Abstract
Solvent interactions with adsorbed moieties involved in surface reactions are often believed to be similar for different metal surfaces. However, solvents alter the electronic structures of surface atoms, which in turn affects their interaction with adsorbed moieties. To reveal the importance of metal identity on aqueous solvent effects in heterogeneous catalysis, we studied solvent effects on the activation free energies of the O–H and C–H bond cleavages of ethylene glycol over the (111) facet of six transition metals (Ni, Pd, Pt, Cu, Ag, Au) using an explicit solvation approach based on a hybrid quantum mechanical/molecular mechanical (QM/MM) description of the potential energy surface. A significant metal dependence on aqueous solvation effects was observed that suggests solvation effects must be studied in detail for every reaction system. The main reason for this dependence could be traced back to a different amount of charge-transfer between the adsorbed moieties and metals in the reactant and transition states for the different metal surfaces.
Highlights
Solvent interactions with adsorbed moieties involved in surface reactions are often believed to be similar for different metal surfaces
In summary, we hypothesized that since solvents can modify the electronic structure of a metal surface, thereby affecting the stability of reacting moieties, the metal identity plays a significant role for solvation effects on elementary reactions
We investigated aqueous-phase effects on the free energy of activation of the initial O–H and C–H bond cleavages of ethylene glycol over the (111) surface of six transition metals, including Ni, Pd, Pt, Cu, Ag, and Au, to disclose the role of metal identity on solvation effects
Summary
Solvent interactions with adsorbed moieties involved in surface reactions are often believed to be similar for different metal surfaces. The role of solvents in catalytic transformations occurring at a solid-liquid interface is typically ascribed to: heightened importance of mass transfer effects, nature of solvent (polarity etc.)[35,36,37], competitive adsorption between solvent molecules and adsorbed moieties[32,38,39], direct participation of the solvent in the reaction coordinate[40], and/or relative stabilization of reactant, transition and/or product state of elementary reactions[41,42,43] These effects in turn can lead to a change in reaction mechanism, reaction kinetics, selectivity, and overall catalyst lifetime. We have previously developed such a hybrid QM/MM model, named eSMS (explicit solvation model for metal surfaces)[54], which considers the long-range electrostatic interaction of the solvent molecules in the electronic structure calculation of the active site and applied it to the free energy calculation of the initial dehydrogenation and dehydroxylation of an adsorbed ethylene glycol (EG) moiety on Pt(111) in the presence of liquid water[55]
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