JPH10192713A - Exhaust gas purifying catalyst and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the NOx purifying performance in a lean atmosphere for which a sufficient activity is not exhibited by the conventional catalyst and to allow the catalyst to function sufficiently as a ternary catalyst. SOLUTION: A platinum-on-zeolite first catalyst is arranged in the preceding stage with respect to the exhaust gas flow in this exhaust gas purifying catalyst. A second catalyst contg. alumina carrying each of at least one kind selected from a group consisting of platinum. palladium, rhodium and iridium and a multiple oxide shown by (La1-x Ax )1-α BO1-δ (0<x<1, 0<α<0.2, 0<=δ<=1, A is barium and/or potassium, and B is at least one kind selected from a group consisting of iron, cobalt, nickel and manganese) is arranged in the subsequent stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification system for purifying hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine of an automobile or the like. The present invention relates to a catalyst and a method of using the same, and more particularly to an exhaust gas purifying catalyst having excellent NOx purification performance in an oxygen-excess atmosphere and a method of using the same.

[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”. When a conventional three-way catalyst is applied in a lean atmosphere, there has been a problem that the effect of excessive oxygen makes the NOx purification action insufficient. For this reason, NOx
There has been a demand for the development of a catalyst that can purify methane.

Conventionally, NOx in a lean atmosphere has been
Various catalysts for improving the purification performance have been proposed, and are roughly classified into two types. One is to oxidize and purify NOx using HC in the exhaust gas as a reducing agent, and the other is to absorb NOx in a lean atmosphere and emit NOx in a stoichiometric or fuel-rich (rich) atmosphere. It purifies.

[0004] As a representative of the former, for example, JP-A-63-100919 discloses a catalyst in which copper (Cu) is supported on zeolite.

On the other hand, as a representative of the latter, for example, JP-A-5-168860 discloses a catalyst in which lanthanum or the like is supported on platinum (Pt) and lanthanum is used as a NOx absorbent.

[0006]

However, the above-mentioned conventional NOx purification catalyst (for example, a Cu-supported zeolite catalyst)
And NOx absorption catalyst (for example, Pt-lanthanum catalyst)
Due to its characteristics, the former cannot achieve a sufficient purifying action if the HC / NOx ratio in the exhaust gas is small, and the latter does not reach the saturation when the steady running in a lean atmosphere causes the NOx absorption amount to reach saturation. NOx purification performance is insufficient, the performance after durability is not sufficient, and NOx cannot be purified under a wide range of operating conditions.

Accordingly, an object of the present invention is to improve the NOx purifying performance under a lean atmosphere, which has not exhibited sufficient activity with a conventional catalyst, and to function as a three-way catalyst. It is an object of the present invention to provide an exhaust gas purifying catalyst which can be sufficiently developed.

It is another object of the present invention to provide a method of using an exhaust gas purifying catalyst in which the NOx purifying action of the exhaust gas purifying catalyst of the present invention can be exhibited particularly effectively.

[0009]

According to a first aspect of the present invention, there is provided a catalyst for purifying exhaust gas, wherein a first catalyst including a platinum-supported zeolite is disposed in front of an exhaust stream, and is formed of a group consisting of platinum, palladium, rhodium and iridium. Alumina supporting at least one noble metal selected from the above for each selected noble metal element, and the following general formula

(Equation 2) And a second catalyst comprising the composite oxide represented by

Further, in order to suppress HC adsorption and poisoning by platinum in the catalyst, the exhaust gas purifying catalyst according to claim 2 is characterized in that the first catalyst further contains rhodium and / or iridium. I do.

Further, in order to further enhance the above-mentioned effect of the exhaust gas purifying catalyst according to the second aspect, the exhaust gas purifying catalyst according to the third aspect has a first catalyst comprising at least two layers.
It is characterized in that the lower layer contains platinum-supported zeolite and the upper layer contains rhodium and / or iridium.

The exhaust gas purifying catalyst according to claim 2 or 3 further enhances the above-mentioned action more efficiently, suppresses alloying of noble metals, and obtains high thermal durability. The gas purification catalyst is characterized by supporting rhodium and / or iridium on alumina.

