JP2003275588A - Co shift reaction catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical catalyst exhibiting high shift reaction activity even under a reaction condition of high space velocity and small deterioration of the activity even if being used under a condition such that the catalyst is exposed at a high temperature or the atmosphere is fluctuated. <P>SOLUTION: A noble metal is supported on a support composed of a multiple oxide in which ceria and alumina are dispersed in nanometer scale. It is desirable for the multiple oxide to have a characteristic that the fine pore diameter becomes 3.5-100 nm the fine pore volume becomes ≥0.20 cc/g after being fired at 800°C for 5 hr. Alumina works as a barrier among the particles of ceria to suppress the grain growth of seria. Because the decrease of the oxygen storing and releasing ability of the ceria is suppressed further in such a way, the fluctuation of the atmosphere is mitigated to suppress the grain growth of the noble metal. The grain growth of both ceria and the noble metal is suppressed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to carbon monoxide (CO).
A catalyst that performs a CO shift reaction that produces hydrogen (H ₂ ) from hydrogen and water vapor (H ₂ O). More specifically, it has high activity even under conditions of high space velocity and can be used for purification of exhaust gas from fuel cells and internal combustion engines. The present invention relates to a shift reaction catalyst.

[0002]

2. Description of the Related Art The CO shift reaction has been applied to the synthesis of ammonia, the removal of CO in city gas or the like, or the adjustment of the CO / H ₂ ratio in methanol synthesis and oxo synthesis. In recent years, it has also been used for removing CO in a fuel reforming system of an internal reforming fuel cell. this
The CO shift reaction is a reaction that produces H ₂ from CO and H ₂ O, and is also called a water gas shift reaction.

As a catalyst for promoting the CO shift reaction,
For example, Cu-Zn catalysts were announced by Girdler and duPont in the 1960s, and have been widely used until now mainly for plants in factories. Also, W. Hongli et
al, China-Jpn.-US Symp.Hetero. Catal. Relat. Ene
In rgy Probl., B09C, 213 (1982), it was reported that a catalyst prepared by reducing Pt supported on an anatase-type titania carrier at around 500 ° C showed higher CO shift reaction activity. .

It is also known that a catalyst in which γ-Al ₂ O ₃ carries a noble metal such as Pt, Rh and Pd has a CO shift reaction activity. Furthermore carrying the Cu on γ-Al ₂ O ₃ catalyst, γ-Al ₂ O ₃
It has also been reported that CO shift reaction activity is higher than that of catalysts loaded with precious metals such as Pt, Rh, and Pd.

By the way, a fuel reforming system for an internal reforming fuel cell mounted on a moving body such as an automobile, or CO in an automobile exhaust gas is reformed into H ₂ and the H ₂ is used to occlude it on a catalyst. As a catalyst for a CO shift reaction used in an exhaust gas purification system that reduces NO _x , the size of the catalytic reactor is limited, so it is necessary to show high activity even under reaction conditions with a large space velocity. .

However, the conventional Cu-Zn-based catalyst has a problem that its activity is low under a reaction condition having a large space velocity. Therefore, the internal reforming fuel cell fuel reforming system,
Alternatively, under reaction conditions with a large space velocity such as an automobile exhaust gas purification system, it becomes difficult to efficiently convert CO into H ₂ . The CO shift reaction is an equilibrium reaction, and the higher the reaction temperature, the more disadvantageous the conversion of CO to H ₂ . The Cu-Zn-based catalyst therefore be raised much reaction temperature for the purpose of supplementing the activity of a large reaction conditions space velocity, it can not be efficiently converted into H ₂ and CO.

Further, when the CO shift reaction catalyst is used in a fuel reforming system of an internal reforming fuel cell, an automobile exhaust gas purification system, etc., the reaction field temporarily becomes a high temperature atmosphere depending on the use conditions. Therefore, in that case, Cu, which is an active species of the Cu-Zn-based catalyst, or γ
There is also a problem that Cu of a catalyst in which Cu is supported on -Al ₂ O ₃ is grain-grown to lower the activity, and it becomes more difficult to efficiently convert CO to H ₂ .

