JP2006341206A - Carbon monoxide selective oxidation catalyst and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for improving much more the CO selective oxidation activity of a platinum component-containing CO selective oxidation catalyst under a low temperature condition by causing a low-temperature-active component to achieve a sufficient working result. <P>SOLUTION: Cuprous oxide is furthermore incorporated in the CO selective oxidation catalyst obtained by depositing the platinum atom-containing platinum component on an inorganic carrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 low-pollution power sources 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 a problem, an attempt has been made to improve CO selective oxidation activity in a low temperature region by further adding a transition metal atom such as a copper atom or an iron atom in addition to a platinum atom as a low temperature activation component ( 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 a catalyst is prepared by such a method, there is a problem that a sufficient activity improvement effect is not always obtained. In other words, the temperature range of the low temperature activation component and the platinum component may be separated, or one component is coated with the other component on the surface of the inorganic carrier on which the catalyst component is supported. In other words, the effect cannot be fully exhibited.

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

The present inventor has conducted intensive research to solve the above-described problems, and searched for a preferable component as a low-temperature activation component in the process. As a result, it has been found that when cuprous oxide (Cu ₂ O) containing a monovalent copper atom is employed as a low-temperature activation component, CO selective oxidation activity under low-temperature conditions can be improved, and the present invention is completed. It came.

  That is, the present invention is a carbon monoxide selective oxidation catalyst in which a platinum component containing a platinum atom is supported on an inorganic carrier, further comprising cuprous oxide, and a carbon monoxide selective oxidation catalyst characterized in that It is.

  Moreover, this invention is a manufacturing method of the carbon monoxide selective oxidation catalyst which has the process of preparing the inorganic support | carrier containing cuprous oxide, and carrying | supporting the platinum component containing a platinum atom on the said inorganic support | carrier. .

  According to the CO selective oxidation catalyst of the present invention, cuprous oxide added in addition to the platinum component can sufficiently function as a low temperature activation component. Therefore, according to the present invention, a CO selective oxidation catalyst having excellent CO selective oxidation activity under low temperature conditions can be provided.

  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 a copper atom among these transition metal atoms, and conducted earnest research in order to further improve the catalytic activity of the CO selective oxidation catalyst. As a result, it has been found that when a copper atom is contained in the form of cuprous oxide, the CO selective oxidation activity under low temperature conditions can be improved.

Note that the mechanism by which CO selective oxidation activity is improved by the addition of cuprous oxide (Cu ₂ O) containing a monovalent copper atom has not yet been clarified. However, the presence of cuprous oxide 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 . Presumed to be. In addition, it has been estimated that a mechanism in which electrons are attracted from a platinum atom to a copper atom due to the presence of a copper 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 preferred preparation method, when a platinum selective component and a copper component are simultaneously supported on an inorganic carrier, a CO selective oxidation catalyst containing platinum and copper atoms is produced. 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, copper atoms are similarly supported on the surface of the inorganic carrier as copper atom metal particles or oxide (eg, copper oxide) particles. At this time, when attention is paid to one particle of the inorganic carrier, a platinum component and a copper component coexist on the surface of the inorganic carrier particle. In many cases, it is considered that platinum metal particles and copper oxide are 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 copper component such as copper oxide. Or conversely, the copper 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 attempted to control the existence state of the platinum component and the copper component on the surface of the inorganic carrier. Specifically, by containing copper atoms in the form of cuprous oxide (Cu ₂ O), it is possible to prevent the platinum component and the copper component from being simultaneously supported on the inorganic carrier, and the above-described problem due to the coating described above. I tried to solve the problem.

That is, the first of the present invention is a carbon monoxide selective oxidation catalyst in which a platinum component containing a platinum atom is supported on an inorganic carrier, and further containing cuprous oxide, carbon monoxide It is a selective oxidation catalyst. 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. Then, characterized in that the copper atoms contained in the form of cuprous oxide (Cu 2 _O). 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 a platinum component 30 is supported on the surface of an inorganic carrier 20. The inorganic carrier 20 contains alumina 22 as a main component. Furthermore, inorganic carrier 20 has on its surface, with a cuprous _(Cu 2 O) layer 24 oxide made of cuprous oxide _(Cu 2 O). 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 component 30 is a catalyst component consisting only of platinum atoms. However, the platinum component 30 is not limited to a component composed of only platinum atoms, and for example, a component composed of platinum oxide (platinum monoxide (PtO), platinum dioxide (PtO ₂ ), etc.) or a mixture of platinum and platinum oxide. Or a component 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.

