JPH0338893B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention deals with carbon monoxide (hereinafter referred to as CO), hydrocarbons (hereinafter referred to as HC), and nitrogen oxides (hereinafter referred to as NOx) in exhaust gas emitted from internal combustion engines, etc., especially automobiles. This invention relates to a catalyst for purifying engine exhaust gas, which is used to reduce emissions. (Conventional technology) Conventionally, CO, HC,
As a catalyst for purifying NOx, alumina (Al ₂ O ₃ ) supported on noble metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) is used. In addition, in order to improve the catalytic performance of these precious metals, we have developed an oxygen storage effect (the effect of capturing oxygen from exhaust gas and contributing to the purification of the catalyst).
Catalysts have been manufactured in which cerium oxide (CeO ₂ ), which is a certain substance, is contained in an alumina coating layer along with precious metals to improve the purification rate of exhaust gas. However, catalyst components of noble metals and base metals, and oxygen storage capacity imparting agents (hereinafter referred to as OSC) such as cerium oxide
The method of coexisting and supporting the alumina coating layer has the following problems. (a) Since the OSC agent is uniformly supported on the alumina coat layer, it is not necessarily supported in areas near the pores that are likely to come into contact with exhaust gas. In other words, most of the OSC agents are carried in parts of the exhaust gas that are difficult to diffuse, and do not participate in the purification reaction, making it impossible to obtain a high purification rate. (b) The thermal instability of the OSC agent adversely affects the catalyst components and alumina due to the increased direct contact between the agent and the catalyst components. (c) Since the OSC agent and the catalyst component are supported together, the two form a compound, reducing the dispersibility of the catalyst component and reducing exhaust gas purification performance. In addition, a catalyst layer containing Pt, Pd, etc. is provided on the catalyst carrier, and in order to protect the catalyst layer, an oxide consisting of alumina or a mixture of alumina and cerium oxide (0.1 to 0.5% by weight relative to alumina) is used. A method in which a coating layer is provided has been proposed (see Japanese Patent Application Laid-Open No. 60-5230).
In the case of this known technology, the coating layer containing a trace amount of cerium oxide is provided for the purpose of protecting the catalyst layer, and since the concentration of cerium oxide that acts as an OSC agent is extremely low, it does not affect the oxygen storage capacity effect. It was hardly what I expected. (Object of the Invention) The present invention has been made in view of the above-mentioned problems, and by forming a coating layer containing a large amount of OSC agent on the upper surface of the catalyst layer containing a catalyst component made of noble metal or base metal, catalyst The purpose is to significantly improve the purification performance of (Means for achieving the object) In the present invention, as a means for achieving the above object, a coating layer containing a large amount of OSC agent is provided on the upper surface of the catalyst layer supported on a catalyst carrier and containing a catalyst component. ing. Here, as the catalyst component, known components such as Pt, Rh, and Pd, and mixtures of two or more thereof are used. In addition, the ingredients of the OSC agent include cerium oxide (CeO ₂ ), nickel oxide (NiO), and iron oxide (Fe ₂ O ₃
Alternatively, known components such as FeO) and mixtures of two or more thereof are used, but _CeO2 is the most effective. Furthermore, the composition of the coating layer is 50 to 95% by weight.
It consists of an OSC agent and the remainder activated alumina.
The coating consists of OSC agent, activated alumina,
It is carried out using an aqueous slurry consisting of hydrated alumina and other dispersants. The easiest way is to
The coating layer can be formed by coating a slurry using two components: OSC agent and hydrated alumina. An example of the thus formed exhaust gas purifying catalyst is shown enlarged in FIG. Here, reference numeral 1 indicates a catalyst carrier, 2 indicates a catalyst layer, and 3 indicates a coating layer. As the catalyst carrier 1, a honeycomb structure made of ceramics such as cordierite, a heat-resistant metal, or various carriers made of heat-resistant inorganic fibers are used. (Operation) A catalyst having the above structure exhibits extremely superior exhaust gas purification performance compared to a conventional catalyst in which an active catalyst component and an OSC agent are impregnated in the same layer. Generally, as the OSC agent content in the coating layer decreases, the catalyst performance gradually decreases, and below 50%, the catalyst performance decreases rapidly. The reason is that as the concentration of the OSC agent decreases, it is no longer able to interact with the active catalyst components. By the way, as an OSC agent
Figure 2 shows the results of measuring the change in CO purification rate (%) at 400°C with respect to the content (wt%) of CeO ₂ in the coating layer using CeO ₂ . The catalyst component used here was platinum (Pt)
and rhodium (Rh) (same as in Example 1 described later), and the content of CeO ₂ can be changed by changing the weight ratio of cerium oxide and boehmite (total weight fixed at 930 g). I have to. In this result, the activation measurement conditions were air-fuel ratio A/F = 14.7 ± 0.9, space velocity SV = 60000/Hr.
