First-principle analysis of the dissociative adsorption of formic acid on rutile TiO 110/

The adsorption of formic acid HCOOH.on the rutile TiO2 110.surface, where HCOOH dissociates into formate HCOO.and hydrogen H., has been analyzed with first-principles density functional calculations. A p 2=1.geometry can be observed for high exposure, while only local c 4=2.domains are detected for lower exposure. After desorption of some HCOOH at higher temperatures the p 2=1.geometry becomes unstable and the remaining molecules form a disordered structure. A direct and simultaneous observation of H and HCOO is difficult, but the calculations show that coadsorption of H is necessary to stabilize the p 2=1.geometry. Some of the vibrational modes also show a slight dependence on the supply of H and might give experimentally accessible hints concerning the role of H. An interesting aspect concerns the surface diffusion of HCOO: while HCOO molecules behave rather immobile on the surface in the c 4=2.domains and in the disordered structure, they show a high mobility along thew001xdirection in a p 2=1.-like environment. As it turns out, the reason for these findings can be found in the complex movement of HCOO molecules, which includes the coadsorbed HCOO`H compound as a whole. q2000 Elsevier Science B.V. All rights reserved