Scenarios of polaron-involved molecular adsorption on reduced TiO2(110) surfaces.

The polaron introduced by the oxygen vacancy (Vo) dominates many surface adsorption processes and chemical reactions on reduced oxide surfaces. Based on IR spectra and DFT calculations of NO and CO adsorption, we gave two scenarios of polaron-involved molecular adsorption on reduced TiO2(110) surfaces. For NO adsorption, the subsurface polaron electron transfers to a Ti:3d-NO:2p hybrid orbital mainly on NO, leading to the large redshifts of vibration frequencies of NO. For CO adsorption, the polaron only transfers to a Ti:3d state of the surface Ti5c cation underneath CO, and thus only a weak shift of vibration frequency of CO was observed. These scenarios are determined by the energy-level matching between the polaron state and the LUMO of adsorbed molecules, which plays a crucial role in polaron-adsorbate interaction and related catalytic reactions on reduced oxide surfaces.