JP5204633B2 - Catalyst for selectively oxidizing carbon monoxide, method for reducing carbon monoxide concentration, and fuel cell system - Google Patents

Description

  The present invention relates to a catalyst for selectively oxidizing carbon monoxide, a method for producing the catalyst, carbon monoxide by selectively oxidizing carbon monoxide from a raw material gas containing hydrogen and carbon monoxide using the catalyst. The present invention relates to a method for reducing the concentration, an apparatus for producing a high-concentration hydrogen-containing gas using the catalyst, and a fuel cell system using them.

  A fuel cell has a feature that high efficiency can be obtained because a free energy change caused by a fuel combustion reaction can be directly taken out as electric energy. In addition to the fact that it does not emit harmful substances, it is being developed for various uses. In particular, solid polymer fuel cells are characterized by high power density, compactness, and operation at low temperatures.

  In general, a gas mainly composed of hydrogen is used as a fuel gas for a fuel cell. The raw fuel for obtaining the fuel gas includes natural gas, hydrocarbons such as LPG, naphtha and kerosene, alcohols such as methanol and ethanol, and ethers such as dimethyl ether. However, since carbon atoms other than hydrogen atoms are present in these raw fuels, it is inevitable that impurities derived from carbon are mixed in the fuel gas supplied to the fuel cell.

  Among these impurities, carbon monoxide poisons noble metals such as platinum used as an electrode catalyst for fuel cells. Therefore, when carbon monoxide is present in the fuel gas, the fuel cell cannot obtain sufficient power generation characteristics. Particularly in fuel cells that operate at low temperatures, the electrode catalyst strongly adsorbs carbon monoxide and is susceptible to poisoning. For this reason, in the polymer electrolyte fuel cell system, it is essential that the concentration of carbon monoxide in the fuel gas is reduced.

  As a method for reducing the carbon monoxide concentration in the fuel gas, a method in which carbon monoxide in the reformed gas obtained by reforming the raw fuel is reacted with water vapor and converted into hydrogen and carbon dioxide, so-called aqueous Gas shift reactions are possible. However, this method usually can reduce the carbon monoxide concentration in the fuel gas only to about 0.5 to 1% by volume. The resistance of a fuel cell electrode catalyst to carbon monoxide varies depending on the metal species used. In general, in order for a fuel cell to operate efficiently, the concentration of carbon monoxide in the fuel gas is 100 ppm by volume or less. It is desirable that In order to obtain such a carbon monoxide concentration, it is not sufficient only by the treatment by the water gas shift reaction, and the carbon monoxide concentration reduced to about 0.5 to 1% by volume by the water gas shift reaction is further reduced. Is required.

  As a method for further reducing the carbon monoxide concentration, a method of adsorptive separation of carbon monoxide and a method of membrane separation can be considered. However, although the hydrogen purity obtained by these methods is high, there are problems that the apparatus cost is high and the apparatus size is large, which is not practical.

On the other hand, the chemical method does not have the above-described problem and can be said to be a more realistic method. As a chemical method, a method of methanating carbon monoxide, a method of oxidizing to carbon dioxide, and the like can be considered. Further, a two-stage treatment method in which carbon monoxide is methanated in the former stage and oxidized in the latter stage has been proposed (see Patent Document 1).
JP-A-11-86892

  The method of simply methanating carbon monoxide is not suitable from the viewpoint of efficiency because it causes loss of hydrogen as fuel for the fuel cell. Even in the two-stage treatment method, loss of hydrogen in the previous stage is inevitable. Therefore, it is appropriate to employ a method in which carbon monoxide is oxidized to carbon dioxide. What is important in this method is that carbon monoxide mixed in a trace amount or a small amount in a large excess of hydrogen is selectively oxidized and methanated to obtain a target concentration of carbon monoxide in the product gas. It is to reduce to. For this purpose, it is common to use a catalyst containing Ru and Pt supported on a carrier.

