钛改性对γ-Fe2O3选择催化还原脱硝性能强化机制的分子模拟研究

采用密度泛函理论（DFT）研究了典型过渡金属Ti掺杂改性对γ-Fe₂O₃选择催化还原（NH₃-SCR）脱硝性能强化影响的作用机制。构建了单Ti和双Ti在γ-Fe₂O₃（001）表面的不同Fe位置的掺杂模型，计算了表面掺杂形成能，探讨了O₂、NO和NH₃分子在Ti掺杂前后的γ-Fe₂O₃（001）表面的吸附特性，并进行了反应机理分析。结果表明，单Ti倾向于掺杂在八面体Fe_oct位，双Ti倾向于两个Fe_oct位。Ti的掺杂增强了催化剂表面对O₂的吸附能力，吸附性能随Ti掺杂量增加而增强。单Ti和双Ti的掺杂都抑制了NO以N端在催化剂表面的吸附。Ti能够强化NH₃的吸附，增强了Lewis酸位，有利于SCR反应。Ti的掺杂增大了NO₂生成的反应能垒，降低了γ-Fe₂O₃低温区的SCR反应。Ti的掺杂抑制了NH和N的形成，避免了NH₃的过度氧化，提高NH₃的利用率，有利于SCR反应，并且抑制了通过E-R机理产生的N₂O，具有良好的N₂选择性。Ti的掺杂能够改善γ-Fe₂O₃在NH₃-SCR中还原NO的性能。

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.