JPH09220470A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ternary catalyst having improved NOx removing performance in a lean atmosphere and excellent in durability. SOLUTION: At least two kinds of catalysts are arranged in a flow of exhaust gas from an engine. A zeolite-contg. catalyst carrying copper is disposed on the upper stream side and a catalyst contg. at least one kind of transition metal selected from among Fe, Co, Ni and Mn, Ba, La and at least one kind of noble metal selected from among Pt, Pd and Rh is disposed on the downstream side. The transition metal, Ba and La are partially or entirely in the form of a multiple oxide and the latter catalyst consists of an inner layer contg. the multiple oxide and a surface layer contg. the noble metal and silica-alumina.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas discharged from internal combustion engines such as gasoline and diesel automobiles and boilers.
The present invention also relates to an exhaust gas purifying catalyst that purifies nitrogen oxides (NOx), and particularly to an exhaust gas purifying catalyst that has excellent NOx purifying performance in an oxygen excess atmosphere.

[0002]

2. Description of the Related Art In recent years, fuel-efficient vehicles are expected to be realized from the viewpoints of exhaustion of petroleum resources and global warming, and particularly lean-burn vehicles are desired to be developed for gasoline vehicles. . In lean-burn vehicles, the exhaust gas atmosphere during lean-burn running is the theoretical air-fuel state (hereinafter,
An oxygen-excess atmosphere (hereinafter referred to as "lean atmosphere") is obtained as compared with a "stoichiometric state". When a conventional three-way catalyst is applied in a lean atmosphere, there is a problem that the NOx purification action becomes insufficient due to the influence of excess oxygen. Therefore, even in an oxygen excess atmosphere, NO
It has been desired to develop a catalyst that can purify x.

Conventionally, NOx has been used in a lean atmosphere.
Various catalysts for improving purification performance have been proposed. As a typical example thereof, lanthanum or the like as disclosed in JP-A-5-168860 is platinum (Pt).
There is a catalyst in which lanthanum is carried on and used as a NOx absorbent. It absorbs NOx in a lean atmosphere,
N in a stoichiometric condition or in an excess fuel (rich) atmosphere
It is intended to release and purify Ox.

However, the catalyst disclosed in Japanese Unexamined Patent Publication No. 5-168860 has a problem that the NOx absorption capacity is insufficient. For the purpose of solving such a problem, for example, in Japanese Unexamined Patent Publication No. 5-261287, Kaihei 5-31765
No. 2 and JP-A-6-31139 disclose an exhaust gas purifying catalyst using an alkali metal or an alkaline earth metal. Further, JP-A-6-142458 and JP-A-6-262040 disclose exhaust gas purifying catalysts containing an alkali metal, an alkaline earth metal, a rare earth metal and an iron group metal.

[0005]

However, the above-mentioned conventional exhaust gas purifying catalyst has no NO in a lean atmosphere.
The x absorption performance is insufficient, and particularly the NOx absorption performance after endurance is insufficient.

Further, in such a NOx absorption type catalyst, since the NOx absorbed in the lean atmosphere has to be purified in the stoichiometric or rich state, the function as a three-way catalyst is also required at the same time, but as described above. If a considerable amount of alkali metal or alkaline earth metal is added in order to obtain a sufficient NOx absorption function, the strong basicity of alkali metal or alkaline earth metal will affect the catalytic performance and reduce the oxidizing ability of precious metals. , H as a three-way catalyst
There is a problem that the conversion performance of C and CO becomes insufficient. Furthermore, since the noble metal and the NOx absorbent contact each other,
There is a problem that the NOx purification reaction is hindered.

Therefore, the object of the present invention is to provide NO in a lean atmosphere which has not been sufficiently activated by conventional catalysts.
It is intended to provide an exhaust gas purifying catalyst that can improve x purification performance and that can sufficiently exhibit the function as a three-way catalyst even after endurance.

[0008]

As a result of research for solving the above problems, the present inventors have found that at least one transition metal selected from the group consisting of iron, cobalt, nickel and manganese, barium and lanthanum The present invention was found to improve the NOx absorption performance in a lean atmosphere by including a composite oxide composed of and a noble metal selected from the group consisting of platinum, palladium and rhodium, and arrived at the present invention.