Further, when the catalyst for CO shift reaction is used in the fuel reforming system of the internal reforming type battery, the higher the concentration of H ₂ O in the CO shift reaction is, the more easily the reaction of producing H ₂ proceeds. -Zn-based catalysts are generally used under the condition that the H ₂ O / CO ratio is 2 or more.

However, in order to carry out this reaction in a limited environment such as an automobile, a water tank for storing a large amount of water, a large evaporator and the like are required, so that there is a problem that the apparatus becomes large. Further, in order to supply water vapor, a large amount of energy for evaporating water is required, which lowers the energy efficiency of the entire system.

Therefore, it is recalled to use a noble metal which is more active than the base metal and is expected to be stable in a high temperature atmosphere. However, as described above, γ-Al ₂ O ₃ contains Pt, Rh,
A catalyst supporting a noble metal such as Pd has lower activity than a catalyst supporting Cu on γ-Al ₂ O ₃ . In addition, in a catalyst in which Pt is supported on a carrier composed of anatase type titania, strong interaction (SMSI: strong metal support interacti
on) is known to occur. Therefore, when exposed to the reaction gas in the low temperature range of 200 ℃ ~ 400 ℃ included in the normal use conditions, Pt is covered by a part of the carrier component by SMSI, and the activity is remarkably reduced due to the decrease of active sites. There is a problem called.

On the other hand, in the example of Japanese Patent Laid-Open No. 2001-316682, CO containing ceria, Pt, Pd and Fe supported on an alumina carrier is used.
A shift reaction catalyst is described. Also Applied Cat
alysis B: Environmental 15 (1998) 107-114, T.
Bunluesin et al. Explain the CO shift reaction mechanism of a catalyst for CO shift reaction in which Pt, Pd, and Rh are supported on ceria.

SMSI is unlikely to occur between the ceria and the precious metal, and the problem that the active points of the precious metal decrease due to the SMSI is unlikely to occur. In addition, ceria contributes to the activation of water vapor (H ₂ O), and noble metal contributes to the activation of CO. Therefore, the use of a catalyst in which ceria and noble metal coexist has the effect of promoting the CO shift reaction. .

By the way, the solid catalyst is generally composed of primary particles which are one crystallite and secondary particles which are aggregates thereof. Generally, pores are formed inside the secondary particles, that is, in the gaps between the primary particles. Has been done. Generally, in a flow-type reaction, if the reaction condition is low space velocity, the reaction product diffuses and reacts inside the pores, but under the reaction condition of high space velocity, the reaction product becomes difficult to diffuse into the pores, and the reaction There is a tendency for the solid surface available to be reduced. The tendency is more remarkable for solids having smaller pores.

The ceria as a solid carrier in the above-mentioned prior art occupies most of the fine pores having a pore diameter of 3.2 nm or less, so that the reaction product diffuses and reacts in the reaction under the reaction condition of high space velocity. There are problems that the solid surface used is small and the CO shift reaction activity is low. Therefore, in an environment where it is used in the exhaust gas of automobiles, it is difficult to sufficiently express the CO shift reaction due to the high space velocity. Further, when used under the condition of being exposed to a high temperature or changing the atmosphere, ceria easily grows into grains, and the oxygen storage / release capacity of ceria also decreases accordingly. Therefore, noble metal grain growth is inevitable in an oxidizing atmosphere. Therefore, due to the grain growth of both ceria and precious metals,
There is also a problem that CO shift reaction activity decreases.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and exhibits high CO shift reaction activity even under high space velocity reaction conditions, and is exposed to high temperatures and atmospheres. The purpose of the present invention is to make it a practical catalyst with a small decrease in activity even when it is used under conditions where the temperature fluctuates.

[0016]

The features of the catalyst for CO shift reaction of the present invention for solving the above-mentioned problems are that ceria and alumina are
A noble metal is supported on a carrier containing a complex oxide dispersed on the nm scale.

It is desirable that the composite oxide has such a property that after being baked at 800 ° C. for 5 hours, the pore volume with a pore size of 3.5 to 100 nm is 0.20 cc / g or more, and the central pore size is 15 to 65 nm.
Is desirable. Further, it is particularly desirable that the pore volume of the pore size of 3.5 to 100 nm is 0.30 cc / g or more after firing at 800 ° C for 5 hours, and the central pore size is 25 to
65 nm is particularly desirable. Further, it is desirable that the composite oxide contains 50 to 90% by weight of ceria.

