JP3330154B2 - Exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for purifying exhaust gas, and more particularly to a catalyst for purifying exhaust gas discharged from an internal combustion engine of an automobile or the like. More specifically, among the harmful components contained in the exhaust gas of the internal combustion engine, hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (N
O _X) of a three-way catalyst for purifying the same time, a catalyst for purifying exhaust gases having improved durability in a high temperature range.

[0002]

2. Description of the Related Art Numerous catalysts have been proposed to purify exhaust gas discharged from an internal combustion engine of an automobile or the like. Of these numerous catalysts, hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (N
O _X) the three-way catalyst capable of purifying the same time has become the mainstream.

[0003] The conventional three-way catalyst is obtained by supporting a refractory inorganic oxide and one or more catalyst components on a honeycomb support made of cordierite or metal. In this case, as the refractory inorganic oxide, for example, alumina,
Alumina / silica or silica is used. Also,
Platinum (Pt), palladium (P
d), rhodium (Rh), cerium (Ce), lanthanum (La), zirconium (Zr) and the like. The refractory inorganic oxide and the catalyst component can be supported in any combination.

[0004] Such a three-way catalyst is generally prepared as follows. First, the catalyst component is dispersed and supported on the refractory inorganic oxide powder alone or in combination to form a catalyst composition. Next, the catalyst composition may be coated on the honeycomb carrier. Alternatively, it may be prepared by coating a honeycomb carrier with a refractory inorganic oxide and then immersing the carrier in an aqueous solution containing one or more catalyst components.

However, the above-mentioned conventional three-way catalyst has insufficient durability in a high temperature range, and there is a problem that the use of the catalyst at a high temperature deteriorates the catalytic performance. The first reason is that
That is, the specific surface area of the refractory inorganic oxide such as alumina supported on the support decreases. The second reason is that catalyst components such as platinum, palladium, rhodium, and cerium supported in the refractory inorganic oxide are sintered (agglomerated).

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to provide a hydrocarbon (HC),
Improved three-way catalyst for purifying carbon monoxide (CO) and nitrogen oxides (NO _X) at the same time, to improve the durability in time of high temperature use is to and to suppress a decrease in catalytic performance.

[0007]

In order to solve the above problems, in the present invention, cerium and zirconium among the catalyst components supported on an alumina coat layer formed on a carrier are contained in cerium oxide fine particles. Zirconium oxide was supported as a solid oxide in a solid solution, and lanthanum was supported as lanthanum oxide.

[0008] The exhaust gas purifying catalyst according to the present invention is a catalyst in which an alumina coat layer containing at least one catalyst component selected from the group consisting of platinum, palladium and rhodium is formed on an inorganic refractory catalyst carrier. A composite oxide in which zirconium oxide is solid-dissolved in cerium oxide in an amount of 10 to 40% by weight based on the alumina coat layer, It is characterized by containing 2 to 20% by weight of lanthanum oxide.

The method for producing an exhaust gas purifying catalyst according to the present invention is a method for producing an exhaust gas purifying catalyst in which an alumina coat layer containing a catalyst component is formed on an inorganic refractory catalyst carrier. ) A cerium oxide powder having a crystal particle size of 50 to 300 A (angstrom) is immersed in a zirconium oxynitrate solution, and dried, and
B. Firing at 1 ° C. for 1 to 5 hours to obtain a composite oxide in which cerium oxide is solid-dissolved with 5 to 15% by weight of zirconium oxide; and (b) the composite oxide, lanthanum oxide;
A slurry obtained by mixing γ-alumina and alumina hydrate with water so that the composite oxide accounts for 10 to 40% by weight of the entire alumina coat layer and the lanthanum oxide accounts for 2 to 20% by weight of the entire alumina coat layer And coating the slurry on the inorganic refractory catalyst support, drying and calcining; and (c) selecting the support obtained from the step (b) from the group consisting of platinum, palladium and rhodium. Impregnating with a solution containing one or more catalyst components.

As the inorganic refractory catalyst carrier in the present invention, a cordierite carrier or a metal carrier can be used as in the case of the conventional three-way catalyst. In either case,
Usually, it is used in the form of a honeycomb carrier. Preferred carriers are cordierite honeycomb carriers.

The alumina coat layer in the present invention may be the same as that used in the conventional three-way catalyst, for example, a gamma alumina layer. The amount of the alumina coat layer is preferably 50 to 200 g (hereinafter referred to as 50 to 200 g / l-cat) per liter of the volume of the finally formed catalyst.