  The shape of the platinum component is not particularly limited and may be any shape such as a spherical shape, a needle shape, a cubic shape, and an indefinite shape, but the platinum component is preferably a spherical shape.

In the first form, the inorganic carrier 20 is mainly composed of alumina 22 as described above, and has a cuprous oxide (Cu ₂ O) 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.

“Cuprous oxide (Cu ₂ O)” is an oxide of copper containing monovalent copper. The presence of cuprous oxide (Cu ₂ O) in the catalyst can be confirmed by an X-ray diffraction method.

In the form shown in FIG. 1, the cuprous oxide (Cu ₂ O) layer 24 is formed on the entire surface of the inorganic carrier 20, but it is not limited to such a form. For example, a form in which a cuprous oxide (Cu ₂ O) 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, and β alumina. 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 35-120 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 component 30 and cuprous oxide (Cu ₂ O) during production of the catalyst may deteriorate, and the catalytic activity may be reduced. On the other hand, if the specific surface area of the inorganic carrier 20 is too large, the platinum component 30 is not sufficiently supported on the cuprous oxide (Cu ₂ O) layer 24 present on the surface layer of the inorganic carrier 20 in some cases, and the catalytic activity is also the same. May 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 5 μm, more preferably 1.0 to 3.5 μm, and still 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 cuprous oxide (Cu ₂ O) layer 24 formed on the surface layer of the inorganic carrier 20 is not particularly limited. However, the thickness of the cuprous oxide (Cu ₂ O) layer 24 is preferably as thin as several nm to 0.5 μm. The thickness of the cuprous oxide (Cu ₂ O) layer 24 can be appropriately controlled by adjusting the copper atom content, the copper concentration in the copper solution at the time of catalyst preparation, the pH of the solution, and the like.

In the form shown in FIG. 1, cuprous oxide (Cu ₂ O) exists only on the surface layer of the inorganic carrier 20. However, it is not restricted only to such a form, and cuprous oxide (Cu ₂ O) may exist in the alumina 22 inside the inorganic support 20 depending on the case.

The area ratio of the portion where the cuprous oxide (Cu ₂ O) layer 24 occupies the surface area of the inorganic carrier 20 is preferably as high as 50 to 100%, for example. In the form shown in FIG. 1 (first form), since the cuprous oxide (Cu ₂ O) layer 24 is formed on the entire surface of the inorganic carrier 20, the area ratio is 100%. Here, when this area ratio is too small, there is a possibility that the effect due to the inclusion of copper 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 cuprous oxide (Cu ₂ O) layer 24 can be formed on the surface, a compound other than alumina is used. May be used as the main component of the inorganic carrier 20. 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 component for adsorbing CO and a copper component that promotes 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 monovalent copper atom to the total amount of the platinum atom and the monovalent copper atom in the cuprous oxide is preferably 50 mass. % And less than 100% by mass, more preferably 80 to 90% by mass, and still more preferably 80 to 85% by mass. In other words, in the CO selective oxidation catalyst of the present invention, the molar ratio (Cu / Pt) of the content of monovalent copper atoms in the cuprous oxide to the content of platinum atoms is preferably Is 3 to 65, more preferably 11 to 20. When these values are within the above range, the balance between the CO adsorption effect by the platinum atoms and the CO oxidation promotion effect by the monovalent copper 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 monovalent copper atom in the CO selective oxidation catalyst of the present invention is not particularly limited, but the platinum atom content is preferably relative to the total amount of the catalyst. About 0.2-3.0 mass%, More preferably, it is 0.4-2.0 mass%. Similarly, the content of monovalent copper atoms is preferably about 0.6 to 12% by mass, more preferably 1.5 to 10% by 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 copper 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 total amount of platinum atoms is about 0.4 to 2.0% by mass, and the monovalent copper atoms are about 1.5 to 10.0% by mass. 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 if the monovalent copper atom is about 0.5 to 5.0% by mass, about -1.0% by mass. In addition, in this application, content of a platinum atom and a copper atom means the quantity converted into a metal atom unless there is particular notice. The above-mentioned various values related to the platinum and copper contents are calculated from the amounts of platinum raw material and copper 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 support 20 as particles similar to the platinum component 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 cobalt, manganese, nickel, and iron may be contained. As long as the effects of the present invention are not impaired, a divalent copper atom may be contained in some cases. These atoms are preferably contained in a form that does not cover the platinum component 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 a perovskite oxide. The amount of metal atoms other than platinum atoms and monovalent copper 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 first embodiment of the CO selective oxidation catalyst shown in FIG. 1, as described above, the platinum component 30 is supported on the cuprous oxide (Cu ₂ O) layer 24 formed on the surface layer of the inorganic carrier 20. Yes. According to such a configuration, the platinum component 30 is not covered with other components. For this reason, the platinum component 30 can fully adsorb CO. Further, copper atoms are present on the surface of the inorganic carrier 20 as cuprous oxide (Cu ₂ O) constituting the cuprous oxide (Cu ₂ O) 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 monovalent copper 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 step of preparing an inorganic carrier containing cuprous oxide (inorganic carrier preparation step), and a step of supporting a platinum component containing platinum atoms on the inorganic carrier (supporting step). And a method for producing a carbon monoxide selective oxidation catalyst. 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 cuprous oxide (Cu ₂ O) 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 cuprous oxide (Cu ₂ O), one prepared by itself may be used, and when the product is commercially available, the product may be purchased and used.

