Computational Investigation of Aqueous-Phase Effects on the Dehydrogenation and Dehydroxylation of Polyols over Pt(111)

Prediction of solvation effects on the kinetics of elementary reactions occurring at metal-water interfaces is of high importance for the rational design of catalysts for the biomass and electrocatalysis communities. A lack of knowledge of the reliability of various computational solvation schemes for processes on metal surfaces is currently a limiting factor. Using a multilevel quantum mechanical/molecular mechanical (QM/MM) description of the potential energy surface, we determined characteristic time and length scales for typical free-energy perturbation (FEP) calculations of bond cleavages in ethylene glycol, a sugar surrogate molecule, over Pt(111). Our approach is based on our explicit solvation model for metal surfaces and the repetition of FEP calculations to estimate confidence intervals. Results indicate that aqueous phase effects on the free energies of elementary processes can be determined with 95% confidence intervals from limited configuration space sampling and the fixed charge approximation used in the QM/MM-FEP methodology of smaller 0.1 eV. Next, we computed the initial O-H, C-H, and C-OH bond cleavages in ethylene glycol over Pt(111) in liquid water utilizing two different metal-water interaction potentials. Our calculations predict that aqueous phase effects are small (<0.1 eV) for the C-H bond cleavage and the activation barrier of the C-OH bond cleavage. In contrast, solvation effects are large (>0.35 eV) for the O-H bond cleavage and the reaction free energy of the C-OH bond scission. While the choice of a different Pt-water force field can lead to differences in predicted solvation effects of up to 0.2 eV, the differences are usually smaller (<0.1 eV), and the trends are always the same. In contrast, implicit solvation methods appear to currently not be able to reliably describe solvation effects originating from hydrogen bonding for metal surfaces even qualitatively.