Liquid Phase Effects on Adsorption Processes in Heterogeneous Catalysis

A hybrid QM/MM approach for computing solvation effects on free energies of adsorption at solid-liquid interfaces has been proposed and validated against experimental solvation free energies of phenol adsorption on the Pt(111) surface. A large, endergonic solvation free energy is predicted for phenol adsorption at 298 K, ΔΔGads = 1.48 eV, that agrees with experimental data to within 0.10 eV, which is on the order of the experimental uncertainty. To elucidate the significance of the adsorbed moiety and metal identity on the solvation effect, the aqueous solvation effect on the adsorption free energies of carbon monoxide (CO), ethylene glycol (EG), and phenol (Ph) over the (111) facet of Pt and Cu surfaces at 298 K was computed. Next, the importance of the different types of interactions between the adsorbate and the water molecules, i.e., electrostatic, van der Waals and hydrogen bonding, was quantified, and the root causes of relative (de)stabilization of each adsorbed species were identified. The water environment destabilized all adsorbed species irrespective of the metal surface, with the largest impact on the largest adsorbate. Independent of adsorbed moieties, more destabilization was predicted over Pt(111) than over the Cu(111) surface, which is attributed to larger charge-transfer effects (net charge on adsorbate) on Cu relative to Pt.