JP2005131471A - Co modification catalyst and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CO modification catalyst showing superior CO modification capacity even with a low H<SB>2</SB>O/CO ratio and a low metal carrying amount, and its production method. <P>SOLUTION: This CO modification catalyst formed with Pt and Re carried on a titania carrier of an anatase type contains 0.1 mass% or less of halogen, and has 0.5-15 g/L of carried Pt and Re per unit volume of the titania carrier. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a CO shift catalyst and a method for producing the same.

  A fuel cell is an energy conversion device that converts chemical energy of fuel directly into electrical energy. Compared to thermal power generation that performs similar energy conversion, fuel cells are less thermodynamically constrained and can obtain energy with high efficiency, and have less environmental impact. Has been done.

  Fuel cells are classified into solid polymer type (PEFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), solid electrolyte type (SOFC), alkaline type (AFC), etc., depending on the type of electrolyte. Among these, the polymer electrolyte (PEFC) fuel cell has no electrolyte dissipation, can be started at room temperature, and can be downsized. Application to various uses is expected.

As a fuel source of the polymer electrolyte fuel cell, a hydrogen-enriched gas obtained by steam reforming a hydrocarbon such as natural gas or naphtha or an alcohol such as methanol is used. However, this hydrogen-enriched gas contains carbon monoxide (CO) as one of by-products, and CO poisons Pt used as an electrode of the polymer electrolyte fuel cell and generates power. It will cause the decrease. Therefore, before being supplied to the fuel cell, CO is selectively transformed and removed by a water gas conversion reaction (CO + H ₂ O → CO ₂ + H ₂ ), and the CO content in the hydrogen-enriched gas is 1% or less. It has been reduced to be.

  Until now, Cu—Zn-based catalysts have been used for the water gas conversion reaction. However, Cu-Zn-based catalysts have low oxidation resistance, and when used for small fuel cells such as home use and in-vehicle use that are frequently started and stopped, the activity tends to deteriorate, so maintenance is frequently performed. There was a problem of having to.

In addition to the Cu—Zn-based catalyst, for example, Pt or a catalyst in which Pt and Re are supported on various metal oxides (Patent Document 2), Pt or Pt and Re are supported on a zirconia support. Catalysts (Patent Document 1, Non-Patent Documents 1, 2, and 4) and catalysts in which Pt and Re are supported on a rutile type titania carrier have been proposed (Non-Patent Documents 3 and 4).
Japanese Patent No. 3215680 International Publication WO01 / 003828 Pamphlet Igarashi Tetsu et al., Low-Temperature Water Gas Shift Reaction over Pt-Re / ZrO2 Catalysts, 86th Catalysis Conference Discussion Session A Preliminary Proceedings, Catalysis Society of Japan, 2000, 404 Satoshi Igarashi et al., Characterization of Pt-Re / ZrO2 catalyst for low-temperature water gas shift reaction, 88th Catalysis Conference, Proceedings of Conference A, Catalysis Society of Japan, 2001, 233 pages Satoshi Igarashi et al., Structure and function of Pt-Re / TiO2 catalyst for low-temperature water gas shift reaction, 90th Catalysis Conference, Conference B Preliminary Proceedings, Catalytic Society, 2002, pp. 413-415 Satoshi Igarashi et al., Characterization of Supported Pt-based Catalysts for Low-Temperature Water Gas Shift Reaction, The 92nd Catalysis Conference Discussion Session A Preliminary Proceedings, Catalysis Society of Japan, 2003, 175 pages

However, all of the catalysts disclosed in the above-mentioned patents or non-patent documents employ metals such as Pt and Re, and these are expensive and have limited resources. Need to be reduced. Further, the reaction temperature is high, due to the reverse shift reaction, H ₂ and CO and CO ₂ from the CO ₂ to the CO methanation occurs. In order to reduce these problems, development of a catalyst having higher selective oxidation property is expected.

  The present invention has been made paying attention to the above-described circumstances, and an object thereof is to provide a CO conversion catalyst capable of converting CO with high efficiency even with a low metal loading and a method for producing the same. It is in.

Another object of the present invention is to provide a CO conversion catalyst that exhibits excellent CO conversion ability at low temperature and low H ₂ O / CO (molar ratio).

  The CO conversion catalyst of the present invention is summarized in that Pt (platinum) and Re (rhenium) are supported on an anatase-type titania support.

  A CO conversion catalyst in which Pt and Re are supported on an anatase-type titania support can perform a CO conversion reaction with high efficiency, and is more resistant to oxidation than a conventionally used Cu-Zn-based catalyst. It is excellent.

  The halogen content in the CO conversion catalyst is preferably 0.1% by mass or less.

  The supported amounts of Pt and Re per unit volume of the anatase-type titania carrier are preferably 0.5 to 15 g / L, respectively.

