JP2010227798A - Exhaust gas purifying catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve excellent oxygen storage ability with a small amount of an oxygen storage material. <P>SOLUTION: The exhaust gas purifying catalyst 1 includes a base material 2 provided with one or more through-holes where an exhaust gas flow, and a catalyst layer 3 supported by the wall surface of the through-hole and including a lower layer 3L facing the wall surface and an upper layer 3U facing the wall surface holding the lower layer 3L therebetween. The lower layer 3L includes a first part 3LF containing a first platinum group element and a first oxygen storage material and a second part 3LR positioned on the downstream side of the first part 3LF and containing a second platinum group element and a second oxygen storage material. The upper layer 3U contains a third platinum group element and a heat resistant carrier. The oxygen storage capacity of the first oxygen storage material is larger compared to the second oxygen storage material, and the oxygen storage speed of the second oxygen storage material is higher compared to the first oxygen storage material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst.

  As described in Patent Document 1, a catalyst for exhaust gas purification sometimes adopts a multilayer structure for the catalyst layer. For example, when a two-layer structure is used for the catalyst layer and different platinum group elements are supported on the upper layer and the lower layer, it may be possible to achieve performance that is difficult to achieve when a single-layer structure is used for the catalyst layer. .

  Among such exhaust gas purifying catalysts, there are catalysts in which the catalyst layer contains an oxygen storage material such as cerium oxide. When an oxygen storage material is used, oxygen can be stored in the oxygen storage material when excess oxygen is present in the exhaust gas. Therefore, fluctuations in the composition of the exhaust gas can be suppressed, and therefore excellent exhaust gas purification performance can be achieved.

Japanese Patent Laid-Open No. 7-60117

  In order to suppress fluctuations in the composition of the exhaust gas, more oxygen storage material may be contained in the catalyst layer. However, in this case, the pressure loss increases. Therefore, it is desirable to achieve superior oxygen storage capacity with a smaller amount of oxygen storage material.

  Therefore, an object of the present invention is to make it possible to achieve excellent oxygen storage capacity with a small amount of oxygen storage material.

  According to the first aspect of the present invention, the base material provided with one or more through-holes through which exhaust gas flows, the wall surface of the through-hole, and the lower layer facing the wall surface and the lower layer sandwiched therebetween A catalyst layer including an upper layer facing the wall surface, wherein the lower layer is positioned downstream of the first portion, the first portion containing the first platinum group element and the first oxygen storage material, A second portion containing a second platinum group element and a second oxygen storage material, wherein the upper layer contains a third platinum group element and a refractory carrier, and the first oxygen storage material is the second oxygen An exhaust gas purifying catalyst is provided, wherein the oxygen storage amount is larger than that of the storage material, and the second oxygen storage material has an oxygen storage rate higher than that of the first oxygen storage material.

  According to the second aspect of the present invention, the base material provided with one or more through-holes through which the exhaust gas flows, the wall surface of the through-hole, and the lower layer facing the wall surface and the lower layer sandwiched therebetween A catalyst layer including an upper layer facing the wall surface, wherein the lower layer is positioned downstream of the first portion, the first portion containing the first platinum group element and the first oxygen storage material, A second portion containing a second platinum group element and a second oxygen storage material, wherein the upper layer contains a third platinum group element and a refractory carrier, and each of the first and second oxygen storage materials Is an oxide containing at least one of cerium and zirconium, and the ratio of cerium in the first oxygen storage material is higher than the ratio of cerium in the second oxygen storage material. A purification catalyst is provided.

  According to the present invention, it is possible to achieve an excellent oxygen storage capacity with a small amount of oxygen storage material.

1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. Sectional drawing which expands and shows a part of catalyst for exhaust gas purification shown in FIG. The graph which shows the oxygen storage rate obtained about the oxygen storage material. The graph which shows the oxygen storage amount obtained about the oxygen storage material. The graph which shows the oxygen storage amount obtained about the catalyst for exhaust gas purification. The graph which shows the example of the relationship between the ceria content of an upstream part or a downstream part, and the oxygen storage amount of the exhaust gas purification catalyst.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the exhaust gas-purifying catalyst shown in FIG. In FIG. 2, white arrows indicate the flow direction of the exhaust gas.

