Trapping Nitric Oxide by Surface Hydroxyls on Rutile TiO₂(110)

Hydroxyls are omnipresent on oxide surfaces under ambient conditions. While they unambiguously play an important role in many catalytic processes, it is not well-understood how these species influence surface chemistry at atomic scale. We investigated the adsorption of nitric oxide (NO) on a hydroxylated rutile TiO₂(110) surface with scanning tunneling microscopy (STM), X-ray/ultraviolet photoemission spectroscopy (XPS/UPS), and density functional theory (DFT) calculations. At room temperature adsorption of NO is only possible in the vicinity of a surface hydroxyl, and leads to a change of the local electronic structure. DFT calculations confirm that the surface hydroxyl-induced excess charge is transferred to the NO adsorbate, which results in an electrostatic stabilization of the adsorbate and, consequently, a significantly stronger bonding.