In a catalyst containing Ru, when calcination in air is performed as a means for removing anions such as chlorine contained in a Ru precursor used for loading, a toxic Ru oxide is generated at the same time. Since the oxide has sublimability, there is a problem that the amount of Ru supported decreases (see Non-Patent Document 1). For this reason, in the production of a catalyst that usually contains Ru, calcination in air is not performed, and an anion removal step using a basic solution is provided before performing a reduction treatment in a liquid phase or a gas phase.
“Catalyst Chemistry”, Kodansha Scientific, p. 153

On the other hand, in a catalyst in which Ru and Pt are supported on a support, Pt moves from the support in the anion removal step using an alkaline solution, and a loss of the Pt amount occurs, or an egg shell structure (active near the surface layer of the catalyst particles). There is a problem that the structure in which components are unevenly distributed is lost.
As a result of intensive research on the above problems, the present inventors have used H ₂ Pt (OH) ₆ as a Pt source and supported Pt in a basic solution, so that a desired target can be obtained without Pt migration or loss. It has been found that a catalyst can be obtained. When a selective oxidation reaction of carbon monoxide in a raw material gas containing carbon monoxide and hydrogen is performed using the catalyst, a wider O ₂ / CO ratio (moles) than in the case of using a conventional catalyst. The present invention has been completed by finding that a high-concentration hydrogen-containing gas having a CO concentration reduced to 10 ppm by volume or less can be produced.

The present invention contains Ru and Pt supported on a support made of an inorganic oxide containing at least one selected from alumina, silica, zirconia and titania, and the Pt is H ₂ Pt (OH) ₆ as a Pt source. The present invention relates to a catalyst for selectively oxidizing carbon monoxide, which is used and supported in a basic solution.
The present invention also relates to the catalyst described above, wherein the basic solution is an aqueous NaOH solution.
The present invention also relates to the catalyst described above, which is obtained by supporting Pt after supporting Ru on the carrier.

Furthermore, the present invention is a method for producing a catalyst for selectively oxidizing carbon monoxide containing Ru and Pt supported on a support made of an inorganic oxide containing at least one selected from alumina, silica, zirconia and titania. The present invention relates to a method for producing the catalyst, wherein, when Pt is supported, H ₂ Pt (OH) ₆ is used as a Pt source and supported in a basic solution.

In the present invention, a raw material gas containing hydrogen and carbon monoxide and an oxygen-containing gas are brought into contact with the catalyst described above, and the carbon monoxide in the raw material gas is selectively oxidized to obtain a carbon monoxide concentration. It relates to a method of reducing.
The present invention also provides a reactor filled with the catalyst described above, a supply line for a source gas containing hydrogen and carbon monoxide connected to the reactor, and a supply of an oxygen-containing gas connected to the reactor. And an apparatus for producing a high-concentration hydrogen-containing gas by reducing the carbon monoxide concentration in the raw material gas.
Furthermore, the present invention relates to a fuel cell system characterized in that a high-concentration hydrogen-containing gas supplied from the above-described apparatus is supplied as a cathode-side fuel.

According to the present invention, H ₂ Pt (OH) ₆ is used as a Pt source, and Pt is supported on a predetermined support in a basic solution, so that a desired catalyst can be produced without Pt migration and loss. can do. When a selective oxidation reaction of carbon monoxide in a raw material gas containing carbon monoxide and hydrogen is performed using the catalyst, a wider O ₂ / CO ratio is obtained than when a conventional catalyst is used. In the range, a highly concentrated hydrogen-containing gas having a CO concentration reduced to 10 ppm by volume or less can be produced. Furthermore, by using such a high-concentration hydrogen-containing gas having a reduced CO concentration as a raw material gas, it becomes possible to operate the fuel cell stably for a long time.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the catalyst for selectively oxidizing carbon monoxide of the present invention, as the support, at least one inorganic oxide selected from alumina, silica, zirconia and titania is used. Among these, alumina is more preferable. As alumina, α-alumina and γ-alumina are preferably used, and γ-alumina is particularly preferable from the viewpoint of high affinity with Ru.

There are no particular limitations on the shape, size, and molding method of the carrier, and it may be one in which an appropriate binder is added during molding to improve moldability.
As the shape of the carrier, one having a spherical or cylindrical shape is more preferable. The spherical or columnar shape here does not mean strictly a sphere or column, but a part of the shape is deformed, but it can be recognized as being substantially spherical or columnar. Also included.
Further, when the carrier is spherical, the particle diameter is not particularly limited, but from the viewpoint of contact efficiency with the raw material gas, the average diameter is preferably in the range of 1 to 5 mm, particularly preferably 1 to 3 mm. .