In order to efficiently realize the NOx absorbing action and the purifying action of the exhaust gas purifying catalyst according to any one of claims 1 to 4, the exhaust gas purifying catalyst according to claim 5 comprises The catalyst comprises at least two layers, and the lower layer contains the composite oxide.

Further, in order to further enhance the NOx purifying action of the exhaust gas purifying catalyst according to any one of the first to fifth aspects, the exhaust gas purifying catalyst according to the sixth aspect is characterized in that the upper layer of the second catalyst has rhodium. And / or iridium.

Further, in order to exhibit an effective NOx absorption / release cycle of the exhaust gas purifying catalyst of the present invention,
The method for using an exhaust gas purifying catalyst according to claim 7 is to use the exhaust gas purifying catalyst of the present invention in a lean burn engine vehicle in which an air-fuel ratio repeats stoichiometry and a range of 15 to 50. Features.

[0016] The first catalyst in the exhaust gas purifying catalyst of the present invention is provided upstream of the exhaust gas flow. The amount of platinum supported on the platinum-supported zeolite catalyst in the first catalyst was N
The present invention is not particularly limited as long as the Ox purification performance and the three-way catalyst performance can be sufficiently obtained. However, if it is less than 0.1 g, there is no sufficient NOx purification performance, and even if it exceeds 10 g, no significant improvement in characteristics is observed. 0.1 L / L of exhaust gas purification catalyst.
1 to 10 g is preferred.

As the zeolite as the platinum-carrying substrate, those having a high specific surface area and excellent heat resistance are preferably used in order to secure the dispersibility of the catalytically active component.
Ferrierite and the like. The amount of zeolite used is 50
g, there is no sufficient NOx purification performance.
From the point that no significant improvement in characteristics is observed even when used more, 50 to 300 g per liter of the exhaust gas purifying catalyst of the present invention is used.
Is preferred. In order to further improve the heat resistant specific surface area, for example, a rare earth element, zirconium, or the like may be added.

Next, in the exhaust gas purifying catalyst of the present invention, the second catalyst is provided at a stage subsequent to the exhaust gas flow.
The second catalyst in the exhaust gas purifying catalyst of the present invention includes platinum,
At least one selected from the group consisting of rhodium, palladium and iridium is used. For example, Pt and R
Various combinations of h, Pd and Rh, only Pd, etc. are possible.

The content of the noble metal is not particularly limited as long as the NOx absorption capacity and the three-way catalyst performance are sufficiently obtained.
If the amount is less than 0.1 g, sufficient ternary performance cannot be obtained, and
g of the exhaust gas purifying catalyst of the present invention.
0 g is preferred.

A heat-resistant inorganic material having a large specific surface area is suitable for the base material for supporting the noble metal, in order to secure the dispersibility of the noble metal, particularly, the dispersibility of the noble metal after durability. Is desirable. Alumina to which a rare earth element, zirconia, or the like is added to increase the heat resistant specific surface area may be used. If the amount of the alumina used is less than 50 g per 1 L of the catalyst of the present invention, sufficient dispersibility of the noble metal cannot be obtained, and if it is used more than 300 g, the performance is deteriorated.

The composite oxide contained in the second catalyst is
The following general formula

(Equation 3) It is represented by

The composite oxide used in the exhaust gas purifying catalyst of the present invention contains a rare earth metal, an alkali metal and / or an alkaline earth metal, and at least one transition metal. Lanthanum is preferably used as the rare earth metal, potassium is used as the alkali metal, barium is used as the alkaline earth metal, and iron, cobalt, nickel and manganese can be suitably used as the transition metal.

A composite oxide such as the above-described perovskite-type oxide has characteristics of causing oxygen deficiency, easily adsorbing NOx via the generated oxygen deficiency, and absorbing NOx in a lean atmosphere. Utilization makes it possible to improve NOx purification performance.

Further, the perovskite-type oxide may cause a solid-phase reaction with the alumina-based oxide in the catalyst composition to deactivate the activity. In order to suppress this, there are a method of pre-coating lanthanum or the like on the alumina-based oxide and a method of using a material having low reactivity with perovskite such as zirconia. On the other hand, by slightly losing the A site of the perovskite-type oxide from the stoichiometric ratio as in the present invention, the solid-phase reaction between the perovskite-type oxide and another oxide (alumina or the like) in contact therewith To suppress
It has become possible to improve the thermal stability.

