JPS6271541A - Production of catalyst for cleaning up exhaust gas of engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration in catalyst activity by depositing a catalyst layer on a catalyst carriage and forming a coating layer mixed and coated with CeO2 and alumina subjected to a heating treatment thereon. CONSTITUTION:This invention relates to the ternary catalyst for the exhaust gas discharged from an internal-combustion engine, more particularly automobile, in which the catalyst layer 2 contg. the catalyst component consisting of platinum, palladium and/or rhodium is deposited on the catalyst carrier 1 and the coating layer 3 coated by subjecting CeO2 to the heating treatment for 1-5hr at 800-1,000 deg.C and mixing the same with alumina is formed on the catalyst layer 2. Then the thermal stability of CeO2 in the coating layer is improved; therefore, the performance deterioration by sintering of the CeO2 under a high- temp. condition is prevented without the formation of a compd. by the catalyst component and the CeO2 and the cleaning up performance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to the treatment of carbon monoxide (hereinafter referred to as CO) and hydrocarbons (hereinafter referred to as CO) in exhaust gas emitted from internal combustion engines, etc., especially automobiles.
Related to a method for manufacturing a catalyst for purifying engine exhaust gas used to reduce HC (hereinafter referred to as HC) and nitrogen oxide (hereinafter referred to as NOX) (prior technology) Conventionally, Co5HC and NOx in automobile exhaust gas have been purified. Platinum (Pt), rhodium (Rh),
Precious metals such as palladium (Pd) are converted into alumina (ALos).
Shino is used. In addition, in order to improve the catalytic performance of these precious metals, we are investing in funding for cerium oxide (Cent), which has an oxygen storage effect (the effect of taking in oxygen from exhaust gas and contributing to the purification of the catalyst).
Catalysts have been manufactured in which they are included in the alumina coating layer to increase the purification rate of exhaust gas.

However, the method of coexisting and supporting catalyst components of noble metals and metals and an oxygen storage capacity imparting agent (hereinafter referred to as O8C agent) such as cerium oxide on an alumina coat layer has the following problems. Ta.

(a) Since the OSC agent is uniformly supported on the alumina coat layer, it is not necessarily supported in the area near the bore where it is likely to come into contact with exhaust gas. In other words, many O8C agents are
It is carried in parts of the exhaust gas that are difficult to diffuse, and does not participate in the purification reaction, making it impossible to obtain a high purification rate.

(b) Thermal instability of the O8C agent adversely affects the OSC agent due to its increased direct contact with the catalyst components and alumina.

(c) Since the OSC agent is supported together with the catalyst component, both of them form a compound, reducing the dispersibility of the catalyst component and reducing the exhaust gas purification performance.

In addition, a catalyst layer containing Pt, Pd, etc. is provided on the catalyst carrier, and in order to protect the catalyst layer, alumina or alumina and cerium oxide (0.1 to 0 in weight ratio to alumina) is provided.
．． 5%) has been proposed (see Japanese Patent Laid-Open No. 60-5230). In the case of this known technique, the content of Ce Ot is too small, so no effect on oxygen storage capacity can be expected. Therefore, a method can be considered to increase the CeOt content in the coating layer, but in that case, the catalyst surface is exposed to exhaust gas and becomes high temperature, so the crystal growth of CeOt contained in the coating layer is inhibited. As a result, sintering occurs and the particle size of Cent increases, which may lead to a problem of significantly reducing catalyst activity.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and when forming a coating layer containing Cent on the upper surface of a catalyst layer containing a catalyst component made of a noble metal or a base metal, CeO7 is added in advance. The purpose of the high-temperature heat treatment is to prevent a decrease in catalyst activity due to interning of C e O2 in a high-temperature state.

(Means for achieving the object) In the present invention, as a means for achieving the above object, a catalyst layer containing at least one type of catalyst component selected from the group consisting of platinum, palladium, and ronram is provided on a catalyst carrier. is supported, and 800 to 10 Cent is supported on the catalyst layer.
After heat treatment at 00°C for 1 to 5 hours, the mixture is mixed with alumina to form a coating layer.

Here, as the catalyst component, known components such as Pt and Rh5Pd, and mixtures of two or more thereof are used.

