Heterogeneous Ketone Hydrodeoxygenation for the Production of Fuels and Feedstocks from Biomass

In this work, we describe a simple, heterogeneous catalytic system for the hydrodeoxygenation (HDO) of 5-nonanone and 2,5-hexanedione, which we use as model compounds for more complex biomass-derived molecules. We present the stepwise reduction of ketones by using supported metal and solid acid catalysts to identify the intermediates en route to hydrocarbons. Although monoketone HDO can be achieved rapidly using moderate conditions (Ni/SiO₂.Al₂O₃, HZSM-5, 200 °C, 1.38 MPa H₂, 1 h), quantitative γ-polyketone HDO requires higher pressures and longer reaction times (Pd/Al₂O₃, HZSM-5, 2.76 MPa H₂, 5 h), although these are more facile conditions than have been reported previously for γ-polyketone HDO. Stepwise HDO of the γ-polyketone shows the reaction pathway occurs through ring-closure to a saturated tetrahydrofuran species intermediate, which requires increased H₂ pressure to ring-open and subsequently to fully HDO. This work allows for further understanding of bio-derived molecule defunctionalization mechanisms, and ultimately aids in the promotion of biomass as a feedstock for fuels and chemicals.