Mechanistic Study of Selective Catalytic Reduction of NOx with NH3 over Mn-TiO2: A Combination of Experimental and DFT Study

Mn-TiO 2 oxide catalyst has been studied intensively for selective catalytic reduction (SCR) of NO with NH 3 due to its extraordinarily good low-temperature performance. However, the mechanism of SCR on Mn-TiO 2 still remains unclear, especially with regard to the decomposition pathway of the NH 2 NO intermediate and the reason for the decreasing N 2 selectivity with the increasing of temperature. In this work, we attempt to provide a molecular level understanding of these questions via a combination of DFT and experimental study. A complete catalytic cycle of the SCR reaction was proposed based on a model in which Mn is doped into the TiO 2 (101) surface by quantum-chemical DFT+U calculations. In situ DRIFTS experiments were performed to provide evidence to the important intermediates as proposed in the reaction mechanism. The doping Mn enhances NH 3 adsorption and activation due to its lower conduction band. NH 2 NO can decompose into N 2 and H 2 O fast via a concerted H migration step. The decreasing selectivity with rising temperature can be explained by the deep oxidation of NH 3 . This study provides atomic-scale insights into the catalytic cycle and the important role of doping Mn in NH 3 –SCR reaction on Mn-TiO 2 catalysts, which is of significance for the design of high activity low-temperature SCR catalysts.