Mechanistic Study of Ethanol Dehydrogenation over Silica-Supported Silver

A silica‐supported Ag catalyst has been shown to be an efficient heterogeneous catalyst for the oxidant‐free dehydrogenation of ethanol into acetaldehyde. The reaction mechanism has been investigated by in situ FTIR spectroscopy. The kinetic isotope effects for proton and hydride ion have been studied by using CH3CD2OH and CH3CH2OD as labeled reactants. The results indicate that OH bond activation and the formation of a hydrogen‐bonded complex take place on the silica support and that the Ag particles are necessary for the activation of the CH bond. The kinetic isotope effect (kH/kD) is 1.9 for CH3CD2OH and 1.8 for CH3CH2OD. The concerted mechanism of CH cleavage on the Ag sites and proton ion on the silica sites is proposed to account for the results of the spectroscopic and kinetic experiments. Every mechanism should have a silver lining: Ethanol is selectively converted into acetaldehyde over Ag supported on silica. The Ag particles and SiOH groups of silica act in a complementary manner in a concerted mechanism, which is proposed based on in situ FTIR spectroscopic studies and kinetic experiments with specifically deuterated ethanol. The proposed mechanism shows the way for the design of efficient supported Ag catalysts.