Hydrodesulfurization of Dibenzothiophene on TiO2-x-Modified Fe-Based Catalysts: Electron Transfer Behavior between TiO2-x and Fe Species

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 alpha/beta-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.