  The exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 is a monolith catalyst. The exhaust gas-purifying catalyst 1 includes a base material 2 made of ceramics or metal such as cordierite. The base material 2 is provided with one or a plurality of through holes. Here, as an example, the base material 2 is assumed to be a substantially cylindrical monolith honeycomb base material.

  A catalyst layer 3 is formed on the partition wall of the substrate 2, that is, on the wall surface of the through hole provided in the substrate 2. Another layer may be interposed between the substrate 2 and the catalyst layer 3.

The catalyst layer 3 includes a lower layer 3L and an upper layer 3U.
The lower layer 3L is formed on the partition wall of the substrate 2. The lower layer 3L includes a first portion 3LF and a second portion 3LR located downstream of the first portion 3LF. In the exhaust gas-purifying catalyst 1, a portion corresponding to the first portion 3LF is a substantially cylindrical upstream portion, and a portion corresponding to the second portion 3LR is a substantially cylindrical downstream portion. The first portion 3LF and the second portion 3LR may be in contact with each other or may be separated from each other.

The first portion 3LF contains a first platinum group element and a first oxygen storage material.
The first platinum group element is, for example, at least one of platinum, palladium, and rhodium. Typically, the first platinum group element is at least one of platinum and palladium.

  The content of the first platinum group element per unit volume in the upstream portion is, for example, in the range of 0.5 g / L to 1.5 g / L. When this value is increased, the oxygen storage amount and oxygen storage rate of the first oxygen storage material increase. However, in this case, in addition to an increase in the heat capacity of the upstream portion, sintering tends to occur. If this value is reduced, the oxygen storage amount and oxygen storage speed of the first oxygen storage material are reduced, and it becomes difficult to achieve sufficient exhaust gas purification performance.

  The first oxygen storage material has a larger oxygen storage capacity than the second oxygen storage material described later. The first oxygen storage material is preferably ceria or a first composite oxide containing cerium. Typically, the first oxygen storage material is a first composite oxide.

  The first composite oxide preferably contains cerium and zirconium. The first composite oxide may be a single composition composite oxide or a mixture of a plurality of composite oxides.

  In the first composite oxide, the cerium content in terms of oxide, that is, the ceria content is, for example, in the range of 50 to 80% by mass. If the ceria content is small or large, it is difficult to achieve a large oxygen storage amount.

  The first composite oxide may further contain a rare earth element other than cerium. For example, the first composite oxide may be a composite oxide containing cerium, zirconium, praseodymium, and lanthanum.

  As rare earth elements other than cerium, for example, one or more of praseodymium, lanthanum, yttrium, and neodymium can be used. When a rare earth element other than cerium is used, the content in terms of the oxide of the rare earth element other than cerium in the first composite oxide is, for example, in the range of 5 to 20% by mass. For example, when the first composite oxide includes praseodymium and lanthanum, the praseodymium oxide content in the first composite oxide is in the range of 5 to 9% by mass, and the lanthanum oxide content is 1 It shall be in the range of 5 mass%.

  In the first composite oxide, the sum of the cerium content and the zirconium content in terms of oxide, that is, the sum of the ceria content and the zirconia content is, for example, in the range of 80 to 95 mass%. When this value is small or large, a large oxygen storage amount may not be achieved.

  The first portion 3LF may further contain a heat resistant carrier. As the heat-resistant carrier, for example, alumina can be used.

  The content of the first oxygen storage material per unit volume in the upstream portion is, for example, in the range of 25 g / L to 150 g / L. When this value is small, a large oxygen storage amount may not be achieved. When this value is large, the heat resistance of the upstream portion may be insufficient, or the exhaust gas purification ability may be insufficient.

The second portion 3LR contains a second platinum group element and a second oxygen storage material.
The second platinum group element is, for example, at least one of platinum, palladium, and rhodium, and is typically at least one of platinum and palladium. The second platinum group element may be the same as or different from the first platinum group element. Here, as an example, the first and second platinum group elements are equal to each other.

