JP2007000703A - Reforming catalyst, method of manufacturing reforming catalyst and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reforming catalyst suppressing precipitation of carbon in reforming a fuel and enabling stable steam reforming, its manufacturing method and a fuel cell system using it. <P>SOLUTION: The reforming catalyst is employed to reform a hydrocarbon type raw fuel for fuel cells into a fuel gas. In the catalyst, an active ingredient derived from a hydroxide precursor is carried in a support with high dispersion. The high-dispersion carrying of the active ingredient with small particle sizes in a support leads to easy reaction of the catalyst with hydrocarbons in steam reforming, ensuring good progressing of steam reforming and preventing covering of carbon film due to direct decomposition of hydrocarbons (HCs). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reforming catalyst for improving the performance stability of a CO treatment apparatus when removing residual CO after reforming raw fuel for fuel cells such as kerosene into fuel gas, and production of the reforming catalyst The present invention relates to a method and a fuel cell system.

  In recent years, polymer electrolyte fuel cells (PEFC) are expected to be applied as power sources in a wide range of fields such as automobile power sources and distributed power sources because of their low pollution and high thermal efficiency. Several methods are conceivable for supplying hydrogen as the fuel to the fuel cell. For example, a method using an efficient hydrogen production apparatus is promising. In such hydrogen production, methanol, methane, or the like is used as a raw material. Used as Methanol is easily synthesized from fossil fuels in an inexpensive liquid fuel, and has a characteristic that it can be converted to hydrogen relatively easily using a catalyst. In addition, kerosene can be used as a raw fuel instead of methane, propane, etc., but in any case, it is necessary to reform the raw fuel first.

For example, FIG. 2 shows an example of a fuel reformer when kerosene is used as a raw fuel.
As shown in FIG. 2, the fuel reformer 10 includes a reformer body 12 having a reforming catalyst that reforms raw fuel 11 such as kerosene into hydrogen (H ₂ ), and the reformer body 12 is modified. CO conversion catalyst unit 14 for converting CO present in the reformed gas 13 into carbon dioxide, and CO removal catalyst for removing CO remaining in the fuel gas after the CO conversion to obtain a CO-free fuel gas 15 Part 16.

Here, in the reformer body 12, when methane is used as a raw material, the reforming catalyst generates a reaction of the following formula (formula (1)) at about 700 ° C. and reforms containing hydrogen. Gas 13 is obtained.
CH ₄ + H ₂ O → CO + 3H ₂ (1)

The reformed gas thus obtained contains a large amount of carbon monoxide, and this CO acts as a poisoning substance that inhibits the function of the fuel cell. Therefore, in the CO shift catalyst section 14 having a CO shift catalyst such as Cu—Zn provided at the rear stage of the reformer body 12, a shift reaction is caused at about 200 to 450 ° C., and the following reaction (formula ( 2)) to convert CO to carbon dioxide.
CO + H ₂ O → CO ₂ + H ₂ (2)

The reformed gas that has passed through the CO conversion catalyst section 14 has carbon monoxide usually reduced and removed to about 3000 to 4000 ppm, but the fuel gas introduced into the fuel cell main body is applied to the electrode of the polymer electrolyte fuel cell. Since a platinum catalyst is mainly used, it is usually necessary to have a CO concentration of 20 ppm or less, preferably 10 ppm or less. If the concentration is as it is, the battery is poisoned. Therefore, for example, by providing a CO removal catalyst portion 16 having a CO removal catalyst such as Pt or Ru in the downstream of the CO shift catalyst portion 14, the following reaction (formula (3)) is caused to generate further carbon monoxide. Removal is performed (Patent Documents 1 and 2).
CO + 1 / 2O ₂ → CO ₂ (3)

Japanese Patent Laid-Open No. 2003-47855 JP 2004-89813 A

By the way, the catalyst used for the steam reforming reaction generally uses Ru and Ni as catalytic active components and a heat-resistant oxide typified by α-alumina as a carrier.
However, in the case where the reforming catalyst is used and the supply amount of water vapor is small, or the water vapor supply is unstable and the water vapor is temporarily low, carbon deposition is caused by the direct decomposition of hydrocarbons. .
The reason for this is related to the acidic site (reaction site) present in the catalyst. This acidic site is also the active site for the steam reforming reaction, which is the main reaction, so it is easy to suppress carbon deposition. There is a problem that it cannot be eliminated.