In a bench engine, the exhaust gas temperature is 850.
This is an evaluation using a catalyst after a durability test operated at ℃ for 300 hours. According to this, CeO ₂ is 50
% or less, the CO purification rate drops significantly.
It is obvious that other OSC agents also exhibit a similar tendency. On the other hand, when the content of the OSC agent increases, the catalytic activity improves, but because the bonding force of the OSC agent itself is weak, the physical strength (peeling resistance) decreases and the durability decreases. By the way, the content (wt%) of CeO ₂ in the coating layer using CeO ₂ as the OSC agent
When we performed a peel test by changing the
The results shown in 1 were obtained. Here, peeling amount = (coat adhesion amount before test - coat adhesion amount after test) / (coat adhesion amount before test) Also, as a test method, use a cylindrical test piece with a diameter of 1 inch and a height of 1 inch. Heat at 600℃ for 30 minutes, then 25
After repeating the procedure of cooling in water at ℃ three times,
A method of thoroughly drying and measuring the amount of peeling was adopted.

[Table] From the results of the above peel test, CeO ₂ in the coating layer
It can be seen that the content is preferably 95% or less. It is obvious that other OSC agents also exhibit a similar tendency. If the adhesion ratio of the coating layer to the catalyst carrier is less than 5% by weight, the surface of the catalyst layer cannot be effectively coated, resulting in a rapid decline in catalyst performance, and if it exceeds 40% by weight, active components and exhaust gas Since contact with gas is inhibited, catalyst performance rapidly decreases. Taking this into consideration, it is desirable that the adhesion ratio of the coating layer be 5 to 40% by weight. Note that the thickness of the coating layer is preferably 20 to 40 μm. Some preferred embodiments of the present invention will be described below. Example 1 γ-alumina 160g, boehmite 160g, water 500g
cc. and 4 c.c. of concentrated nitric acid were mixed and stirred for 10 hours using a homomixer to obtain a slurry for coating an alumina wash. After immersing a honeycomb catalyst carrier (made of cordierite) in this slurry and pulling it up, the excess slurry was removed by high-pressure air blowing, and the heating rate was 200.
It was placed in an electric furnace set at °C/Hr and fired to 600 °C. This alumina-coated catalyst carrier is coated with Pt of 200
After immersing for about 15 seconds in a mixed aqueous solution obtained by mixing chloroplatinic acid with a Rh content of 100 g/ and rhodium chloride with an Rh content of 100 g/c.
It was dried at 600°C for 1 hour and then fired at 600°C for 2 hours. Precious metal content after firing is platinum (Pt) 1.0g/
, Rhodium (Rh) 0.2g/. The amount of the catalyst layer 2 thus obtained was 14% by weight based on the catalyst carrier 1. Next, cerium oxide 810g, boehmite 120g
g and 600 c.c. of water were mixed and stirred using a homomixer,
A slurry for coating with an OSC agent was obtained. The catalyst carrier to which alumina and precious metals were attached was immersed in this slurry for about 20 seconds and then pulled out. Excess slurry was removed by high-pressure air blowing, and the carrier was dried and fired under the same conditions as the alumina coating. By this,
Exhaust gas purification in which a coating layer 3 consisting of 90% by weight cerium oxide and 10% by weight γ-alumina is formed on the upper surface of a catalyst layer 2 (containing Pt and Rh) formed on a catalyst carrier 1. A catalyst was obtained (see Figure 1). The amount of the coating layer 3 deposited was 25% by weight based on the catalyst carrier 1. Example 2 In the active catalyst component impregnation process (i.e., the process of impregnating an alumina-coated catalyst carrier with a noble metal), platinum (Pt) was added to the catalyst carrier using a mixed aqueous solution of chloroplatinic acid, rhodium chloride, and palladium chloride.
