JP2006320863A - Catalyst for cleaning exhaust gas and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas, which has excellent performance even after an endurance test at high temperature and the manufacturing cost of which is reduced by reducing the amount of a noble metal to be used therein and to provide a method for manufacturing the catalyst for cleaning exhaust gas, wherein the catalyst capable of keeping the reduced state of Rh even after the endurance test at high temperature can be manufactured easily. <P>SOLUTION: The catalyst 1 for cleaning exhaust gas is manufactured by forming a plurality of catalyst layers (the first catalyst layer 3 and the second catalyst layer 4) on a base material 2. A Rh catalyst layer (the second catalyst layer 4) contains a carrier 5 consists mainly of zirconia, a Rh particle (a noble metal particle 6) supported on the carrier 5 and a binding member 7 which exists among carriers 5 and consists mainly of zirconia. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst for purifying exhaust gas containing hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx) and the like discharged from an internal combustion engine represented by an automobile, and a method for producing the same.

The exhaust gas emitted from internal combustion engines such as automobiles contains harmful gases such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). An exhaust gas purification catalyst is used for purification. The amount of exhaust gas purifying catalyst used is rapidly increasing with the tightening of exhaust gas regulations. An exhaust gas purification catalyst is a catalyst in which noble metal particles (eg, Pt, Pd, Rh, etc.) are supported on a carrier (eg, alumina (γ-Al ₂ O ₃ )). The amount of noble metal used also tends to increase. However, not only is there a limit to the amount of precious metal reserves in the ground, but the cost of precious metals is high, and researches are being actively conducted to reduce the amount of precious metals used and maximize the activity of the catalyst.

The exhaust gas purification catalyst is a catalytic reaction in which the reaction proceeds on the surface of the noble metal particles, and the activity of the catalyst is substantially proportional to the surface area of the noble metal particles. For this reason, a catalyst in which noble metal particles having a small particle diameter (for example, a particle diameter of 1 nm or less) are uniformly dispersed on the surface of the carrier is supported, and the surface area of the noble metal particles is increased to increase the activity of the catalyst. However, since noble metal particles having a small particle diameter have a large surface energy and easily aggregate, it is necessary to suppress aggregation of the noble metal particles. For this reason, a catalyst is disclosed in which a coating layer made of a metal oxide is further formed on noble metal particles supported on the surface of the carrier (see Patent Document 1). According to this catalyst, a decrease in the activity of the catalyst due to thermal deterioration is prevented by forming a coating layer and suppressing the movement of the noble metal particles.
JP 2003-117393 A

  However, in the conventional catalyst, it is possible to suppress the movement of the noble metal particles by forming a coating layer, but there is still a possibility that the activity of the catalyst is lowered.

  For example, Pt, Pd, Rh, etc. are used as the noble metal particles.In particular, Rh is an element indispensable for exhaust gas purification catalysts, has high conversion performance from a low temperature range, and has a wide ternary window width. It is a very effective element against atmospheric changes.

When Pt and Pd are used as noble metal particles other than Rh, the surface area of the noble metal particles tends to decrease due to the phase transition of the support and the thermal aggregation of the noble metal itself at a high temperature, resulting in a decrease in the performance of the catalyst. However, when Rh is used as noble metal particles, in addition to the decrease in surface area due to the phase transition of the support and thermal aggregation of the noble metal itself, Rh ₂ O ₃ produced by oxidation of Rh There was a risk that the catalyst activity would be reduced by solid solution in (Al ₂ O ₃ ) and higher oxidation.

Further, not only the durability deterioration due to exhaust gas but also the heat treatment at the time of catalyst production has a risk that the Rh particles easily dissolve in Al ₂ O ₃ .

  In particular, in recent years, there is a tendency that the exhaust gas purification catalyst is installed directly under the manifold close to the engine, and the exhaust gas temperature becomes higher during high-speed travel, and therefore the exhaust gas purification catalyst is often exposed to high temperatures. For this reason, it is important to maintain the activity of the catalyst even in a high temperature environment.

  The present invention has been made in order to solve the above-described problems. That is, the exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst in which a plurality of catalyst layers are formed on a substrate, and is mainly composed of zirconia. The gist of the present invention is to have an Rh catalyst layer including a carrier, a Rh particle supported on the carrier, and a binding member mainly composed of zirconia existing between the carriers.

