NOx exhaust gas purifying catalyst

摘要

The present invention provides an NOx purifying catalyst that removes NOx with sufficient efficiency even under low temperature operation such as diesel engine automobiles. An NOx purifying catalyst for processing NOx in exhaust gas by rich/lean control of the air-fuel ratio of the exhaust gas, includes a first catalytic layer containing ²-zeolite having iron and/or cerium elements, and a second catalytic layer including a noble metal and cerium oxide-based material; in which the second and the first catalytic layers are coated on a support in that order so that the first catalytic layer is the uppermost layer. The NOx purifying catalyst purifies NOx as showed in Reaction Formulations (1) to (4).
€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ Lean condition 1: NO + 1/2O 2 -> NO 2 €ƒ€ƒ€ƒ€ƒ€ƒ(1)
€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ Rich condition: CO + H 2 O †’ CO 2 €ƒ€ƒ€ƒ€ƒ€ƒ(2)
€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ NO x + H 2 †’ NH 3 €ƒ€ƒ€ƒ€ƒ€ƒ(3)
€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ Lean condition 2: NO x + NH 3 + O 2 -> N 2 + H 2 O€ƒ€ƒ€ƒ€ƒ€ƒ(4)