Exhaust gas purification apparatus, exhaust gas purification method, and sulfur component trapping agent for internal combustion engine

Abstract

An object of the present invention is to provide a new exhaust gas purification apparatus for an internal combustion engine operated under a condition of an air fuel ratio leaner than a theoretical air fuel ratio, a method for purification of exhaust gas and an exhaust gas purification catalyst, which is suitable for suppressing degradation of the NOx purification catalyst by sulfur components. An exhaust gas purification apparatus for an internal combustion engine, which comprises an exhaust gas passage for an internal combustion engine into which exhaust gas of lean air fuel ratio and rich or stoichiometric air fuel ratio flows, a NOx trapping catalyst that functions to trap NOx in the exhaust gas when the air fuel ratio is lean, a sulfur component trapping agent for trapping sulfur components in the exhaust gas, which is disposed before the NOx trapping catalyst, and a catalyst for oxidizing the sulfur components, which is disposed before the sulfur component trapping agent, wherein the sulfur component trapping agent has a trapping rate of 85 % or more of an amount of inflow sulfur in a trapping test at a flow rate of 150 ppm SO3-5% O2—balance being N2 gas per 1.5 moles of the sulfur trapping agent at 300° C. and a space velocity of 30,000 / h for 1 hour; and the sulfur component trapping agent has a release rate of sulfur amount of 5 % or less of sulfur trapped in the sulfur component trapping agent in a release test under a flow of a 3000 ppm H2-600 ppm C3H6-3000 ppm O2-3.5 % CO—balance being N2 gas at a temperature elevation rate of 10° C. / min from 250 to 750° C. at an sulfur component trapping agent entrance, after the trapping test.

Description

TECHNICAL FIELD [0001] The present invention relates to an exhaust gas purification apparatus and exhaust gas purification method for an internal combustion engine operated under a lean burn condition, wherein fuel is leaner than a theoretical air / fuel ratio. BACKGROUND ART [0002] In recent years, there have been attention to lean burn engines for lean fuel combustion in terms of an air fuel ratio. The air fuel ratio represents a ratio of air to fuel in gas. [0003] Three way catalysts that have been used for exhaust gas purification of engines for theoretical air fuel ratio (stoichiometry) combustion have difficulty in purifying NOx. Thus, exhaust gas purifying catalysts for lean burn engines are investigated. One of them is disclosed in Japanese patent laid-open 11-319564(Patent publication 1) is disclosed. The publication discloses one of NOx absorbing metal oxides selected from alkali metals, alkaline earth metals and rare earth metals and a noble metal supported on a porous supp...

AI Technical Summary

Benefits of technology

[0009] The S purge makes fuel cost worse because it employs rich air fuel ratio. When a large amount of sulfur components adheres to the NOx trapping catalyst or NOx purification catalyst, an amount of a reducing agent for removing sulfur components as the amount of adhered sulfur components increases. As a result, a degree of rich air fuel ratio becomes large (the air fuel ratio becomes small), which makes the fuel cost worse. Further, once a large amount of sulfur components adhere to the NOx trapping catalyst, sulfur components that strongly react with the NOx trapping agent are hard to be removed thereby to lower the purification performance.

[0011] According to the technologies disclosed in Japanese patent laid-open 8-192051 (Patent document 2), adhesion of sulfur components to the NOx trapping catalyst at the time of lean air fuel ratio is suppressed and NOx trapping performance becomes lower.

[0015] An object of the present invention is to provide a sulfur component trapping agent that removes the above-mentioned disadvantages and can trap sulfur components for a long time, an exhaust gas purification apparatus and an exhaust gas purification method.

[0019] A still another feature of the present invention resides in that a sulfur component trapping agent is disposed in the previous stage of the NOx trapping catalyst so as to suppress reduction of catalytic activity by the sulfur adhesion and a catalyst for oxidizing sulfur in the exhaust gas is disposed in the previous stage of the sulfur component trapping agent. The sulfur trapping agent includes a support that holds sulfur components in the exhaust gas.

[0030] The sulfur component trapping agent or the exhaust gas purification apparatus according to the present invention can suppress degradation of the NOx purification catalyst for the internal combustion engine, which is operated under the lean burn condition of which the air fuel ratio is leaner than that of theoretical air fuel ratio.

[0031] Further, the present invention can provide an internal combustion engine for automobiles and an exhaust gas purification apparatus that has good fuel consumption, suppressed degradation of a NOx purification catalyst caused by sulfur component and a small amount of sulfur component emission.

Problems solved by technology

Three way catalysts that have been used for exhaust gas purification of engines for theoretical air fuel ratio (stoichiometry) combustion have difficulty in purifying NOx.

However, it has been known that since the exhaust gas from the lean burn engines contains SOx derived from sulfur contained in gasoline, activity of the catalysts is deteriorated by SOx, which reacts with components in the NOx trapping catalysts.

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