  The method for producing an exhaust gas purifying catalyst of the present invention comprises a catalyst slurry comprising at least a catalyst powder in which Rh particles are supported on a carrier mainly composed of zirconia and a zirconia sol as a binding member, on the substrate or the catalyst. The gist is to form the Rh catalyst layer on the substrate or on the catalyst layer by drying and firing after coating on the layer.

According to the exhaust gas purifying catalyst of the present invention, the catalyst layer is formed of a material mainly composed of zirconia (ZrO ₂ ), thereby suppressing a decrease in Rh activity due to a reaction between Rh and a base material component, and after high-temperature durability. However, since the Rh particles can maintain a highly active reduced state, the catalyst performance is excellent, and the amount of noble metal used can be reduced to reduce the cost.

  According to the method for producing an exhaust gas purification catalyst of the present invention, by using zirconia sol as a catalyst slurry at the time of production, it is possible to easily maintain a reduced state of Rh even after high temperature durability and to produce a catalyst having excellent catalytic performance. it can.

  Hereinafter, an exhaust gas purification catalyst and a method for manufacturing the same according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a cross-sectional view of an exhaust gas purification catalyst according to an embodiment of the present invention. As shown in FIG. 1, the exhaust gas purification catalyst 1 forms a first catalyst layer 3 (inner layer) on a substrate 2 and forms a second catalyst layer 4 (surface layer) on the first catalyst layer 3. is doing.

The first catalyst layer 3 (the inner layer) is a noble metal particles 6 carried on the carrier 5 that mainly composed of Al ₂ O _3, forming a coupling member 7 which is mainly composed of Al ₂ O ₃ between the carrier 5 is doing. The noble metal particles 6 in the first catalyst layer 2 are either Pt particles or Pd particles.

Second catalyst layer (top layer) 4, the coupling member 10 zirconia supports Rh particles 9 on the carrier 8 composed mainly of (ZrO _2), and zirconia (ZrO ₂₎ as a main component between the carrier 8 And an Rh catalyst layer carrying Rh particles.

Here, Rh particles are fine particles of about several nanometers, and the surface thereof is oxidized and exists as Rh ₂ O ₃ , but when the type of support in the catalyst or the catalyst is exposed to a high temperature environment, it deteriorates at a high temperature. Rh ₂ O ₃ is further oxidized to become highly oxidized Rh. Highly oxidized Rh has lower catalytic performance than Rh ₂ O ₃ , and the state of highly oxidized Rh is generally corrected by comparing the main energy of the carrier with the binding energy of Rd 3d5 / 2 orbital by XPS surface analysis. Is known to be 309 eV or higher. In particular, when Al ₂ O ₃ is contained in the support, Rh tends to exist as high-oxidized Rh in a solid solution in Al ₂ O ₃ and immediately after the preparation of the catalyst, Rh 3d5 / 2 The orbital coupling energy is over 309.9 eV.

On the other hand, when the carrier or the binding member of the second catalyst layer (surface layer) 4 is formed of a material mainly composed of zirconia (ZrO ₂ ), solid solution of Rh in the carrier can be suppressed. As a result, even after the exhaust gas purification catalyst is oxidized at 900 ° C. for 3 hours under an air stream, it can be maintained at a binding energy of 309.9 eV or less, which is close to the reduced state of Rh, and the deterioration of the catalyst performance can be suppressed. it can.

  For this reason, the exhaust gas purifying catalyst has a binding energy of Rh3d5 orbits by XPS surface analysis, which is subjected to charge correction with the main component of the carrier carrying Rh particles after being endured for 3 hours or more in an air stream at 900 ° C., 307.4 eV or more and 309.9 eV or less.

Rh is not only if they are supported directly on the Al ₂ O _3, when contains Al ₂ O ₃ in the catalyst layer containing Rh, Rh is moved by sintering after high-temperature durability, stable May aggregate on Al ₂ O ₃ . This applies not only to the case where Al ₂ O ₃ is used as the support, but also to a sol containing Al added as a binder during the production of the catalyst slurry. In the present invention, in the Rh catalyst layer, in order to suppress the production of highly oxidized Rh, which causes a decrease in the activity of the catalyst, the amount of Al ₂ O ₃ can be limited to maintain the catalyst performance even after high temperature durability. . Therefore, the amount of Al ₂ O ₃ present in the Rh-containing layer of the catalyst after production is preferably 10 or less in terms of molar ratio (Al ₂ O ₃ / Rh).

