JPH0811182B2 - Exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to harmful components such as hydrocarbons (HC) and carbon monoxide (C) in exhaust gas discharged from internal combustion engines of automobiles.
O) and nitrogen oxides (NO _x ) at the same time with high efficiency.

(Prior Art) As conventional exhaust gas purifying catalysts, particularly automobile exhaust gas purifying catalysts, Japanese Patent Laid-Open Nos. 52-116779 and 54-159391 have been used.
As described in Japanese Patent Publication No. JP-A-2003-242, after depositing activated alumina powder containing cerium in advance on the surface of a monolithic carrier substrate, platinum, rhodium, palladium and the like, or a catalytic metal formed by a combination thereof was carried. A catalyst is disclosed.

(Problems to be Solved by the Invention) However, in such a conventional exhaust gas purifying catalyst, the oxygen (O ₂ ) storage capacity of the cerium oxide contained in the alumina coat layer causes the catalyst to be a catalytically active component. Some rhodium becomes oxidised and reduces NO _x activity. Further, palladium supported on activated alumina, under a high temperature, and dissociation into metal oxide, cause re-oxidation, rapid results sintering proceeds, especially pairs NO _X in the ternary region There is a problem that the activity decreases.

(Means for Solving Problems) The present invention has been made in view of such conventional problems, and at least one of rhodium and palladium is used as a praseodymium partially stabilized zirconia (Pr-PSZ). ) And lanthanum oxide are supported on the alumina coating layer, and the oxygen permeability of the partially stabilized zirconia (PSZ) in the lattice reduces the O ₂ storage capacity of the coating layer, thereby preventing the rhodium from becoming oxidized. In addition, by sharing oxygen between lanthanum oxide and palladium, the dissociation of palladium oxide to metal is prevented, and the catalyst layer that controls the sintering process improves NO _x activity. , also solves the above problems by providing one or two by oxidation activity of platinum and rhodium and palladium on the layer having the O ₂ storage ability of cerium oxide It is.

 The present invention will be described in detail below.

Activated alumina, which is generally used as a catalyst support substrate, undergoes crystal rearrangement at high temperature and is crystallographically stable α-
It becomes an inert alumina called alumina. The rearrangement of activated alumina to inactive α-alumina is not preferable because it reduces the dispersibility of a catalytically active component of a noble metal such as platinum, rhodium or palladium, and promotes sintering. For this reason, the addition of rare earth oxides is generally known for the purpose of improving the heat resistance of activated alumina and raising the crystal transition temperature. In addition, since catalysts for treating automobile exhaust gas are required to have three-way catalytic activity in particular, in many cases, cerium oxide having an O ₂ storage ability is added in expectation of controlling the atmosphere on the catalytically active component. However, due to the O ₂ storage capacity of cerium oxide, the oxidative activity in the rich region (O ₂ deficient region) is enhanced, so CO +
Since the 1 / 2O ₂ → CO ₂ reaction is promoted and the 2NO + 2CO → N ₂ + 2CO ₂ reaction is inhibited, the ternary NO _X activity is insufficient, so in the present invention, it is formed on the monolith carrier. The catalyst layer is a layer mainly for purifying CO and HC, and mainly NO _X.
It is intended to improve the three-way catalytic activity by dividing it into layers for the purpose of purification.

The catalyst layer whose main purpose is to purify CO and HC is to use cerium-supported activated alumina obtained by using a cerium nitrate solution, impregnating and supporting 3 to 5% by weight of cerium in terms of metal, and then drying and firing. At this time, the supported amount of cerium is 3
If it is less than 5% by weight, heat resistance cannot be sufficiently improved, and if it exceeds 5% by weight, the specific surface area of activated alumina is relatively decreased, which is not preferable. Next, cerium oxide is added to the catalyst layer in order to have the ability to adsorb and desorb oxygen. The amount of addition is 10 wt% to 30 wt% as cerium metal in the catalyst layer. If the amount of cerium added is less than 10% by weight, it will not be possible to have a sufficient oxygen adsorption / desorption capacity, and even if it is added in excess of 30% by weight, the oxygen adsorption / desorption capacity cannot be expected to increase, rather the specific surface area of the catalyst layer Is lowered and dispersion of catalyst components such as platinum and rhodium is hindered, which is not preferable. Then, above,
Cerium-supporting activated alumina and cerium oxide are put into a porcelain ball mill pot together with a nitric acid acidic boehmite alumina sol, and mixed and ground to obtain a coating slurry. The alumina content of the nitric acid boehmite alumina sol used at this time is 3% by weight to 12% by weight. When the alumina content is less than 3% by weight, the adhesion of the coat layer to the cordierite monolithic carrier is insufficient, which is inconvenient. On the other hand, if it exceeds 12% by weight, the viscosity of the slurry increases and the coating property deteriorates, which is inconvenient.
The boehmite alumina contained in the catalyst layer is 10% by weight to
It is preferably 15% by weight. This is because if it is less than 10% by weight, the adhesion to the monolith carrier is deteriorated, and if it exceeds 15% by weight, the ratio of alumina from boehmite alumina in the catalyst layer is relatively increased. Since the alumina is not subjected to treatment such as cerium addition for improving heat resistance, it is thermally unstable, so that the heat resistance of the catalyst layer is reduced,
Not preferred.