The noble metal preferably contains at least Pt.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the CO shift reaction catalyst of the present invention, a noble metal is supported on a carrier containing a complex oxide in which ceria and alumina are dispersed on a nm scale. Since ceria has a basic site, it is excellent in activating H ₂ O, and noble metal is excellent in activating CO. As a result, high CO shift reaction activity is expressed. And the composite oxide is ceria and alumina nm
Since they are dispersed on a scale, when exposed to a high temperature atmosphere, alumina serves as a barrier between ceria particles, and the grain growth of ceria is suppressed. Further, this suppresses the decrease in the oxygen storage / release capacity of ceria, so that the atmosphere variation is alleviated and the grain growth of the noble metal is suppressed. Therefore, grain growth of both ceria and precious metals is suppressed, and high CO shift reaction activity is maintained.

Here, the nm-scale dispersion means that even when measured using a microanalyzer having a high resolution of about 1 nm,
It refers to a dispersed state that is not observed as independent particles. An example of such a microanalyzer is a FE-STEM scanning transmission electron microscope such as "HD-2000" manufactured by Hitachi, Ltd.

The state in which ceria and alumina are dispersed on the nm scale is confirmed by performing a minute range analysis of one non-overlapping particle with a beam diameter of about 0.5 nm using EDS of FE-STEM. be able to. And as a result of this minute range analysis, 90% or more of the composite oxide was Ce and
It is desirable that the composition ratio of Al is within ± 20%. FE-STEM is a Field Effect-Scanning Transm.
Abbreviation for ission Electron Microscopy, EDS is En
Abbreviation for Energy Dispersion Spectroscopy.

It is desirable that the composite oxide has such a property that after firing at 800 ° C. for 5 hours, the volume of pores having a pore diameter of 3.5 to 100 nm is 0.20 cc / g or more. Also, after firing at 800 ℃ for 5 hours, the volume of pores with a diameter of 3.5-100 nm is 0.30cc /
It is particularly desirable to have a characteristic of g or more. From the lower limit of 3.5 nm that can be measured in principle using a mercury porosimeter
A pore having a pore diameter of 100 nm is called a so-called mesopore, and since the mesopore has a pore volume of 0.20 cc / g or more, CO
And H ₂ O diffuse into the inside of the pores. Therefore, since the surface area used for the reaction is large, high CO shift reaction activity is exhibited. If such a property is not possessed, the gas diffusivity is lowered, and the CO shift reaction activity is lowered under the reaction conditions of high space velocity.

The central pore diameter of the composite oxide is 15 to 65 nm.
Is particularly desirable, and it is particularly desirable that it is 25 to 65 nm. If the central pore diameter is less than 15 nm, the gas diffusivity is reduced, and the CO shift reaction activity is reduced under the reaction conditions of high space velocity. On the other hand, when the central pore diameter exceeds 65 nm, it is considered that the primary particles are rearranged and aggregated due to high temperature, and the pore volume of the mesopores is likely to decrease.

The composite oxide preferably contains 50 to 90% by weight of ceria. When the amount of ceria is less than 50% by weight, it becomes difficult to activate H ₂ O and the CO shift reaction activity decreases. On the other hand, if the amount of ceria exceeds 90% by weight, the amount of alumina that serves as a barrier is small, so that grain growth is likely to occur in ceria, and as a result, the effect of alleviating the atmospheric fluctuation is reduced and the precious metal also grows grains. Therefore, the CO shift reaction activity decreases.

To produce the composite oxide of the present invention,
First, a ceria precursor, an alumina precursor, or a compound of these precursors is precipitated from an aqueous solution containing a cerium compound and an aluminum compound or a solution containing water.

Salts are generally used as the cerium compound and the aluminum compound, and as the salt, nitrates, chlorides, acetates, sulfates and the like can be used. Water and alcohols can be used as the solvent for uniformly dissolving the salt. Further, for example, aluminum hydroxide, nitric acid, and water may be mixed and used as a raw material of aluminum nitrate.