When an inorganic carrier containing cuprous oxide (Cu ₂ O) is prepared by itself, for example, an inorganic carrier raw material (for example, an alumina raw material) is supported with copper atoms and baked, whereby the surface is oxidized first. An inorganic carrier (for example, alumina) in which copper (Cu ₂ O) is generated may be obtained. Hereinafter, a specific method for preparing an inorganic carrier by such a method will be described by taking as an example the case where the main component of the inorganic carrier is alumina. However, it is of course possible to prepare the inorganic carrier by other methods.

  First, an alumina raw material for supporting copper 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 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 the alumina raw material prepared above.

  In the step of preparing the copper solution, first, a copper compound that is a copper raw material 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.

  Examples of the copper compound that is a copper 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 copper solution include water and ethanol, but are not limited thereto.

  The concentration of copper in the copper 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 copper 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 a copper atom in an inorganic support, a desired component may be added to the copper 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, the copper atoms dissolved in the copper 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 copper solution may be brought into contact at room temperature to 80 ° C. for about 0.5 to 8 hours.

  After carrying | supporting a copper atom on an alumina raw material, this is dried as needed. 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 supporting copper atoms is fired. Thus, inorganic carrier containing cuprous oxide (Cu 2 _O), specifically, cuprous oxide on the surface (Cu 2 _O) alumina produced 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. By firing under such relatively high temperature conditions, cuprous oxide (Cu ₂ O) can be generated while suppressing the generation of cupric oxide (CuO) to a minimum. 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, the platinum component is supported on the inorganic carrier prepared in the 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 a platinum component 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 copper atoms on an 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 by considering the final content of platinum atoms and copper 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, the platinum component grows 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 second embodiment differs from the first embodiment described above, containing the form of platinum component and the copper component (cuprous oxide (Cu 2 _O)) is different.

As shown in FIG. 2, in the CO selective oxidation catalyst 10 of the second form, a cuprous oxide (Cu ₂ O) component 40 is supported on the surface of the inorganic carrier 20, and the surface of the cuprous oxide component 40 is further supported. In which the platinum component 30 is supported. 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 component 30 in the second form of the present invention is the same as the form described in the description of the first form.

As described above, in the second embodiment, the platinum component 30 is supported on the surface of the cuprous oxide (Cu ₂ O) component 40. The cuprous oxide (Cu ₂ O) component 40 is made of cuprous oxide (Cu ₂ O). However, in some cases, other substances such as cobalt oxide (Co ₃ O ₄ ) may be included in the cuprous oxide (Cu ₂ O) component 40 in an amount of about 1 to 10% by mass.

The shape of the cuprous oxide (Cu ₂ O) component is not particularly limited, and may be any shape such as a spherical shape, a needle shape, a cubic shape, or an indefinite shape, but is preferably a spherical shape. When it is spherical, the average particle size of the cuprous oxide (Cu ₂ O) component 40 is not particularly limited. However, it is usually about 0.5 to 3.0 μm, preferably 0.3 to 2.0 μm, and more preferably 0.1 to 1.0 μm. If the average particle size of the cuprous oxide (Cu ₂ O) component 40 is too small, aggregation tends to occur, and the dispersibility of platinum may ultimately be deteriorated. On the other hand, if the average particle size of the cuprous oxide (Cu ₂ O) component 40 is too large, the dispersibility is poor, and aggregation of platinum may occur, so that sufficient catalyst performance may not be obtained.