The obtained slurry is coated on a monolith carrier containing cordierite as a main component and dried at 120 to 130 ° C for 1 hour, and then in an air atmosphere at 500 ° C to 700 ° C, more preferably at 600 ° C to 650 ° C. Bake for hours. Baking temperature is 500 ℃
In the following, boehmite alumina is sufficiently pyrolyzed and γ
-Without aluminization, and above 700 ° C, the specific surface of the coating layer decreases, and catalyst components such as platinum, rhodium,
Dispersibility of palladium and the like is hindered, which is not preferable. Next, the obtained coating carrier is immersed in a nitric acid solution of dinitrodiammineplatinum, a rhodium nitrate solution, a dinitrodiamminepalladium solution, or a mixed solution thereof, and one of a predetermined amount of platinum, rhodium, or palladium or It carries two types. The noble metal solution used at this time may be a chloride solution, for example, a chloroplatinic acid solution or a rhodium chloride solution, but chlorine ions remain in the catalyst layer, which results in inhibiting platinum and rhodium metalization.
It is not preferable because it lowers the initial catalyst activity. After supporting a predetermined amount of platinum and rhodium, in order to prevent deviation of the catalyst components due to the movement of water during drying, after rapid drying with a microwave dryer, in a combustion gas atmosphere, 350 ℃ ~ 600
The catalyst layer is formed by baking at 0 ° C. for 1 hour. This time,
When the firing temperature is 350 ° C. or lower, salts of platinum, rhodium, palladium and the like are not sufficiently decomposed, and when the firing temperature is 600 ° C. or higher, sintering of platinum, rhodium and palladium occurs, which is not preferable. The components supported on the catalyst layer are platinum and rhodium, and the supported amounts are platinum 0.28 g / l to 0.77 g / l, rhodium 0.04 g / l to 0.15 g / l, and palladium 0.5 g / l to 1.5. The g / l range is particularly preferred. Below the respective lower limits, sufficient catalytic activity cannot be expected, and above the respective upper limits, the catalytic activity is improved but cost competitiveness is lost, which is disadvantageous.

One or two of platinum, rhodium, and palladium are used as a catalyst component in the catalyst layer. Platinum and palladium, which have been conventionally used for the oxidation reaction of CO and HC, have high reaction activity in a complete oxidizing atmosphere. On the contrary, the reaction activity is decreased by exposure to the ternary region and the rich region.
This is because palladium stabilizes as palladium oxide (PdO) in an oxidizing atmosphere, but in the ternary region or the rich region where the oxygen partial pressure decreases, PdO → Pd (metal) dissociation reaction and Pd → PdO This is because the reoxidation reaction to palladium occurs and the sintering of palladium is promoted. Further, it is known that this reaction is promoted in the presence of platinum, which is not preferable. On the other hand, platinum and rhodium-based materials have an O ₂ storage capacity of ceria, so rhodium is in an oxidized state and the ternary activity is reduced even in a region with a low oxygen partial pressure, but it does not inhibit the oxidation activity. Good results can be expected.

