Patent ID: 8414837
Filing Date: 2013-04-09
Classification: B01D,B01J,F01N,Y02T

Abstract:
1. A selective reduction catalyst for decreasing NOx contained in an exhaust gas of a diesel engine by reacting NOx with a urea-based liquid comprising: a first catalytic layer, which is provided in an exhaust passage of the diesel engine, and which is formed to be porous for allowing an exhaust gas together with ammonia derived from hydrolysis of the urea-based liquid to pass therethrough; and a second catalytic: layer, which is stacked on exhaust-gas downstream-side surface of the first catalytic layer, and which is formed to be porous for allowing the exhaust gas together with ammonia released from the first catalytic layer to pass therethrough; wherein the first catalytic layer a comprises an iron-zeolite catalyst to exhibit catalytic activity by the function of the ammonia as a reducing agent to decrease 60% or more of NOx contained in the exhaust gas within an exhaust-gas temperature range of 150 to 400° C.; wherein the second catalytic layer comprises one or more kinds of a single catalyst, a mixed catalyst, and a complex oxide catalyst selected from a group consisting of iron-alumina, iron-zirconia, iron-ceria, and iron-titania, in a manner to exhibit catalytic activity by the function of the ammonia as a reducing agent to decrease 60% or more of NOx contained in the exhaust gas within an exhaust-gas temperature range of 400 to 700° C. which range is higher than the temperature range where the first catalytic layer exhibits the catalytic activity; and wherein both the first and second catalytic layers cooperatively exhibit catalytic activity to decrease 70% or more of NOx contained in the exhaust gas within an exhaust-gas temperature range of 150 to 700 ° C.