PURPOSE: To enhance high-calorie gas converting capacity, by supporting catalyst components which are the combination of manganese oxide and a platinum group metal with iron and/or cobalt by a carrier comprising silica and/or alumina.
CONSTITUTION: Iron and/or cobalt, manganese and a platinum group metal are infiltrated in a carrier made of silica and/or alumina in a nitrate or chloride aqueous soluton form by a spray, scattering or immersing means. Subsequently, drying, ammonia treatment, thermal cracking and hydrogen reducing processes are successively applied to the impregnated carrier to prepare a reducing catalyst. The supporting quantity of iron and/cobalt is pref. 3-15 % by weight of the total catalyst and the atomic ratio of iron and/or cobalt to manganese is preferably 5:1-5:4 and the atomic ratio of iron and/or cobalt to the platinum group metal is preferably 30:1-5:2.