The catalyst of the present invention is a catalyst containing Ru and Pt metals supported on a carrier made of the inorganic oxide.
There is no particular limitation on the method for supporting the metal, and an impregnation method using a metal salt solution in which a salt of the metal to be supported is dissolved in a solvent, an equilibrium adsorption method, and a competitive adsorption method are preferably employed. Of these, the impregnation method is preferable.
There is no particular limitation on the number of times of loading, and it is preferable to load all at the same time or in several times in the loading step.

The Ru metal salt is not particularly limited as long as it dissolves in a solvent. For example, RuCl ₃ .nH ₂ O, Ru (NO ₃ ) ₃ , K ₂ (RuCl ₅ (H ₂ O)) , (NH ₄ ) ₂ RuCl ₆ , (Ru (NH ₃ ) ₆ ) Br ₃ , Ru (NH ₃ ) ₆ Cl ₃ , Na ₂ RuO ₄ , K ₂ RuO ₄ , Ru (CO) ₅ , [Ru (NH ₃ ) ₅ Cl] Cl ₃ , Ru ₃ (CO) ₁₂ and Ru (C ₅ H ₇ O ₂ ) ₂ . A plurality of metal salts may be mixed and used.
The solvent is not particularly limited as long as it dissolves the metal salt. For example, water, methanol, ethanol, propanol, citric acid aqueous solution, oxalic acid aqueous solution, acetic acid aqueous solution, sodium hydroxide aqueous solution, ammonia aqueous solution. Etc. are used.

When carrying Pt, it is important to use H ₂ Pt (OH) ₆ as a Pt source and carry it in a basic solution. That is, Pt is supported on the carrier by immersing the carrier in a solution in which H ₂ Pt (OH) ₆ is dissolved in a basic solution.

The basic solution is not particularly limited as long as it dissolves H ₂ Pt (OH) _6. For example, LiOH aqueous solution, NaOH aqueous solution, KOH aqueous solution, RbOH aqueous solution, CsOH aqueous solution, LiHCO ₃ aqueous solution, NaHCO _{3 can be used} . ₃ aqueous solution, KHCO ₃ aqueous solution, RbHCO ₃ aqueous solution, CsHCO ₃ aqueous solution, Li ₂ CO ₃ aqueous solution, Na ₂ CO ₃ aqueous solution, K ₂ CO ₃ aqueous solution, Rb ₂ CO ₃ aqueous solution, Cs ₂ CO ₃ aqueous solution, ammonia water, (NMe ₄ ) OH solution, (NEt ₄ ) OH solution, (NPr ₄ ) OH solution, (NBu ₄ ) OH solution, (NHMe ₃ ) OH solution, (NHEt ₃ ) OH solution, (NHPr ₃ ) OH solution, (NHBu ₃ ) OH solution, liquid ammonia and the like. Of these, an aqueous NaOH solution is particularly preferred. A plurality of basic solutions may be mixed and used.
As a density | concentration of NaOH aqueous solution, the range of 0.1 mass% to 50 mass% is preferable, More preferably, it is the range of 5 mass% to 20 mass%.

In the catalyst of the present invention, the order in which Ru and Pt are supported on the carrier is not particularly limited, but it is preferable to support Pt after supporting Ru.
In addition, it is preferable to carry out liquid phase reduction with a NaBH ₄ solution or the like after Ru and Pt are supported on a carrier.

The amount of Ru supported on the carrier is not particularly limited, but is preferably 0.01 to 10% by mass, and particularly preferably 0.03 to 2% by mass with respect to the carrier. When the amount of Ru supported is less than 0.01% by mass, the catalyst performance for the selective oxidation reaction of CO cannot be sufficiently obtained, which is not preferable. On the other hand, when the loading amount of Ru exceeds 10% by mass, the methanation reaction is greatly accelerated, and the reaction heat makes it difficult to control the reaction.
The amount of Pt supported on the carrier is not particularly limited, but is preferably 0.01 to 1% by mass and particularly preferably 0.01 to 0.1% by mass with respect to the carrier. When the amount of Pt supported is less than 0.01% by mass, the catalyst performance for the oxidation reaction of CO cannot be sufficiently obtained, which is not preferable. On the other hand, when the amount of Pt supported exceeds 1% by mass, it is not preferable because it is difficult to reduce the CO concentration.

