JPH0628731B2 - Exhaust gas purification catalyst manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a catalyst used for purifying exhaust gas of various combustion devices or automobiles in which rapid heat and rapid cooling conditions are severe, that is, thermal shock resistance is strongly required.

Conventional Technology Conventionally, as a catalyst carrier, alumina, cordierite,
Mullite or the like is used, but since it has a small specific surface area other than alumina, it has been used by forming a film of alumina or the like on the surface of a carrier and supporting a catalytic metal on this film. For example, in Japanese Examined Patent Publication (Kokoku) No. 50-9749, an aqueous composition is prepared from colloidal boehmite and activated alumina particles having a large specific surface area, which is uniformly adhered to a catalyst carrier and heated to a temperature of 400 to 500 ° C. A method of forming an activated alumina layer is described.

However, in terms of heat resistance, the activated alumina coating is rapidly converted into α when the temperature exceeds 1000 ° C., resulting in an agglomeration action on the supported metal. Therefore, investigations on improving the heat resistance of activated alumina are underway.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the prior art, as the activated alumina deteriorates due to heat, that is, as the specific surface area of the activated alumina decreases, the catalytic performance decreases. Therefore, it is necessary to take measures against heat deterioration to prevent deterioration of catalyst performance.

Further, even with respect to lead poisoning resistance, a longer life is required.

Means for Solving the Problems In order to solve the above-mentioned problems, in the present invention, an aqueous composition composed of titania-alumina prepared by a coprecipitation method is adhered on a carrier and then calcined at a temperature of 500 ° C. or higher. To form a coating layer of titania-alumina on the surface of the carrier, and carry a catalyst on the coating layer to form an exhaust gas purifying catalyst.

In recent years, as environmental standards are becoming more stringent, it is desired to improve exhaust gas purification performance. What is required for catalytic performance is ternary performance, heat resistance, lead poisoning resistance, thermal shock resistance, and the like.

In the present invention, by providing a coating layer of titania-alumina, it is effective against heat deterioration. In the coating layer, the catalyst such as platinum is highly dispersed on the titania, and the alumina layer functions sufficiently as a porous structure. Therefore, even when the titania / alumina layer is thermally deteriorated, platinum or the like dispersed on the titania is hardly directly affected by the thermal deterioration of alumina. Moreover, the catalytic metal such as platinum supported on the titania effectively acts on Pb and S poisons and is less likely to be poisoned.

Example 1 As an example of a method for preparing an aqueous titania-alumina composition, urea is added in an amount of about 5 times to a mixed solution of titanium sulfate and aluminum nitrate in an equimolar ratio, and 90 parts of this solution is added. A uniform co-precipitated gel was precipitated by holding it at ℃ for about 6 hours. The precipitate was filtered and repeatedly washed with water until sulfate and nitrate ions were not detected. About 30 wt% of pure water was added to the obtained titania-alumina gel.
The aqueous composition of Similarly, an aqueous composition of titania-alumina was prepared using various materials. Also in that case, a coprecipitated gel is formed so that titania and alumina are equimolar, and after filtering the precipitate, excess anions,
The cation was removed.

The titania-alumina aqueous composition obtained as described above was used to form a honeycomb cross section of 100 cm ² , length of 1 cm, and cell wall thickness of 0.25 m.
A honeycomb carrier with m and a cell diameter of 1.0 mm × 1.0 mm was coated by a dipping method, dried at 80 ° C. for 1 hour, and then heat-treated at 500 ° C. for 1 hour to form a titania-alumina film on the surface of the carrier. Then, the catalyst was impregnated with a platinum salt aqueous solution and subjected to a reduction treatment in a hydrogen atmosphere at 300 ° C. to support about 10 mg of platinum per 100 m of the carrier to obtain a catalyst.

For the performance evaluation of these catalysts, carbon monoxide (CO)
The purification rate was measured under the following conditions.

Space velocity 70,000 hr ⁻¹ CO concentration 200 ppm Catalyst temperature 250 ° C. Further, as a life test, the CO purification rate after heat treatment at 800 ° C. for 1000 hours was measured in the same manner. The performance of the catalyst using the aqueous composition containing only titania or alumina is also shown.

As is clear from this result, TiO ₂ -A obtained by the urea method
_The catalyst with a ₂ O ₃ coating showed excellent performance.

