Bifunctional catalyst of CuMn-HZSM-5 for selective catalytic reduction of NO and CO oxidation under oxygen atmosphere

Simultaneous removal of NOx and CO from steel sintering has attracted great attention because it is difficult to balance the catalyst reducibility and surface acidity merely using metal oxides or zeolite catalysts. In this study, a mixed CuMn-HZSM-5 catalyst was prepared via an impregnation method. The optimized sample exhibited excellent performance with 90% NO conversion and 100% CO conversion at 175 °C. The activity window of the catalyst was coincident with the actual demand of sintering flue gas control at 150-250℃. The active component CuMn suppressed the excessive Lewis acid sites on the zeolite support for NH3 adsorption, while the reducibility of the catalyst also decreased compared with that of pure CuMn metal oxides. This synergistic effect was beneficial for the reduction of NH3 nonselective oxidation with O2. In addition, both the DFT and DRIFTS results revealed that NO conversion was improved by CO introduction at low temperature, since NO could adsorb on the CO-preadsorbed sites for the reduction to N2 via the O atoms of Mn3c sites, i.e., adsorbed CO could also serve as a reductant to reduce NO to N2, which provides another reaction pathway in SCR reactions. Moreover, the NO2− and N2O2− species were observed in the spectra as key intermediates to oxidize CO to CO2, which are also the promoters for CO control.