Active Sites on Ti–Ce Mixed Metal Oxides for Reactive Adsorption of Thiophene and Its Derivatives: A DFT Study

Density functional theory was used to investigate the mechanistic aspects of the adsorption of sulfur-containing compounds over Ti–Ce mixed metal oxides. We elucidate the promotional effect of the Ce dopant on TiO2 and report the importance of oxygen vacancy-bound molecular oxygen as an active site on Ti–Ce mixed metal oxides for adsorption of thiophenic sulfur. The presence of surface-activated molecular oxygen leads to the oxidation of the sulfur, thus providing strongly bound sulfoxide and sulfone species. Ce doping of TiO2 makes the oxidation process feasible both thermodynamically and kinetically. Surface oxygen vacancy sites act as catalytic sites in an adsorption cycle. DRIFTS results corroborate the presence of vacancy bound molecular oxygen. Our DFT calculations also examine thiophene and methyl-, dimethyl-, benzo-, and dibenzothiophenes adsorbed on TiO2 and Ce-doped TiO2 (001), (101), and (100) surfaces.