  The gist of the method for producing a CO conversion catalyst of the present invention is that Pt and Re are supported on the support by impregnating an aqueous solution containing a platinum salt and a rhenium salt into an anatase-type titania support and heating.

  As the anatase-type titania carrier, it is recommended to use a carrier baked at 500 ° C to 800 ° C.

  The CO conversion catalyst of the present invention is excellent in oxidation resistance and exhibits high CO conversion ability even with a small amount of supported metal (Pt, Re), so that the amount of metal used is reduced compared to conventional CO conversion catalysts. This is advantageous in terms of cost.

  In addition, since the CO shift catalyst of the present invention can sufficiently advance the CO shift reaction even at a high space velocity (GHSV), further miniaturization of the fuel gas reforming system for the fuel cell can be expected. .

  The CO conversion catalyst of the present invention has the greatest feature in that Pt and Re are supported on an anatase type titania support.

  In general, three kinds of crystal structures of titania, anatase type (a), rutile type (b), and brookite type (c), are known, each having a structure as shown in FIG. Yes. As is clear from FIG. 1, they have different crystal structures and, of course, their properties are also different.

  In the present invention, among the above-mentioned titania, anatase titania is used as a carrier. Rutile-type titania also exhibits a certain effect as a CO conversion catalyst. However, when anatase-type titania is used as a carrier for a CO conversion catalyst, CO can be converted with higher efficiency than rutile-type titania. it can. The carrier of the present invention is preferably composed of only anatase type titania. However, as long as the effect of the present invention is not impaired, a crystal structure such as a rutile type or a brookite type is part of the carrier. May be present.

The anatase-type titania carrier used for the CO conversion catalyst of the present invention preferably has a BET specific surface area of 10 to 200 m ² / g.

  The CO conversion catalyst of the present invention is obtained by supporting Pt and Re as essential components in the anatase-type titania. The Pt-Re catalyst has a higher activity and a longer life than when Pt is used alone. The reason why the Pt-Re catalyst can carry out the CO shift reaction with high efficiency in this way is considered to be because the highly dispersed state of Pt on the catalyst support is stably maintained by using Re together. .

  Since Pt is expensive and has limited resources, it is preferable to reduce the loading amount as much as possible. Preferably, the amount of Pt supported per unit volume of the anatase type titania carrier is 15 g / L or less, more preferably 10 g / L or less, further preferably 5 g / L or less, and preferably 0.5 g / L or more. More preferably, it is 1.0 g / L or more, and still more preferably 1.5 g / L or more. If the amount of Pt supported exceeds the above range, the cost increases. On the other hand, if the amount is less than the above range, it is difficult to obtain the CO shift effect.

  When the amount of Pt supported is expressed as an amount per 100 parts by mass of the anatase-type titania carrier, Pt is preferably 1.5 parts by mass or less, more preferably 1.0 parts by mass or less, and still more preferably 0. 0.5 parts by mass or less, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.15 parts by mass or more.

  The amount of Re supported anatase titania carrier per unit volume is preferably 15 g / L or less, more preferably 10 g / L or less, still more preferably 5 g / L or less, and 0.5 g / L or more. It is preferable that it is 1.0 g / L or more, more preferably 1.5 g / L or more. Since Re is also expensive like Pt, the cost increases when the supported amount exceeds the above range, whereas if it is less than the above range, the effect of adding Re tends to be difficult to obtain.

  The amount of Re supported per 100 parts by mass of the anatase-type titania carrier is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, further preferably 0.15 parts by mass or more. It is recommended that the amount be 0.5 parts by mass or less, more preferably 1.0 parts by mass or less, and still more preferably 0.5 parts by mass or less.

  The total amount of Pt and Re contained in the CO conversion catalyst of the present invention is preferably 0.1 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the support. More preferably, it is 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, more preferably 1.5 parts by mass or less, and further preferably 1 part by mass or less. As described above, since both Pt and Re are expensive, it is not preferable to use the Pt and Re beyond the above range because the cost is increased. On the other hand, when it is less than the above range, the CO conversion efficiency may decrease. The ratio of Re to Pt is not limited, but Pt: Re is preferably 1: 1 (mass ratio).

  Furthermore, in addition to the above-mentioned Pt and Re, other metals such as Ru, Rh, Pd and Ir may be supported on the CO conversion catalyst of the present invention. This is because these other metals have an effect of promoting and stabilizing the catalytic action of Pt. In addition, when using these other metals, it is preferable that the loading amount with respect to a support | carrier is 0.05 mass% or more and 0.5 mass% or less.

  The supported metal may be present on the surface of the carrier or may be uniformly distributed throughout the carrier.

  The CO conversion catalyst of the present invention is preferably one in which the halogen content in the carrier carrying the above-described Pt, Re, etc. is suppressed to 0.1% by mass or less. The halogen in the catalyst may corrode peripheral devices and piping metal members, and may reduce the CO conversion rate and increase the production of by-products. Therefore, it is recommended to reduce the amount of halogen (particularly Cl) contained in the support as much as possible. More preferably, it is 0.05 mass% or less, More preferably, it is 0.01 mass% or less. Of course, 0% is most preferable.

