation catalyst according to any one of claims 1 to 5, wherein a content of the platinum atom with respect to the total amount of the catalyst is 0.2 to 2.5 mass%.   The carbon monoxide selective oxidation catalyst according to any one of claims 1 to 6, wherein a content of the cobalt atom with respect to the total amount of the catalyst is 0.6 to 12% by mass. Preparing an inorganic carrier containing cobalt aluminate;
A step of supporting platinum particles on the inorganic carrier;
The manufacturing method of the carbon monoxide selective oxidation catalyst which has these. Preparing an inorganic support containing the cobalt aluminate,
A step of supporting cobalt atoms on the alumina raw material;
Firing the alumina material carrying the cobalt atoms to obtain alumina with cobalt aluminate formed on the surface;
The manufacturing method of Claim 8 which has these.