JPH1157484A - Exhaust gas cleaning catalyst and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst and method of using the exhaust gas cleaning catalyst capable of demonstrating a sufficient NOx cleaning action of the catalyst, which catalyst has a high NOx cleaning capacity under a lean atmosphere in which catalysts of the prior arts could not demonstrate sufficient activity and has an excellent NOx purification capacity even after high temperature endurance. SOLUTION: This exhaust gas cleaning catalyst contains zeorite carrying at least one kind of noble metal selected from the group consisting of platinum, palladium, rhodium and iridium and alumina, the content of the zeorite carrying the noble metal is 30-200 g per liter of the catalyst and 20-300 g of the alumina per liter of the catalyst is contained and the alumina has an average particle size of 1-30 μm, a small-pore volume of 0.1-1.0 cc/g and a specific area of 50-500 m<2> . This exhaust gas cleaning catalyst is used for a vehicle of a lean burn engine or a diesel engine wherein air fuel ratio of stoichiomerty and air-fuel ratio within a range of 15-50 are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a gasoline-powered vehicle,
The present invention relates to an exhaust gas purifying catalyst for purifying hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) in exhaust gas discharged from an internal combustion engine such as a diesel vehicle and a method of using the same, and particularly to oxygen. exhaust gas purifying catalyst excellent in purification performance of the NO _x under rich atmosphere and the use thereof.

[0002]

2. Description of the Related Art In recent years, in view of the problem of depletion of petroleum resources and the problem of global warming, realization of low fuel consumption vehicles is expected, and development of lean burn vehicles is particularly desired for gasoline vehicles. . In lean-burn vehicles, the exhaust gas atmosphere during lean-burn operation is based on the theoretical air-fuel condition
An oxygen-excess atmosphere (hereinafter, referred to as a “lean atmosphere”) as compared to “stoichiometric state”. In a lean atmosphere, when adapted to a conventional three-way catalyst, NO _x purification action from the effects of excess oxygen is disadvantageously insufficient. For this reason, NO _x
There has been a demand for the development of a catalyst that can purify methane.

Conventionally, NO _x in a lean atmosphere has been
Various catalysts for improving the purification performance have been proposed. For example, JP-A-1-135541 proposes a catalyst in which a noble metal such as Pt is supported on zeolite.

[0004] The zeolite contained in the exhaust gas purifying catalyst has a molecular sieve characteristic of the zeolite which affects the adsorption of gas on a noble metal which is an active species, and NO _x
It promotes a purification reaction. However, the conventional of the NO _x purification catalyst, the zeolite used as carrier substrates from the susceptible to degradation by heat and water vapor, there is a problem that the purification performance after high-temperature durability becomes insufficient.

[0005]

SUMMARY OF THE INVENTION
An object of the described invention is to improve the NO _x purification performance in a lean atmosphere, which did not show sufficient activity with the conventional catalyst, and to achieve an excellent N 2 even after high temperature durability.
An object of the present invention is to provide an exhaust gas purifying catalyst having O _x purifying performance.

[0006] The object of the invention according to claims 3 and 4 is as follows.
It is to provide the use of an exhaust gas purifying catalyst that _the NO _x purification action of the exhaust gas purifying catalyst can be particularly effectively the expression of the present invention.

[0007]

According to a first aspect of the present invention, there is provided an exhaust gas purifying catalyst comprising zeolite carrying at least one noble metal selected from the group consisting of platinum, palladium, rhodium and iridium; and alumina. The noble metal-supported zeolite is contained in an amount of 30 to 200 g per liter of the catalyst, and alumina is contained in an amount of 30 to 200 g per liter of the catalyst. The average particle diameter of the alumina is 1 to 30 μm, and the pore volume is 0.1 to 1. 0 cc / g, specific surface area 50-500 m ²
/ G.

[0008] In the exhaust gas purifying catalyst according to the present invention, the carried amount of at least one noble metal selected from the group consisting of platinum, palladium, rhodium and iridium is 0.1 to 10 g per liter of the catalyst. It is characterized by.