  The content of the second platinum group element per unit volume in the downstream portion is, for example, in the range of 0.1 g / L to 1.0 g / L. Increasing this value increases the oxygen storage amount and oxygen storage rate of the second oxygen storage material. However, in this case, in addition to an increase in the heat capacity of the upstream portion, sintering tends to occur. If this value is reduced, the oxygen storage amount and oxygen storage rate of the second oxygen storage material are reduced, and it becomes difficult to achieve sufficient exhaust gas purification performance.

  Note that the content of the second platinum group element per unit volume in the downstream portion may be the same as or different from the content of the first platinum group element per unit volume in the upstream portion.

  The second oxygen storage material has a higher oxygen storage rate than the first oxygen storage material. The second oxygen storage material is, for example, a second composite oxide containing cerium and zirconium. The second composite oxide may be a single composition composite oxide or a mixture of a plurality of composite oxides.

  In the second composite oxide, the cerium content in terms of oxide, that is, the ceria content is, for example, in the range of 20 to 40% by mass. If the ceria content is small or large, it is difficult to achieve a high oxygen storage rate.

  The second composite oxide may further contain a rare earth element other than cerium. For example, the second composite oxide may be a composite oxide containing cerium, zirconium, lanthanum, and yttrium.

  As the rare earth elements other than cerium of the second composite oxide, for example, those described above with respect to the first composite oxide can be used. In the case of using a rare earth element other than cerium, the content of the second composite oxide in terms of an oxide of a rare earth element other than cerium is, for example, in the range of 3 to 15% by mass. For example, when the second composite oxide contains lanthanum and yttrium, the lanthanum oxide content in the second composite oxide is in the range of 1 to 5% by mass, and the yttrium oxide content is 2 It shall be in the range of 10 mass%.

  In the second composite oxide, the sum of the cerium content and the zirconium content in terms of oxide, that is, the sum of the ceria content and the zirconia content is, for example, in the range of 85 mass% to 97 mass%. To do. When this value is small or large, a large oxygen storage amount may not be achieved.

  The second part 3LR may further contain a heat-resistant carrier. As the heat-resistant carrier, for example, alumina can be used.

  The content of the second oxygen storage material per unit volume in the downstream portion is, for example, in the range of 25 g / L to 150 g / L. When this value is small, a large oxygen storage amount may not be achieved. When this value is large, the heat resistance of the downstream portion may be insufficient, or the exhaust gas purification ability may be insufficient.

The ratio L _F / L _R of the length L _F along the exhaust gas flow direction of the first portion 3LF and the length L _R along the exhaust gas flow direction of the second portion 3LR is, for example, 0.3 to Within the range of 0.8. When the ratio L _F / L _R is small, it is difficult to achieve a large oxygen storage amount. When the ratio L _F / L _R is large, it is difficult to suppress fluctuations in the composition of the exhaust gas.

  The upper layer 3U is formed on the lower layer 3L. Another layer may be interposed between the upper layer 3U and the lower layer 3L.

The thickness T _U of the upper layer 3U may be equal to or different from the thickness T _{L of the} thicker one of the first portion 3LF and the second portion 3LR, for example. For example, the thickness T _U may be smaller than the thickness T _L. In this case, the ratio T _U / T _L of the thickness T _U to the thickness T _L may be in the range of 0.2 to 1.

The thickness T _U of the upper layer 3U is, for example, in the range of 0.05 mm to 0.1 mm. If the upper layer 3U is thin, it is difficult to achieve high exhaust gas purification performance. If the upper layer 3U is thick, the diffusion of the exhaust gas into the lower layer 3L may be hindered.

  The upper layer 3U contains a third platinum group element and a refractory carrier. The upper layer 3U may further contain a third oxygen storage material.

  The third platinum group element is, for example, at least one of platinum, palladium, and rhodium, and is typically rhodium.