  The halogen content in the CO shift catalyst can be quantified by an analysis method using a high temperature combustion ion chromatography method, a fluorescent X-ray elemental analyzer, an ICP emission analyzer, or the like. Further, the amount of halogen contained in the cleaning solution used for the cleaning treatment (described later) for reducing the amount of halogen in the carrier may be analyzed by ion chromatography.

  The shape of the CO conversion catalyst of the present invention is not particularly limited, and various forms such as a granular shape, a cylindrical shape, a spherical shape, a pellet shape, and a honeycomb shape can be adopted. Further, the size of the CO conversion catalyst may be appropriately determined according to the filling properties of the reactor, which will be described later, but the particle size is preferably about 1 to 5 mm, more preferably 2 to 4 mm. .

  Next, a method for producing the CO conversion catalyst of the present invention will be described.

  The method for producing the CO conversion catalyst of the present invention is not particularly limited, and examples thereof include a method of producing an anatase-type titania carrier and supporting Pt and Re on the carrier. The method for producing the anatase-type titania carrier is not particularly limited as long as the anatase-type crystal structure is maintained, a method of firing a commercially available anatase-type titania powder, a Ti-containing salt or an aqueous solution of a compound, A method of preparing titania powder from a mineral containing Ti, and drying and firing it can be employed. Examples of a method for preparing titania powder from an aqueous solution of a salt or compound containing Ti include a precipitation method by hydrolysis, a precipitation method by neutralization, and a thermal hydrolysis method.

Examples of the salts and compounds containing Ti include titanium alkoxides such as Ti (O—iPr) ₄ , and salts containing titanium such as TiCl ₄ , Ti (SO ₄ ) ₂ , and TiOSO ₄ . These raw materials may be appropriately selected and used according to the above-described production method.

Examples of a method for preparing anatase-type titania powder using a Ti-containing mineral (ilmenite, rutile ore, etc.) as raw materials include a sulfuric acid method and a chlorine method. For example, when the sulfuric acid method is employed, anatase-type titania powder can be prepared as follows. First, ilmenite (titanium mineral) is finely pulverized, dried, dissolved in concentrated sulfuric acid, and iron contained in the ilmenite ore is separated as iron sulfate (FeSO ₄ ). The resulting solution is then hydrolyzed to precipitate titanium as metatitanic acid (TiO (OH) ₂ ). Thereafter, the obtained metatitanic acid is roasted in a high-temperature rotary kiln or the like to obtain anatase-type titania powder.

  The obtained anatase-type titania powder is molded into an appropriate shape and size and then fired. As the molding method, any conventionally known molding method can be used. Examples thereof include a method of spraying water on anatase-type titania powder and granulating and molding, a method such as extrusion molding and compression molding. Moreover, you may use a binder etc. in the case of shaping | molding. The binder is not particularly limited, and any organic or inorganic substance can be used as long as it is usually used at the time of preparing the carrier. Examples thereof include organic binders such as stearic acid and oleic acid, and inorganic binders such as bentonite. Can do.

  The firing treatment is preferably performed at 500 ° C. or higher and 800 ° C. or lower in an air stream. More preferably, it is 600 degreeC or more and 700 degrees C or less. This is because when the firing temperature is less than the lower limit, it is difficult to obtain mechanical strength as a carrier. On the other hand, when the upper limit is exceeded, the crystal structure of titania tends to easily transition from the anatase type to the rutile type. In addition, since firing at a high temperature tends to reduce the surface area of the particles, it is preferable to perform the firing treatment within the above range from the viewpoint of improving the reaction efficiency by highly dispersing the Pt and Re on the support. .

  Pt and Re are supported on the anatase-type titania carrier prepared as described above. Conventionally known methods such as an impregnation method, a coprecipitation method, a competitive adsorption method, and an ion exchange method can be employed for supporting Pt and Re on an anatase type titania carrier. For example, when Pt and Re are supported by an impregnation method, a method in which an aqueous solution of a salt containing Pt is impregnated in a carrier and then an aqueous solution of a salt containing Re is impregnated; an aqueous solution of a salt containing Re is impregnated in the carrier And then impregnating with an aqueous solution of a salt containing Pt; a method of impregnating a carrier with an aqueous solution of a salt containing Pt and a salt containing Re, or an aqueous solution of a salt containing Pt or Re by spraying on the carrier Among these methods, a method of impregnating a carrier with an aqueous salt solution containing Re and then impregnating an aqueous solution of salt containing Pt is preferable. In order to impregnate the active ingredients (Pt and Re) even inside the carrier, it is effective to degas the pores in advance or to employ a competitive adsorption method.

