JPH0433494B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a three-way catalyst for exhaust gas purification. Alumina, a relatively thin film of activated alumina,
A wash coating layer is formed by adhering it to the surface of a honeycomb-shaped carrier made of refractory materials such as silica, alumina-silica, cordierite, mullite, zirconia, silicon carbide, and silicon nitride, and copper, nickel, and cobalt are applied to the catalyst carrier. , platinum, palladium,
Catalysts are already known which are impregnated and supported with a catalytically effective component such as rhodium or which is used together with the catalytically active component during wash coating. Since the quality of this relatively thin activated alumina film (wash coating layer) determines the catalyst performance, the wash coating layer has a large surface area and does not peel off even when subjected to vibration or thermal shock. It is necessary to firmly adhere to the carrier. Therefore, the main component of the conventional wash coating layer is activated alumina, which has a large specific surface area, has pores suitable for use as a catalyst, and has good adhesion to the carrier. However, a wash coating layer made only of activated alumina lacks heat resistance and has insufficient durability when used under harsh conditions. Therefore, in order to improve the durability of the catalyst, rare earth elements are used in combination. In this case, the conventional method has been to use alumina as the main component and supplementarily add rare earth elements to it. A method of using rare earth elements in the wash coating layer is proposed in Japanese Patent Laid-Open No. 87839/1987. In this method, wash coating is performed using a suspension consisting of a soluble salt of a rare earth element and alumina. However, this method can only be used when the weight ratio of the total rare earth element oxide to the total weight of the wash coating is at most 50% or less. This is because, as stated in the same publication, if the ratio of the total rare earth element oxides increases further, the purification performance of the catalyst will be significantly reduced. That is, in conventional wash coating layers, total rare earth element oxides have not been used in a larger amount than activated alumina. The present inventors investigated a method for producing a liquid composition of rare earth elements with high activity and good adhesion suitable for washing coating, and a method for adding rare earth elements by using the composition for washing coating. , Catalyst for gas purification (JP-A-57-
119834), in which a liquid composition of near-neutral rare earth elements is used in a larger amount than the conventional amount of rare earth elements used in the wash coating, the purification performance of the catalyst does not deteriorate, but rather increases. It has been found that the catalytic activity and thermal properties after supporting the catalytic active component are significantly improved compared to alumina coatings obtained by conventional methods. An object of the present invention is to provide a gas purifying catalyst that has a coating film with good adhesion, and has excellent catalytic activity and thermal properties. Another object of the present invention is to provide an excellent catalyst (three-way catalyst) that can simultaneously remove nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO). The purpose of the above is to form a film of a composition consisting of a rare earth element oxide and activated alumina on the surface of an inert carrier, and the rare earth element oxide accounts for 40 to 65% by weight of the composition. , the rare earth element oxide contains cerium oxide and lanthanum oxide, the total amount of the cerium oxide and the lanthanum oxide is 70% by weight or more of the rare earth element oxide, and the cerium oxide and the lanthanum oxide (Ce/La) is 0.5 to 3, and the film supports at least one platinum group element selected from the group consisting of platinum, palladium, and rhodium. This is achieved using a three-way exhaust gas purification catalyst. As the inert carrier, for example, a honeycomb type carrier made of a refractory material such as alumina, silica, alumina-silica, cordierite, mullite, zirconia, silicon carbide, silicon nitride, etc. is used. The rare earth element oxide includes cerium oxide and lanthanum oxide, and the cerium oxide and lanthanum oxide account for 70% by weight or more of the total rare earth element oxide. The remainder consists of oxides of rare earth elements other than cerium and lanthanum, such as praseodymium, neodymium, samarium, europium, dysprosium, and itteribium. In the present invention, the rare earth element oxide is present in an amount of 40 to 65% by weight, preferably 50 to 65% by weight of the composition forming the coating.
