Adsorption and dissociation of H2O on a w(111) surface:: A computational study

The adsorption and dissociation of water on a W(111) surface have been studied at the density functional theory (DFT) level in conjunction with the projected augmented wave approach. The potential energy surface of the water decomposition on the W(111) surface was constructed. It was shown that the barriers for the stepwise H2O dehydrogenation reaction, H2O -> 2H((ads)) + O((ads)), are 1.8 (for HO-H bond activation) and 15.9 (for the O-H bond activation) kcal/mol. The entire process, W(111) + H2O -> 2H((ads)) + O((ads)), is 54.4 kcal/mol exothermic. Calculations show that the formation of W(111)-O + H-2((gas)) from W(111) + H2O is also exothermic by 23.7 kcal/mol. These results are in good agreement with the temperature-programmed desorption and high-resolution electron energy loss spectroscopy data. On the basis of the calculated PES, we predicted kinetic rate constants for the dissociative adsorption of H2O on the W(111) surface. The structure, vibrational frequency, and binding energy of the W(111)-H2O, W(111)-OH, W(111)-O, and W(111)-H systems were also predicted. It was shown that the most favorable structure of W(111)-H2O corresponds to the coordination of water through its oxygen lone pairs with the W(111) surface (at its top position). The preferable binding sites for the OH, O, and H fragments are top, top, and bridge sites, respectively. The stepwise dissociative adsorption mechanism of H2O on the W(111) surface has also been confirmed by DFT molecular dynamics simulations.