The precipitation method is carried out by mainly adjusting the pH by adding ammonia water or the like, and the precursor of the more characteristic composite oxide can be prepared by various adjusting methods. For example, from an aqueous solution containing a cerium compound and an aluminum compound or a solution containing water, a method of precipitating these oxide precursors or compounds of these precursors at substantially the same time, or prior to the precipitation of the alumina precursor. There is a method of precipitating a ceria precursor (or vice versa).

Regarding the former method of precipitating substantially at the same time, a method of instantaneously adding ammonia water or the like and vigorous stirring, or a method of adjusting the pH at which the ceria precursor and the alumina precursor start to precipitate by adding hydrogen peroxide or the like. After that, there is a method of depositing a precipitate with aqueous ammonia.

Regarding the latter, the time required for neutralization with ammonia water or the like is set to be sufficiently long, preferably
A method of neutralizing for 10 minutes or more, or a pH at which a ceria precursor precipitates while monitoring the pH or a pH at which an alumina precursor precipitates, such as stepwise neutralization or maintaining such a pH. There is a method of adding a buffer solution.

In addition to ammonia water, an aqueous solution in which ammonium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate or the like is dissolved, or an alcohol solution can be used. Ammonia and ammonium carbonate that volatilize during firing are particularly preferable. In addition, the pH of the alkaline solution is preferably 9 or more because it promotes the precipitation reaction of the precursor.

By aging the precipitate in the presence of water,
A more uniform composite oxide can be manufactured. This aging step is preferably performed at room temperature or higher, preferably 100 to 200 ° C, more preferably 100 to 150 ° C. 100
If the heating temperature is lower than 0 ° C, the time required for aging becomes long. At temperatures higher than 200 ° C, the vapor pressure becomes extremely high, so a large-scale device that can withstand high pressure is required.
The manufacturing cost is very high, which is not preferable.

If the solution containing the precipitate is heated as it is to evaporate it to dryness and then calcined, the aging step can be carried out during evaporation to dryness, but at room temperature or higher, preferably 100 ° C.
It is better to hold and aged above.

Then, the thus obtained precipitate is
It is desirable to disperse again in water, strongly disperse using a homogenizer, and then calcine. As a result, it is possible to produce a composite oxide having a characteristic that after calcination at 800 ° C. for 5 hours, the pore volume having a pore diameter of 3.5 to 100 nm is 0.20 cc / g or more, and further 0.30 cc / g or more.
When strongly dispersing, it is desirable to add a surfactant. Addition of a surfactant can prevent aggregation of primary particles and increase the pore volume of mesopores.

The calcination of the precipitate may be carried out in the atmosphere, and the temperature is preferably in the range of 300 to 900 ° C. Firing temperature is 3
When it is lower than 00 ° C, the stability as a carrier is substantially lost. In addition, firing at a temperature higher than 900 ° C causes a decrease in specific surface area, and is unnecessary from the viewpoint of usage as a carrier.

The carrier referred to in the present invention may include the above-mentioned composite oxide, and may be composed only of the above-mentioned composite oxide,
The composite oxide powder may be mixed with another porous oxide powder to form a mixture. As the other porous oxide, one or more kinds of alumina, ceria, zirconia, titania, silica and the like can be used. When the carrier is a mixture of the composite oxide powder and the porous oxide powder, the content of the composite oxide powder is preferably 50% by weight or more. If the amount of the above complex oxide powder in the carrier is less than this, the CO shift reaction activity decreases and it is not practical.

Noble metals supported on the carrier include Pt and R
It can be selected from h, Pd, Ir and the like, but it is preferable that at least Pt is contained. The CO shift reaction activity is particularly improved by supporting at least Pt. The amount of the noble metal supported is preferably 0.1 to 10 g per 100 g of the carrier. If the loading amount is less than this, the CO shift reaction activity is low, and if the loading amount is more than this, the CO shift reaction activity is saturated and grain growth between the noble metals may occur.

The catalyst for CO shift reaction of the present invention is contacted with a gas containing at least CO and H ₂ O to generate hydrogen with high activity by the CO shift reaction. It is particularly preferable to use exhaust gas from an internal combustion engine such as an automobile as such gas. Although the exhaust gas from the internal combustion engine has a high space velocity, the CO shift reaction catalyst of the present invention exhibits a high CO shift reaction activity even in a gas having such a high space velocity.

