JPH09927A - Catalyst for exhaust gas purifying apparatus of engine and method of manufacturing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] To effectively prevent thermal deterioration of an oxidation catalyst and to effectively improve the purification ability of HC components separated from the HC adsorbent layer. A catalyst for an exhaust gas purifying apparatus installed in an exhaust system of an engine, comprising an HC adsorbent layer 3 supported on a catalyst carrier composed of a monolith type carrier 1, and an HC adsorbent layer 3 supported on the HC adsorbent layer 3. Exhaust gas purifying apparatus for an engine, which comprises cerium oxide particles 4 and an oxidation catalyst 5 supported on the cerium oxide particles 4, and the particle size 4 of the cerium oxide particles 4 is set within a range of 30 to 200 nm. Catalyst and method for producing the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust gas purifying catalyst for purifying HC components contained in engine exhaust gas and a method for producing the same.

[0002]

2. Description of the Related Art Generally, the exhaust gas of an engine mounted on an automobile contains air pollutants such as HC (hydrocarbons). Although the exhaust gas purifying device is installed to oxidize and purify the HC component in the exhaust gas, the exhaust gas purifying catalyst is heated to 2
If the activation temperature is not higher than about 50 ° C., there is a problem that a sufficient purification function cannot be obtained. In particular, since the HC concentration in the exhaust gas is high immediately after the engine is started, it is desired to effectively oxidize and purify this HC component.

Therefore, for example, Japanese Unexamined Patent Publication No. 3-262541
As shown in the publication, an HC adsorbent layer composed of a zeolite layer is formed on a monolith type carrier, and an oxidation catalyst composed of a noble metal oxide such as platinum, palladium and rhodium is applied to the HC adsorbent layer. A supported catalyst for an exhaust gas purifying device of an engine has been proposed.

The above exhaust gas purifying catalyst removes the HC component contained in the exhaust gas of the engine from the zeolite layer when the oxidation catalyst is in an inactive state where it is not sufficiently heated immediately after the engine is started. By adsorbing it on the HC adsorbent layer, the HC component is prevented from being released into the atmosphere, and after the oxidation catalyst is heated by the exhaust gas and activated, the zeolite layer is formed by the catalytic action of the oxidation catalyst. It is configured to promote the oxidation of the HC component that has separated from and to purify it.

[0005]

When the above-mentioned oxidation catalyst is used for a long period of time, its purification performance tends to decrease due to its thermal deterioration. It is considered that this is because the noble metal oxide forming the oxidation catalyst is thermally deteriorated and reduced, and the oxidation catalyst made of, for example, palladium oxide is changed to palladium having low activity.

In order to prevent the purifying ability of the above-mentioned oxidation catalyst from decreasing, cerium oxide (C
eO ₂ ) powder as a co-catalyst and H
H supported on the C adsorbent layer and separated from the HC adsorbent layer
It is preferable to prevent the oxidation catalyst from being reduced by bringing the C component into contact with oxygen released from the cerium oxide. Further, in the case of such a configuration, the HC component separated from the HC adsorption layer can be effectively oxidized by the oxygen released from the cerium oxide.

However, the cerium oxide is usually carried as powder on the HC adsorbent layer by a wash coating method in which the HC adsorbent layer is immersed in a slurry containing the powder. The cerium oxide powder has a particle size of about 2 μm (2 × 10 ⁻⁶ m), which is considerably larger than the particle size of the oxidation catalyst.
H supported on the C adsorbent layer and released from the HC adsorbent layer
It is unavoidable that the probability of the C component coming into contact with oxygen released from the cerium oxide becomes low. Therefore, although the cerium oxide particles are carried on the HC adsorbent layer, there is a problem that the purification performance of the HC component cannot be effectively improved.

In order to reduce the particle size of the cerium oxide particles, the HC adsorbent layer is impregnated with a solution prepared by dissolving a cerium compound such as cerium nitrate in water or the like, and then calcined. It is also conceivable to change the cerium component in the solution into cerium oxide particles.
However, according to the above method, the particle size of the cerium oxide particles is 20 nm (2 × 10 ⁻⁸ m) or less, which is about the same as or smaller than the noble metal oxide forming the oxidation catalyst, and therefore the oxygen storage capacity is reduced. There is a problem that it becomes insufficient and the thermal deterioration of the oxidation catalyst cannot be effectively prevented.

The present invention has been made to solve the above problems, and can effectively prevent thermal deterioration of an oxidation catalyst and purify HC components separated from the HC adsorbent layer. It is an object of the present invention to provide a catalyst for an exhaust gas purifying apparatus of an engine and a method for manufacturing the same, which can effectively improve the above.