The substitution amount of the A site is 0 <X <1 and is not particularly limited. However, in order to obtain a sufficient NOx absorption capacity, it is particularly preferable that 0.2 ≦ X <1.

If the value of α exceeds 0.2, a single-phase perovskite structure is not formed, so that 0 <α <0.2 is preferable. The value of δ is 0 ≦ Y ≦ 1, but from the viewpoint of stability of the crystal structure, it is particularly preferable that 0 ≦ Y ≦ 0.5.

The amount of the composite oxide functioning as a NOx absorbing material is not particularly limited as long as it exhibits an NOx absorbing effect. However, if it is less than 30 g, a sufficient NOx absorbing ability cannot be obtained, and if it is more than 200 g, Since no significant improvement in characteristics is observed even when used, 30 liters per liter of the catalyst of the present invention is used.
~ 200 g is preferred.

The composite oxide used in the present invention, particularly the partially substituted perovskite oxide, exhibits the ability to absorb NOx in a lean atmosphere together with the partially substituted amount thereof. It is considered that NOx is oxidized to NO ₂ on the composite oxide and is absorbed in the vicinity of barium and / or potassium on the surface of the composite oxide in the form of a nitric acid group or a state close thereto. Therefore, the composition of the composite oxide for effectively absorbing NOx under a lean atmosphere is as follows:
Nitrate containing barium and / or potassium may be easily manufactured, and further, it is important to contain a transition metal element capable of oxidizing NOx to NO _2.

The method for installing the first catalyst and the second catalyst in the exhaust system is as follows: the first catalyst is installed in a stage preceding the exhaust gas flow, and the second catalyst is installed in a stage subsequent to the exhaust gas flow. It is important to use a known method such as a method in which two types of catalysts are mounted and arranged in one catalytic converter or a method in which the two types of catalysts are installed in separate converters. it can. The installation position of the catalyst is not particularly limited,
For example, a position immediately below the manifold, a position under the floor, and the like can be given. 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.

Thus, by arranging the first catalyst in the first stage and the second catalyst in the second stage, when the exhaust gas atmosphere becomes lean, the oxygen excess due to the platinum-supported zeolite in the first catalyst is reduced. The combination of the NOx reduction action in the atmosphere and the NOx absorption action by the composite oxide in the second catalyst provides high NOx purification performance, and provides excellent NOx purification performance that cannot be obtained by simply mixing each alone. It has become possible.

That is, since the NOx reduction reaction requires HC, it is preferable that the concentration of HC be high. However, according to the present invention, a powder in which platinum is loaded on zeolite that adsorbs HC is disposed upstream of the exhaust flow. Therefore, a large amount of HC is supplied to the platinum in the first catalyst, and a high NOx reducing action is obtained.

In the NOx absorption reaction, on the contrary, it is preferable that the amount of HC is small. However, according to the present invention, since HC is adsorbed or purified by the first catalyst of the preceding stage, the mixed oxide of the succeeding stage has a gas containing less HC. Is supplied, and a high NOx absorbing action is obtained. The N of such a composite oxide
The Ox absorption effect cannot be obtained by simply mixing the individual components of the composite oxide alone, and this is due to the effect of the composite components of the composite oxide being composited.

Each of the constituent elements of the composite oxide exerts the above-mentioned effects to the maximum when all of them contained in the catalyst are complexed, but at least a part of the complex oxide forms a complex. Even if it is possible, the above effect can be sufficiently obtained. Each constituent element of the composite oxide can exist as a composite oxide without being separated as a separate oxide even after thermal endurance, and this can be confirmed by, for example, X-ray diffraction measurement.

When the exhaust gas atmosphere changes from lean to stoichiometric, NOx is released from the composite oxide.
NOx purification can be effectively performed by repeating a cycle of purifying this with the noble metal-supported alumina powder contained in the second catalyst of the present invention. In addition, the catalyst of the present invention has a high NOx absorption function even after heat endurance. This is because the composite oxide has a perovskite structure with a small proportion of A site, and a solid phase reaction with another component (for example, alumina). Was avoided.