  The content of the third platinum group element per unit volume of the exhaust gas-purifying catalyst 1 is, for example, in the range of 0.05 g / L to 0.5 g / L. When this value is increased, the oxygen storage amount and oxygen storage rate of the third oxygen storage material increase. However, in this case, in addition to an increase in the heat capacity of the upper layer 3U, sintering tends to occur. If this value is reduced, the oxygen storage amount and oxygen storage rate of the third oxygen storage material are reduced, and it becomes difficult to achieve sufficient exhaust gas purification performance.

  The third oxygen storage material is ceria or a third composite oxide containing cerium. Typically, the third oxygen storage material is a third composite oxide.

  The third composite oxide contains cerium and zirconium. The third composite oxide may be a single composition composite oxide or a mixture of a plurality of composite oxides.

  In the third composite oxide, the cerium content in terms of oxide, that is, the ceria content is, for example, in the range of 10% by mass to 40% by mass. If the ceria content is small or large, it is difficult to achieve a large oxygen storage amount.

  The third composite oxide may further contain a rare earth element other than cerium. For example, the third composite oxide may be a composite oxide containing cerium, zirconium, neodymium, and lanthanum.

  As the rare earth element other than cerium of the third composite oxide, for example, those described above with respect to the first composite oxide can be used.

  In the case where a rare earth element other than cerium is used, the content of the third composite oxide in terms of an oxide of a rare earth element other than cerium is, for example, in the range of 3 to 20% by mass. For example, when the third composite oxide contains neodymium and lanthanum, the content of neodymium oxide in the third composite oxide is in the range of 1 to 10% by mass, and the content of lanthanum oxide is 2 It shall be in the range of 10 mass%.

  In the third composite oxide, the sum of the cerium content and the zirconium content in terms of oxide, that is, the sum of the ceria content and the zirconia content is, for example, 60% by mass or less, typically 20% by mass. % To 40% by mass.

  As the heat-resistant carrier, for example, alumina can be used. In the upper layer 3U, the content of the heat-resistant carrier is, for example, in the range of 20 g / L to 100 g / L.

  The content of the third oxygen storage material per unit volume of the exhaust gas purification catalyst 1 is, for example, in the range of 25 g / L to 150 g / L. When this value is small, a large oxygen storage amount may not be achieved. When this value is large, the heat resistance may be insufficient or the exhaust gas purification ability may be insufficient.

  Examples of the present invention will be described below.

<Manufacture of oxygen storage material OSM1>
The oxygen storage material OSM1 was produced by the following method.
First, cerium nitrate [Ce (NO ₃ ) ₃ ] and zirconium oxynitrate [ZrO (NO ₃ ) ₂ ] were dissolved in 500 mL of deionized water. Cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 10:90, respectively.

To this aqueous solution, a 10 wt% aqueous ammonium hydroxide (NH ₄ OH) solution was added dropwise at room temperature to cause coprecipitation. Subsequently, this aqueous solution was stirred for 60 minutes. The aqueous solution was then filtered and the filter cake was washed thoroughly with deionized water. The coprecipitation product thus obtained was dried at 110 ° C.

  The coprecipitated product was then calcined at 500 ° C. for 3 hours in air. Thereafter, the calcined product was pulverized in a mortar, and the powder obtained thereby was calcined in the atmosphere at 800 ° C. for 5 hours. Hereinafter, the powder thus obtained is referred to as “oxygen storage material OSM1”.

A part of the oxygen storage material OSM1 was extracted and subjected to X-ray diffraction analysis. As a result, it was confirmed that the oxygen storage material OSM1 was composed of a complex oxide represented by the chemical formula: (Ce, Zr) O ₂ .

<Manufacture of oxygen storage material OSM2>
A powder was obtained by the same method as described for the oxygen storage material OSM1, except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 20:80, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM3”.

<Manufacture of oxygen storage material OSM3>
A powder was obtained by the same method as described for the oxygen storage material OSM1 except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 30:70, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM3”.

<Manufacture of oxygen storage material OSM4>
A powder was obtained by the same method as described for the oxygen storage material OSM1 except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 40:60, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM4”.

<Manufacture of oxygen storage material OSM5>
A powder was obtained by the same method as described for the oxygen storage material OSM1 except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 50:50, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM5”.

<Manufacture of oxygen storage material OSM6>
A powder was obtained by the same method as described for the oxygen storage material OSM1, except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 60:40, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM6”.

