PNNL

Abstract

The adsorption of cyclohexane, benzene, and alkyl-substituted benzene derivatives is studied on rutile TiO2(110) by a combination of molecular beam dosing, temperature programmed desorption, and density functional theory (DFT). An inversion analysis is used to extract the coverage dependent desorption energies from TiO2(110). The values of the suitable prefactors are derived from simple statistical mechanical models assuming different limits in the adsorbate mobility on the surface. The prefactor values determined using the vibrational frequencies from DFT calculations corroborate this analysis and show that the adsorbates are mobile in 1- or 2-dimensions on corrugated TiO2(110) surface. The adsorption of benzene derivatives is found to be dominated by the dative Lewis acid-base interactions of the p system with the surface Ti ions. While the desorption energy generally increases with increasing the length and the number of substituents, the difference between the desorption energies decreases as the number and length of substituents is increased. This is a consequence of the destabilization of the optimum bonding configuration of the benzene ring and the alkyl groups with their increasing length and number. The absolute saturation coverages of uncompressed layers correspond approximately to one molecule per two Ti5c sites and decrease slightly with increasing molecule size in a good agreement with van der Waals sizes of the molecules.