  In view of the above problems, an object of the present invention is to provide a reforming catalyst, a method for producing the reforming catalyst, and a fuel cell system capable of suppressing the deposition of carbon during reforming of the fuel and performing the steam reforming stably. To do.

  A first invention of the present invention for solving the above-described problem is a reforming catalyst for reforming a hydrocarbon-based raw fuel for a fuel cell into a fuel gas, and an activity having a hydroxide as a precursor. The reforming catalyst is characterized in that the components are highly dispersed and supported on a carrier.

  A second invention is the reforming catalyst according to the first invention, wherein the particle size of the active ingredient having a hydroxide as a precursor is 5 nm or less.

  A third invention is the reforming catalyst according to the first or second invention, wherein the active component is at least one of Ru, Rh, and Ni.

A fourth invention is the invention according to any one of the first to third inventions, wherein the carrier is one of Al ₂ O ₃ , ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ , and Pr ₂ O _3. The reforming catalyst is characterized by the above.

A fifth invention is a reforming catalyst for reforming a hydrocarbon-based raw fuel for a fuel cell into a fuel gas, wherein the active component is at least one of Ru, Rh, and Ni, and the active component is A reforming catalyst characterized in that the carrier to be supported is Al ₂ O ₃ and one or a combination of two or more of ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ , Pr ₂ O _3. is there.

  A sixth invention is the reforming catalyst according to any one of the third to fifth inventions, characterized in that the carrier coexists with a basic oxide.

  A seventh invention is the reforming catalyst according to the sixth invention, wherein the basic oxide is an alkaline earth metal.

  An eighth invention is the reforming catalyst according to the fifth invention, wherein the carrier is made amorphous.

A ninth aspect of the invention, in any one of the invention of the first to sixth, in the reforming catalyst, wherein the specific surface area of the carrier is 5~80m ² / g.

  A tenth aspect of the invention is a method for producing a reforming catalyst characterized in that an aqueous solution of nitrate, acetate or chloride as a carrier component is neutralized and precipitated with an alkali and then calcined.

  An eleventh invention is the method for producing a reforming catalyst according to the tenth invention, wherein an alkaline earth metal is added during the neutralization precipitation.

  A twelfth aspect of the invention is a method for producing a reforming catalyst according to the tenth or eleventh aspect of the invention, wherein the neutralized precipitate is washed.

  A thirteenth aspect of the invention is a method for producing a reforming catalyst characterized in that an active metal salt is neutralized with an alkali and then slurried, a predetermined amount of support is immersed in a hydroxide slurry, and then calcined.

  A fourteenth invention is characterized in that a raw fuel is reformed by a reformer having any one of the reforming catalysts of the first to ninth inventions, and the reformed fuel gas is generated in a fuel cell. The fuel cell system uses a hydrocarbon fuel.

  According to the reforming catalyst of the present invention, carbon deposition as a side reaction can be prevented, the lifetime of the active component can be improved, and a stable steam reforming reaction can be performed.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment and an Example. In addition, constituent elements in the following embodiments and examples include those that can be easily assumed by those skilled in the art or those that are substantially the same.

[Embodiment of the Invention]
The first reforming catalyst of the present invention is a reforming catalyst for reforming a hydrocarbon-based raw fuel for a fuel cell into a fuel gas, and an active component having a hydroxide as a precursor is highly dispersed and a carrier. It is carried on the surface.

The active ingredient having a hydroxide as a precursor preferably has a particle size of 5 nm or less.
By supporting the active ingredient having such a small particle size on the support in a highly dispersed state, the steam reforming proceeds well by reacting with the hydrocarbon in the steam reforming, and the coating of the carbon film by the direct decomposition of HC is achieved. Is prevented.