On the other hand, in order to improve the heat resistance of activated alumina, the catalyst layer whose main purpose is purification of NO _X is to use a lanthanum nitrate solution, impregnate and carry 3 to 5% by weight of lanthanum in terms of metal, and then dry and calcine. The obtained lanthanum-added activated alumina is used. At this time, if the supported amount of lanthanum is less than 3% by weight, heat resistance cannot be sufficiently improved, and if it exceeds 5% by weight, a so-called perovskite type complex oxide (ABO ₃ ) is formed, which is not suitable as active alumina. Since the characteristics change, it is inconvenient in considering activated alumina as a dispersion material of a noble metal as in the present invention. Next, lanthanum hydroxide is added to the catalyst layer for the purpose of providing a hydrogen supply capability and an oxide ability of palladium, and praseodymium partially stabilized zirconia is added as an antioxidant of rhodium. Among the reasons for the addition, the hydrogen generating ability of lanthanum hydroxide will be explained as follows. The praseodymium partially stabilized zirconia is obtained by solution-mixing praseodymium nitrate and zirconia nitrate, coprecipitating a hydroxide with an alkali such as ammonia, and firing.
Lanthanum hydroxide La (OH) ₃ placed in the exhaust gas system is decomposed by exhaust heat to become La ₂ O ₃ , but at this time, water (H ₂ O) with extremely high reaction activity is formed. This water reacts with NO _X to reduce it to N ₂ , and also contributes to the reduction and metalation of Rh, which is a catalytically active metal. The lanthanum once oxidized reacts with water in the exhaust gas to become lanthanum hydroxide again, and the reaction is recycled. The reason why lanthanum hydroxide is used here is that the OH group it possesses can be directly utilized in the reaction.For example, in the case of lanthanum carbonate, lanthanum oxalate, etc., they must be used as an oxide to support the reaction. Since its decomposition temperature is as high as 750 ℃ or higher, it is only effective for vehicles with high exhaust temperature. Further, since the molecules of CO ₂ gas generated during decomposition are large, macroscopic pores, which are not desired for the invention, are generated in the coat layer, which is not preferable. Next, if the palladium used as the catalytically active component is essentially oxidized and the stable state is not maintained, the palladium particles will be maximized. Therefore, it is preferable to form and stabilize a La-Pd-O-based composite oxide by combining with lanthanum. For the above reasons, 6 wt% to 18 wt% of lanthanum metal is added to the catalyst layer. If the amount of lanthanum added is less than 6% by weight, sufficient hydrogen generating ability and Pd oxidizing ability cannot be obtained, and if more than 18% by weight is added, hydrogen generating ability and Pd oxidizing ability are expected to increase. On the contrary, it rather reduces the specific surface area of the catalyst layer and hinders the dispersion of the catalyst components such as palladium and rhodium, which is not preferable.

Next, praseodymium partially stabilized zirconia used as an antioxidant for rhodium is partially stabilized by
The fact that lattice defects are formed in the crystal structure of zirconia and oxygen permeability is increased is clear from its application to oxygen sensors. By having this property, the presence of oxygen around rhodium can be reduced, and as a result, it becomes possible to suppress the oxidation of rhodium. For the above reasons, the catalyst layer contains 4 wt% of zirconium metal.
8% by weight is added. Further, the ratio of praseodymium to zirconium is a sufficient amount for partial stabilization, that is, 8% by weight to 12% by weight. If the amount of zirconium in the catalyst layer is less than 4% by weight, the sufficient antioxidant effect of rhodium cannot be obtained, and even if it is added in excess of 8% by weight, the antioxidant effect cannot be expected to increase, rather the ratio of the catalyst layer is It is not preferable because it reduces the surface area and hinders the dispersion of catalyst components such as palladium and rhodium. If the ratio of praseodymium to zirconium is less than 8% by weight, partial stabilization of zirconia is insufficient, and if it exceeds 12% by weight, praseodymium oxide can be formed alone and has a strong O ₂ storage capacity. Is not preferable because it causes the oxidation state.

Next, the lanthanum-supporting activated alumina, the lanthanum hydroxide powder, and the praseodymium partially stabilized zirconia powder are put into a porcelain ball mill pot together with a nitric acid boehmite alumina sol, and mixed and ground to obtain a coating slurry. The alumina content of the nitric acid acidic boehmite alumina sol used at this time is 3% by weight to 12% by weight.
If the alumina content is less than 3% by weight, the adhesion of the coat layer to the cordierite monolithic carrier is insufficient, which is inconvenient. On the other hand, if it exceeds 12% by weight, the viscosity of the slurry increases and the coating property deteriorates, which is inconvenient. The boehmite alumina contained in the catalyst layer is 10
It is desirable to be in the range of 15% by weight to 15% by weight. If it is less than 10% by weight, the adhesion to the monolith carrier is deteriorated, and if it exceeds 15% by weight, the alumina ratio from boehmite alumina in the catalyst layer is relatively increased. The alumina is not preferable because it has not been subjected to a treatment such as lanthanum addition for improving heat resistance and is thermally unstable, so that the heat resistance of the catalyst layer is lowered.

The obtained slurry is coated on the catalyst carrier supporting platinum and rhodium and dried at 120 to 130 ° C for 1 hour, and then in air atmosphere at 500 ° C to 700 ° C, more preferably 50 ° C.
Bake at 0 ° C to 600 ° C for 2 hours. At a firing temperature of 500 ° C or lower, boehmite alumina is not sufficiently thermally decomposed to form α-alumina, and at 600 ° C or higher, it is already supported,
Catalyst components such as platinum and rhodium are not preferable because they receive an extra heat history. Next, the obtained coated carrier is
It is immersed in a mixed solution of either a dinitrodiammine palladium nitric acid solution or an aqueous solution of palladium nitrate and an aqueous solution of rhodium nitrate to carry a predetermined amount of palladium and rhodium. The noble metal solution used at this time may be a chloride solution, that is, a palladium chloride solution or a rhodium chloride solution, but chloride ions remain in the catalyst layer, and palladium,
As a result of inhibiting the oxide or metallization of rhodium, the initial catalytic activity is reduced, which is not preferable. In addition, chlorine ions have a strong selective adsorption property, and as a result, the noble metal ions are carried inside rather than on the surface of the coating layer,
It may be possible to reach already-supported, platinum, or rhodium layers, which is not preferable because it goes against the purpose of the separation-supporting of the present invention. It should be noted that the dinitrodiammine palladium nitric acid solution and the palladium nitrate solution may be used separately because there is no obvious difference.