[0038]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

(Example 1) Aluminum nitrate nonahydrate
0.2 mol (75.1 g) was mixed with 2000 ml of deionized water,
It was dissolved by stirring with a propeller stirrer for 5 minutes. Concentration there
304 g of 28 wt% cerium nitrate aqueous solution (0.5 in terms of CeO ₂₎
(Corresponding to mol) was mixed and stirred for 5 minutes. To the obtained mixed aqueous solution, 177 g of 25% ammonia water was added, and further
The solution was stirred for 10 minutes to obtain an aqueous solution containing a precipitate. This was subjected to an aging step of heat-treating at 120 ° C. for 2 hours under a pressure of 2 atm to ripen the precipitate.

Then, filtration was performed using a suction filter to obtain a filter cake. The filter cake was dispersed again in 500 ml of ion-exchanged water using a propeller stirrer, 9.1 g of alkylamine-based ionic surfactant (“Armac T50” manufactured by Lion Co., Ltd.) was added, and the rotor diameter was 1
Using a homogenizer with 7 mm and a gap of 1 mm, 10,000 rpm
Mixed for 5 minutes. Then filter using a suction filter,
The obtained filter cake is baked at 400 ° C. for 5 hours to obtain Ce.
O ₂ —Al ₂ O ₃ composite oxide powder was prepared. The resulting composite oxide powder is composed of about 89% by weight CeO ₂ and about 11% by weight Al ₂ O ₃ .

This composite oxide powder was impregnated with a predetermined amount of a dinitrodiammine platinum nitric acid solution having a predetermined concentration, and the powder was placed in the atmosphere 3
By firing at 00 ° C. for 3 hours, 5 wt% of Pt was supported. This was further molded into pellets having a particle size of 0.5 to 1.0 mm by a conventional method to prepare a pellet catalyst.

Example 2 Aluminum nitrate nonahydrate
A composite oxide powder was prepared in the same manner as in Example 1 except that 56 mol (211 g), 304 g of a cerium nitrate aqueous solution having a concentration of 28% by weight (corresponding to 0.5 mol in terms of CeO ₂ ) and 251 g of 25% ammonia water were used. A pellet catalyst was prepared similarly by supporting Pt. The obtained composite oxide powder is about 75% by weight.
CeO ₂ and about 25 wt% Al ₂ O ₃ .

(Example 3) Aluminum nitrate nonahydrate
0.2 mol (75.1 g) was mixed with 2000 ml of deionized water,
It was dissolved by stirring with a propeller stirrer for 5 minutes. Concentration there
304 g of 28 wt% cerium nitrate aqueous solution (0.5 in terms of CeO ₂₎
(Corresponding to mol) was mixed and stirred for 5 minutes. To the obtained mixed aqueous solution, 177 g of 25% ammonia water was added, and further
The solution was stirred for 10 minutes to obtain an aqueous solution containing a precipitate. Then, the aqueous solution containing the precipitate is heated at a heating rate of 100 ° C / hr,
A CeO ₂ —Al ₂ O ₃ composite oxide powder was prepared by firing at 00 ° C. for 5 hours. The resulting composite oxide powder is composed of about 89% by weight CeO ₂ and about 11% by weight Al ₂ O ₃ .

Using this composite oxide powder, Pt was supported in the same manner as in Example 1 to prepare a pellet catalyst.

(Example 4) Aluminum nitrate nonahydrate 0.
56 mol (211 g) and 304 g of cerium nitrate aqueous solution (CeO ₂
(Compared to 0.5 mol) and 251 g of 25% aqueous ammonia were used to prepare a composite oxide powder in the same manner as in Example 3, and similarly Pt was carried to prepare a pellet catalyst.
The resulting composite oxide powder is composed of about 75% by weight CeO ₂ and about 25% by weight Al ₂ O ₃ .

(Comparative Example 1) 304 g (Ce) of an aqueous cerium nitrate solution having a concentration of 28% by weight was used without using aluminum nitrate nonahydrate.
Oxide powder was prepared in the same manner as in Example 1 except that 136 g of 25% aqueous ammonia and 0.5 g of O ₂ ) were used, and Pt was similarly carried to prepare a pellet catalyst. The obtained oxide powder is composed only of CeO ₂ .

