JPH0418914A - Catalytic converter - Google Patents

Abstract

PURPOSE:To enhance the efficiency in removing NOx exhausted from an engine by using a first wash coat layer of Cu/zeolite structure and depositing noble- metal elements such as Pt on a second wash coat layer. CONSTITUTION:The first wash coat layer 22 of Cu/zeolite structure is formed on a carrier 15, the second wash coat layer 23 consisting of Al2O3 is formed thereon, and plural noble metals such as Pt, Rh and Pd are deposited thereon. The NOx exhausted in the steady running of a lean burn engine is decomposed by the catalytic converter at the active site of the Cu/zeolite structure of the layer 22, and the HC, CO and NOx exhausted from the engine in the transient running carried out with the theoretical air-to-fuel ratio are simultaneously reduced at the active site of the noble-metal elements such as Pt, Rh and Pd deposited on the second layer 23. Namely, the efficiency of the catalytic converter in removing NOx is enhanced.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention aims to improve the purification efficiency of NOx emitted from an engine in which a lean mixture or a mixture at a stoichiometric air-fuel ratio is burned. This article relates to a catalytic converter that can be used.

(Prior Art) It is known that one method for improving the fuel consumption rate of an engine is to burn a lean mixture in the engine. This kind of engine is called a lean burn engine. Lean NOx having a Cu/zeolite structure and having a purification efficiency characteristic curve shown in Fig. 4 is used as a catalyst for decomposing NOx emitted from such a lean burn engine.
x catalyst was used. Note that the Cu/zeolite structure refers to a structure in which Cu is supported on a zeolite structure, a crystal structure consisting of Aρ and Si.

(Problems to be Solved by the Invention) Incidentally, in the lean burn engine, the engine burns a lean air-fuel mixture during steady operation, and burns an air-fuel mixture at a stoichiometric air-fuel ratio during transient operation such as during acceleration.

However, when a conventional lean NOx catalyst is used to purify the exhaust gas of a lean pan engine, the engine burns the air-fuel mixture at the stoichiometric air-fuel ratio during transient operations such as during acceleration, resulting in large amounts of emissions near the stoichiometric air-fuel ratio. It was not possible to completely purify the generated NOx. This is as shown in Figure 4.
This is because the NOx purification efficiency of the conventional NOx catalyst is about 50% near the stoichiometric air-fuel ratio.

The present invention has been made in view of the above points, and its purpose is to provide a catalytic converter that can improve the purification efficiency of NOx emitted from an engine that burns a lean mixture or a mixture at a stoichiometric air-fuel ratio. It is about providing.

[Structure of the invention] (Means for solving the problem) Forming first and second wash coat layers on a carrier,
The first washcoat layer has a Cu/zeolite structure, and the second washcoat layer is coated with Pt, Rh, and P.
This is a catalytic converter characterized by carrying one or more noble metal elements such as d.

(Function) NOX emitted during steady operation of a lean burn engine
is decomposed by the active sites of the Cu/zeolite structure of the first washcoat layer, and during transient operation at the stoichiometric air-fuel ratio, the H C, CC/,
P with NOx supported on the second washer coat layer
The active sites of noble metal elements such as t, Rh, and Pd are simultaneously reduced.

(Example) A catalytic converter according to an example of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the state of support on a carrier, FIG. 2 is a sectional view taken along the axial direction of the catalytic converter, and FIG. 3 is a sectional view taken along the radial direction of the catalytic converter.

First, in FIG. 2, 11 is a catalyst controller 7<--. This catalytic converter 11 has a cylindrical cross section,
Its outer periphery is composed of an intake section 12 into which exhaust gas flows, a container section 13 where a catalyst is housed, and a discharge section 14 from which purified exhaust gas is discharged.

Furthermore, 15 is a carrier made of ceramic or metal and having a l\nicum shape. A countless number of cells [6] surrounded in four directions by the carrier 15 are formed in the axial direction.

Then, regarding the structure on the carrier 15, the first +'pj
Explain with reference to. A first coating layer 22 having a Cu/zeolite structure is formed on the carrier 15, and an Ag2 coating layer 22 is formed on the first coating layer 22.
A second washcoat layer 23 made of O3 is formed. On this second wash coat layer 23, Pt
, Rh, and Pd are supported.

By using the catalyst controller 7 configured as described above, NOx emitted during steady operation of the lean burn engine is promoted to be decomposed by the active sites of the Cu/zeolite structure of the first washcoat layer 22. , during transient operation when operating at the stoichiometric air-fuel ratio, HC discharged from the engine,
At the same time, the active sites of noble metal elements such as ptRh and Pd supported on the second washcoat layer 23 are reduced. In other words, the NOx purification efficiency of the catalytic converter according to one embodiment of the present invention is shown by the solid line in FIG.

In the above embodiment, the second washcoat layer 23 supports a plurality of noble metal elements such as Pt, Rh, and Pd, or may support a single noble metal element among them.

Furthermore, the first washcoat layer 22 and the second washcoat layer 23 may be reverse layers.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to improve the purification efficiency of NOx emitted from an engine that is burned with a lean mixture or a mixture with a stoichiometric air-fuel ratio. Can provide catalytic converter.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing a state in which a contact contourer according to an embodiment of the present invention is supported on a carrier, Fig. 2 is a cross-sectional view along the axial direction of the catalytic converter, and Fig. 3 is a diameter of the catalytic converter. FIG. 4, which is a sectional view along the direction, is a characteristic diagram showing the relationship between NO8 purification efficiency and air-fuel ratio. 11. Catalytic converter, 15. Support, 22. The second wosonyu coat layer, 23. The second wosonyu coat layer.

Claims (1)

[Claims] First and second washcoat layers are formed on the carrier, the first washcoat layer has a Cu/zeolite structure, and the second washcoat layer has Pt, Rh.
A catalytic converter characterized by carrying one or more precious metal elements such as , Pd, etc.