After loading a predetermined amount of palladium and rhodium, in order to prevent the catalyst component from shifting due to the movement of water during drying, it is rapidly dried by a microwave dryer, and then in a combustion gas atmosphere at 350 ° C to 600 ° C for 1 hour. Then, the catalyst layer is formed by firing. At this time, if the combustion temperature is 350 ° C. or lower, the palladium and rhodium salts are not sufficiently decomposed, and if the combustion temperature is 600 ° C. or higher, sintering of palladium and rhodium occurs, which is not preferable. The component supported on the catalyst layer is palladium,
Rhodium, the loading amount of palladium is 0.22 g / l ~ 0.7
7g / l, rhodium set in the range of 0.03g / l ~ 0.15g / l.
When palladium and rhodium are below the respective lower limit values, sufficient catalytic activity cannot be expected, and above the respective upper limit values, the catalytic activity is improved, but cost competitiveness is lost, which is disadvantageous. A honeycomb three-way catalyst is formed by forming a catalyst layer having each of the above-mentioned active functions on a monolith carrier, and at this time, is a CO or HC active layer formed on the surface and an NO _X active layer formed inside? , Or NO _X
The active layer is formed on the surface and the CO and HC active layers are formed inside, or in both cases, both layers are divided to form an exhaust gas purifying catalyst.

(Examples) Hereinafter, the present invention will be described with reference to Examples, Comparative Examples and Test Examples.

Example 1 Activated alumina powder 10 containing γ-alumina as a main component
To 00 g, add a solution of 96.34 g of cerium nitrate in 1000 g of ion-exchanged water, stir well, and then in the oven 15
After drying at 0 ° C. for about 3 hours, it was calcined in an air stream at 600 ° C. for 2 hours to obtain a cerium-containing activated alumina powder. Next, 2478 g of nitric acid-acidic boehmite alumina sol (sol obtained by adding 10% by weight HNO ₃ to 10% by weight suspension of boehmite alumina), 1006 g of the activated alumina powder, and 516 g of cerium oxide powder were put into a ball mill pot, and 8 It was pulverized for a time to obtain a slurry. The obtained slurry was applied to a monolith carrier substrate (1.7 l, 400 cells), dried at 130 ° C for 1 hour, and then calcined at 650 ° C for 2 hours in an air atmosphere. At this time, the coating amount was set to 220 g / piece. Furthermore, 0.96 g of platinum and 0.096 g of rhodium per carrier are added to this carrier,
A catalyst support was obtained by impregnating and supporting with a dinitrodiammine platinum nitric acid solution and a rhodium nitrate mixed aqueous solution, rapidly drying using a microwave dryer and then calcining at 600 ° C. for 1 hour in a combustion gas atmosphere. Next, 1000 g of the activated alumina powder
In contrast, a solution of 93.45 g of lanthanum nitrate dissolved in 1000 g of ion-exchanged water was added, stirred well, and then placed in an oven at 150
After drying at ℃ for 3 hours, it was baked at 600 ℃ for 2 hours in an air stream to obtain a lanthanum-containing activated alumina powder. Next, 2478 g of nitric acid-acidified boehmite alumina sol, 1006 g of the above-mentioned lanthanum-containing activated alumina powder, 275.5 g of lanthanum hydroxide powder, and 179.8 g of praseodymium partially stabilized zirconia (Pr-PSZ) were put into a ball mill pot and ground to obtain a slurry. It was The resulting slurry is applied to the catalyst carrier, and 130
After drying at ℃ for 1 hour, it was baked at 650 ℃ for 2 hours. The coating amount at this time was set to 120 g / piece. Further on this carrier,
0.96 g of palladium and 0.096 g of rhodium per carrier
Using a mixed aqueous solution of dinitrodiammine palladium nitric acid solution and rhodium nitrate, impregnated and supported, rapidly dried using a microwave dryer, and then calcined in a combustion gas atmosphere at 600 ° C. for 1 hour to obtain a catalyst 1. The catalyst 1 is platinum 0.562 g / l, palladium 0.562 g / l, rhodium 0.113 g / l,
It contains cerium 32.4 g / l, lanthanum 8.5 g / l and Pr-PSZ 0.5 g / l.

