JPH06170235A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To provide a catalyst for purification of exhaust gas capable of efficient removal of NOx, CO and hydrocarbon in exhaust gas discharged from the internal-combustion engine of an automobile, etc., when the fuel-air ratio of the exhaust gas is in the range from a stoichiometric state to a lean burning state. CONSTITUTION:A first coating layer of an inorg. material based on activated alumina and contg. platinum and/or palladium is formed on a honeycomb carrier, a second coating layer of an inorg. material based on activated alumina and contg. rhodium is formed on the first coating layer and a third coating layer of an inorg. material based on cerium oxide and powdery zeolite subjected to ion exchange with copper or cobalt is further formed on the second coating layer to obtain the objective catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to exhaust gas purification for purifying hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) which are harmful components emitted from internal combustion engines such as automobiles. For catalysts.

[0002]

2. Description of the Related Art Conventionally, a number of catalysts for purifying exhaust gas have been proposed, and Japanese Patent Laid-Open No. 1-127044 discloses a catalyst for purifying exhaust gas using zeolite. In this exhaust gas purifying catalyst, as a catalyst structure, a honeycomb carrier is provided with a first catalyst layer in which a noble metal is supported on alumina and a second catalyst layer in which copper (Cu) is ion-exchanged with zeolite is provided on the honeycomb catalyst, so that NO _x in the exhaust gas when the oxygen concentration is higher than the theoretical value (lean-burn atmosphere)
Is reduced and removed efficiently even in a lean-burn atmosphere.
O _x, CO, by purifying HC, thereby improving the catalyst performance.

[0003]

However, in such a catalyst layer, the first catalyst layer, which is advantageous for the oxidation reaction using alumina containing a noble metal, and the zeolite ion-exchanged with Cu are used, and NO in a lean burn atmosphere is used. the first in favor of _x reduction removal 2
With the catalyst used as the catalyst layer, the air-fuel ratio (A / F) does not have sufficient catalyst activity under the conditions of stoichiometry during normal running, and the air-fuel ratio is efficiently changed from stoichiometric to lean-burn state with N
_Ox , CO, HC cannot be purified. In addition, the performance deterioration after durability deterioration is large and sufficient NO _x , CO, HC
Can not be purified. Therefore, an object of the present invention is to solve the problems of the conventional exhaust gas purifying catalyst and to provide an exhaust gas purifying catalyst capable of efficiently purifying NO _x , CO and HC from a stoichiometric state to a lean burn state. is there.

[0004]

Means for Solving the Problems The catalyst of the present invention, which has achieved the above object, comprises a honeycomb carrier and a first coat layer made of an inorganic material containing activated alumina containing at least one of platinum and palladium as a main component. A second coating layer formed on the coating layer and made of an inorganic material containing activated alumina containing rhodium as a main component, and further provided thereon a zeolite powder ion-exchanged with copper (Cu) or cobalt (Co) and cerium oxide. And a third coat layer made of an inorganic material containing as a main component.

[0005]

[Operation] Next, the operation will be described. In the exhaust gas purifying catalyst of the present invention, the surface of the first coating layer and the second coating layer containing a noble metal as an active component is composed of zeolite powder ion-exchanged with Cu or Co and an inorganic material containing cerium oxide as a main component. It has a third coat layer. The Cu or Co ion-exchanged zeolite powder and the inorganic substance containing cerium oxide as the main component have NO _x conversion performance in the lean region of engine exhaust gas containing a large amount of oxygen. For the catalyst layer containing a noble metal, the first coat layer and the second coat layer are made of activated alumina mainly composed of Pt and / or Pd-supported alumina and activated alumina mainly composed of Rh-supported alumina. In the preparation stage and during use of the catalyst, there is no decrease in activity due to alloying of Pt and / or Pd with Rh, etc., and it has excellent catalyst conversion performance in the stoichiometric region, so from the stoichiometric region to the lean region It has excellent exhaust gas purification performance in a wide range.

[0006] In addition, the third coat layer uses an inorganic material composed mainly of cerium oxide and zeolite powder ion-exchanged with Cu or Co. The cerium oxide has an oxygen storage capacity and an ability to promote a water gas shift reaction. There is
It functions as a co-catalyst component of zeolite that ion-exchanges Cu or Co. As a result, the action of NO _x purification of the zeolite ion-exchanged with Cu or Co works from a lower temperature and the action of suppressing the durability deterioration of the zeolite occurs.
It has excellent NO _x purification over a wide temperature range even after durability deterioration.

