JP2003305364A - Aqueous gas shift reaction catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a aqueous gas shift reaction catalyst with high catalytic reactivity and oxidation resistance. <P>SOLUTION: This aqueous gas shift reaction catalyst comprises a metal oxide on which at least one metal selected from a metal group A (Pt, Pd, Ni, Ir, Rh, Co, Os, Ru, Fe, Re, Tc, and Mn) and at least one metal selected from a metal group B (Au, Ag, and Cu) are deposited. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water gas shift reaction catalyst for producing carbon dioxide and hydrogen from carbon monoxide and water.

[0002]

2. Description of the Related Art The water gas shift reaction is a reaction that plays an important role in an industrial hydrogen production process and is represented by the following reaction formula.

CO + H ₂ O → CO ₂ + H ₂ This reaction is an increase in hydrogen of methane reformed gas (H ₂ + CO + CO ₂ ), H ₂ / CO _{2 in} a methanol synthesis plant, an ammonia synthesis plant, etc. It is used to adjust the ratio.

Especially when high-purity hydrogen is required, this reaction is usually carried out in the following two-step reaction. In the one-step reaction, a high temperature shift catalyst such as Fe-Cr mixed oxide catalyst is used,
By conducting the reaction in the temperature range of 310-450 ℃, the CO concentration becomes 2
It can be reduced to ~ 3%. In the two-step reaction, Cu-Zn-A
l Using a low temperature shift catalyst such as a complex oxide catalyst,
By conducting the reaction at -240 ° C, the CO concentration can be reduced to 1% or less.

In a fuel cell using methane, gasoline or the like as fuel, hydrogen is produced by the following process.

Fuel → [fuel reformer] → hydrogen → [fuel cell] The reaction in the fuel reformer requires a catalyst, and is usually carried out by the following three-step catalytic reaction. Of the catalytic reactions, the latter two reactions (2) and (3) mainly aim to remove CO in hydrogen gas. (1) Steam reforming reaction (2) Water gas shift reaction (CO conversion reaction) (3) CO selective oxidation reaction or methanation reaction The above fuel cell has been attempted to be applied to a small fuel cell for household use, For that purpose, it is necessary to downsize the fuel reformer. However, since the water gas shift reaction of the two-step reaction (2) has a slower reaction rate than the one-step reaction (1) and the three-step reaction (3), a large amount of catalyst is required and the fuel cell becomes large. Will end up. Therefore, a water gas shift catalyst that reacts at high speed is desired.

As a solution to the problem, a method using a noble metal catalyst having a higher activity than the base metal catalyst has been considered.
Side reaction (methanation) at high temperature in reactions using precious metal catalysts
Occurs and consumes hydrogen.

Further, as a water gas shift catalyst capable of reducing the CO concentration, a copper catalyst can be mentioned as a catalyst which has been proven so far. However, in the copper-based catalyst, while the copper is kept in the reduced state in the operating state of the catalyst, when the operation of the fuel cell system is stopped, the catalyst and the air come into contact with each other to become copper oxide, and when restarted. Since copper oxide is reduced and heat is generated, the catalyst is thermally deteriorated.

Up until now, DC Grenoble and MM. Has been cited as a document listing the metal species active in the water gas shift reaction.
Estadt, J. Catal., 67, 90 (1981) and the like are known.
Also, as a document on the reaction of producing methane from CO and hydrogen, see MA Vannice, "CATALYSIS Science and Tech.
nology ", Springer-Verlag, Vol.3, p.139 (1982) and the like are known.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a catalyst for a water gas shift reaction which has high catalytic activity and oxidation resistance.

[0011]

In view of the above-mentioned problems of the prior art, the present inventor has conducted earnest research on a catalyst for a water gas shift reaction, and as a result, at least two catalysts having different characteristics have been obtained.
It was found that a catalyst for a water gas shift reaction, which can suppress methanation while maintaining high catalytic activity at high temperature, can be obtained by dispersing and supporting a kind of metal on an oxide surface, and completed the present invention. .

That is, the present invention provides the following water gas shift catalyst.

