New insights in single-step hydrodeoxygenation of glycerol to propylene by coupling rational catalyst design with systematic analysis

Abstract

Glycerol-to-propylene routes involve overlapped hydrodeoxygenation (HDO) events on the active sites of heterogeneous catalysts which stability in aqueous media is a challenge. Herein, we proposed a rationalized approach to develop such catalysts by using hydrophobic-inert silica supports to protect highly reactive sub-2 nm Mo particles against leaching and sintering. Propylene yield from 84.1 % to 65.6 % were obtained on MoOx nanoparticles at space-velocity ∼1.7 h−1 and H2-pressure ∼50 bar. Carburizing MoOx nanoparticles to β-Mo2C leads to an extremely efficient HDO catalyst, featuring, unprecedented TOFpropylene ranging from ∼153.1 h−1 to 226.4 h−1, while η-MoC phase gave better hydrogenation activity. Coupling in-situ XPS and kinetic data reveal that Mo5+, Mo3+ and Mo2+-C species play a critical role in the HDO events. Glycerol-to-propylene progresses over MoOx via successive Mo5+/Mo6+ and Mo3+/Mo4+ cycles, while over β-Mo2C/η-MoC, it occurs mostly on carbidic-oxycarbide surface. Surface accumulation of CxHyOz species caused Moδ+ re-oxidation, which hinders the HDO events.