A catalyst formed on catalyst carrier 1 was prepared in exactly the same manner as in Example 1, except that 0.28 g/, rhodium (Rh) 0.14 g/, and palladium (Pd) 0.98 g/ were deposited. An exhaust gas purification catalyst was obtained in which a coating layer 3 consisting of 90% by weight cerium oxide and 10% by weight γ-alumina was formed on the upper surface of layer 2 (containing Pt, Rh, and Pd). (See Figure 1). In this example as well, the amount of the coating layer 3 deposited was 25% by weight based on the catalyst carrier 1. Example 3 In the active catalyst component impregnation process (i.e., the process of impregnating the alumina-coated catalyst support with a noble metal), palladium (Pd) 1.4 g/m was deposited on the catalyst support using an aqueous palladium chloride solution. The catalyst layer 2 (containing Pd) formed on the catalyst carrier 1 was prepared by the same method as in Example 1, and was coated with 90% by weight of cerium oxide and 10% by weight of γ-alumina. An exhaust gas purifying catalyst having a coating layer 3 formed thereon was obtained (see FIG. 1). In this example as well, the amount of the coating layer 3 deposited was 25% by weight based on the catalyst carrier 1. Example 4 Catalyst layer 2 ( 90 wt% nickel oxide and 10 wt% on the top surface (including Pt, Ph)
An exhaust gas purifying catalyst was obtained in which a coating layer 3 made of γ-alumina was formed (see FIG. 1). In this example as well, the amount of the coating layer 3 deposited was 25% by weight based on the catalyst carrier 1. Example 5 A slurry for coating an OSC agent was prepared in the same manner as in Example 1 above, except that iron oxide (e.g., Fe ₂ O ₃ ) was used instead of cerium oxide, and a slurry was coated on the catalyst carrier 1. Catalyst layer 2 formed on
90 wt% iron oxide and 10 on the top surface (including Pt, Rh)
An exhaust gas purifying catalyst was obtained in which a coating layer 3 consisting of γ-alumina of % by weight was formed (first
(see figure). In addition, also in this example, the coating layer 3
The amount of adhesion was 25% by weight based on the catalyst carrier 1. A purification performance evaluation test was conducted by comparing the purification performance of the exhaust gas purification catalyst obtained in each of the above examples with a conventionally known catalyst, that is, a catalyst made by mixing an active catalyst component and an OSC agent. , the results shown in FIGS. 3 to 5 were obtained. Here, Comparative Examples 1 to 3 were prepared as follows. Comparative Example 1 315 g of activated alumina, 100 g of cerium oxide, 4 c.c. of concentrated nitric acid, and 700 c.c. of water were mixed and stirred using a homomixer to obtain a slurry for coating alumina and OSC agent. Using this slurry, alumina and OSC were applied to a honeycomb catalyst carrier in the same manner as in each of the above examples.
coated with the agent. The amount of this coating layer deposited was 25% by weight based on the catalyst carrier, and the proportion of cerium oxide in the coating layer was 25% by weight. Using the same method as in Example 1, this catalyst carrier was further impregnated with 1.0 g of platinum (Pt) and 0.2 g of rhodium (Rh) into the coating layer to obtain a catalyst. Comparative Example 2 After coating alumina and OSC agent using the same method and conditions as in Comparative Example 1, Pt, Rh, and Pd were coated with OSC using the same method and conditions as in Example 2.
