Biomass pyrolysis produces a pool of small-molecule organic molecules that could ideally be catalytically upgraded to stabilized intermediates, which can then be converted to fuel-range hydrocarbons. Furans, in particular, are attractive target intermediates from biomass fast pyrolysis vapors, and catalytic strategies to convert pyrolysis vapors to furans are under development. Acetaldehyde and glycoaldehyde have been identified as the major components of pyrolysis vapors, and thus we have investigated the mechanism of furan formation from these compounds over H-ZSM-5, which is a well-characterized, industrially important zeolite. We considered the two T5 cluster models (T1 and T12 catalytic sites) and a QM/MM ONIOM model of H-ZSM-5 to investigate the catalytic reaction mechanisms of furan formation and to understand the effects of system size on reactivity. Two different pathways, concerted and stepwise, were considered when examining the dehydration and deprotonation steps. The two stepwise processes lead to the dehydration first and an intermolecular proton transfer mediated to form 2,3-dihydrofuran-3-ol (product of first hydration) or furan (product of second hydration) with slightly lower barrier compare via a concerted mechanism. The overall trends of energy barriers are very similar across the models used, with the exception of the carbocation intermediate. These results suggest that zeolites may stabilize intermediates that are not stable in the gas phase.

Density functional theory study of furan formation in H-ZSM-5

248th National Meeting (2014)

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