Structure Sensitivity in Hydrogenation Reactions on Pt/C in Aqueous-phase

Hydrogenation of phenol and of the benzaldehyde carbonyl group catalyzed by Pt are structure sensitive in aqueous phase. The intrinsic reaction rates are directly proportional to the average size of the Pt particles. This trend is indifferent of the genesis of the reduction equivalents, i.e., dissociation of H-2 or proton reduction under cathodic potential. It is concluded that the structure sensitivity is caused by the ensemble size sensitivity of the adsorption of the aromatic molecules, which is favored on (100) and (111) surfaces of larger particles. For electrocatalytic reduction, this structure sensitivity implies that hydrogen evolution increases in rate relative to hydrogen addition to reacting substrates as the size of Pt particles decreases.