Solvent-Controlled Product Distribution in Vanillin Hydrogenation over a N-Doped Carbon-Supported Nickel Catalyst

Solvent-controlled hydrogenation of vanillin to 4-hydroxymethyl-2-methoxyphenol(HMP) or 2-methoxy-4-methylphenol (MMP) is an attractive topic inthe field of bio-oil utilization. Herein, a nickel-based catalystsupported on a N-doped carbon material (Ni-N-C) was prepared by facileball milling mixing and subsequent high-temperature calcination. Theas-prepared Ni-N-C-800 catalyst showed more than 99% MMPyield and good stability using pure H2O as a solvent underthe given conditions. By using the mixed solvent H2O/ethylacetate with a volume ratio of 1:5, the hydrogenation was convenientlytuned to produce the intermediate product HMP. Density functionaltheory (DFT) calculations further showed that the intermolecular forcesof HMP interacting with ethyl acetate were much stronger than thoseinteracting with H2O. Ethyl acetate could raise the energybarrier to keep vanillin hydrogenation in the intermediate HMP stage,and H2O reduced the energy barrier to accelerate the finalproduct MMP formation.