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

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.

Images