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

The mechanisms of adsorption and dissociation of CO_x (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-μ³-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 β-CO configuration, WCO(II-μ²-C1, 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 CO_2(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 O) on the W(111) surface. We also have predicted the rate constants for CO₂ and CO dissociation on the W(111) surface.