[0010]

The invention according to claim 1 is
A catalyst for an exhaust gas purifying apparatus installed in an exhaust system of an engine, comprising an HC adsorbent layer carried on a catalyst carrier, cerium oxide particles carried on the HC adsorbent layer, and the cerium oxide particles. A supported oxidation catalyst is provided, and the particle diameter of the cerium oxide particles is set within the range of 30 to 200 nm.

According to a second aspect of the present invention, in the catalyst for an exhaust gas purifying apparatus for an engine according to the first aspect, an HC adsorbent layer made of zeolite is supported on a carrier.

According to a third aspect of the present invention, there is provided a method for producing a catalyst for an exhaust gas purifying apparatus installed in an exhaust system of an engine, wherein an HC adsorbent is supported on a catalyst carrier to form an HC adsorbent layer. After that, the cerium compound solution is impregnated and supported on the HC adsorbent layer, and the cerium compound solution layer is impregnated with an aqueous ammonia solution in an undried state of the cerium compound solution. By reacting with the component, while aggregating the cerium component in the cerium compound solution, by changing it to cerium hydroxide to form cerium hydroxide particles, by firing the cerium hydroxide particles and dehydration treatment. The cerium oxide particles are generated, and the cerium oxide particles are made to carry an oxidation catalyst.

According to a fourth aspect of the present invention, in the method for producing a catalyst for an exhaust gas purifying apparatus for an engine according to the first aspect, a solution in which a palladium compound is dissolved in cerium oxide particles carried on the HC adsorbent layer Is impregnated with the cerium oxide particles to support the oxidation catalyst made of palladium oxide.

According to a fifth aspect of the present invention, in the method for producing a catalyst for an exhaust gas purifying apparatus for an engine according to the third or fourth aspect, the amount of cerium oxide particles carried with respect to the carrier volume is in the range of 50 to 100 g / l. The amount of impregnation of the cerium compound solution with respect to the HC adsorbent layer is set so that

The invention according to claim 6 is the above claims 3 to 5.
In the method for producing a catalyst for an exhaust gas purifying apparatus for an engine according to any one of items 1 to 4, the particle diameter of the cerium oxide particles produced by firing the cerium hydroxide particles is 30 to 2
The ammonia concentration of the aqueous ammonia solution is set so as to fall within the range of 00 nm.

[0016]

According to the invention described in claim 1, since the particle diameter of the cerium oxide particles is set to 30 nm or more, and the cerium oxide particles have a sufficient oxygen storage capacity, the HC is immediately discharged after starting the engine. When the CH component adsorbed in the adsorbent layer desorbs from the HC adsorbent layer, oxygen necessary for oxidizing the HC component is released from the cerium oxide particles. Further, since the particle diameter of the cerium oxide particles is set to 200 nm or less and the cerium oxide particles can be supported on the HC adsorption layer at an appropriate density, the HC component separated from the HC adsorbent layer is the cerium oxide particles. Will surely come into contact with.

According to the second aspect of the present invention, since the HC adsorbent layer is formed of zeolite having excellent heat resistance and HC adsorbability, the adsorbability is lowered due to thermal deterioration of the HC adsorbent layer. Is effectively prevented, and a large amount of the HC component discharged immediately after the engine is started is effectively adsorbed to the HC adsorbent layer.

According to the third aspect of the invention, after the cerium compound contained in the cerium compound solution as fine particles is supported on the HC adsorbent layer, the cerium compound aggregates to form an aggregate having a predetermined diameter. By being formed and converted into cerium oxide through cerium hydroxide, cerium oxide particles having an appropriate particle size are generated.

According to the fourth aspect of the invention, the oxidation catalyst composed of palladium oxide which is activated at a low temperature is effectively supported on the HC adsorbent layer, and the palladium component effectively purifies the HC component. At the same time, the thermal deterioration of the palladium oxide is effectively prevented by the oxygen released from the cerium oxide particles.

According to the fifth aspect of the present invention, the impregnated amount of the cerium compound solution in the HC adsorbent layer is set to an appropriate amount, the cerium compound solution is spread over the entire HC adsorbent layer, and the cerium compound is used. The generated cerium oxide particles are not released from the HC adsorbent layer and are supported at an appropriate position.

According to the sixth aspect of the invention, the cerium compound is aggregated and formed by changing the reaction rate of the cerium compound in the cerium compound solution and ammonia in accordance with the ammonia concentration of the aqueous ammonia solution. The particle size of the cerium hydroxide particles is adjusted. Then, by firing the cerium hydroxide particles,
It has a sufficient oxygen storage capacity and at a proper density, HC
Cerium oxide particles having an appropriate particle size that can be supported on the material adsorption layer are generated.

