JPS6324419B2 - - 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 for detoxifying and removing 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 that alumina particles, mainly in the form of catalytically active calcined alumina particles dispersed in water, are applied to a monolith base material, and then the monolith base material coated with the alumina particles is calcined. A method is disclosed. The three-way catalyst obtained by supporting platinum and rhodium on a monolithic base material obtained in this way is insufficient to meet current air pollution control standards because it is prone to pore clogging by phosphorus and zinc. It is. Therefore, the inventors of the present invention proposed a patent application filed in 1983-
No. 81928, an aqueous composition comprising activated alumina, a water-soluble aluminum salt, and a rare earth compound containing at least lanthanum carbonate is prepared, and the prepared aqueous composition is coated on a monolith substrate,
Next, we proposed a method to form a rare earth element-containing porous film on a monolith substrate 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, rhodium, and palladium 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. As a three-way catalyst, a three-way catalyst is generally made of platinum as the main component and rhodium is supported as an essential component of the three-way catalyst in an amount of 1/20 to 1/5 of platinum, but due to resource constraints of platinum, Since platinum is expensive, it is desired to put into practical use a three-way catalyst consisting of platinum, rhodium, and palladium in which part of the platinum is replaced with palladium. However, this three-way catalyst consisting of platinum, rhodium, and palladium tends to alloy with platinum, rhodium, and palladium when exposed to high temperatures, so this catalyst has the drawbacks of low catalytic activity and unstable durability. have. As a result of research by the present inventors, it has been found that this alloying of platinum, rhodium, and palladium is difficult to occur when the exhaust gas of an internal combustion engine has a rich composition, but easily occurs even at a relatively low temperature when the exhaust gas is lean. The reason is that platinum interacts with oxygen in the lean exhaust gas, and the particle size of platinum increases significantly. This is because at that time, alloying of platinum, rhodium, and palladium occurs. This phenomenon is caused by the presence of platinum on the outer surface of the catalyst carrier.
This is more noticeable in catalysts that support rhodium and palladium at a higher density, and alloying of platinum, rhodium, and palladium also occurs when platinum, rhodium, and palladium are supported adjacently or overlappingly on a catalyst carrier. easy. The present 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, which exhibits excellent activity and remarkable durability over a long period of time. . That is, the present invention provides a monolithic base material containing porous oxides containing cerium oxide, activated alumina, and at least one basic oxide selected from lanthanum oxides and oxides of Group A elements of the periodic table. A basic carrier is formed by applying a high quality coating, and the carrier is immersed in a mixed solution consisting of an acidic dinitrodiamminoplatinum nitric acid solution, an aqueous rhodium chloride solution, and an acidic palladium chloride hydrochloric acid solution to which an organic acid has been added. It is characterized by supporting platinum, rhodium and palladium at the same time. In the present invention, basicity means, for convenience, that the metal oxide has a property of exhibiting a PH value of 9.0 or higher as measured by a PH meter when immersed in pure water. 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 blowing air through the channel, and after further blowing heated air, it was placed in an electric furnace and continued baking.
Remove from the electric furnace after gradual cooling. Repeat the above coating operation as necessary,
Forming 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 on a monolith base material. . Next, a catalyst supporting liquid is prepared. Dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ]
An acidic solution of nitric acid, an aqueous rhodium chloride solution, and an acidic solution of palladium chloride in hydrochloric acid are mixed, an organic acid is added, and the mixture is stirred. Organic acids that can be used in the present invention include pyromellitic anhydride, citric acid, tricarballylic acid, and the like. Next, in order to support the catalyst on the monolithic carrier, the monolithic carrier is immersed in the prepared catalyst supporting liquid. At this time, platinum, rhodium, palladium, and organic acids are competitively adsorbed onto the adsorption sites of the monolithic carrier. As a result, platinum, rhodium, and palladium can be prevented from being supported adjacent to or overlapping the monolithic carrier. Furthermore, the organic acid also prevents platinum, rhodium and palladium from being densely supported on the outer surface of the monolithic support. The monolithic carrier is pulled up from the catalyst-supporting liquid, the droplets inside the cell are blown away with an air stream, and the monolithic carrier is rapidly dried with hot air. By the method described above, it is possible to manufacture the integrated three-way catalyst for internal combustion engine exhaust gas purification in which platinum, rhodium, and palladium 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 70-120m ² /g, average packing density
0.69-0.75g/cc of 2-4mm sphere of activated alumina manufactured by Cataler Industries Co., Ltd. with cerium nitrate (Ce)
(NO ₃ ) _{3.6H 2} O 0.5 mol/l aqueous solution (350 ml) was sprayed, then dried at 110°C for 2 hours, then 500 ml in air.
