Hydrogen adsorption and reaction on the rutile TiO2(011)-2x1 surface was investigated by a combination of high-resolution scanning tunnelling microscopy and density functional theory calculations. Hydroxyl formation on the reconstructed surface was weak, and hydroxyls have only been observed on one of the three different surface oxygen sites. Recombination of hydrogen and desorption of H2 was prevented by a large kinetic barrier. Instead, hydrogen was removed from the surface at elevated temperature by diffusion into the bulk. This was contrasted with photo-induced processes investigated by UV-irradiation under ultra-high vacuum conditions, which led to desorption of hydrogen from the surface, indicating a photo-induced lowering of the reaction barrier. These studies were also compared to previous studies on the rutile TiO2(110) surface where different thermal and photo-induced processes were reported. These differences were explained by three competing reaction pathways: (i) bulk diffusion, (ii) H2 recombination, and (iii) water formation at the surface by lattice oxygen abstraction. The dependence of the reaction on the hydrogen-adsorption energies as well as on kinetic diffusion and reaction barriers and pathways could explain the observed differences between these two surface orientations.

Diffusion and Reaction of Hydrogen on Rutile TiO2(011)-2x1: the Role of Surface Structure. Tao, J., Cuan, Q., Gong, X.Q., Batzill, M.: Journal of Physical Chemistry C, 2012, 116[38], 20438-46