(Comparative Example 2) γ-Al ₂ O ₃ powder (specific surface area 200
m ² / g) was impregnated with a predetermined amount of a cerium nitrate aqueous solution having a predetermined concentration, and the composite oxide powder was prepared by firing in the air at 500 ° C. for 2 hours. This complex oxide powder contains approximately 38% by weight of CeO ₂
And about 62% by weight of Al ₂ O _3.
It corresponds to the composite oxide described in the examples of the publication.

Using this composite oxide powder, Pt was supported in the same manner as in Example 1 to prepare a pellet catalyst.

<Test / Evaluation> The composite oxide powder prepared in each of the examples and the comparative examples was exposed to 800
Firing was performed at 5 ° C. for 5 hours, and then the pore distribution was measured using a mercury porosimeter. The pore distribution curves of the composite oxide powders prepared in Example 1 and Example 3 are extracted and shown in FIG. It can be seen from FIG. 1 that the composite oxide powders prepared in Examples 1 and 3 have a large pore volume of pores having a pore diameter of 100 nm or less, and in particular, the composite oxide powders prepared in Example 1 are It can be seen that the pores with a diameter of 100 nm or less have a sharp distribution.

The values of the central pore diameter and the pore volume of pores having a pore diameter of 3.5 to 100 nm calculated from the pore distribution curve of each sample are shown in FIGS. 2 and 3. In ordinary oxide powders, the higher the temperature is, the more solid phase reaction takes place between the primary particles and the primary particles agglomerate. Get smaller. However,
3, the composite oxide powders prepared in Examples 1 to 4, especially the composite oxide powders prepared in Examples 1 to 2
Even after firing at a high temperature, it can be seen that the pore volume is larger and the central pore diameter is larger than the composite oxide powders or oxide powders prepared in Comparative Examples 1 and 2. Further, in the composite oxide powder prepared in Comparative Example 2, the pore volume was too small and the central pore diameter was unknown.

Next, for each of the pellet catalysts prepared in each Example and each Comparative Example, 4 minutes of lean gas and 1 minute of rich gas shown in Table 1 were alternately switched and flowed,
An endurance test was conducted in which the temperature of the entering gas was 700 ° C and the sample was heated and held for 5 hours. The specific surface area of each catalyst before and after the durability test was measured by the BET method, and the results are shown in FIG. The CO pulse adsorption method was used to measure the Pt dispersity of each catalyst before and after the durability test, and the results are shown in FIG.

[0052]

[Table 1] From FIG. 4, the catalysts of Examples 1 to 4 have a larger specific surface area after the durability test than the catalyst of Comparative Example 1. It is considered that this is because the catalysts of Examples 1 to 4 all use CeO ₂ —Al ₂ O ₃ composite oxide as a carrier, and Al ₂ O ₃ acts as a barrier to suppress the grain growth of CeO ₂ . Further, from FIG. 5, it is understood that the catalysts of Examples 1 to 4 have higher Pt dispersity after the durability test than Comparative Examples 1 and 2. This is because Al ₂ O ₃ becomes a barrier,
In the catalysts of Examples 1 to 4, Ce was used as compared with the catalysts of Comparative Examples 1 and 2.
It is considered that the grain growth of O ₂ was suppressed, and the reduction of the oxygen storage / release capacity due to CeO ₂ was suppressed, so that the ability to alleviate the atmospheric fluctuation was high and the grain growth of Pt was also suppressed.

Next, each catalyst after the endurance test was placed in an atmospheric pressure fixed bed flow type catalyst evaluation device, and CO: 1.8%, H 2
15% at 500 ° C while flowing a model gas consisting of ₂ O: 10% and the balance N _{2 at a} rate of 10 L / min for 2 g of catalyst.
A pretreatment of holding for minutes was performed. After that, while flowing the same model gas in the same manner, the temperature is raised from 100 ° C to 400 ° C at a heating rate of 15 ° C / min.
The temperature was raised to ° C. At this time, the volume of each pellet catalyst is about 3 ml, and the space velocity is about 200,000 hr ⁻¹ . The CO conversion was continuously measured for each catalyst during the temperature increase. Results are shown in FIG. Yet another experiment confirms that the CO conversion rate is equal to the H ₂ production rate.