  In the production of the CO conversion catalyst of the present invention, it is preferable to use a complex salt containing Pt. Among the above complex salts, halogen-free ammine complex salts, nitro complex salts, nitroammine complex salts, ethylenediamine complex salts, and the like are particularly preferable. Specific examples include dinitrodiammine platinum (II), hexaammine platinum (IV) hydrochloride, and tetraammine platinum. (II) Hydrochloride etc. are mentioned.

  When a salt containing halogen is used as the salt containing Pt, it is preferable to impregnate the anatase-type titania carrier with the Pt component and then reduce the amount of halogen contained in the carrier. Halogen in the carrier can be reduced by drying the carrier and then washing with water or a suitable washing solution, or by heating at a temperature of 250 to 600 ° C. However, since it is difficult to completely remove the halogen in the support even by these treatments, it is desirable to employ a starting material that does not contain a halogen.

  As the salt containing Re to be supported on the CO conversion catalyst of the present invention, it is preferable to employ a halogen-free compound. Examples of such a salt containing Re include ammonium perrhenate (VII) and rhenium oxide (VII).

  The CO conversion catalyst of the present invention is preferably obtained by impregnating an aqueous solution containing the above-described platinum salt and rhenium salt into an anatase-type titania carrier and heating it so that Pt and Re are supported on the carrier. . That is, it is also a preferred embodiment that after the anatase-type titania carrier impregnated with Pt and Re is dried, the salt is thermally decomposed, reduced (activated), and the like. The heat treatment is preferably performed at 300 to 600 ° C. for 10 to 60 minutes. Further, the CO conversion catalyst of the present invention is preferably subjected to a reduction treatment at 300 ° C. to 600 ° C. for about 10 to 60 minutes in a hydrogen stream before use. This is because by performing such a treatment, impurities such as residual salts in the carrier are decomposed and reduced and removed, so that a catalyst capable of converting CO with higher efficiency can be obtained.

The CO conversion catalyst of the present invention is preferably used when converted into CO ₂ and H ₂ by a reaction (water gas conversion reaction) represented by the following formula (1).
(Formula 1)
CO + H ₂ O → CO ₂ + H ₂ (1)

  Therefore, the CO conversion catalyst of the present invention can be applied to various gases as long as it contains CO, but is particularly suitable for the reformed gas supplied to the fuel cell.

The reformed gas supplied to the fuel cell is obtained mainly by reacting natural gas, methanol or the like with water vapor, and in the reformed gas, CO and CO ₂ together with H _{2 as} the main component. It is included. For example, city gas (natural gas, CH ₄ : 88 mol%, C ₂ H ₆ : 6 mol%, C ₃ H ₈ : 3 mol%, C ₄ H ₁₀ : 3 mol%) was used as the raw material for the reformed gas. In some cases, about 10 mole percent CO is present in the reformed gas. If the catalyst of the present invention is used, the CO content can be reduced with high efficiency without reducing the amount of H ₂ in the reformed gas. In addition, when using city gas for a raw material, it is preferable to remove beforehand the sulfur content contained as an odorant in this city gas.

The reformed gas supplied to the fuel cell is usually sent to the CO selective oxidation step for further reducing the CO amount after the reaction (1). In this step, since 1 to 3 times the amount of O ₂ present in the gas obtained by the CO shift reaction is supplied, H ₂ is also oxidized along with the oxidation of CO. However, since the CO conversion catalyst of the present invention has a high CO conversion rate, the CO content in the product gas can be reduced, and the amount of H ₂ consumed in the CO selective oxidation process can be reduced, thereby improving the hydrogen generation efficiency. Can be made.

  Note that the CO conversion catalyst of the present invention can be suitably used not only for the case where the above natural gas or the like is used as a raw material, but also for reducing CO in reformed gas using coal or coke oven gas as a raw material. .

  As a reaction apparatus for carrying out the above-mentioned shift reaction, an atmospheric pressure fixed bed flow type reactor, a fluidized bed reactor or the like can be used. The amount of catalyst charged into these reactors is not particularly limited, and may be determined as appropriate according to the size of the reactor, the amount of reformed gas to be treated, and the like.

The space velocity (GHSV) when introducing the reformed gas (CO-containing gas) into the reaction tube is preferably 500 h ⁻¹ or more and 10000 h ⁻¹ or less (dry gas standard, the same applies hereinafter). If the space velocity exceeds the above range, the CO conversion rate tends to decrease. On the other hand, if the space velocity is below the above range, it is not practical.

During the CO shift reaction, the ratio of H ₂ O to CO contained in the CO-containing gas, H ₂ O / CO (molar ratio) is preferably as low as possible, specifically 6 or less, more preferably 4 Hereinafter, it is 2 or more, more preferably 2.5 or more. The H ₂ O is mixed with a CO-containing gas in the state of water vapor. Therefore, particularly when used in a polymer electrolyte fuel cell in which a hydrogen generator is integrated, since the operating temperature of the polymer electrolyte fuel cell is low, the heat generated in the battery body (cell part) is generated. When it is difficult to use and H ₂ O / CO exceeds the above-mentioned range, it is necessary to provide a steam generator for CO-containing gas modification, which causes the downsizing of the apparatus and the power generation efficiency as a fuel cell. Become. On the other hand, when the amount is less than the above range, the CO shift reaction does not proceed because the amount of H ₂ O is small, and the removal of CO tends to be insufficient.

