(541b) Solvation Effects on Carbonyl Group Hydrogenation over Transition Metal Catalysts

Carbonyl group hydrogenation over metal catalysts has been a classical reaction for trying to understand solvation effects in catalysis. Experimentally, it is well-established that in the vapor phase, Pt and Pd are much better hydrogenation catalysts than Ru. However, in liquid water, Ru is usually more active than Pt and Pd. Along these lines, Demir et al. showed that already water vapor inhibits the rate of the carbonyl group hydrogenation in acetone over Pt while it enhances the rate over Ru.¹ Recently, Zhao et al. claimed that for furfural hydrogenation over Pd catalysts in liquid water, proton-coupled electron transfer steps accelerate the hydrogenation of the carbonyl group.² This claim has been questioned by Yu et al., who showed quite convincingly that liquid water does not act as a co-catalyst in the rate-controlling step of this reaction.³ To obtain a deeper understanding of carbonyl group hydrogenation over transition metal catalysts in water, we studied the 2-butanone hydrogenation over transition metal catalysts with our explicit solvation method for metal surfaces (eSMS). In these studies, liquid water was both a co-catalyst and a solvent. Without considering water as a co-catalyst, computational studies cannot explain the experimental observation of an acceleration of the carbonyl group hydrogenation over Ru catalysts. The main difference between Ru and other group VIII transition metals is a difference in the rate controlling step. Over Ru, hydrogenation of the carbonyl oxygen atom is rate controlling while it is the hydrogenation of the carbonyl carbon atom over most transition metals. Interestingly, we observe a strong solvent stabilization by water acting as a co-catalyst only for the hydrogenation at the O-atom, explaining experimental observations.

1. J Catal 2021, 403, 215-227.
2. Nat Commun 2022, 13 (1), 7154.
3. Nat Catal 2019, 2 (5), 431-436.