According to a third aspect of the present invention, the exhaust gas purifying catalyst of the present invention is used for a lean burn engine vehicle in which the air-fuel ratio repeats stoichiometry and a range of 15 to 50. It is characterized by doing.

A method of using an exhaust gas purifying catalyst according to a fourth aspect is characterized in that the exhaust gas purifying catalyst of the present invention is used for a diesel engine vehicle.

BEST MODE FOR CARRYING OUT THE INVENTION

As the noble metal in the exhaust gas purifying catalyst of the present invention, at least one selected from the group consisting of platinum, palladium, rhodium and iridium is used. For example, various combinations such as Pt and Rh, Pd and Rh, Pt and Id, and Pd alone are possible. The content of the noble metal is
Although absorption of NO _x performance and three-way catalyst performance is not particularly limited as long enough to give less than 0.1g and not sufficient ternary performance is obtained, even significant improving characteristics by using more than 10g is seen In view of this, 0.1 to 10 g is preferable per 1 L of the exhaust gas purifying catalyst of the present invention.

The zeolite as a substrate for supporting the noble metal is not particularly limited as long as it has a knitted three-dimensional structure. For example, pentasil-type zeolite, Y-type zeolite, mordenite, ferrierite and the like are desirable. The amount of zeolite used is 30 to 20 per liter of the catalyst of the present invention.
If the amount is less than 0 g, the effect of optimizing the gas adsorption state on the noble metal of the zeolite cannot be sufficiently obtained, and even if the amount is more than 200 g, a significant effect of increasing the amount cannot be obtained.

Alumina has an average particle size of 1 to 30 μm, a pore volume of 0.1 to 1.0 cc / g, and a specific surface area of 10 to 5 μm.
There is no particular limitation as long as it is 00 m ² / g, and various types can be used. If the average particle size is less than 1 μm, the layer density increases and gas diffusion is not sufficient,
If it exceeds 30 μm, the contact surface between zeolite and alumina becomes insufficient, and the effect of alumina to suppress the aggregation of particles cannot be sufficiently obtained. If the pore volume and specific surface area are less than the above ranges, the contact surface between zeolite and alumina will not be sufficient, and if it exceeds the above ranges, no significant improvement effect will be obtained.

The amount of alumina used is 30 per liter of the catalyst.
When the amount is less than 30 g, the effect of suppressing the aggregation of alumina cannot be sufficiently obtained, and even when the amount is more than 200 g, a significant effect of increasing the amount cannot be obtained.

In order to increase the heat resistant specific surface area of the above-mentioned zeolite or alumina, a rare earth element or zirconium can be added thereto.

The exhaust gas purifying catalyst of the present invention as described above, by including a noble metal loaded zeolite and alumina, it is possible to obtain high _the NO _x purification performance even after high-temperature durability. This is because the agglomeration of the noble metal-supported zeolite is suppressed by mixing the alumina, the noble metal, which is the active species, is kept in a highly dispersed state, and gas diffusion in the catalyst layer is suppressed by suppressing the agglomeration. It depends on what you can secure.

The exhaust gas purifying catalyst of the present invention can be used especially for lean-burn engine vehicles and diesel engine vehicles in which the air-fuel ratio repeats stoichiometry and a range of 15 to 50. Such With usage, NO _x absorption and release cycle is established very effectively, thereby enabling particularly efficient _the NO _x purification.

As the noble metal raw material compound for preparing a catalyst used in the present invention, nitrates, carbonates, ammonium salts, acetates, halides, oxides and the like can be used in combination. Is preferable from the viewpoint of improving the catalyst performance. The method for supporting the noble metal is not limited to a special method, and various methods such as a well-known evaporation and drying method, a precipitation method, an impregnation method, and an ion exchange method can be used as long as the components are not significantly unevenly distributed. For the support on the zeolite, the ion exchange method is desirable from the viewpoint of ensuring the dispersibility of the noble metal.