From FIG. 6, it is clear that under the reaction conditions of a high space velocity of about 200,000 hr ^-1 , the catalyst of each Example shows higher CO shift reaction activity from the low temperature region than the catalyst of each Comparative Example. Is. Based on the results of FIGS. 1 to 5, the high CO shift reaction activity of the catalysts of the respective examples is considered to be due to the suppression of grain growth of CeO ₂ and Pt. Further, the catalysts of Examples 1 to 2 are the same as those of Examples 3 to
It is clear that the higher CO shift reaction activity than the catalyst of No. 4 is due to the existence of large pores with a large pore volume, and the pore size after calcination at 800 ° C for 5 hours. It is apparent that it is particularly preferable to use a complex oxide having a pore volume of 3.5 to 100 nm of 0.20 cc / g or more and a central pore diameter of 15 nm or more as a carrier.

[0055]

EFFECTS OF THE INVENTION That is, according to the catalyst for CO shift reaction of the present invention, a high activity is exhibited under the reaction conditions of high space velocity, and the activity can be maintained even when exposed to high temperature conditions or atmospheric fluctuation conditions. it can. Therefore, it is most suitable for use in exhaust gas from an internal combustion engine such as an automobile engine, and is extremely useful as an exhaust gas purification catalyst for reducing and purifying NO _x or a hydrogen generation catalyst for fuel cells.

[Brief description of drawings]

FIG. 1 is a graph showing pore distribution curves of complex oxide powders manufactured in Examples 1 and 3.

FIG. 2 is a graph showing pore volumes of composite oxide powders or oxide powders manufactured in Examples and Comparative Examples after firing at 800 ° C.

FIG. 3 is a graph showing the central pore size of composite oxide powders or oxide powders manufactured in Examples and Comparative Examples after firing at 800 ° C.

FIG. 4 is a graph showing the specific surface area of each catalyst of Examples and Comparative Examples.

FIG. 5 is a graph showing the Pt dispersity of each catalyst of Examples and Comparative Examples.

FIG. 6 is a graph showing the relationship between the temperature and the CO conversion of each catalyst of Examples and Comparative Examples.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C01B 3/48 B01D 53/36 ZAB (72) Inventor Chiwa Ando Nagakute-cho, Aichi-gun, Aichi Prefecture No. 41 1 Toyota Central Research Institute Co., Ltd. (72) Inventor Naoki Takahashi Nagachite Aichi-gun Aichi-gun, Nagakute-cho Sideways Yokoido No. 41 No. 1 Toyota Central Research Institute Co., Ltd. (72) Inventor Akihiko Suda Aichi-gun, Aichi Prefecture F-Term in Toyota Central Research Institute Co., Ltd. 1 at 41, Yokomichi, Nagakute, Nagaminato (D) CA01 CA02 CA14 CC26 EA02Y EC06X EC06Y EC07X EC07Y EC08X EC08Y EC15X EC15Y EC16X EC16Y ED06 FC08 4G140 EA09 EB34

Claims (8)

[Claims] 1. A catalyst for CO shift reaction, comprising a noble metal supported on a carrier containing a complex oxide in which ceria and alumina are dispersed on a nm scale. 2. The CO shift reaction according to claim 1, wherein the composite oxide has a characteristic that after calcination at 800 ° C. for 5 hours, the pore volume with a pore size of 3.5 to 100 nm is 0.20 cc / g or more. catalyst. 3. The CO shift reaction according to claim 1, wherein the composite oxide has a characteristic that after firing at 800 ° C. for 5 hours, the volume of pores having a pore size of 3.5 to 100 nm is 0.30 cc / g or more. catalyst. 4. The central pore diameter of the composite oxide is 15 to 65 nm.
The catalyst for CO shift reaction according to any one of claims 1 to 3. 5. The central pore diameter of the composite oxide is 25 to 65 nm.
The catalyst for CO shift reaction according to any one of claims 1 to 3. 6. The catalyst for CO shift reaction according to claim 1, wherein the composite oxide contains ceria in an amount of 50 to 90% by weight. 7. The CO shift reaction catalyst according to claim 1, wherein the noble metal contains at least platinum. 8. The catalyst for CO shift reaction according to claim 1, which is used in contact with exhaust gas of an internal combustion engine.