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 higher value products 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 cellulose 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 first studied ethanol dehydration on HZSM-5 to determine optimal system size, density functional theory (DFT) and basis set. The ethanol dehydration is chosen due to the simplicity of reaction and also dehydration is an important process during the upgrading of biomass pyrolysis products. We considered a QM/MM ONIOM model of HZSM-5 to investigate the catalytic reaction mechanisms of furan formation in the T12 catalytic sites. Two different pathways, concerted and stepwise, were considered when examining the dehydration and deprotonation steps. The stepwise processes lead to the dehydration first and an intermolecular proton transfer mediated to form 2,3-dihydrofuran-3-ol (product of first dehydration) or furan (product of second dehydration) with slightly lower barrier compare via a concerted mechanism. Our computational results are in reasonable agreement with a concurrent experimental study of isotopically labeled glycoaldehyde and acetaldehyde upgraded over HZSM-5 (SAR = 30) from 100-300 C using a pyroprobe GC-MS system.<br/><br/>

Mechanistic study of furan formation in HZSM-5 using quantum mechanical modeling

249th National Meeting (2015)

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