JPH0474534A - Exhaust gas purifying catalyst - Google Patents

Abstract

PURPOSE:To obtain a catalyst having good purifying efficiency even in an oxidative atmosphere by providing alumina containing platinum and/or palladium, alumina containing rhodium supported on zirconium oxide and iridium- containing alumina on a single base material. CONSTITUTION:The first layer of alumina containing platinum and palladium, the second layer of alumina containing rhodium mainly supported on zirconium oxide and the third layer of a alumina containing iridium in its surface layer are provided on a single base material composed of cordierite or the like. The exhaust gas purifying catalyst thus obtained generates no sudden lowering of NOx purifying efficiency not only in a reductive atmosphere but also in an oxidative atmosphere while keeps heat resistance.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is directed to the treatment of hydrocarbons (IIc), -carbon oxides (IIc), which are harmful components in exhaust gas emitted from internal combustion engines such as automobiles.
Co), relates to an exhaust gas purification catalyst that efficiently purifies nitrogen oxides (NOX).

(Prior art) Conventional exhaust gas purification catalysts include those having a layer of alumina containing platinum (Pt), palladium (Pd), and rhodium (Rh) on a single base material, or those having a layer of alumina containing platinum (Pt), palladium (Pd), and rhodium (Rh) on a single base material; A number of catalysts have been proposed, including those with a first layer of alumina containing one or both of platinum and palladium, and a second layer of alumina containing rhodium.

(Problem to be Solved by the Invention) However, in the conventional exhaust gas purification catalyst as described above, the amount of oxygen exceeds the theoretical amount required to completely oxidize reducing agents such as HC, Co, and ■2. However, when used in an atmosphere with little oxygen, that is, a reducing atmosphere, it produces good NOx
However, in an oxidizing atmosphere with a large amount of oxygen, the NOx purification rate suddenly decreases.

(Means for Solving the Problems) Under the current circumstances, the inventors have attempted to solve the above problems (as a result of intensive research, they have focused on the fact that iridium (Ir) has a NOx purifying effect, and have incorporated Ir into the coating layer of the catalyst. If the same amount of Ir is supported on the coating layer, the thickness of the coating layer is about 100 μm in the case of a single layer.
Ir is dispersed and supported at 00 μm. However, when there are three coat layers and a thickness of about 100 μm, each layer has a thickness of about 33 μm, and Ir is supported on the outermost layer of 33 μm, so that the Ir concentration is higher than that in a single layer. Therefore, the higher the metal concentration, the more likely it is to contribute to the reaction. Based on this, a layer made of alumina containing Ir is provided in the layer exposed to exhaust gas (hereinafter referred to as the surface layer or third layer), and a second layer below the surface layer is made of rhodium mainly supported on zirconium oxide. It has been confirmed that by providing an alumina layer containing alumina, it is possible to prevent a rapid decrease in the NOx purification rate in an oxidizing atmosphere, and the present invention has been achieved.

That is, the exhaust gas purifying catalyst of the present invention has a first layer made of alumina containing one or both of platinum and palladium on a single base material, and a second layer made of alumina containing rhodium supported mainly on zirconium oxide. and a third layer made of alumina containing iridium.

(Function) In the present invention, an alumina layer containing Ir is provided on the surface layer, and an alumina layer containing rhodium supported mainly on zirconium oxide is provided on the second layer below the surface layer, so that it is heat resistant. While maintaining its properties, the NOx purification rate does not drop significantly even in an oxidizing atmosphere as well as a reducing atmosphere.

The amount of Ir added is preferably in the range of 0.23 to 4.59 g per single element.

(Examples) The present invention will be explained below with reference to Examples, Comparative Examples, and Test Examples.

The support is made by coating alumina on an integrated support made of cordierite on a sharp edge, and its composition is a layer of alumina containing palladium as the first layer, and a layer of rhodium supported mainly on zirconium oxide as the second layer. a third layer of alumina containing
A catalyst was prepared using an alumina layer containing iridium as a layer.

Activated alumina powder whose main component is γ-alumina,
It is immersed in a dinitrodiaminopalladium aqueous solution of 25 g/f in terms of palladium metal, dried, and then fired.
A powder was obtained. A washcoat slurry was produced by ball milling this powder with water and acetic acid. A cordierite monolithic support having a volume of 1.31 and containing 400 channels per square inch of cross-sectional area was then immersed in the washcoat slurry. Subsequently, the excess liquid was wiped off with compressed air, and the integrated product was dried to remove free water, and then baked at 400°C for 1 hour to obtain 160g
/32 carrier was coated with alumina to form the first layer.

Next, the same activated alumina powder as above was impregnated with zirconia nitrate so that the amount of zirconium was 3% by weight and fired to obtain a zirconium-supported alumina powder. This zirconium-supported alumina powder was immersed in an aqueous rhodium nitrate solution, dried, and then fired to obtain a powder. A washcoat slurry was produced by ball milling this powder with water and acetic acid. The first layer palladium-alumina carrier described above was then immersed in the wash coat. Subsequently, the excess liquid was wiped off with compressed air, and the integrated product was dried, fired, and coated to give 40 g/12 carrier as a second layer.

Next, the same activated alumina powder as above was immersed in an aqueous solution of hexachloroiridic acid, dried, and then fired to obtain a powder. A washcoat slurry was produced by ball milling this powder with water and acetic acid. Then, the carrier having the first layer of palladium-containing alumina layer and the second layer of rhodium-zirconium oxide-containing alumina layer was immersed in the washcoat slurry. Subsequently, the excess liquid was wiped off with compressed air, and this integrated product was dried and fired, weighing 40 g, #! - A coating that becomes a carrier and serves as a third layer.

