(638g) Impact of Ceria Doping Into Titania Anatase On the Adsorption of Sulfur: A Density Functional Theory Study

Adsorptive desulfurization is a novel technique developed to meet the ever increasing constraints on sulfur in fuels.  An adsorbent selective towards thiophene and its derivative species will minimize the energy requirement for desulfurization and will allow the process to be carried out at ambient conditions. Our previous experiments showed that a Ti-Ce mixed metal oxide (90%Ti, 10% Ce) is an effective material for the process. We use density functional theory (DFT) to characterize the interaction of thiophene and its derivatives with metal oxide surfaces, and specifically examine the impact of effect of cerium doping on adsorption capacity. The adsorption of sulfur containing molecules like thiophene and its alkyl derivatives (methyl and dimethyl thiophenes) was studied on the (001), (101) and (100) surfaces of pure TiO₂ (anatase) and Ce-doped TiO₂. Computational results showed that over-oxidized surfaces, which are formed by the adsorption of oxygen to the surface Ti atoms, are the best for the adsorption process and are highly selective to the sulfur-containing compounds due to the formation of a sulfone-like species on the surface. The formation of over-oxidized adsorption sites was examined and a number of possibilities were explored. Such sites were found to be formed when a surface defect was treated with oxygen. Cerium doping has been shown to promote the formation of such surface defects through experiments. Computational results suggest that doping Cerium into a titania anatase crystal promotes the adsorption of oxygen to a surface vacancy. A catalytic process, in which O vacancies adjacent to cerium atoms act as active sites, is proposed for formation of surface sulfone species during the adsorption process.