Getting insight into the CO tolerance over Co-modified MnSm/Ti catalyst for NH3-SCR of NOx at low temperature: Experiments and DFT studies

Abstract

The existence of carbon monoxide (CO) in industrial boilers flue gas can suppress the performance of the selective catalytic reduction with NH3 (NH3-SCR) for NOx removal at low temperatures over the Mn-based catalyst, and the related mechanism is needed to be revealed for improving the NH3-SCR performance. In this work, the effects of CO on the NH3-SCR performance over MnSm/Ti catalyst were studied, and the CO tolerance of the catalyst with cobalt (Co) modification at low temperatures was evaluated. The DFT calculations were performed to reveal the mechanism for the modification of Co over the MnSm/Ti catalyst. The NOx conversion for MnSm/Ti catalyst decreased by 15.2%-21.4% at 150–300 ℃ due to the presence of CO in the NH3-SCR reaction atmosphere. After introducing Co into MnSm/Ti catalyst, the NOx conversion for MnSmCo/Ti catalyst only decreased by 8.9%-13.8% at 150–300 ℃ with the presence of CO. It was evidenced that the CO tolerance of the MnSm/Ti catalyst was enhanced with the Co modification. The characterizations of catalysts revealed that the adsorptions of NH3 and NO over the MnSm/Ti catalyst were inhibited by the presence of CO in the mixed atmosphere. Furthermore, the presence of CO in the flue gas resulted in the formation of carbonates, bicarbonates, and bridging formate on the surface of the MnSm/Ti catalysts, which would cause a decrease in the content of Mn4+ and Oα on the surface of the catalyst surface. Introducing Co into MnSm/Ti catalyst could enhance the adsorption of NH3 by forming more Lewis acid sites over the MnSmCo/Ti catalyst. The contents of Mn4+ and Oα over MnSmCo/Ti catalyst were increased via the strong electronic interaction between Co ions and Mn ions. DFT calculations proved that the adsorption of CO over the catalyst was suppressed by the modification of Co with the change of the adsorption energy of CO from −167.25 kJ/mol to −53.82 kJ/mol. Additionally, the Co modification facilitated the decomposition of the carbonate formed over the catalyst with the energy barrier of related reactions decreasing from 214.67 kJ/mol to 24.45 kJ/mol, thus improving the CO tolerance of the catalyst.