It is necessary to remove the solvent after the metal is supported on the carrier, but this can be done by adopting any method of natural drying in air, heat drying, or deaeration drying under reduced pressure. .
In the produced catalyst, chloride ions derived from the metal salt used for the carrier or support may remain, but the chloride ion concentration needs to be 100 ppm by mass or less. The residual concentration of the chloride ions is preferably 80 mass ppm or less, particularly preferably 50 mass ppm or less. Chloride ions having a residual concentration of more than 100 ppm by mass promote the aggregation of the supported metal and reduce the activity of the catalyst for selective oxidation of CO.
When the catalyst produced by the above method is put to practical use, reduction with hydrogen is usually performed as a pretreatment. As the conditions, the temperature can be 100 to 800 ° C., preferably 150 to 250 ° C., and the time can be 1 to 5 hours, preferably 1 to 3 hours.

  The raw material gas containing carbon monoxide and hydrogen used in the method of selectively oxidizing carbon monoxide and reducing the carbon monoxide concentration of the present invention is usually a starting raw material of fuel gas for fuel cells (raw fuel). ) Or a gas mainly composed of hydrogen obtained by subjecting an oxygen-containing hydrocarbon such as alcohol or ether to a reforming reaction by various methods. The raw fuel includes natural gas, LPG, naphtha, kerosene, gasoline or various equivalents thereof, hydrocarbons such as methane, ethane, propane and butane, various alcohols such as methanol and ethanol, and ethers such as dimethyl ether. Etc. are used.

  The method for reforming the raw fuel is not particularly limited, and examples thereof include various methods such as a steam reforming method, a partial oxidation reforming method, and an autothermal reforming method. Any of these methods can be employed in the present invention.

If raw fuel containing sulfur is supplied to the reforming process as it is, the reforming catalyst will be poisoned and will not exhibit activity, and its life will be shortened, so the raw fuel will be desulfurized prior to the reforming reaction. It is preferable to do. The conditions for the desulfurization treatment vary depending on the type of raw fuel and the sulfur content, and thus cannot be generally stated. However, the reaction temperature is usually preferably 10 to 450 ° C, particularly preferably 10 to 300 ° C. The reaction pressure is preferably from normal pressure to 1 MPa, and particularly preferably from normal pressure to 0.2 MPa. Preferably in the range of 0.01～15H ^-1 when SV raw materials is a liquid, more preferably in the range of 0.05～5H ^-1, range 0.1～3H ^-1 are particularly preferred. When using the raw fuel gas is preferably in the range of 100～10,000H ^-1, more preferably in the range of 200～5,000H ^-1, range 300～2,000H ^-1 are particularly preferred.

Further, although the reforming reaction conditions are not necessarily limited, usually, the reaction temperature is preferably 200 to 1,000 ° C, particularly preferably 500 to 850 ° C. The reaction pressure is preferably from normal pressure to 1 MPa, and particularly preferably from normal pressure to 0.2 MPa. GHSV (space velocity) is preferably 100～100,000H ^-1, more preferably 300~50,000h ^-1, 500~30,000h ^-1 is particularly preferred.
The gas (reformed gas) obtained by the reforming reaction contains hydrogen as a main component, but other components include carbon monoxide, carbon dioxide, water vapor, and the like.

  In the method for reducing the carbon monoxide concentration of the present invention, it is possible to directly use the reformed gas as a raw material gas, but the reformed gas is pretreated in advance to reduce the carbon monoxide concentration to some extent. A thing may be used. Examples of such pretreatment include a method of reacting carbon monoxide in the reformed gas with water vapor to convert it into hydrogen and carbon dioxide in order to reduce the concentration of carbon monoxide in the reformed gas, so-called water gas shift reaction. . Examples of the pretreatment other than the water gas shift reaction include a method of adsorptive separation of carbon monoxide or a method of membrane separation.

In the method for reducing the carbon monoxide concentration of the present invention, the raw material gas is obtained by subjecting the reformed gas to a water gas shift reaction in order to reduce the carbon monoxide in the reformed gas and increase the hydrogen concentration. Is preferable. Thereby, reduction of a carbon monoxide density | concentration can be made more effective. The reaction conditions for the water gas shift reaction are not necessarily limited depending on the composition of the reformed gas and the like, but the reaction temperature is usually preferably 120 to 500 ° C, and particularly preferably 150 to 450 ° C. The reaction pressure is preferably from normal pressure to 1 MPa, and particularly preferably from normal pressure to 0.2 MPa. GHSV is preferably 100~50,000h ^-1, especially 300～10,000H ^-1 are preferred.

