Insight into the NH3-Assisted Selective Catalytic Reduction of NO on β-MnO2(110): Reaction Mechanism, Activity Descriptor, and Evolution from a Pristine State to a Steady State

To understand the molecular-level reaction mechanism and crucial activity-limiting factors of the NH3-SCR process catalyzed by MnO2-based oxide to eliminate NO (4NH3 + 4NO + O2 →4N2 + 6H2O) at middle–low temperature, a systematic computational investigation is performed on β-MnO2(110) by first-principles calculations together with microkinetic analysis. Herein, the favored reaction pathways are unveiled. (i) NH3 tends to adsorb at the unsaturated Lewis acid Mn5c site on MnO2(110) and then partially dissociates into NH2* (assisted by the surface lattice Obri) at the steady state, triggering the subsequent reactions. (ii) Interestingly, NO, either in the gas phase or at the adsorbed state, can readily react with NH2* to give the key intermediate NH2NO, with the former (i.e., the Eley–Rideal pathway) being slightly more kinetically preferred. (iii) NH2NO conversion is identified to proceed easily to N2 through the dehydrogenation/hydrogenation processes NH2NO → NHNO → NHNOH → N2 + H2O. (iv) The removal of th...