JP2009255084A - Catalyst for purifying exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas which is excellent in heat resistance and exhibits catalytic activity even at a low temperature region, and can exhibits catalytic performance immediately after starting an engine. <P>SOLUTION: The catalyst for purifying exhaust gas comprises a catalyst carrier, and a noble metal supporting part formed on the catalyst carrier. The noble metal supporting part has a supporting part component, and a noble metal catalyst supported by the supporting part component. The noble metal catalyst consists only of rhodium. The supporting part component supporting only the rhodium consists of an oxide component which does not contain a cerium oxide and consists of a zirconium oxide, and an activated alumina powder supporting the oxide component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst, which simultaneously removes carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx), which are harmful components contained in exhaust gas from an internal combustion engine such as an automobile. The present invention relates to an exhaust gas purifying catalyst.

Conventionally, as a catalyst for exhaust gas purification, a refractory inorganic oxide is supported on a ceramic catalyst carrier, and the refractory inorganic oxide is supported together with a noble metal element serving as a catalyst and a compound that stably holds the noble metal element. Is formed.
In Patent Document 1 (Japanese Patent Laid-open No. Sho 63-1116741), cerium added as a compound that stabilizes and holds the above-mentioned noble metal element suppresses the growth of cerium oxide particles under high temperature exhaust gas purification conditions. In order to maintain purification performance, a catalyst is disclosed in which zirconium oxide is partly present in cerium oxide as a complex oxide or solid solution.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2-43951) discloses zirconia as an exhaust gas purifying catalyst having excellent durability even under severe conditions such as a high-temperature oxidizing atmosphere and having high purifying performance even in a low temperature range. Or, a cerium oxide stabilized by one selected from the group consisting of zirconia, yttria and calcia, and activated alumina of a refractory inorganic oxide carrying a catalyst metal made of rhodium, platinum and palladium as a honeycomb carrier A supported catalyst is disclosed. However, these exhaust gas purification catalysts have a problem that even if they are active in a high temperature range, the catalyst does not necessarily become active in a low temperature atmosphere immediately after starting the engine and does not exhibit sufficient purification performance. That is, the exhaust gas purification performance cannot be fully exhibited unless the catalyst is warmed to a certain temperature or more.

JP 63-1116741 A JP-A-2-43951

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to improve the catalyst activity in a low temperature range and the heat resistance of the catalyst itself, and to activate the catalyst promptly after the engine is started.

  The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having a catalyst carrier and a noble metal supporting part formed on the catalyst carrier, wherein the noble metal supporting part is supported on a supporting part component and the supporting part component. The noble metal catalyst is made of only rhodium, and the supporting part component supporting only the rhodium includes an oxide component not containing cerium oxide and consisting of zirconium oxide, and the oxide component. It is characterized by comprising activated alumina powder carrying

  Further, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having a catalyst carrier and a noble metal carrying part formed on the catalyst carrier, wherein the noble metal carrying part comprises a carrying part component and the carrying part component. The noble metal catalyst is composed of only rhodium, and the support component that supports only the rhodium is formed of at least a mixed oxide powder of zirconium and cerium and an activated alumina powder. It is characterized by being.

When the total amount of the mixed oxide of zirconium and cerium is 100 mol%, zirconium is preferably 75 mol% or more.
A second noble metal supporting part is further formed on the catalyst carrier, and the second noble metal supporting part has a supporting part component and a noble metal catalyst supported on the supporting part component, The noble metal catalyst is preferably composed of at least one selected from noble metal components such as platinum and palladium other than rhodium.

  Further, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having a catalyst carrier and a noble metal carrying portion formed on the catalyst carrier, wherein the noble metal carrying portion includes a first noble metal carrying portion and a first noble metal carrying portion. The first noble metal carrying part has a carrying part component and a noble metal catalyst made of only rhodium supported on the carrying part component, and the second noble metal carrying part comprises: The supporting part component having a supporting part component and a noble metal catalyst made of at least one kind selected from noble metal components such as platinum and palladium other than rhodium supported on the supporting part component, and supporting the noble metal catalyst made only of rhodium. Is characterized by comprising an oxide component composed of zirconium oxide and cerium oxide, and an activated alumina powder carrying the oxide component.