It accounts for 60% by weight. Outside this range, the effect of improving catalyst performance is small, as is clear from the examples below. In the present invention, the weight ratio (Ce/La) of cerium oxide to lanthanum oxide is 0.5 to 3.
Outside this range, the effect of improving catalyst performance is small, as is clear from the examples below. Next, a method for producing the catalyst of the present invention will be described. First, a rare earth element liquid composition is manufactured as follows. That is, an aqueous solution containing 1 mol of a single salt or a mixture of two or more of soluble salts of rare earth elements such as lanthanum, cerium, praseodymium, neodymium, samarium, coropium, dysprosium, and itteribium is reacted with those salts. Gradually add 10 to 30 times, preferably 15 to 25 times, the stoichiometric amount of ammonia in water.
Stir for 30-60 minutes to neutralize. After neutralization, the solution is allowed to stand, the supernatant liquid is removed by decantation, and the precipitate is separated using a centrifuge. Next, this precipitate is repulped into 20 to 30 g of deionized water, thoroughly stirred, and then separated using a centrifuge. If these operations are repeated until the supernatant becomes PH=10 or less, the precipitate and washing solution will not separate if left to stand naturally during repulping, so the suspended matter that has reached this state is separated using a centrifuge. If the precipitate is taken out, shaken vigorously with a shaker or by hand, and then heated at a temperature of 60°C or higher, preferably 75-80°C for 2 hours or more, the viscosity of the suspension will change and the color will noticeably change. A liquid composition of rare earth elements is obtained. The colloidal liquid composition thus obtained can remain a uniform liquid composition even when stored for a long period of time, and the concentration of the rare earth element in the liquid composition can be adjusted by diluting it with water as necessary. The rare earth liquid composition and activated alumina produced in this way are combined so that the total amount of rare earth element oxide is
It is mixed in an amount of 40 to 65% by weight, preferably 50 to 60% by weight. The mixture of activated alumina and rare earth liquid composition is thoroughly mixed to form a uniform suspension composition. This suspension composition may be used as it is, but when acetic acid is used in combination, the operation of the wash coating is improved. After washing the suspension composition above,
After calcining at ~700°C for 1 to several hours, impregnating and supporting the catalyst active ingredient on a carrier using an impregnating solution as in the conventional method, and subjecting it to dry reduction and wet reduction in the same manner as in the conventional method. Reduction treatment is carried out by any method, or in the suspension composition,
A catalyst active component is dispersed in activated alumina, and the noble metal-containing activated alumina obtained by reduction is mixed therein and then subjected to wash coating. After the wash coating, the mixture is calcined at 400 to 500° C. for one to several hours. A preferred example of the production of the catalyst of the present invention will be described in detail below. 50 parts by weight of activated alumina, 50 parts by weight of a rare earth liquid composition obtained by reacting a soluble salt of a rare earth element with ammonia, and 4 parts by weight of acetic acid are mixed and thoroughly mixed in a ball mill. Using the obtained suspension composition, a cordierite honeycomb carrier is wash-coated, and after drying, it is calcined at 700°C for 1 to 3 hours. As a catalyst impregnation liquid for this honeycomb carrier, per 1000ml of carrier,
2.5 to 15 mmol and 0.5 to 3 mmol of dinitrodiaminoplatinum and nitrodiaminorhodium, preferably 5 to 10 mmol and 1 to 2 mmol, respectively.
Prepare a stirred mixture of mol and 4 mmol of azodicarbonamide. Add this impregnating liquid to 40
The honeycomb carrier is impregnated after heating to ~70°C, preferably 50 to 60°C, and then reduction is performed. Since the present invention is configured as described above, a catalyst with excellent thermal stability, durability, and catalyst purification performance can be obtained. The catalyst of the present invention can be used, for example, in a three-way catalytic reaction containing CO, HC, and NO according to the test method described in the Examples below.