Preferably, the first catalyst further contains rhodium and / or iridium to obtain the exhaust gas purifying catalyst according to claim 2. The content of rhodium and / or iridium is not particularly limited as long as the NOx purification performance and the three-way catalyst performance can be obtained. Since it is not observed, the amount is preferably 0.1 to 10 g per liter of the exhaust gas purifying catalyst of the present invention.

The platinum in the first catalyst has a strong ability to adsorb HC, and in some cases, the NOx purification performance is reduced due to poisoning of HC. However, when the composition further contains rhodium and / or iridium, HC adsorption poisoning of platinum is suppressed, and NOx can be efficiently purified.

Preferably, the first catalyst has at least 2
A catalyst for purifying exhaust gas according to claim 3 is obtained by comprising a layer comprising the above-mentioned platinum-supported zeolite in a lower layer and the above-mentioned rhodium and / or iridium in an upper layer.

In order to sufficiently exert the effect of suppressing the adsorption and poisoning of HC, it is desirable that the exhaust gas contacts rhodium and / or iridium before reaching the platinum-supported zeolite. It is important to include rhodium and / or iridium in the upper layer portion that is believed to occur earlier.

The rhodium and / or iridium is preferably supported on alumina. Thus, the exhaust gas purifying catalyst according to the fourth aspect is obtained. The substrate for supporting rhodium and / or iridium has a dispersibility of the noble metal,
In particular, in order to ensure the dispersibility of the noble metal after durability, a heat-resistant inorganic material having a large specific surface area is suitable, and alumina is particularly preferable. Activated alumina to which a rare earth element, zirconia, or the like is added to increase the heat resistant specific surface area may be used. If the amount of activated alumina used is less than 50 g per liter of the catalyst of the present invention, sufficient dispersibility of noble metal cannot be obtained, and 300 g
50 to 3 from the point that performance decreases when more is used
It is preferably 00 g. By supporting platinum, rhodium and iridium on separate substrates, alloying of noble metals can be suppressed, and high post-heat durability performance can be obtained.

Preferably, the second catalyst comprises at least two layers, and the lower layer contains the composite oxide to obtain the exhaust gas purifying catalyst according to claim 5, and the upper layer further comprises rhodium and / or rhodium. By including iridium, the exhaust gas purifying catalyst according to claim 6 can be obtained.

With such a configuration, both the NOx absorbing action and the purifying action of NOx released from the absorbent can be achieved. This is because HC is once purified in the upper layer, so that exhaust gas with less HC reaches the lower layer, and as a result, NO
This is because the x-absorbing action is enhanced, and the upper layer can contact exhaust gas with a high HC concentration, so that the NOx released from the absorbent can be efficiently purified.

The exhaust gas purifying catalyst of the present invention can be used particularly for a lean burn engine vehicle in which the air-fuel ratio repeats stoichiometry and a range of 15 to 50. With such a usage method, NOx
The absorption / release cycle is established very effectively, and particularly efficient NOx purification becomes possible.

As the noble metal raw material compound for preparing the 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 known evaporation and drying method, a precipitation method, an impregnation method, and an ion exchange method can be used as long as there is no significant uneven distribution of components. In particular, the ion-exchange method is preferably used for loading on zeolite, since a sufficient amount of noble metal can be loaded on the active site.

The composite oxide used in the present invention is prepared by mixing nitrates, acetates or carbonates of the respective constituent elements of the composite oxide in a desired composition ratio of the composite oxide, calcining the mixture, and pulverizing the mixture. After the solid-phase reaction to be subjected to heat treatment and firing, nitrate, acetate or carbonate, hydrochloride, citrate, etc. of each constituent element of the composite oxide are mixed in a desired composition ratio of the composite oxide, and then dissolved in water. If necessary, an alkaline solution such as NH ₄ OH or NH ₃ CO ₃ may be added dropwise to form a precipitate, which can be prepared by a known method such as a coprecipitation method in which the precipitate is filtered, dried, and fired. By such a method, at least a part of each component constituting the composite oxide can be composited.

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

For use in the present invention thus obtained,
The first catalyst and the second catalyst can be obtained by pulverizing the platinum-supported zeolite, the composite oxide and the noble metal-supported alumina to form a slurry, coating the catalyst support, and calcining at a temperature of 400 to 900 ° C. it can.

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 is suppressed, which is extremely advantageous when the catalyst is used for an automobile or the like.