It was baked at ℃ for 1 hour to obtain a CeO ₂ .Al ₂ O ₃ composite oxide. 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. Nissan Chemical Industry Co., Ltd. Alumina Sol AS-200
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. was prepared. Next, a commercially available cordierite honeycomb carrier was pre-soaked in deionized water, pulled out, and the water present in the cells was blown away with a stream of air. The carrier used here was cylindrical with a diameter of 30 mm and a length of 50 mm, with a wall thickness of approximately
It has 300 0.3 mm square cells/in ² parallel flow paths in the longitudinal direction. After pouring the coating suspension onto this carrier, first blow off the excess suspension clogging the cells with compressed air at a pressure gauge pressure of 0.5Kg/ ^cm2 , and then blow it off 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, and then
After ventilating the air heated to 250℃ for 1 hour, it is placed in an electric furnace and the temperature reaches 800℃ in 2 hours, then for another 1 hour.
It was continued to be baked, and then gradually cooled and taken out from the electric furnace. Each of the above operations was performed twice to obtain a basic carrier with a coating amount of about 5 g/piece. BET the specific surface area of this coating film
The result was 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 . 5g of this coating film and 70ml of water were mixed, stirred for 90 minutes, left to stand, and the pH of the mixture was measured.
It was 9.5. Dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] nitric acid acid solution containing 28 mg of platinum, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
Add pyromellitic anhydride C ₁₀ H ₂ O ₆ 76 to 70 ml of a solution containing 28 mg of palladium chloride in an acidic solution of hydrochloric acid.
mg was added to obtain a catalyst-supported solution. The basic support is immersed in the catalyst support solution for 90 minutes while the solution is flowing, then pulled out, the droplets inside the cell are blown away with an air stream, and then rapidly dried with hot air at 150℃ to support platinum, rhodium, and palladium. A catalyst was obtained. This catalyst is based on its total weight
0.12% by weight platinum, 0.024% by weight rhodium and
It contained 0.12% by weight of palladium. Example 2 Dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] containing 28 mg of platinum in nitric acid acid solution, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
A catalyst was produced in the same manner as in Example 1, except that 74 mg of citric acid, C ₆ H ₈ O ₇ .H _{2 O} , was added to 70 ml of a solution containing 28 mg of palladium chloride in hydrochloric acid. Example 3 Dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] containing 28 mg of platinum in nitric acid acid solution, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
62 mg of tricarballylic acid C ₆ H ₈ O ₆ in 70 ml of a mixed solution containing 28 mg of palladium chloride in hydrochloric acid acidic solution.
A catalyst was produced in the same manner as in Example 1 except that . 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 gradually added, followed by 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ and 49.9 g of strontium carbonate SrCO ₃ 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 a coating suspension was prepared by gradually adding 244.5 g of CeO ₂ Al ₂ O ₃ composite oxide powder, then adding 10.4 g of aluminum nitrate Al(NO ₃ ) ₃ and 66.7 g of barium carbonate BaCO ₃ A catalyst was produced in the same manner as in Example 1. Comparative example 1 Nissan Chemical Industries, Ltd. Alumina Sol AS-200
In a solution of 210g and 56.7g of ion-exchanged water.
Example 1 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 in a similar manner. 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.
Example 2 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 in a similar manner. 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.