  When the total amount of zirconium and cerium in the oxide component supported on the activated alumina powder is 100 mol%, the supported amount of zirconium is preferably 75 mol% or more.

  In the exhaust gas purifying catalyst of the present invention, rhodium, which is a catalyst metal, is supported on a support layer rich in zirconium oxide, so that the stability of rhodium is increased and the heat resistance is improved as compared with conventional catalysts. Even after the endurance test, it has high purification performance and can exhibit purification performance in a relatively low temperature range. Therefore, even after the engine is started, the catalyst activity can be shown quickly and the exhaust gas can be purified.

It is explanatory drawing of the aging conditions of the catalyst in a test example. 4 is a bar graph of 50% purification temperatures of HC, CO, and NOx of catalysts of Example 1 and Comparative Example 1 in a test example. It is a bar graph of the cross purification rate of the catalyst of Example 1 and Comparative Example 1 in a test example.

  The exhaust gas purifying catalyst of the present invention comprises a catalyst carrier, an inorganic oxide support layer formed on the catalyst support, and a noble metal catalyst supported on the support layer. A feature of the present invention is that it has a supporting layer in which rhodium as a noble metal catalyst is supported on activated alumina powder supporting zirconium oxide. By supporting rhodium as a noble metal catalyst in the vicinity of zirconium oxide, it is possible to improve the purification characteristics of rhodium and to maintain the stability and durability of rhodium.

  The rhodium is more effective as a purification catalyst than the case where rhodium is supported on activated alumina or activated alumina containing cerium oxide. Furthermore, the support layer in which rhodium is supported on the support layer component in which an inferior amount of cerium oxide is mixed with the activated alumina supporting zirconium is also improved in the rhodium purification characteristics and maintains the stability and durability of rhodium. be able to.

With respect to the amounts of zirconium oxide and cerium oxide supported on the activated alumina powder, when the total amount of zirconium and cerium is 100 mol%, the amount of zirconium supported is 75 mol% or more. If the amount of cerium added is 25 mol% or more, the low temperature activity of the catalyst is lost, which is not preferable.
The activated alumina powder is preferable because lanthanum is dissolved to stabilize the activated alumina and the supported oxide and noble metal catalyst are stabilized, thereby improving the purification performance of the catalyst.

  The above-mentioned support layer formed on the catalyst support is coated on the catalyst support in the form of a slurry of a mixture of rhodium supported on active alumina powder supported by mixing zirconium oxide and, if necessary, cerium oxide. A uniform support layer can be formed. When the oxide such as activated alumina powder is supported in a slurry, it is preferable to form the support layer using a slurry in which rhodium as a noble metal catalyst is previously supported on the oxide powder. Thereby, the rhodium of the catalyst metal can be uniformly dispersed on the zirconium oxide, can be stabilized, can increase the heat resistance of the catalyst, and can effectively exhibit the catalytic activity.

  On the catalyst carrier, an active alumina powder carrying a noble metal catalyst such as platinum or palladium, and a carrying component comprising cerium oxide and zirconium oxide are mixed with the above carrying component carrying rhodium to obtain a uniform slurry. Can be supported on a catalyst carrier to form a catalyst. As the catalyst carrier, for example, a monolith carrier having a honeycomb structure made of ceramics or metal can be used.

  The second exhaust gas purifying catalyst of the present invention is formed by supporting a support layer supporting rhodium and a noble metal catalyst other than rhodium on a mixture of a mixed oxide of zirconium and cerium and activated alumina. Yes. By constituting the support layer component supporting rhodium with a mixed oxide with cerium rich in zirconium, the stability of rhodium can be maintained and the cross purification rate of the purification catalyst can be further increased.

  This mixed oxide can be formed, for example, by mixing dissolved solutions of cerium and zirconium, coprecipitating with ammonia water, and firing the product. In this case, the amount of zirconium is preferably 75 mol% or more in the mixed oxide in order to enhance the stability of the catalyst and maintain the catalytic activity. In this case, rhodium may be directly supported on a mixed oxide of zirconium and cerium and then mixed with activated alumina to form a support layer as a slurry. The active alumina powder used can form a stable support layer without dissolving lanthanum in solid solution.

