Insights into the enhanced activity and SO2 resistance of air oxidation treated Mn-Fe doped biochar catalyst in the low-temperature catalytic reduction of NOx with NH3

Abstract

In this study, a sustainable two-stage air oxidation (TAO) was employed to prepare Fe modified MnOx-biochar catalyst (C-O2-MF-O2) instead of high temperature treatment and/or chemical activation for selective catalytic reduction of NO with NH3 (NH3-SCR). The collaborative effect of Fe modification and TAO on the physicochemical properties and catalytic performance of catalysts was systematically studied. Compared with counterpart catalysts treated with two-stage N2 (C-N2-MF-N2) or one-stage O2 (C-O2-MF-N2, C-N2-MF-O2), C-O2-MF-O2 showed obvious enhanced physicochemical properties (SBET, pore properties, high-valance metal ratio, chemisorption oxygen (Oα) content), superior catalytic performance, achieving 91.3% NO conversion with nearly 100% N2 selectivity at 150 °C, and much better H2O and SO2 resistance. It is worth noting that TAO facilitated the redox performance of MnOx after Fe modification to generate more dispersed high-valance metal (Mn4+ and Fe3+), thereby favoring the low-temperature SCR activity of the catalyst. Further, the in situ DRIFTS studies revealed TAO produced remarkable effects on the adsorption behaviors of NH3, NO and SO2, and the corresponding mechanisms of catalyst activity enhancement and SO2 resistance were proposed. Generally, TAO could be a favorable avenue to prepare catalysts with binary active metals for improving performance of NH3-SCR.