[0022]

1 and 2 show an embodiment of a catalyst for an exhaust gas purifying apparatus for an engine according to the present invention. The exhaust gas purifying catalyst comprises a monolithic carrier 1 having a plurality of through holes 2 into which exhaust gas discharged from an engine is introduced, and an HC carried on the inner wall surface of the through holes 2 of the monolithic carrier 1. An adsorbent layer 3 and a co-catalyst composed of cerium oxide (CeO ₂ ) 4 supported on the HC adsorbent layer 3,
It consists of an oxidation catalyst 5 supported on this cerium oxide.

The HC adsorbent layer 3 may be made of any material as long as it has a large number of pores for adsorbing HC components and has a predetermined heat resistance. And the above HC
When zeolite is used as the adsorbent layer 3, one having a Cavan ratio of any value can be used, but in order to effectively adsorb various HC components, the pore diameter is set to a predetermined value. FAU-type zeolite (Y-type zeolite), MFI-type zeolite (ZSM5) formed above the specified value
Alternatively, it is desirable to use β-type zeolite.

The particle size of the cerium oxide particles 4 is set within the range of 30 to 200 nm. That is, the particle diameter of the cerium oxide particles 4 is 30 nm (3 × 10 3) so that sufficient oxygen can be stored therein.
^-8 m) or more, and the particle size is set to 200 nm (2 × 10 ^-7 m) or less so that the cerium oxide particles 4 can be supported on the HC adsorbent layer 3 at an appropriate density. ing.

The oxidation catalyst 5 is made of palladium oxide (Pd
O), platinum oxide (PtO) or rhodium oxide (R
hO) and other noble metal oxides, which are supported on the surface of the cerium hydroxide particles 4 alone or in a composite state. The amount of the oxidation catalyst 5 carried with respect to the carrier volume of the monolithic carrier 1 is set within the range of 0.1 to 15 g / l.

An example of the method for producing the catalyst for the exhaust gas purifying apparatus will be described below. First, the monolith type carrier 1 is formed of a heat resistant metal material or a ceramic material, and 20 wt% of hydrated alumina or silica sol as a binder and an appropriate amount of water are added to the zeolite constituting the HC adsorbent layer. After the slurry is prepared by adding, the monolithic carrier 1 is dipped in the slurry to adhere the slurry to the carrier 1.

After the excess slurry is blown off by air blow, the slurry attached to the monolith type carrier 1 is baked at a temperature of about 500 ° C. for about 1 hour to form the monolith type carrier 1. The HC adsorbent layer 3 made of zeolite having a large number of pores is supported on the inner wall surface of each through hole 2.

If necessary, the HC adsorbent layer 3 may be used.
A composite of ion exchange species or impregnation species composed of Pd (palladium), Pt (platinum), Rh (rhodium), Co (cobalt), Ni (nickel), Fe (iron), or the like, or a simple substance thereof. It is desirable that the metal is modified by ion exchange, supporting, impregnation, or the like to function as an oxidation catalyst.

Then, cerium nitrate (Ce (NO ₃ ) ₃ )
The cerium nitrate is adsorbed on the HC adsorbent layer 3 by immersing one end of the monolithic carrier 1 in a container filled with a predetermined amount of a cerium nitrate solution prepared by dissolving a cerium compound consisting of The solution is impregnated and supported. For example, when a monolithic carrier 1 having a capacity of 25 ml used experimentally is impregnated with a cerium nitrate solution prepared by dissolving 4.43 g of cerium nitrate in 4 ml of ion-exchanged water, the monolithic carrier is The supported amount of the cerium nitrate with respect to 1 is about 177 g / l, and the supported amount of the cerium oxide particles 4 obtained by firing the cerium nitrate is about 70 g / l.

In the above cerium nitrate solution, the amount of cerium oxide particles 4 formed by the cerium component in the solution is 50 to 100 g based on the volume of the monolithic carrier 1.
The impregnated amount is set so that it falls within the range of / l. This is because when the supported amount of the cerium oxide particles 4 is less than 50 g / l, the amount of the ion-exchanged water also decreases and the cerium nitrate solution cannot be spread over the entire HC adsorbent layer 3, and When the loading amount of the cerium oxide particles 4 is more than 100 g / l, the amount of the ion-exchanged water is correspondingly large, and when the cerium nitrate solution is loaded on the HC adsorbent layer 3, as shown in FIG. As shown in FIG. 3, a layer of cerium nitrate solution 6 is formed so as to cover the surface of the HC adsorbent layer 3, and when the cerium oxide particles 4 are generated, the cerium oxide particles 4 are separated from the HC adsorbent layer 3 at a position away from the HC adsorbent layer 3. Is deposited, and the cerium oxide particles 4 cannot be supported at an appropriate position.