In the present invention, among the catalyst components supported on the alumina coat layer, Pt, Rh and / or Pd
May be contained in the same manner as in the prior art. Generally, the supported amounts of these catalyst components are as follows, respectively. Pt; 0 to 2.0 g / l-cat, preferably 0.5 to
1.5 g / l-cat Rh; 0 to 0.6 g / l-cat, preferably 0.1 to
0.4 g / l-cat Pd; 0-4.0 g / l-cat, preferably 0-2.
0 g / l-cat

The characteristic structure of the present invention is that, among the catalyst components supported on the alumina coat layer, particularly, Ce,
Zr and La are supported. Therefore, this characteristic configuration will be described next.

Ce and Zr have a crystal grain size of 50-30.
It is added as a composite oxide in which 5 to 15% by weight of zirconium oxide is dissolved in cerium oxide of 0A. Such a composite oxide can be obtained by immersing a zirconium oxynitrate solution in cerium oxide powder, drying it, and firing it. The firing conditions are from 600 to 800
C. for 1 to 5 hours is preferred. The reason why the crystal particle diameter of cerium oxide is set to 50 to 300 A is that if it exceeds 300 A, solid solution with zirconium oxide hardly occurs, and if it is less than 50 A, lanthanum is used in a firing step for forming an alumina coat layer. And / or solid solution with alumina is likely to occur. Also, the reason why the solid solution amount of zirconium oxide is 5 to 15% by weight is that if it is less than 5% by weight, the formation of a composite oxide with cerium oxide is insufficient, and if it exceeds 15% by weight, excess zirconium oxide is formed. This is because they are generated and deteriorate the catalytic performance.

The amount of the composite oxide to be carried is 10 to 40% by weight of the entire coating layer. If the content is less than 10% by weight, the O ₂ storage effect of cerium is insufficient, and if the content exceeds 40% by weight, the alumina content is small and adversely affects the loading of Pt, Pd, Rh and the like.

On the other hand, La is supported as lanthanum oxide. The carrying amount is 2 to 20% by weight of the whole coat layer. If less than 2% by weight, the effect of adding lanthanum is not seen,
If the content exceeds 20% by weight, the influence of the interaction between ceria and alumina becomes too large, and the catalyst performance is reduced. The exhaust gas purifying catalyst according to the present invention can be manufactured, for example, as follows.

First, a slurry is prepared from the above-mentioned composite oxide of cerium oxide and zirconium oxide, γ-alumina, lanthanum oxide, alumina hydrate and water, and the slurry is coated on the above-mentioned catalyst carrier. dry. At this time, the amounts of the composite oxide, γ-alumina, lanthanum oxide, and alumina hydrate in the slurry are set so as to obtain the desired contents described above for each component. After performing this step twice, firing is performed to form a γ-alumina layer on the catalyst support. The γ-alumina coat layer thus formed contains the composite oxide and lanthanum oxide.

Next, the carrier on which the alumina coat layer is formed is impregnated with a solution containing platinum, rhodium and / or palladium, so that Pt, Rh and / or Pd is carried on the alumina coat layer. To obtain the catalyst of the present invention. For carrying Pt, for example, a dinitrodiammineplatinum solution can be used. For carrying Rh, for example, a rhodium nitrate solution can be used. For supporting Pd, for example, a palladium nitrate solution can be used.

[0019]

The exhaust gas purifying catalyst according to the present invention uses fine cerium oxide powder having a high specific surface area and stabilized with zirconium, so that it has excellent heat resistance and prevents aggregation of the catalyst components. You. Also, by adding lanthanum oxide, the heat resistance of alumina is maintained,
The catalyst performance is also improved. Therefore, it exhibits particularly high durability when used in a high temperature range.

Because of such excellent heat resistance, the exhaust gas purifying catalyst of the present invention can be used in a high temperature range.
It is possible to prevent a decrease in surface area of a refractory inorganic oxide such as alumina and a decrease in catalytic performance due to agglomeration of catalyst components.

