||Flue gases produced in combustion processes, such as coal-fired power plants, automobiles, smelters, etc., contains huge amount of nitrogen and sulfur oxides, carbon monoxide and particulates. They contribute significantly to atmospheric pollution and some of them are stringently controlled by legistration. Although there are many methods to convert nitrogen and sulfur oxides in flue gases into environmentally compatible products, none of these methods can convert both gases into products in a single reactor simultaneously. The invention provides a new process, which reduce nitrogen and sulfur oxides by carbonyl sulfide over suitable catalysts to nitrogen and high purity elemental sulfur at low temperature. Lowering the reaction temperature of the reactions has enormous advantages in terms of savings in capital investment and operational costs. The process is novel and single-stage. It can apply in the simultaneous, dry and catalytic conversion of sulfur dioxide and nitrogen oxides from gases produced in combustion process into environmentally compatible products and saleable elemental sulfur.