  In the method for reducing the carbon monoxide concentration of the present invention, the carbon monoxide concentration in the raw material gas is usually 0.1 to 2% by volume. On the other hand, the hydrogen concentration in the raw material gas is usually 40 to 85% by volume. The source gas may contain, for example, nitrogen, carbon dioxide, etc. as components other than carbon monoxide and hydrogen.

Although it does not specifically limit as an oxygen containing gas used in the method of reducing the carbon monoxide density | concentration of this invention, Air and oxygen are mentioned, Air is preferable. The molar ratio (O ₂ / CO) of oxygen in the oxygen-containing gas and carbon monoxide in the raw material gas is not particularly limited, but the oxygen-containing gas is supplied so as to be in the range of 0.5 to 3.0. It is preferable. For example, when the carbon monoxide concentration in the raw material gas is 0.5% by volume, the molar ratio is more preferably in the range of 0.5 to 2.5. When the molar ratio is less than 0.5, oxygen is insufficient in terms of stoichiometry, so that the oxidation reaction of carbon monoxide does not proceed sufficiently. On the other hand, when the molar ratio is greater than 3.0, side reactions such as a decrease in hydrogen concentration, an increase in reaction temperature due to reaction heat, and methane formation are likely to occur due to hydrogen oxidation.

The reaction pressure in the method for reducing the carbon monoxide concentration of the present invention is preferably in the range of normal pressure to 1 MPa, particularly preferably normal pressure to 0.2 MPa in consideration of economics and safety of the fuel cell system. The reaction temperature is not particularly limited as long as the carbon monoxide concentration can be reduced. However, the reaction rate tends to be low at low temperatures and the selectivity tends to decrease at high temperatures. In particular, 100 to 300 ° C. is preferable. If GHSV is too high, the oxidation reaction of carbon monoxide is difficult to proceed. On the other hand, if it is too low, the apparatus needs to be enlarged, so the range of 1,000 to 50,000 h ⁻¹ is preferable, particularly 3,000 to 3,000. A range of 30,000 h ⁻¹ is preferred.

  By the method for reducing the carbon monoxide concentration of the present invention, the carbon monoxide concentration in the raw material gas can be reduced to 100 volume ppm or less, preferably 50 volume ppm or less, and most preferably 10 volume ppm or less. Therefore, by using the gas having a reduced carbon monoxide concentration obtained by this method as the fuel gas of the fuel cell, poisoning and deterioration of the catalyst containing the noble metal used for the electrode of the fuel cell are suppressed. This makes it possible to operate the fuel cell with high power generation efficiency and long life.

  In the apparatus for reducing the carbon monoxide concentration in the raw material gas of the present invention and producing a high-concentration hydrogen-containing gas, a reactor for performing a selective oxidation reaction of carbon monoxide is filled with the catalyst of the present invention. . The type of the reactor is not limited, but a continuous flow type fixed bed reactor is preferable. The reactor is connected to a supply line for a source gas containing hydrogen and carbon monoxide. The other of the source gas supply lines is preferably connected to a water gas shift reactor.

  Further, an oxygen-containing gas supply line is connected to the reactor. Here, “the oxygen-containing gas supply line is connected to the reactor” means that the oxygen-containing gas supply line is directly connected to the reactor, and upstream of the reactor. It is connected to the supply line of the source gas and means both of the modes in which the source gas and the oxygen-containing gas are supplied to the reactor in a premixed state.

  As described above, the oxygen-containing gas is preferably air, and in that case, the other of the supply lines is preferably connected to an air blower.

  Next, the fuel cell system of the present invention will be described in detail.

  FIG. 1 is a schematic view showing a preferred example of a fuel cell system according to the present invention. In the fuel cell system shown in FIG. 1, the raw fuel in the raw fuel tank 3 flows into the desulfurizer 5 through the raw fuel pump 4. At this time, if necessary, the hydrogen-containing gas can be supplied from the selective oxidation reactor 11 to the desulfurizer 5. The desulfurizer 5 can be filled with, for example, a sorbent containing copper-zinc or nickel-zinc. The raw fuel desulfurized by the desulfurizer 5 is mixed with water supplied from the water tank 1 via the water pump 2, then introduced into the vaporizer 6 and further fed into the reformer 7.