Example 3 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 in a similar manner. Comparative Example 4 Dinitrodiamminoplatinum [Pt(NH ₃ ) ₃ (NO ₂ ) ₂ ] containing 28 mg of platinum in nitric acid acid solution, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
A catalyst was produced in the same manner as in Example 1, except that 70 ml of a solution containing 28 mg of palladium chloride in hydrochloric acid was used as the catalyst supporting liquid. Comparative Example 5 Dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] containing 28 mg of platinum in nitric acid acid solution, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
A catalyst was produced in the same manner as in Example 5, except that 70 ml of a solution containing 28 mg of palladium chloride in hydrochloric acid was used as the catalyst supporting liquid. Comparative Example 6 Dinitrodiamminoplatinum [Pt(NH ₃ ) ₃ (NO ₂ ) ₂ ] containing 28 mg of platinum in nitric acid acid solution, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
A catalyst was produced in the same manner as in Example 6, except that 70 ml of a solution containing 28 mg of palladium chloride in hydrochloric acid was used as the catalyst supporting liquid. Comparative Example 7 Dinitrodiamminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] containing 28 mg of platinum in nitric acid acid solution, rhodium 5.6
Rhodium chloride aqueous solution containing mg and palladium
A catalyst was produced in the same manner as in Example 7, except that 70 ml of a solution containing 28 mg of palladium chloride in hydrochloric acid was used as the catalyst supporting liquid. Comparative Example 8 A basic carrier was immersed in a catalyst support solution of 70 ml of palladium chloride hydrochloric acid acidic solution containing 28 mg of palladium for 60 minutes, pulled up, the droplets in the cell were blown away with an air stream, and rapidly dried with hot air at 150°C. did. Next, platinum
Dinitrodiamminoplatinum [Pt] containing 28mg
(NH ₃ ) ₂ (NO ₂ ) ₂ ] It was immersed in 70 ml of a nitric acid acidic solution for 90 minutes in a catalyst-supporting solution, then pulled out, the droplets in the cell were blown away with an air stream, and it was rapidly dried with hot air at 150°C. Next, a rhodium chloride aqueous solution containing 5.6 mg of rhodium.
The cell was immersed in 70 ml of catalyst-supporting solution for 60 minutes, pulled out, and the droplets inside the cell were blown away with an air stream, and rapidly dried with hot air at 150°C to obtain a catalyst supporting platinum, rhodium, and palladium. The catalyst contained, by weight, 0.12% platinum, 0.024% rhodium, and 0.12% palladium, based on its total weight. Comparative Example 9 Except that 76 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 28 mg of platinum to prepare a catalyst support solution. A catalyst was produced in the same manner as in Comparative Example 8. Durability Test For the catalysts obtained in Examples 1 to 7 and Comparative Examples 1 to 9, the exhaust gas purification rate was measured by the following method using automobile exhaust to evaluate the catalytic activity. The above catalyst was filled in 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. It 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.
FID was used for HC, and magnetic type was used for oxygen. A/
For F determination, ELTINGE,
SAE680144) method was used. The catalyst inlet gas temperature was 380°C, and the 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 9 all had substantially the same exhaust gas purification rates. Next, durability tests were conducted on the catalysts obtained in Examples 1 to 7 and Comparative Examples 1 to 9 using automobile exhaust using the above engine. The test conditions were: catalyst inlet gas temperature 680℃, SV20×10 ⁴ hr ^-1 , stoichiometric air-fuel ratio A/
F14.5, durability test time was 30 hours, and fuel containing 0.03 g of phosphorus and 0.01 g of lead per gallon was used for the phosphorus poisoning accelerated deterioration test. These test conditions are equivalent to actual vehicle driving of 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] 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
A basic carrier is formed by applying a porous film containing at least one basic oxide selected from oxides of group elements, and the carrier is mixed with dinitrodiamminoplatinum nitrate to which an organic acid is added. A method for producing a catalyst for purifying internal combustion engine exhaust gas, which comprises immersing the catalyst in a mixed solution consisting of an acidic solution, an aqueous rhodium chloride solution, and an acidic solution of palladium chloride in hydrochloric acid, thereby simultaneously supporting platinum, rhodium, and palladium on the carrier.