PURPOSE: To decompose by reduction nitrogen oxides in exhaust with a high oxygen concentration and to improve a nitrogen conversion ratio by mounting a specified metal element on the surface of a carrier of a phosphate composition comprising Cu, Zr, P, and O and having a specified crystal phase.

CONSTITUTION: A carrier containing at least Cu, Zr, P, and O has a Zr/Cu molar ration of 3.9-4.1 and a P/Cu molar ratio of 5.9-6.1. The X-ray diffractometry of the powder of the carrier of a phosphate composition indicates the interplanar spacings of 4.45±0.1, 3.98±0.08, 3.78±0.08, 3.35± 0.07, 3.14±0.07, 3.05±0.05, 2.88±0.05, 2.80±0.05, 2.75±0.05, and 2.56±0.05. One or more kinds of metal elements selected from Ag, Mn, Co, Ni, and Zn are mounted on the surface of the carrier. The phosphate composition of this kind has an activity of decomposition by reduction of NOx even in an atmosphere with a high oxygen concentration.