NO can be removed from exhaust gas streams by placing soluble cobalt salts and ethylenediamine (H2NCH2CH2NH2) into basic solutions. The cobalt ethylenediamine acts as a homogeneous catalyst to oxidize NO into soluble nitric dioxide and realize the oxidation and absorption of nitric oxide simultaneously. The dissolved oxygen in equilibrium with the residual oxygen in the exhaust gas stream acts as the oxidant. Lime desulfurization scrubbers can be retrofitted for combined removal of SO2 and NOx from the flue gas by adding cobalt ethylenediamine to lime slurries. The experimental results in a bench-scale scrubber indicate that such a catalyst system can maintain a high NO removal for a long time. NO removal rate increases with a feed oxygen concentration up to 7.8% or higher. According to the experiments performed, a minimum of 0.02 M of CaO is necessary to ensure a high NO removal rate when 1500 PPM of SO2 is present in the feed. The NO removal rate remains the same with an excess of CaO, due to solubility limitations. The optimal temperature is about 50 degreesC. More than 90% of NO and nearly 100% of SO2 in the feed gas are removed by the Co(en)(3)(3+) in a CaO slurry scrubbing solution.