The coating layer containing the agent was impregnated with the same noble metal deposition amount as in Example 2 (i.e., Pt0.28g/, Rh0.14
A catalyst of 0.98 g/Pd/) was obtained. Comparative Example 3 After coating alumina and an OSC agent using the same method and conditions as in Comparative Example 1, Pd was impregnated into the OSC agent-containing coating layer using the same method and conditions as in Example 3. A catalyst with the same noble metal deposition amount (ie, Pd 1.4 g/) was obtained. In addition, the activity measurement conditions are air-fuel ratio A/F = 14.7±
0.9, space velocity SV = 60000/Hr, and an evaluation test was conducted using the catalyst after a 300Hr endurance test on a bench engine. According to the results of the above evaluation tests, the exhaust gas purifying catalysts according to the embodiments of the present invention significantly purify exhaust gas from a low temperature state compared to conventionally known catalysts, that is, those of Comparative Examples 1 to 3. It can be seen that the performance has been improved. Example 6 As shown in FIG. 6, γ-
The product obtained by supporting alumina and catalyst components (Pt and Rh) was first immersed in a semi-liquid paraffin solution, and then 440 g of cerium oxide, 110 g of hydrated alumina, 500 c.c. of water, and 5 c. of concentrated nitric acid. After being immersed in the slurry liquid consisting of c. for about 20 seconds, excess slurry liquid is removed by high-pressure air blowing. Thereafter, by drying at 130°C for 1 hour and baking at 600°C for 1 hour, an exhaust gas purifying catalyst was obtained in which the coating layer 3 containing a large amount of cerium oxide was formed only on the half side to which the liquid paraffin did not adhere. Ta. When this catalyst is used with the side on which the coating layer 3 is formed as the outlet side, there is no coating layer containing cerium oxide, which has relatively poor heat resistance, on the inlet side where the temperature is high, preventing thermal deterioration of the cerium oxide. It becomes possible to do so. The range in which the covering layer 3 is formed is A ₂ /A ₁ = 7/3 to A 2 /A ₁ when the length of the part with the covering layer formed and the length of the part without the covering layer are respectively A ₁ and A 2 .
Although it is assumed to be 3/7, it is preferable to set A ₁ /A ₂ =1. Example 7 As shown in Figure 7, γ-alumina and catalyst components (Pt and Rh) were supported on a cylindrical catalyst carrier 1 in the same manner as in Example. , 1/ of the opening diameter on both sides of the opening.
After pasting a label with a diameter of 2, immersing it in a slurry consisting of 440 g of cerium oxide, 110 g of hydrated alumina, 500 c.c. of water, and 5 c.c. of concentrated nitric acid, the excess slurry was removed by high-pressure air blowing. Remove by. After that, remove the label and heat at 130℃ for 1 hour.
After drying for an hour, by baking at 600℃ for 1 hour,
An exhaust gas purifying catalyst was obtained in which the coating layer 3 containing a large amount of cerium oxide was formed only on the outer peripheral portion where the label was not attached. Since this catalyst does not have the coating layer 3 formed on the inner peripheral side that comes into direct contact with high-temperature exhaust gas, it is possible to prevent thermal deterioration of cerium oxide, which has relatively poor heat resistance. In addition,
The range in which the coating layer 3 is formed is B ₂ /2B ₁ =7/3 to 3/7, where the width of the coating layer forming part and the width of the coating layer non-forming part are _B1 and _B2 , respectively. However, it is preferable to set B ₂ / ₂ B ₁ =1. A comparative example (an example of an example of the present invention) in which a coating layer containing a large amount of cerium oxide was formed over the entire catalyst carrier was conducted to evaluate the purification performance of the exhaust gas purifying catalysts of Examples 6 and 7. ) are shown in FIGS. 8 to 10. The above evaluation test was measured after engine aging (exhaust gas temperature: 900°C, 100 hours of operation), and the activity measurement conditions were: air-fuel ratio A/F =
14.7±0.9, space velocity SV=60000/Hr. According to the above results, the catalysts of Examples 6 and 7 were
The purification performance is slightly improved compared to that of the comparative example, and this shows that there is no deterioration in the purification performance even if no coating layer is formed on the portions that are prone to thermal deterioration. Therefore, it is possible to save raw materials (OSC agent, etc.) necessary for forming the coating layer. Example 8 Catalyst layer 2 (containing Pt and Rh) formed on catalyst carrier 1 by the same method as in Examples 1 to 5 above
A catalyst having a coating layer 3 containing a large amount of cerium oxide formed on its upper surface is immersed in an alumina slurry solution consisting of 70 g of hydrated alumina, 70 g of γ-alumina, and 200 c.c. of water for about 20 seconds and then pulled up. Thereafter, excess alumina slurry was removed by high-pressure air blowing, dried at 130°C for 1 hour, and then fired in an electric furnace at 550°C for 1 hour. As a result, as shown in FIG. 11,