[0007]

EXAMPLES The present invention will be described below with reference to Examples, Comparative Examples and Test Examples. Example 1 Activated alumina powder 1000 containing γ-alumina as a main component
Platinum with dinitrodiammine platinum solution for g
The mixture was added to 1.5 wt% and stirred well, dried in an oven at 150 ° C for 3 hours, and calcined in an air stream at 400 ° C for 2 hours. 1400 g of this platinum-supported activated alumina, 936 g of cerium oxide, 320 g of activated alumina containing γ-alumina as the main component, nitric acid boehmite sol (obtained by adding 10 wt% HNO ₃ to 10 wt% suspension of boehmite alumina) 2221 g of sol) was put into a ball mill pot and pulverized for 8 hours to obtain a slurry. The obtained slurry was applied to a monolith carrier substrate (1.3 L, 400 cells), dried, and then baked at 400 ° C. for 2 hours in an air atmosphere to form a first coat layer. The coating amount at this time is after firing
It was set to be 160 g / piece.

Next, a solution of rhodium nitrate in Rh was added to 1000 g of activated alumina powder containing γ-alumina as a main component.
After adding 1% by weight and stirring well, it was dried and calcined in the same manner to prepare a rhodium-supporting alumina powder. 500 g of this rhodium-supported alumina powder, 637 g of nitric acid-acidified boehmite sol, and 265 g of activated alumina powder containing γ-alumina as a main component were put into a ball mill pot, and 8
The slurry obtained by pulverizing for an hour was applied so that the coating amount after baking was 40 g / piece, dried, and then baked in an air atmosphere at 400 ° C. for 2 hours to form a second coat layer.

Further, Cu powder is ion-exchanged with a 0.2 mol / L copper nitrate or copper acetate solution to obtain a zeolite powder 18.
20 g, 1150 g of silica sol (solid content 20%), 70 g of cerium oxide powder, and 1100 g of water were charged into a magnetic ball mill,
The slurry obtained by crushing was applied to the above-mentioned carrier after the amount of coating 160
After coating so as to be g / piece and drying, it was baked in air at 400 ° C. for 2 hours to form a third coat layer to prepare catalyst No.1.

Example 2 The amount of cerium oxide added to the third coat layer was changed to Ce in the catalyst layer.
As catalyst No. 1 in the same manner as in Example 1 except that 15% by weight of Ce was used instead of 3% by weight of catalyst No.
2 was prepared.

Monolith honeycomb carrier as in Example 1
(1.3 L, 400 cells) was coated with a first coat layer containing Pt and a second coat layer containing Rh. Further, 1550 g of zeolite powder ion-exchanged with Cu using a 0.2 mol / L copper nitrate or copper acetate solution on the second coat layer, 1150 g of silica sol (solid content 20%) and cerium oxide (Ce).
340 g of O ₂ ) powder and 1100 g of water were put into a magnetic ball mill, and the slurry obtained by pulverizing was applied so that the applied amount was 130 g / piece, dried, and then baked in air at 400 ° C. for 2 hours to make the third coat. Layers were formed to prepare catalyst No.2.

Example 3 A catalyst No. 3 was prepared in the same manner as the catalyst No. 1 of Example 1 except that cobalt was used instead of copper as the ion exchange metal species.

Monolith honeycomb carrier as in Example 1
(1.3 L, 400 cells) was coated with a first coat layer containing Pt and a second coat layer containing Rh. In addition, this second
1820 g of Co powder ion-exchanged with 0.2 mol / L cobalt nitrate or cobalt acetate solution on the coating layer, 1150 g of silica sol (solid content 20%), 70 g of cerium oxide (CeO ₂ ) powder, and 1100 g of water are magnetic. Put in a ball mill and pulverize the resulting slurry to obtain a coating weight of 130 g.
Then, the catalyst No. 3 was prepared by coating and drying so that the number becomes 1 / piece, and baking in air at 400 ° C. for 2 hours to form a third coat layer.

Example 4 A catalyst No. 4 was prepared in the same manner as the catalyst No. 1 of Example 1 except that palladium was used instead of platinum as the noble metal of the first coat layer.

