JPH0312933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing an exhaust gas purifying catalyst. More specifically, the present invention relates to a method for producing a catalyst (three-way catalyst) that can simultaneously remove nitrogen oxides (NOx), hydrocarbon compounds (HC), and carbon monoxide (CO) from exhaust gas emitted from internal combustion engines and the like. The three-way catalyst reduces the oxidized component NOx in exhaust gas to harmless nitrogen gas, and also oxidizes the reducing components HC and CO to convert them into harmless carbon dioxide (CO ₂ ) and water. It is required that the reduction reaction be carried out simultaneously, rapidly, and over a long period of time, and for this reason, NOx, HC and
Not only does it need to have high catalytic activity against all components of CO, but it also needs to have high low-temperature activity that starts the catalytic reaction at low temperatures, and a wide range from low to high temperature ranges. It is necessary that the activity can be maintained for a long time even when used in a wide temperature range. It is also required to have excellent poisoning resistance against lead, phosphorus, sulfur, and the like. Conventionally, platinum-rhodium, palladium-rhodium, and platinum-palladium-rhodium are used as three-way catalysts, but these
Although it has a certain degree of activity, it is still not satisfactory, and the catalyst performance deteriorates significantly during long-term use.Furthermore, air-fuel conversion (A/F), which can simultaneously remove the three components with a certain high purification rate, is still not satisfactory. The drawback was that the width (window) was narrow. The present invention provides a method for producing a more desirable exhaust gas purifying catalyst that does not have the above-mentioned drawbacks. That is, the present invention provides (a) at least one soluble salt of a platinum group element selected from the group consisting of palladium, platinum, and rhodium; (b) H ₃ PMo ₁₂ O ₄₀ , H ₃ PW ₁₂ O ₄₀ , H _{4 SiMo12O40 ,}
At least one heteropoly compound selected from the group consisting of H ₄ SiW ₁₂ O ₄₀ and compounds in which the hydrogen atom in these compounds is replaced with another cation, and (c) having at least one multiple bond. This is a method for producing a catalyst for exhaust gas purification, which comprises impregnating and supporting at least one organic nitrogen compound containing a nitrogen atom or an amino group on a refractory carrier, and then calcining it. In the production method of the present invention, a soluble salt of palladium, platinum or rhodium is used. In the present invention, one or more of these soluble salts can be used. The heteropoly compounds that can be used in the present invention include H ₃ PMo ₁₂ O ₄₀ , H ₃ PW ₁₂ O ₄₀ , H ₄ SiMo ₁₂ O ₄₀ ,
H ₄ SiW ₁₂ O ₄₀ and hydrogen atoms in these compounds can be combined with other cations such as Zn ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ ,
It is a compound substituted with Pd ²⁺ , Ag ⁺ , Mn ²⁺ , La ³⁺ , Ce ³⁺ . In the present invention, one or more of these heteropoly compounds can be used. Organic nitrogen compounds containing a nitrogen atom or an amino group having at least one multiple bond that can be used in the present invention are, for example, urea, azodicarbonamide, cystine, biurea, acetamide. In the present invention, one or more of these organic nitrogen compounds can be used. In the production method of the present invention, catalyst components are generally supported on a carrier such as a honeycomb made of a refractory material in accordance with a conventional method. At this time, it is usually preferable to apply an activated alumina coating (wash coating) to the surface of the carrier to make the surface catalytically active, as in the conventional method. In the production method of the present invention, the carrier volume is 1000 ml.
The usual amount ratio of soluble salt of platinum group element to
It is preferable to impregnate and support the organic nitrogen compound at a molar ratio of 10 mmol and a molar ratio of 0.5 to 3 times that of the soluble salt of the platinum group element. In the present invention, a soluble salt of palladium, platinum and/or rhodium is prepared in the same manner as in the conventional method, this is mixed with the above organic nitrogen compound, and the above heteropoly compound is added in the form of a powder or a solution. The impregnating liquid obtained by adding the impregnating liquid to the impregnating liquid is sufficiently stirred and heated to impregnate and support the carrier in the same manner as in the conventional method. Palladium, platinum and/or rhodium and the heteropoly compound can be impregnated and supported on the carrier separately, but in order to obtain better durability, it is preferable to use a mixed impregnating solution. After impregnating and supporting the carrier, it is calcined in air at 250 to 450°C, preferably 300 to 350°C, for one to several hours, and then, if necessary, a reduction treatment is performed. The reduction treatment may be carried out by either dry reduction or wet reduction as in conventional methods.