Since the catalyst used in the present invention also needs to function as a three-way catalyst at the time of stoichiometry, additives conventionally used in three-way catalysts may be further added. Ceria and barium, which alleviates HC adsorption and poisoning to noble metals, and zirconia, which contributes to improving the heat resistance of Rh.

Although the use of the exhaust gas purifying catalyst of the present invention is not particularly limited, it is particularly preferable to use the catalyst for lean burn engine vehicles in which the air-fuel ratio repeats stoichiometry and a range of 15 to 50. The effect of the exhaust gas purifying catalyst of the present invention can be effectively exhibited. D / F
= 15, both the NOx reduction performance and the NOx absorption performance are small and the combined effect is slight, and D / F =
The performance does not deteriorate in an atmosphere exceeding 50, but no significant improvement in performance is observed in a higher region.

[0050]

The present invention will be described below with reference to the following examples and comparative examples. Example 1 A zeolite powder was impregnated with a dinitrodiammine platinum aqueous solution, dried and calcined at 400 ° C. for 1 hour to obtain a platinum-supported zeolite powder (powder A). The platinum concentration of this powder A was 1.0% by weight. Activated alumina powder is impregnated with rhodium nitrate solution and iridium nitrate solution,
Calcination was carried out at a temperature of 1 hour for 1 hour to obtain rhodium and iridium-supported activated alumina powder (powder B). The rhodium and iridium concentrations of this powder B were 0.3% by weight and 0.6% by weight, respectively.
Met.

852 g of powder A and 4 parts of activated alumina
8 g and water 900 g were put 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), and the excess slurry in the cells was removed by an air flow to remove the excess slurry.
After drying at 30 ° C., it was baked at 400 ° C. for 1 hour. This operation was performed twice to obtain a carrier a having a coat layer weight of 150 g / L.

720 g of the above powder B and 1 part of activated alumina
80 g and water 900 g were put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to the carrier, and the excess slurry in the cell was removed by an air stream, dried at 130 ° C., and calcined at 400 ° C. for 1 hour to obtain a catalyst-1 having a coat layer weight of 200 g / L. Obtained as the first catalyst.

The activated alumina powder was impregnated with a palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour to obtain a palladium-supported activated alumina powder (powder C). The Pd concentration of this powder C was 3.0% by weight.

Citric acid was added to a mixture of lanthanum carbonate, barium carbonate and cobalt carbonate, dried and calcined at 700 ° C. to obtain powder D. This powder D had a metal atom ratio of lanthanum / barium / cobalt = 2/2/5.

The activated alumina powder was impregnated with a rhodium nitrate solution, dried and calcined at 400 ° C. for 1 hour to obtain a rhodium-supported activated alumina powder (powder E). Rh of this powder E
The concentration was 2.0% by weight.

450 g of the powder C and 36 g of the powder D
0 g, activated alumina 90 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 added to a cordierite monolithic carrier (1.0
L, 400 cells), and the excess slurry in the cells was removed by an air stream and dried at 130 ° C.
Calcination was carried out at 1 ° C. for 1 hour to obtain a carrier (a) having a coat layer weight of 100 g / L.

90 g of the powder E and 360 g of the powder C
g, activated alumina 450 g and water 900 g were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid is adhered to the carrier a, excess slurry in the cell is removed by an air stream and dried at 130 ° C.
It was baked at 00 ° C. for 1 hour to obtain a catalyst-2 having a coat layer weight of 200 g / L as a second catalyst.

With respect to the exhaust gas flow, the above-mentioned catalyst-1 was arranged at the former stage and the above-mentioned catalyst-2 was arranged at the latter stage to obtain the exhaust gas purifying catalyst of the present invention.

Example 2 A powder F was obtained by using potassium carbonate instead of barium carbonate in the preparation of powder D, and was prepared in the same manner as in Example 1 except that powder F was used instead of powder D in preparing catalyst-2. As a result, catalyst-3 was obtained. With respect to the exhaust gas flow, the catalyst-1 obtained in Example 1 was arranged at the front stage, and the catalyst-3 was arranged at the rear stage to obtain the exhaust gas purifying catalyst of the present invention.

