DFT characterization of adsorption and diffusion mechanisms of H, As, S, and Se on the zinc orthotitanate(0 1 0) surface

Zinc orthotitanate (ZTO) is a promising material for removal of multiple contaminant species from fuel gas streams. The ZTO(0 1 0) surface, which consists of both oxygen rich and metal rich sides, was previously predicted to be the lowest energy ZTO surface. We present density functional theory calculations examining adsorption and diffusion of atomic S, Se, As, and H on the oxygen rich and metal rich ZTO(0 1 0) surfaces. S and Se share similar bonding and diffusion mechanisms on the metal rich ZTO(0 1 0) surface, whereas As and H bind in similar ways to the oxygen rich surface. S and Se have adsorption sites involving Zn:Zn bridges whereas As and H prefer to bind at sites involving O:O bridges on the surface. H forms a hydroxyl-like bond with length of 1.0 Å. Se and S have small activation energy barriers for atomic diffusion from the lowest energy adsorption site to the nearest low energy site. At temperatures around 800 K we predict from our results that Se and S are approximately equal in diffusivity while being far more mobile on the surface than either H or As.