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 NH3 on W-doped CeO2 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 (1) Lewis acid site reaction, (ii) Bronsted 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 CeO2 catalysts for NH3-SCR reaction was discussed by analyzing the role of oxygen vacancy, the synergistic effect between surface acidity and reducibility, and the difference from NH3-SCR reaction on V2O5-based catalysts. Our results show that the oxygen vacancy on the surface which creates two Ce3+ cations plays a critical catalytic role in the NH3-SCR reaction, where adsorbed N2O2- species can be readily formed and then acts as a precursor for SCR reaction, opening a unique reaction pathway. The formation of adsorbed NO2 species on W-doped CeO2 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 NH3-SCR reaction on W-doped CeO2 catalysts, which is of significance for the design of highly active ceria-based SCR catalysts.