On the other hand, with trace amounts using Al ₂ O _3, the Al ₂ O ₃ is made to function as an immobilizing material to prevent sintering of the Rh particles (anchor) can also be enhanced catalytic performance. If to function for Al ₂ O ₃ immobilizing material, Al ₂ O ₃ amount is preferably 5 or less in the molar ratio of Rh / Al ₂ O _3. When the amount of Al ₂ O ₃ is more than 5 in a molar ratio of _{Rh / Al 2 O 3, Al} 2 O 3 than the immobilizing material, a high oxidation Rh Rh is rather a solid solution in the Al ₂ O ₃ This is because the tendency becomes high and the catalyst performance is lowered.

Further, it is preferable to use an oxide containing zirconia (ZrO ₂ ) as a main component as the carrier for the Rh catalyst layer. Rh does not cause chemical action with zirconia (ZrO ₂ ), and high oxidation Rh is not formed even after high temperature durability, and the catalytic performance can be maintained. However, when the support is formed only from zirconia (ZrO ₂ ), the heat resistance of the support is low, the specific surface area of the support decreases after high-temperature durability, the aggregation of Rh particles supported on the support proceeds, and Rh The catalyst performance decreases due to the decrease in surface area. Therefore, in order to suppress the high-temperature degradation of zirconia (ZrO _2), 2-group elements, transition metal elements, in particular, it is preferable that the composite oxide and a rare earth element and zirconia (ZrO _2). For example, elements that form a composite oxide that suppresses high-temperature degradation of zirconia (ZrO ₂ ) are generally Ca, Ti, Mn, Fe, Sr, Y, Mo, Ba, La, Ce, Pr, Nd Or W etc. can be mentioned, Furthermore, you may form complex oxide from three or more types of illustrated elements. When forming the composite oxide, it is preferable that the content of zirconia (ZrO ₂ ), which is the main component of the carrier, is at least 65 mol% or more. This is because when the content of zirconia (ZrO ₂ ) is less than 65 mol%, the original function of zirconia (ZrO ₂ ) is impaired, and the high-temperature durability is significantly reduced. In particular, when a complex oxide is formed with a transition metal element and the content of the transition metal element in the complex oxide increases, oxygen contained in the complex oxide containing the transition metal element is released at a low temperature. This is because oxygen may oxidize Rh into a highly oxidized Rh state.

In a conventional catalyst using Al ₂ O ₃ as a support, when Rh is supported at a low concentration of 1.0 wt% or less, the interface between Rh and Al ₂ O ₃ increases, and Rh becomes highly oxidized Rh immediately after catalyst preparation. It is easy to exist. In the present invention, a catalyst layer is formed using a support mainly composed of zirconia (ZrO ₂ ) in which Rh does not become highly oxidized Rh, thereby supporting noble metal particles at a low concentration and the amount of noble metal used. Even if the amount is reduced, the catalyst performance can be improved.

  The effect of the exhaust gas purification catalyst becomes significant when the amount of Rh in the catalyst is 0.30 g / L or less. Further, when the catalyst contains at least one of Pt particles or Pd particles, the total noble metal amount in each catalyst layer is 0.7 g / L or less.

  Conventionally, the amount of noble metal used by the exhaust gas purification catalyst is about 2 g / L to 4 g / L, but according to the exhaust gas purification catalyst, when the amount of Rh in the catalyst is 0.30 g / L or less, the effect Becomes remarkable and the catalyst performance is improved. In the case where at least one of Pt particles or Pd is contained in addition to Rh particles in the plurality of catalyst layers, the amount of noble metal in the catalyst can be 0.7 g / L or less. Further, the above exhaust gas purification catalyst can maintain excellent catalyst performance even after high temperature durability. As a result, the amount of precious metal used can be significantly reduced without reducing the catalyst performance, thereby reducing costs.

  Next, the manufacturing method of the exhaust gas purification catalyst according to the embodiment of the present invention will be described.

The method of manufacturing the exhaust gas purifying catalyst according to an embodiment of the present invention, a catalyst powder Rh particles are supported on a support composed mainly of zirconia (ZrO _2), zirconia as a binding member (ZrO ₂₎ sol After the catalyst slurry mixed with at least is applied on the base material or the catalyst layer, it is dried and fired to form the Rh catalyst layer on the base material or the catalyst layer.