  Similarly, the second exhaust gas purifying catalyst of the present invention may be supported by adding a support layer supporting platinum in addition to rhodium as a noble metal catalyst. It is preferable to use platinum supported on an oxide of cerium and zirconium like rhodium. And it is preferable that also in the ratio of cerium and zirconium as a total, the zirconium molar ratio is high, that is, the molar percentage of zirconium is 75 or more.

  The total amount of oxide supported on the support layer is such that the amount of cerium and zirconium is 0.1 to 0.4 mol / L and 0.1 to 0.6 mol / L, respectively, per liter of catalyst capacity. desirable. When the amount of cerium in the catalyst is less than 0.1 mol / L, the oxygen storage amount decreases and the catalytic activity decreases. On the other hand, if it exceeds 0.4 mol / L, the performance is only slightly improved, which is not preferable in terms of cost. When the amount of zirconium is less than 0.1 mol / L, the stability of rhodium decreases, which is not preferable. Moreover, even if it adds exceeding 0.6 mol / L, since the improvement of the stability of a catalyst is slight and it becomes expensive, it is unpreferable.

  The supported amount of rhodium is preferably 0.01 to 5 g per liter of catalyst capacity. A rhodium loading of less than 0.01 g / L is not preferable because sufficient catalytic activity cannot be obtained. On the other hand, if it exceeds 5 g / L, even if the amount of rhodium supported is increased further, the performance improvement is slight and expensive. When platinum is supported, the supported amount is 0.1 to 5 g. When the loading is less than 0.1 g / L, there is a possibility that sufficient catalytic activity may not be obtained, which is not preferable. On the other hand, if the amount exceeds 5 g / L, the improvement in performance is slight and expensive even if the amount of platinum supported is increased.

  By adopting a structure in which such a noble catalyst metal, rhodium, is supported on a support layer rich in zirconium oxide, the catalyst activity in a low temperature region can be increased as compared with a catalyst supported uniformly with the same composition. it can. That is, in the catalyst of the present invention, the 50% purification temperature of the catalyst after the durability test can be lowered, and the problem of low temperature activity can be realized.

  The exhaust gas purifying catalyst is an exhaust gas purifying catalyst comprising a catalyst carrier and a noble metal supporting layer formed on the catalyst carrier. The noble metal supporting layer includes a supporting layer component and a noble metal supported on the supporting layer component. The noble metal catalyst contains rhodium, and the support layer component supporting the rhodium includes an oxide component composed of at least one of zirconium oxide and cerium oxide, and the oxide component. When the total amount of zirconium and cerium in the oxide component supported on the activated alumina powder is 100 mol%, the supported amount of zirconium is 75 mol% or more. Also good.

The total amount of zirconium and cerium of 100 mol% represents the atomic mole of each atom of zirconium and cerium in percentage.
The activated alumina powder is preferably a stabilized alumina powder in which lanthanum is dissolved.
The support layer component is preferably formed from a slurry of the activated alumina on which the zirconium oxide is previously supported.

When the total amount of zirconium and cerium in the oxide component in the supporting layer component supporting rhodium is 100 mol%, the supported amount of zirconium is preferably 90 mol% or more.
The noble metal catalyst further includes another noble metal catalyst which is a noble metal catalyst other than rhodium, and the supporting layer component supporting the other noble metal catalyst is an oxidation comprising at least one of zirconium oxide and cerium oxide. It is preferable to consist of a physical component and the activated alumina powder which carries this oxide component.
The exhaust gas purifying catalyst is an exhaust gas purifying catalyst comprising a catalyst carrier and a noble metal supporting layer formed on the catalyst carrier. The noble metal supporting layer is supported on a supporting layer component and the supporting layer component. The noble metal catalyst comprises rhodium and another noble metal catalyst that is a noble metal catalyst other than rhodium, and the supporting layer component includes a rhodium supporting part for supporting the rhodium, and the non-rhodium other than the rhodium. The rhodium supporting part is formed of at least a mixed oxide powder of zirconium and cerium and an activated alumina powder, and the mixed oxidation in the rhodium supporting part. When the total amount of zirconium and cerium in the product powder is 100 mol%, the supported amount of zirconium is 75 mol% or more and less than 100 mol%. Ri, the other noble metal-supported unit, the mixed oxide powder and at least zirconium and cerium, may be formed by the activated alumina.