From the above, Catalyst 1 with a coating layer of 240 g/ff1-carrier was obtained. The amount of palladium supported was 1.53 g/piece, the amount of rhodium was 0.31 g/piece, and the amount of iridium was 1.56 g/piece.

Example 2 Catalyst 2 was also obtained in the same manner as in Example 1 except that dinitrodiaminoplatinum was used in the first layer and platinum was supported instead of palladium.

Actual Deterioration I''1 Catalyst 3 was obtained in the same manner as in Example 1 except that palladium and platinum were supported on the first layer using their respective starting salts. In addition, palladium 0.77 g/piece, platinum 0.7
It was supported at a weight of 7 g/piece.

Comparison A catalyst was prepared by coating an integral support made of flaming cordierite with alumina to form a support, and making the structure a single layer with an alumina layer containing palladium and rhodium.

Alumina powder similar to that used in Example 1 was immersed in an aqueous dinitrodiaminopalladium solution, dried, and then fired to obtain a powder. At the same time, a similar alumina powder was immersed in an aqueous rhodium nitrate solution, dried, and then fired to obtain a powder. A washcoat slurry was produced by ball milling these two powders with water and acetic acid.

Then, a 1.3r cordierite monolithic carrier similar to that used in Example 1 was immersed in the washcoat slurry. Subsequently, the excess liquid was wiped off with compressed air, and the integrated product was dried to remove free water, and then heated for 40 minutes.
It was calcined at 0°C for 1 hour and coated with alumina to give 240g/ff-carrier, thereby obtaining catalyst A. In addition,
The amount of palladium is 1.53g/piece, the amount of rhodium is 0.31
g/piece.

Catalyst B was obtained in the same manner as in Comparative Example 1 except that palladium was replaced with platinum.

A catalyst C was obtained in the same manner as in Comparative Example 1 except that the noble metals were changed to platinum, palladium, and rhodium. In addition, platinum is 0.77 g/piece, palladium 0.77 g/piece
rhodium was supported at a concentration of 0.31 g/piece.

Comparison Alumina was coated on an integrated support made of Masudo cordierite to form a support, and the first layer was an alumina layer containing palladium, and the second layer was an alumina layer containing rhodium, and a catalyst was prepared. did.

Alumina powder similar to that used in Example 1 was immersed in a dinitrodiaminopalladium aqueous solution, dried, and then fired to obtain a powder. A washcoat slurry was produced by ball milling this powder with water and acetic acid. A 1.31 cordierite monolithic carrier similar to that used in Example 1 was then immersed in the washcoat slurry. Subsequently, the excess liquid was wiped off with compressed air, the integrated product was dried to remove free water, and then calcined at 400 °C for 1 hour and coated with alumina to give 200 g/ρ-support. This was the first layer.

Next, the same activated alumina powder as above was immersed in an aqueous rhodium nitrate solution, dried, and then fired to obtain a powder.

A washcoat slurry was produced by ball milling this powder with water and acetic acid. Then, the carrier provided with the first palladium-containing alumina layer described above was immersed in the wash coat slurry. Subsequently, the excess liquid was wiped off with compressed air, and this integrated product was dried, fired, and coated to a weight of 40 g/θ-carrier to form a second layer.

From the above, a catalyst layer of 240 g of coat layer/Q-carrier was obtained. In addition, the amount of palladium is 1.53 g/piece, and the amount of rhodium is 0.
The weight was 31 g/piece.

Comparison Basis 1 Catalyst E was obtained in the same manner as in Comparative Example 4 except that palladium was replaced with platinum.

Catalyst F was obtained in the same manner as in Comparative Example 4 except that the starting salts of palladium and platinum were supported in the first layer. In addition, palladium 0.77g/piece, platinum 0.77g/piece
g/piece.

Comparison 1 Catalyst G was obtained in the same manner as in Example 1, except that the third layer was removed.

Northern Flame ■ In Comparative Example 1, iridium was further impregnated into the aluminum to form the three components of palladium, rhodium, and iridium to obtain catalyst H. In addition, the amount of palladium is 1.53 g
The amount of rhodium was 0.31 g'/piece, and the amount of iridium was 1.56 g'/piece.

Test Basis Catalysts 1 to 3 obtained in Examples 1 to 3 and catalysts A to 3 obtained in Comparative Examples 1 to 8 were subjected to engine durability under the following conditions, and the conversion rate of each component was determined to be A/F13. 4-16.0
Measured by bench engine evaluation in the range of .

Catalyst inlet temperature 650°C Endurance time 25 hours Endurance mode 10 modes Engine Space velocity equivalent to 2200cc displacement
Approximately 70,000H Durable log gas atmosphere Co 0.4-0.6% 0□ 0.5±0.1% No 1001000 pp 2500ppm CO□ 14.9±0.1% Evaluation-JLJr-Production evaluation catalyst inlet Conditions 400″C Frequency 1.0ΔA/F 10.1 Engine Displacement equivalent to 2000cc A/F measurement range 14.0 to 15.7 The test results are shown in Table 1.

(Effects of the Invention) As described above, according to the present invention, the structure of the conventional exhaust gas purifying catalyst is changed to include a layer made of alumina containing iridium on the surface layer, and furthermore, the layer below the surface layer is mainly made of alumina. Since it is equipped with a layer of alumina containing rhodium supported on zirconium oxide, it maintains heat resistance while also reducing NO in an oxidizing atmosphere as well as a reducing atmosphere.
This provides the effect that the purification rate of X does not drop sharply.

Claims (1)

[Claims] 1. A first layer consisting of alumina containing one or both of platinum and palladium on a single base material, a second layer consisting of alumina containing rhodium supported mainly on zirconium oxide, and a third layer consisting of alumina containing iridium. An exhaust gas purifying catalyst characterized by having layers.