Selective Hydrodeoxygenation of Lignin-Derived Phenols to Cyclohexanols over Co-Based Catalysts

Cyclohexanols are important feedstock for polymers, spices, and medicines production in industry. In this work, a series of cobalt-based catalysts with different supports were prepared and used to catalyze lignin-derived phenols to cyclohexanols. Among the catalysts, Co/TiO2 showed the best hydrodeoxygenation (HDO) activity. An equivalent of propylcyclohexanol (>99.9%) was achieved under 1 MPa H2, 200 °C for 2 h. According to the characterization results of transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area analysis, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD) and NH3-TPD, the particle size and dispersion of Co could have important influence on catalytic activity. For Co/TiO2, the SMSI effect may significantly affect the catalytic activity. The influences of different temperature, H2 pressure and reaction time on the eugenol conversion by Co/TiO2 were explored. 99% yield of propylcyclohexanol could even be obtained under 0.4 MPa H2, 180 °C for 8 h. This should be the mildest condition that has been reported for HDO of eugenol to propylcyclohexanol catalyzed by non-noble metal catalyst. On the basis the mechanism and substrates extension studies, all the Co-based catalysts selected in this study showed high activity to cleave the Caryl–OCH3 bond before the hydrogenation of the aromatic ring when the −OCH3 group substituted at ortho-position.