The catalyst for purifying exhaust gas according to claim 1 has at least one transition metal selected from the group consisting of iron, cobalt, nickel and manganese, barium, lanthanum and platinum on a refractory inorganic carrier. At least one noble metal selected from the group consisting of palladium, rhodium, and the transition metal, barium, and lanthanum are partly or wholly complex oxides.

In order to further improve the HC and CO activities of the catalyst, the exhaust gas purifying catalyst according to claim 2 is selected from the group consisting of iron, cobalt, nickel and manganese on a refractory inorganic carrier. At least one transition metal, barium, and a catalyst inner layer containing a complex oxide containing lanthanum, at least one precious metal selected from the group consisting of platinum, palladium and rhodium, containing the above complex oxide And a catalyst surface layer containing no silica-alumina.

Further, in order to further enhance the NOx absorbing action of the exhaust gas purifying catalyst according to claim 1 or 2, the exhaust gas purifying catalyst according to claim 3 has at least two catalysts in an engine exhaust gas flow. A copper-containing zeolite-containing catalyst is provided upstream of the exhaust gas flow, and downstream of the exhaust gas flow.
Alternatively, the catalyst described in 2 is arranged.

Further, in order to further improve the NOx purification performance of the exhaust gas purifying catalyst according to any one of claims 1 to 3, claim 4
The exhaust gas purifying catalyst as described above is characterized in that, in the exhaust gas purifying catalyst according to any one of claims 1 to 3, silica in the silica alumina is 0.5 to 20% by weight.

At least one selected from the group consisting of platinum, palladium and rhodium is used as the noble metal used in the exhaust gas purifying catalyst of the present invention. The content of the noble metal in the catalyst is not particularly limited as long as sufficient NOx absorption capacity and three-way catalyst performance during stoichiometry are obtained,
If the amount is less than 0.1 g, sufficient ternary performance cannot be obtained, and
The amount is preferably 0.1 to 10 g per 1 L of the catalyst, since no significant improvement in properties is observed even if the amount is used in excess of g.

The transition metal used in the exhaust gas purifying catalyst of the present invention is at least one selected from the group consisting of iron, cobalt, nickel and manganese. The content of the transition metal in the catalyst is preferably 1 to 100 g per 1 L of the catalyst in terms of metal oxide weight. If it is less than 1 g, the NOx absorption performance of the complex oxide cannot be sufficiently obtained, and if it exceeds 100 g, no significant amount increasing effect can be obtained.

Further, the content of lanthanum used in the exhaust gas purifying catalyst of the present invention is preferably 1 to 100 g per 1 L of the catalyst in terms of metal oxide weight. 1 g
If it is less than 100 g, the NOx absorption performance of the composite oxide cannot be sufficiently obtained, and if it exceeds 100 g, a significant effect of increasing the amount cannot be obtained.

The content of barium used in the exhaust gas purifying catalyst of the present invention is 1 L of the catalyst in terms of metal oxide weight.
Per barium is preferably 1 to 100 g.
If the amount is less than this, sufficient NOx absorption capacity cannot be obtained,
In addition, a significant amount increase effect cannot be obtained even if a larger amount is added.

The transition metal, lanthanum, and barium are partly or wholly complexed to form a composite oxide of the component. It is preferable that all of the above-mentioned components contained in the complex oxide are complexed, but at least a part thereof may be complexed. By using the composite oxide having the above composition, the NOx oxidation reaction required for NOx absorption is further enhanced, and an excellent NOx absorption action is obtained.

By using such a composition of the present invention, it is possible to enhance the ability to purify NOx emitted from the absorbent. This is because the composite oxide is NO
This is because it is excellent in the action of absorbing x, and platinum, palladium or rhodium is excellent in the ability to purify NOx released from the composite oxide.

In particular, the exhaust gas purifying catalyst according to claim 2 is formed by combining the catalyst inner layer containing the composite oxide and the catalyst surface layer containing the noble metal. The complex oxide should not be contained in the surface layer of the catalyst, because this is to maintain the oxidation performance of noble metals for HC and CO at a sufficiently high level without deteriorating.

