Hydrodesulfurization of Dibenzothiophene on TiO_2–<i>x</i>-Modified Fe-Based Catalysts: Electron Transfer Behavior between TiO_2–<i>x</i> and Fe Species

Abstract

Appropriate electronic structure is vital to promote the catalytic performance of active species. In this work, TiO2–x was employed to regulate active Fe species to the electron-rich state, causing remarkable synergetic effects in which the sulfur removal rates of Fe-based catalysts were increased by 10–40% and reaction rate constants were also increased by around 100% (pure Fe-based catalysts) and 30% (Fe-Zn bimetallic catalysts). The results of characterization and DFT calculations show that the strong electron-donating effect of TiO2–x on Fe species can promote the dispersion of Fe species and weaken the Fe–O and Fe–S/FeZn–S bonds, resulting in the increases in sulfidation degrees by around 3.5% and enrichments of coordinatively unsaturated sites or sulfur vacancies. In addition, weaker Al–OH peaks caused by TiO2 can also facilitate the increase in sulfidation degrees of Fe-based catalysts. Furthermore, hydrodesulfurization/direct desulfurization ratios are decreased by adding TiO2–x, attributed to the electron-rich Fe species that makes C–S bonds and α/β-H more vulnerable to attacks. Slight changes in acidity caused by TiO2–x have little effect on the catalytic performances of Fe-based catalysts. This work lays a solid foundation for industrial application of eco-friendly and economical Fe-based catalysts in the HDS field.