Simultaneously achieving selective catalytic reduction of NOx with NH3 and catalytic oxidation of CO with O2 over one finely optimized bifunctional catalyst Mn2Cu1Al1Ox at low temperatures

Abstract

For coke oven flue gases, the simultaneous removal of NOx and CO pollutants is highly demanded but still remains a big challenge. So far there isn't a single efficient catalyst that can simultaneously achieve selective catalytic reduction of NOx by NH3 and the catalytic oxidation of CO to CO2 in the presence of excessive O2 at low temperatures (180–220 °C). Here, we report a bifunctional catalyst Mn2Cu1Al1Ox that possesses dual active sites and is highly active for both NH3-SCR and CO oxidation reactions under the above mentioned conditions. By tuning the redox properties and surface oxygen vacancies, the optimized Mn2Cu1Al1Ox catalyst achieved high conversions of both NOx and CO in the NH3-NO-CO-O2 system, with a NOx conversion of 86.8% and a CO conversion of 100% at 200 °C. The active reaction sites and the interaction principal between NH3-SCR and CO oxidation reactions were thoroughly investigated by well-designed experiments, in-situ DRIFTS and DFT calculations. It was revealed that NH3 and CO competed for the same active sites, which significantly influenced the catalytic performance of Mn3Al1Ox and Cu3Al1Ox for CO oxidation reactions. For the bifunctional Mn2Cu1Al1Ox catalyst, CO is more easily adsorbed on the Cu sites, while NH3 is more inclined to adsorb on the Mn sites, which enables both NH3-SCR and CO oxidation reactions to proceed simultaneously on one catalyst. The improvement of CO oxidation performance on Mn2Cu1Al1Ox catalyst is mainly attributed to the reduced Jahn-Teller effect of Cu atoms by doping into Mn3O4, which leads to the lift of d-band center and finally enhances the CO adsorption.