  In the exhaust gas-purifying catalyst, rhodium, which is a catalyst metal, is supported on a support layer rich in zirconium oxide, so that the stability of rhodium is increased and heat resistance is improved as compared with conventional catalysts. Even after the endurance test, it has high purification performance and can exhibit purification performance in a relatively low temperature range. Therefore, even after the engine is started, the catalyst activity can be shown quickly and the exhaust gas can be purified.

  Hereinafter, specific examples will be described.

Example 1
Activated alumina powder containing 3 mol% of lanthanum was immersed in an aqueous zirconium nitrate solution, stirred, dried and fired to obtain lanthanum-containing activated alumina powder supporting zirconium.

  This zirconium oxide-supported active alumina powder was immersed in an aqueous rhodium nitrate solution and dried to obtain a powder in which rhodium was fixed. A slurry A was obtained by slurrying the rhodium-fixed activated alumina powder with an aqueous nitric acid solution, a binder and deionized water. Next, the activated alumina powder containing 3 mol% of lanthanum is immersed in a solution in which a cerium nitrate solution and a zirconium nitrate solution are mixed (a solution having a large amount of cerium in the ratio of cerium and zirconium), and after stirring, Ammonia water was added thereto, dried and fired to obtain a powder in which cerium oxide and zirconium oxide were supported on lanthanum-containing activated alumina.

  Furthermore, this powder was immersed in a dinitrodiamine platinum solution and dried to obtain a cerium oxide and zirconium oxide-supported activated alumina powder on which platinum was fixed. The activated alumina powder carrying cerium oxide and zirconium oxide with platinum fixed thereon was slurried with an aqueous nitric acid solution, a binder and deionized water to obtain slurry B. Slurry A and slurry B were mixed at a ratio of 1: 1, and coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried and fired to obtain catalyst 1.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.21 mol / L, Zr 0.29 mol / L, La 0.03 mol / L.

(Example 2)
The activated alumina powder containing 3 mol% of lanthanum is immersed in a mixed solution of cerium nitrate solution and zirconium nitrate solution (solution with a large amount of zirconium in the ratio of cerium and zirconium), and after stirring, ammonia water is added to the solution. Was added, dried and fired to obtain a powder in which cerium oxide and zirconium oxide were supported on lanthanum-containing activated alumina.

  The oxide-supporting activated alumina powder was immersed in an aqueous rhodium nitrate solution and dried to obtain a powder in which rhodium was fixed. A slurry A was obtained by slurrying this rhodium-fixed oxide-supporting activated alumina powder with an aqueous nitric acid solution, a binder and deionized water. Next, the activated alumina powder containing 3 mol% of lanthanum is immersed in a solution in which a cerium nitrate solution and a zirconium nitrate solution are mixed (a solution having a large amount of zirconium in the ratio of cerium and zirconium), and after stirring, Ammonia water was added thereto, dried and fired to obtain a powder in which cerium oxide and zirconium oxide were supported on lanthanum-containing activated alumina.

  Further, the above oxide-supported powder was immersed in a dinitrodiamine platinum solution and dried to obtain an activated alumina powder on which platinum was fixed. A slurry B was obtained by slurrying the activated alumina powder carrying the above-mentioned oxide on which platinum was fixed with an aqueous nitric acid solution, a binder and deionized water. Slurry A and slurry B were mixed at a ratio of 1: 1, and coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried and fired to obtain catalyst 2.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.14 mol / L, Zr 0.36 mol / L, La 0.03 mol / L.

