Tunable products of 5-hydroxymethylfurfural oxidation by Zn/Co-ZIF derived catalysts

As a bio-based platform compound, 5-hydroxymethylfurfural (HMF) can be effectively converted into other high value-added derivatives. Here we report two non-noble metal catalysts for the selective oxidation of HMF, NC and Co@NC are easily obtained by pyrolysis of ZIF-8 and ZIF-67, respectively. The NC and Co@NC catalysts oxidized HMF to FFCA (Select. 95%) and FDCA (Select. 98%), respectively, using O2 as oxidant. Experimental and theoretical studies show that pyridinic N and graphitic N in NC has high catalytic activity for the oxidation of carbonyl groups in HMF to FFCA, while the synergistic effect of Co-N in Co@NC can completely oxidize HMF to FDCA. DFT calculations show that, compared with NC, the Co@NC containing Co-N exhibits a lower energy barrier during the aerobic oxidation of HMF to FDCA. And Co-N leads to the conversion of electrons from N to Co and promotes the activation of O2 to form O2-, and then oxidize HMF to FDCA. Interestingly, our reaction system is universal, and could achieve almost 100% conversion of various furfural substrates to corresponding carboxylic acid. This study may provide a new/highly efficient catalysts for biomass conversion.