Abstract:
The promoting effect of a typical transition metal Ti in the Ti-modified
γ-Fe
2O
3 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-Fe
2O
3(001) surface were constructed; the surface doping formation energy was calculated, the adsorption characteristics of O
2, NO and NH
3 molecules on
γ-Fe
2O
3 (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 O
2 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 NH
3, which is beneficial to SCR reaction. The doping of Ti increases the energy barrier of NO
2 formation and reduces the SCR reaction of
γ-Fe
2O
3 at low temperature. The doping of Ti can inhibit the formation of NH and N, avoid the excessive oxidation of NH
3, and improve the utilization of NH
3, which are beneficial to the SCR reaction by suppressing the N
2O produced by the E-R mechanism and enhancing the selectivity to N
2. As a result, the Ti doping can significantly improve catalytic performance of
γ-Fe
2O
3 in the NH
3-SCR of NO.