The reformer 7 is heated by a heating burner 18. Although the anode off gas of the fuel cell 17 is mainly used as the fuel for the heating burner 18, the raw fuel discharged from the raw fuel pump 4 can be supplemented as necessary. As the catalyst filled in the reformer 7, a catalyst containing nickel, ruthenium, rhodium or the like can be used.
The reformed gas containing hydrogen and carbon monoxide thus produced is subjected to a water gas shift reaction by the high temperature shift reactor 9 and the low temperature shift reactor 10. The high temperature shift reactor 9 is filled with a catalyst such as a catalyst containing iron-chromium, and the low temperature shift reactor 10 is filled with a catalyst such as a catalyst containing copper-zinc.

  The gas flowing out of the high temperature shift reactor 9 and the low temperature shift reactor 10 is then led to the selective oxidation reactor 11. The selective oxidation reactor 11 is filled with the catalyst of the present invention. The raw material gas is mixed with air supplied from the air blower 8, and selective oxidation of carbon monoxide is performed in the selective oxidation reactor 11 in the presence of the catalyst. By this method, the carbon monoxide concentration is reduced to such an extent that it does not affect the characteristics of the fuel cell.

  The polymer electrolyte fuel cell 17 includes an anode 12, a cathode 13, and a solid polymer electrolyte 14, and a fuel gas containing high-purity hydrogen with a reduced carbon monoxide concentration obtained by the above method on the anode side. However, the air sent from the air blower 8 is introduced to the cathode side after performing a suitable humidification treatment if necessary (a humidifier is not shown). At this time, a reaction in which hydrogen gas becomes protons and emits electrons proceeds at the anode, and a reaction in which oxygen gas obtains electrons and protons to become water proceeds at the cathode. In order to promote these reactions, platinum black and Pt catalyst or Pt-Ru alloy catalyst supported on activated carbon are used for the anode, and platinum black and Pt catalyst supported on activated carbon are used for the cathode. Usually, both the anode and cathode catalysts are formed into a porous catalyst layer together with polytetrafluoroethylene, a low molecular weight polymer electrolyte membrane material, activated carbon and the like as required.

  Next, the aforementioned porous catalyst layer is laminated on both sides of a polymer electrolyte membrane known by a trade name such as Nafion (DuPont), Gore (Gore), Flemion (Asahi Glass), Aciplex (Asahi Kasei). By doing so, MEA (Membrane Electrode Assembly) is formed. Further, the fuel cell is assembled by sandwiching the MEA with a separator having a gas supply function, a current collecting function, particularly an important drainage function in the cathode, and the like made of a metal material, graphite, carbon composite and the like. The electric load 15 is electrically connected to the anode and the cathode. The anode off gas is consumed in the heating burner 18. The cathode off gas is discharged from the exhaust port 16.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

(Manufacture of catalyst)
The amount of water absorbed by the carrier is RuCl ₃ .nH ₂ O which is 0.5% by mass based on the mass of the carrier as metal Ru, and H ₂ PtCl ₆ which is 0.03% by mass based on the mass of the carrier as metal Pt. Using a solution dissolved in an amount of ion-exchanged water corresponding to the above, it was supported on a commercially available γ-alumina carrier (spherical with an average particle diameter of 2.5 mm) by an impregnation method. After the moisture was removed from the obtained metal-supported carrier by drying, it was impregnated with a 10% by mass NaOH aqueous solution to remove anions, and further subjected to liquid phase reduction with a NaBH ₄ solution to obtain Ru / Pt / Al _2. An O ₃ catalyst was produced. This catalyst is referred to as catalyst A. When the residual chlorine ion concentration of the catalyst A was measured, it was 60 ppm by mass based on the mass of the catalyst.

Commercially available γ− by impregnation using a solution in which RuCl ₃ .nH ₂ O, which is 0.5% by mass based on the mass of the carrier as metal Ru, is dissolved in an amount of ion-exchanged water corresponding to the amount of water absorbed by the carrier. It was supported on an alumina carrier. After removing moisture by drying the obtained Ru-supported carrier, H ₂ PtCl ₆ that is 0.03% by mass based on the mass of the carrier as metal Pt is added to 10% by mass of NaOH corresponding to the amount of water absorbed by the carrier. A solution dissolved in an aqueous solution was used for supporting by an impregnation method, and at the same time, anion derived from Ru chloride and H ₂ PtCl ₆ was removed. This was further subjected to liquid phase reduction with a NaBH ₄ solution to produce a Ru / Pt / Al ₂ O ₃ catalyst. This catalyst is referred to as catalyst B. When the residual chlorine ion concentration of the catalyst B was measured, it was 58 mass ppm based on the mass of the catalyst.