Next, after the excess water in the cerium nitrate solution 4 carried on the HC adsorbent layer 3 is evaporated to a semi-dried state, the solution is filled with a predetermined amount of aqueous ammonia solution, By immersing one end of the monolithic carrier 1 and impregnating the HC adsorbent layer 3 with an aqueous ammonia solution, the cerium nitrate solution 4 reacts with the ammonia solution to form cerium nitrate in the cerium nitrate solution 4. While aggregating the components, this is converted into cerium hydroxide to form particles.

That is, by replacing the nitrate group of cerium nitrate contained in the cerium nitrate solution with the hydroxyl group of ammonia water, the cerium nitrate is changed to cerium hydroxide and the cerium hydroxide is condensed. A cerium hydroxide particle having a predetermined diameter is formed from the aggregate.

Then, the cerium hydroxide particles carried on the HC adsorbent layer 3 are heated to about 1 ° C. at a temperature of about 500 ° C.
The cerium hydroxide particles are converted into cerium oxide particles 4 by baking for a long time and dehydration treatment, and the cerium oxide particles 4 are supported on the HC adsorbent layer 3.

If the amount of the aqueous ammonia solution used to form the cerium hydroxide particles is too small, the aqueous ammonia solution cannot be spread all over the HC adsorbent 3, and the amount of the aqueous ammonia solution is too small. If it is too large, the cerium component in the cerium nitrate solution 4 supported on the HC adsorbent layer 3 will dissolve out from the HC adsorbent layer 3, and cerium hydroxide particles will be formed at a position away from the HC adsorbent layer 3. It causes inconvenience such as

Therefore, the impregnation amount of the aqueous ammonia solution with respect to the HC adsorbent 3 must be set to an appropriate amount so that the above-mentioned inconvenience does not occur. For example, in the case of the monolithic carrier 1 having a capacity of 25 ml which is used experimentally, it is desirable to set the impregnation amount of the aqueous ammonia solution to about 3 ml.

Further, as shown in FIG. 4, the particle diameter of the cerium hydroxide particles 4 can be variously changed according to the concentration of the aqueous ammonia solution, and the concentration of the aqueous ammonia solution is within the range of 14 to 28%. By setting, the particle size of the cerium oxide particles 4 generated by firing the cerium hydroxide particles can be set within the above range of 30 to 200 nm.

For example, in the experimental example using the monolith type carrier 1 having a capacity of 25 ml, when the impregnation amount of the aqueous ammonia solution was set to 3 ml and the ammonia concentration was set to 28%, the results shown in FIG. As shown, it was confirmed that the particle diameter of the cerium oxide particles 4 was about 30 nm. Further, when the ammonia concentration of the aqueous ammonia solution was set to 14%, it was confirmed that the particle diameter of the cerium oxide particles 4 was about 200 nm, as shown in FIG.

This is because when the ammonia concentration of the aqueous ammonia solution is high, the nitrate group of the cerium nitrate contained in the cerium nitrate solution and the hydroxyl group of the aqueous ammonia solution are rapidly replaced, and the above hydroxylation is performed. It is considered that this is because the above reaction is completed before cerium grows into large aggregates. On the other hand, when the ammonia concentration of the aqueous ammonia solution is high, the nitrate group of the cerium nitrate is slowly replaced with the hydroxyl group, and the cerium hydroxide is a large aggregate while the reaction is completed. It is thought to be to grow up.

In the graph shown in FIG. 4, when the ammonia concentration is low, the particle size of the cerium oxide flow varies greatly. This is because, in the experimental example using the monolith type carrier 1 having a capacity of 25 ml, when the ammonia concentration of the aqueous ammonia solution whose impregnation amount was set to 3 ml was less than 17%, the HC of the monolith type carrier 1 was
It is considered that the whole amount of cerium nitrate in the cerium nitrate solution impregnated in the adsorbent layer 3 cannot be converted into cerium hydroxide, and a part thereof remains as cerium nitrate having a relatively small particle size. .

Next, the monolithic carrier 1 carrying the HC adsorbing layer 3 and the cerium oxide particles 4 is impregnated into an aqueous nitric acid solution in which a noble metal compound such as palladium nitrate is dissolved, so that the noble metal compound is cerium oxide. After adhering to the surface of the particles 4, the particles are baked and oxidized to support the oxidation catalyst 5 made of a noble metal oxide such as palladium oxide on the surfaces of the cerium oxide particles 4.

