JPS6324418B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a catalyst for purifying internal combustion engine exhaust gas, and more specifically, it relates to a method for manufacturing a catalyst for purifying exhaust gas from an internal combustion engine, and more specifically, it relates to a method for manufacturing a catalyst for purifying exhaust gas from an internal combustion engine. The present invention relates to a method for producing an integrated structure three-way catalyst for purifying internal combustion engine exhaust gas, which detoxifies and removes NOx by simultaneously oxidizing or reducing it. A method for forming an activated alumina coating on the surface of a monolithic base material (hereinafter referred to as a monolith base material) having a large number of ventilation holes is known. for example,
Japanese Patent Publication No. 56-27295 discloses a method in which alumina particles mainly consisting of catalytically active calcined alumina particles dispersed in water are applied to a monolith base material, and then the monolith base material to which the alumina particles are applied is applied. A method of baking is disclosed. The three-way catalyst obtained by supporting platinum and rhodium on a monolithic base material thus obtained is susceptible to pore clogging by phosphorus and zinc and is insufficient to meet current air pollution control standards. It is. Therefore, in Japanese Patent Application No. 1981-81928, the present inventors prepared an aqueous composition consisting of activated alumina, a water-soluble aluminum salt, and a rare earth compound containing at least lanthanum carbonate, and applied the prepared aqueous composition to a monolith substrate. We proposed a method to form a rare earth element-containing porous film on a monolithic substrate by coating the monolith, followed by drying and firing. That is, the present inventors succeeded in suppressing the clogging of the pores of the catalyst by phosphorus and zinc by applying a porous film containing a rare earth element to the monolith base material. However, even in this case, the three-way catalyst supporting platinum and rhodium using conventional manufacturing techniques was not satisfactory in terms of durability. The composition of the exhaust of an internal combustion engine can be controlled to approximately stoichiometric equilibrium in such a way that oxidation and catalytic reduction of each component of the equilibrium yields water, carbon dioxide, and nitrogen. Commonly used means to control this stoichiometric equilibrium include, among other things, continuously adjusting the ratio of air to fuel entering the engine and/or introducing additional oxygen upstream of the catalyst. It is. Thus, the composition of the exhaust gas from an internal combustion engine changes from a composition containing a relatively excessive amount of oxidizing compounds (hereinafter referred to as a lean composition) to a composition containing a relatively excessive amount of reducing compounds (hereinafter referred to as a rich composition). Or it changes vice versa. In this way, even though the three-way catalyst is used, it is not necessarily exposed only to the exhaust composition of an internal combustion engine controlled to have stoichiometric equilibrium, but is also exposed to rich or lean composition exhaust. Mainly platinum, rhodium is 1/20 to 1/ of platinum.
The disadvantage of the three-way catalyst supported in an amount of 5 is that when exposed to exhaust gas having a lean composition, its activity rapidly decreases at temperatures above 600°C. Investigation into the cause of this revealed that in lean compositions, excessive oxygen contained in the exhaust gas from internal combustion engines interacts with platinum and significantly increases the particle size of the platinum, resulting in a significant decrease in the number of active sites in the catalyst. It turned out that. This phenomenon is more pronounced in catalysts in which platinum is more densely supported on the outer surface of the carrier, and conversely, the growth of platinum particle size is suppressed smaller in catalysts in which platinum is more dispersedly supported from the outer surface to the inside of the carrier. . However, the more platinum is supported from the outer surface to the inside of the carrier, the more platinum becomes ineffective and the more expensive platinum is wasted, so it is necessary to have an appropriate platinum loading distribution. This invention was made in view of the above circumstances, and its purpose is to provide a method for manufacturing a monolithic three-way catalyst for purifying internal combustion engine exhaust gas, which exhibits excellent activity and remarkable durability over a long period of time. It is in. That is, the method of this invention provides a monolith base material with
A basic carrier is formed by applying a porous film containing cerium oxide, activated alumina, and at least one basic oxide selected from lanthanum oxide and oxides of group a elements of the periodic table. The method is characterized in that platinum and rhodium are supported on the carrier using an acidic dinitrodiamminoplatinum nitric acid solution and an aqueous rhodium chloride solution to which an organic acid has been added. In the present invention, basicity refers to the pH measured with a PH meter when a metal oxide is immersed in pure water.
Refers to having the property of having a value of 9.0 or higher. This invention will be explained in detail below. First, on a monolith base material, at least one basic oxide selected from cerium oxide, activated alumina, lanthanum oxide, which is a basic rare earth oxide, and oxides of Group A elements of the periodic table, Prepare a coating suspension for coating. Examples of oxides of Group a elements of the periodic table used in the present invention include MgO, CaO, SrO, BaO, and the like. Next, the monolith substrate is immersed in ion-exchanged water, pulled up, and the ion-exchanged water inside the cell is blown away with a stream of air. After pouring the prepared coating suspension onto the monolith substrate, air is blown to blow away the excess suspension clogging the cells. Next, the thus obtained wet monolithic carrier was dried by passing air through the channels, and after passing heated air through it, it was placed in an electric furnace to continue baking, and then gradually cooled. Remove from electric furnace. The above coating operation is repeated as necessary, and the monolith base material is coated with cerium oxide, activated alumina, at least one basic element selected from lanthanum oxide and oxides of group a elements of the periodic table. oxide and