  Here, examples of the active ingredient include at least one of Ru, Rh, and Ni.

The carrier may be any material as long as it is used as a reforming catalyst for steam reforming. For example, Al ₂ O ₃ , ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ , Pr ₂ O One or more of the _three can be used.

  As a method of highly dispersing such an active ingredient in a carrier, the active metal salt is neutralized with an alkali, and then a slurry is formed in a hydroxide, and a predetermined amount of the carrier is immersed in the hydroxide slurry, and then fired. You just have to do it.

Here, examples of the alkali include ammonia and sodium carbonate, and the neutralization condition is preferably pH 6.5-8.
The amount of the hydroxide slurry in which the carrier is immersed is preferably 0.1 to 5% based on the weight of the carrier.
This is because if the amount is less than 0.1%, there are few active sites acting on the catalytic reaction, and a sufficient reaction rate cannot be obtained. If the amount exceeds 5%, the particles that become active sites tend to agglomerate and can be supported in a highly dispersed state. This is because there is no further supporting effect.
In addition, it is good to make baking into 500-1000 degreeC. When the firing temperature is less than 500 ° C., the reaction temperature is higher, so that the particles that become active sites are likely to agglomerate during the reaction. On the other hand, when the temperature exceeds 1000 ° C., the particles that become active sites are thermally aggregated. This is because it is difficult to promote and achieve high dispersion.

  The catalyst molding is not particularly limited, and for example, a spherical shape, a cylindrical pellet, a Raschig ring, or a persaddle type may be used.

  The active ingredient obtained by such a method has a particle size of 5 nm or less and can be highly dispersed on the carrier surface. This is because the precursor of the active ingredient has a basic hydroxyl group and is firmly bonded to a carrier site having solid acidity, so that thermal aggregation during firing hardly proceeds and a fine particle of 5 nm can be realized.

The second reforming catalyst of the present invention is a reforming catalyst for reforming a hydrocarbon-based raw fuel for a fuel cell into a fuel gas, and the active component is at least one of Ru, Rh, and Ni. In addition, the carrier supporting the active ingredient is Al ₂ O ₃ and one or a combination of two or more of ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ , and Pr ₂ O ₃ .
When Al ₂ O ₃ is used as a component of the support, Al ₂ O ₃ and one or a combination of two or more of ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ , and Pr ₂ O ₃ should be used. In the amorphous state in which the alumina is not crystallized, and when the amorphous state is formed, the hydroxide salt is formed by neutralizing and precipitating with an alkali, and then calcined. The portion of the oxide occupied by water can be made void to form pores, thereby increasing the specific surface area.

In general, composite oxides of alumina and zirconia can increase the α-phase transition temperature of alumina by adding zirconium nitrate to alumina powder and then firing, so that the specific surface area of the composite oxide is 80 m even when fired at 1100 ° C., for example. ² / g.
In addition, when using a sodium salt in alkali precipitation, after alkali precipitation, it wash | cleans and removes a sodium salt actively and suppresses beta formation of an alumina.

  As described above, by neutralizing with alkali due to the presence of zirconia other than alumina, the alumina can be made amorphous, and the amount of voids in the carrier can be increased to achieve a high specific surface area.

In preparing the high surface area carrier, an aqueous solution of nitrate, acetate or chloride as a carrier component is neutralized and precipitated with an alkali and then baked.
The resulting support has a specific surface area of 5 to 80 m ² / g and an average pore size of 10 to 50 nm.

Here, examples of the alkali include ammonia and sodium carbonate, and the neutralization condition is preferably pH 7-9.
Firing is preferably performed at 700 to 1100 ° C. When the calcination temperature is less than 700 ° C., the pore structure of the support is likely to change during the reaction, which promotes thermal aggregation of active sites. On the other hand, when the calcination temperature exceeds 1100 ° C., the alumina contained in the support Since the α phase transition occurs and the specific surface area is greatly reduced, it is not preferable.