  Since the water gas conversion reaction is an exothermic reaction, the reverse reaction tends to occur as the temperature rises, and the processing amount tends to decrease. Therefore, the reaction temperature (catalyst layer temperature) is preferably as low as possible. Specifically, the temperature is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, preferably 500 ° C. or lower, more preferably 300 ° C. or lower.

  Since the gas obtained by the above-described process has a sufficiently reduced CO content, it can be suitably used for other fuel cells using hydrogen as a fuel other than solid polymer fuel cells.

The CO conversion catalyst of the present invention is excellent in oxidation resistance and capable of reaction at a low H ₂ O / CO ratio, and is therefore suitable for a hydrogen generator provided in a small fuel cell system such as in-vehicle or home use. Can be used. In addition, since a high CO conversion rate is exhibited even with a low metal loading, it is advantageous in terms of cost.

The fuel cell system to which the CO conversion catalyst of the present invention is applied is not particularly limited. For example, the fuel cell system includes a fuel cell body and a reformer that reforms a hydrocarbon-based fuel into H _2. I just need it.

The fuel cell body takes out electric energy by chemical reaction using H ₂ as a raw material. The fuel cell body may be any material that uses H ₂ as a raw material, and in particular, a gas diffusion electrode in which an ion exchange membrane (solid polymer electrolyte) is used as an electrolyte and a Pt-based noble metal catalyst is supported on carbon as an electrode. It is preferable to use a polymer electrolyte fuel cell (PEFC) provided with the electrodes on both surfaces of the ion exchange membrane.

  The reformer includes a reforming unit that performs a steam reforming reaction that reforms fossil fuel such as natural gas with steam by a steam reforming reaction to reform the hydrogen-rich reformed gas, and the steam reforming The constituent elements include a CO conversion part that reduces the amount of CO contained in the reformed gas obtained by the reaction by a CO conversion reaction, and a CO selective oxidation part that further reduces the CO concentration. The CO shift catalyst of the present invention is provided in the CO shift section.

Since the fuel cell system to which the CO conversion catalyst of the present invention is applied has the above-described reformer, it can be supplied to the fuel cell main body after sufficiently reducing the CO content. In addition, the CO conversion catalyst of the present invention provided in the CO conversion section is a later step because the water gas conversion reaction can proceed with high efficiency at a low temperature and a low H ₂ O / CO ratio. The load in the CO selective oxidation reaction can be reduced. In addition, the energy efficiency of the fuel cell system is high, and the fuel cell system itself can be downsized, and is particularly suitable as a fuel cell system for home use or on-vehicle use.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples. However, the following experimental examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the present invention are included in the technical scope of the present invention. It is.

[Evaluation of CO conversion removal performance]
1 ml of catalyst is filled into a reaction tube of an atmospheric pressure fixed bed flow reactor and diluted with 200 ml / min of N ₂ in a 20 ml / min H ₂ stream for 2.5 hours until the catalyst layer temperature reaches 450 ° C. Then, the temperature was raised and held at the same temperature for 30 minutes, and the reduction treatment was performed beforehand. Next, after the catalyst layer is adjusted to a predetermined temperature, the CO-containing gas mixed with water vapor so that the ratio H ₂ O / CO (molar ratio) of water vapor to CO in the CO-containing gas (introduced gas) becomes 3 in space. The CO conversion reaction was carried out by supplying the reaction tube at a rate (GHSV) of 3000 h ⁻¹ . The composition of the product gas discharged from the reaction tube outlet with the temperature of the catalyst layer kept substantially constant is analyzed by gas chromatography with a thermal conductivity detector (manufactured by Shimadzu Corporation), and the CO conversion rate is calculated. Asked. Note that the CO-containing gas composition used at this time, H _2: 78 mol%, CO: 10 mol%, CO _2: is 12 mol%.
(Formula 2)

In the formula, [CO] ₀ represents the CO molar concentration in the raw material gas, and [CO] represents the CO molar concentration in the product gas. The same applies to [CO ₂ ] ₀ and [CO ₂ ].

[Measurement of Cl content in CO conversion catalyst]
The amount of Cl contained in the CO shift catalyst was measured by a high-temperature combustion ion chromatograph method (ion chromatograph, manufactured by Dionex).