Commercially available γ− is obtained by an impregnation method using a solution in which RuCl ₃ · nH ₂ O, which is 0.5% by mass based on the mass of the carrier as metal Ru, is dissolved in ion-exchanged water in an amount corresponding to the water absorption amount of the carrier. It was supported on an alumina carrier. After removing moisture by drying the obtained Ru-supported carrier, H ₂ Pt (OH) ₆ that is 0.03% by mass based on the mass of the carrier as metal Pt is added in an amount corresponding to the amount of water absorbed by the carrier. A solution dissolved in a mass% NaOH aqueous solution was supported by an impregnation method, and at the same time, anion derived from Ru chloride was removed. This was further subjected to liquid phase reduction with a NaBH ₄ solution to produce a Ru / Pt / Al ₂ O ₃ catalyst. This catalyst is referred to as catalyst C. When the residual chlorine ion concentration of the catalyst C was measured, it was less than the detection limit of measurement (50 ppm by mass on the basis of the mass of the catalyst).

Commercially available γ-alumina support by an impregnation method using a solution in which H ₂ PtCl ₆ that is 0.1% by mass based on the mass of the support as metal Pt is dissolved in an amount of ion-exchanged water corresponding to the amount of water absorbed by the support Supported by After removing moisture from the obtained Pt-supported carrier by drying, it was impregnated with 10% NaOH aqueous solution to remove anions derived from H ₂ PtCl ₆ . This was further subjected to liquid phase reduction with a NaBH ₄ solution to prepare a Pt / Al ₂ O ₃ catalyst. This catalyst is referred to as catalyst D.

Commercially available γ− by impregnation using a solution in which H ₂ PtCl _6, which is 0.1% by mass based on the mass of the carrier as metal Pt, is dissolved in a 10% by mass NaOH aqueous solution in an amount corresponding to the amount of water absorbed by the carrier. It was supported on an alumina carrier. This was further subjected to liquid phase reduction with a NaBH ₄ solution to produce a Pt / Al ₂ O ₃ catalyst. This catalyst is referred to as catalyst E.

Commercially available by impregnation method using a solution in which H ₂ Pt (OH) ₆ that is 0.1% by mass based on the mass of the carrier as metal Pt is dissolved in a 10% by mass NaOH aqueous solution in an amount corresponding to the amount of water absorbed by the carrier. Of γ-alumina support. This was further subjected to liquid phase reduction with a NaBH ₄ solution to produce a Pt / Al ₂ O ₃ catalyst. This catalyst is referred to as catalyst F.

(Selective oxidation of carbon monoxide)
12 ml of each catalyst was filled in each reaction tube and reduced at 200 ° C. for 1 hour in a hydrogen stream.
Next, hydrogen (H ₂ ) 59 volume%, carbon monoxide (CO) 5,000 volume ppm, carbon dioxide (CO ₂ ) 20.2 volume%, water vapor (H ₂ O) 20.3 volume% as source gases. A raw material gas consisting of air and air were supplied to the catalyst layer, and a selective oxidation reaction of carbon monoxide in the raw material gas was performed. The reaction conditions were normal pressure, GHSV 8,000 h ⁻¹ , reaction temperature (catalyst layer inlet temperature) 130 ° C. Moreover, the feed rate of air, the molar ratio of CO _{O 2} and the raw material gas _(O 2 / CO) was adjusted to be 2.5, the reaction was started. When the reaction was stabilized after 30 minutes, the CO concentration in the effluent gas at the outlet of the reaction tube was measured. Next, the air supply rate was reduced so that O ₂ / CO was 2.4, and after stabilization for 30 minutes, the CO concentration in the effluent gas at the outlet of the reaction tube was measured again. Similarly hereafter, O 2 _/ CO is reduced the feed rate of air to decrease at 0.1 intervals, the CO concentration in the effluent gas at the outlet of the reaction tube at each stage was measured and the O _{2 /} CO is Repeated until 0.9.

(Comparative Example 1)
Using catalyst A, a selective oxidation reaction of carbon monoxide was performed by the above-described operation. From the measured value of the CO concentration in the effluent gas at the outlet of the reaction tube at each stage, the lower limit value of O ₂ / CO that allows the CO concentration to be 10 ppm by volume or less is determined, and the results are shown in Table 1.

