Dissociative adsorption of formic acid and diffusion of formats on the TiO2(110) surface: the role of hydrogen

Formic acid (HCOOH) dissociates on the rutile TiO2(110) surface into format e (HCOO) and H. Certain ordered structures for HCOO have been observed for different coverages. In the present work, the role of hydrogen in the stabi lity of these structures and also in the process of HCOO diffusion has been studied by means of ab initio density functional calculations. Our calcula tions show that coadsorption of H is necessary to stabilize the high-covera ge p(2 x 1) geometry. They furthermore explain the observed high mobility o f HCOO in a p(2 x 1)-like environment which is caused by a rather complex m ovement of HCOO together with H. This process cannot operate at lower cover ages and for isolated molecules, which therefore makes HCOO immobile, as su ggested by experiment. (C) 2000 Elsevier Science B.V. All rights reserved.