Redox & acidity optimizing of LDHs-based CoMnAl mixed oxides for enhancing NH3-SCR performance

Abstract

A series of Co4−xMnxAl1 mixed metal oxides were obtained via calcining the CoMnAl layered double hydroxides (LDHs) and employed as catalysts in low-temperature NH3-SCR. The results proposed that Co3Mn1Al1-500 catalyst possessed broader temperature window than all other control catalysts Co4Al1-500, Mn4Al1-500 due to its synergistic effect of Co and Mn species. Furthermore, the catalytic behavior of the obtained CoMnAl mixed oxides catalysts were sensitive to calcination temperature and less affected by Co/Mn molar ratios, where Co3Mn1Al1-500 exhibited excellent DeNOx activity (NOx yield above 90%), N2 selectivity and sulfur tolerance in the temperature range of 120–280 °C. Multiple characterization manifested that the outstanding catalytic behavior of Co3Mn1Al1-500 could be attributed to its more favourable ratios of Mn4+ to Mn3+, Co3+ to Co2+ and plentiful surface adsorbed oxygen species which consequently provided stronger redox property and multiple acid sites. Furthermore, kinetics analysis verified that the calculated activation energy significantly decreased over Co3Mn1Al1-500 in low-temperature NH3-SCR reaction.