A preferred example of the production of the catalyst of the present invention will be explained in detail below. It is obtained by mixing 1 part by weight of an alumina liquid composition produced from boehmite (see JP-A-53-45314) and 2.5 parts by weight of activated alumina, and reacting 80 parts by weight of the mixture with a soluble salt of a rare earth compound with ammonia. Mix 20 weight of the rare earth liquid composition and thoroughly mix with a ball mill. The obtained liquid composition is used to wash-coat a cordierite honeycomb carrier, and after drying, it is calcined at 700°C for 1 to 3 hours. As a catalyst impregnating solution for this honeycomb carrier, per 1000 ml of the carrier, 5 to 100 mmol of a soluble salt such as palladium chloride, nitroaminopadium, palladium tetraammine dichloride, etc., preferably 10 to 40 mmol, 1.0 to 2.0 times that amount of urea, and 12 - trihydrogen molybdophosphate or
A stirred mixture of 0.01 to 10 mmol, preferably 0.05 to 1 mmol, of trihydrogen 12-tungstophosphate or a heteropoly compound derived therefrom is prepared. This impregnating liquid is heated at 50-90℃, preferably at 70-80℃.
After heating, impregnating the honeycomb carrier, and drying
Calcining is performed at 300 to 350°C for 1 to 3 hours, followed by reduction. A soluble salt such as rhodium chloride or nitrodiaminorhodium is added per 1000 ml of the honeycomb-supported palladium catalyst as a catalyst impregnating solution.
0.1 to 10 mmol, 0.5 to 2.0 mmol of azodicarbonamide, 0.1 to 0.3 mmol of cystine, and trihydrogen 12-molybdophosphate or 12-
A stirred mixture of 0.005 to 1 mmole of trihydrogen tungstophosphate or a heteropoly compound derived therefrom is prepared. This impregnation solution is heated to 40 to 70°C, preferably 50 to 60°C, impregnated into the supported palladium catalyst, dried, calcined at 300 to 350°C for 1 to 3 hours, and then reduced. The catalyst obtained by the production method of the present invention has a reaction time of up to 50% purification rate for each component in a three-way catalytic reaction including CO, HC, and NO according to the test method described in the example below, without the addition of a heteropoly compound. When compared with the catalyst of Furthermore, even when comparing the average purification rate obtained by averaging the purification rates in each A/F with and without the addition of a heteropoly compound, the catalyst obtained by the present invention is better than the catalyst without the addition of a heteropoly compound. The average purification rate was always high, and it was found that the air-fuel ratio range of the catalyst obtained by the present invention was expanded. Furthermore, the catalyst obtained according to the present invention and the catalyst without the addition of heteropoly compounds were used at 950%
It was found that the performance of the catalyst obtained according to the present invention was significantly improved even when the average purification rates were compared after heat treatment at ℃ for 10 hours. 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. such as CO, HC, 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 50 parts by weight of alumina monohydrate and 40 parts by weight of 1N acetic acid were kneaded and dried, and the dried product was peptized in 117 parts by weight of water to obtain a colloidal liquid composition. 160 parts by weight of an alumina mixture was prepared in a ratio of 2.5 parts by weight of activated alumina to _1/3 part by weight of Al ₂ O in this colloidal liquid composition. On the other hand, aqueous ammonia and cerium nitrate were reacted, then shaken and heated to obtain a colloidal cerium liquid composition. Add 40 parts by weight of this colloidal cerium liquid composition to 160 parts by weight of the alumina mixture, and add water to it.
1000 parts by weight was added and mixed and kneaded for 16 hours in a small ball mill. This liquid mixture was used to wash-coat a cordierite honeycomb carrier (300 sems/in ² ), and after drying, it was calcined at 700° C. for 3 hours. A palladium chloride solution containing 2 g of Pd and an aqueous complex solution containing palladium and an equal weight part of urea are prepared for the honeycomb carrier ₁ subjected to the wash coating. PMo ₁₂ O ₄₀ ) from 0.1 to 5
g was added and thoroughly stirred. Add this impregnating liquid to 70~80%
It is heated to 350 °C and impregnated into a honeycomb carrier, and after drying
Calcined at ℃ for 3 hours, then reduced, then heated to 700℃
Catalyst samples Nos. 1 to 8 were produced by calcining for 3 hours.
