Mechanistic Study of Ethanol Dehydrogenation over Silica‐Supported Silver

Abstract

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 abstraction 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 abstraction on the silica sites is proposed to account for the results of the spectroscopic and kinetic experiments.

Recent Breakthroughs in the Conversion of Ethanol to Butadiene

“…Sels et al used a silver promoter to enhance performances of their MgO-SiO 2 , MgO-COK-12 and MgO-MCM-41 catalysts-poorly active in the dehydrogenation of ethanol [29]. Supported Ag nanoparticles are well-known for their ability to dehydrogenate alcohols in the absence of oxidants [58,59]. Silver particles were introduced into the catalysts by aqueous impregnation with AgNO 3 and were subsequently calcined, but were not reduced prior to catalytic testing.…”

“…Early investigations having identified silver/zirconium system as the most active for the production of butadiene, it was thoroughly investigated. Such investigations include: the aldol condensation of acetaldehyde over silica-supported zirconium oxide, the dehydrogenation of ethanol over silica-supported silver and the MPVO reduction of crotonaldehyde over Zr-containing catalyst-all reactions believed to occur in the Kagan reaction pathway [54,59,68].…”

Catalytic Performance and Reaction Pathways of Cu/SiO₂ and ZnO/SiO₂ for Dehydrogenation of Ethanol to Acetaldehyde

“…Metal catalysts using Cu 9) 14) , Ni _ Co 15) , Ag 16) and Pd 17) were mainly studied. In particular, Cu catalysts have been most commonly studied and the reaction kinetics 9), 12) and reaction mechanisms 14), 16) are reported.…”

“…ZnO is rare as a main catalyst element but is often reported as a catalyst component 9) or catalyst support 15), 17) . ZnO without metal catalyst, Ni _ Co, showed dehydrogenation activity at 350 K 15) .…”

“…ZnO without metal catalyst, Ni _ Co, showed dehydrogenation activity at 350 K 15) . Dehydrogenation occurred on ZnO at 523 K although the conversion of ethanol was one order lower than that on Pd catalysts supported on various metal oxides 17) .…”