Selective tandem hydrogenation and rearrangement of furfural to cyclopentanone over CuNi bimetallic catalyst in water

Tandem catalysis for the hydrogenation rearrangement of furfural (FA) provides an attractive solution for manufacturing cyclopentanone (CPO) from renewable biomass resources. The CuNi/Al-MCM-41 catalyst was synthesized and afforded excellent catalytic performance with 99.0% conversion and 97.7% selectivity to CPO in a near-neutral solution under 2.0 MPa H2 at 160 °C for 5 h, much higher than those on other molecular sieve supports including MCM-41, SBA-15, HY, and ZSM-5. A small amount of Al highly dispersed in MCM-41 plays an anchoring role and ensures the formation of highly dispersed CuNi bimetallic nanoparticles (NPs). The remarkably improved catalytic performance may be attributed to the bimetallic synergistic and charge transfer effects. In addition, the initial FA concentration and the aqueous system pH required precise control to minimize polymerization and achieve high selectivity of CPO. Fourier transform infrared spectroscopy and mass spectra results indicated that polymerization was sensitive to pH values. Under acidic conditions, FA and intermediate furfuryl alcohol polymerize, while the intermediate 4-hydroxy-2-cyclopentenone mainly polymerizes under alkaline conditions, blocking the cascade of multiple reactions. Therefore, near-neutral conditions are most suitable for minimizing the impact of polymerization. This study provides a useful solution for the current universal problems of polymerization side reactions and low carbon balance for biomass conversion.