<Manufacture of oxygen storage material OSM7>
A powder was obtained by the same method as described for the oxygen storage material OSM1 except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 70:30, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM7”.

<Manufacture of oxygen storage material OSM8>
A powder was obtained by the same method as described for the oxygen storage material OSM1 except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratio in terms of ceria and zirconia was 80:20, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM8”.

<Manufacture of oxygen storage material OSM9>
Powder was obtained by the same method as described for the oxygen storage material OSM1 except that cerium nitrate and zirconium oxynitrate were mixed so that the mass ratios of ceria and zirconia were 90:10, respectively. It was. Hereinafter, this powder is referred to as “oxygen storage material OSM9”.

Table 1 below summarizes the ratio of cerium and zirconium in these oxygen storage materials OSM1 to OSM9, specifically, the mass ratio converted to ceria and zirconia.

<Measurement of oxygen storage rate>
50 g of oxygen storage material OSM2 was weighed and added to 500 mL of deionized water. The powder P1 was sufficiently dispersed in deionized water by performing ultrasonic stirring for 10 minutes, and then a dinitrodiamine platinum nitric acid solution was added to the slurry. The concentration and addition amount of the dinitrodiamine platinum nitrate solution were adjusted so that the platinum content of the solid content was 0.71% by mass.

  Thereafter, the slurry was suction filtered. As a result of subjecting the filtrate to inductively coupled radio frequency plasma (ICP) spectroscopy, it was found that almost all of the platinum in the slurry was present in the filter cake.

  The filter cake was then dried at 110 ° C. for 12 hours. Then, this was baked at 500 degreeC for 1 hour in air | atmosphere.

  Subsequently, the pellet which consists of the powder obtained in this way was manufactured. These pellets were subjected to heat treatment at 1100 ° C. for 5 hours in an air atmosphere.

  Subsequently, while the pellets are heated to 600 ° C., the atmosphere surrounding the pellets is a first nitrogen atmosphere containing carbon monoxide at a concentration of 0.2% by volume and a first nitrogen atmosphere containing oxygen at a concentration of 1% by volume. It was switched alternately every 2 minutes between 2 nitrogen atmospheres. The switching of the atmosphere was continued for a while, and the amount of oxygen occluded by the pellets was measured from when the atmosphere was switched to the second nitrogen atmosphere until 5 seconds passed. And the oxygen storage rate was calculated | required from this occluded oxygen amount.

  Specifically, oxygen was occluded in the pellet for 5 seconds after the atmosphere was switched to the second nitrogen atmosphere. Then, oxygen was released from these pellets, and this oxygen release amount was defined as the amount of oxygen occluded by the pellets. The molar ratio between the oxygen stored in these pellets and the ceria contained in these pellets was calculated, and this molar ratio was defined as the oxygen storage rate.

  For the oxygen storage materials OSM3, OSM4, OSM6, and OSM8, the oxygen storage rate was determined by the same method as described for the oxygen storage material OSM2.

  FIG. 3 is a graph showing oxygen storage rates obtained for the oxygen storage materials OSM2 to OSM4, OSM6, and OSM8. In the figure, the horizontal axis indicates the ceria content of the oxygen storage material, and the vertical axis indicates the oxygen storage rate. As shown in FIG. 3, the smaller the ceria content of the oxygen storage material, the greater the oxygen storage rate.

<Measurement of oxygen storage amount>
Pellets were produced using the oxygen storage material OSM2 by the same method as described above. These pellets were subjected to heat treatment at 1100 ° C. for 5 hours in an air atmosphere.

  Next, while the pellets are heated to 600 ° C., the atmosphere surrounding the pellets is a first nitrogen atmosphere containing carbon monoxide at a concentration of 2% by volume and a second nitrogen containing oxygen at a concentration of 1% by volume. The atmosphere was alternately switched every minute. The switching of the atmosphere was continued for a while, and the amount of oxygen occluded by the pellets was measured from the switching of the atmosphere to the second nitrogen atmosphere until the lapse of 2 minutes. And the oxygen storage rate was calculated | required from this occluded oxygen amount.