Conventionally, Al ₂ O ₃ is used as a carrier of Rh catalyst layer, it is common to Al ₂ O ₃ is used sols even when using a carrier other than _{Al 2 O 3, Al 2 O} 3 The strength of the catalyst layer formed from the sol was high. Therefore, when the durably the exhaust gas purifying catalyst in a high temperature environment, when Rh is thermally agglomerated, moved over Al ₂ O ₃ sol from of Al ₂ O ₃ used as the binder, Rh is on Al ₂ O ₃ A stable highly oxidized Rh was formed and dissolved in Al ₂ O ₃ , and the catalyst performance was lowered. Therefore, in the manufacturing method of the catalyst according to the present invention, by using a zirconia reference to sol mainly containing (ZrO _2), further oxide zirconia (ZrO ₂₎ as a main component as the carrier, Rh is It is possible to suppress solid solution in the carrier and the coupling member.

Thus, in order to form a catalyst layer by uniformly coating a catalyst on honeycomb cordierite or metal foil as a base material, it is necessary to make the catalyst into a slurry and apply the catalyst slurry uniformly. When slurrying catalyst, zirconia loaded with zirconia (ZrO ₂₎ powder of Rh particles on a carrier mainly composed of (ZrO _2), zirconia is a binder (ZrO ₂₎ may be mixed with the sol. Note that the binder is required to have a binding property with the catalyst powder of zirconia (ZrO ₂ ) as a carrier and a peel resistance when moisture is removed after application to the substrate.

Furthermore, the particle diameter of primary particles of zirconia (ZrO ₂ ) forming the carrier used here is preferably 200 nm or less. This is because, when the particle size of the primary particles of zirconia (ZrO ₂ ) is 200 nm or less, the specific surface area of the support increases, and the Rh particles are highly dispersed in the support, thereby improving the catalyst performance. Here, the primary particles of zirconia (ZrO ₂ ) mean the smallest unit particles that constitute particles that can be observed by SEM, TEM, etc. Further, the primary particles cannot be confirmed by TEM at the time of catalyst production. It also includes irregular fine particles or colloids.

The primary particle size of the zirconia (ZrO ₂ ) sol is preferably 100 nm or less. This is because, zirconia (ZrO ₂₎ the particle size of the primary particles of the sol exceeds 100 nm, the ZrO ₂ as a sol not enter well between ZrO ₂ particles as a carrier during slurry manufacturing, peeling or the like occurs after the coating, This is because the catalyst performance deteriorates. Therefore, by making the particle size of the primary particles of ZrO ₂ in the ZrO ₂ sol 100 nm or less, the ZrO ₂ sol penetrates to every corner between the catalyst particles, and as a result, it can be peeled off even after coating of the slurry. It can be set as a solid catalyst layer without any.

  Hereinafter, more specific description will be made using examples.

Example 1
In a solution obtained by dissolving 40.4 g of cerium nitrate hexahydrate in 159.6 ml of ion-exchanged water, 184 g of active alumina (specific surface area 180 m ² / g) was dispersed, and stirred with a magnetic stirrer for about 1 hour. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour in an air stream. The obtained powder was dispersed in a mixed solution of 6.54 g of dinitrodiamine platinum nitrate acidic aqueous solution (manufactured by Tanaka Kikinzoku Co., Ltd., 8.83 wt%) and 193.5 ml of ion-exchanged water, and stirred with a magnetic stirrer for 1 hour. did. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour in an air stream to obtain a cerium-supported alumina catalyst powder carrying Pt 0.3 wt%.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and then shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

Next, in a solution in which 4.01 g of rhodium nitrate aqueous solution (13.81 wt% manufactured by Tanaka Kikinzoku Co., Ltd.) and 156 ml of ion-exchanged water were mixed, zirconium oxide (manufactured by Daiichi Rare Element Chemical Industries, Ltd., specific surface area) 95 m ² / g) 196 g was dispersed and stirred with a magnetic stirrer for about 1 hour. This was evaporated to dryness, pulverized and sized, and then fired at 400 ° C. for 1 hour in an air stream to obtain zirconium oxide carrying Rh 0.3 wt%.

363.6 g of the obtained catalyst powder, 351 g of commercially available nitric acid acidic zirconia sol (ZrO ₂ -10 wt%), and 285.4 g of ion-exchanged water were each put into a magnetic pot, shaken and ground with alumina balls, and a catalyst slurry for the surface layer was obtained. Obtained. The particle diameter of the surface layer catalyst slurry was 3.5 μm.

