Tracking the Mechanism of Electrocatalytic Hydrodeoxygenation of Propylguaiacol by Electrochemical Membrane-Inlet Mass Spectrometry

Abstract Lignocellulose-derived bio-oils require hydrodeoxygenation (HDO) to reduce their oxygen content for integration into conventional fuels. Electrocatalytic HDO (eHDO) offers a sustainable alternative to traditional high-temperature, high-pressure processes, but its mechanism remains debated. This study demonstrates the use of electrochemical membrane-inlet mass spectrometry (EC–MIMS) with a polydimethylsiloxane (PDMS) membrane to monitor in situ the eHDO of propylguaiacol (PG), a model molecule present in lignocellulosic bio-oils, to propylcyclohexane (PCH) on Pt in acidic media. By coupling EC–MIMS with isotopic labeling (H2O/D2O), we elucidate the proton transfer pathways during three sequential key steps: demethoxylation, dehydroxylation, and aromatic ring hydrogenation. The results reveal that ring hydrogenation follows a hydrogen atom transfer (HAT) mechanism, while demethoxylation and dehydroxylation could proceed via a tautomerization-assisted pathway. This work introduces EC–MIMS as a powerful tool for tracking apolar products in electrocatalysis and providing mechanistic insights critical for optimizing bio-oil valorization.