Exhaust gas purifying system and catalyst

a technology of exhaust gas purification system and catalyst, which is applied in the direction of physical/chemical process catalyst, metal/metal-oxide/metal-hydroxide catalyst, and separation process, etc. it can solve the problem that the catalytic activity (for oxidation) of platinum and rhodium cannot be sufficiently demonstrated, and the catalyst cannot reduce nox

Inactive Publication Date: 2001-06-28
NISSAN MOTOR CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Hitherto three-way catalysts for simultaneously oxidizing carbon monoxide (CO) and hydrocarbons (HC) and reducing nitrogen oxides (NOx) have been extensively used as exhaust gas purifying catalysts installed to internal combustion engines of automotive vehicles and the like, However, such catalysts cannot reduce NOx particularly when exhaust gas of the engine is oxygen-excessive (i.e., has an air-fuel ratio leaner than stoichiometric value).
That is, the NOx reducing method requires to periodically lower the oxygen concentration in exhaust gas in an engine operating region where exhaust gas takes the oxygen-excessive atmosphere.
This makes it impossible to obtain fuel economy improvement effect due to vehicle running on oxygen-excessive air-fuel mixture having an air-fuel ratio leaner than the stoichiometric value.
Additionally, in the above NOx reducing method, the catalyst contains a large amount of alkali metal and alkaline earth metal for the purpose of trapping NOx in the oxygen-excessive atmosphere of exhaust gas, and therefore a catalytic activity (for oxidation) of platinum and rhodium cannot be sufficiently exhibited when exhaust gas is low in temperature.
However, such the NOx reducing catalyst or the three-way catalyst disposed downstream of the NOx reducing catal...

Method used

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  • Exhaust gas purifying system and catalyst

Examples

Experimental program
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Effect test

example 1

(A) Preparation of a Closed Coupled Three-way Catalyst HC and CO Reforming Devices)

[0052] Pt, Pd and Rh (noble metals) and Ce and Zr (added components) were carried on activated alumina powder thereby to prepare catalytic powder. The catalytic powder was formed into slurry. This slurry was coated on a ceramic honeycomb-type monolithic substrate having a volume of 1.3 liters and formed with a plurality of axially extending cells each of which is defined by axially extending thin walls, so that the walls of the cells were coated with the slurry. Thereafter, the coated monolithic substrate was blown with air stream to remove excessive slurry in the cells, and dried at 130.degree. C. and then fired at 400.degree. C. for 1 hour. As a result, a closed coupled three-way catalyst was obtained carrying the noble metals in a total amount of 500 g per one cubic feet of the monolithic substrate, in which a weight ratio of Pt / Pd / Rh was 1 / 1 / 100 / 1 / 4. The closed coupled three-way catalyst was desig...

example 2

[0061] A closed coupled catalyst was prepared in the same manner as that in Example 1.

[0062] A NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 1 with the exception that 15 g of Cs was carried per one liter of the monolithic substrate.

[0063] An exhaust gas purifying system of Example 2 was constructed similarly to that in Example 1.

example 3

[0064] A closed coupled catalyst was prepared in the same manner as that in Example 1.

[0065] A NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 1 with the exception that the catalyst C was further impregnated with barium acetate and magnesium acetate so that 10 g of Ba (calculated as oxide) and 5 g of Mg (calculated as oxide) were carried per one liter of the monolithic substrate.

[0066] An exhaust gas purifying system of Example 3 was constructed similarly to that in Example 1.

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Abstract

An exhaust gas purifying system for an automotive internal combustion engine which discharges oxygen-excessive exhaust gas under lean-burn operation. The exhaust gas purifying system comprises a NOx reducing catalyst for reducing NOx in the presence of at least hydrogen serving as reducing agent. The NOx reducing catalyst is disposed in an exhaust gas passageway of the engine. The NOx reducing catalyst includes a porous substrate, and platinum and cesium carried on the porous substrate. A catalyst is disposed in the exhaust gas passageway in order to produce hydrogen so as to enrich the oxygen-excessive exhaust gas with hydrogen before the oxygen-excessive exhaust gas reaches the NOx reducing catalyst. The oxygen-excessive exhaust gas enriched with hydrogen is introduced through the exhaust gas passageway to the NOx reducing catalyst. Here, the oxygen-excessive exhaust gas enriched with hydrogen is brought into contact with the NOx reducing catalyst under a condition in which temperature of at least one of the NOx reducing catalyst and the oxygen-excessive exhaust gas enriched with hydrogen is within a range of from 250 to 600° C.

Description

BACKGROUND OP THE INVENTION[0001] This invention relates to improvements in an exhaust gas purifying system for purifying exhaust gas discharged from an internal combustion engine, a furnace, a burner or the like, and more particularly to the exhaust gas purifying system for effectively reducing nitrogen oxides (NOx) in oxygen-excessive exhaust gas discharged from the engine under lean-burn operation.[0002] Hitherto three-way catalysts for simultaneously oxidizing carbon monoxide (CO) and hydrocarbons (HC) and reducing nitrogen oxides (NOx) have been extensively used as exhaust gas purifying catalysts installed to internal combustion engines of automotive vehicles and the like, However, such catalysts cannot reduce NOx particularly when exhaust gas of the engine is oxygen-excessive (i.e., has an air-fuel ratio leaner than stoichiometric value). In this regard, Japanese Patent No. 2600492 discloses a so-called rich spike process as a method of reducing NOx when exhaust gas of the eng...

Claims

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Application Information

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IPC IPC(8): B01D53/94B01J23/58F01N3/10F01N3/20F01N13/02
CPCB01D53/9454B01D53/9495B01D2251/104B01D2259/804F01N3/206F01N2240/30F01N2570/14F01N2610/04Y02C20/10Y02T10/22F01N13/009Y02T10/12Y02A50/20
Inventor HANAKI, YASUNARISUGA, KATSUO
Owner NISSAN MOTOR CO LTD
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