  Also in the second form, the form of the inorganic support 20 is not particularly limited, and a conventionally known inorganic support is preferably used in the catalyst preparation field. 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 preferred forms of the respective contents of the platinum component and the cuprous oxide (Cu ₂ O) component and the ratio of these contents are the same as those described in the description of the first embodiment.

Also in the second form, similarly to the first form, metal atoms other than the platinum component and the cuprous oxide (Cu ₂ O) component can be contained as the catalyst metal. The types and amounts of metal atoms contained in addition to the platinum component and the cuprous oxide (Cu ₂ O) component are the same as those described in the description of the first embodiment. These metal atoms may be supported on the cuprous oxide (Cu ₂ O) component 40 in the form of an alloy with platinum, or may be included in the cuprous oxide (Cu ₂ O) component 40.

In some cases, the platinum-supported cuprous oxide (Cu ₂ O) component may be directly used as a CO selective oxidation catalyst without being supported on the inorganic carrier.

[Action and effect]
In the second embodiment of the CO selective oxidation catalyst shown in FIG. 2, as described above, the platinum component 30 is further supported on the cuprous oxide (Cu ₂ O) component 40 supported on the surface of the inorganic carrier 20. ing. With such a configuration, the platinum component 30 is not covered with other components. For this reason, the platinum component 30 can fully adsorb CO. The copper atoms are present on the surface of the inorganic carrier 20 as the cuprous oxide (Cu ₂ O) component 40. For this reason, the oxidation of CO adsorbed by platinum atoms to CO ₂ can be sufficiently promoted.

  Therefore, both the mechanism of CO adsorption by platinum atoms and promotion of CO oxidation by monovalent copper atoms can proceed efficiently even by the CO selective oxidation catalyst of the second form. 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 is, for example, a platinum component supported on the surface of a cuprous oxide (Cu ₂ O) component, and the obtained platinum-supported cuprous oxide (Cu ₂ O) component is used as an inorganic carrier. It can be produced by dispersing it on the surface. Hereinafter, such a manufacturing method will be described in the order of steps.

[Copper oxide (Cu ₂ O) component preparation step]
First, a cuprous oxide (Cu ₂ O) component is prepared. Since the preferable form of the cuprous oxide (Cu ₂ O) component prepared in this step has already been described, the description thereof is omitted here.

As the cuprous oxide (Cu ₂ O) component, one prepared by itself may be used, and when the product is commercially available, the product may be purchased and used.

When the cuprous oxide (Cu ₂ O) component is prepared by itself, for example, a coprecipitation method can be used. Hereinafter, a specific method for preparing a cuprous oxide (Cu ₂ O) component by a coprecipitation method will be described (see also Example 2 described later). However, it is of course possible to prepare the cuprous oxide (Cu ₂ O) component by other methods.

  First, a copper compound that is a copper raw material is prepared. Furthermore, a solvent for dissolving the copper compound is prepared. Thereafter, the copper compound is added to the prepared solvent, and stirred as necessary to prepare a copper solution.

The copper compound is a copper material, may compound described above it can be used as well in the field of preparation of the inorganic carrier containing cuprous oxide (Cu 2 _O).

  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 in the copper solution is not particularly limited, but can be appropriately adjusted in consideration of the amount of the inorganic carrier and platinum component used for the preparation of the catalyst and the loading method. In addition,
Here, when it is desired to contain a metal atom other than the copper atom in the cuprous oxide (Cu ₂ O) component, a desired component may be added to the copper 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, an appropriate precipitant is added to the copper solution prepared above to obtain a precipitate containing copper hydroxide.

  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 precipitating agent may be added to the copper 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 copper 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, cuprous oxide (Cu ₂ O) powder is 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 cuprous oxide (Cu ₂ O) may be pulverized and sieved to select only particles having a desired particle diameter.

[Platinum loading process]
Next, the prepared cuprous oxide (Cu 2 _O) the surface of the component in the [cuprous oxide (Cu 2 _O) component preparation step] above, supporting the platinum component. Thus, cuprous (Cu 2 _O) platinum supported cuprous oxide platinum component on the surface of the component is carried (Cu 2 _O) component oxide is obtained.