By adopting the two-layer structure, the function of absorbing NOx is shared by the inner layer of the catalyst, and the function of purifying the released NOx is shared by the surface layer of the catalyst. Here, the emission NOx purification action is improved by removing transition metals, barium, and lanthanum, which interfere with NOx purification, from the catalyst surface layer, and by removing NO from the catalyst surface layer.
x By dispersing palladium and rhodium, which are purification components, on silica-alumina, which has many acid points, the interaction between precious metals and HC (hydrocarbons) in exhaust gas is strengthened, and H
This is because the reaction of converting C and NOx into CO ₂ , N _{2 and} H ₂ O is promoted.

As the base material for supporting the noble metal in the surface layer of the catalyst, an inorganic material having a large number of acid sites is suitable for enhancing the interaction between the noble metal and HC in the exhaust gas, and silica alumina is particularly preferable. This significantly improves the NOx purification performance. The silica-alumina contained in the catalyst is preferably an alumina containing 0.5 to 20% by weight of silica. If it is less than 0.5% by weight, the amount of acid sites on the silica aluminum is not sufficiently obtained, so that the NOx purification activity is insufficient, and if it exceeds 20% by weight, the dispersibility retaining ability of the noble metal is insufficient. Activity after endurance deteriorates. If the amount of silica-alumina used is less than 10 g per liter of catalyst, sufficient noble metal dispersibility cannot be obtained and the performance deteriorates. Even if it is used in excess of 180 g, NOx absorption performance does not improve and a significant increase effect is obtained. Therefore, the amount is preferably 10 to 180 g. The amount of the noble metal-supporting base material used is not particularly limited, but is preferably 50 to 300 g per 1 L of the catalyst.

Further, for the purpose of promoting the NOx absorbing action in the inner layer of the catalyst as well, 0.1 g to 1 g per 1 L of the catalyst is used.
It is also possible to contain 0 g of noble metal. For the precious metal-supporting base material in the catalyst inner layer, a heat-resistant inorganic material having a high specific surface area is suitable for ensuring the dispersibility of the precious metal, alumina,
Silica alumina, zirconia, etc. can be used.
In particular, activated alumina is preferable, and activated alumina to which a rare earth element, zirconium or the like is added may be used to increase the heat resistant specific surface area.

In the invention according to claim 3, the content of the Cu-supporting zeolite catalyst provided on the upstream side with respect to the exhaust gas flow is not particularly limited as long as it exhibits a NOx purification action, but from 50 g If the amount is small, sufficient NOx reduction performance cannot be obtained, and even if it is used in excess of 300 g, no significant performance improvement can be seen.
00 g is preferred. In order to improve the catalytic activity and durability, for example, Co, Ca, P, Ce, Nd or the like may be added. As a method for supporting Cu, any known method can be used, but from the viewpoint of the dispersibility of Cu and the Cu ⁺ (monovalent) state, it can be supported on zeolite by ion exchange. preferable. As the zeolite, those having high activity after Cu ion exchange and excellent heat resistance are preferably used, and examples thereof include pental-type zeolite, Y-type zeolite, mordenite, and ferrierite.

The Cu-supported zeolite catalyst according to claim 1,
In the method of installing the catalyst in the exhaust system according to claim 2, the Cu-supported zeolite catalyst is installed upstream of the exhaust gas flow, and the catalyst of claim 1 or 2 is installed downstream of the exhaust gas flow. It is important to use a known method such as a method of mounting and arranging two kinds of catalysts in one catalytic converter, or a method of installing the two kinds of catalysts in separate converters. You can By once contacting the exhaust gas with the Cu-supported zeolite catalyst, the absorption action of the NOx absorption catalyst in the subsequent stage is enhanced. The absorption action is, for example, that the oxidation of NOx necessary for NOx absorption in the Cu-supported zeolite catalyst rapidly progresses to assist the function of the NOx absorbent, and that the Cu-supported zeolite catalyst favors HC, which is convenient for NOx absorption. It is considered that the NOx and O ₂ concentrations are converted.

The installation position of the catalyst is not particularly limited, and examples thereof include a position directly under the manifold and a position under the floor. If the purification performance is not sufficient with one catalyst in each of the first and second stages of the catalyst system, one or both of the first and second stages may be further provided, or multiple catalysts may be added.

