Promoting effect of Ti in the Ti-modified γ-Fe₂O₃ catalyst on its performance in the selective catalytic reduction of NO with ammonia, a DFT calculation study

The promoting effect of a typical transition metal Ti in the Ti-modified γ-Fe₂O₃ catalyst on its performance in the selective catalytic reduction (SCR) of NO with ammonia was investigated by density functional theory (DFT) calculation. Various doping models of single Ti and double Ti at different Fe sites on the γ-Fe₂O₃(001) surface were constructed; the surface doping formation energy was calculated, the adsorption characteristics of O₂, NO and NH₃ molecules on γ-Fe₂O₃ (001) surface before and after Ti doping were compared, and the reaction mechanism was analyzed. The results illustrate that single Ti atom tends to be doped at octahedral Feoct site, whereas two Ti atoms at two Feoct sites. The adsorption of O₂ onto the catalyst surface can be enhanced through the Ti doping; moreover, the enhancement increases with an increase in the doping content of Ti. Both single Ti and double Ti doping inhibit the N-terminal adsorption of NO on the catalyst surface. Ti can enhance the Lewis acid sites and promote the adsorption of NH₃, which is beneficial to SCR reaction. The doping of Ti increases the energy barrier of NO₂ formation and reduces the SCR reaction of γ-Fe₂O₃ at low temperature. The doping of Ti can inhibit the formation of NH and N, avoid the excessive oxidation of NH₃, and improve the utilization of NH₃, which are beneficial to the SCR reaction by suppressing the N₂O produced by the E-R mechanism and enhancing the selectivity to N₂. As a result, the Ti doping can significantly improve catalytic performance of γ-Fe₂O₃ in the NH₃-SCR of NO.