Mechanistic study of dehydration in HZSM-5 using density functional theory

Fast pyrolysis of lignocellulosic biomass has been considered as a promising thermochemical technology to convert biomass to biofuels, because this technique is compatible with current petroleum refinery infrastructure and the yield of pyrolysis oil can achieve up to 75 wt%. But biomass pyrolysis oil produces a pool of small-oxygenated organic molecules, which contains water up to 35-40%. Catalytic vapor phase upgrading (VPU) has been focused to upgrade the pyrolysis oil using various catalysts to produce lower-oxygen-content intermediates. Dehydration is an important reaction in deoxygenation and coupling reactions during the upgrading of biomass pyrolysis oils. Therefore we are presenting mechanistic study of two dehydration reactions (ethanol and furan) in HZSM-5. Ethanol dehydration reaction first performed to decide optimal system size, density functional theory (DFT) method and basis set. Furan derivatives, or furans, in particular, became our second target intermediates, since furans can either be converted into aromatic hydrocarbon and olefins, or serve as a feedstock for diesel fuels. QM/MM ONIOM model calculations in HZSM-5 were performed to investigate the catalytic reaction mechanisms in the T12 catalytic sites. We examined both concerted and step-wise dehydration reactions using our target molecules (ethanol and furan). Our results were related GC-MS experimental results to elucidate our proposed mechanisms and found in-depth experimental support.