  Then, the catalyst slurry for the inner layer is put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry is removed by an air flow, dried at 120 ° C, and fired in an air stream at 400 ° C. did. Then, the catalyst slurry for surface layers was apply | coated similarly. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Example 2
In a solution obtained by dissolving 40.4 g of cerium nitrate hexahydrate in 159.6 ml of ion-exchanged water, 184 g of active alumina (specific surface area 180 m ² / g) was dispersed, and stirred with a magnetic stirrer for about 1 hour. This was evaporated to dryness, pulverized and sized, and then fired at 400 ° C. for 1 hour in an air stream. This powder was impregnated with Pd using a palladium nitrate solution (manufactured by Tanaka Kikinzoku Co., Ltd.) in the same manner as in Example 1 to obtain a catalyst powder of cerium-supported alumina supporting 0.3 wt% of Pd.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and then shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

  Next, using the same method as in Example 1, a rhodium nitrate solution was impregnated to obtain a zirconium oxide catalyst powder carrying Rh 0.2 wt%.

363.6 g of the obtained catalyst powder, 351 g of commercially available acidic zirconia nitrate sol (ZrO ₂ -10 wt%), and 285.4 g of ion-exchanged water were each put into a magnetic pot, and then shaken and pulverized with alumina balls to obtain a catalyst slurry for the surface layer. Got. The particle diameter of the surface layer catalyst slurry was 3.5 μm.

  Then, the catalyst slurry for the inner layer is put into a cordierite honeycomb carrier (900 cells / 2.5 mil), excess slurry is removed with an air stream, dried at 120 ° C, and fired in an air stream at 400 ° C. did. Then, the catalyst slurry for surface layers was apply | coated similarly. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Example 3
In a solution obtained by dissolving 40.4 g of cerium nitrate hexahydrate in 159.6 ml of ion-exchanged water, 184 g of active alumina (specific surface area 180 m ² / g) was dispersed and stirred with a magnetic stirrer for about 1 hour. This was evaporated to dryness, pulverized and sized, and then fired at 400 ° C. for 1 hour in an air stream. This powder was impregnated with Pt in the same manner as in Example 1 using a palladium nitrate solution (Tanaka Kikinzoku Co., Ltd.) and dinitrodiamine platinum nitrate acidic solution (Tanaka Kikinzoku Co., Ltd.), and Pt 0.2 wt. A cerium-carrying alumina carrying% was obtained.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and then shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

  Next, using a coprecipitation method, zirconium oxide and neodymium oxide were mixed at a molar ratio of 80:20 to obtain a mixed oxide. The mixed oxide was impregnated with a rhodium nitrate solution in the same manner as in Example 1 to obtain a catalyst powder carrying Rh 0.2 wt%.

363.6 g of the obtained catalyst powder, 65 g of commercially available zirconium hydroxide powder (ZrO ₂ -10 wt%), 42 g of 10% nitric acid, and 572.4 g of ion-exchanged water were each put into a magnetic pot, shaken and ground with alumina balls, and the surface layer A catalyst slurry was obtained. The particle diameter of the surface layer catalyst slurry was 3.5 μm.

  Then, the catalyst slurry for the inner layer is put into a cordierite honeycomb carrier (900 cells / 2.5 mil), excess slurry is removed with an air stream, dried at 120 ° C, and fired in an air stream at 400 ° C. did. Next, the catalyst slurry for the surface layer was applied in the same manner. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Example 4
Using the same method as in Example 1, a cerium-supported alumina catalyst powder on which Pd 0.3 wt% was supported was obtained.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and then immersed and ground together with alumina balls to obtain a catalyst slurry for the inner layer. The particle diameter of the inner layer catalyst slurry was 3.1 μm.

  Further, using the same method as in Example 3, zirconium oxide in which Rh 0.1 wt% was supported on a mixed oxide prepared by coprecipitation so that zirconium oxide and lanthanum oxide had a molar ratio of 80:20 was used. A powder was obtained.

  Using 363.6 g of the obtained catalyst powder, slurry was obtained in the same manner as in Example 3 to obtain a catalyst slurry for the surface layer. The particle diameter of the surface layer catalyst slurry was 2.9 μm.

  After that, the inner layer catalyst slurry was put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry was removed with an air stream, dried at 120 ° C, and fired in an air stream at 400 ° C. . Next, the catalyst slurry for the surface layer was applied in the same manner. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Example 5
Using the same method as in Example 1, a cerium-supported alumina catalyst powder on which Pd 0.3 wt% was supported was obtained.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and then shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The obtained inner layer catalyst slurry had a particle size of 3.0 μm.