Example 3 The procedure of Example 1 was repeated except that powder G was prepared at a platinum loading of 2.0% by weight in the preparation of powder A, and powder G was used instead of powder A in the preparation of catalyst-1. Catalyst
4 was obtained. The catalyst-4 for the exhaust gas purification of the present invention was obtained by arranging the above catalyst-4 at the preceding stage and the catalyst-2 obtained in Example 1 at the latter stage with respect to the exhaust gas flow.

Example 4 A powder H was obtained in the same manner as in Example 1 except that a rhodium nitrate solution and an iridium nitrate solution were used instead of the rhodium nitrate solution in the preparation of the powder E. This powder H
Have a Rh and Ir concentration of 1.0% by weight and 1.0% by weight, respectively.
Met. Catalyst-5 was obtained in the same manner as in Example 1, except that Powder H was used instead of Powder E in the preparation of Catalyst-2. For the exhaust gas flow, the catalyst-1 obtained in Example 1
Was disposed in the first stage, and the above-mentioned catalyst-5 was disposed in the second stage to obtain the exhaust gas purifying catalyst of the present invention.

Example 5 The catalyst-4 obtained in Example 3 was arranged at the front stage and the catalyst 5 obtained in Example 4 was arranged at the latter stage with respect to the exhaust gas flow. A catalyst was obtained.

Example 6 189 g of the powder A obtained in Example 1 and 18
0 g, 81 g of activated alumina, and 900 g of water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry liquid. This slurry liquid was added to a cordierite monolithic carrier (1.0
L, 400 cells), and the excess slurry in the cells was removed by an air stream and dried at 130 ° C.
Calcination was carried out at ℃ for 1 hour. This operation was performed twice to obtain Catalyst-6 having a coat layer weight of 200 g / L. For the exhaust flow,
By arranging the above-mentioned catalyst-6 in the first stage and the catalyst-2 obtained in Example 1 in the second stage, an exhaust gas purifying catalyst of the present invention was obtained.

Example 7 405 g of powder C and 45 g of powder E obtained in Example 1
Powder D, 180 g, activated alumina 270 g, water 90
0 g was 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 an air stream, dried at 130 ° C., and fired at 400 ° C. for 1 hour. This operation was performed twice to obtain Catalyst-7 having a coat layer weight of 200 g / L. With respect to the exhaust gas flow, the catalyst-1 obtained in Example 1
The catalyst 7 was arranged at the subsequent stage to obtain an exhaust gas purifying catalyst of the present invention.

Example 8 The catalyst for purification of exhaust gas of the present invention was arranged in such a manner that the catalyst-6 obtained in Example 6 was arranged in the front stage and the catalyst 7 obtained in Example 7 was arranged in the latter stage. A catalyst was obtained.

Example 9 The operation of mixing 5.2 kg of a 0.2 mol / L aqueous copper nitrate solution and 2 kg of zeolite powder, stirring and filtering was repeated three times, then dried and calcined to obtain a Cu-supported zeolite powder. (Powder I) was obtained. The Cu concentration of this powder I was 4%. 810 g of the above powder I, silica sol (solid content: 20
%) 450 g and 540 g of water are put into a magnetic ball mill,
The mixture was pulverized to obtain a slurry liquid. This slurry liquid is used as a cordierite monolithic carrier (1.0 L, 400 cells)
After drying at 130 ° C. and baking at 400 ° C. for 1 hour, catalyst-8 having a coat layer weight of 200 g / L was obtained. With respect to the exhaust gas flow, the above-mentioned catalyst-8 was arranged at the preceding stage, and the catalyst-2 obtained in Example 1 was arranged at the later stage to obtain the exhaust gas purifying catalyst of the present invention.

Example 10 The catalyst for purification of exhaust gas of the present invention was obtained by arranging the catalyst of Example 2 in the preceding stage and the catalyst 8 of Example 9 in the latter stage with respect to the exhaust gas flow.

Example 11 Activated alumina powder was impregnated with a palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour to obtain palladium-supported activated alumina powder (powder J). The Pd concentration of this powder J was 1.5% by weight. Powder C in the preparation of catalyst-2
Catalyst-9 was obtained in the same manner as in Example 1 except that powder J was used instead of. The catalyst for exhaust gas purification of the present invention was obtained by arranging the catalyst-1 obtained in Example 1 at the front stage and the catalyst -9 at the rear stage with respect to the exhaust gas flow.