Experimental examples conducted to confirm the performance of the exhaust gas purifying apparatus catalyst manufactured as described above will be described below. For this experiment, the monolithic carrier 1
In addition, 120 g / l and 70 g / l of the HC adsorbent layer 3 made of Y-type zeolite with the Caban ratio set to 80, the cerium oxide particles 4 as the co-catalyst, and the oxidation catalyst 5 made of palladium oxide were respectively provided. A catalyst for an exhaust gas purifying device, which was supported at a rate of 10 g / l and in which the particle diameter of the cerium oxide particles 4 was set to various values, was used.

That is, when the cerium hydroxide particles were produced, the ammonia concentration was set to 28%, so that the particle diameter of the cerium oxide particles 4 was set to about 30 nm, and the ammonia concentration was set to 14%. %, The particle diameter of the cerium oxide particles 4 is set to 200 nm.
The second embodiment is set to a certain level, and the cerium component in the cerium nitrate solution is directly fired without using the aqueous ammonia solution to convert it into cerium oxide particles, thereby setting the particle size to 20 nm or less. By comparing the first comparative example with cerium oxide as a powder on the HC adsorbent layer by the wash-coat method, the particle size of the cerium oxide was reduced to 2
A second comparative example having a thickness of 000 nm or more was used.

Then, each of the above exhaust gas purifying device catalysts contains 1500 ppmC of HC component and 0.6% of CO.
(Carbon monoxide) and 0.1% NOx (nitrogen oxide)
And a simulated exhaust gas composed of 0.6% O ₂ (oxygen), 14% CO ₂ (carbon dioxide) and balance nitrogen gas at a space velocity (SV) of 55000 h ^−1. However, the temperature at which 50% of the above HC is purified, that is, HC
When the half temperature of the component was measured, the data shown in FIG. 7 was obtained. From this data, each of the exhaust gas purifying device catalysts has a half-life temperature of 165 to 170.
It was confirmed that the oxidation catalyst was activated at a relatively low temperature within the range of ° C.

The HC contained in the above simulated exhaust gas
The unit ppm C indicating the concentration of each component is a value obtained by converting each HC component into a monovalent carbon component. For example, when the simulated exhaust gas contains 500 ppm of methane (C3H6), when expressed in the above unit, it becomes 1500 ppmC.

Then, after carrying out atmospheric heat treatment on the respective exhaust gas purifying device catalysts at a temperature of 900 ° C. for about 50 hours, the same experiment was conducted by supplying the above-mentioned simulated exhaust gas. As indicated by the slanted lines, in the first and second examples of the present invention, the half temperatures of the HC components are 230 ° C. and 225 ° C., respectively, and the activity of the oxidation catalyst is significantly reduced. It was confirmed that there was not.

On the other hand, in the comparative example 1 in which the particle diameter of the cerium oxide particles is small, the half temperature is 26.
It was 0 ° C, and it was confirmed that the activity of the oxidation catalyst was significantly impaired. In the comparative example 1 in which the particle diameter of the cerium oxide particles is large, the half temperature is 19
It was 0 ° C, and it was confirmed that the activity of the oxidation catalyst was hardly reduced. From the first experimental data, it can be seen that the larger the particle diameter of the cerium oxide particles is, the less the thermal degradation of the oxidation catalyst is.

Further, the first and second embodiments and the first and second embodiments
A catalyst for an exhaust gas purifying apparatus, in which cerium oxide particles having a particle diameter corresponding to that of the second comparative example is carried and a capacity of a monolith type carrier is set to 3000 ml, is installed in an automobile, and an FTP standard of US standard test mode is used. When a running test was performed in the 1 mode and the Y1 purification rate, that is, the exhaust gas purification rate in the low temperature state in the initial stage after the engine start was measured, the experimental data as shown in FIG. 8 was obtained.

From the above-mentioned second experimental data, in the first and second embodiments of the present invention, the purification rate of the HC component is 8 in both cases.
It was 0% or more, and it was confirmed that the HC component was effectively oxidized and purified by the oxygen released from the cerium oxide particles. On the other hand, in the above-mentioned first and second comparative examples, it was confirmed that the purification rate of the HC component was less than 80%, and sufficient purification ability could not be obtained.

In the above-mentioned first comparative example, it is considered that the particle size of the cerium oxide particles is too small, so that the oxygen storage capacity thereof is low and sufficient oxygen cannot be obtained for oxidizing the HC component. . Further, in the first comparative example, since the particle size of the cerium oxide particles is too large,
It is considered that this is because the HC component separated from the HC adsorbing component cannot be effectively brought into contact with oxygen released from the cerium oxide particles.