The catalyst carrier used in the present invention can be appropriately selected and used from known catalyst carriers, and examples thereof include a honeycomb carrier having a monolith structure made of a refractory material, a metal carrier and the like. The shape of this catalyst carrier is not particularly limited, but it is usually preferable to use it in a honeycomb shape, and as this honeycomb material,
In general, many cordierite materials such as ceramics are used, but it is also possible to use a honeycomb made of a metal material such as ferritic stainless steel, and 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 is suppressed, which is extremely advantageous when the catalyst is used for an automobile or the like.

In the method of supporting the composite oxide in the production of the exhaust gas purifying catalyst of the present invention, a monolith carrier is coated with a water-soluble slurry obtained by pulverizing a powder of an inorganic carrier such as alumina by a wet method, and then dried. After that, it is fired and then impregnated with an aqueous solution containing the metal salt of each component constituting the composite oxide, or the aqueous solution containing each metal salt of the composite oxide component is dried and fired to obtain the oxidation. There is a method in which an object powder is prepared in advance, the powder is mixed with a powder such as alumina, and a water-soluble slurry pulverized by a wet method is coated on a monolith carrier, dried and baked to be carried.

[0028]

The present invention will be described with reference to the following examples and comparative examples. Embodiment 1 FIG . The activated alumina powder was impregnated with a rhodium nitrate aqueous solution, dried and then calcined at 400 ° C. for 1 hour to obtain an Rh-supported activated alumina powder (powder A). The Rh concentration of this powder A was 2.0% by weight. The activated alumina powder was impregnated with an aqueous palladium nitrate solution, dried and then baked at 400 ° C. for 1 hour to obtain a Pd-supported activated alumina powder (powder B). The Pd concentration of this powder B was 2.0% by weight. 5 silica
% Of the silica-alumina powder was impregnated with a rhodium nitrate aqueous solution, dried, and then baked at 400 ° C. for 1 hour to obtain Rh-supported silica-alumina powder (powder C). Rh of this powder C
The concentration was 2.0% by weight. A silica-alumina powder containing 5% of silica was impregnated with an aqueous palladium nitrate solution, dried and then baked at 400 ° C. for 1 hour to obtain a Pd-supported silica-alumina powder (powder D). The Pd concentration of this powder D is 2.
It was 0% by weight.

The above Rh-supported activated alumina powder A was added to 53
g, 266 g of Pd-supported activated alumina powder B, 581 g of activated alumina powder, and 900 g of water in a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This slurry liquid was used as a cordierite monolith carrier (1.3 L, 400 L
(Cell), the excess slurry in the cell was removed by an air flow, and the coating was dried at 130 ° C. and then baked at 400 ° C. for 1 hour to obtain a material having a coat layer weight of 100 g / L-carrier.

The coating layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and fired to give a coating layer weight of 1
60 g / L-carrier material was obtained. The content of barium, lanthanum, and manganese in the material was 20 g / L in terms of oxide.

The above Rh-supported silica-alumina powder C was added to 53
g, 266 g of Pd-supported silica-alumina powder D, 581 g of silica-alumina powder containing 5% by weight of silica and 900 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 the above-mentioned material of 160 g / L-carrier, the excess slurry in the cell was removed by an air flow, dried at 130 ° C., and then baked at 400 ° C. for 1 hour to give a coat layer weight of 260 g / L. A carrier exhaust gas purification catalyst 1 was obtained.

Embodiment 2 FIG. An exhaust gas purifying catalyst 2 was obtained in the same manner as in Example 1 except that silica alumina containing 2% by weight of silica was used.

Example 3 Exhaust gas purifying catalyst 3 was obtained in the same manner as in Example 1 except that silica-alumina containing 18% by weight of silica was used.

Example 4 A silica-alumina powder containing 5% by weight of silica was impregnated with an aqueous rhodium nitrate solution, dried and then calcined at 400 ° C. for 1 hour to obtain Rh-supported silica-alumina powder (powder E). The Rh concentration of this powder E is 10.0.
% By weight. Further, a silica-alumina powder containing 5% by weight of silica was impregnated with an aqueous palladium nitrate solution, dried and then baked at 400 ° C. for 1 hour to obtain a Pd-supported silica-alumina powder (powder F). The Pd concentration of this powder F was 10.
It was 0% by weight.

