Insight into the promotional effect of Mn-modified nitrogenous biochar on the NH3-SCR denitrification activity at low temperatures

Abstract

A series of Mn-doped nitrided cotton straw biochar catalysts were prepared, and the effect of Mn doping on the denitrification activity at low temperatures was investigated. The microstructure and surface chemistry of the catalyst were studied. The results showed that the low-temperature denitrification activity of the Mn-doped nitride cotton straw biochar was significantly improved, and the optimal reactivity temperature was broadened. The catalyst with 6 wt% Mn/NCAC-1.5-7 (Mn(6)/NCAC-1.5-7) removed 100 % of NO in the temperature range of 140–200 °C, and the N2 selectivity is close to 100 % throughout the reaction temperature interval of 50–260 °C. The presence of many different Brønsted and Lewis acid sites on the catalyst enhanced its NH3 adsorption capacity. The monodentate nitrite produced by Mn doping could be reduced by NH3 at low temperatures, which may be why the doping of Mn improved the low-temperature denitrification activity of the catalyst. In addition, an Eley-Rideal (E-R) mechanism existed for the reaction of adsorbed NH3 linked to Lewis acid sites with gaseous NO over Mn-modified nitrided cotton straw biochar catalysts. There was also a Langmuir-Hinshelwood (L-H) mechanism between the adsorbed NH3 and adsorbed NO states. The E-R mechanism dominated the low temperature NH3-SCR reaction.