Mechanistic effects of solvent systems on the Ni-Sn-catalyzed hydrodeoxygenation of lignin derivatives to none-oxygenates

The presence of water in organic systems usually inhibits the activity of the reaction. In the biphasic system composed of water-decane, the distribution of lignin-derived m-cresol hydrodeoxygenation (HDO) products catalyzed by Ni-Sn was affected by the presence of water. Water can facilitate the hydrogenation process by the dissociation of water to produce H protons. However, the formation of complete deoxidation products may be inhibited because of the catalyst surface reconstruction and the low solubility in an aqueous system. DFT calculation theoretically revealed that the presence of water not only can lower the barrier and stabilize the transition state but also can affect the rupture of the C-Ar-O bond. Also, the significant characteristics of solvent action were explained by the hydrogenation and the solvatochromic parameters. Among them, m-cresol has a good performance in hydrocarbon solvents (CnH2n) and hydrogen bond donor (HBD) solvents. However, the catalytic activity decreases in alcohols due to the synergistic effects like H-bonds and competitive adsorption between the solvent and the substrate. The mechanism of the solvent effects with different properties can provide a reference for the subsequent expansion of the system in a wide range. Therefore, the synergy between the solvent and the catalyst provides a promising method for upgrading reclaimed chemicals from lignin.