Rh-supported activated alumina powder A53g obtained in Example 1 and Pd-supported activated alumina powder B266g,
581 g of activated alumina powder and 900 g of water were put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was used as a cordierite monolith carrier (1.3 L,
(400 cells), the excess slurry in the cells was removed by an air flow, and the coating was dried at 130 ° C. and then baked at 400 ° C. for 1 hour to obtain a material having a coat layer weight of 100 g / L-carrier.

The coating layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and baked to give a coating layer weight of 1
60 g / L-carrier material was obtained. Barium, lantern,
The manganese content was 20 g / L in terms of oxide.

The Rh-supported silica-alumina powder E was added to 53
g, 266 g of Pd-supported silica-alumina powder F, 581 g of silica-alumina powder containing 5% by weight of silica and 900 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 the material of the above-mentioned 160 g / L-carrier, excess slurry in the cell was removed by an air stream, dried at 130 ° C., and then baked at 400 ° C. for 1 hour to give a coat layer weight of 180 g / L. -A carrier exhaust gas purification catalyst 4 was obtained.

Example 5 A silica-alumina powder containing 5% by weight of silica was impregnated with an aqueous rhodium nitrate solution, dried and then baked at 400 ° C. for 1 hour to obtain Rh-supported silica-alumina powder (powder G). The Rh concentration of this powder G was 1.3% by weight. A silica-alumina powder containing 5% by weight of silica was impregnated with an aqueous palladium nitrate solution and dried to give 400
Firing at 1 ° C. for 1 hour gave a Pd-supported silica-alumina powder (powder H). The Pd concentration of this powder H was 1.3% by weight.

53 g of the Rh-supported activated alumina powder A obtained in Example 1 and 266 of the Pd-supported activated alumina powder B were obtained.
g, activated alumina powder (581 g) and water (900 g) were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This slurry liquid was used as a cordierite monolith carrier (1.
(3 L, 400 cells), remove excess slurry in the cells by air flow and dry at 130 ° C., then
The material was baked at 0 ° C. for 1 hour to obtain a material having a coat layer weight of 100 g / L-carrier.

The coating layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and baked to give a coating layer weight of 1
60 g / L-carrier material was obtained. The content of barium, lanthanum, and manganese in the material was 20 g / L in terms of oxide.

The Rh-supported silica-alumina powder G was added to 53
g, 266 g of Pd-supported silica-alumina powder H, 581 g of silica-alumina powder containing 5% by weight of silica and 900 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 the above-mentioned 160 g / L-carrier, the excess slurry in the cell was removed by an air stream, dried at 130 ° C., and then baked at 400 ° C. for 1 hour to give a coat layer weight of 310 g / L-carrier. Thus, the exhaust gas purifying catalyst 5 was obtained.

Example 6 900 g of activated alumina powder,
900 g of water was charged into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite-based monolith carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air flow, and the temperature was adjusted to 130 ° C.
And dried at 400 ° C for 1 hour, and coat layer weight 1
A material of 00 g / L-carrier was obtained.

The coat layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and baked to give a coat layer weight of 1
60 g / L-carrier material was obtained. The content of barium, lanthanum, and manganese in the material was 20 g / L in terms of oxide.

635 g of Pd-supported silica-alumina powder D obtained in Example 1, 265 g of silica-alumina powder containing 5% by weight of silica, and 900 g of water were charged into a magnetic ball mill and mixed and ground to obtain a slurry liquid. . This slurry liquid was adhered to the above-mentioned material of 160 g / L-carrier, the excess slurry in the cell was removed by an air flow, and dried at 130 ° C., and then baked at 400 ° C. for 1 hour, and the coating layer weight 26
An exhaust gas purifying catalyst 6 of 0 g / L-carrier was obtained.

Example 7 A silica-alumina powder containing 5% by weight of silica was impregnated with a dinitrodiamine platinum aqueous solution, dried and calcined at 400 ° C. for 1 hour to obtain a platinum-supported silica-alumina powder (powder I). The Pt concentration of this powder I was 2.0% by weight.

900 g of activated alumina powder and 900 g of water
It was put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed with an air stream, and dried at 130 ° C, followed by firing at 400 ° C for 1 hour, Coat layer weight 100g /
An L-carrier material was obtained.

The coat layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and baked to give a coat layer weight of 1
60 g / L-carrier material was obtained. The content of barium, lanthanum, and manganese in the material was 20 g / L in terms of oxide.

