The invention provides a catalyst in which a potassium-manganese-cerium composite oxide is supported in 3DOM (three-dimensionally ordered macroporous materials), and preparation and an application of the catalyst. The catalyst is prepared by taking a three-dimensionally ordered oxide as a carrier and a composite oxide of an alkali metal, a transition metal and a rare earth metal as active components. The catalyst takes the oxide with a three-dimensionally ordered macroporous structure as the carrier and the cheap alkali metal (potassium), the transition metal (manganese) and the rare earth element (cerium) as the active components; a pore structure in the carrier has a large pore size; pores are distributed uniformly; pore passages are arrayed tidily and orderly; nano particles of the active components are distributed uniformly in the carrier; and particle size distribution is relatively narrow.