[Preparation of anatase-type titania carrier]
Anatase type titania powder (manufactured by Daiichi Rare Element Chemical Co., Ltd., prototype) was granulated by spraying with distilled water while stirring with a mixer (carrier particle diameter: 2 to 3 mm) and dried at 50 ° C. The obtained granular material was heated in a baking furnace in an air stream of 400 ml / min over 1.5 hours until the baking temperature reached 600 ° C., and subjected to a baking treatment for 1 hour at the same temperature, anatase type A titania carrier (packing density 999 g / L) was obtained.

Catalyst 1
The obtained anatase-type titania carrier (packing density 999 g / L) was impregnated with an aqueous solution of ammonium perrhenate (VII) so that the amount of Re supported on 1 L of the carrier was 3.44 g. Dry for more than an hour. The dried material was heated in a baking furnace in a 400 ml / min air stream until the baking temperature reached 430 ° C. over 1.5 hours, and a baking process was performed for 30 minutes at the same temperature. Thereafter, the mixture is allowed to cool to 60 ° C. or less, and then heated in a 20 ml / min H ₂ stream diluted with 400 ml / min N ₂ over 2.5 hours until the reduction temperature reaches 450 ° C. Then, the reduction treatment was performed by holding at the same temperature for 30 minutes.

  Next, the tetraammineplatinum (II) hydrochloride solution is impregnated so that the amount of Pt supported on 1 L of anatase-type titania carrier is 3.44 g, and drying, firing and reduction treatment are performed in the same manner as in the case of Re. A CO shift catalyst was obtained. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported. In addition, although Cl content contained in this catalyst 1 was measured by the high temperature combustion ion chromatography method, Cl was not detected from the catalyst 1.

Catalyst 2
A catalyst was prepared in the same manner as the catalyst 1 except that the amount of Re and Pt supported on 1 L of anatase type titania support was 0.86 g. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported.

Catalyst 3
A catalyst was prepared in the same manner as Catalyst 1 except that the amount of Re and Pt supported on 1 L of anatase-type titania carrier was 1.72 g. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported.

Catalyst 4
A catalyst was prepared in the same manner as Catalyst 1 except that the amount of Re and Pt supported on 1 L of anatase-type titania carrier was 6.87 g. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported.

Catalyst 5
A catalyst 5 was prepared in the same manner as the catalyst 1 except that the calcination temperature of anatase titania was 500 ° C. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported.

Catalyst 6
A catalyst 6 was prepared in the same manner as the catalyst 1 except that the calcination temperature of anatase titania was set to 700 ° C. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported.

Catalyst 7
A catalyst 7 was prepared in the same manner as the catalyst 1 except that the calcination temperature of anatase titania was 800 ° C. Table 1 shows the carrier preparation conditions and the amounts of Pt and Re supported.

Catalyst 8
A catalyst 8 carrying Pt and Re was prepared in the same manner as the catalyst 1 except that the rutile type titania support was prepared by setting the firing temperature of the titania support to 900 ° C. The supported amount of Re and Pt with respect to 1 L of rutile-type titania carrier (packing density: 1843 g / L) was 3.44 g. Table 1 shows the carrier preparation conditions, the supported amounts of Pt and Re, and the like.

Catalyst 9
A catalyst 9 supporting only Pt was prepared in the same manner as the catalyst 1 except that Re was not used as the supporting metal. Table 1 shows the carrier preparation conditions and the amount of Pt supported.

Catalyst 10
Catalyst 10 was prepared in the same manner as Catalyst 1 except that hexachloroplatinic (IV) acid (hexahydrate) was used as a starting material for Pt. The amount of Re and Pt supported on 1 L of anatase-type titania carrier was 3.44 g. Table 1 shows the carrier preparation conditions, the supported amounts of Pt and Re, and the like. The Cl content of the catalyst 10 was 0.14% by mass.

Catalyst 11
The rutile type titania powder (catalyst society reference catalyst, JRC-TIO-3) is compressed with a manual compression molding machine at a pressure of about 40 MPa for 60 seconds, and the resulting solid is pulverized (particle size 0.5 to 1 mm) and a carrier composed of rutile-type titania (packing density 1281 g / L) was prepared.

  A catalyst carrying Pt and Re was prepared in the same manner as Catalyst 1 so that the amount of Pt and Re supported on 1 L of the obtained rutile-type titania carrier was 3.44 g. Table 1 shows the carrier preparation conditions, the supported amounts of Pt and Re, and the like.

Catalyst 12
ZrO ₂ powder (Daiichi Rare Element Chemical Co., Ltd.) was granulated by spraying with distilled water while stirring with a mixer (carrier particle diameter: 2 to 3 mm), and dried at 50 ° C. In granules obtained fired furnace, air stream of 400 ml / min, the firing temperature is raised over a period of 1.5 hours to a 700 ° C., from ZrO ₂ baked by keeping at the same temperature for 1 hour The resulting carrier (packing density 1029 g / L) was prepared.

