A noble metal and an NO.sub.x sorption member are loaded on a support which includes composite particles having a structure including a core portion in which ZrO.sub.2 is a major component and a superficial portion formed on a surface of the core portion and including an oxide, whose basicity is lower than ZrO.sub.2, more than the core portion. The composite particles exhibit a high basicity at the inside and a low basicity on the surface by Al.sub.2O.sub.3 or TiO.sub.2 which exists more in the surface. Accordingly, the sulfur-poisoning resistance is improved, and, at the same time, the post-durability NO.sub.x purifying ability is improved.