Item 1. Metal species group A (Pt, Pd, Ni, Ir, Rh,
At least one selected from Co, Os, Ru, Fe, Re, Tc, Mn) and at least one selected from the metal species group B (Au, Ag, Cu) are supported on the metal oxide. A catalyst for a water gas shift reaction characterized by:

Item 2. The metal oxide is (i) zinc oxide, iron oxide, copper oxide, lanthanum oxide, titanium oxide, cobalt oxide, zirconium oxide, magnesium oxide, beryllium oxide, nickel oxide, chromium oxide, scandium oxide,
A metal oxide of a single metal selected from the group consisting of cadmium oxide, indium oxide, tin oxide, manganese oxide, vanadium oxide, cerium oxide, aluminum oxide and silicon oxide, (ii) zinc, iron, copper, lanthanum, titanium,
Cobalt, zirconium, magnesium, beryllium,
A composite oxide of two or more kinds of metals selected from the group consisting of nickel, chromium, scandium, cadmium, indium, tin, manganese, vanadium, cerium, aluminum and silicon, or (iii) and at least one kind of (i) Item 1 which is a mixture of at least one of ii)
The catalyst for water gas shift according to 1.

Item 3. The metal species A is Pt and the metal species B is Au
And the metal oxide is titanium oxide and / or cerium oxide.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Metal species group A (Pt, Pd, Ni, Ir, Rh,
At least one selected from Co, Os, Ru, Fe, Re, Tc, Mn) and at least one selected from the metal species group B (Au, Ag, Cu) were allowed to coexist on the surface of the same metal oxide. When a catalyst was prepared and a water gas shift reaction using the catalyst was examined, it was found that the catalyst had an effect that the activity was high at a high temperature, the methanation reaction could be suppressed, and a high hydrogen yield could be achieved. It was

That is, the present invention provides a metal oxide and a metal species A.
And a metal species B.

The metal species A in the present invention is highly active in water gas shift, but is also active in methanation at the same time, and is an element of the 7th to 10th groups (Pt, Pd) in the above-mentioned periodic table. , Ni, Ir, Rh, Co, Os, Ru, Fe, Re, Tc,
Examples include one or more metal species selected from Mn).
Pt, Pd, Ni, Rh, Ru and the like are preferable. More preferably, Pt is mentioned from the viewpoint of high catalytic activity.

The metal species B in the present invention is active in the water gas shift, but has a very small methanation activity.
One, two or more metal species selected from u, Ag, Cu). Preferably, Au, Cu or the like is used. More preferably, from the viewpoint of high catalytic activity and methanation suppressing effect,
Au is mentioned.

The metal oxide in the present invention is not particularly limited as long as it is an oxide species generally selected for the purpose of carrying a dispersed metal species. For example, zinc oxide, iron oxide, copper oxide, lanthanum oxide, titanium oxide, cobalt oxide, zirconium oxide, magnesium oxide, beryllium oxide, nickel oxide, chromium oxide, scandium oxide, cadmium oxide, indium oxide, tin oxide, manganese oxide, A metal oxide of a single metal selected from vanadium oxide, cerium oxide, aluminum oxide, silicon oxide, or the like, or
Zinc, iron, copper, lanthanum, titanium, cobalt, zirconium, magnesium, beryllium, nickel, chromium,
Examples thereof include complex oxides of two or more elements selected from scandium, cadmium, indium, tin, manganese, vanadium, cerium, aluminum, silicon and the like.
If necessary, it is also possible to use a mixture of at least one selected from the above-mentioned single metal metal oxides and at least one selected from complex oxides. Among these, preferably, titanium oxide, cerium oxide, cerium-zirconium composite oxide, iron oxide, zirconium oxide, aluminum oxide, cerium-lanthanum composite oxide, and the like, more preferably titanium oxide, cerium oxide, cerium. -Zirconium composite oxide and the like are mentioned, and in particular, titanium oxide, cerium oxide, and cerium-zirconium composite oxide are particularly preferable from the viewpoint of high catalytic activity and stability.

The shape of the metal oxide is not particularly limited,
For example, in addition to powder, it can be used in a pre-molded state or fixed to various supports.