For details of this step, [Platinum] in the method for producing a CO selective oxidation catalyst according to the first embodiment of the present invention is used except that the cuprous oxide (Cu ₂ O) component prepared above is used instead of the inorganic carrier. This is the same as that described in the column “Supporting step”.

[Platinum-supported cuprous oxide (Cu ₂ O) component dispersion step]
Subsequently, the platinum-supported cuprous oxide (Cu ₂ O) component obtained in the above [Platinum support step] is 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 cuprous oxide (Cu ₂ O) component and the inorganic carrier 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. At this time, the platinum-supported cuprous oxide (Cu ₂ O) component and the amount of the inorganic carrier used are determined in consideration of the final content of the platinum component and the cuprous oxide (Cu ₂ O) component in the obtained catalyst. By doing so, it can be adjusted appropriately. Hereinafter, an example of a dispersion method will be described. For example, a platinum-supported cuprous oxide (Cu ₂ O) component and an inorganic carrier are mixed, charged in a pot mill container with alumina balls having a diameter of about 5 mm by dry or wet (for example, water is added), and vibrated. And a method of pulverizing and mixing.

(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. Third Embodiment also, as compared with the first embodiment and the second embodiment described above, containing the form of platinum component and cuprous oxide (Cu 2 _O) component are different.

As shown in FIG. 3, the third embodiment of the CO selective oxidation catalyst 10 includes a platinum catalyst component 50 in which a platinum component 30 is supported on the surface of an inorganic carrier 20 and a cuprous oxide (Cu ₂ O) component 40. It has a mixed configuration. 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 component 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, the platinum component 30 is supported on the surface of the inorganic carrier 20 to constitute the platinum catalyst component 50. A preferable form of the inorganic carrier 20 on which the platinum component 30 is supported is the same as the form described in the description of the second embodiment. However, in the third embodiment, the average particle size of the inorganic carrier 20 is preferably 1.0 to 4.0 μm, more preferably 2.0 to 3.0 μm.

In some cases, an inorganic carrier having a cuprous oxide (Cu ₂ O) layer on the surface layer as described in the description of the first embodiment may be used as the inorganic carrier 20 of the third embodiment. Good. In other words, it can be said that the CO selective oxidation catalyst of the first aspect of the present invention is further mixed with a cuprous oxide (Cu ₂ O) component.

In the third mode, the preferable mode of the cuprous oxide (Cu ₂ O) component 40 mixed with the platinum catalyst component 50 is the same as the mode described in the description of the second mode. Here, in the third embodiment, in consideration of the miscibility with the platinum catalyst component 50 and the cuprous oxide _(Cu 2 O) component 40, oxide compared to the second embodiment cuprous _(Cu 2 O) component 40 The average particle size is preferably slightly reduced, preferably 0.5 to 1.5 μm, more preferably 0.1 to 1.0 μm. However, the technical scope of the present invention is not limited only to the form having such a particle size.

The preferred forms of the respective contents of the platinum component and the cuprous oxide (Cu ₂ O) component and the ratio of these contents are the same as those described in the description of the first embodiment.

Also in the third embodiment, metal atoms other than the platinum component and the cuprous oxide (Cu ₂ O) component can be contained as in the first embodiment. The types and amounts of metal atoms contained in addition to the platinum component and the cuprous oxide (Cu ₂ O) component 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 cuprous oxide (Cu ₂ O) component 40.

[Action and effect]
In the CO selective oxidation catalyst of the third embodiment shown in FIG. 3, the platinum component 30 is supported on the surface of the inorganic carrier 20 separately from the cuprous oxide (Cu ₂ O) component, as described above, and the platinum catalyst component 50. With such a configuration, the platinum component 30 is not covered with other components. For this reason, the platinum component 30 can fully adsorb CO. The copper component is also present separately from the platinum catalyst component 50 in the form of a cuprous oxide (Cu ₂ O) component 40. For this reason, the oxidation of CO adsorbed by platinum atoms to CO ₂ can be sufficiently promoted.

  Therefore, both the mechanism of CO adsorption by the platinum component and promotion of CO oxidation by the monovalent copper atom 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 third form of the CO selective oxidation catalyst is prepared by, for example, preparing a platinum catalyst component powder by supporting a platinum component on the surface of an inorganic carrier, and the obtained platinum catalyst component powder and cuprous oxide (Cu ₂ O). It can be produced by mixing the component powders. Hereinafter, such a manufacturing method will be described in the order of steps.

