Boron, nitrogen co-doped biomass-derived multilayer-graphene encapsulated Co nanoparticles as highly efficient catalysts for the selective hydrodeoxygenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran

Abstract

Highly efficient conversion of biomass derivative 5-hydroxymethylfurfural (HMF) into biofuel 2,5-dimethylfuran (DMF) using non-noble metal catalysts is attractive but challenging. In this work, boron (B), nitrogen (N) co-doped biomass-derived multilayer-graphene encapsulated Co catalysts (Co@BNG) were prepared and applied in the selective hydrodeoxygenation of HMF to DMF. Extensive analyses demonstrated that the synergistic effect between carbon layer confinement and B, N co-doping facilitated the formation of ultrafine Co nanoparticles, which in turn promoted Co reduction and increased the amount of metal Co. Specifically, B doping induced the formation of more defects and increased the amount of pyridinic-N and Co-Nx. More significantly, B doping promoted the formation of electron-deficient Co centers (Co-Nx/B) by transferring more electrons from Co to the adjacent B and N, which could act as Lewis acid sites for C=O activation and subsequent C-OH breaking during the hydrogenation-hydrogenolysis of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) and DMF. Remarkably, in-situ DRIFTS revealed that Co@B0.2NG preferentially activated C=O/C-OH groups to produce 5-methyfurfuryl alcohol (MFA), the critical intermediate that determines the formation of DMF. Furthermore, theoretical calculations further confirmed that B doping strengthened the electronic interactions between Co and neighboring N/B atoms to form electron-deficient Co centers. Significantly, Co-B1N3C model displayed the optimal adsorption (H2, HMF, and BHMF) and desorption (H* and DMF) behaviors, along with the lowest activation energy for the rate-determining step of BHMF to MFA. Encouragingly, Co@B0.2NG exhibited exceptional recyclability and gave 99.9 % yield of BHMF at 100 ℃ and 99.2 % yield of DMF at 140 ℃. This work offers a new approach for the development of non-noble metal catalysts that are highly efficient, durable, and low-cost for the hydrodeoxygenation of renewable biomass into high-value compounds.