Example 2 Lanthanum-containing activated alumina powder 1006 described in Example 1
g, nitric acid boehmite alumina sol 2478 g, lanthanum hydroxide powder 275.5 g, and praseodymium partially stabilized zirconia (Pr-PSZ) 179.8 g were put into a ball mill pot, and the slurry obtained by crushing for 8 hours was composed mainly of cordierite. Apply to a monolith carrier substrate (400 cells, 1.7 liters)
After drying at ℃ for 1 hour, calcination at 650 ℃ for 2 hours in an air atmosphere. The coating amount at this time was set to 220 g / piece.
Furthermore, 0.955 g of palladium per carrier,
0.096 g of rhodium was impregnated and supported using a mixed aqueous solution of dinitrodiammine palladium and rhodium nitrate, rapidly dried using a microwave dryer, and then calcined at 600 ° C for 1 hour in a combustion gas atmosphere to obtain a catalyst carrier. It was Next, cerium-containing activated alumina powder 10 obtained in the same manner as in Example 1
06 g, nitric acid boehmite alumina sol 2478 g, and cerium oxide powder 516 g were put into a ball mill pot, and the slurry obtained by pulverizing for 8 hours was applied to the catalyst carrier, and the slurry was applied at 130 ° C. for 1 hour.
After being dried for an hour, it was baked at 650 ° C. for 2 hours in an air atmosphere. The coating amount at this time was set to 120 g / piece. Furthermore, 0.955 g of platinum and 0.09 of rhodium were added to this carrier per carrier.
6 g of dinitrodiammine platinum nitric acid solution and rhodium nitrate mixed aqueous solution were impregnated and supported, rapidly dried using a microwave dryer, and then calcined at 600 ° C. for 1 hour in a combustion gas atmosphere to obtain catalyst 2. This catalyst 2 is 0.562 g / l of platinum,
Palladium 0.562g / l, Rhodium 0.113g / l, Cerium 17.6
It contains g / l, lanthanum 15.5 g / l and Pr-PSZ 10.4 g / l.

Example 3 1006 g of cerium-containing activated alumina powder obtained in the same manner as in Example 1, 516 g of cerium oxide powder and 2478 g of nitric acid boehmite alumina sol were put into a ball mill pot, and the resulting slurry was crushed to obtain a monolith carrier substrate (1.7 l, 40
0 cell), dried at 130 ° C. for 1 hour, and then baked at 600 ° C. for 2 hours. The coating amount at this time was set to 220 g / piece. Furthermore, 0.955 g of platinum and 0.096 g of rhodium were impregnated and supported on this carrier using a mixed solution of dinitrodiammine platinum nitric acid solution and rhodium nitrate, followed by rapid drying using a microwave dryer, and then 600 ° C. The catalyst carrier was obtained by firing in a combustion gas atmosphere for 1 hour.

Next, 1268 g of the lanthanum-containing activated alumina powder obtained in the same manner as in Example 1, 137.8 g of the lanthanum hydroxide powder, 66.7 g of praseodymium partially stabilized zirconia (Pr-PSZ), and 2478 g of nitric acid boehmite alumina sol were charged into a ball mill pot. And crushed for 8 hours to obtain a slurry. The resulting slurry was applied to the catalyst carrier, dried at 130 ° C for 1 hour, and then calcined at 650 ° C for 2 hours. The coating amount at this time is 1
Set to 20g / piece. Furthermore, for each carrier,
Palladium 0.955 g and rhodium 0.096 g were impregnated and supported using a mixed aqueous solution of dinitrodiammine palladium nitric acid solution and rhodium nitrate, rapidly dried using a microwave dryer, and then baked at 600 ° C for 1 hour in a combustion gas atmosphere. The catalyst 3 was obtained. The catalyst 3 is platinum 0.562g / l, palladium 0.562g / l, rhodium 0.113g / l, cerium 32.4g / l,
It contains lanthanum 4.2g / l and Pr-PSZ 2.8g / l.

Example 4 In Example 2, the lanthanum-containing activated alumina powder 12
Catalyst 4 was obtained in the same manner, except that 68 g, lanthanum hydroxide powder 137.8 g, praseodymium partially stabilized zirconia (Pr-PSZ) 66.7 g and nitric acid-acidic boehmite alumina sol 2478 g were charged in the ball mill pot. This catalyst 4 is platinum.
It contains 562 g / l, palladium 0.562 g / l, rhodium 0.113 g / l, cerium 17.6 g / l, lanthanum 7.8 g / l, Pr-PSZ 5.2 g / l.

