Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Alloyed Cu-Ni Encapsulated in Biochar Catalysts

Alloyed Cu-Ni encapsulated in carbon was prepared by loading Ni and Cu onto biochar (BC) through an initial wetness impregnation method under mild conditions. The bimetallic catalysts were exploited to perform selective hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF). 2,5-Dimethylfurfural (DMF), a promising liquid fuel/fuel additive, could be obtained from HMF with the highest yield of 93.5% under the optimized conditions. During HMF HDO, two key intermediates, 5-methylfurfural (MFF) and 2,5-dihydroxymethylfuran (DHMF), dominating two distinct conversion pathways were systematically investigated by Arrhenius kinetics analysis. In addition, the turnover frequencies (TOFs) of HDO reaction over Cu-Ni/BC corresponding with Cu amount were thoroughly discussed, finding that the electron transfer from Cu to Ni in the alloy structure was beneficial to the HDO reaction and the conversion pathways can be regulated by reaction temperature variation. Importantly, the synergy of HDO of HMF by alloyed Cu-Ni metal and Lewis acid sites from oxide NiOx were hence clarified by systematic catalyst characterizations. The Cu-Ni/BC catalyst is stable for at least five consecutive runs to obtain the stabilized 81.9% of DMF since the third run.