Theoretical design of transition metal-doped TiO2 for the selective catalytic reduction of NO with NH3 by DFT calculations

Abstract

Many transition metal oxides supported on TiO₂ have been studied for the selective catalytic reduction (SCR) of NO with NH₃. However, a trade-off exists between the low-temperature activity and N₂ selectivity. To identify the critical factors influencing the activity and N₂ selectivity, we chose a series of metal (V, Cr, Mn, Fe, Co, Mo, and Ce)-doped TiO₂(101) slabs to investigate the NH₃-SCR mechanism by the DFT method. The reaction energy and barrier of every elementary step via the N₂ and N₂O formation paths were calculated. The apparent activation energies for N₂ (E_app-1) and N₂O (E_app-2) formation can represent the activity and N₂ selectivity, respectively. The obtained E_app-1 and E_app-2 for all the 3d and 4d transition metal-doped TiO₂ catalysts suggested that Mn-, Co-, Ni-, Cu-, Zn-, Pd-, Ag-, and Cd–TiO₂ had good low-temperature activity, while TiO₂, Cr-, Fe-, Zr-, and Ce–TiO₂ had high N₂ selectivity. Besides, the linear relationships between E_app-1, E_app-2, and the surface oxygen activity indicated that the doping of transition metals affects the surface oxygen activity by the doping effect, electronic structure, and atomic size, leading to different activity and N₂ selectivity. This study built a simple model to design transition metal-doped TiO₂ with good low-temperature activity and N₂ selectivity, which has significance for designing excellent SCR catalysts for practical application.