(Example 3)
Catalyst 3 was obtained in the same manner as in Example 2 except that the supported ratio of cerium oxide and zirconium oxide was changed to activated alumina powder.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.16 mol / L, Zr 0.34 mol / L, La 0.03 mol / L.

Example 4
A cerium-zirconium coprecipitate formed by adding ammonia water in a mixed solution of cerium nitrate solution and zirconium nitrate solution (a solution containing a large amount of zirconium in the ratio of cerium to zirconium) is dried and calcined to obtain cerium. A zirconium mixed oxide was obtained.

The mixed oxide of cerium and zirconium and the activated alumina powder were immersed in a rhodium nitrate solution and dried to obtain an activated alumina powder containing the mixed oxide in which rhodium was fixed.
A slurry A was obtained by slurrying this rhodium-fixed powder with an aqueous nitric acid solution and deionized water.

A cerium-zirconium coprecipitate formed by adding ammonia water in a mixed solution of cerium nitrate solution and zirconium nitrate solution (a solution containing a large amount of cerium in the ratio of cerium and zirconium) is dried and calcined to obtain cerium. A zirconium mixed oxide was obtained.
This mixed oxide of cerium and zirconium and activated alumina powder were immersed in a dinitrodiamine platinum solution and dried to obtain a mixed oxide-containing activated alumina powder in which platinum was fixed.

A slurry B was obtained by slurrying the rhodium-fixed powder with an aqueous nitric acid solution and deionized water.
Slurry A and slurry B were mixed at a ratio of 1: 1, and coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried and fired to obtain catalyst 4.
The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.16 mol / L, Zr 0.34 mol / L, La 0.03 mol / L.

(Example 5)
A cerium-zirconium coprecipitate formed by adding ammonia water in a mixed solution of cerium nitrate solution and zirconium nitrate solution (a solution containing a large amount of zirconium in the ratio of cerium and zirconium) is dried and calcined to cerium. A zirconium mixed oxide was obtained.

The cerium and zirconium oxides were immersed in a rhodium nitrate solution and dried to obtain a mixed oxide powder in which rhodium was fixed.
A slurry A was obtained by slurrying the mixed oxide powder of cerium and zirconium with fixed rhodium, activated alumina, nitric acid aqueous solution and deionized water.
A cerium-zirconium coprecipitate formed by adding ammonia water in a mixed solution of cerium nitrate solution and zirconium nitrate solution (a solution containing a large amount of cerium in the ratio of cerium and zirconium) is dried and calcined to obtain cerium. A zirconium mixed oxide was obtained.

This mixed oxide powder of cerium and zirconium was immersed in a dinitrodiamine platinum solution and dried to obtain a powder on which platinum was fixed.
A slurry B was obtained by slurrying this rhodium-fixed cerium and zirconium mixed oxide powder, activated alumina powder, nitric acid aqueous solution and deionized water.
Slurry A and slurry B were mixed at a ratio of 1: 1, and coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried and fired to obtain catalyst 5.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.16 mol / L, Zr 0.34 mol / L, La 0.03 mol / L.

(Comparative Example 1)
Activated alumina containing 3 mol% lanthanum was immersed in an aqueous rhodium nitrate solution and dried to obtain a powder in which rhodium was fixed.

  Slurry was obtained by thrilling the rhodium-fixed powder with an aqueous nitric acid solution and deionized water. Next, activated alumina containing 3 mol% lanthanum was immersed in a dinitrodiamine platinum solution and dried to obtain a powder on which platinum was fixed. Slurry B was obtained by thrilling the platinum-fixed powder with an aqueous nitric acid solution and deionized water.

  Slurry A and slurry B were mixed at a ratio of 1: 1, and coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried and fired to obtain catalyst 2. The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, and La 0.03 mol / L.

(Comparative Example 2)
The activated alumina powder was immersed in a cerium nitrate solution, dried and fired to obtain a cerium-containing alumina powder. The cerium-supporting activated alumina powder was immersed in a rhodium nitrate solution and dried to obtain a powder in which rhodium was fixed. A slurry A was obtained by slurrying the rhodium-fixed powder with an aqueous nitric acid solution and deionized water.