  Specifically, oxygen was occluded in the pellets for 2 minutes after the atmosphere was switched to the second nitrogen atmosphere. Then, oxygen was released from these pellets, and this oxygen release amount was defined as the oxygen storage amount.

  For the oxygen storage materials OSM2 to OSM4, OSM6, and OSM8, the oxygen storage amount was determined by the same method as described for the oxygen storage material OSM2.

  FIG. 4 is a graph showing oxygen storage amounts obtained for the oxygen storage materials OSM2 to OSM4, OSM6, and OSM8. In the figure, the horizontal axis indicates the ceria content of the oxygen storage material, and the vertical axis indicates the oxygen storage amount. As shown in FIG. 4, the larger the ceria content of the oxygen storage material, the greater the oxygen storage amount.

<Manufacture of catalyst C1>
The exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 was produced by the following method.
First, a platinum nitrate aqueous solution containing 1.0 g of platinum, 100 g of an oxygen storage material OSM6, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water are mixed to obtain a slurry. Prepared. Hereinafter, this slurry is referred to as “slurry S1”.

  Next, the entire amount of the slurry S1 was coated only on the upstream portion of the monolith honeycomb substrate 2, here, the portion from one end of the monolith honeycomb substrate 2 to the half of its entire length. Here, a cordierite monolith honeycomb substrate having a volume of 1.0 L was used. The monolith honeycomb substrate 2 was dried at 150 ° C. for 1 hour. Thereby, the unfired first portion 3LF was formed on the monolith honeycomb substrate 2.

  Next, a platinum nitrate aqueous solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM3, 50 g of alumina powder, an alumina sol with a solid content of 20 g, and deionized water are mixed together to obtain a slurry. Prepared. Hereinafter, this slurry is referred to as “slurry S2”.

  Next, the entire amount of the slurry S2 was coated only on the downstream portion of the previous monolith honeycomb substrate 2, here, only the portion from the other end of the monolith honeycomb substrate 2 to the half of its total length. The monolith honeycomb substrate 2 was dried at 150 ° C. for 1 hour. Thereby, the unfired second portion 3LR was formed on the monolith honeycomb substrate 2. That is, an unfired lower layer 3L was obtained. Note that the dimensions of the first portion 3LF and the second portion 3LR in the exhaust gas flow direction were equal to each other.

  Thereafter, an aqueous rhodium nitrate solution containing 0.1 g of rhodium, 50 g of oxygen storage material OSM2, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water are mixed to obtain a slurry. Prepared. Hereinafter, this slurry is referred to as “slurry S3”.

  Subsequently, the entire monolith honeycomb substrate 2 was coated with the entire amount of the slurry S3. The monolith honeycomb substrate 2 was fired at 500 ° C. for 1 hour. Thereby, the upper layer 3U was formed on the lower layer 3L.

  As described above, the exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 was completed. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C1”.

<Manufacture of catalyst C2>
Exhaust gas purification catalyst having the same structure as exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 except that the composition of lower layer 3L was uniform was produced by the following method.

  First, a platinum nitrate aqueous solution containing 1.0 g of platinum, 100 g of an oxygen storage material OSM6, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water are mixed to obtain a slurry. Prepared. Hereinafter, this slurry is referred to as “slurry S4”.

  Next, the entire monolith honeycomb substrate was coated with the entire amount of the slurry S4. Here, the same monolith honeycomb substrate as used in the production of the catalyst C1 was used as the monolith honeycomb substrate. This monolith honeycomb substrate was dried at 150 ° C. for 1 hour. As a result, an unfired lower layer was formed on the monolith honeycomb substrate.

  Subsequently, the entire monolith honeycomb substrate was coated with the same amount of the slurry S3 as that used in the production of the catalyst C1. The monolith honeycomb substrate was fired at 500 ° C. for 1 hour. Thereby, the upper layer was formed on the lower layer.

  The exhaust gas purification catalyst was completed as described above. Hereinafter, the exhaust gas-purifying catalyst is referred to as “catalyst C2”.