Comparing the reaction temperature at which each component reaches a purification rate of 50% with the catalyst of the present invention not based on specific bonds, the reaction is achieved at a temperature of 10 to 40°C. Furthermore, even if the average purification rate obtained by averaging the purification rates at each air-fuel ratio (A/F) is compared depending on the presence or absence of a catalyst with a specific bond, the catalyst of the present invention is always better than a catalyst without a specific bond. The average purification rate is high, which expands the air-fuel ratio range of the catalyst of the present invention. Furthermore, when the catalyst of the present invention and the catalyst not based on specific bonds were heat treated at 950° C. for 10 hours and their average purification rates were compared, the performance of the catalyst of the present invention was significantly improved. The catalyst of the present invention as described above is applied to a catalyst for purifying automobile exhaust gas, but it is also applicable to industrial waste gas, household fuel waste gas, various deodorizing devices, etc.
It can be applied to an extremely wide range of applications such as NOx purification. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited thereto. Example 1 In 80 parts by weight of 8 mol/aqueous ammonia
20 parts by weight of 0.2 mol/cerium nitrate was gradually added and stirred for 60 minutes. After stirring, the mixture was allowed to stand still, the supernatant liquid was decanted, and the remaining suspension was separated using a continuous centrifuge. The precipitate was repulped with 60 parts by weight of deionized water and separated using a centrifuge in the same manner. 1 part by weight of deionized water was added to the obtained precipitate, which was shaken for 60 minutes using a shaker, and then heated at 85° C. for 2 hours to obtain a colloidal cerium liquid composition. The pulp concentration in the liquid composition was about 20%. A colloidal lanthanum liquid composition was obtained using lanthanum nitrate by a method similar to the above method. The pulp concentration in the liquid composition was about 20%. 15 to 80 parts by weight of these cerium and lanthanum liquid compositions as oxides and 20 to 85 parts by weight of γ-alumina.
400 parts by weight of water was added to 100 parts by weight of a mixture consisting of 4 parts by weight of acetic acid and 4 parts by weight of acetic acid, and the mixture was mixed for 8 hours in a ball mill to prepare alumina slurry Nos. 1 to 13 for wash coating containing cerium and lanthanum. Comparative Example 1 40 parts by weight of a 1N acetic acid solution was added to 50 parts by weight of alumina manufactured by Condea, and the mixture was kneaded in a kneader for 10 minutes. This kneaded material was transferred to a plastic container, cured at room temperature for 60 minutes, and then dried at 110° C. for 6 hours. After cooling this dry product to room temperature, it was gradually peptized in 117 parts by weight of water and cured for 5 hours with stirring to obtain a colloidal liquid composition. The alumina concentration was approximately 25%. 28 parts by weight of cerium oxide or lanthanum oxide was added to 50 parts by weight of this colloidal liquid composition, 100 parts by weight of γ-alumina, and 300 parts by weight of water, and the mixture was mixed in a ball mill for 16 hours to form a comparative wash coating containing a rare earth element. Nos. 1 and 2 were prepared. Example 2 Cerium oxide 42%, lanthanum oxide 40%
%, the balance is 0.4mol/0.4mol/of rare earth nitrate consisting of rare earth oxides such as praseodymium and neodymium.
10 parts by weight at a concentration of 8 mol/aqueous ammonia 40
It was gradually added to each part by weight and stirred for 60 minutes. After stirring, the mixture was separated in the same manner as in Example 1. The precipitate was repulped with 120 parts by weight of deionized water and separated using a centrifuge in the same manner as in Example 1. 1 part by weight of deionized water was added to the resulting precipitate, which was vigorously shaken for 60 minutes using a shaker, and then heated at 80° C. for 2 hours to obtain a colloidal rare earth mixed liquid composition. The pulp concentration in the liquid composition was about 25%. Alumina slurries Nos. 14 to 18 for wash coating containing rare earth elements were prepared from this liquid composition in the same manner as in Example 1. Test Example 1 Using the liquid composition for wash coating prepared in Examples 1 to 2 and the wash coating composition prepared in Comparative Example 1, a cordierite honeycomb carrier (cell density: 300 cells/ ⁱⁿ² ) was coated with approximately A 15% wash coating was applied. After coating with water, it was calcined at 650°C for 3 hours. This honeycomb carrier 1 was impregnated with an aqueous solution of a complex of dinitrodiaminoplatinum containing 1.3 g of platinum, 1 part by weight of platinum, 2 parts by weight of azodicarbonamide and 1 part by weight of cystine, and after drying, it was subsequently impregnated as rhodium.
