(691g) C-O Bond Hydrogenolysis over Metal/Lewis Acid Catalysts
In the recent years, substantial research effort has been devoted to the production of fuels and chemicals from lignocellulosic biomass, since the latter is the only source of renewable carbon. Selective hydrogenolysis of biomass derivatives, such as furfuryl alcohol to methyl furan, entails removal of oxygen and hydrogenation of the side group and remains a challenge. We have recently reported that hydrogenolysis can proceed at high yield using an alcohol as a hydrogen donor over a mixed metal/metal oxide catalyst, such as Ru/RuO2/C [1-4]. However, the mechanism and the active site remain elusive.
In this work, we perform density functional theory (DFT) and microkinetic modeling to identify the hydrogenolysis mechanism of furfuryl alcohol to form 2-methyl furan with a hydrogen donor (2-propanol), for which mechanistic features were recently revealed using isotopic labeling and mass fragmentation kinetics . We compare results on the multifunctional catalyst to pure metallic Ru and RuO2 . We show that RuO2 is more effective at hydrogenation of the C=O via the MPV reaction than Ru. On the other hand, the oxide is not as effective at deoxygenating the side group. In contrast, Ru is an effective deoxygenation catalyst, but can get poisoned by oxygen. We identify a concerted C-O bond scission/C-H formation in furfuryl alcohol over an oxygen vacancy of RuO2to be facile with a low reaction barrier, yielding an easily desorbed 2-methyl furan. The synergy of metal and oxide is elucidated. The mechanism is in agreement with isotopic labeling observations . Finally, Crystal Orbital Hamilton Population analysis reveals the role of electron delocalization in lowering the reaction barrier.
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