Adsorption and dissociation of COx (x=1, 2) on W(111) surface :: A computational study

The mechanisms of adsorption and dissociation of COx (x = 1, 2) molecules on the W(111) surface have been investigated at the periodic density functional theory (DFT) level in conjunction with the projector-augmented wave (PAW) approach. The molecular structures, vibrational frequencies, and binding energies of W(111)/CO2, W(111)/CO, W(111)/C, and W(111)/O systems were analyzed. It was found that the most favorable adsorption configuration of W(111)/CO2 is the WCO2(IV-mu(3)-C2, O1, O1) configuration, where the bent CO2 molecule is located at the threefold-shallow site of the surface. The W(111)-CO2 bonding energy is calculated to be -37.6 kcal/mol. For the W(111)/CO, the beta-CO configuration, WCO(II-mu(2)-Cl, O1), with CO at the bridge site, is energetically the most favorable one. The calculated W(111)-CO adsorption energy is -37.9 kcal/mol. The C and O atoms are bound preferentially at the bridge and top sites, respectively. Potential energy surface for the decomposition of CO2 on W(111) has been constructed using the nudged elastic band (NEB) method. It was shown that the overall reaction CO2(g) + W(111) --> LM1 --> LM2 --> P1 is exothermic by 61.0 kcal/mol and does not require thermal activation energy. Therefore, we expect the CO2 molecule to be in its dissociative adsorption state (into atomic C and 0) on the W(111) surface. We also have predicted the rate constants for CO2 and CO dissociation on the W(111) surface.