Oxygen vacancy-enhanced hydrogen spillover on a bifunctional PdFe/TiO2−x catalyst for highly selective direct hydrodeoxygenation of carbonyl compounds

Abstract

Achieving direct cleavage of CO bonds in biomass under mild conditions to generate high-value-added products via catalytic hydrogenation remains a substantial challenge. We developed a Pd–Fe bimetallic catalyst supported on oxygen vacancy (O_v)-enriched TiO₂ for the direct cleavage of CO bonds, and as a result, up to 99% yield of 2-methoxy-4-methylphenol (MMP) was achieved from the conversion of vanillin (VAN) at 140 °C under atmospheric H₂ pressure. This study utilizes O_v to enhance hydrogen spillover levels during the reaction process and proposes a novel reaction pathway that avoids the formation of alcohol intermediates. Mechanistic investigations reveal that surface O_v facilitates hydrogen spillover, enabling active hydrogen migration from Pd–Fe sites to TiO₂ to form Ti–H species. Through synergistic Pd–Fe bimetallic effects and metal–support interfacial interactions, direct hydrodeoxygenation (HDO) of VAN is achieved, ultimately generating MMP with high selectivity. The catalyst demonstrates excellent stability and broad substrate suitability, maintaining uncompromised activity after five catalytic cycles.