The HC thus supported on the catalyst carrier 1
An exhaust gas purifying catalyst comprising an adsorbent layer 3, a cerium oxide particle 4 supported on the HC adsorbent layer 3, and an oxidation catalyst 5 supported on the cerium oxide particle 4, wherein the cerium oxide particle 4 to 30-200nm
Since the cerium oxide particles 4 are set within the range, it is possible to prevent the cerium oxide particles 4 from being carried on the HC adsorbent layer 3 in a depopulated state due to the particle size being too large, and the cerium oxide particles 4 can be prevented. It is possible to prevent the oxygen storage capacity from being insufficient due to the too small particle size.

Therefore, the HC component released from the HC adsorbent layer 3 can be surely brought into contact with the cerium oxide particles 4, and the HC component can be reliably oxidized by the oxygen released from the cerium oxide particles 4. . Therefore, the oxidation catalyst 5 supported on the cerium oxide particles 4 is prevented from being reduced by the HC component and its activity is prevented from decreasing, and thermal deterioration of the oxidation catalyst 5 can be effectively suppressed.

When the HC adsorbent layer 3 is formed of zeolite having excellent heat resistance and HC adsorbability as described above, a large amount of H emitted immediately after the engine is started.
The C component can be effectively adsorbed to the HC adsorbent layer 3, and thermal deterioration of the HC adsorbent layer 3 can be prevented to maintain the adsorbability of the HC component in a good state for a long period of time. You can

In addition, a cerium nitrate solution prepared by dissolving cerium nitrate in water was used to carry H on the monolithic carrier 1.
The C adsorbent layer 3 is impregnated and supported, and after the cerium nitrate solution is semi-dried, an aqueous ammonia solution is impregnated into the HC adsorbent layer 3 to react with the cerium nitrate in the cerium nitrate solution. According to the manufacturing method configured to form cerium hydroxide particles by changing the cerium nitrate into cerium hydroxide while aggregating the cerium nitrate, a cerium hydroxide having a predetermined diameter with a simple structure is formed. Cerium hydroxide particles can be formed.

Therefore, the cerium oxide particles 4 having an appropriate particle size can be supported on the HC adsorbent layer 3 by baking the cerium hydroxide particles and subjecting them to dehydration treatment. Therefore, the cerium oxide particles 4 can effectively prevent thermal deterioration of the oxidation catalyst 5, and the co-catalyst function of the cerium oxide particles 4 can effectively purify HC components. The catalyst for gas purifier can be easily manufactured.

Further, a solution in which a palladium compound is dissolved is impregnated into the cerium oxide particles 4 supported on the HC adsorbent layer 3 and then baked to support the oxidation catalyst 5 made of palladium oxide. In the case of the above configuration, the cerium oxide particles 4 can be easily supported by the oxidation catalyst 5 made of palladium oxide which is activated at a low temperature. While effectively preventing the oxidation catalyst 5 made of the palladium oxide from being reduced and thermally deteriorated by the oxygen released from the cerium oxide particles 4,
H that is released from the HC adsorbent layer 3 by utilizing this oxygen
The C component can be effectively purified.

Further, in the method for producing a catalyst for an exhaust gas purifying apparatus for an engine, H is adjusted so that the supported amount of the cerium component with respect to the carrier capacity is in the range of 50 to 100 g / l.
According to the above configuration in which the impregnation amount of the cerium nitrate solution with respect to the C adsorbent layer 3 is set, the cerium nitrate solution can be surely spread over the entire HC adsorbent layer 3, and the cerium compound in the solution can be used. The cerium oxide particles 4 can be supported at appropriate positions on the HC adsorbent layer 3 without releasing the generated cerium oxide particles 4 from the HC adsorbent layer 3.

Furthermore, in the method for producing a catalyst for an exhaust gas purifying apparatus for an engine, the particle size 4 of cerium oxide produced by firing cerium hydroxide particles is 30.
Since the ammonia concentration of the aqueous ammonia solution is set to fall within the range of up to 200 nm, the cerium oxide particles 4 can surely suppress the thermal deterioration of the oxidation catalyst, and the HC component separated from the HC adsorbent layer 3 can be obtained. It is possible to easily manufacture a catalyst for an exhaust gas purification device that can reliably purify the exhaust gas.

That is, even if the ammonia concentration of the aqueous ammonia solution is kept constant and the reaction time or reaction temperature between the aqueous ammonia solution and the cerium compound is changed, or the amount of the aqueous ammonia solution is changed, the coagulation of the cerium compound is changed. It is possible to control the particle size of the cerium oxide stream 4 formed by the assembly. However, in these methods, the cerium compound cannot be adequately changed to cerium hydroxide due to the reaction time being too short, or the amount of the aqueous ammonia solution is too large so that the cerium compound is contained in the HC adsorbent layer. Since there is a problem that the particles are separated from the cerium oxide particles 3, it is desirable to control the particle size of the cerium oxide particles 4 by adjusting the ammonia concentration of the aqueous ammonia solution as described above.