[Platinum loading process]
First, a platinum component is supported on the surface of an inorganic carrier. Thereby, the powder of a platinum catalyst component is 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 component prepared above and the cuprous oxide (Cu ₂ O) component 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 component prepared above and a cuprous oxide (Cu ₂ O) component are prepared.

A preferred form of the cuprous oxide (Cu 2 _O) component is prepared in this step, the [cuprous (Cu 2 _O) component preparation step oxidation] of [Method] of the second aspect of the invention described above It is the same as that of the form demonstrated.

The specific method of mixing is not particularly limited, and conventionally known knowledge regarding mixing of powder components can be appropriately referred to. At this time, the amount of the platinum catalyst component and the cuprous oxide (Cu ₂ O) component to be mixed takes into consideration the final content of the platinum component and the cuprous oxide (Cu ₂ O) component in the obtained catalyst. By doing so, it can be adjusted appropriately. Incidentally, no particular limitation is imposed on the mixing method, the same method as [platinum supported cuprous oxide (Cu 2 _O) component dispersing step] in [Manufacturing Method] of the second aspect described above may be employed.

(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 reformer 110. In the 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 reformer 110 is sent to the shift reactor 120, and the CO concentration in the reformed gas is reduced 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. A combustor 150 is provided to combust the spent fuel and oxidant, the evaporator 160 uses the heat of combustion to evaporate water, and generates steam used in the 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 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 copper nitrate as a copper raw material was added to distilled water as a solvent and stirred to prepare a copper solution. Next, the prepared boehmite alumina powder was impregnated into the copper solution, and copper atoms were supported on the boehmite alumina. Further, after boehmite alumina supporting copper atoms was dried at 120 ° C. for 24 hours or more, it was calcined in an electric furnace at 800 ° C. for 5 hours to obtain an inorganic carrier (cuprous oxide (Cu ₂ O) on the surface). Was produced. The average particle size of the obtained inorganic carrier was about 5 μm. Further, generation of cuprous oxide (Cu 2 _O), the surface of the resulting inorganic carrier is confirmed by presenting with shades of light blue.

[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 monovalent copper atom with respect to the whole quantity of the catalyst obtained was controlled by adjusting the quantity of a platinum raw material and a copper 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 as measured above are shown in Table 1 below together with the content values of the platinum atoms and monovalent copper atoms. In addition, the value of the mass ratio of monovalent copper atoms (Cu / Pt + Cu) to the total amount of platinum atoms and monovalent copper atoms, calculated from these values, and the content of platinum atoms of 1 The value of the molar ratio (Cu / Pt) of the content of valent copper atoms is also 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.

[Copper oxide (Cu ₂ O) component preparation step]
Cuprous oxide (Cu ₂ O) was prepared by a coprecipitation method. First, copper nitrate which is a copper raw material was prepared. Then, this predetermined amount was added to distilled water as a solvent and stirred to prepare a copper nitrate solution. Next, a 2.5% aqueous ammonia solution was gradually added dropwise to the copper nitrate solution to form a copper hydroxide 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 a powder of cuprous oxide (Cu ₂ O) component exhibiting a light blue color tone. . In addition, the average particle diameter of the obtained cuprous oxide (Cu ₂ O) was 2.3 μm.

[Platinum loading process]
A platinum solution was prepared in the same manner as in Example 1. Subsequently, the powder of the cuprous oxide (Cu ₂ O) component prepared above was impregnated in the platinum solution, and platinum atoms were supported on the powder of the cuprous oxide (Cu ₂ O) component. Further, cuprous oxide (Cu ₂ O) supporting platinum atoms was dried at 120 ° C. for 8 hours, and then baked in an electric furnace at 460 ° C. for 2 hours to obtain cuprous oxide (Cu ₂ O). The platinum component was grown on the surface of) to obtain platinum-supported cuprous oxide (Cu ₂ O).

[Platinum-supported cuprous oxide (Cu ₂ O) component dispersion step]
As an inorganic carrier material, an unfired boehmite alumina powder similar to that in Example 1 was prepared. This inorganic carrier raw material was baked by the same method as in Example 1 except that no copper atom was supported to prepare an inorganic carrier (alumina). In addition, the average particle diameter of the obtained inorganic carrier was 4.4 μm.

