Patent ID: 7662743

Claim:
An NOx purifying catalyst for purifying NOx in exhaust gas discharged from an internal combustion engine with air-fuel ratios controlled to be lean and rich, comprising: a first catalytic layer that includes a β-zeolite having at least one element selected from the group consisting of iron and cerium elements; a second catalytic layer that includes a noble metal and cerium oxide-based material; wherein 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, NOx passes through the first catalytic layer and is oxidized and adsorbed on the second catalytic layer in the lean condition, NOx adsorbed on the second catalytic layer is converted to NH 3 by the reaction with a reductant on the second catalytic layer, the NH 3 is then transferred to and adsorbed on the first catalytic layer in the rich region, and the NH 3 reacts with NOx to be converted to and water, and wherein the content of the noble metal changes in the direction from the first catalytic layer to the support.