Fe_(3)O_(4) andγ-Fe_(2)O_(3) with a reverse spinel structure have been widely applied as environmentally benign catalysts.Clarifying the catalytically active sites(CASs)of Fe_(3)O_(4) andγ-Fe_(2)O_(3) plays a crucia...Fe_(3)O_(4) andγ-Fe_(2)O_(3) with a reverse spinel structure have been widely applied as environmentally benign catalysts.Clarifying the catalytically active sites(CASs)of Fe_(3)O_(4) andγ-Fe_(2)O_(3) plays a crucial role in improving the efficiency of related reactions.However,the surface adsorption and electronic properties at the atomic level of Fe_(3)O_(4) andγ-Fe_(2)O_(3) are not fully understood.Here,the molecules adsorbed at the tetrahedral(Fetet)and octahedral(Feoct)sites on the Fe_(3)O_(4) andγ-Fe_(2)O_(3) surfaces are considered by density functional theory with the Hubbard-U method.According to the results of adsorption energy,as a whole,γ-Fe_(2)O_(3) is more favorable to adsorb oxygen than Fe_(3)O_(4).Furthermore,the electronic structure and periodic natural bond orbital results clearly reveal that O_(2) at the octahedral sites of Fe_(3)O_(4) and at the tetrahedral sites ofγ-Fe_(2)O_(3) obtains more charge;namely,the Feoct ions of Fe_(3)O_(4) and the Fetet ions ofγ-Fe_(2)O_(3) act as CASs in the activation of O_(2).To ensure the accuracy of the results,the adsorption of CO,H_(2)O,NH_(3) and NO is calculated comparatively.The results suggest that Fe_(3)O_(4) andγ-Fe_(2)O_(3) with the same crystal structure reflect different CASs.This work provides a foundation for understanding the redox and catalytic application of iron oxides;more importantly,the different CASs of Fe_(3)O_(4) andγ-Fe_(2)O_(3) have not been proposed before.展开更多
基金the Natural Science Foundation of China(Grant No.21873038 and 21573088)the Opening Foundation of the State Key Laboratory of Chemo/Biosensing and Chemometrics of Hunan University and the Young Scholar Training Program of Jilin University.
文摘Fe_(3)O_(4) andγ-Fe_(2)O_(3) with a reverse spinel structure have been widely applied as environmentally benign catalysts.Clarifying the catalytically active sites(CASs)of Fe_(3)O_(4) andγ-Fe_(2)O_(3) plays a crucial role in improving the efficiency of related reactions.However,the surface adsorption and electronic properties at the atomic level of Fe_(3)O_(4) andγ-Fe_(2)O_(3) are not fully understood.Here,the molecules adsorbed at the tetrahedral(Fetet)and octahedral(Feoct)sites on the Fe_(3)O_(4) andγ-Fe_(2)O_(3) surfaces are considered by density functional theory with the Hubbard-U method.According to the results of adsorption energy,as a whole,γ-Fe_(2)O_(3) is more favorable to adsorb oxygen than Fe_(3)O_(4).Furthermore,the electronic structure and periodic natural bond orbital results clearly reveal that O_(2) at the octahedral sites of Fe_(3)O_(4) and at the tetrahedral sites ofγ-Fe_(2)O_(3) obtains more charge;namely,the Feoct ions of Fe_(3)O_(4) and the Fetet ions ofγ-Fe_(2)O_(3) act as CASs in the activation of O_(2).To ensure the accuracy of the results,the adsorption of CO,H_(2)O,NH_(3) and NO is calculated comparatively.The results suggest that Fe_(3)O_(4) andγ-Fe_(2)O_(3) with the same crystal structure reflect different CASs.This work provides a foundation for understanding the redox and catalytic application of iron oxides;more importantly,the different CASs of Fe_(3)O_(4) andγ-Fe_(2)O_(3) have not been proposed before.