Example 5 In Example 1, the cerium-containing activated alumina powder 10
06 g, cerium oxide (516 g), and nitric acid-acidic boehmite alumina sol (2478 g) were mixed and pulverized to obtain a slurry, which was applied to obtain a carrier. The coating amount at this time was set to 220 g / piece. Furthermore, 0.96 g of palladium per carrier is added to this carrier,
A catalyst carrier was obtained in the same manner as in Example 1, after impregnating and supporting with a dinitrodiammine palladium nitric acid solution. Lanthanum-containing activated alumina powder 1006 was added to the obtained catalyst carrier.
g, nitric acid acidic boehmite alumina sol 2478g, lanthanum hydroxide 275.5g, praseodymium partially stabilized zirconia (Pr
-PSZ) 179.8 g of pulverized slurry was applied. The coating amount at this time was set to 120 g / piece. After this, palladium
0.96 g and 0.191 g of rhodium were impregnated and supported using a dinitrodiammine palladium nitric acid solution and a rhodium nitrate solution, and then a catalyst 5 was obtained in the same manner. This catalyst 5 is palladium
It contains 1.124 g / l, rhodium 0.113 g / l, cerium 32.4 g / l, lanthanum 8.5 g / l, Pr-PSZ 5.6 g / l.

Example 6 In Example 2, lanthanum-containing activated alumina powder 10
06 g, nitric acid acidic boehmite alumina sol 2478 g, lanthanum hydroxide powder 275.5 g, and praseodymium partially stabilized zirconia (Pr-PSZ) 179.8 g were mixed and pulverized to obtain a carrier by applying a slurry. The coating amount at this time was set to 220 g / piece. Furthermore, 0.955 g of palladium and rhodium of 0.
191 g of dinitrodiammine palladium nitric acid solution and rhodium nitrate solution were impregnated and supported, and then a catalyst carrier was obtained in the same manner. To the obtained catalyst carrier, 1006 g of cerium-containing activated alumina powder, 516 g of cerium oxide, and 2478 g of nitric acid-acidic boehmite alumina sol were mixed and pulverized, and the resulting slurry was applied. The coating amount at this time was set to 120 g / piece. Thereafter, 0.96 g of palladium was impregnated and supported using a dinitrodiammine palladium nitric acid solution, and then a catalyst 6 was obtained in the same manner. This catalyst 6 is palladium 1.124 g / l, rhodium 0.113 g / l, cerium 17.6 g / l, lanthanum 15.5 g / l, Pr-P
Contains SZ 10.4 g / l.

Example 7 In Example 3, the cerium-containing activated alumina powder 10
A slurry obtained by mixing and pulverizing 06 g, 516 g of cerium oxide powder, and 2478 g of nitric acid-acidic boehmite alumina sol was applied to obtain a carrier. The coating amount at this time was set to 220 g / piece. Further, a catalyst carrier was obtained in the same manner except that 0.96 g of palladium was impregnated and supported on each of the carriers by using a dinitrodiammine palladium nitric acid solution. 1268 g of activated alumina powder containing lanthanum, 137.8 g of lanthanum hydroxide powder, 66.7 g of partially stabilized praseodymium zirconia (Pr-PSZ), nitric acid acidic boehmite alumina sol 2
A slurry obtained by mixing and grinding 478 g was applied. The coating amount at this time was set to 120 g / piece. After that, 0.96 g of palladium and 0.191 g of rhodium per carrier were impregnated and supported using a dinitrodiammine palladium nitric acid solution and a rhodium nitrate solution, and then a catalyst 7 was obtained in the same manner. This catalyst 7 contains 1.124 g / l of palladium, 0.113 g / l of rhodium, 32.4 g / l of cerium, 4.2 g / l of lanthanum and 2.8 g / l of Pr-PSZ.

Example 8 In Example 4, lanthanum-containing activated alumina powder 12
68 g, lanthanum hydroxide powder 137.8 g, praseodymium partially stabilized zirconia (Pr-PSZ) 66.7 g, and nitric acid boehmite alumina sol 2478 g were mixed and pulverized to obtain a carrier by applying a slurry. The coating amount at this time was set to 220 g / piece. Further, 0.96 g of palladium and 0.191 g of rhodium per one carrier were impregnated and supported using a dinitrodiammine palladium nitric acid solution and a rhodium nitrate solution, and then a catalyst carrier was obtained in the same manner. A slurry obtained by mixing and crushing 1006 g of cerium-containing activated alumina powder, 516 g of cerium oxide powder, and 2478 g of nitric acid-acidic boehmite alumina sol was applied to the obtained catalyst carrier. The coating amount at this time was set to 120 g / piece. After that, 0.96 g of palladium was impregnated and supported using a dinitrodiammine palladium nitric acid solution, and then a catalyst 8 was obtained in the same manner. This catalyst 8 is 1.124 g / l of palladium,
Rhodium 0.113g / l, cerium 17.6g / l, lanthanum 7.8g /
l, Pr-PSZ 5.2 g / l.

