(425c) Hydrodeoxygenation of Aliphatic Lignin Pyrolysis Vapors with Bulk MoO3

Molybdenum trioxide (MoO₃) has shown strong potential as an active phase for the hydrodeoxygenation (HDO) of lignin pyrolysis vapors due to its high oxophilicity, low hydrogen pressures, and selectivity towards aromatic products. However, the overall catalytic efficiency is hindered by sequential hydrogenation of unsaturated aliphatic co-generated products, making the resulting deoxygenated mixture less valuable and incompatible with the existing petrochemical infrastructure. To better understand how the selectivity of alkenes could be controlled, further evaluation of linear oxygenate HDO was required. This was accomplished by employing a continuous packed bed reactor with an online gas chromatograph to measure the reaction kinetics of acetone and isopropanol across bulk MoO₃. It was observed that the rate of acetone HDO had a -0.2 reactant order while isopropanol HDO occurred significantly faster with a 0 reaction order. An increase in carbon chain length to 2-pentanone and 2-pentanol showed similar -0.4 and 0 reaction orders, respectively. Thus, it can be concluded that carbonyl groups needed to be hydrogenated to weaken the carbon-oxygen bond before a facile dehydration step to form an alkene. Further, the strong adsorption of the carbonyl oxygen to the MoO₃ surface resulted in surface competition with H₂ activation, leading to a negative reaction order.