A catalytic exhaust gas purification device and method for the reduction of nitrogen oxides from an exhaust gas of a fossil-fired power plant, having a heating gas duct along a flow direction and having a reactor chamber which is arranged in the heating gas duct is provided. In the reactor chamber there are arranged a first reduction reactor for the reduction of nitrogen oxides NOx to form water H2O and nitrogen N2, an oxidation reactor, which is connected downstream of the first reduction reactor in the flow direction, for the oxidation of nitrogen monoxide NO to form nitrogen dioxide NO2, and a second reduction reactor, which is connected downstream of the oxidation reactor in the flow direction, for the reduction of nitrogen oxides NOx to form water H2O and nitrogen N2. A reduction of nitrogen oxides NOx from an exhaust gas of a fossil-fired power plant is achieved.