Comparative Example 1 1000 g of activated alumina powder containing γ-alumina as a main component
On the other hand, a cerium-containing activated alumina powder was obtained by adding a solution of 96.34 g of cerium nitrate dissolved in 1000 g of ion-exchanged water, drying and firing. Next, 2478 g of nitric acid-acidified boehmite alumina sol, 1006 g of the above activated alumina, and 516 g of cerium oxide powder were put into a ball mill pot and pulverized for 8 hours to obtain a slurry. The obtained slurry was applied to a monolith carrier substrate (1.7 l, 400 cells), dried at 130 ° C for 1 hour, and then calcined at 650 ° C for 2 hours in an air atmosphere. The coating amount at this time was set to 220 g / piece. Further on this carrier,
0.96 g of platinum and 0.096 g of rhodium per carrier are impregnated and supported using a mixed aqueous solution of dinitrodiammine platinum nitric acid solution and rhodium nitrate solution, using a microwave dryer.
After being rapidly dried, it was calcined at 600 ° C. for 1 hour in a combustion gas atmosphere to obtain a catalyst carrier. Next, the activated alumina powder 1000
A solution prepared by dissolving 93.45 g of lanthanum nitrate in 1000 g of ion-exchanged water was added to g, dried and calcined to obtain a lanthanum-containing activated alumina powder. Next, 2478 g of nitric acid-acidified boehmite alumina sol, 1186 g of the above activated alumina powder, and 275.5 g of lanthanum hydroxide powder were put into a ball mill pot and pulverized for 8 hours to obtain a slurry. The obtained slurry was applied to the catalyst carrier, dried at 130 ° C for 1 hour, and then calcined at 650 ° C for 2 hours. The coating amount at this time was set to 120 g / piece. Furthermore, 0.96 g of palladium and 0.096 g of rhodium were added to this carrier, and dinitrodiammine palladium nitric acid solution,
A catalyst A was obtained by impregnating and supporting with a mixed aqueous solution of a rhodium nitrate solution, rapidly drying with a microwave dryer, and then calcining at 600 ° C. for 1 hour in a combustion gas atmosphere. This catalyst A contains 0.562 g / l of platinum, 0.562 g / l of palladium, 0.113 g / l of rhodium, 32.4 g / l of cerium, and 8.5 g / l of lanthanum.

Comparative Example 2 In Comparative Example 1, cerium-containing activated alumina powder 10
A slurry obtained by mixing and crushing 06 g, 516 g of cerium oxide powder, and 2478 g of nitric acid-acidic boehmite alumina sol was applied to a monolith carrier. The coating amount at this time was set to 220 g / piece. Furthermore, 0.96 g of platinum and rhodium per carrier
After 0.096 g was contained and supported using a mixed solution of dinitrodiammine platinum nitrate solution and rhodium nitrate, a catalyst carrier was obtained in the same manner. This catalyst carrier contained 1006 g of lanthanum-containing activated alumina powder, 275.5 g of lanthanum hydroxide, 179.8 g of commercially available zirconium oxide powder, and nitric acid-acidic boehmite alumina sol.
A slurry obtained by mixing and crushing 2478 g was applied. At this time, the coating amount was set to 120 g / piece. Further, 0.96 g of palladium and 0.096 g of rhodium per one carrier were impregnated and supported using a mixed solution of a dinitrodiammine palladium nitric acid solution and rhodium nitrate, and then a catalyst B was obtained in the same manner. This catalyst B is platinum 0.562g / l, palladium 0.562g / l, rhodium
It contains 0.113 g / l, cerium 32.4 g / l, lanthanum 8.5 g / l and zirconium 5.6 g / l.

Comparative Example 3 In Comparative Example 1, cerium-containing activated alumina powder 10
A slurry obtained by mixing and pulverizing 06 g, 516 g of cerium oxide powder, and 2478 g of nitric acid-acidic boehmite alumina sol was applied, and a carrier was obtained in the same manner as below. The coating amount at this time is 220 g
/ Set to pieces. Next, 0.48 g of platinum and 0.96 g of palladium per one carrier were impregnated and supported using a mixed nitric acid solution of dinitrodiammineplatinum and dinitrodiamminepalladium to obtain a catalyst carrier in the same manner. Furthermore, lanthanum-containing activated alumina powder 1186 g, lanthanum hydroxide powder 275.5
g and nitric acid boehmite alumina sol 2478 g were mixed and pulverized to obtain a slurry, which was applied to the catalyst carrier and then dried and calcined. The coating amount at this time was set to 120 g / piece. Next, in this carrier, 0.48 g of platinum and 0.096 g of rhodium per carrier
A catalyst C was obtained in the same manner as above, except that a mixed nitric acid solution of dinitrodiammine platinum and rhodium nitrate was impregnated and supported. This catalyst C is platinum 0.562g / l, palladium 0.562g
/ l, rhodium 0.113g / l, cerium 32.4g / l, lanthanum 8.5
Contains g / l.