Among them, those prepared from Ti (NO ₃ ) ₄ or Ti (SO ₄ ) ₂ and A (NO ₃ ) ₃ were excellent. In the comparative example, the performance of using TiO ₂ alone is poor in the initial stage, but the life characteristic is A ₂
It was superior to the one using O ₃ alone. A ₂ O
Those using No. ₃ tended to have a large difference in deterioration between the initial test and the life test.

Therefore, it is considered that in the TiO ₂ —A ₂ O ₃ coating film according to the present invention, A ₂ O ₃ largely contributes to the performance in the initial stage, and TiO ₂ contributes to the life.

Good results were obtained with an aqueous composition of titania-alumina prepared by the heterogeneous precipitation method using aqueous ammonia, but slightly inferior to the urea method.

Here, as the carrier, a mixture of lime aluminate and fused silica in a weight ratio of 1: 3 was kneaded with water, extruded into a honeycomb shape, dried and heat treated at 1000 ° C. However, the carrier usable in the present invention is not limited to this, and may be a carrier composed of cordierite or mullite. However, in consideration of the adhesion between the coating film and the carrier, a honeycomb carrier having porosity and a low expansion coefficient is desirable.

Exhibited excellent characteristics in <Example 2> Example 1 Ti (SO _{4) 2} and A
The heat treatment temperature of the (NO ₃ ) ₃ catalyst in the catalyst using the titania-alumina coating by the urea method was examined.
The results are shown in Table 2.

From this result, if the heat treatment temperature is too low, the platinum carried later will be buried in the coating, resulting in a shorter life. Further, even if the temperature is too high, the characteristics as titania-alumina cannot be exhibited. Therefore, the optimum temperature is 600 to 800 ° C.

Example 3 Ti (SO ₄ ) ₂ showing excellent characteristics in Examples 1 and ₂
The performance of a honeycomb carrier having a titania-alumina coating of A (NO ₃ ) ₃ and A (NO ₃ ) ₃ as an automobile catalyst was evaluated.

The carrier has a honeycomb cross-sectional area of 100 cm ² , a length of 8 cm, a cell wall thickness of 0.25 mm, and a cell diameter of 1.0 mm × 1.0 mm.

After impregnating the above carrier with an aqueous cerium nitrate solution, 500
Cerium oxide is supported by 20 g per carrier by heat treatment at ℃, then impregnated with an aqueous solution containing a platinum salt and a rhodium salt, and subjected to reduction treatment in a hydrogen atmosphere at 300 ℃, 1 g of platinum per carrier, 5 rhodium
g was supported.

The performance test was performed by using a V-4 engine of 1.5, and was installed at a place where the exhaust gas temperature at the stoichiometric air-fuel ratio was 450 ° C. and measured.

The initial characteristics of the catalyst are shown in the figure. In order to further test the catalyst life, the catalyst layer temperature is 800 ° C and the space velocity is 60000.
An endurance test was conducted using leaded gasoline for 100 hours at hr ^-1 . Then, the subsequent performance was measured as in the initial stage.

The evaluation method is hydrocarbon (HC), CO, nitric oxide (N
The air-fuel ratio width in which the purification rate of O) was 80% was measured and evaluated as the window width.

As a result, the initial window width was 0.25 and 0.17 after the heat treatment at 800 ° C. for 200 hours. As described above, the catalyst of the present invention exhibited sufficient performance even for automobiles and maintained durability against Pb and S poisoning.

Effect of the Invention The catalyst according to the present invention has improved heat resistance and lead poisoning resistance, and can be widely used as a catalyst for various combustion equipment and automobiles.

[Brief description of drawings]

The figure shows the performance of the catalyst of the example of the present invention as an automobile catalyst.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B01J 23/56 301 A 8017-4G

Claims (3)

[Claims] 1. An aqueous composition composed of titania-alumina prepared by a coprecipitation method is uniformly deposited on a carrier, and then 5
A titania-alumina coating layer is formed on the surface of the carrier by firing at a temperature of 00 ° C. or higher, and a platinum group metal,
Alternatively, a method for producing an exhaust gas-purifying catalyst, which comprises supporting a platinum group metal and a rare earth metal oxide. 2. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the aqueous composition comprising titania-alumina is prepared by coprecipitation with urea or ammonia. 3. The exhaust gas-purifying catalyst according to claim 1 or 2, wherein the aqueous composition comprising titania-alumina is prepared from a titanium-aluminum chloride, nitrate or sulfate by a coprecipitation method. Manufacturing method.