METHOD AND APPARATUS FOR PURIFYING EXHAUST GAS

摘要

PROBLEM TO BE SOLVED: To expand a temperature range in which a high nitrogen oxide purification rate is obtained and to control the generation of sulfate by making the average particle size of noble metal particles supported on the inlet side smaller than that of noble metal particles supported on the outlet side of a catalyst. SOLUTION: A monolithic catalyst converter 3 is installed in the exhaust gas route 2 of a diesel engine 1, and a reducing agent supply apparatus 4 which gasifies light oil to supply the gas into exhaust gas is installed on the upstream side. A monolithic catalyst converter 3 receives a monolithic catalyst in which a honeycomb support substrate is coated with a Pt catalyst with different average particle sizes. The average particle size of Pt of the monolithic catalyst is made to be two-stage support structure from the inlet side end surface in the exhaust gas flow direction to the middle and from the middle to the outlet side end surface. The Pt particles with a smaller average particle size than that of the particles on the outlet side are arranged on the inlet side, and the particles with a larger average particle size than that of the particles on the inlet side are arranged on the outlet side. In this way, NOx can be reduced and purified efficiently in a wide temperature range from low to high temperatures, and the generation of sulfate can be controlled.