Further, as the catalyst for the water gas shift reaction of the present invention, a metal-immobilized oxide in which a metal species is immobilized on a metal oxide is particularly preferable. In the case where the metal is immobilized on the oxide as described above, the contact area between the metal and the oxide is increased, and excellent catalytic performance can be exhibited. Even when the metal is immobilized on the oxide, the metal has a particle size of 2 to 10 n.
It is preferable that the particle size is about m, and the particle size is 2 to 4n.
It is more preferably about m.

As a method of immobilizing the metal species on the metal oxide, a known method can be used. For example: ・ Impregnation method (GC Bond and PA Sermon, Gold Bull.
102 (1973) 6 etc.)-Coprecipitation method (JP-A-60-238148, etc.)-Precipitation precipitation method (JP-A-62-155937, JP-A-3-97623)
JP, JP-A-63-252908, JP-A-2-252610, etc.)-Colloid mixing method (Tsubota S., Nakamura T., Tanaka
K., and Haruta M., Catal. Lett., 56 (1998) 131) ・ Gas phase graphing method (JP-A-9-122478) ・ Liquid phase graphing (Okumura M., and Haruta M., C
hem. Lett., (2000) 396) and the like. The catalyst according to the present invention comprises (1) metal species A
And then the metal species B is supported, (2) the metal species B is supported, and then the metal species A is supported, and (3) the metal species A and the metal species B are simultaneously supported. Can also be prepared. In order to support both the metal species A and the metal species B more uniformly and achieve higher catalytic activity, it is preferable to employ a method of simultaneously supporting both components as in (3).

The following compounds may be mentioned as starting materials. Examples of the precursor of the metal species A or the metal species B include, for example,
Water-soluble compounds of metals (for example, chloroauric acid, chloroplatinic acid,
Nickel chloride, palladium chloride, nickel nitrate, palladium nitrate, etc.); metal acetylacetonato complex (eg,
Platinum acetylacetonato complex etc.), metal dibenzylidene acetone complex (eg palladium dibenzylidene acetone complex etc.), metal cyclooctadiene complex (eg
Examples thereof include compounds that vaporize by heating such as nickel cyclooctadiene complex).

Examples of the raw material of the metal oxide include nitrates, sulfates, acetates and chlorides of various metals. Specifically, nitrates such as cerium nitrate and aluminum nitrate, sulfates such as iron sulfate, aluminum sulfate and titanium sulfate, acetates such as iron acetate and aluminum acetate, chlorides such as cerium chloride, titanium trichloride and titanium tetrachloride. Things etc. are mentioned.

After the precipitate is deposited by the known method mentioned above, the precipitate is dried. In order to finally bring the precursors of the metal species A and B into a metal state, the precipitate is subjected to reduction treatment under various reducing gas atmospheres in which hydrogen, carbon monoxide, etc. are diluted with nitrogen, helium, argon, etc. . As the reducing gas, for example, hydrogen gas diluted with nitrogen gas in an amount of about 1 to 10 vol%, carbon monoxide gas, or the like can be used. The reduction treatment temperature may be appropriately selected from the range of known reduction conditions, and is usually preferably room temperature to about 600 ° C., and 200 to 400 to obtain stable and fine metal particles.
A temperature of about ° C is more preferable. The reduction treatment time is, for example, 1 to
About 12 hours is preferable.

Further, in order to oxidize and decompose the impurities in the precipitate, it may be fired at a high temperature in an oxygen atmosphere prior to the above reduction treatment. The term “under an oxygen atmosphere” means under air or under a mixed gas in which oxygen is diluted with nitrogen, helium, argon or the like.

It is also possible to employ a method of reducing by contacting with a reducing agent in the liquid phase. Examples of the liquid phase include water and methanol. Examples of the reducing agent include hydrazine and sodium citrate. The reaction temperature is preferably, for example, room temperature to 100 ° C. The reaction time is preferably about 1 minute to 10 hours, for example.

The content of the metal species A and B in the catalyst of the present invention is 0.1 to 30% by weight based on the total amount of the catalyst.
It is sufficient that the degree is about 0.
More preferably, it is about 1 to 10% by weight. Further, the content ratio of the metal species A and the metal species B may be any of 1:99 to 99: 1. More preferably, it is 1:99 to 1: 1.

