Patent ID: 8372366

Claim:
A NOx purifying catalyst used for purification of NOx in exhaust gas emitted from an internal combustion engine in which an air/fuel ratio is controlled to be in a lean or rich state, wherein: the catalyst comprises a first catalyst layer and a second catalyst layer; NOx passes through the first catalyst layer, and the NOx having thus passed through is oxidized and adsorbed by the second catalyst layer, in the lean state; the NOx thus adsorbed by the second catalyst layer is converted to NH 3 by a reducing component on the second catalyst layer, and then the NH 3 is adsorbed by transferring to the first catalyst layer, in the rich state; the NH 3 subsequently reacts with NOx to be converted to nitrogen and water; the first catalyst layer includes a cerium oxide-based material and a beta zeolite having elemental iron; the second catalyst layer includes a noble metal, a cerium oxide-based material, and a heat resistant inorganic oxide; and the second catalyst layer and the first catalyst layer are sequentially laminated on a carrier, and the first catalyst layer is formed so as to be a top layer, wherein the second catalyst layer is configured so that content of the noble metal decreases sequentially or step-wise from a side of the first catalyst layer toward a carrier side thereof.