103 g of the Rh-supported silica-alumina powder C obtained in Example 1, 532 g of the platinum-supported silica-alumina powder I, 265 g of silica-alumina containing 5% by weight of silica, and 900 g of water were charged into a magnetic ball mill,
The mixture was pulverized to obtain a slurry liquid. This slurry liquid was adhered to the above-mentioned material of 160 g / L-carrier, excess slurry in the cell was removed by an air stream, dried at 130 ° C., and then baked at 400 ° C. for 1 hour to give a coat layer weight of 260 g /
An L-carrier exhaust gas purification catalyst 7 was obtained.

Example 8 Platinum-supported silica-alumina powder I
In the same manner as in Example 7 except that the Pd-supported silica-alumina powder D obtained in Example 1 is used instead of
Exhaust gas purification catalyst 8 was obtained.

Example 9 The activated alumina powder was impregnated with a dinitrodiamine platinum aqueous solution, dried and then baked at 400 ° C. for 1 hour to obtain a platinum-supported silica alumina powder (powder J). The Pt concentration of this powder J was 2.0% by weight.

Example 2 was repeated except that the platinum-supported silica alumina powder J was used in place of the Pd-supported activated alumina powder B and the platinum-supported silica alumina powder I obtained in Example 7 was used in place of the Pd-supported silica alumina powder D. Exhaust gas purifying catalyst 9 was obtained in the same manner as in Example 1.

Example 10 Rh-supported activated alumina powder A
In the same manner as in Example 1 except that Pd-supporting activated alumina powder B is used instead of Rh and Pd-supporting silica alumina powder D is used instead of Rh-supporting silica alumina powder C.
An exhaust gas purifying catalyst 10 was obtained.

Example 11 An exhaust gas purifying catalyst 11 was obtained in the same manner as in Example 1 except that iron acetate was used instead of manganese acetate.

Example 12 An exhaust gas purifying catalyst 12 was obtained in the same manner as in Example 1 except that cobalt acetate was used instead of manganese acetate.

Example 13 An exhaust gas purification catalyst 13 was obtained in the same manner as in Example 1 except that nickel acetate was used instead of manganese acetate.

Example 14 After mixing 5.2 Kg of 0.2 mol / L copper nitrate aqueous solution and 2 Kg of zeolite powder,
The operations of stirring and filtering were repeated three times, and then dried and calcined to obtain Cu-supporting zeolite powder (powder K). The Cu concentration of this powder was 5% by weight.

810 of the above Cu-supporting zeolite powder K was added.
g, silica sol (solid content 20%) 450 g, water 54
It was put into a 0 g magnetic ball mill, mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed with an air stream, and dried at 130 ° C, followed by firing at 400 ° C for 1 hour, Coat layer weight 200g
A material for the / L-carrier was obtained. The coat layer weight 200 g /
The material of the L-carrier was placed before the exhaust gas flow, Example 1
The exhaust gas purifying catalyst 1 obtained in step 1 was placed in the latter stage to obtain an exhaust gas purifying catalyst 14.

Example 15 An exhaust gas purifying catalyst 15 was obtained in the same manner as in Example 14 except that the exhaust gas purifying catalyst 7 obtained in Example 7 was used instead of the exhaust gas purifying catalyst 1.

Example 16 An exhaust gas purification catalyst 16 was obtained in the same manner as in Example 14 except that the exhaust gas purification catalyst 8 obtained in Example 8 was used instead of the exhaust gas purification catalyst 1.

Example 17 An exhaust gas purifying catalyst 17 was obtained in the same manner as in Example 14 except that the exhaust gas purifying catalyst 19 obtained in Example 9 was used in place of the exhaust gas purifying catalyst 1.

Example 18 An exhaust gas purifying catalyst 18 was obtained in the same manner as in Example 14 except that the exhaust gas purifying catalyst 10 obtained in Example 10 was used in place of the exhaust gas purifying catalyst 1.

Example 19 An exhaust gas purification catalyst 19 was obtained in the same manner as in Example 14 except that the exhaust gas purification catalyst 12 obtained in Example 12 was used in place of the exhaust gas purification catalyst 1.

Comparative Example 1 An exhaust gas purification catalyst 20 was obtained in the same manner as in Example 1 except that silica alumina containing 0.2% by weight of silica was used.

