Addition of ruthenium, rhodium, platinum, palladium, iridium, cobalt and molybdenum can be carried out to any of zeolite, iron and a mixture of zeolite and iron, but it is preferably to support on iron or a mixture of zeolite and iron by impregnation. when ruthenium and other metals are impregnated and supported on a zeolite, a step of grinding and mixing thereafter is required so as to bring iron