To obtain a triple-layer exhaust gas purifying catalyst having, on a catalyst carrier 1, a catalyst layer 2 containing an active catalyst component consisting of Pt and Rh, a coating layer 3 containing a large amount of cerium oxide, and a protective layer 4 containing only an alumina component. was completed. The thickness of the protective layer 4 obtained at this time was about 30μ. With this configuration, thermal deterioration of CeO ₂ contained in the coating layer 3 is prevented by the protective layer 4. Further, the protective layer 4 also has a poisoning prevention effect on the coating layer 3. The appropriate thickness of the protective layer 4 is 20 to 40 μm. If it is less than 20 μm, it will not be effective as a protective layer against heat and poisoning, and if it is more than 40 μm, it will be too thick and will not be used as a wash coat for exhaust gas. Diffusion within the tank becomes insufficient, and purification performance deteriorates. An evaluation test was conducted on the purification performance of the exhaust gas purification catalyst of Example 8, and the results of comparison with a comparative example (an example of an example of the present invention, in which no protective layer 4 was formed) are shown in Figures 12 to 14. As shown in the figure. The above evaluation test was conducted after driving the actual vehicle for 200 hours, and the activation measurement conditions were: air-fuel ratio A/F = 14.7 ± 0.9, space velocity SV = 60000/
It was considered Hr. According to this, the one of this example is
It can be seen that the purification performance is superior to that of the comparative example in which the protective layer 4 is not formed. Example 9 The exhaust gas purifying catalyst of this example has a catalyst layer 2, a catalyst layer 2,
It has a triple-layer structure including a covering layer 3 and a protective layer 4, and the protective layer 4 contains an oxide of an alkaline earth metal (CaO in this example). That is, the composition of the alumina slurry in the above example was 50 g of hydrated alumina, 60 g of γ-alumina,
A catalyst having a triple layer structure in which calcium oxide was contained in the protective layer 4 was obtained by using the same method and conditions as in Example 8 except that 50 g of calcium acetate and 200 c.c. of water were used. The thickness of the protective layer 4 obtained at this time was about 30μ. In this way, by containing the alkaline earth metal in the protective layer 4,
This can prevent phosphorus (P), a poisonous substance contained in engine oil, from vitrifying on the coated surface. Note that, among alkaline earth metals, calcium oxide (CaO) is particularly effective as a vitrification inhibitor. In addition, the amount of alkaline earth metal to be added is appropriately 10 to 30% by weight based on the weight of the protective layer 4 after firing, and if it is less than 10% by weight, the vitrification prevention effect will not be sufficient;
If it exceeds % by weight, the physical strength of the wash coat decreases and it becomes easy to peel off. Note that the thickness of the protective layer 4 is suitably 20 to 40 μm, as in Example 8. An evaluation test was conducted on the purification performance of the exhaust gas purification catalyst of Example 9, and the results of comparison with a comparative example (an example of an example of the present invention, in which no protective layer 4 was formed) are shown in Figures 15 to 17. As shown in the figure. The above evaluation test was conducted after driving the actual vehicle for 200 hours, and the activation measurement conditions were: air-fuel ratio A/F = 14.7 ± 0.9, space velocity SV = 60000/
It was considered Hr. However, in order to increase the amount of phosphorus adhering to the catalyst, an additive was added to increase the amount of phosphorus in the engine oil to 1.0% by weight for an engine with a LOC of 20,000 km/.
According to this, it can be seen that the cleaning performance of this example is superior to that of the comparative example in which the protective layer 4 is not formed. Example 10 In the exhaust gas purification catalyst of this example, the catalyst layer is composed of γ-alumina, but the raw material for the coating layer containing a large amount of OSC agent is α-alumina/hydrated alumina = 95/5. It has an alumina composition of ~60/40 (weight ratio). That is, a γ-alumina coat of about 40 μm was provided on a cordierite catalyst carrier by a conventional method, and catalyst components (Pt 1.0 g/, Rh 0.2 g/) were supported on this, and this was coated with 100 g of α-alumina and water. Japanese alumina
10g, cerium oxide 440g, water 500c.c., concentrated nitric acid 3c.c.
The catalyst with the above structure was immersed in a slurry liquid for about 20 seconds, removed by high-pressure air blowing, dried at 130°C for 1 hour, and fired in an electric furnace at 550°C for 1 hour. Obtained. This catalyst has little change in alumina crystals even when exposed to heat, and there is almost no decrease in pores, so physical strength at high temperatures (catalyst cracking, cord peeling, etc.) is improved, and durability is improved. In addition, when the amount of hydrated alumina is less than α-alumina/hydrated alumina = 95/5, the bonding strength between alumina and the alumina and the OSC agent becomes weaker.