In the present invention, the above-mentioned catalyst may be supported on a support carrier having various shapes for the purpose of using it in a more practical form. Examples of the support carrier include alumina, silica, cordierite, zeolite, titanium oxide and the like. The shape of the carrier is not particularly limited, and for example,
Powder, spherical, granular, honeycomb, foam, fibrous,
All the shapes generally used as catalyst carriers at present, such as cloth, plate, and ring, can be used.

The catalyst of the present invention is mainly composed of carbon monoxide,
It can be effectively used for the purpose of producing hydrogen from a mixed gas containing four gases of water, carbon dioxide and hydrogen to reduce the carbon monoxide concentration. The catalyst of the present invention is suitable for any of a water gas shift reaction that produces carbon dioxide and hydrogen from a gas containing carbon monoxide and water, and a reverse water gas shift reaction that produces carbon monoxide and water from a gas containing carbon dioxide and hydrogen. Also shows activity. The water gas shift reaction and the reverse water gas shift have an inverse reaction relationship with each other, and when the reaction proceeds to the maximum at a certain temperature, a mixed gas of four kinds of carbon monoxide, water, carbon dioxide, and hydrogen having a chemical equilibrium composition. Becomes Even when four gases of carbon monoxide, water, carbon dioxide, and hydrogen coexist in the reaction gas from the beginning, the water gas shift reaction or the reverse water gas shift reaction proceeds until the equilibrium composition is reached.

The pressure of the water gas shift reaction using the catalyst of the present invention is not particularly limited, and it can be used from normal pressure to high pressure conditions such as 100 atm. In particular, in order to suppress methane production more effectively, it is desirable to carry out the reaction near atmospheric pressure.

The temperature in the water gas shift reaction using the catalyst of the present invention varies depending on the type of metal oxide used and other conditions, but may be, for example, about 100 to 450 ° C. The catalyst of the present invention is, in particular, 250 ° C. to 450 ° C.
At a reaction temperature of about ℃, it shows high water gas shift reaction activity and very little problematic methane by-product.

The mixing ratio of carbon monoxide and water in the raw material gas is not particularly limited, but the concentration range of carbon monoxide is 1 to 30 Vol% with respect to the total raw material gas, and the amount of water vapor is equal to that of carbon monoxide ( Vol) or more, preferably double equivalent (Vol) or more is particularly effective. Also, the range of space velocity is not particularly limited.

[0035]

INDUSTRIAL APPLICABILITY The water gas shift reaction catalyst of the present invention has higher activity than that of conventional catalysts, can achieve a high hydrogen yield, and can suppress the production of methane at high temperatures. Therefore, the water gas shift reactor can be downsized.

In a home fuel cell system, etc.,
It is known that when the equipment is stopped at night, the catalyst comes into contact with air, and metal species such as copper are oxidized to cause a decrease in activity. The catalyst of the present invention has oxidation resistance by selecting a metal species that is not oxidized in the air for both metal species A and B (for example, platinum as the metal species A and gold as the metal species B), and can be activated on a daily basis. It can also be effectively used for applications to fuel cell devices that repeatedly stop.

[0037]

EXAMPLES Examples will be shown below to further clarify the features of the present invention, but the present invention is not limited thereto.

Example 1 0.57 mmol of chloroauric acid [HAuCl ₄ .4H ₂ O] and 0.19 mmol of chloroplatinic acid [H ₂ PtCl ₆ .6H ₂ O] were dissolved in 1000 ml of distilled water to prepare an aqueous NaOH solution. Was added dropwise to adjust the pH to 7. To this, 5 g of titanium oxide powder (average particle size 30 nm) was added, and the mixture was mixed at 70 ° C for 1 hour.
Stir for hours. After that, the precipitate was thoroughly washed with distilled water, dried, and passed under a diluted hydrogen flow (3 vol% diluted with N _2).
Hydrogen gas), a reduction treatment at 400 ° C. for 2 hours to give a gold-platinum supported titanium oxide catalyst [Au-Pt / TiO 2
₂ , metal loading 3 wt%, Au: Pt = 3: 1] was obtained. Then, using the obtained catalyst, the activity for the water gas shift reaction was examined by the following method.

