Mechanistic Study of Selective Catalytic Reduction of NO with NH3 on W-Doped CeO2 Catalysts: Unraveling the Catalytic Cycle and the Role of Oxygen Vacancy

The reaction mechanism of selective catalytic reduction (SCR) of NO with NH 3 on W-doped CeO 2 catalysts was systematically investigated using density functional theory calculations corrected by on-site Coulomb interactions (DFT+U). A complete catalytic cycle was proposed, which consists of four steps, namely (i) Lewis acid site reaction, (ii) Brønsted acid site reaction, (iii) oxygen vacancy reaction, and (iv) catalyst regeneration. The calculated key intermediates in these four steps are in good agreement with previous experimental results, which indicates that our suggested catalytic cycle is rational. The catalytic nature of W-doped CeO 2 catalysts for NH 3 -SCR reaction was discussed by analyzing the role of oxygen vacancy, the synergistic effect between surface acidity and reducibility, and the difference from NH 3 -SCR reaction on V 2 O 5 -based catalysts. Our results show that the oxygen vacancy on the surface which creates two Ce 3+ cations plays a critical catalytic role in the NH 3 -SCR reaction, where adsorbed N 2 O 2 2– species can be readily formed and then acts as a precursor for SCR reaction, opening a unique reaction pathway. The formation of adsorbed NO 2 species on W-doped CeO 2 facilitates the SCR reaction via Langmuir–Hinshelwood mechanism with a relative low energy barrier. This study provides atomic-scale insights into the catalytic cycle and the important role of oxygen vacancy in NH 3 -SCR reaction on W-doped CeO 2 catalysts, which is of significance for the design of highly active ceria-based SCR catalysts.