  The activated alumina powder was immersed in a cerium nitrate solution, dried and fired to obtain a cerium-containing alumina powder. The cerium-supporting activated alumina powder was immersed in a dinitrodiamine platinum solution and dried to obtain a powder on which platinum was fixed. A slurry B was obtained by slurrying the platinum-fixed powder with an aqueous nitric acid solution and deionized water. Slurry A and slurry B were mixed at a ratio of 1: 1, and coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried and fired to obtain catalyst 2.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, and La 0.03 mol / L.

(Comparative Example 3)
A catalyst was prepared in the same manner as in Example 2 except that the ratio of cerium and zirconium in the rhodium support was changed to 30:70 as shown in Table 1 and the platinum support was only zirconium.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.75 mol / L, Zr 0.425 mol / L, La 0.03 mol / L.

(Comparative Example 4)
A catalyst was prepared in the same manner as in Example 2, except that the ratio of cerium and zirconium in the rhodium-carrying part and the platinum-carrying part was changed as shown in Table 1.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.3 mol / L, Zr 0.2 mol / L, La 0.03 mol / L.

(Comparative Example 5)
A catalyst was prepared in the same manner as in Example 2, except that the ratio of cerium and zirconium in the rhodium-carrying part and the platinum-carrying part was changed as shown in Table 1.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.16 mol / L, Zr 0.34 mol / L, La 0.03 mol / L.

(Comparative Example 6)
The activated alumina containing 3 mol% of lanthanum is immersed in a mixed solution of cerium nitrate solution and zirconium nitrate solution (a solution containing a large amount of zirconium in the ratio of cerium and zirconium). After stirring, aqueous ammonia is added to the solution. The lanthanum-containing activated alumina, cerium and zirconium oxide-containing powders were obtained by adding, drying and firing. This mixed powder was slurried with an aqueous nitric acid solution, a binder and deionized water to obtain slurry A.

  The slurry A was coated on a honeycomb carrier having a diameter of 80 mm and a length of 100 mm, dried, dipped in a cerium nitrate solution and a zirconium nitrate solution, dried and fired to form a coat layer. Next, the coating layer was immersed in a dinitrodiamine platinum solution and a rhodium nitrate solution to prepare a catalyst.

  The catalyst composition was Pt 1.5 g / L, Rh 0.3 g / L, Ce 0.125 mol / L, Zr 0.375 mol / L, La 0.03 mol / L. Table 1 shows the composition and composition of each of the above catalysts and the total supported amounts of Ce and Zr.

(Test example)
Two of the catalysts obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were separately attached to a gasoline engine having a displacement of 4000 CC. Under the aging conditions shown in FIG. An endurance test was conducted for 20 hours at a gas temperature of 800 ° C. and an exhaust gas temperature of 1050 ° C. in the center of the catalyst.

  As shown in FIG. 1, the aging condition is a cycle in which one cycle is 30 seconds. The first 10 seconds in one cycle is controlled by the theoretical air fuel consumption A / F = 14.6, and then the fuel is 26 seconds. Increase to the eye and maintain the state of A / F = 13 from the 10th to the 16th. In addition, by introducing secondary air from the 16th to the 30th, A / F = 14.8 is controlled from the 16th to the 25th, and the control is continued until the 30th. . From the 16th second of the cycle, the temperature in the center of the catalyst increases and reaches 1050 ° C., and from the 26th second, the durability test starts from 1050 ° C. under excess oxygen.

  Each of the catalysts subjected to the above durability test was then attached to a gasoline engine having a displacement of 2000 CC, and the catalyst performance was evaluated. The evaluation conditions were such that the engine speed was controlled at 1400 rpm and the theoretical air-fuel consumption A / F = 14.6, and the temperature at the catalyst inlet was varied to obtain 50% purification temperatures for HC, CO, and NOx. Table 2 shows the cross purification rate of HC-NOx and CO-NOx and the evaluation results. The amounts of the noble metal catalysts in Table 1 are all the same amount, which indicates that they are due to differences in the composition of the supporting part and the supporting state.