Using 0.12 g of the above catalyst, the raw material gas (C
O 1.3%, H ₂ O 3.1%, CO ₂ 0.4%, H ₂
5.0%, He 90.2% volume ratio mixed gas) 10
After flowing at a normal pressure at a flow rate of 3 ml / min and once raising the temperature to 350 ° C. in the reaction gas, the catalytic activity for the water gas shift reaction at each temperature was examined.

The results are shown in FIGS. FIG. 1 shows CO conversion as an index of catalyst activity with respect to reaction temperature.
FIG. 2 shows the yield of hydrogen which is a target product, and FIG. 3 shows the yield of methane which is a by-product.

Comparative Example 1 A catalyst was prepared under the same conditions as in Example 1 using only chloroauric acid [HAuCl ₄ .4H ₂ O], and a gold-supported titanium oxide catalyst [Au / TiO ₂ , metal-supported amount 2. 4 wt%] was obtained. The reaction was performed under the same conditions as in Example 1 using the obtained catalyst. The results are shown in FIGS.

Comparative Example 2 A catalyst was prepared under the same conditions as in Example 1 using only chloroplatinic acid [H ₂ PtCl ₆ .6H ₂ O], and a platinum-supported titanium oxide catalyst [Pt (0.75) / TiO ₂ , Metal loading 0.75w
t%] was obtained. The reaction was performed under the same conditions as in Example 1 using the obtained catalyst. The results are shown in FIGS.

Comparative Example 3 A catalyst was prepared under the same conditions as in Example 1 using only chloroplatinic acid [H ₂ PtCl ₆ .6H ₂ O], and a platinum-supported titanium oxide catalyst [Pt (3) / TiO ₂ , Metal loading 3 wt%] was obtained. The reaction was performed under the same conditions as in Example 1 using the obtained catalyst. The results are shown in FIGS.

Example 2 Example 1 was performed using cerium oxide instead of titanium oxide.
A catalyst was prepared under the same conditions as described above, and a gold-platinum-supported cerium oxide catalyst [Au-Pt / CeO ₂ , metal loading 3 wt%,
Au: Pt = 3: 1] was obtained. The reaction was performed under the same conditions as in Example 1 using the obtained catalyst. The results are shown in Figure 4 ~
6 shows. FIG. 4 shows the CO conversion as an index of catalyst activity with respect to the reaction temperature, FIG. 5 shows the yield of hydrogen which is the target product, and FIG. 6 shows the yield of methane which is a by-product.

Comparative Example 4 A catalyst was prepared under the same conditions as in Example 1 using only chloroauric acid [HAuCl ₄ .4H ₂ O], and a gold-supported cerium oxide catalyst [Au / CeO ₂ , metal loading 3 wt% was used. ] Was obtained.
Using the obtained catalyst, the reaction was carried out under the same conditions as in Example 2. The results are shown in FIGS.

Comparative Example 5 A catalyst was prepared under the same conditions as in Example 1 using only chloroplatinic acid [H ₂ PtCl ₆ .6H ₂ O], and a platinum-supported cerium oxide catalyst [Pt / CeO ₂ , metal loading amount was used. 3 wt%] was obtained. Using the obtained catalyst, the reaction was carried out under the same conditions as in Example 2. The results are shown in FIGS.

From these results, the following characteristics of the catalyst of the present invention are clear.

FIGS. 1 to 3 show the characteristics of the Au-Pt / TiO ₂ catalyst for the catalyst system using titanium oxide as a carrier, such as Au / TiO ₂ and Pt / Ti.
It is shown in comparison with the O ₂ catalyst. From Fig. 1 250 of Au-Pt / TiO ₂ catalyst
CO conversion at temperatures above ℃ is lower than Pt / TiO ₂ , but Au / TiO ₂
It is higher than that of the catalyst, indicating that the activity can be enhanced by adding platinum to gold.