It becomes easier to peel off. Furthermore, if the amount of α-alumina is less than α-alumina/hydrated alumina=60/40, the physical strength and durability at high temperatures, which are the characteristics of α-alumina, cannot be obtained. A purification performance evaluation test was conducted on the exhaust gas purification catalyst of Example 10 above, and comparison was made with a comparative example (an example of an example of the present invention, a catalyst in which the raw material of the coating layer containing the OSC agent is only γ-alumina). The first result is
This is shown in FIGS. 8 to 20. The above evaluation test was measured after thermal aging at 1100°C in the atmosphere for 50 hours, and the activity measurement conditions were: air-fuel ratio A/F = 14.7 ± 0.9, space velocity SV =
It was set as 60000/Hr. In addition, as a result of the peeling test of the coating layer, Table 2
The results shown are obtained. The peel test method involved heating a cylindrical test piece with a diameter of 1 inch and a height of 1 inch at 600℃ for 30 minutes, then cooling it in water at 25℃ three times, and then thoroughly drying it. A method of measuring the amount of peeling is adopted.

[Table] Here, peeling amount = (coat adhesion amount before test -
Coat adhesion amount after test)/(coat adhesion amount before test). From the results of the above tests, it can be seen that the samples of this example are slightly inferior in purification performance compared to those of comparative examples, but are very superior in peeling resistance. In the above embodiments, cerium oxide, nickel oxide, and iron oxide are used as OSC agents, but molybdenum oxide (MoO ₃ ) may be added to these OSC agents. (Effects of the Invention) As described above, according to the present invention, a catalyst layer containing at least one active catalyst component selected from the group consisting of platinum, rhodium, and palladium;
Since it is formed separately from the coating layer containing at least one OSC agent selected from the group consisting of cerium oxide, nickel oxide, and iron oxide,
The active catalyst component and the OSC agent no longer form a compound, which has the excellent effect of improving exhaust gas purification performance compared to the conventional combination of the active catalyst component and the OSC agent. In addition, the content of the OSC agent in the coating layer was increased to 50%.
~95% by weight, which greatly increases the oxygen storage effect of the OSC agent, which also has the effect of significantly improving exhaust gas purification performance. Furthermore, since the upper surface of the catalyst layer is coated with a coating layer containing an OSC agent, the catalyst layer is easily exposed to a reducing atmosphere, which has the advantage of further improving the NOx purification performance in exhaust gas.

[Brief explanation of the drawing]

FIG. 1 is an enlarged view showing an example of the exhaust gas purification catalyst according to the present invention, and FIG. 2 is a graph showing the exhaust gas relative to the CeO ₂ content (wt%) in the coating layer of the exhaust gas purification catalyst according to the present invention. Characteristic diagrams showing changes in CO purification rate (%) in gas, Figures 3, 4 and 5 are for Examples 1 to 5 of the present invention and Comparative Examples 1 to 3.
FIG. 6 is a perspective view of the exhaust gas purifying catalyst according to Example 6 of the present invention, and FIG. 7 is a characteristic diagram showing the results of the purification performance evaluation test with Example 7 of the present invention. The end view of the purification catalyst, FIGS. 8, 9, and 10 are characteristic diagrams showing the results of the purification performance evaluation test of Examples 6 and 7 of the present invention and the comparative example, and FIG. 11 is the characteristic diagram of the present invention. Enlarged view showing an example of the exhaust gas purifying catalyst according to Examples 8 and 9 of the invention, No. 12
FIG. 13 and FIG. 14 show Example 8 of the present invention.
FIG. 15, FIG. 16, and FIG. 17 are characteristic diagrams showing the results of the purification performance evaluation test of Example 9 of the present invention and the comparative example. , Fig. 18, Fig. 19 and Fig. 2
FIG. 0 is a characteristic diagram showing the results of a purification performance evaluation test of Example 10 of the present invention and a comparative example. 1...Catalyst carrier, 2...Catalyst layer, 3...Coating layer.

Claims (1)

[Claims] 1. A catalyst layer supported on a catalyst carrier and containing at least one catalyst component selected from the group consisting of platinum, rhodium, and palladium, and cerium oxide provided on the catalyst layer and acting as an oxygen storage ability imparting agent. , at least one oxide selected from the group consisting of nickel oxide and iron oxide.
A catalyst for purifying exhaust gas from an engine, comprising a coating layer of alumina containing 95% by weight.