Origin of Ammonia Selective Oxidation Activity of SmMn2O5 Mullite: A First-Principles-Based Microkinetic Study.

Abstract

Based on first-principles calculations and microkinetic analysis, the reaction routes and origin of the activity of SmMn2O5 mullite for the selective catalytic oxidation of ammonia (NH3-SCO) are systematically investigated on three low-index surfaces under experimentally operating conditions. Key influencing factors and contributions of different iconic intermediate species (NH*, N2H4*, and HNO*) to the overall reaction process have been identified. In detail, Mn4+ serves as the primary active site for NH3 adsorption, while lattice oxygen participates in the dehydrogenation of NH3 on (010)4+ and (001)4+ surfaces. Furthermore, the (010)4+ surface shows both the best activity and the highest N2 selectivity at low temperatures via the synergy effect of exposed Mn-Mn dimers and the most labile O2 atoms. We further evaluate the potential catalytic performances of six A-site doped (010)4+ facets, among which La, Pr, and Nd dopings are predicted to possess better catalytic performances. Our study provides deep insights into the microscope reaction mechanisms and provides the specific optimization strategy for NH3-SCO on mullite oxides.