More preferably, the carrier coexists with a basic oxide.
The basic oxide is preferably an alkaline earth metal such as MgO, CaO or SrO.
This is to neutralize Lewis acid sites present on the surface of a carrier component such as alumina with an alkaline earth metal so that hydrocarbons prevent direct adsorption to Lewis acid sites and prevent carbon coating. .

As a result, an active component such as Ru is supported on the carrier having a high specific surface area with high dispersion, so that the steam reforming reaction proceeds well, and carbon deposition due to direct decomposition of hydrocarbons is prevented.
In addition, by combining the support with an alkaline earth metal, it has a high specific surface area and can neutralize the Lewis acid point, preventing sintering of active components such as Ru, and supporting with high dispersion It is possible to prevent carbon precipitation by preventing adsorption of hydrocarbons directly to the support.

  By using the reforming catalyst of the present invention, the side reaction can be suppressed and the steam reforming reaction can be performed stably.

Hereinafter, a power generation system of a fuel cell to which a reformer using the reforming catalyst of the present invention can be applied will be described with reference to the drawings.
FIG. 1 is a conceptual diagram showing a power generation system of a PEFC type fuel cell.
As shown in FIG. 1, a PEFC type fuel cell power generation system (PEFC power generation system) 1000 according to this embodiment includes a fuel electrode 1002-1 that supplies a fuel gas 1001, and an air electrode 1002-2 that supplies air 1003. The fuel cell 1002 including the cooling unit 1002-3 that supplies the refrigerant 1004 and removes the heat generated by the electrochemical reaction during operation, and the fuel gas 1001 supplied to the fuel electrode 1002-1 are modified from the raw fuel 1005. And a fuel reformer 1006 for generating the electric power, and the electric power is generated by the fuel supplied to the fuel electrode 1002-1 to obtain the DC power 1020 from the fuel cell 1002. This power generation system 1000 is configured to fully automatically start, generate, stop, and alarm / protect a fuel cell by a control system (not shown).

  Examples of the raw fuel 1005 by the reformer include gaseous fuels such as natural gas (city gas: 13A, for example) and LPG. Further, a desulfurization apparatus 1007 using the desulfurizing agent according to the present invention is provided in order to remove the S component contained in the natural gas and LPG.

The raw fuel 1005 desulfurized by the desulfurizer 1007 is reformed by the fuel reformer 1006. Here, the reforming of the raw fuel 1005 is mainly performed by a steam reforming reaction in a reforming catalyst (not shown) of the reformer body 1006-1A of the fuel reformer 1006-1 of the fuel reformer 1006. Done. That is, the raw fuel 1005 and the steam 1009 are mixed and circulated through the reforming catalyst layer, and the reformer burner 1006-1B is used to perform the steam reforming reaction (when using city gas, for example, at a temperature of 700 to 800 ° C. Is performed by causing CH ₄ + H ₂ O → CO + 3H ₂ ). As the reforming catalyst, the first reforming catalyst or the second reforming catalyst described above is used. Further, the reformed fuel gas 1001 may pass through a CO shift catalyst unit 1006-2 and a PROx (PReferent Oxidation) catalyst unit 1006-3 as necessary.

  The cooling line L1 for the refrigerant 1004 is provided with a heat radiating portion 1010 that exchanges heat, for example, with water or air, and radiates heat when heat is generated in fuel cell power generation. Further, in this system, like the heat dissipating part 1010 and the like, various heat sources are made using heat generated accompanying the fuel cell power generation reaction.

  In the system shown in FIG. 1, when fuel cell power generation is started, the raw fuel 1005 is supplied to the reformer burner 1006-1B to raise the temperature of the reformer body 1006-1A, which is suitable for steam reforming. After the predetermined temperature condition is satisfied, the raw fuel 1005 is supplied to reform the fuel gas 1001. Thereafter, the obtained fuel gas 1001 is further reformed as necessary, and then supplied to the fuel electrode 1002-1 to start power generation. The exhaust gas from the fuel electrode 1002-1 is sent to the reformer burner 1006-1B and burned there to use unreacted gas.

