Ni nanoparticles embedded in nitrogen doped carbon derived from metal-organic frameworks for the efficient hydrogenation of vanillin to vanillyl alcohol

The selective hydrogenation of oxygen containing functional groups is of great importance for the high value utilization of biomass resources such as lignin. However, it remains a great challenge to design and synthesize non-noble metal catalysts with high efficiency for the hydrogenation of lignin derivatives under mild reaction conditions. Here, a promising non-noble Ni@CN (CN: nitrogen doped carbon) catalyst was fabricated by direct pyrolysis of Ni metal-organic frameworks (Ni-ZIF). Characterization results reveal that the Ni nanoparticles (NPs) are embedded in nitrogen doped carbon, and the size of Ni NPs increases with the rising pyrolysis temperature. The severe aggregation of the particles of the Ni@CN composite occurs when the pyrolysis temperature is higher than 525 °C. The as-prepared Ni@CN catalysts were tested for selective hydrogenation of the aldehyde group of vanillin (lignin monomer molecule) for the purpose of producing vanillyl alcohol. The Ni@CN-425 catalyst obtained at a pyrolysis temperature of 425 °C exhibits the highest catalytic performance for the selective hydrogenation of vanillin to vanillyl alcohol. A vanillin conversion of 99.5% and vanillyl alcohol selectivity of 98.3% are achieved under a low temperature of 80 °C. In addition, Ni@CN-425 presents excellent stability in the hydrogenation reaction of vanillin. This work provides some useful insights into the design of novel non-noble metal catalysts with high efficiency for selective hydrogenation of oxygen containing functional groups in lignin derivatives. The Ni@CN catalyst fabricated by a facile and feasible method presents high efficiency in the selective hydrogenation of vanillin under mild conditions.