Density Functional Theory Study on the Role of Ceria Addition in TixCe1-xO2 Adsorbents for Thiophene Adsorption

A TixCe1-xO2-based material has been reported as a potential adsorbent for ultradeep adsorptive desulfurization of liquid hydrocarbon fuels. To understand the roles of TiO2 and CeO2 in the adsorbent, density functional theory (DFT) calculations examined the energetics of adsorption site formation and corresponding thiophene adsorption energies on surfaces of TiO2 anatase, CeO2, and Ce-doped anatase. Compared with pure anatase surfaces, thiophene binds more strongly to Ce-doped anatase surfaces. O-rich sites (with activated O-2) bind strongly to thiophene, but the formation of the O-rich sites is favored only on higher energy surfaces such as anatase (001) and ceria (100). The formation of a TixCe1-xO2 mixed surface decreases the relative surface formation energy of anatase (001), and thus a greater fraction of the (001) facet could be exposed on the adsorbent. Ceria may also act as an oxygen storage reservoir, providing oxygen for the formation of O-rich sites that strongly adsorb thiophenic species.