Catalyst for purifying oxygen rich exhaust gas

Abstract

The invention relates to a first catalyst for purifying an exhaust gas. The first catalyst has a substrate and a catalytic coating formed thereon. This catalytic coating has first and second grains. The first grain includes a porous carrier supporting thereon at least one of palladium and rhodium. The second grain includes a double oxide supporting thereon at least one of platinum and palladium. This double oxide is represented by a formula of (La.sub.1-x A.sub.x).sub.1-.alpha. BO.sub..delta. where A is at least one element selected from barium, potassium and cesium, B is at least one of iron, cobalt, nickel and manganese, 0<X<1, 0<.alpha.<0.2, and .delta. is a number such that a net electric charge of the first double oxide becomes zero. The invention further relates to a second catalyst similar to the first catalyst. The first grain of the second catalyst includes a porous carrier supporting thereon at least one of platinum, palladium, rhodium and iridium. The second grain of the second catalyst includes a double oxide represented by a formula of (La.sub.1-x A.sub.x).sub.1-.alpha. BZr.sub..beta. O.sub..delta. where A, B, x, .alpha. and .delta. are defined as above and 0<.beta.<1. The first and second catalysts are each improved in NOx absorption capability and capable of purifying NOx contained in an oxygen rich exhaust gas, even after the passage of an exhaust gas of high temperature for a long time through these catalysts.