(Comparative Example 2)
The same operation as in Comparative Example 1 was performed except that the catalyst B was used. The results are shown in Table 1.

Example 1
The same operation as in Comparative Example 1 was performed except that the catalyst C was used. The results are shown in Table 1.

From Table 1, selective oxidation of carbon monoxide in a raw material gas containing carbon monoxide and hydrogen by using H ₂ Pt (OH) ₆ as a Pt source and using a catalyst supporting Pt in an aqueous NaOH solution. It can be seen that the CO concentration can be reduced to 10 volume ppm or less in a wide O ₂ / CO range.

(Reference Example 1)
The catalyst D was subjected to elemental analysis of Pt to determine the amount of Pt supported. Further, when the catalyst particles were cut at a plane passing through the center of the particles and the cross section was observed, it was visually observed that Pt turned gray was supported almost uniformly from the outer surface to the inside of the catalyst particles. It was. The results are shown in Table 2.
In addition, this reference example 1 and the following reference examples 2 and 3 were performed for the purpose of examining the distribution of Pt in the catalyst particles in the Ru-Pt supported catalyst according to the present invention. That is, in the Ru—Pt supported catalyst according to the present invention, it is difficult to observe the distribution of Pt because of the small amount of supported Pt and the influence of Ru having a relatively large amount of supported. Therefore, the distribution of Pt was observed using a model catalyst in which Ru was not supported and the amount of Pt supported was increased.

(Reference Example 2)
The same analysis as in Reference Example 1 was performed except that Catalyst E was used. The results are shown in Table 2.

(Reference Example 3)
The same analysis as in Reference Example 1 was performed except that the catalyst F was used. The results are shown in Table 2.

From Table 2, it can be seen that the use of H ₂ Pt (OH) ₆ and the method of supporting Pt in an aqueous NaOH solution does not cause movement or loss of Pt in the catalyst production stage. Further, it is suggested that the catalyst produced by the above method has an egg shell structure in which Pt is unevenly distributed only in the vicinity of the outer surface of the catalyst particles.

(Example 2)
When the product gas obtained by the selective oxidation reaction of carbon monoxide in Example 1 was introduced into the anode electrode of the polymer electrolyte fuel cell in FIG.

It is the schematic which shows an example of the fuel cell system of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water tank 2 Water pump 3 Raw fuel tank 4 Raw fuel pump 5 Desulfurizer 6 Vaporizer 7 Reformer 8 Air blower 9 High temperature shift reactor 10 Low temperature shift reactor 11 Selective oxidation reactor 12 Anode 13 Cathode 14 Solid height Molecular electrolyte 15 Electric load 16 Exhaust port 17 Polymer electrolyte fuel cell 18 Heating burner

Claims (7)

It contains Ru and Pt supported on a carrier made of an inorganic oxide containing at least one selected from alumina, silica, zirconia and titania, and the Pt is basic using H ₂ Pt (OH) ₆ as a Pt source A catalyst for selectively oxidizing carbon monoxide, which is supported in a solution.   The catalyst according to claim 1, wherein the basic solution is an aqueous NaOH solution.   The catalyst according to claim 1 or 2, wherein the catalyst is obtained by supporting Pt after supporting Ru on the carrier. A method for producing a catalyst that selectively oxidizes carbon monoxide containing Ru and Pt supported on a support made of an inorganic oxide containing at least one selected from alumina, silica, zirconia, and titania, comprising: In carrying the catalyst, the catalyst is produced in a basic solution using H ₂ Pt (OH) ₆ as a Pt source.   A source gas containing hydrogen and carbon monoxide and an oxygen-containing gas are brought into contact with the catalyst according to claim 1 to selectively oxidize carbon monoxide in the source gas. A method of reducing carbon monoxide concentration.   A reactor filled with the catalyst according to any one of claims 1 to 3, a supply line of a source gas containing hydrogen and carbon monoxide connected to the reactor, and connected to the reactor An apparatus for producing a high-concentration hydrogen-containing gas by reducing the carbon monoxide concentration in the raw material gas, comprising at least an oxygen-containing gas supply line.   A fuel cell system, wherein the high-concentration hydrogen-containing gas supplied from the apparatus according to claim 6 is supplied as a cathode-side fuel.

Images