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

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 N-2 selectivity. To identify the critical factors influencing the activity and N-2 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 N-2 and N2O formation paths were calculated. The apparent activation energies for N-2 (Eapp-1) and N2O (Eapp-2) formation can represent the activity and N-2 selectivity, respectively. The obtained Eapp-1 and Eapp-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 N-2 selectivity. Besides, the linear relationships between Eapp-1, Eapp-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 N-2 selectivity. This study built a simple model to design transition metal-doped TiO2 with good low-temperature activity and N-2 selectivity, which has significance for designing excellent SCR catalysts for practical application.

Automated summary

In this study, different transition metals doped on TiO2 were investigated using the DFT method to analyze the factors influencing the activity and N-2 selectivity of SCR catalysts. The results showed that the doping of transition metals affected the surface oxygen activity, leading to varied activity and N-2 selectivity. A simple model was established to design transition metal-doped TiO2 catalysts with good low-temperature activity and N-2 selectivity.