Further, using the same method as in Example 4, a mixed oxide prepared by a coprecipitation method so that zirconium oxide and praseodymium oxide had a molar ratio of 80:20 was obtained. Next, the resulting mixed oxide was further added to a solution obtained by mixing 4.01 g of rhodium nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., 13.81 wt%) and 4.07 g of aluminum nitrate nonahydrate in 156 ml of ion-exchanged water. 196 g was dispersed and stirred with a magnetic stirrer for about 1 hour. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C for 1 hour in an air stream to obtain catalyst powder carrying Rh 0.3wt% and Al ₂ O ₃ 0.3wt% respectively. It was.

363.6 g of the obtained catalyst powder, 351 g of commercially available nitric acid acidic zirconia sol (ZrO ₂ -10 wt%), and 285.4 g of ion-exchanged water were each put into a magnetic pot, and shaken and ground together with alumina balls to obtain a catalyst slurry for the surface layer. Got. The particle diameter of the surface layer catalyst slurry was 3.5 μm.

  After that, the inner layer catalyst slurry was put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry was removed with an air stream, dried at 120 ° C, and fired in an air stream at 400 ° C. . Next, the surface catalyst slurry was applied in the same manner. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Example 6
Using the same method as in Example 1, a catalyst powder of cerium-supported alumina on which 0.4 wt% of Pd was supported was obtained.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry for the inner layer. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

  Further, a catalyst powder in which Rh 0.3 wt% was supported on a mixed oxide prepared by a coprecipitation method so that the molar ratio of zirconium oxide and aluminum oxide was 99: 1 using the same method as in Example 5. Got.

363.6 g of the obtained catalyst powder, 351 g of commercially available nitric acid acidic zirconia sol (ZrO ₂ -10 wt%), and 285.4 g of ion-exchanged water were each put into a magnetic pot, shaken and ground with alumina balls, and a catalyst slurry for the surface layer was obtained. Obtained. The particle diameter of the surface layer catalyst slurry was 3.5 μm.

  After that, the inner layer catalyst slurry is put into a cordierite honeycomb carrier (900 cells / 2.5 mils), excess slurry is removed with an air stream, dried at 120 ° C, and fired in an air stream at 400 ° C. did. Next, the surface catalyst slurry was applied in the same manner. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Example 7
Using the same method as in Example 1, a cerium-supported alumina catalyst powder on which Pt 0.3 wt% was supported was obtained.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and ground together with alumina balls to obtain a catalyst slurry for the surface layer.

  Further, using the same method as in Example 1, a catalyst powder of zirconia oxide carrying Rh 0.3 wt% was obtained.

  363.6 g of the obtained catalyst powder, 50.0 g of zirconium oxide, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry for the inner layer.

  After that, the catalyst slurry for the inner layer was put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry was removed with an air stream, dried at 120 ° C, and in an air stream at 400 ° C. Baked. Thereafter, a surface catalyst slurry was applied in the same manner to obtain a catalyst of Example 7. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Comparative Example 1
In a solution obtained by dissolving 40.4 g of cerium nitrate hexahydrate in 159.6 ml of ion-exchanged water, 184 g of active alumina (specific surface area 180 m ² / g) was dispersed, and stirred with a magnetic stirrer for about 1 hour. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour in an air stream. This powder was dispersed in a mixed solution of 6.54 g of dinitrodiamineplatinic acid aqueous solution (manufactured by Tanaka Kikinzoku Co., Ltd., 8.83 wt%) and 193.5 ml of ion-exchanged water, and stirred with a magnetic stirrer for 1 hour. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour in an air stream to obtain a cerium-supported alumina catalyst powder on which Pt 0.3 wt% was supported.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry for the inner layer. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

Next, 196 g of alumina (specific surface area 180 m ² / g) was dispersed in a solution obtained by mixing 4.01 g of an aqueous rhodium nitrate solution (Tanaka Kikinzoku Co., Ltd., 13.81 wt%) and 156 ml of ion-exchanged water. Stir with a magnetic stirrer for hours. This was evaporated to dryness, ground and sized, and then calcined at 400 ° C. for 1 hour in an air stream to obtain an aluminum oxide catalyst powder carrying Rh 0.3 wt%.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and ground together with alumina balls to obtain a catalyst slurry for the surface layer. The particle diameter of the surface layer catalyst slurry was 2.8 μm.