<Manufacture of catalyst C3>
The first portion 3LF is formed using the slurry S2 instead of the slurry S1, and the second portion 3LR is formed using the slurry S1 instead of the slurry S2. The exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 was produced. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C3”.

Table 2 below summarizes the slurries used in the production of these catalysts C1 to C3, and the oxygen storage materials, precious metals and precious metal contents contained in these slurries.

<Performance evaluation 1>
The oxygen storage amount was measured for each of the catalysts C1 to C3.
Specifically, the catalyst C1 is installed in the engine bench tester, and an air-fuel ratio sensor is installed in an exhaust pipe that guides exhaust gas discharged from the engine to the catalyst C1, and the exhaust gas discharged by the catalyst C1 is guided to the external environment. An oxygen sensor was installed in the exhaust pipe. Under control using the output from the air-fuel ratio sensor, the air-fuel ratio of the exhaust gas discharged from the engine is changed from 15.0 (fuel lean) to 14.0 (fuel rich) at regular time intervals. The change in the oxygen concentration in the exhaust gas discharged from the catalyst C1 was detected using an oxygen sensor. The temperature of the catalyst bed was maintained in the range of 500 to 600 ° C. The arithmetic average of the response delay time of the oxygen concentration change with respect to the change from fuel lean to fuel rich was determined, and the oxygen storage amount of the catalyst C1 was calculated from this average value. For the catalysts C2 and C3, the oxygen storage amount was obtained by the same method as described above for the catalyst C1.

  FIG. 5 is a graph showing the oxygen storage amount obtained for the catalysts C1 to C3. In the figure, the vertical axis represents the oxygen storage amount. As shown in FIG. 5, the catalyst C1 had a larger oxygen storage amount than the catalysts C2 and C3.

<Manufacture of catalyst C4>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM1, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S5”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was manufactured by the same method as described above for catalyst C1 except that first portion 3LF was formed using slurry S5 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C4”.

<Manufacture of catalyst C5>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM2, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S6”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C1, except that first portion 3LF was formed using slurry S6 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C5”.

<Manufacture of catalyst C6>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM4, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S7”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C1, except that first portion 3LF was formed using slurry S7 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C6”.

<Manufacture of catalyst C7>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM5, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S8”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C1, except that first portion 3LF was formed using slurry S8 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C7”.

<Manufacture of catalyst C8>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM6, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S9”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C1, except that first portion 3LF was formed using slurry S9 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C8”.

<Manufacture of catalyst C9>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM7, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S10”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C1, except that first portion 3LF was formed using slurry S10 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C9”.

<Manufacture of catalyst C10>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 1.0 g of platinum, 100 g of oxygen storage material OSM8, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S11”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C1, except that first portion 3LF was formed using slurry S11 instead of slurry S1. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C10”.

<Manufacture of catalyst C11>
First, a platinum nitrate aqueous solution containing 1.0 g of platinum, 100 g of an oxygen storage material OSM3, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water are mixed to obtain a slurry. Prepared. Hereinafter, this slurry is referred to as “slurry S13”.

  Next, a platinum nitrate aqueous solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM2, 50 g of alumina powder, alumina sol with a solid content of 20 g, and deionized water are mixed to obtain a slurry. Prepared. Hereinafter, this slurry is referred to as “slurry S14”.

  Except that the first portion 3LF is formed using the slurry S13 instead of the slurry S1, and the second portion 3LR is formed using the slurry S14 instead of the slurry S2, the same method as described above for the catalyst C1 is used. The exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 was produced. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C11”.

<Manufacture of catalyst C12>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM4, 50 g of alumina powder, an alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S15”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was produced by the same method as described above for catalyst C11, except that slurry S15 was used instead of slurry S14 to form second portion 3LR. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C12”.

<Manufacture of catalyst C13>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM5, 50 g of alumina powder, an alumina sol with a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S16”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was manufactured by the same method as described above for catalyst C11, except that slurry S16 was used instead of slurry S14 to form second portion 3LR. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C13”.