The raw material for preparing a catalyst used in the present invention may contain a trace amount of impurities as long as it does not interfere with the above-mentioned action. For example, strontium contained in barium, lanthanum, neodymium contained in cerium, And samarium.

In the present invention thus obtained,
The catalyst for purifying exhaust gas of the present invention can be obtained by pulverizing a noble metal-supported zeolite and alumina to form a slurry, coating the slurry on a catalyst carrier, and calcining the catalyst at a temperature of 400 to 900 ° C.

The catalyst carrier can be appropriately selected from known catalyst carriers, and includes, for example, a honeycomb carrier and a metal carrier having a monolith structure made of a refractory material. Although the shape of the catalyst carrier is not particularly limited, it is usually preferable to use a honeycomb shape. As the honeycomb material, cordierite materials such as ceramics are generally used.
It is also possible to use a honeycomb made of a metal material such as a ferritic stainless steel, and further, the catalyst powder itself may be formed into a honeycomb shape. By making the shape of the catalyst into a honeycomb shape, the area of the catalyst and the exhaust gas becomes large, and the pressure loss can be suppressed.

[0022]

The present invention will be described below with reference to examples and comparative examples. Example 1 ZSM5 type zeolite was impregnated with an aqueous solution of dinitrodiammine Pt, dried and calcined at 400 ° C. for 1 hour to obtain a Pt-supported zeolite powder (powder A). The Pt concentration of this powder A was 3.0% by weight.

426 g of the powder A, the average particle size after pulverization is 10 μm, the pore volume is 0.3 cc / g, and the specific surface area is 150
426 g of m ² / g activated alumina powder (powder B), 240 g of silica sol (solid content: 20%), and 710 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.0 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. Coating layer weight 150g /
An exhaust gas purifying catalyst of the present invention, which is an L-carrier, was obtained.

Example 2 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that an aqueous solution of Rh nitrate was used instead of the aqueous solution of dinitrodiammine Pt in Example 1.

Example 3 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that an aqueous solution of Pd nitrate was used instead of the aqueous solution of dinitrodiammine Pt in Example 1.

Example 4 An exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1 except that an aqueous solution of IrCl was used instead of the aqueous solution of dinitrodiammine Pt in Example 1.

Example 5 ZSM5 type zeolite was impregnated with an aqueous solution of dinitrodiammine Pt, dried and calcined at 400 ° C. for 1 hour to obtain a Pt-supported zeolite powder (powder C) having a Pt-supporting concentration of 2% by weight.

606 g of the powder C, 246 g of the powder B obtained in Example 1, and 2 parts of silica sol (solid content: 20%).
40 g and 710 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.0 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. An exhaust gas purifying catalyst of the present invention having a coat layer weight of 150 g / L-carrier was obtained.

Example 6 ZSM5 type zeolite was impregnated with an aqueous solution of dinitrodiammine Pt, dried and calcined at 400 ° C. for 1 hour to obtain a Pt-supported zeolite powder (powder D) having a Pt-supporting concentration of 5% by weight.

246 g of the powder D, 606 g of the powder B obtained in Example 1, and 2 parts of silica sol (solid content: 20%)
40 g and 710 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.0 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. An exhaust gas purifying catalyst of the present invention having a coat layer weight of 150 g / L-carrier was obtained.

Example 7 Instead of alumina in Example 1, the average particle size was 5 μm.
m, pore volume 0.8 cc / g, specific surface area 210 m ² / g
Except that the alumina powder (powder E) was used, an exhaust gas purifying catalyst of the present invention was obtained in the same manner as in Example 1.

Example 8 ZSM5 type zeolite was impregnated with an aqueous solution of dinitrodiammine Pt and an aqueous solution of Rh nitrate, dried and calcined at 400 ° C. for 1 hour to obtain a zeolite powder carrying Pt and Rh (powder F).
I got The powder F had a Pt concentration of 3.0% by weight and an Rh concentration of 3.0% by weight. An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the powder F was used instead of the powder A in Example 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that ZSM5 type zeolite powder was used instead of activated alumina.
An exhaust gas purifying catalyst was obtained.