The high temperature heat treatment is performed at a temperature of 800 to 1000°C for 1 to 5 hours. In addition, heat treatment at 800°C or lower for 1 hour or less will have a weak effect and thermal stability cannot be sufficiently improved, and heat treatment at 1000°C or higher for 5 hours or longer will cause the Cent. Crystallization may be promoted and catalyst performance may deteriorate due to thermal deterioration. By the way, H for the heat treatment temperature of Cent
When the change in C purification rate was investigated, the results shown in Figure 2 were obtained. The catalyst component of the catalyst used in this test was P
tl, Og/11, Rho, 2g/11,
The heat treatment time was 3 hours at each temperature. Also,
The durability test was conducted at 900°C for 50 hours, and the activity test was conducted at an air-fuel ratio A/F = 14.5, a space velocity S, and a V = 6.
It was conducted at 0000/fir.

From the results of the above test, the heat treatment temperature is 800.
It turns out that the range of -1000 degreeC is preferable.

The composition of the coating layer is preferably 50 to 95% by weight of CeOt and the balance of activated alumina, and the coating is performed using an aqueous slurry consisting of CeO2, activated alumina, hydrated alumina, and other dispersants. conduct.

An example of an exhaust gas purifying catalyst manufactured by the above manufacturing method is shown in an enlarged scale in FIG. Here, numeral 1 represents a catalyst carrier, 2 represents a catalyst layer, and 3 represents a coating layer. As the catalyst carrier 1, a honeycomb structure made of ceramics such as cordierite or various carriers made of heat-resistant metals and heat-resistant inorganic fibers are used.

(Function) As mentioned above, by heat-treating CeO2 in advance at 800 to 1000°C for 1 to 5 hours, the thermal stability of CeO7 is increased, and the crystal growth of CeO3 is suppressed in a high temperature state. Excellent performance can be maintained against thermal deterioration.

Hereinafter, preferred embodiments of the present invention will be described.

Example γ-alumina 160g, boehmite 160g, water 500g
cc.

4 cc of concentrated nitric acid was mixed and stirred using a homomixer for 10 hours to obtain a slurry for an alumina wash coat.

A honeycomb catalyst carrier (made of cordierite) was immersed in this slurry and pulled up, the excess slurry was removed by high-pressure air blowing, dried at 130°C for 1 hour, and then calcined at 550°C for 1 hour.

This alumina-coated catalyst carrier was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride at a predetermined concentration, pulled up, dried at 200°C for 1 hour, and then calcined at 600°C for 2 hours. The precious metal content after firing is platinum (PL) 1. o
g/Q, rhodium (Rh) 0.2 g/(l tear) ta.

CeO2 powder 8 was then heat-treated at 900°C for 3 hours.
00g and 200g of hydrated alumina were combined using a ball mill, and 1100cc of water was added to this mixed powder and kneaded to obtain a slurry liquid for coating the coating layer. While stirring the slurry liquid, the previously prepared catalyst carrier was immersed, and then pulled up and the excess slurry liquid was removed by high-pressure air blowing.
Thereafter, it was dried at 150°C for 3 hours and fired at 700°C for 3 hours. As a result, 80% by weight of Ce is deposited on the upper surface of the catalyst layer 2 (containing Pt and Rh) formed on the catalyst carrier
An exhaust gas purifying catalyst was obtained in which a coating layer 3 consisting of O2 and 20% by weight of γ-alumina was formed (see FIG. 1).

In addition, an evaluation test was conducted by comparing the tt C purification performance of the exhaust gas purification catalyst obtained in the above example after the heat resistance test with that of the catalyst (comparative example) that was not subjected to Cent heating pretreatment. The results shown in FIGS. 3 and 4 were obtained.

The activity measurement conditions were air-fuel ratio A/F=14.7±0.
9. Evaluation test was conducted with space velocity S, V = 600 (to/fir).

According to the results of the above evaluation test, the performance difference between the exhaust gas purification catalyst manufactured according to the example of the present invention and the comparative example is as follows.
This is not obvious when the catalyst is fresh or when the catalyst temperature is relatively low, but it becomes apparent when the catalyst temperature becomes high. This is nothing but the result that sintering of Ce Ot was suppressed by the heating pretreatment.

In this example, the content of cerium oxide in the coating layer is 80% by weight, but CeO.

The content can range from 50 to 95% by weight.

Generally, as the CeO content in the coating layer decreases, the catalyst performance gradually decreases, and below 50%, the catalyst performance decreases rapidly. The reason is that when the concentration of CeO decreases, interaction with the active ingredient is no longer obtained. By the way, CeO in the coating layer.

