Patent ID: 6479026
Filing Date: 2002-11-12
Classification: B01D

Abstract:
A method of denitrating exhaust gas for removing nitrogen oxides by catalytic reduction, in which a nitrogen-oxide-containing exhaust gas is introduced into a catalyst-filled reaction chamber and ammonia is added in an excessive amount of reducing agent, the method comprising the steps of: introducing exhaust gas and ammonia into a first denitrating catalyst layer disposed on an upstream side in the gas stream to remove nitrogen oxides; supplying the gas into a first ammonia decomposing catalyst layer disposed on a downstream side from the first denitrating catalyst layer to control the ammonia content to be suitable for the subsequent denitrating process, wherein the first ammonia decomposing catalyst layer having ability to oxidatively decompose unreacted ammonia into nitrogen and nitrogen oxides; then supplying the gas into a second denitrating catalyst layer disposed on a downstream side of the first ammonia decomposing catalyst layer; and supplying the gas into a second ammonia decomposing catalyst layer disposed on a downstream side of the second denitrating catalyst layer to remove the residual ammonia, the second ammonia decomposing catalyst layer being provided with a catalyst which can oxidatively decompose the residual ammonia into nitrogen and nitrogen oxides or a catalyst which can oxidatively decompose the residual ammonia into nitrogen oxides wherein the catalyst used in the second ammonia decomposing catalyst layer contains one or more oxides selected from the group consisting of silica, titania and zirconia as catalyst support, and one or more metals selected from the group consisting of platinum, rhodium, palladium, ruthenium and iridium as active metal.