Constructing of Mn4+-O-PdOx sites in SmMn2O5 Mullite: Novel and Highly-Active reactive centers for Low-Temperature methane combustion

Pd-based catalysts have been widely investigated for CH4 combustion yet they still suffer from inefficiency at low temperatures. Herein, a novel strategy was implemented to create a new type of highly active and stable Mn4+-O-PdOx center by doping Pd into SmMn2O5 lattice and modifying it with acid etching. Compared with the impregnation-method, T50 of the catalyst (SMPO-OA) synthesized by this strategy was reduced by 210 °C, and TOF value increased more than 6 times at 260 °C. Importantly, it showed the superior thermal stability and water resistance. Various characterization results indicate that Pd successfully occupied the Mn3+ position in the pyramid unit and formed abundant Mn-O-Pd linkage. Acid treatment introduced the unsaturated-coordination Mn4+-O-PdOx center, which showed high-activity for the methane activation. In-situ DRIFTS and Quasi-in-situ XPS indicate that methane oxidation on the SMPO-OA surface followed MvK mechanism, and activation ability of CH bond at low temperature was markedly improved.