In the above embodiment, the cerium compound solution formed by dissolving the cerium compound composed of cerium nitrate in water is impregnated into the HC adsorbent layer 3. A cerium compound such as cerium acetate or cerium sulfate may be used as the substance, and ethanol, ether, or the like may be used as the solution of the cerium compound solution.

In the above embodiment, after the cerium compound solution impregnated in the HC adsorbent layer 3 is made semi-dried,
Although the example configured to be impregnated with the aqueous ammonia solution has been described, when the amount of the cerium compound solution is properly set and there is no risk of the cerium compound being washed out,
The aqueous ammonia solution may be impregnated immediately after the impregnation with the cerium compound solution.

Further, in the above embodiment, the monolith type exhaust gas purifying apparatus provided with the catalyst carrier composed of the monolith type carrier 1 having the plurality of through holes 2 through which the exhaust gas is introduced has been described. The present invention can also be applied to a pet-type exhaust gas purification device configured so that an HC adsorbent layer is formed on a carrier.

On the HC adsorbent layer 3, cerium oxide particles 4 having an oxygen storage capacity and neodymium oxide particles having a function of suppressing a sintering phenomenon in which the oxidation catalyst 5 is thermally deteriorated and aggregated are formed. The layer may be supported, or the cerium oxide particles 4 may be configured to support the neodymium oxide particles and the oxidation catalyst in the same layer. In such a case, the neodymium oxide particles effectively suppress the thermal deterioration of the oxidation catalyst 5 and prolong the catalytic function of the oxidation catalyst 5 for purifying the HC component separated from the HC adsorbent layer 3. It can be kept in good condition for a period of time.

[0063]

As described above, according to the invention of claim 1, the HC adsorbent layer supported on the catalyst carrier and the H adsorbent layer
In a catalyst for an exhaust gas purifying apparatus, which comprises cerium oxide particles supported on a C adsorbent layer and an oxidation catalyst supported on the cerium oxide particles, the particle diameter of the cerium oxide particles is set to 200 nm or less. By carrying the cerium oxide particles at an appropriate density without causing a situation in which the cerium oxide particles are carried on the HC adsorbent layer in a depopulated state due to the particle size of the cerium oxide particles being too large, HC separated from the HC adsorbent layer
The component can be reliably brought into contact with the cerium oxide particles to purify them.

The particle size of the cerium oxide particles is 30
Since the thickness is set to nm or more, oxygen necessary for purifying the HC component can be stored in the cerium oxide particles. Therefore, the reduction of the oxidation catalyst carried on the cerium oxide particles by the HC components separated from the HC adsorbent layer is suppressed by the oxygen released from the cerium oxide particles, and the heat of the activity of the oxidation catalyst is reduced. There is an advantage that deterioration can be effectively prevented.

According to the second aspect of the present invention, since the HC adsorbent layer is formed of zeolite having excellent heat resistance and HC adsorbability, a large amount of HC component discharged immediately after the engine is started is used as the HC adsorbent layer. In addition to being effectively adsorbed, the HC adsorbent layer can be prevented from thermal deterioration and the adsorbability of the HC component can be maintained in a good state for a long period of time.

Further, in the invention according to claim 3, the HC adsorbent layer supported on the catalyst carrier is impregnated with the cerium compound solution containing the cerium compound so as to support,
In a non-dried state of the cerium compound solution, an aqueous ammonia solution is impregnated into the HC adsorbent layer to react with the cerium compound in the cerium compound solution layer, and the cerium compound is agglomerated to form cerium hydroxide. Since the cerium hydroxide particles are changed so as to form the cerium hydroxide particles, it is possible to form the cerium hydroxide particles having a predetermined diameter and composed of the above-mentioned aggregate of cerium hydroxide with a simple structure.

Therefore, by baking the cerium hydroxide particles and subjecting them to a dehydration treatment, it is possible to support cerium oxide particles having an appropriate particle size on the HC adsorbent layer, and the cerium oxide particles allow the oxidation catalyst to be supported. To easily produce a catalyst for an exhaust gas purifying device, which can effectively prevent the thermal deterioration of the exhaust gas and effectively oxidize and purify the HC component by the co-catalyst function of the cerium oxide particles. You can

Further, in the invention according to claim 4, the cerium oxide particles supported on the HC adsorbent layer are impregnated with a solution in which a palladium compound is dissolved, whereby the oxidation catalyst made of palladium oxide is added to the cerium oxide particles. Since it is configured to be supported on the cerium oxide particles, it is possible to easily support an oxidation catalyst composed of palladium oxide that is activated at a low temperature as the oxidation catalyst on the cerium oxide particles. Therefore,
While effectively preventing the oxidation catalyst made of palladium oxide from being thermally deteriorated by the oxygen released from the cerium oxide particles, the palladium component effectively oxidizes the HC component released from the HC adsorbent layer. It has the advantage that it can be purified.

