Oxygen vacancy engineering of Ru/MnOx to enhance water-assisted proton hopping for phenol hydrodeoxygenation

Abstract

The catalytic conversion of lignin-derived phenols to their corresponding aliphatic alcohols constitutes a pivotal industrial process for generating polymer precursors, including ketones, carboxylic acids, and amine derivatives. In this study, three kinds of manganese oxides (MnO₂, Mn₂O₃, and Mn₃O₄) were synthesized through a facile hydrothermal or precipitation method, followed by Ru nanoparticle deposition and applied to selective hydrodeoxygenation (HDO) of lignin-derived phenol to cyclohexanol in the aqueous phase. Among the three Ru/MnO_x catalysts, Ru/MnO₂ showed the highest catalytic activity for HDO of phenol. Complete phenol conversion (100%) and 99% cyclohexanol selectivity were achieved under mild aqueous-phase conditions (1 MPa H₂, 343 K for 3 h), surpassing those of their Mn₂O₃- and Mn₃O₄-supported counterparts. According to the characterization results of X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction of hydrogen (H₂-TPR), more surface oxygen vacancies on Ru/MnO₂ favored the adsorption of water, which assisted the proton hopping across the surface of MnO₂, enhancing hydrogenation activity.