Comparative Example 4 1006 g of cerium-containing activated alumina powder, 516 g of cerium oxide powder, and 2478 g of nitric acid-acidic boehmite alumina sol were mixed and pulverized, and the resulting slurry was applied to a monolith carrier (400 cells, 1.7 l) to obtain a carrier. The coating amount at this time is 34
It was set to 0g / piece. Next, 0.96 g of platinum, 0.96 g of palladium, and 0.19 g of rhodium per carrier were impregnated and supported using a mixed nitric acid solution of dinitrodiammineplatinum, dinitrodiamminepalladium, and rhodium nitrate, and then using a microwave dryer. After rapid drying, 1 at 600 ℃ in combustion gas atmosphere
It was calcined for an hour to obtain catalyst D. This catalyst D is 0.562 g of platinum
/ l, palladium 0.562g / l, rhodium 0.113g / l, cerium
Contains 53.6 g / l.

Comparative Example 5 2563 g of silica and 1437 g of activated alumina granular carrier containing 3% by weight of cerium in terms of metal were mixed in a ball mill, and 6
After crushing for an hour, the cordierite-integrated carrier (400 cells, 1.7 liters) was coated and calcined at 650 ° C for 2 hours. The coating amount at this time was set to 340 g / piece. Further, this carrier was immersed in a mixed aqueous solution of chloroplatinic acid, palladium chloride and rhodium chloride, and reduced in a H ₂ / N ₂ stream.
Platinum, palladium, and rhodium were set to 0.96 g, 0.96 g, and 0.19 g per carrier, respectively. Next, the catalyst E was obtained by calcining in a combustion gas stream at 600 ° C. for 2 hours. The catalyst E was platinum 0.562 g / l, palladium 0.562 g / l, rhodium 0.
It contains 113 g / l and 6.6 g / l cerium.

Comparative Example 6 2563 g of alumina sol and 1437 g of activated alumina granular carrier,
After crushing with a ball mill for 6 hours, it was coated on a cordierite-integrated carrier (400 cells, 1.7 liters) and baked at 650 ° C for 2 hours. The coating amount at this time was set to 340 g / piece. Next, with an aqueous solution of cerium nitrate Ce (NO ₃ ) ₃ , 28 g / piece in terms of cerium metal was attached, dried at 120 ° C. for 3 hours, and then baked at 600 ° C. for 2 hours in an air stream. Furthermore, it is immersed in a mixed aqueous solution of chloroplatinic acid, palladium chloride, and rhodium chloride, and 0.96 g of platinum, 0.96 g of palladium per carrier,
After loading 0.19g of rhodium, 2 at 600 ℃ in combustion gas stream
It was calcined for a time to obtain a catalyst F. The catalyst F is platinum 0.562 g / l,
Palladium 0.562, Rhodium 0.113g / l, Cerium 16.47g /
contains l.

Test Example Catalysts 1 to 8 obtained from Examples 1 to 8 and catalysts A to F obtained in Comparative Examples 1 to 6 were subjected to a durability test under the following conditions,
A performance evaluation test was conducted, and the results are shown in Table 1.

Durability test conditions Catalyst integrated precious metal catalyst Catalyst outlet gas temperature 750 ° C Space velocity Approx. 70,000 Hr ^-1 Endurance time 100 hours Engine displacement 2200cc Endurance inlet gas atmosphere CO 0.4 to 0.6% O ₂ 0.5 ± 0.1% NO 1000ppm HC 2500ppm CO ₂ 14.9 ± 0.1% (Effects of the Invention) As described above, according to the present invention, rhodium and palladium praseodymium partially stabilized zirconia (Pr-PSZ) and an alumina coat layer containing lanthanum oxide are supported on the partially stabilized zirconia (PSZ). ) Oxygen permeability in the lattice reduces the O ₂ storage capacity of the coating layer, thereby preventing rhodium from being in an oxidized state, and
Oxygen is shared between lanthanum oxide and palladium to prevent dissociation of palladium oxide from metal to metal.
_X activity is improved, and platinum and rhodium on the layer with O ₂ storage capacity by cerium oxide have oxidation activity, so that low-cost palladium can be effectively utilized and high three-way catalytic activity can be achieved. By having it, the effect that the catalyst cost can be reduced can be obtained.

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Claims (1)

[Claims] 1. An alumina coat layer comprising cerium-added activated alumina and cerium oxide, platinum as a catalyst component,
At least one of palladium and rhodium is used as a catalyst component in an alumina coating layer composed of a layer carrying one or two of palladium and rhodium, lanthanum-added activated alumina, and praseodymium partially stabilized zirconia and lanthanum oxide. A catalyst for purifying exhaust gas, characterized in that a layer supporting the is separated and arranged on a carrier.