  After that, the catalyst slurry for the inner layer was put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry was removed with an air stream, dried at 120 ° C, and in an air stream at 400 ° C. After calcination, the catalyst of Comparative Example 1 was obtained by applying the surface catalyst slurry in the same manner. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Comparative Example 2
Disperse 184 g of activated alumina (specific surface area 180 m ² / g) in a solution of 6.54 g of dinitrodiamine platinum nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., 8.83 wt%) and 193.5 ml of ion-exchanged water. The mixture was stirred for 1 hour with a magnetic stirrer. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour under an air stream to obtain an alumina catalyst powder carrying Pt 0.3 wt%.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

Next, 196 g of titanium oxide (specific surface area 5 m ² / g) was dispersed in a solution obtained by mixing 4.01 g of rhodium nitrate aqueous solution (13.81 wt%, Tanaka Kikinzoku Co., Ltd.) and 156 ml of ion-exchanged water, and about 1 Stir with a magnetic stirrer for hours. This was evaporated to dryness, ground and sized, and then calcined at 400 ° C. for 1 hour in an air stream to obtain a titanium oxide catalyst powder carrying Rh 0.3 wt%.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and ground together with alumina balls to obtain a catalyst slurry for the surface layer. The particle diameter of the surface layer catalyst slurry was 2.8 μm.

  After that, the catalyst slurry for the inner layer was put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry was removed with an air stream, dried at 120 ° C, and in an air stream at 400 ° C. Baked. Thereafter, a surface layer catalyst slurry was applied in the same manner to obtain a catalyst of Comparative Example 2. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

Comparative Example 3
In a solution in which 6.54 g of dinitrodiamine platinum nitrate acidic aqueous solution (8.83 wt% manufactured by Tanaka Kikinzoku Co., Ltd.) and 193.5 ml of ion-exchanged water are mixed, 184 g of active alumina (specific surface area 180 m ² / g) is dispersed, The mixture was stirred with a magnetic stirrer for 1 hour. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour in an air stream to obtain an alumina catalyst powder carrying Pt 0.3 wt%.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and pulverized with alumina balls to obtain an inner layer catalyst slurry. The particle diameter of the inner layer catalyst slurry was 2.8 μm.

Next, 196 g of silica (specific surface area 100 m ² / g) is dispersed in a solution in which 4.01 g of rhodium nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., 13.81 wt%) and 156 ml of ion-exchanged water are mixed. Stir with a magnetic stirrer for 1 hour. This was evaporated to dryness, pulverized and sized, and then calcined at 400 ° C. for 1 hour in an air stream to obtain a silica catalyst powder carrying Rh 0.3 wt%.

  363.6 g of the obtained catalyst powder, 50.9 g of boehmite, 42.0 g of 10% nitric acid, and 575.3 g of ion-exchanged water were each put into a magnetic pot, and shaken and ground together with alumina balls to obtain a catalyst slurry for the surface layer. The particle diameter of the surface layer catalyst slurry was 2.8 μm.

  After that, the catalyst slurry for the inner layer was put into a cordierite honeycomb carrier (900 cells / 2.5 mil), the excess slurry was removed with an air stream, dried at 120 ° C, and in an air stream at 400 ° C. Baked. Thereafter, the catalyst slurry for the surface layer was applied in the same manner to obtain a catalyst of Comparative Example 3. At this time, the coating amount of the inner layer catalyst slurry and the surface layer catalyst slurry was 100 g / L.

The performance of each of the catalysts of Examples 1 to 7 and Comparative Examples 1 to 3 shown in Table 1 below was evaluated.

  First, the catalysts of Examples 1 to 7 and Comparative Examples 1 to 3 were mounted on the exhaust system of a 3500 cc V-type 6-cylinder engine (manufactured by Nissan Motor Co., Ltd.). The catalyst position was adjusted so that the temperature was 700 ° C., and the operation was performed for 50 hours. At this time, unleaded gasoline was used as fuel.

After enduring the catalyst, a part of each catalyst was cut out, and each catalyst having a catalyst capacity of 40 cc was incorporated into a simulated exhaust gas distribution device. After that, the model gas with the composition shown in Table 2 was circulated through the simulated exhaust gas distribution device at a gas flow rate of 40 L / min, and the catalyst temperature was raised from room temperature to 400 ° C at a rate of 10 ° C / min. The temperature T (° C.) at which 50% is 50% was examined.

