Catalytic Hydrogenolysis of Lignins into Phenolic Compounds over Carbon Nanotube Supported Molybdenum Oxide

Lignin represents the most abundant source of renewable aromatic resources, and the depolymerization of lignin has been identified as a prominent challenge to produce low-molecular-mass aromatic chemicals. Herein, we report a nanostructured MoOx/CNT, which can serve as an efficient catalyst in hydrogenolysis of enzymatic mild acidolysis lignins (EMALs) derived from various lignocellulosic biomass, thus giving monomeric phenols in high yields (up to 47 wt %). This catalyst showed high selectivity toward phenolic compounds having an unsaturated substituent, because the cleavage of C–O bonds in β-O-4 units is prior to reduction of double bonds by MoOx/CNT under a H2 atmosphere, which was confirmed by examination of lignin model compound reactions. The effects of some key parameters such as the influence of solvent, temperature, reaction time, and catalyst recyclability were also examined in view of monomer yields and average molecular weight. This method constitutes an economically responsible pathway for lignin valorization, which is comparable to the performance of precious-metal catalytic systems in terms of activity, reusability, and biomass feedstock compatibility.