A theoretical study of the chemisorption of H2O and H2S on the Ti2O3(102) non-polar surface

Abstract

Density functional molecular cluster calculations have been used to investigate the interaction of two Brønsted acids (H₂X, X = O, S) with the Ti₂O₃(102) 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 (L^b_s). 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 L^a_s-SH (L^a_s = surface Lewis acid site) and L^b_s-H surface species. Independently of the adsorption character, molecular or dissociative, the valence band maximum of Ti₂O₃(102) is negligibly perturbed upon chemisorption, while the conduction band minimum extensively participates to the H₂X–Ti₂O₃(102) interaction. The H₂O–substrate bonding is dominated by a donation from the adsorbate in-plane and out-of-plane lone pairs into L^a_s empty levels, whereas all the valence orbitals of the HS fragment participate in the L^a_s-S bond to a similar extent.