[0021]

Embodiments of the present invention will be described below. Example 1

A zirconium oxynitrate solution is immersed in cerium oxide powder having a crystallite diameter of 100 A, dried, and calcined at 700 ° C. for 2 hours to form a solid solution of 5% by weight of zirconium oxide in cerium oxide. Further, a composite oxide of cerium and zirconium oxide was obtained. The slurry comprising the obtained composite oxide, γ-alumina, lanthanum oxide, alumina hydrate, and water was coated on a cordierite honeycomb carrier and dried. This step was performed twice and fired at 700 ° C. for 1 hour to form a γ-alumina layer containing 20% by weight of the cerium-zirconium composite oxide and 5% by weight of lanthanum (coat A).

The γ-alumina layer formed by the coating A has a coating amount of 120 g / l-cat, cerium of 0.18 mol / l-cat, zirconium of 0.013 mol / l-cat, and lanthanum. 0.0
It contained 5 mol / l-cat.

The carrier thus obtained is impregnated with a dinitrodiammineplatinum solution and a rhodium nitrate solution to form Pt,
Rh was 1.2 g / l-cat and 0.2 g / l-, respectively.
The catalyst was carried on Cat to obtain Catalyst 1. Example 2

A zirconium oxynitrate solution is immersed in a cerium oxide powder having a crystallite diameter of 100 A, dried, and calcined at 700 ° C. for 2 hours to form a solid solution of 10 wt% zirconium oxide in the cerium oxide. A composite oxide of cerium and zirconium oxide was obtained. The slurry comprising the obtained composite oxide, γ-alumina, lanthanum oxide, alumina hydrate, and water was coated on a cordierite honeycomb carrier and dried. This step was performed twice and calcined at 700 ° C. for 1 hour to form a γ-alumina layer containing 20% by weight of the cerium-zirconium composite oxide and 5% by weight of lanthanum (coat B).

The γ-alumina layer formed by the coating B has a coating amount of 120 g / l-cat, 0.17 mol / l-cat of cerium, 0.026 mol / l-cat of zirconium, and lanthanum. 0.0
It contained 5 mol / l-cat.

The carrier thus obtained is impregnated with a dinitrodiammineplatinum solution and a rhodium nitrate solution, and Pt,
Rh was 1.2 g / l-cat and 0.2 g / l-, respectively.
Cat 2 was obtained by carrying cat. Example 3

A zirconium oxynitrate solution is immersed in cerium oxide powder having a crystallite diameter of 300 A, dried, and fired at 700 ° C. for 2 hours to form a solid solution of 10% by weight of zirconium oxide in cerium oxide. A composite oxide of cerium and zirconium oxide was obtained. The slurry comprising the obtained composite oxide, γ-alumina, lanthanum oxide, alumina hydrate, and water was coated on a cordierite honeycomb carrier and dried. This step was performed twice and fired at 700 ° C. for 1 hour to form a γ-alumina layer containing 20% by weight of the cerium-zirconium composite oxide and 5% by weight of lanthanum (coat C).

The γ-alumina layer formed by the coating C has a coating amount of 120 g / l-cat, 0.17 mol / l-cat of cerium, 0.026 mol / l-cat of zirconium, and lanthanum. 0.0
It contained 5 mol / l-cat.

The carrier thus obtained is impregnated with a dinitrodiammineplatinum solution and a rhodium nitrate solution to form Pt,
Rh was 1.2 g / l-cat and 0.2 g / l-, respectively.
Catalyst 3 was obtained by carrying cat. Comparative Example 1

A slurry comprising γ-alumina, cerium oxide powder having a crystallite diameter of 50 A, lanthanum oxide, alumina hydrate, and water was coated on a cordierite honeycomb carrier, and dried. Perform this step twice,
For 1 hour to form a γ-alumina layer containing 20% by weight of cerium and 5% by weight of lanthanum (coat D).

The γ-alumina layer formed by the coating D has a coating amount of 120 g / l-cat and contains 0.19 mol / l-cat of cerium and 0.05 mol / l-cat of lanthanum. Was something.

The carrier thus obtained is impregnated with a dinitrodiammineplatinum solution and a rhodium nitrate solution, and Pt,
Rh was 1.2 g / l-cat and 0.2 g / l-, respectively.
Cat 4 was obtained by carrying cat. Comparative Example 2

Γ-alumina, cerium oxide powder having a crystallite size of 100 A, on a cordierite honeycomb carrier,
A slurry consisting of zirconium oxide, alumina hydrate, and water was coated and dried. This step is performed twice, and 7
By baking at 00 ° C. for 1 hour, a γ-alumina layer containing 20% by weight of cerium and 5% by weight of zirconium was formed (coat E).