The platinum-supported cuprous oxide (Cu ₂ O) prepared above was dispersed on the surface of the inorganic support prepared in the same manner to prepare a CO selective oxidation catalyst. Specifically, it was dispersed by wet pulverization mixing using 5 mm alumina balls to obtain a CO selective oxidation catalyst according to the second embodiment of the present invention. In addition, content of the platinum atom and monovalent copper atom with respect to the whole quantity of the catalyst obtained was controlled by adjusting the quantity of a platinum raw material and a copper 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 present invention was carried out using the same method as in Example 1 except that the firing temperature at the time of preparing the inorganic carrier and the contents of platinum atoms and monovalent copper atoms were the values shown in Table 1 below. A CO selective oxidation catalyst of the first form 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 by supporting copper 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 copper solution as in Example 1 and dried at 120 ° C. for 24 hours or longer to support copper atoms on boehmite alumina. Next, the obtained copper-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 copper-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 cuprous oxide (Cu ₂ O) was not generated in this comparative example. Moreover, the platinum and copper content with respect to the whole quantity of the catalyst obtained was controlled by adjusting the quantity of a platinum raw material and a copper 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.

(Comparative Example 2)
In the [cuprous oxide (Cu ₂ O) component preparation step], CO _{2 was} prepared by the same method as in Example 2 except that the firing condition of the copper hydroxide precipitate was set at 500 ° C. for 2 hours. A selective oxidation catalyst was obtained. In addition, since the obtained catalyst did not exhibit light blue color tone, it was confirmed that cuprous oxide (Cu ₂ O) was not generated in this comparative example. Moreover, the platinum and copper content with respect to the whole quantity of the catalyst obtained was controlled by adjusting the quantity of a platinum raw material and a copper 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 (30 mL; inner diameter: 4 mm) to obtain a catalyst sample.

For the catalyst sample obtained above, model gas (H ₂ : 38 vol%, CO ₂ : 16 vol%, H ₂ O: 23 vol%, CO: 0.6 vol%, O ₂ : 0.9 vol) %, N ₂ : 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 conducted. 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.

The results in Table 2 indicate that the CO conversion can be improved by adding copper atoms in the form of cuprous oxide (Cu ₂ O) 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 cuprous oxide (Cu ₂ O) layer,
30 Platinum component,
40 cuprous oxide (Cu ₂ O) component,
50 platinum catalyst component,
100 fuel cell system,
110 reformer,
120 shift reactor,
130 CO concentration reduction device for polymer electrolyte fuel cell,
140 polymer electrolyte fuel cell,
150 combustion equipment,
160 Evaporator.

Claims (8)

A carbon monoxide selective oxidation catalyst in which a platinum component containing a platinum atom is supported on an inorganic carrier,
A carbon monoxide selective oxidation catalyst, further comprising cuprous oxide.   The carbon monoxide selective oxidation catalyst according to claim 1, wherein the cuprous oxide is contained in the inorganic support.   3. The mass ratio of the monovalent copper atom to the total amount of the platinum atom and the monovalent copper atom in the cuprous oxide is more than 50 mass% and less than 100 mass%. Carbon monoxide selective oxidation catalyst.   The carbon monoxide selection according to any one of claims 1 to 3, wherein a molar ratio of a monovalent copper atom content in the cuprous oxide to a platinum atom content is 3 to 65. Oxidation catalyst.   The carbon monoxide selective oxidation catalyst according to any one of claims 1 to 4, wherein a content of the platinum atom is 0.2 to 3.0 mass% with respect to a total amount of the catalyst.   The carbon monoxide selection according to any one of claims 1 to 5, wherein a content of monovalent copper atoms contained in the cuprous oxide is 0.6 to 12 mass% with respect to a total amount of the catalyst. Oxidation catalyst. Preparing an inorganic support containing cuprous oxide;
Supporting a platinum component containing a platinum atom on the inorganic carrier;
The manufacturing method of the carbon monoxide selective oxidation catalyst which has these. Preparing an inorganic support containing the cuprous oxide,
A step of supporting copper atoms on the inorganic carrier raw material;
Firing the inorganic carrier material carrying the copper atoms to obtain an inorganic carrier with cuprous oxide formed on the surface;
The manufacturing method of Claim 7 which has these.

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