Comparative Example 2 An exhaust gas purifying catalyst 21 was obtained in the same manner as in Example 1 except that silica alumina containing 30% by weight of silica was used.

Comparative Example 3 53 g of Rh-supporting activated alumina powder A obtained in Example 1, 266 g of Pd-supporting activated alumina powder B, 581 g of activated alumina powder, and 90 parts of water.
It was put into a 0 g magnetic ball mill, mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed with an air stream, and dried at 130 ° C, followed by firing at 400 ° C for 1 hour, Coat layer weight 100g
A material for the / L-carrier was obtained.

The coat layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and fired to give a coat layer weight of 1
60 g / L-carrier material was obtained. The content of barium, lanthanum, and manganese in the material was 20 g / L in terms of oxide.

106 g of Rh-supporting silica alumina powder E obtained in Example 14 and Pd-supporting silica alumina powder F
532 g and 900 g of water were put into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This slurry liquid is
60 g / L-After being adhered to the material of the carrier, the excess slurry in the cell was removed by an air stream, and dried at 130 ° C.,
Baking at 400 ° C. for 1 hour, coat layer weight 167 g / L-
A catalyst 22 for purifying the exhaust gas of the carrier was obtained.

Comparative Example 4 A rhodium nitrate aqueous solution was impregnated into silica-alumina powder containing 5% by weight of silica, dried and calcined at 400 ° C. for 1 hour to obtain Rh-supported silica-alumina powder (powder L). The Rh concentration of this powder was 1.0% by weight. A silica-alumina powder containing 5% by weight of silica was impregnated with an aqueous palladium nitrate solution, dried and then baked at 400 ° C. for 1 hour to obtain a Pd-supported silica-alumina powder (powder M). The Pd concentration of this powder M was 1.0% by weight.

53 g of Rh-supporting activated alumina powder A and 266 of Pd-supporting activated alumina powder B obtained in Example 1 were obtained.
g, activated alumina powder (581 g) and water (900 g) were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This slurry liquid was used as a cordierite monolith carrier (1.
(3 L, 400 cells), remove excess slurry in the cells by air flow and dry at 130 ° C., then
The material was baked at 0 ° C. for 1 hour to obtain a material having a coat layer weight of 100 g / L-carrier.

The coat layer weight 100 g / L-The carrier material was impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and fired to give a coat layer weight of 1
60 g / L-carrier was obtained. The content of barium, lanthanum and manganese in the material is 20 g / oxide.
L.

53 g of Rh-supporting silica alumina powder G and 2 g of Pd-supporting silica alumina powder H obtained in Example 5 were obtained.
66 g, 581 g of silica-alumina powder containing 5% by weight of silica, and 900 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid is
After being attached to 60 g / L-carrier, the excess slurry in the cell was removed by an air flow and dried at 130 ° C., 400
Firing at 1 ° C. for 1 hour gave an exhaust gas purifying catalyst 23 having a coat layer weight of 360 g / L-carrier.

Comparative Example 5 Rh-supported silica-alumina powder C
Exhaust gas purifying catalyst 24 was obtained in the same manner as in Example 1 except that Rh-supporting activated alumina powder A was used in place of Pd, and Pd-supporting active alumina powder B was used in place of Pd-supporting silica alumina powder D. .

Comparative Example 6 103 g of the Rh-supported silica alumina powder C obtained in Example 1, 532 g of the Pd-supported silica alumina powder D, 265 g of activated alumina powder, and 900 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed with an air stream, and dried at 130 ° C, followed by firing at 400 ° C for 1 hour, Coat layer weight 1
A material of 00 cell / L-carrier was obtained.

Weight of coat layer 100 g / L-The material of the carrier is impregnated and supported with a mixed aqueous solution of barium acetate, manganese acetate and lanthanum acetate, dried and fired to give a coat layer weight of 1
60 g / L of exhaust gas purifying catalyst 25 was obtained. The contents of barium, lanthanum and manganese in the exhaust gas purification catalyst were each 20 g / L in terms of oxide.

Comparative Example 7 Exhaust gas purifying catalyst 2 was prepared in the same manner as in Example 1 except that manganese acetate was not used.
6 was obtained. The total coat weight of this exhaust gas purification catalyst is 2
It was 40 g / L.