As shown in Table 2, in each of the catalysts of Examples 1 to 5, the 50% purification temperatures of HC, CO, and NOx are lower even after the endurance test than the catalysts of Comparative Examples 1 to 6. . That is, it can be seen that the catalyst is active even in a low temperature range and the catalyst maintains heat resistance. Furthermore, the value of the cross purification rate is also high.
Comparative Example 6 is a catalyst in which a coating layer in which cerium and zirconium are simultaneously supported on alumina is formed, and then a catalyst metal is supported. The 50% purification temperature is high and the cross purification rate is the lowest. Comparative Example 1 is a single coating layer of alumina. The cross purification rate and the 50% purification temperature are improved as compared with Comparative Example 6, but the 50% purification temperature is lower than in each Example. In Comparative Example 2, when no zirconium is contained, the cross purification rate and the 50% purification temperature are not sufficient. Comparative Example 3 is an example in which cerium is abundant in the rhodium-carrying part and does not exist in the platinum-carrying part. Comparative Example 4 is a case where the amount of rhodium and platinum carrying part co-cerium is large, and in this case as well, it does not show sufficient purification performance compared to the examples. Comparative Example 5 is a case where the rhodium carrying part has a large amount of cerium, and the purification performance is not sufficient as compared with Example 3 having the same amount of cerium and zirconium as a total.

Example 1 is a catalyst composition corresponding to Claims 1 and 4, Examples 2 and 3 are catalyst compositions corresponding to Claims 5 and 6, and Examples 4 and 5 are Claims 2, 3 and 4. The corresponding catalyst composition is used. As described above, all the catalysts of the present invention have excellent exhaust gas purification performance.
Further, the 50% purification temperature and the cross purification rate of the catalyst after the durability test for Example 3 and Comparative Example 1 are shown in FIGS.

  As shown in Table 2 and FIGS. 2 and 3, the catalyst of the present invention has excellent purification performance even after the durability test, and has high exhaust gas purification performance even in a low temperature range.

Claims (6)

In an exhaust gas purifying catalyst having a catalyst carrier and a noble metal support formed on the catalyst carrier,
The noble metal supporting part has a supporting part component and a noble metal catalyst supported on the supporting part component,
The noble metal catalyst consists only of rhodium,
The catalyst for purifying exhaust gas, characterized in that the supporting part component supporting only rhodium comprises an oxide component not containing cerium oxide and consisting of zirconium oxide, and an activated alumina powder supporting the oxide component. . In an exhaust gas purifying catalyst having a catalyst carrier and a noble metal support formed on the catalyst carrier,
The noble metal supporting part has a supporting part component and a noble metal catalyst supported on the supporting part component,
The noble metal catalyst consists only of rhodium,
The exhaust gas purifying catalyst, wherein the supporting part component supporting only rhodium is formed of at least a mixed oxide powder of zirconium and cerium and an activated alumina powder.   The exhaust gas-purifying catalyst according to claim 2, wherein the mixed oxide of zirconium and cerium is 75 mol% or more when the total amount is 100 mol%. A second noble metal support is further formed on the catalyst carrier,
The second noble metal support has a support component and a noble metal catalyst supported on the support component,
The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the noble metal catalyst comprises at least one selected from noble metal components such as platinum and palladium other than rhodium. In an exhaust gas purifying catalyst having a catalyst carrier and a noble metal support formed on the catalyst carrier,
The noble metal carrying portion includes a first noble metal carrying portion and a second noble metal carrying portion,
The first noble metal supporting part has a supporting part component, and a noble metal catalyst made of only rhodium supported on the supporting part component,
The second noble metal support has a support component and a noble metal catalyst made of at least one selected from precious metal components such as platinum and palladium other than rhodium supported on the support component.
Exhaust gas purification characterized in that the supporting part component supporting the noble metal catalyst composed only of rhodium is composed of an oxide component composed of zirconium oxide and cerium oxide and an activated alumina powder supporting the oxide component. Catalyst.   The exhaust gas-purifying catalyst according to claim 5, wherein the supported amount of zirconium is 75 mol% or more when the total amount of zirconium and cerium in the oxide component supported on the activated alumina powder is 100 mol%.

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