Ambient-pressure and low-temperature upgrading of lignin bio-oil to hydrocarbons using a hydrogen buffer catalytic system

Abstract

Catalytic hydrodeoxygenation is an essential step for bio-oil upgrading. However, hydrodeoxygenation usually requires a high hydrogen pressure and high temperature due to the good stability of the C–O bonds. Here we report an effective multiphase hydrodeoxygenation of lignin-based bio-oil at temperatures <100 °C and hydrogen pressures <1 atm using a synergetic catalyst system that consists of a low redox potential H4SiW12O40 (SiW12) and suspended Pt-on-carbon (Pt/C) particles. We propose that SiW12 plays three critical roles in bio-oil hydrodeoxygenation. First, it quickly oxidizes the H2 gas to form reduced SiW12 in the presence of Pt/C. Second, it transfers both electrons and H+ ions to the bulk phase to form active H* or H2 on the Pt/C surface. Third, the formation of the oxonium ion in a SiW12 superacid solution reduces the deoxygenation energy. The SiW12-enhanced proton-transfer hydrodeoxygenation mechanism is supported by density functional theory computations. As a result of the hydrogen buffer and acidic effect, up to a 90% yield of hydrocarbons (cyclohexane, benzene and their derivatives) was achieved from the hydrodeoxygenation of phenol and its derivatives. Bio-oil derived from biomass has great potential as a more sustainable fuel but its formation typically relies on energy-intensive processes. Liu et al. show how a tri-phase hydrogen-transfer catalytic system can drive hydrodeoxygenation in water under mild conditions to achieve up to 90% hydrocarbon yield.