Dinitrodiammine palladium solution was added to 1000 g of activated alumina powder containing γ-alumina as a main component so as to be 1.5% by weight of palladium, and the mixture was similarly dried and calcined at 400 ° C. for 2 hours in an air stream. went. 1400 g of this palladium-supported activated alumina, 936 g of cerium oxide, 320 g of activated alumina containing γ-alumina as a main component, and nitric acid boehmite sol (obtained by adding 10 wt% HNO ₃ to 10 wt% boehmite alumina suspension) 2221 g of sol) was put into a ball mill pot and pulverized for 8 hours to obtain a slurry. The obtained slurry was applied to a monolith carrier substrate (1.3 L, 400 cells), dried, and then calcined at 400 ° C. for 2 hours in an air atmosphere.
A coat layer was formed. The coating amount at this time was set to 160 g / piece. Preparation and application of the rhodium-supported powder and preparation and application of the zeolite powder coating layer were carried out in the same manner as in Example 1 to obtain catalyst No. 4.

Example 5 A catalyst N was prepared in the same manner as in Example 4, except that platinum-supported alumina and a palladium-supported alumina layer were applied as the first coat layer of the catalyst No. 4 in place of the palladium-supported alumina layer.
o.5 was prepared.

As a slurry of platinum-supported alumina and palladium-supported alumina layers, 2.1% by weight of platinum and palladium were used.
Catalyst No. 4 except that 2.1% by weight of platinum-supported activated alumina and 700 g of palladium-supported alumina were used, respectively.
Catalyst No. 5 was prepared in the same manner as in. As the zeolite powder used here, ZSM-5 zeolite, mordenite, ferrierite, or the like can be used.

Comparative Examples 1 and 2 In Comparative Example 1, catalyst No. 101 was prepared by coating only the catalyst layers containing the noble metal of the first coat layer and the second coat layer in the same manner as in Example 1, followed by drying and firing. It was used as a catalyst.

A catalyst No. 201 was prepared by applying only zeolite powder having Cu ion-exchanged to a monolith carrier substrate (1.3 L, 400 cells) at 260 g / unit, and used as a catalyst of Comparative Example 2.

Test Examples For the catalysts of the respective Examples and Comparative Examples, each catalyst was filled in an experimental converter, and after being subjected to durability under the following conditions with engine exhaust gas, performance was evaluated under the following conditions using an exhaust model gas. An evaluation test was conducted. A / F in the test
The evaluation results (after endurance) at = 14.7 are shown in Table 3, and A / F = 18.0.
Table 4 shows the evaluation results (after endurance).

[0021]

[Table 1] Durability condition engine Displacement 2000cc Durability temperature: 650 ° C Durability time: 100 hours Durability medium inlet emission CO 0.4-0.6% O ₂ 0.5 ± 0.1% NO 1500ppm HC 1000ppm CO ₂ 14 9.9% ± 0.1%

[0022]

[Table 2] Performance evaluation conditions Catalyst capacity: 0.12L Evaluation device: Exhaust model gas evaluation device (gas used is cylinder gas) Catalyst inlet temperature 400 ° C Space velocity approx. 20,000h ^-1 A / F = 14.7 equivalent model gas HC = 1600 ppm (C1 converted) NO = 1000ppm CO = 1.08% CO 2 = 14.0% O 2 = 0.9% H 2 O = 10% H 2 = 0.4% N 2 balance a of Model gas equivalent to /F=18.0 HC = 2500 ppm (C1 conversion) NO = 500 ppm CO ₂ = 14.0% CO = 1200 ppm H ₂ O = 10% O ₂ = 4.5% N ₂ balance

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

As described above, the exhaust gas purifying catalyst of the present invention comprises a honeycomb carrier, and a first coat layer made of an inorganic material containing activated alumina containing at least one of platinum and palladium as a main component. A second coating layer made of an inorganic material containing activated alumina containing rhodium as a main component, which is provided on the coating layer, and a Cu or Co ion-exchanged zeolite powder and a cerium oxide powder which are further provided on the coating layer. By including the third coat layer made of an inorganic material as a component, the catalyst has a catalytic activity from the stoichiometric region to the lean region even after deterioration of durability.

Front Page Continuation (72) Inventor Naoki Kachi 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. A first coat layer made of an inorganic material whose main component is activated alumina containing at least one of platinum and palladium on a honeycomb carrier, and a main component of activated alumina containing rhodium provided on the coating layer. 2nd consisting of inorganic material
An exhaust gas purifying catalyst comprising a coat layer and a third coat layer formed on the coat layer, the zeolite powder being ion-exchanged with copper or cobalt, and an inorganic substance containing cerium oxide as a main component. .