Patent ID: 8375704

Claim:
An exhaust system, comprising: an exhaust line through which combusted exhaust gas is exhausted outside; a nitrogen oxide purification catalyst that is mounted on the exhaust line and uses unburned fuel or hydrocarbon to reduce one part of nitrogen oxide in the exhaust gas, and diffuse the other part thereof to store therein; an injector that injects fuel into the exhaust line; a fuel cracking catalyst that is disposed between the injector and the nitrogen oxide purification catalyst to activate the additionally injected fuel from the injector through thermal decomposition so as to generate a reducing agent of high reactivity; a control portion that controls the injector to additionally inject the fuel in a predetermined condition such that the nitrogen oxide purification catalyst uses the activated reducing agent to detach and reduce the nitrogen oxide that is stored therein; wherein the nitrogen oxide purification catalyst includes first and second catalyst layers, the first catalyst layer being disposed close to the exhaust gas, and the second catalyst layer being disposed adjacent to the first catalyst layer; wherein the first catalyst layer reduces a portion of nitrogen oxide contained in the exhaust gas through an oxidation-reduction reaction with the unburned fuel or the hydrocarbon contained in the exhaust gas, and diffuses remaining portion of the nitrogen oxide to the second catalyst layer; and wherein the second catalyst layer stores the diffused nitrogen oxide, and releases the stored nitrogen oxide by a fuel additionally injected in a predetermined period such that the stored nitrogen oxide is reduced at the first catalyst layer, a catalyzed particulate filter mounted on the exhaust line to trap and eliminate particulate materials in the exhaust gas; and an oxidation catalyst that oxidizes pollutant materials that are included in the exhaust gas, wherein the injector, the oxidation catalyst, the catalyzed particulate filter, the fuel cracking catalyst, and the nitrogen oxide purification catalyst are sequentially disposed in a flow direction of the exhaust gas; wherein the control portion controls the injector to inject fuel when a ratio of the hydrocarbon in the exhaust gas to the nitrogen oxide stored in the nitrogen oxide purification catalyst is lower than a predetermined value; wherein the first catalyst layer includes at least one of zeolite catalysts and metal catalysts supported in porous alumina; and wherein the second catalyst layer includes a noble metal and an NOx storing material.