  Furthermore, XPS surface analysis was performed on each catalyst after durability. Specifically, the binding energy of the Rh 3d5 orbit was measured using a composite surface analyzer (manufactured by PHI, ESCA-5600). The X-ray source was Mg-Kα ray (1253.6 eV) and operated at 300 W. Further, as a sample at the time of measurement, a sample which was pulverized with a menor mortar and then manually compacted and molded was used, and the sample surface was analyzed with a composite surface analyzer having a vacuum degree of 10-8 Pa. Here, the surface means a depth of 4 nm from the outermost layer of the sample, and the photoelectron extraction angle is 45 °.

  Further, charge correction was performed from the peak top binding energy value of the carrier component in each catalyst. For example, when the main component of the carrier is zirconia, the Zr3d5 peak top binding energy is corrected as 182.2 eV, and when the carrier main component is alumina, the Al2p peak top binding energy is 74.7 eV. Corrected.

Table 3 shows the measurement results.

  As shown in Table 3, the binding energies of Rh3d5 orbits in Comparative Examples 1 to 3 all exceeded 311 eV, and it was found that Rh was in a highly oxidized state. As a result, the temperature of NOxT50 was 265. It was found that the catalyst performance was deteriorated above ℃. On the other hand, in each of the examples, the Rh3d5 orbital binding energy showed a value in the range of 309.6 eV to 309.6 eV, and it was found that the reduced state of Rh can be maintained. In particular, the temperature of NOxT50 in Examples 1 to 6 was lower than that of the comparative example, indicating that the temperature of NOxT50 was 247 ° C. or lower. Further, in Example 7, the temperature of NOxT50 was 260 ° C. as compared with each of the above-mentioned examples, and the catalyst performance was lowered. This is because the catalyst of the present invention was used for the slurry for the inner layer. Conceivable.

It is sectional drawing of the exhaust gas purification catalyst which concerns on embodiment of this invention.

Explanation of symbols

1 ... Exhaust gas purification catalyst,
2 ... base material,
3 ... 1st catalyst layer (inner layer),
4 ... 2nd catalyst layer (surface layer),
5 ... carrier,
6 ... Precious metal particles (Pt particles, Pd particles),
7: coupling member,
8 ... carrier,
9 ... Rh particles,
10: coupling member,

Claims (9)

An exhaust gas purification catalyst having a plurality of catalyst layers formed on a substrate,
Exhaust gas purification comprising an Rh catalyst layer comprising a carrier mainly composed of zirconia, Rh particles supported on the carrier, and a binding member mainly composed of zirconia existing between the carriers. catalyst. An exhaust gas purification catalyst having a plurality of catalyst layers formed on a substrate,
After having an Rh catalyst layer containing Rh particles mainly composed of zirconia and having been endured for 3 hours or more in an air stream at 900 ° C., charge correction was performed with the main component of the carrier carrying the Rh particles. An exhaust gas purifying catalyst characterized in that the binding energy of Rh 3d5 orbit by XPS surface analysis is 307.4eV or more and 309.9eV or less.   The exhaust gas purification catalyst according to claim 1 or 2, wherein the Rh catalyst layer contains at least 65 mol% of zirconia. Wherein Rh catalyst layer comprises Al ₂ O ₃ to at least one of the carriers or coupling member, molar ratio of Al ₂ O ₃ with respect to _{Rh (Al 2 O 3 / Rh} ) is 0.01 to 10 The exhaust gas purification catalyst according to any one of claims 1 to 3.   Furthermore, the noble metal particles of at least one of Pt or Pd are contained in the plurality of catalyst layers, the total noble metal amount in each catalyst layer is 0.7 g / L or less, and the noble metal amount of Rh is 0.30 g / L. The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the exhaust gas purification catalyst is L or less.   The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the carrier and the coupling member are manufactured using zirconia having a primary particle diameter of 200 nm or less.   The exhaust gas purification catalyst according to any one of claims 1 to 6, wherein the coupling member is manufactured using a zirconia sol having a primary particle diameter of 100 nm or less.   A catalyst slurry in which at least a catalyst powder in which Rh particles are supported on a support mainly composed of zirconia and a zirconia sol as a binding member is applied to a substrate or a catalyst layer is applied to the substrate or the catalyst layer, and then dried and fired. And an Rh catalyst layer is formed on the base material or the catalyst layer.   The method for producing an exhaust gas purification catalyst according to claim 8, wherein a zirconia sol having a primary particle diameter of 100 nm or less is used as the coupling member.

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