Comparative Example 8 Exhaust gas purifying catalyst 2 was prepared in the same manner as in Example 1 except that barium acetate was not used.
7 was obtained. The total coat weight of this exhaust gas purification catalyst is 2
It was 40 g / L.

Comparative Example 9 Exhaust gas purification catalyst 2 was prepared in the same manner as in Example 1 except that lanthanum acetate was not used.
8 was obtained. The total coat weight of this exhaust gas purification catalyst is 2
It was 40 g / L.

Table 1 shows the catalyst compositions of the exhaust gas purifying catalysts 1-28 obtained in the above Examples 1-19 and Comparative Examples 1-9.

[0079]

[Table 1]

Test Example The catalysts and catalyst systems of Examples 1 to 19 and Comparative Examples 1 to 9 were evaluated for catalyst activity under the following conditions at the initial stage and after endurance. For the activity evaluation, an automatic evaluation device using a model gas simulating the exhaust gas of an automobile was used.

Endurance condition A catalyst is attached to the exhaust system of the engine 4400 cc, and 600
Durability was performed by operating at 50 ° C. for 50 hours.

Evaluation conditions In the catalyst activity evaluation, each catalyst was mounted on the exhaust system of an engine with a displacement of 2000 cc, A / F = 14.6 (stoichiometric state) for 30 seconds, and then A / F = 22 (lean atmosphere).
The operation was performed for one cycle for 30 seconds, and the average conversion was measured. The average conversion when A / F = 14.6 (stoichiometric state) and the average when A / F = 22 (lean atmosphere) The conversion rate was averaged to obtain a total conversion rate. This evaluation was performed at the initial stage and after the durability test, and the catalytic activity evaluation value was determined by the following formula.

[0083]

[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.

[0085]

[Table 2]

[0086]

As described above, according to the present invention, by specifying the structure of the exhaust gas purifying catalyst, NOx can be effectively absorbed in the oxygen excess region, and the conventional catalyst is sufficient. NOx purification performance in a lean atmosphere where no activity is obtained can be improved, and the function as a three-way catalyst can be sufficiently exhibited even after endurance. By using a composite oxide having a specific composition, NO
Excellent NOx due to increased NOx oxidation reaction required for x absorption
A significant effect that an absorbing action can be obtained is obtained.

Further, according to the present invention, the exhaust gas purifying catalyst has a two-layer structure in which the precious metal-supporting layer is the surface layer and the complex oxide layer is the upper layer and the lower layer are the upper and lower layers. It is possible to secure sufficient three-way catalyst performance while obtaining the NOx absorption function.

Further, the exhaust gas purifying catalyst of the present invention comprises a copper-containing zeolite-containing catalyst on the upstream side of the exhaust gas flow,
By arranging the above catalyst according to the present invention on the downstream side,
In addition to the above effects, an excellent effect that the absorption action of the NOx absorption catalyst can be further improved is obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/46 311 B01J 23/78 A 23/656 29/072 A 23/78 F01N 3/28 301Z 29/072 B01D 53/36 102H F01N 3/28 301 102B 104A B01J 23/64 104A

Claims (4)

[Claims] 1. On a refractory inorganic support, at least one transition metal selected from the group consisting of iron, cobalt, nickel and manganese, barium, lanthanum, and selected from the group consisting of platinum, palladium and rhodium. An exhaust gas purifying catalyst comprising at least one kind of noble metal, and the transition metal, barium, and lanthanum are part or all of a complex oxide. 2. A catalyst inner layer containing a complex oxide containing at least one transition metal selected from the group consisting of iron, cobalt, nickel and manganese, barium and lanthanum on a refractory inorganic support, An exhaust gas purifying catalyst comprising: a catalyst surface layer containing at least one noble metal selected from the group consisting of platinum, palladium and rhodium, and containing silica-alumina containing no complex oxide. 3. At least two catalysts are provided in an engine exhaust gas flow, a copper-containing zeolite-containing catalyst is arranged upstream of the exhaust gas flow, and a catalyst according to claim 1 is arranged downstream. A characteristic exhaust gas purification catalyst. 4. The exhaust gas purifying catalyst according to claim 1, wherein the silica in the silica alumina is 0.5 to 20 wt%.