  Since the power generation system of this PEFC type fuel cell performs desulfurization with the desulfurization apparatus 1007 using the desulfurization agent for hydrocarbon fuel described above, stable desulfurization can be performed from a low temperature region to a high temperature region over a long period of time. And a highly reliable fuel cell system can be provided.

"Method for preparing catalyst"
First, a method for preparing the carrier will be described.
Preparation of carrier (ZrO ₂ · Al ₂ O ₃ ) of Example 1 A predetermined amount of aluminum nitrate and zirconium nitrate are dissolved in ion-exchanged water, and ion-exchanged water is added until the pH becomes 4.0. While keeping the temperature at 40 ° C., 1N ammonia water is gradually added dropwise with stirring until pH 7.0 is reached. Continue to stir for 2 hours and age. At this time, since the pH gradually decreases, ammonia water was dropped as needed to maintain pH 7.0. The precipitate thus obtained was washed with water and dried at 120 ° C. to obtain an oxide precursor serving as a carrier. This precursor is a composite hydroxide salt containing zirconia and alumina as a result of analysis by X-ray diffraction method. The primary particle diameter is 5 nm or less from the half-value width of the X-ray diffraction spectrum according to the Serrer equation. It was confirmed that the amorphous state was not progressed.
Subsequently, this hydroxide was calcined in a calcining furnace at 1000 ° C. for 24 hours to obtain an oxide carrier (carrier number 1) containing zirconia and alumina.

Preparation of the carriers of Examples 2 to 8 According to the same preparation method as that of the carrier of Example 1, except that some nitrates were changed to chlorides and acetates, and further the constituent elements were changed to cerium, neodymium, lanthanum and praseodymium. The carriers of Examples 2 to 8 (carrier numbers 2 to 8) were obtained.
A list of carrier preparations is shown in Table 1.
In Table 1, * 1) is a value calculated from the half-value width of the X-ray diffraction spectrum according to the Scherrer equation, and * 2) is a value after firing at 1000 ° C. for 24 hours.

"High dispersion addition of basic oxide to the carrier"
The carrier (carrier Nos. 1 to 8) shown in Table 1 is added to ion-exchanged water and stirred to form a slurry. Further, alkaline earth metal nitrate is added, and 1N ammonia water is added thereto to adjust the pH to 7.0. The precipitate containing the carrier was washed with water and filtered, and calcined at 500 ° C. for 5 hours in a calcining furnace to obtain Example carriers 1 to 8 containing a basic oxide. The carrier prepared by the above method is saturated at the acidic point by the temperature programmed desorption program method (TPD method) in which pyridine is saturatedly adsorbed on the carrier at 200 ° C. and the amount of pyridine desorbed by gradually raising the temperature is recorded. The degree of harm was measured.

In the TPD method, if the amount of pyridine desorbed is large, there are many acidic points, and if the temperature of desorption is high, it means that a strong acid point is present. Table 2 shows a list of preparations of carriers containing basic oxides.
In the preparation list of the carrier containing the basic oxide in Table 2, the amount of pyridine desorbed by the temperature increase to 650 ° C. in the TPD method was calculated as the ratio of the adsorbed pyridine amount.

"Supporting active ingredients"
First, 1N ammonia water was added to a 5 wt% aqueous solution of ruthenium nitrate (Ru (NO ₃ ) ₄ ) until the pH became 7.5 to prepare a slurry containing black ruthenium hydroxide.
A slurry containing nickel hydroxide and rhodium hydroxide was obtained in the same manner.
Subsequently, a predetermined amount of a slurry containing the catalyst component hydroxide salt was added to the carriers shown in Table 2 (Example carriers 1 to 8), and the catalyst components were supported by evaporation to dryness. In this state, since the catalyst component is a hydroxide, the catalyst of Example (Catalyst Nos. 1 to 8) was obtained by calcining at 700 ° C. for 5 hours. A predetermined amount of a slurry containing ruthenium hydroxide and nickel hydroxide was added to an alumina carrier containing α-alumina and zirconia to prepare evaporated catalysts 9-12.
The comparative catalyst was prepared by impregnating a nitrate of each element into a support and evaporating to dryness. The catalyst list is shown in Table 3.

