Carbon-encapsulated Ni catalysts derived from citrate complexes for highly efficient hydrogenation of furfural to tetrahydrofurfuryl alcohol

The development of highly dispersed non-precious metal nanocatalysts is of great importance for the biomass hydrogenation. In this work, a precursor of Ni-citrate complex was formed by using cheap citric acid as a complexing agent and carbon source, and a highly dispersed nickel catalyst with a carbon-encapsulated structure was successfully prepared by a facile pyrolysis. The catalyst obtained at a pyrolysis temperature of 400 °C (Ni-CA-400) displayed a larger specific surface area, richer defect sites in the carbon layer, and uniform Ni nanoparticles (4.8 ± 0.7 nm). In the furfural (FAL) hydrogenation reaction, Ni-CA-400 delivered a high tetrahydrofurfuryl alcohol yield of 99.8 % under mild conditions (80 °C, 5 mmol FAL, 25 mg catalyst), maintaining relatively constant hydrogenation activity and Ni particle size in five consecutive cycles. The excellent catalytic performance and stability of Ni-CA-400 can be attributed to its unique carbon-encapsulated structure, which not only effectively avoids the migration and aggregation of active Ni particles during the preparation process, but also protects the metal Ni nanoparticles from oxidation in exposure to air. The kinetic studies showed that Ni-CA-400 exhibited high turnover frequency (TOF) for the hydrogenation of both CO and CC, making it a potential industrial catalyst for FAL hydrogenation.