The obtained ZrO ₂ support was loaded with Pt and Re in the same manner as in the above catalyst 1 except that hexachloroplatinic (IV) acid (hexahydrate) was used as a starting material for Pt. Prepared. The amount of Pt and Re supported on 1 L of ZrO ₂ carrier was 3.44 g, respectively. Table 1 shows the carrier preparation conditions, the supported amounts of Pt and Re, and the like.

Catalyst 13
Other than using CeO ₂ granules (manufactured by Kishida Chemical Co., Ltd.) as a carrier, not firing the carrier, and using hexachloroplatinum (IV) acid (hexahydrate) as a starting material for Pt Prepared Catalyst 13 in the same manner as Catalyst 1 above. The amount of Pt and Re supported on 1 L of the carrier (packing density 2151 g / L) was 3.44 g, respectively. Table 1 shows the conditions for preparing the carrier used in this catalyst, the supported amounts of Pt and Re, and the like.

Catalyst 14
Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd.) was used as a carrier, the carrier was not calcined, and hexachloroplatinum (IV) acid (hexahydrate) was used as a starting material for Pt. Except for the above, the catalyst 14 was prepared in the same manner as the catalyst 1 described above. The amount of Pt and Re supported on 1 L of the catalyst support (packing density 540 g / L) was 3.44 g. Table 1 shows the conditions for preparing the carrier used in this catalyst, the supported amounts of Pt and Re, and the like.

[Experimental Example 1 Comparison of CO conversion rate by crystal structure or carrier type]
Using the catalysts 1, 5 to 8 and 11 to 14, an evaluation test of CO conversion removal performance was performed. The composition of the CO-containing gas used at this time, H _2: 78 mol%, CO: 10 mol%, CO _2: was 12 mol%. The results are shown in Table 2 and FIG. Further, the catalysts 1, 5 to 8 and 11 were measured using a powder X-ray diffractometer (manufactured by Rigaku Corporation). FIG. 2 shows an X-ray diffraction spectrum.

  From FIG. 2, it can be confirmed that the carriers of Catalyst 5, Catalyst 1 and Catalyst 6 that were calcined at 500 ° C., 600 ° C., and 700 ° C. have a crystal structure of anatase titania. On the other hand, in the catalyst 8 calcined at 900 ° C., the same peak as that of the catalyst 11 using rutile titania as the carrier can be confirmed, and the crystal structure is changed from anatase type to rutile type by the calcining treatment of the carrier. It can be seen that it has changed. Moreover, it can confirm that the catalyst 7 which baked at 800 degreeC is the state in which the crystal structure of the anatase type and the rutile type was mixed (CO conversion rate: 62.5%, catalyst layer temperature: 239 degreeC).

  FIG. 3 shows that when the carrier has an anatase type crystal structure, it has the same CO conversion rate regardless of the firing temperature. On the other hand, from the CO conversion rate of the catalyst 7 having a structure containing rutile-type titania as part of the support and the catalyst 8 in which the crystal structure of the support is transferred to the rutile-type titania due to an increase in the firing temperature, It can be seen that as the rutile structure increases, the CO conversion rate decreases.

  Further, from Table 2, it can be seen that catalysts 1, 5 and 6 using anatase-type titania as a support show higher CO conversion rates than catalysts 12 to 14 using an oxide of Zr, Ce and Al as a support. It can be seen (for example, catalyst 1, CO conversion rate 91.8%).

[Experimental example 2 Comparison of effects with Re]
Using the catalyst 1 and the catalyst 9, a CO conversion removal performance evaluation test was performed. The product gas was analyzed while changing the catalyst layer temperature and the reaction was stable, and the CO conversion rate was determined. The results are shown in FIG.

  As shown in FIG. 4, the catalyst 1 carrying Re together with Pt shows higher CO conversion ability than the catalyst 9 carrying Pt alone. It can also be seen that in the catalyst 1, the CO shift reaction proceeds with high efficiency from the low temperature region.

[Experimental example 3 Comparison of effects with and without Cl]
Using the catalyst 1 and the catalyst 10, an evaluation test of CO conversion removal performance was performed. The generated gas was analyzed in a state where the reaction was stable at various catalyst layer temperatures, and the CO conversion rate was determined. The results are shown in FIG. In addition, Cl content in the catalysts 1 and 10 measured by the high temperature combustion ion chromatography method was catalyst 1: not detected and catalyst 10: 0.14% by mass.

  From FIG. 5, catalyst 1 using tetraammineplatinum (II) hydrochloride as a Pt precursor (Cl content: undetected) is a catalyst using hexachloroplatinic (IV) acid (hexahydrate) containing Cl. It can be confirmed that the CO conversion rate is higher than 10 (Cl content: 0.14% by mass). Moreover, it turns out that the CO conversion catalyst satisfying the requirements of the present invention can convert CO with high efficiency even at a low catalyst layer temperature (200 to 250 ° C.).

[Experimental example 4 Comparison of effects due to difference in metal loading]
An evaluation test of CO conversion removal performance was performed using the above catalysts 1 to 4, and the CO conversion rate depending on the amount of Pt and Re supported was compared.