<Manufacture of catalyst C14>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM6, 50 g of alumina powder, an alumina sol with a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S17”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was manufactured by the same method as described above for catalyst C11, except that slurry S17 was used instead of slurry S14 to form second portion 3LR. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C14”.

<Manufacture of catalyst C15>
A slurry was prepared by mixing a platinum nitrate aqueous solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM7, 50 g of alumina powder, alumina sol having a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S18”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was manufactured by the same method as described above for catalyst C11, except that slurry S18 was used instead of slurry S14 to form second portion 3LR. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C15”.

<Manufacture of catalyst C16>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM8, 50 g of alumina powder, an alumina sol with a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S19”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was manufactured by the same method as described above for catalyst C11, except that slurry S19 was used instead of slurry S14 to form second portion 3LR. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C16”.

<Manufacture of catalyst C17>
A slurry was prepared by mixing an aqueous platinum nitrate solution containing 0.5 g of platinum, 100 g of oxygen storage material OSM9, 50 g of alumina powder, an alumina sol with a solid content of 20 g, and deionized water. . Hereinafter, this slurry is referred to as “slurry S20”.

  Exhaust gas purification catalyst 1 shown in FIGS. 1 and 2 was manufactured by the same method as described above for catalyst C11 except that slurry S20 was used instead of slurry S14 to form second portion 3LR. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C17”.

Tables 3 and 4 below summarize the slurries used in the production of these catalysts C4 to C17 and the oxygen storage materials, precious metals and precious metal contents contained in these slurries.

<Performance evaluation 2>
For each of the catalysts C4 to C17, the oxygen storage amount was measured by the same method as performed in the performance evaluation 1.

  FIG. 6 is a graph showing oxygen storage amounts obtained for the catalysts C4 to C17. In the figure, the horizontal axis indicates the ceria content of the oxygen storage material contained in the lower layer of the upstream portion or the downstream portion. The vertical axis represents the oxygen storage amount of the catalyst.

  As shown in FIG. 6, when an oxygen storage material having a ceria content in the range of 50 to 80% by mass in the upstream portion was used, a particularly large oxygen storage amount could be achieved. Even when an oxygen storage material having a ceria content in the range of 20 to 40% by mass in the downstream portion was used, a particularly large oxygen storage amount could be achieved.

  DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification catalyst, 2 ... Base material, 3 ... Catalyst layer, 3L ... Lower layer, 3LF ... 1st part, 3LR ... 2nd part, 3U ... Upper layer.

Claims (5)

  A base material provided with one or more through-holes through which exhaust gas flows, a lower layer supported by the wall surface of the through-hole and facing the wall surface, and an upper layer facing the wall surface with the lower layer interposed therebetween A catalyst layer, and the lower layer is located downstream of the first portion containing the first platinum group element and the first oxygen storage material, and the second platinum group element and the second oxygen. A second portion containing a storage material, wherein the upper layer contains a third platinum group element and a refractory carrier, and the first oxygen storage material has an oxygen storage capacity as compared with the second oxygen storage material. And the second oxygen storage material has an oxygen storage rate higher than that of the first oxygen storage material.   A base material provided with one or more through-holes through which exhaust gas flows, a lower layer supported by the wall surface of the through-hole and facing the wall surface, and an upper layer facing the wall surface with the lower layer interposed therebetween A catalyst layer, and the lower layer is located downstream of the first portion containing the first platinum group element and the first oxygen storage material, and the second platinum group element and the second oxygen. A second portion containing a storage material, wherein the upper layer contains a third platinum group element and a refractory support, and each of the first and second oxygen storage materials contains at least one of cerium and zirconium. An exhaust gas purifying catalyst, characterized in that the ratio of cerium in the first oxygen storage material is higher than the ratio of cerium in the second oxygen storage material.   The ceria content of the first composite oxide is in the range of 50 to 80% by mass, and the ceria content of the second composite oxide is in the range of 20 to 40% by mass. Or the exhaust gas purifying catalyst according to 2.   The exhaust gas purification according to any one of claims 1 to 3, wherein each of the first and second platinum group elements is platinum and / or palladium, and the third platinum group element is rhodium. Catalyst.   The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the upper layer is thinner than the lower layer.

Images