Understanding the mechanism of selective catalytic reduction on spinel TiMn2O4(001) surface

Abstract

Manganese based spinel oxides is one of the most promising catalysts for low temperature selective catalytic reduction (SCR) process due to its high activity and tunable composition. Understanding the molecular-level reaction mechanism of SCR on Mn-containing spinel oxides is of great importance for design and development of appropriate catalyst for low temperature SCR process. In this paper, density functional theory calculations were performed to address the detail SCR reaction pathways between NH3 and NO on spinel TiMn2O4(001) surface. The full SCR process was found to be divided into four sequential stages, including the NH3 chemisorption (stage i), NH2NO formation (stage ii), H migration (stage iii), and products desorption (stage iv). Notably, we found that water molecules could serve as a hydrogen exchanger and play a positive role in promoting the hydrogen migration during stage i and stage iii of the SCR process. Thermodynamically, the overall SCR process is highly exothermic with the reaction energy of -3.054 eV. Kinetically, the formation of NH2NO intermediate was identified as the rate determining step with a moderate activation barrier of 1.064 eV. Our results suggest that the spinel TiMn2O4 is a promising catalyst for low temperature SCR. Moreover, the promoting effect of water on hydrogen diffusion should be also applicable to other chemical reactions involving hydrogen transfer.