Forms a porous film containing Next, this monolithic carrier is immersed in an acidic dinitrodiamminoplatinum nitric acid solution to which an organic acid has been added to support platinum on the monolithic carrier. In the supporting method, first, an organic acid is added to a dinitrodiamminoplatinum nitric acid acidic solution to prepare a platinum catalyst supporting solution. Organic acids that can be used include pyromellitic anhydride, citric acid,
Tricarballylic acid, etc. Next, the monolithic carrier is immersed in a platinum catalyst supporting solution to support platinum on the monolithic carrier. Furthermore, the monolithic carrier is pulled up from the platinum-supporting solution, the droplets inside the cell are blown away with an air stream, and after being rapidly dried with hot air, it is sintered in the air. Next, rhodium is supported on the monolithic carrier. The supporting method is to immerse the monolithic carrier in an aqueous rhodium chloride solution, pull it up, blow away the droplets in the cells with an air stream, and then dry it with hot air. By the method described above, it is possible to manufacture the monolithically structured three-way catalyst for purifying internal combustion engine exhaust gas in which platinum and rhodium are supported according to the present invention. Examples of the present invention will be described below. Example 1 Mainly composed of γ-alumina and δ-alumina,
Average specific surface area 70~ ^120m2 /g, average packing density 0.69~
Cerium nitrate Ce was added to activated alumina 1 made by Cataler Industries Co., Ltd., a 0.75 g/cc 2-4 mm ball.
(NO ₃ ) _{3.6H 2} O 0.5 mol/350 ml of aqueous solution was sprayed, dried at 110°C for 2 hours, and then dried at 500°C in air for 1 hour.
After baking for a while, a CeO ₂ Al ₂ O ₃ composite oxide was obtained. Next, this composite oxide was ground for 60 minutes using a vibration mill to obtain a powder of CeO ₂ Al ₂ O ₃ composite oxide. Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 110g and 197g of ion-exchanged water,
Gradually add 224.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder, then add 10.4 g of aluminum nitrate Al (NO ₃ ) ₃ and 82 g of lanthanum carbonate La ₂ (CO ₃ ) ₃ to form a coating suspension. Prepared. Next, a commercially available cordierite honeycomb carrier was immersed in ion-exchanged water, then pulled out and the water inside the cell was blown away with an air stream. The carrier used here has a diameter of 30 mm and a length of
300 square cells with a 50mm cylindrical shape and a wall thickness of approximately 0.3mm
It has ² channels parallel to the longitudinal direction. After pouring the coating suspension onto this carrier, the excess suspension clogging the cells is first blown away with compressed air at a pressure gauge pressure of 0.5Kg/cm ² , and then blown away from the opposite direction to completely remove the excess suspension clogging the cells. I made sure that there was no clogging. After coating, air at 30°C was passed through the channel of the wet carrier for 30 minutes to dry it.
After ventilating the air heated to ℃ for 1 hour, it was placed in an electric furnace and heated to 800℃ in 2 hours. After reaching 800℃, it continued to be baked for another 1 hour, then gradually cooled and taken out from the electric furnace. Ta. Each of the above operations was repeated twice to obtain a basic carrier with a coating amount of about 5 g/piece. The specific surface area of this coating film was measured by the BET method and was found to be 89 m ² /g. The lanthanum in this coating was measured by X-ray diffraction and was found to be lanthanum oxide La ₂ O ₃ . 5 g of this coating film and 70 ml of water were mixed and left to stir for 90 minutes, and then the pH of the mixture was measured and found to be 9.5. 150 mg of pyromellitic anhydride C ₁₀ H ₂ O ₆ was added to 70 ml of dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid acidic solution containing 842 mg of platinum and stirred to prepare a platinum catalyst support solution. . The above basic carrier was immersed in the platinum catalyst supporting solution for 90 minutes while the solution was flowing, then pulled out and the droplets in the cell were blown away with an air stream, and then rapidly dried with hot air at 150°C, and then heated in air at 250°C. The cell was baked for 1 hour, then immersed in 70 ml of rhodium chloride aqueous solution containing 81 mg of rhodium for 60 minutes while flowing the solution, pulled out, blown off the droplets in the cell with an air stream, and dried with hot air at 150°C. A platinum-rhodium supported catalyst was obtained. This catalyst contains 0.24% platinum and 0.024% platinum based on its total weight.
It contained rhodium. Example 2 Example except that 147 mg of citric acid C ₆ H ₈ O ₇ H _{2 O} was added to 70 ml of dinitrodiamminoplatinum [Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid acidic solution containing 842 mg of platinum/Pt. 1
A catalyst was produced in a similar manner. Example 3 Same as Example 1 except that 123 mg of tricarballylic acid C ₆ H ₈ O ₆ was added to 70 ml of dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid solution containing 842 mg of platinum. A catalyst was prepared in a similar manner. Example 4 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water,
Except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was gradually added, followed by 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ and 33.8 g of calcium carbonate CaCO ₃ to prepare the coating suspension. A catalyst was prepared in a similar manner to Example 1. Example 5 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water,
Except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was gradually added, followed by 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ and 28.5 g of magnesium carbonate MgCO ₃ to prepare the coating suspension. A catalyst was prepared in a similar manner to Example 1. Example 6 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water,