Example 12 In the preparation of Catalyst-1, 720 g of powder B, 180 g of activated alumina powder and 900 g of water were mixed and pulverized, and 50 g of a slurry obtained on a cordierite-based monolith carrier was added to a cordierite monolith carrier.
/ L was obtained in the same manner as in Example 1 except that the step of preliminarily adhering the Pt / zeolite layer was performed before the step of adhering the Pt / zeolite layer.
In the exhaust gas flow, Example 1
Was placed in the subsequent stage to obtain an exhaust gas purifying catalyst of the present invention.

Example 13 In the preparation of Catalyst-2, 90 g of powder E and 3 g of powder C were used.
The step of previously adhering a slurry obtained by mixing and crushing 60 g of 450 g of activated alumina and 900 g of water to 900 g of water to the cordierite-based monolith carrier in an amount of 100 g / L is performed by 450 g of powder C, 360 g of powder D, and activated alumina. 90
g and 900 g of water were mixed and pulverized to obtain a slurry of 10 g.
Catalyst-11 having a coat layer weight of 200 g / L was obtained in the same manner as in Example 1 except that it was performed before the step of attaching 0 g / L. For the exhaust gas flow, the catalyst-1 obtained in Example 1
Was disposed at the front stage and the catalyst-11 was disposed at the rear stage to obtain the exhaust gas purifying catalyst of the present invention.

Example 14 Citric acid was added to a mixture of lanthanum carbonate, barium carbonate, manganese carbonate and cobalt carbonate, dried and calcined at 700 ° C., and lanthanum / barium / manganese / cobalt = 1/2 / metal atomic ratio. 1/5 powder K was obtained. In preparing catalyst-2, except that powder K was used instead of powder D,
Catalyst 12 was obtained in the same manner as in Example 1. With respect to the exhaust gas flow, the catalyst-1 obtained in Example 1 was arranged at the front stage, and the catalyst-12 was arranged at the latter stage, to obtain the exhaust gas purifying catalyst of the present invention.

Comparative Example 1 Catalyst 2 of Example 1 except that lanthanum in powder D was omitted
In the same manner as in the above, catalyst-13 was obtained. The catalyst for exhaust gas purification was obtained by disposing the catalyst-1 obtained in Example 1 at the front stage and the catalyst-13 at the rear stage with respect to the exhaust gas flow.

Comparative Example 2 Catalyst 2 of Example 1 except that barium in Powder D was omitted.
In the same manner as in the above, catalyst-14 was obtained. With respect to the exhaust gas flow, the catalyst-1 obtained in Example 1 was disposed at the front stage and the catalyst-14 was disposed at the rear stage to obtain an exhaust gas purifying catalyst.

Comparative Example 3 Catalyst 1 of Example 1 except that rhodium in powder B was not used
Catalyst 15 was obtained in the same manner as described above. The catalyst for exhaust gas purification was obtained by arranging the catalyst 15 in the preceding stage and the catalyst-2 obtained in Example 1 in the subsequent stage with respect to the exhaust gas flow.

Comparative Example 4 The catalyst of Example 1 was used except that iridium in the powder B was not used.
In the same manner as in Example 1, catalyst 16 was obtained. For the exhaust flow,
The catalyst-2 obtained in Example 1 was placed in the preceding stage of the catalyst-16.
Was disposed at the subsequent stage to obtain an exhaust gas purifying catalyst.

COMPARATIVE EXAMPLE 5 With respect to the exhaust gas flow, the catalyst 15 obtained in Comparative Example 3 was disposed in the front stage, and the catalyst 14 obtained in Comparative Example 2 was disposed in the subsequent stage, and an exhaust gas purifying catalyst was prepared. Obtained.

Comparative Example 6 The catalyst for exhaust gas purification was obtained by arranging the catalyst-2 obtained in Example 1 at the front stage and the catalyst-1 at the rear stage with respect to the exhaust gas flow.