The γ-alumina layer formed by the coating E has a coating amount of 120 g / l-cat and contains 0.19 mol / l-cat of cerium and 0.07 mol / l-cat of zirconium. Was something.

The carrier thus obtained is impregnated with a dinitrodiammineplatinum solution and a rhodium nitrate solution, and Pt,
Rh was 1.2 g / l-cat and 0.2 g / l-, respectively.
Cat 5 was obtained by carrying cat. Characteristic Test Examples The catalysts 1 to 5 obtained as described above were subjected to durability and evaluation tests under the following conditions. <Durability conditions> Engine: 2000 cc, 4-cylinder TBI Durable atmosphere: A / F = 14.6 (stoichiometric air-fuel ratio or stoichiometric) Inlet gas temperature: 700 ° C, 800 ° C, 900 ° C Durability time: 200 hours <Evaluation conditions> Engine : 2000cc, 4 cylinders TBI Dynamic A / F characteristics Amplitude 1A / F Frequency 1Hz Inlet gas temperature: 450 ° C

A / F is ± 1.5 A centered on stoichiometry
/ Sweeping between F, HC, CO, and measuring the gas concentration incoming and outgoing gas concentration of the catalyst of NO _X, was calculated purification rate by the following equation. [(Incoming gas concentration-outgoing gas concentration) / incoming gas concentration] × 100 (1)

A graph is created from this purification rate and A / F,
The intersections of HC and NO _X and CO and NO _X were determined from this graph. Table 1 below shows the obtained cross purification rates.

[0039]

[Table 1] Further, 700 ° C., 800 ° C., 9
FIG. 1 shows the cross-purification rate of HC-NO _X at 00 ° C.

For the evaluation of the temperature characteristics, a heat exchanger is provided between the exhaust gas and the engine to reach the catalyst, the temperature of the exhaust gas entering the catalyst is raised from 150 ° C. to 500 ° C. in 10 minutes, and HC, CO, , 5 purification rate of the NO _X are each
The incoming gas temperature when it reached 0% was measured. The results are shown in Table 2 below.

[0041]

[Table 2] As is clear from Tables 1 and 2 and FIG. 1, the product of the present invention is superior to the conventional product in the catalytic properties particularly on the high temperature side.

[0042]

As described in detail above, since the exhaust gas purifying catalyst of the present invention is excellent in heat resistance, the surface area of a refractory inorganic oxide such as alumina when used in a high temperature range is reduced.
In addition, it is possible to suppress a decrease in catalyst performance due to this.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross purification rate of HC-NO _X.

────────────────────────────────────────────────── (5) References JP-A-5-168927 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53 / 86 B01D 53/94

Claims (2)

(57) [Claims] 1. A catalyst in which an inorganic refractory catalyst carrier is provided with an alumina coat layer containing at least one catalyst component selected from the group consisting of platinum, palladium and rhodium. The layer contains 10 to 40% by weight of crystal particles of the whole alumina coat layer.
A composite oxide in which 5 to 15% by weight of zirconium oxide is dissolved in cerium oxide having a diameter of 50 to 300 A (angstrom) and lanthanum oxide of 2 to 20% by weight of the entire alumina coat layer are contained. Exhaust gas purification catalyst. 2. A method for producing an exhaust gas purifying catalyst in which an alumina coat layer containing a catalyst component is formed on an inorganic refractory catalyst carrier, comprising: (a) a crystal particle diameter of 50 to 300 A (angstrom).
The cerium oxide powder is immersed in a zirconium oxynitrate solution, dried, and calcined at 600 to 800 ° C. for 1 to 5 hours to form a solid solution of 5 to 15% by weight of zirconium oxide in cerium oxide. A step of obtaining an oxide; (b) the composite oxide, lanthanum oxide, γ-alumina and alumina hydrate, wherein the composite oxide is 10 to 40% by weight of the whole alumina coat layer, and the lanthanum oxide is alumina coat. Preparing a slurry by mixing with water so as to be 2 to 20% by weight of the entire layer, coating the slurry on the inorganic refractory catalyst support, drying and firing, and (c) the step (c) b) impregnating the carrier obtained in (b) with a solution containing one or more catalyst components selected from the group consisting of platinum, palladium and rhodium. A method for producing a gas purification catalyst.