Highly efficient and selective hydrogenation of furfural to furfuryl alcohol and cyclopentanone over Cu-Ni bimetallic Catalysts: The crucial role of CuNi alloys and Cu+ species

The selective hydrogenation of furfural derived from biomass is of significant importance in the synthesis of valuable chemical compounds. In this work, Cu-Ni bimetallic catalysts with varying metal ratios were effectively synthesized using the urea deposition method and employed in catalytic hydrogenation of furfural (FA) to furfuryl alcohol (FOL) and cyclopentanone (CPO) in different solvents. The study revealed that the synergistic interaction between Cu and Ni favors the formation of CuNi alloys, thereby facilitating the reduction of CuO and NiO and resulting in larger amount of metallic species (Cu0/+ and Ni0), and promoting the formation of highly dispersed nanoparticles. Moreover, the formed Cu+ species can serve as Lewis acid sites and improve the adsorption of polarized C = O, thus significantly enhancing the selectivity to FOL. More importantly, the cooperation between Cu+ species and water can promote the aqueous-phase hydrogenation-rearrangement (AP-HR) of FA to CPO. Also, in-situ/on-line DRIFTS shows that Cu3Ni1/SiO2 preferentially adsorbs and activates C = O and prefers to form 4-hydroxy-2-cyclopentenone (HCP), which is the key intermediate to form CPO. DFT calculations agree with the in-situ/on-line DRIFTS, showing that Cu3Ni1 (1 1 1) crystal surface with the lowest d-band center and the strongest electronic effects presents the highest adsorption energies of H2, H2O, and FA, the lowest adsorption energies of H*, FOL, and CPO, and the lowest energy barriers of Piancatelli rearrangement of FOL to HCP. Under the optimum conditions, Cu3Ni1/SiO2 gives 99.9 % yield to FOL at 333 K in isopropanol and 96.7 % yield to CPO at 413 K in water. The low cost and high activity of Cu3Ni1/SiO2 make it a potential catalyst for the green production of FOL and CPO in industry.