Comparative Example 7 Catalyst 17 was obtained in the same manner as in Catalyst 1 of Example 1, except that activated alumina powder was used instead of powder A. Catalyst-18 was obtained in the same manner as in Catalyst-2 of Example 1, except that activated alumina powder was used instead of powder D. The catalyst 17 was arranged at the front stage and the catalyst 18 was arranged at the rear stage with respect to the exhaust gas flow to obtain an exhaust gas purifying catalyst.

Comparative Example 8 In the preparation of powder B, the base material was not S
except that the iO ₂ powder, to obtain a catalyst -19 in the same manner as the catalyst -1 in Example 1. Catalyst 20 was obtained in the same manner as in Catalyst 2 of Example 1, except that in preparing powders C and E, the substrate was changed to SiO ₂ powder instead of activated alumina. The catalyst 19 was disposed at the front stage and the catalyst 20 was disposed at the rear stage with respect to the exhaust gas flow to obtain an exhaust gas purifying catalyst.

The compositions of catalysts 1 to 20 used in Examples 1 to 14 and Comparative Examples 1 to 8 are shown in Table 1.

[Table 1]

Test Examples The exhaust gas purifying catalysts obtained in Examples 1 to 14 and Comparative Examples 1 to 8 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 mounted on an exhaust system of 4400 cc engine, and the operation was performed at a catalyst inlet temperature of 600 ° C. for 50 hours to endurance.

Evaluation Conditions The catalyst activity was evaluated by mounting each catalyst on the exhaust system of an engine with a displacement of 1800 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 endurance test, and the catalytic activity evaluation value was determined by the following equation.

(Equation 4)

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]

The exhaust gas purifying catalyst according to claim 1 is
The conventional catalyst can improve the NOx purification performance under a lean atmosphere, which did not show sufficient activity, and can sufficiently exhibit the function as a three-way catalyst. Can be shown.

The exhaust gas purifying catalyst according to claim 2 can suppress HC adsorption and poisoning by platinum, and can purify NOx efficiently, in addition to the above effects.

The exhaust gas purifying catalyst according to the third aspect can further improve the above-mentioned effect of suppressing HC adsorption and poisoning, and can further purify NOx efficiently.

The exhaust gas purifying catalyst according to claim 4 further ensures a sufficient noble metal dispersibility in addition to the above effects,
High heat durability can be obtained by suppressing alloying of noble metals.

In the exhaust gas purifying catalyst according to the fifth aspect, in addition to the above-mentioned effects, the NOx absorbing function and the NOx purifying function can be effectively realized, so that the NOx purifying can be made more efficient.

The exhaust gas purifying catalyst according to claim 6 can further enhance the NOx purifying action in addition to the above effects.

The exhaust gas purifying catalyst according to the seventh aspect can exhibit the effective NOx absorption / release cycle of the exhaust gas purifying catalyst of the present invention particularly efficiently.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI F01N 3/08 F01N 3/28 ZAB 3/10 301B 3/28 ZAB B01D 53/36 102H 301 104A B01J 23/64 104A (72) Inventor Okada Akihide Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture

Claims (7)

[Claims] 1. A first catalyst comprising a platinum-supported zeolite is disposed upstream of an exhaust stream to convert at least one noble metal selected from the group consisting of platinum, palladium, rhodium and iridium into the selected noble metal element. Alumina supported for each and the following general formula: An exhaust gas purifying catalyst comprising: a second catalyst containing a composite oxide represented by the formula: 2. The exhaust gas purifying catalyst according to claim 1, wherein the first catalyst further contains rhodium and / or iridium. 3. The first catalyst comprises at least two layers, a lower layer containing a platinum-supported zeolite, and an upper layer containing rhodium and / or rhodium.
3. The exhaust gas purifying catalyst according to claim 2, further comprising iridium. 4. The exhaust gas purifying catalyst according to claim 2, wherein rhodium and / or iridium is supported on alumina. 5. The method according to claim 1, wherein the second catalyst comprises at least two layers, and the lower layer contains the composite oxide.
4. The exhaust gas purifying catalyst according to 4. 6. The exhaust gas purifying catalyst according to claim 5, wherein the upper layer of the second catalyst contains rhodium and / or iridium. 7. The exhaust gas purifying catalyst according to claim 1, wherein the air-fuel ratio is 15% or less.
A method for using an exhaust gas purifying catalyst, wherein the method is used for a lean burn engine vehicle that repeats a range from 50 to 50.