A catalyst was prepared by impregnating 0.13 g of dinitroamino rhodium and 1 part by weight of rhodium in an aqueous complex solution of 2 parts by weight of azodicarbonamide and 1 part by weight of cystine, followed by hydrogen reduction at 500°C. Regarding the above catalyst samples, the catalytic activity was evaluated under the following test conditions using a new catalyst and a catalyst after being subjected to heat treatment at 950° C. for 10 hours in air. The test results are shown in Table 1. Catalyst performance test conditions (1) Gas composition (volume basis) CO: 1.05% C ₃ H ₈ : 1000 ppm H ₂ : 0.35% CO ₂ : 10% O ₂ : Fluctuation H ₂ O: 10% NO: 2000 ppm N ₂ : Balance ( 2) Space velocity: 150,000/HV (3) Measurement method The air/fuel ratio (A/F) is varied in the range of 14.5 to 15.0 and the average purification rate of CO, HC, and NO is measured during this period. Example 3 Platinum 88 mmol/, Palladium 83 mmol/
An alumina liquid composition prepared from boehmite with 50 ml of a mixed solution of dinitrodiaminoplatinum palladium nitrate and dinitroamino rhodium containing 25 mmol of rhodium (Japanese Unexamined Patent Publication No. 1983-45314)
It was uniformly dispersed in 10 to 30 parts by weight, dried, and then reduced with hydrogen at 500°C. 10~30 parts by weight of the above alumina and 10~30 parts by weight of δ-alumina
50 parts by weight and a cerium and lanthanum liquid composition (as oxide) produced in the same manner as in Example 1
Add 400 parts by weight of water to 100 parts by weight of noble metal-containing alumina slurry consisting of 20 to 80 parts by weight and 4 parts by weight of acetic acid, and mix in a ball mill for 8 hours to obtain alumina slurry No. 1 for water coating containing precious metals, cerium, and lanthanum. 19-27 were prepared. Test Example 2 Using the wash coating composition prepared in Example 3, a cordierite honeycomb carrier (cell density: 300 cells/in ² ) was coated with platinum, palladium, and rhodium contents each per honeycomb carrier.
10-15% to 0.86g, 0.44g and 0.13g
Wash-coated. After coating with water, it was calcined at 500°C for 2 hours. Regarding the above catalyst samples, the catalytic activities of the new catalyst and the durable catalyst were evaluated in the same manner as in Test Example 1. The test results are shown in Table 1.

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Claims (1)

[Claims] 1. A film of a composition comprising a rare earth element oxide and activated alumina is formed on the surface of an inert carrier, and the rare earth element oxide accounts for 40 to 65% by weight of the composition. the rare earth element oxide contains cerium oxide and lanthanum oxide, the total amount of the cerium oxide and the lanthanum oxide is 70% by weight or more of the rare earth element oxide, and the cerium oxide The weight ratio of the substance to the lanthanum oxide (Ce/
A three-way catalyst for exhaust gas purification, characterized in that La) is 0.5 to 3, and at least one platinum group element selected from the group consisting of platinum, palladium, and rhodium is supported on the coating. 2 The above rare earth element oxide is obtained by washing coating a rare earth liquid composition obtained by reacting a soluble salt of a rare earth element with ammonia water and calcining it as a mixed suspension composition with activated alumina. A three-way catalyst for exhaust gas purification according to claim 1.