Catalyst samples No. 1 to 3 are reference examples, and catalyst sample No. 4
-8 are related to the present invention. Comparative Example 1 Comparative catalyst sample No. 1 containing no heteropoly compound was produced in exactly the same manner as in Example 1, except that trihydrogen 12-molybdophosphate was not added. Example 2 For a honeycomb carrier 1 similar to Example 1,
A palladium chloride solution containing 1.3 ^g of Pd and an aqueous complex solution containing urea in an equal weight part to palladium were prepared, and 0.3 to 10 g of silicotungstic acid (H ₄ SiW ₁₂ O ₄₀ ) was added to the aqueous solution. A supported palladium catalyst was produced in the same manner as in Example 1 using this impregnation liquid. For this supported palladium catalyst 1, a palladium chloride solution containing 1.3 ^gr as Rh and a complex aqueous solution containing rhodium, an equal part by weight of azodicarbonamide, and 0.2 parts by weight of cystine were prepared. 0.05 to 0.1 ^g of trihydrogen tungstophosphate (H ₃ PW ₁₂ O ₄₀ ) was added and thoroughly stirred. This impregnating solution was heated to 50 to 60°C and impregnated into the honeycomb-supported palladium catalyst, and after drying it was heated to 300°C.
Catalyst samples Nos. 9 to 17 were produced by calcining at 500° C. for 3 hours, followed by reduction, followed by calcining at 500° C. for 1 hour. Catalyst samples No. 9 to 10 are reference examples, and catalyst samples No. 11 to
No. 17 relates to the present invention. Comparative Example 2 Comparative catalyst sample No. 2 containing no heteropoly compound was produced in exactly the same manner as in Example 2, except that tungstosilicic acid and trihydrogen 12-tungstophosphate were not added. Example 3 For a honeycomb carrier 1 similar to Example 1,
Prepare an aqueous solution consisting of a dinitrodiaminoplatinum nitrate solution containing 1.1 g of Pt, a nitrodiamino rhodium nitrate solution containing 0.1 ^g of Rh, and cystine in an amount of 0.3 times the weight of the total amount of Pt and Rh. - 0.5 to 2.0 g of cobalt 12-tungstophosphate (CO _1,5 PW ₁₂ O ₄₀ ) prepared from trihydrogen tungstophosphate and cobalt carbon was added. Catalyst samples No. 18 to 19 were produced in the same manner as in Example 1 using this impregnating liquid. Comparative Example 3 Comparative catalyst sample No. 3 containing no heteropoly compound was produced in exactly the same manner as in Example 3, except that cobalt 12-tungstophosphate was not added. Example 4 For a honeycomb carrier 1 similar to Example 1,
An impregnation solution containing 0.2 to 4 ^grams of 12-tungstotrihydrogen phosphate was prepared. A honeycomb carrier was impregnated with this impregnating liquid at 30 to 40°C and dried. Using this carrier, catalyst samples Nos. 20 to 22 were produced in the same manner as in Example 3 except that cobalt 12-tungstophosphate was not added. Test Example Regarding the catalyst samples produced in Examples and Comparative Examples, the catalytic activity of the new catalyst and the catalyst after durability heat treatment at 950° C. for 10 hours in air were evaluated. The test conditions are as follows, and the test results are shown in Table 1. Catalyst performance test conditions (1) Gas composition (volume basis) CO: 1.0% C ₃ H ₆ : 1000ppm H ₂ : 0.33% CO ₂ : 10% O ₂ : Fluctuation H ₂ O: 10% NO: 4000ppm N ₂ : Balance (2) Space velocity: 150000/Hr (3) Measurement method Average purification rate of A/F = 14.5 to 15.0

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Claims (1)

[Claims] 1. (a) At least one soluble salt of a platinum group element selected from the group consisting of palladium, platinum, and rhodium; (b) H ₃ PMo ₁₂ O ₄₀ , H ₃ PW ₁₂ O ₄₀ , H _{4SiMo12O40 , _}
At least one heteropoly compound selected from the group consisting of H ₄ SiW ₁₂ O ₄₀ and compounds in which the hydrogen atom in these compounds is replaced with another cation, and (c) having at least one multiple bond. 1. A method for producing a catalyst for exhaust gas purification, which comprises impregnating and supporting at least one organic nitrogen compound containing a nitrogen atom or an amino group on a refractory carrier, followed by calcining.