First principles study of Fenton reaction catalyzed by FeOCl: reaction mechanism and location of active site

Abstract

Fe-based solid catalysts in promoting Fenton reaction to generate ·OH radical has drawn much attention, and interestingly, FeOCl was reported to have superior activity compared with the traditional Fe2O3 catalysts. However, the mechanism of Fenton reaction on FeOCl and the origin of high activity remain unclear. Herein, by virtue of DFT + U calculations, the H2O2 decomposition and conversion mechanism on FeOCl(100) surface were systematically investigated. It is found that on clean FeOCl(100) surface, the exposed [Fe3+–Fe3+] sites can hardly break O–O bond of H2O2 into OH groups, but instead H2O2 tends to dehydrogenate by the surface lattice O, resulting in a series of side reactions and final conversion into O2, while the left H atoms gradually saturate the surface lattice O and reduce Fe3+ into Fe2+. On fully H-covered FeOCl(100), H2O2 can efficiently dissociate at [Fe2+–Fe2+] sites into two OH, but OH binds with Fe2+ so strongly that it cannot desorb as ·OH radical as easily as that on Fe3+. Interestingly, FeOCl(100) tends to be partially protonated in the real acid solution, which, along with H2O2 dehydrogenation, results in the formation of active unit [Fe2+–Fe3+]. On [Fe2+–Fe3+] unit, H2O2 can easily break its O–O bond and OH at Fe3+ can desorb as ·OH radical, while the other OH at Fe2+ couples with the surface H into H2O and finish the catalytic cycle. By comparison, Fe2O3(012) cannot provide enough [Fe2+–Fe3+] active units due to the relative difficulty in H2O2 dehydrogenation, which accounts for its inferior catalytic efficiency for Fenton reaction.