The results of measuring changes in the CO purification rate (%) at 400° C. with respect to the content (% by weight) of CO are shown in FIG. This result shows that the activity measurement conditions are air-fuel ratio A/F=14.
．． 7±0.9, space velocity 5J=60000/Hr,
300 at an exhaust gas temperature of 850℃ in a bench engine
This is an evaluation using a catalyst after a durability test conducted in IIr. According to this, when CeOt falls below 50%, the CO purification rate decreases significantly (・ru).

On the other hand, when the content of CeO increases, the catalytic activity improves, but since the bonding force of CeOy itself is weak, the physical strength (resistance to peeling) decreases and the durability decreases. Incidentally, 1. The content of C e Ot in the coating layer (wt%)
) was changed and a peel test was performed, and the memorial service shown in Man-1 was obtained - here it is! ll amount - (Coat adhesion volume before test - Coat adhesion amount after test) / (Coat adhesion amount before test) Also, as a test method, 600 cylindrical test pieces with a diameter of 1 inch and a height of 1 inch were used.
After repeating the procedure of heating at ℃ for 30 minutes and then cooling in 25 ℃ water for three days, it was thoroughly dried and the amount of peeling was measured.

Table-1 From the results of the above peel test, CeO in the coating layer.

It can be seen that the content is preferably 95% or less.

If the adhesion ratio of the coating layer to the catalyst carrier is less than 5% by weight, the surface of the catalyst layer cannot be effectively coated, resulting in a rapid decline in catalyst performance, and if it exceeds 40% by weight, active components and exhaust gas Since contact with gas is inhibited, catalyst performance rapidly decreases.

Taking this into consideration, it is desirable that the adhesion ratio of the coating layer be 5 to 40% by weight. The thickness of the coating layer is 20
It is desirable to set it to 40μ.

(Effect of the invention) According to the method of the present invention, the active catalyst component (P
t, Rh, etc.) and a catalyst layer containing CeO.

In addition to replacing the catalyst separated from the coating layer containing CeO, carbon in the coating layer is removed by high-temperature heat treatment of CeO.
Since the thermal stability of eO, will be increased,
Not only does the active catalyst component and ceO* not form a compound, but also (:, e
This has the excellent effect of being able to prevent performance deterioration due to Ot interpolation and significantly improving exhaust gas purification performance.

Furthermore, since the top surface of the catalyst layer is covered with a coating layer containing CeO2, the catalyst layer is likely to be in a reducing atmosphere.
There is also the advantage that the purification performance of NOx in exhaust gas is further improved.

[Brief explanation of drawings]

FIG. 1 is an enlarged view showing an example of a catalyst manufactured by the method for manufacturing an exhaust gas purification catalyst according to the present invention, and FIG. 2 is an enlarged view showing the HC purification rate with respect to the heating pretreatment temperature of CeO7 in the manufacturing method of the present invention. FIG. 3 shows the change in the catalyst population temperature (after the heat resistance test) at which the HC purification rate is 50% with respect to the catalyst heating temperature in the catalyst obtained by the example of the present invention and the comparative example. The characteristic diagram shown in Fig. 4 is as follows.
FIG. 5 is a characteristic diagram showing the change in HC purification rate at a catalyst inlet temperature of 400°C with respect to the catalyst heating temperature in Examples and Comparative Examples of the present invention. CO in exhaust gas relative to weight %)
FIG. 3 is a characteristic diagram showing changes in purification rate (%). l...Catalyst carrier 2...Catalyst layer 3...Coating layer Applicant: Mazda Motor Corporation and 1 other person/...
...Catalyst carrier 2...Catalyst layer 3...Covered! 12-layer heat treatment temperature (°C) Catalyst heating temperature ('CX 30 Hr) Catalyst heating temperature ('CX 30 Hr)
℃×50Ir) CeO2 content in the coating layer *ra (…amount %) Figure 5

Claims (1)

[Claims] 1. A catalyst layer containing at least one catalyst component selected from the group consisting of platinum, palladium, and rhodium is supported on a catalyst carrier, and 80% of CeO_2 is placed on the catalyst layer.
A method for producing a catalyst for purifying engine exhaust gas, which comprises heat-treating at 0 to 1000°C for 1 to 5 hours and then mixing with alumina to form a coated coating layer.