Except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was added to the slow mixture, and then 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ and 49.9 g of strontium carbonate SrCO ₃ were added to prepare the coating suspension. A catalyst was produced in the same manner as in Example 1. Example 7 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water,
Except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was gradually added, followed by 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ and 66.7 g of barium carbonate BaCO ₃ to prepare the coating suspension. A catalyst was prepared in a similar manner to Example 1. Comparative example 1 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water,
A coating suspension was prepared in the same manner as in Example 1, except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was gradually added, and then 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ was added to prepare the coating suspension. A catalyst was produced. Comparative example 2 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water,
The same method as in Example 2 was carried out, except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was gradually added, and then 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ was added to prepare the coating suspension. A catalyst was produced. Comparative example 3 Alumina sol AS-200 manufactured by Nissan Chemical Industries, Ltd.
In a solution of 210g and 56.7g of ion-exchanged water.
The same method as in Example 3 was used except that 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder was gradually added, followed by 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ to prepare the coating suspension. A catalyst was produced. Comparative Example 4 A catalyst was prepared in the same manner as in Example 1, except that 70 ml of a dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid solution containing 842 mg of platinum was used as the platinum catalyst supporting solution. Manufactured. Comparative Example 5 A catalyst was prepared in the same manner as in Example 4, except that 70 ml of dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid solution containing 842 mg of platinum was used as the platinum catalyst supporting solution. Manufactured. Comparative Example 6 A catalyst was prepared in the same manner as in Example 5, except that 70 ml of a dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid solution containing 842 mg of platinum was used as the platinum catalyst supporting solution. Manufactured. Comparative Example 7 A catalyst was produced in the same manner as in Example 6, except that 70 ml of dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid solution containing 842 mg of platinum was used as the platinum support solution. did. Comparative Example 8 A catalyst was prepared in the same manner as in Example 7, except that 70 ml of dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid acidic solution containing 842 mg of platinum was used as the platinum catalyst supporting solution. Manufactured. Durability Test For the catalysts obtained in Examples 1 to 7 and Comparative Examples 1 to 8, the exhaust gas purification rate was measured by the following method using automobile exhaust to evaluate the catalytic activity. The above catalyst was packed into a multi-converter equipped with a plurality of reactors arranged concentrically around the central axis of the exhaust flow. The engine is equipped with an electronically controlled fuel injection system, and the test method is the air-fuel ratio oscillation method, which focuses on the theoretical air-fuel ratio A/F (Air-Fuel Ratio) of 14.5, which shows the highest purification ability for HC, CO, and NOx. The device was forcibly vibrated at 1 Hz and ±1.0 A/F, and the purification rate of HC, CO, and NOx3 components in the exhaust gas at this time was measured. The analysis method is NDIR method for CO, CO ₂ and NO, and NDIR method for HC.
Magnetic type FID and oxygen were used. The ELTINGE.SAE680144 method was used to determine A/F. In addition, the catalyst inlet gas temperature is 380℃, SV
(space velocity) was 11×10 ⁴ hr ^-1 . As a result, the catalysts obtained in Examples 1 to 7 and Comparative Examples 1 to 8 had substantially the same exhaust gas purification rate. Next, durability tests were conducted on the catalysts obtained in Examples 1 to 7 and Comparative Examples 1 to 8 using automobile exhaust using the above-mentioned engine. The test conditions were: catalyst inlet gas temperature 680℃, SV20×10 ⁴ hr ^-1 , stoichiometric air-fuel ratio A/F.
14.5, the durability test was 30 hours, the fuel used was one containing 0.03 g of phosphorus and 0.01 g of lead per gallon, and it was a phosphorus poisoning accelerated deterioration test. This durability test condition corresponds to the actual driving of a car for 50,000 km. Next, using the catalyst after the durability test, the exhaust gas purification rate was measured and the catalytic activity was evaluated under the same conditions as those used before the durability test. The exhaust gas purification rate of the catalyst after the durability test is shown in the table below.

【table】

【table】

[Table] Shows carbon dioxide and nitrogen oxides.
It can be seen from the table that the catalyst according to the present invention is far superior in durability compared to catalysts produced by conventional methods. As is clear from the durability tests described above, the manufacturing method of the present invention makes it possible to manufacture an internal combustion engine exhaust purifying catalyst with excellent durability.

Claims (1)

[Claims] 1 A monolithic base material containing cerium oxide, activated alumina, lanthanum oxide, and periodic table a
Dinitrodiamminoplatinum nitric acid acidic solution and chloride, to which a basic carrier is formed by applying a porous film containing at least one basic oxide selected from oxides of group elements, and to which an organic acid is added. A method for producing a catalyst for purifying internal combustion engine exhaust gas, comprising supporting platinum and rhodium on the carrier using an aqueous rhodium solution.