In the invention according to claim 5, the impregnated amount of the cerium compound solution in the HC adsorbent layer is set so that the supported amount of the cerium component with respect to the carrier volume is in the range of 50 to 100 g / l. The cerium nitrate solution can be effectively spread over the entire HC adsorbent layer, and the cerium oxide particles generated by the cerium compound in the nitric acid solution can be supported at appropriate positions without being released from the HC adsorbent layer. Can be made. Therefore, due to the promoter function of the cerium oxide particles, H 2
There is an advantage that a catalyst for an exhaust gas purifying device that can effectively purify the C component can be easily manufactured.

Further, in the invention according to claim 6, the cerium oxide particles produced by firing the cerium hydroxide particles have a particle size within a range of 30 to 200 nm,
Since the ammonia concentration of the aqueous ammonia solution is set, the cerium oxide particles can effectively suppress the thermal deterioration of the oxidation catalyst and can surely purify the HC component separated from the HC adsorbent layer. Has the advantage of being easily manufactured.

[Brief description of drawings]

FIG. 1 is an overall explanatory view showing an embodiment of a catalyst for an exhaust gas purification device according to the present invention.

FIG. 2 is a partially enlarged view illustrating a main part of a catalyst for an exhaust gas purification device.

FIG. 3 is an explanatory diagram showing a state in which a large amount of a cerium compound solution is impregnated.

FIG. 4 is a diagram showing a correspondence relationship between an ammonia concentration and a particle diameter of cerium oxide particles.

FIG. 5 is a micrograph of cerium oxide particles in the first example.

FIG. 6 is a micrograph of cerium oxide particles in a second example.

FIG. 7 is a diagram showing measured values of temperatures at which 50% of HC components contained in exhaust gas are purified.

FIG. 8 is a diagram showing measured values of purification rates of HC components contained in exhaust gas.

[Explanation of symbols]

 1 monolith type carrier 3 HC adsorbent layer 4 cerium oxide particles 5 oxidation catalyst

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kosuke Sumita 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Motor Corporation

Claims (6)

[Claims] 1. A catalyst for an exhaust gas purifying apparatus, which is installed in an exhaust system of an engine, wherein HC is supported on a catalyst carrier.
An adsorbent layer, cerium oxide particles supported on the HC adsorbent layer, and an oxidation catalyst supported on the cerium oxide particles are provided, and the particle diameter of the cerium oxide particles is 30 to 200.
A catalyst for an exhaust gas purifying device of an engine, which is set in a range of nm. 2. A catalyst for an exhaust gas purifying apparatus of an engine according to claim 1, wherein an HC adsorbent layer made of zeolite is carried on a carrier. 3. A method for producing a catalyst for an exhaust gas purifying apparatus installed in an exhaust system of an engine, comprising: HC on a catalyst carrier.
After forming the HC adsorbent layer by supporting the adsorbent, the H
While the C adsorbent layer was impregnated with the cerium compound solution and supported, and the cerium compound solution was not dried,
An aqueous ammonia solution is impregnated into the HC adsorbent layer to react with the cerium component in the cerium compound solution layer, aggregating the cerium component in the cerium compound solution, and converting the cerium component into cerium hydroxide for hydroxylation. After forming the cerium particles, the cerium hydroxide particles are baked and dehydrated to generate cerium oxide particles, and the cerium oxide particles are configured to carry an oxidation catalyst. A method for producing a catalyst for a gas purifier. 4. The cerium oxide particles supported on the HC adsorbent layer are impregnated with a solution in which a palladium compound is dissolved so that an oxidation catalyst composed of palladium oxide is supported on the cerium oxide particles. The method for producing a catalyst for an exhaust gas purifying apparatus for an engine according to claim 3, wherein 5. The HC so that the amount of cerium oxide particles supported with respect to the carrier volume is in the range of 50 to 100 g / l.
The method for producing a catalyst for an exhaust gas purifying apparatus of an engine according to claim 3 or 4, wherein an impregnation amount of the cerium compound solution with respect to the adsorbent layer is set. 6. The particle size of cerium oxide particles produced by firing cerium hydroxide particles is 30 to 200 n.
The method for producing a catalyst for an exhaust gas purifying apparatus of an engine according to any one of claims 3 to 5, wherein the ammonia concentration of the aqueous ammonia solution is set to be within a range of m.