"Evaluation of hydrocarbon reforming performance"
Hydrocarbon reforming performance was evaluated under the reaction conditions shown in Table 4 using a fixed bed flow reactor.
The following parameters were used for evaluating the catalyst performance.
CH ₄ reaction rate (%) = [(production + CO ₂ amount (mol / h)) / (raw material CH ₄ amount (mol / h)) × 100

The evaluation was performed for 2000 hours continuously under the conditions shown in Table 4, and the presence or absence of the effect was judged from the degree of decrease in the CH ₄ reaction rate and the amount of C adhering to the extracted catalyst. The evaluation results of the methane reforming are shown in Table 5.

  From Table 5, it was found that the catalyst of the present invention showed stable performance in the steam reforming reaction of methane.

  As described above, the reforming catalyst according to the present invention prevents carbon precipitation as a side reaction, improves the lifetime of the active component, and is suitable for use in a stable steam reforming reaction of a fuel cell.

It is a conceptual diagram which shows a PEFC type fuel cell system. It is the schematic of the fuel reformer concerning a prior art.

Explanation of symbols

1001 Fuel gas 1002 Fuel cell 1005 Raw fuel 1006 Fuel reformer 1006-1A Reformer body 1006-2 CO shift catalyst unit 1006-3 PROx catalyst unit

Claims (14)

A reforming catalyst for reforming a hydrocarbon-based raw fuel for a fuel cell into a fuel gas,
A reforming catalyst comprising an active component having a hydroxide as a precursor supported on a carrier in a highly dispersed state. In claim 1,
A reforming catalyst characterized in that the particle size of an active ingredient having a hydroxide as a precursor is 5 nm or less. In claim 1 or 2,
A reforming catalyst, wherein the active component is at least one of Ru, Rh, and Ni. In any one of Claims 1 thru | or 3,
A reforming catalyst, wherein the support is one or more of Al ₂ O ₃ , ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ , and Pr ₂ O ₃ . A reforming catalyst for reforming a hydrocarbon-based raw fuel for a fuel cell into a fuel gas,
The active ingredient is at least one of Ru, Rh, Ni;
The carrier carrying the active ingredient is Al ₂ O ₃ and one or a combination of two or more of ZrO ₂ , CeO ₂ , Nd ₂ O ₃ , La ₂ O ₃ and Pr ₂ O _3. Reforming catalyst. In any one of Claims 3 thru | or 5,
A reforming catalyst characterized in that the carrier coexists with a basic oxide. In claim 6,
A reforming catalyst, wherein the basic oxide is an alkaline earth metal. In claim 5,
A reforming catalyst, wherein the carrier is made amorphous. In any one of Claims 1 thru | or 6,
A reforming catalyst, wherein the support has a specific surface area of 5 to 80 m ² / g.   A method for producing a reforming catalyst, characterized in that an aqueous solution of nitrate, acetate or chloride as a carrier component is neutralized and precipitated with an alkali and then calcined. In claim 10,
A method for producing a reforming catalyst, comprising adding an alkaline earth metal during the neutralization precipitation. In claim 10 or 11,
A method for producing a reforming catalyst, wherein the neutralized precipitate is washed. The active metal salt is neutralized with an alkali and then slurried.
A method for producing a reforming catalyst, comprising immersing a predetermined amount of a carrier in a hydroxide slurry, followed by calcination.   A hydrocarbon-based fuel is used, wherein raw fuel is reformed by a reformer having the reforming catalyst according to any one of claims 1 to 9, and the reformed fuel gas is generated in a fuel cell. Fuel cell system.

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