FIG. 3 shows the yield of undesired by-product methane. Pt / TiO ₂ produces methane, but Au / TiO ₂ and
It is shown that Au-Pt / TiO ₂ does not produce methane, and Au-Pt / TiO ₂ catalyst suppresses the production of methane, which is generally a problem with platinum catalysts.

FIG. 2 shows the yield of the desired product hydrogen. Although the yield of Pt / TiO ₂ catalyst is high, the hydrogen yield is lowered at a high temperature of 300 ° C or higher due to methane by-product. Au-P
Since t / TiO ₂ does not generate methane, the hydrogen yield does not decrease even at high temperatures, and a hydrogen yield higher than that of Pt / TiO ₂ can be obtained at 350 ° C.

[0051] The catalyst system of cerium oxide with the carrier in FIGS. 4-6, the features of the Au-Pt / CeO ₂ catalyst Au / CeO ₂ and Pt /
It is shown in comparison with the CeO ₂ catalyst. The effect of coexistence of platinum and gold is similar to that of titanium oxide carrier, and Au-Pt / CeO ₂
In the high temperature, methane production is suppressed, and 250 ℃
A high hydrogen yield can be obtained in the above high temperature range.

[Brief description of drawings]

FIG. 1 is a graph showing reaction temperature and CO conversion rate when various water gas shift reaction catalysts are used.

FIG. 2 is a graph showing reaction temperature and hydrogen yield when various water gas shift reaction catalysts are used.

FIG. 3 is a graph showing reaction temperature and methane yield when various water gas shift reaction catalysts are used.

FIG. 4 is a graph showing reaction temperature and CO conversion rate when various water gas shift reaction catalysts are used.

FIG. 5 is a graph showing reaction temperature and hydrogen yield when various water gas shift reaction catalysts are used.

FIG. 6 is a graph showing reaction temperature and methane yield when various water gas shift reaction catalysts are used.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masatake Haruta             No. 1 Onogawa 16-1, Tsukuba, Ibaraki Prefecture             Tsukuba West Office, National Institute of Advanced Industrial Science and Technology             Within (72) Inventor Atsushi Ueda             1-83-1 Midorigaoka, Ikeda, Osaka Prefecture             AIST Kansai Center (72) Inventor Tetsuhiko Kobayashi             1-83-1 Midorigaoka, Ikeda, Osaka Prefecture             AIST Kansai Center F-term (reference) 4G069 AA03 BA01A BA01B BA02A                       BA05A BA06A BB02A BB02B                       BB04A BB04B BB06A BC11A                       BC18A BC22A BC31A BC33A                       BC33B BC35A BC36A BC39A                       BC42A BC43A BC43B BC54A                       BC58A BC62A BC63A BC64A                       BC66A BC67A BC68A BC70A                       BC71A BC72A BC73A BC74A                       BC75A BC75B CC17 CC26                       EA01Y

Claims (3)

[Claims] 1. A metal species group A (Pt, Pd, Ni, Ir, Rh, Co,
Os, Ru, Fe, Re, Tc, Mn) and at least 1 selected from the metal species group B (Au, Ag, Cu)
A catalyst for a water gas shift reaction, wherein the seed is supported on a metal oxide. 2. The metal oxide is (i) zinc oxide, iron oxide, copper oxide, lanthanum oxide, titanium oxide, cobalt oxide, zirconium oxide, magnesium oxide, beryllium oxide, nickel oxide, chromium oxide, scandium oxide,
A metal oxide of a single metal selected from the group consisting of cadmium oxide, indium oxide, tin oxide, manganese oxide, vanadium oxide, cerium oxide, aluminum oxide and silicon oxide, (ii) zinc, iron, copper, lanthanum, titanium,
Cobalt, zirconium, magnesium, beryllium,
A composite oxide of two or more kinds of metals selected from the group consisting of nickel, chromium, scandium, cadmium, indium, tin, manganese, vanadium, cerium, aluminum and silicon, or (iii) and at least one kind of (i) The water gas shift catalyst according to claim 1, which is a mixture of at least one of ii). 3. The catalyst for water gas shift according to claim 2, wherein the metal species A is Pt, the metal species B is Au, and the metal oxide is titanium oxide and / or cerium oxide.