Comparative Example 2 Instead of activated alumina in Example 1, alumina powder (powder C) having an average particle size after pulverization of 35 μm, a pore volume of 0.05 cc / g and a specific surface area of 40 m ² / g was used. An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the catalyst was used.

Table 1 shows the catalyst compositions of the exhaust gas purifying catalysts obtained in Examples 1 to 8 and Comparative Examples 1 and 2.

[0036]

[Table 1]

Test Examples The exhaust gas purifying catalysts obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were evaluated for initial and endurance catalytic activities under the following conditions. For the activity evaluation, an automatic evaluation device using a model gas simulating the exhaust gas of an automobile was used.

Endurance conditions A catalyst was attached to the exhaust system of a 4400 cc engine, and operation was performed at a catalyst inlet temperature of 600 ° C. for 50 hours to endurance.

Evaluation condition 1 The catalyst activity was evaluated by mounting each catalyst in the exhaust system of a gasoline engine with a displacement of 2000 cc and setting the catalyst inlet temperature to 300 ° C.
A / F = 14.6 (stoichiometric state) for 60 seconds,
Thereafter, operation was performed for one cycle at A / F = 22 (lean atmosphere) for 30 seconds, then at A / F = 50 (lean atmosphere) for 30 seconds, and the average conversion was measured.
Average conversion rate and A when F = 14.6 (stoichiometric state)
/ F = 22 (lean atmosphere) and average conversion
The average conversion when / F = 50 (lean atmosphere) was averaged to obtain the total conversion.

Evaluation condition 2 Each catalyst was mounted on the exhaust system of a diesel engine with a displacement of 2000 cc, and the catalyst inlet temperature was raised from 150 to 450 ° C.
The temperature was raised over a period of 0 min, was determined the highest conversion rate of the NO _x at that time.

The evaluation conditions 1 and 2 were evaluated at the initial stage and after the endurance, respectively, and the catalyst activity evaluation value was determined by the following equation.

(Equation 1)

Table 2 shows the results of the catalyst activity evaluation obtained as the total conversion. The catalytic activity of the example was higher than that of the comparative example, and the effect of the present invention described later could be confirmed.

[0043]

[Table 2]

[0044]

Effects of the Invention claim 1-2 exhaust gas purifying catalyst described in the prior art catalysts to improve _the NO _x purification performance in the lean atmosphere that did not exhibit sufficient activity, excellent further after thermal endurance _the NO _x purification performance can exhibit.

[0045] In the use of the catalyst for purifying exhaust gases according to claim 3-4, wherein the effective absorption of NO _x of the exhaust gas purifying catalyst of the present invention, it is possible to particularly effectively express release cycle.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 53/36 104A

Claims (4)

[Claims] 1. A zeolite supporting at least one noble metal selected from the group consisting of platinum, palladium, rhodium and iridium, and alumina, wherein the noble metal-supported zeolite is 30 to 200 g per liter of catalyst and alumina is 1 liter of catalyst. In an amount of 30 to 200 g per unit, the average particle size of the alumina is 1 to 30 μm, the pore volume is 0.1 to 1.0 cc / g, and the specific surface area is 50 to 500 m ^2.
/ G, the catalyst for purifying exhaust gas. 2. The exhaust gas according to claim 1, wherein the carried amount of at least one noble metal selected from the group consisting of platinum, palladium, rhodium and iridium is 0.1 to 10 g per liter of the catalyst. Gas purification catalyst. 3. The exhaust gas purifying catalyst according to claim 1, wherein the exhaust gas purifying catalyst is used in a lean burn engine vehicle in which an air-fuel ratio alternates between stoichiometry and 15 to 50. How to use catalyst for 4. The exhaust gas purifying catalyst according to claim 1,
A method for using an exhaust gas purifying catalyst, which is used for a diesel engine vehicle.