Density functional theory study on adsorption of thiophene on TiO₂ anatase (0 0 1) surfaces

In order to develop a fundamental understanding of the adsorption mechanism of thiophenic compounds on TiO₂-based adsorbents for ultra-deep desulfurization of liquid hydrocarbon fuels, a density functional theory (DFT) study was conducted on the adsorption of thiophene over the TiO₂ anatase (0 0 1) surface. The perfect, O-poor (with oxygen vacancies), and O-rich (with activated O₂ on the surface) anatase (0 0 1) surfaces were built, and the interaction of thiophene molecule with these surfaces was examined. The adsorption configuration and adsorption energy on the different surfaces and sites were estimated. The results showed that thiophene may be adsorbed on both the perfect and O-poor surfaces through an interaction between the Ti cations on the surface and the S atom in thiophene, whereas on the O-rich surface through an interaction of the activated O atoms (the dissociatively or associatively adsorbed O₂) on the surface with the S atom in thiophene to form a sulfone-like surface species. The adsorption of thiophene on the O-rich surface is significantly stronger than adsorption on the perfect and O-poor surfaces on the basis of the calculated adsorption energies. The results indicate that the activated O₂ on the TiO₂ anatase (0 0 1) surface may play an important role in the adsorption desulfurization over the TiO₂-based adsorbents, and increased concentration of the activated O₂ on the surface may result in improvement of the adsorption capacity of the adsorbents.