A Theoretical Study of the Chemisorption of H2O and H2S on the Ti2O3(10-12) Non-Polar Surface

Density functional molecular cluster calculations have been used to investigate the interaction of two Brønsted acids (H2X, X = O, S) with the Ti2O3(10-12) non-polar surface. Adsorbate geometries, vibrational parameters and chemisorption enthalpies are computed and discussed. According to experimental outcomes [R. L. Kurtz and V. E. Henrich, Phys. Rev. B, 1982, 26, 6682], H2O is molecularly adsorbed, even if one of the O–H bonds is significantly lengthened as a consequence of a short hydrogen bonding between the H atom and a surface Lewis base site (Lbs). This interaction determines the peculiar arrangement of the molecule on the surface. At variance with water, H2S is partially deprotonated upon chemisorption giving rise to Las-SH (Las = surface Lewis acid site) and Lbs-H surface species. Independently of the adsorption character, molecular or dissociative, the valence band maximum of Ti2O3(10-12) is negligibly perturbed upon chemisorption, while the conduction band minimum extensively participates to the H2X–Ti2O3(10-12) interaction. The H2O–substrate bonding is dominated by a donation from the adsorbate in-plane and out-of-plane lone pairs into Las empty levels, whereas all the valence orbitals of the HS fragment participate in the Las-S bond to a similar extent.