In the CO conversion removal performance test, the CO conversion catalyst packed in the reaction tube of the atmospheric pressure fixed bed flow type reactor was diluted with 450 ml / min of N ₂ in a 50 ml / min H ₂ stream, and the catalyst layer temperature was The temperature was raised to 450 ° C. over 2.5 hours, held at the same temperature for 30 minutes, subjected to reduction treatment in advance, and then performed according to the following conditions. The results are shown in FIG.

<Reaction conditions>
Catalyst amount: 10ml
H ₂ O / CO (molar ratio): 3
GHSV: 1000h ^-1
CO-containing gas composition H _2: 78 mol%, CO: 10 mol%, CO _2: 12 mol%
From FIG. 6, it can be seen that when the catalysts 1 to 4 are used, all show a high CO conversion rate from a low catalyst layer temperature. It can also be seen that the CO conversion rate improves as the metal loading increases.

[Experimental Example 5 Comparison of CO conversion rate by GHSV]
Using the catalyst 1, the CO conversion removal performance was evaluated according to the following conditions. The results are shown in FIG. FIG. 7 also shows the results of Experimental Example 4 (Catalyst 1, GHSV: 1000 h ⁻¹ ) together with the CO conversion rate of the catalyst 1.

<Reaction conditions>
Catalyst amount: 10ml
H ₂ O / CO (molar ratio): 3
GHSV: 500 h ^-1
CO-containing gas composition H _2: 78 mol%, CO: 10 mol%, CO _2: 12 mol%
From FIG. 7, it can be seen that the catalyst of the present invention exhibits extremely high activity in GHSV 500h ⁻¹ and 1000 h ⁻¹ (Experimental Example 4, Catalyst 1), which are close to the actual operating conditions of the fuel cell system. In particular, it can be confirmed that under the condition of GHSV 500h ⁻¹ , CO can be transformed with high efficiency even when the catalyst layer temperature is 160 ° C.

[Experimental example 6 durability test]
Using the catalyst 1, the change over time in the CO conversion removal efficiency was examined by the following method, and the durability of the catalyst of the present invention was evaluated.

1. 3 ml of catalyst was filled in a reaction tube of a normal pressure fixed bed flow type reactor and diluted with 450 ml / min of N ₂ in a 50 ml / min H ₂ stream until the catalyst layer temperature reached 450 ° C. The temperature was raised over 5 hours, and the reduction treatment was performed by maintaining the temperature for 30 minutes. Subsequently, a CO-containing gas (composition H ₂ : 78 mol%, CO: 10 mol%, CO ₂ : 12 mol%) mixed with water vapor so that the H ₂ O / CO (molar ratio) is 3 is converted into GHSV1000h ^−1. Then, the CO shift reaction was carried out for 100 hours while maintaining the catalyst layer temperature at about 200 ° C. At regular intervals, the product gas discharged from the catalyst layer outlet was analyzed by gas chromatography to examine the change over time in the CO conversion rate, and the durability of the catalyst was evaluated. The results are shown in FIG.

  FIG. 8 shows that the CO conversion rate is not lowered within the test time, and the catalyst of the present invention is excellent in durability.

In any of the above experimental examples, when a CO shift catalyst satisfying the requirements of the present invention is used, generation of CH ₄ which is a side reaction product during the CO shift reaction is not recognized in the product gas. The reaction selectivity of the CO shift reaction was 100%.

It is a figure which shows the crystal structure of titania. 2 is an X-ray diffraction spectrum showing a crystal structure of a titania carrier of catalysts 1, 5 to 8, 11; 6 is a graph showing the results of Experimental Example 1. 10 is a graph showing the results of Experimental Example 2. 10 is a graph showing the results of Experimental Example 3. 10 is a graph showing the results of Experimental Example 4. 10 is a graph showing the results of Experimental Example 5. 10 is a graph showing the results of Experimental Example 6.

Claims (6)

  A CO conversion catalyst comprising Pt and Re supported on an anatase type titania support.   The CO conversion catalyst according to claim 1, wherein the halogen content in the CO conversion catalyst is 0.1 mass% or less.   The CO conversion catalyst according to claim 1 or 2, wherein the amount of Pt supported per unit volume of the anatase-type titania support is 0.5 to 15 g / L.   The CO conversion catalyst according to any one of claims 1 to 3, wherein the amount of Re supported per unit volume of the anatase-type titania support is 0.5 to 15 g / L. A method for producing the CO shift catalyst according to any one of claims 1 to 4,
A method for producing a CO conversion catalyst, comprising impregnating an aqueous solution containing a platinum salt and a rhenium salt on an anatase-type titania support and supporting Pt and Re on the support by heating.   6. The method for producing a CO conversion catalyst according to claim 5, wherein the anatase-type titania support is obtained by calcining anatase-type titania at 500 ° C. to 800 ° C.