Understanding and predicting the effects of solvents on the energies of adsorbed catalytic reaction intermediates is crucial for understanding solvent effects in liquid-phase catalysis and electrocatalysis. As shown below, differences between adsorption energies of catalytic intermediates in different solvents are dominated by differences in the solvents’ adhesion energies to the solid. Knowing values for solvent / solid adhesion energies is therefore crucial for understanding solvent effects in catalysis. We report here adhesion energies of many liquid solvents to clean Pt(111), Ni(111), MgO(100), and C(0001) surfaces, estimated using measurements of heats of adsorption versus coverage integrated from zero coverage up to thick (bulk-like) multilayer solid films. Within a simple pairwise bond-additivity model, the adsorption energy of a reactant molecule R in liquid solvent S onto the surface of metal M is given by:1 DUads,R(solvent) = DUads,R(gas) + Eadh,S/M.sR – DUsolvation,R(gas)/2 – gS(liq).sR , (1) where DUads,R(gas) is its adsorption energy in gas on the same surface, Eadh,S/M is the solvent / metal adhesion energy per unit area, sR is the surface area occupied by one R molecule, DUsolvation,R(gas) is the solvation energy of R(gas) into S and gS(liq) is the surface energy per unit area of liquid S. The last two terms here nearly cancel (typically differ by &lt;30 kJ/mol), so that the dominant difference between adsorption energies in solvents compared to gas is just Eadh,S/M.sR. This number is large (e.g., 116 kJ/mol for phenol on Pt(111) in water,1 or 91 kJ/mol using the new Eadh,D2O/Pt(111) discussed here), so solvents have a huge effect on adsorption energies. Since gas-phase adsorption energies and sR are commonly known from experiments or DFT, knowing adhesion energies allows estimates of adsorption energies in different solvents. We present new adhesion energies here, not only for metals2 but also for an oxide and graphene surface, for which Eq 1 also applies (i.e., M can be any surface, not limited to metal surfaces).

Effects of solvent on adsorption energies as revealed by experimental adhesion energies of solvents to Pt(111), Ni(111), MgO(100) and C(0001) surfaces

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.