Abstract: An apparatus for catalytic reduction of a nitrogen oxide in a waste gas includes a regenerative heat exchanger containing a heat-storage material consisting at least partially of a catalytic material, inlet and outlet conduits for supplying the waste gases to the heat exchanger and for delivering purified waste gases from the apparatus, respectively, first and second hoods arranged in inlet and outlet conduits respectively, on opposite sides of the heat storage material, a conduit for conducting a gaseous medium through heat exchanger, the gaseous medium flowing, in heat exchanger, through first and second hoods, and a conduit for supplying a reducing agent into the heat exchange for assisting in the catalytic reduction of the nitrogen oxide in the waste gases by the heat-storage material.