Flower-like N-Doped Carbon-Encapsulated Nano Co-CoO _<i>x</i> for the Hydrogenation of 5-Hydroxymethylfurfural

The nano Co-CoOx encapsulated within three-dimensional flower-like N-doped biobased carbon was synthesized through a facile hydrothermal method with urea as the nitrogen source, cobalt acetate as the catalyst precursor, and glucose as both the carbon source and structure-directing agent. The results demonstrated that the catalyst featured a three-dimensional flower-like morphology by self-assembly of two-dimensional carbon nanosheets and thus facilitated mass transfer and exposed more accessible active sites. Besides, the nano Co-CoOx species coated by an ultrathin carbon layer were uniformly embedded within the two-dimensional N-doped carbon nanosheets. In this case, the unique structure significantly protected the nano Co-CoOx species against aggregation and more importantly decorated their electronic properties through strong interaction with the coated carbon layer. The Co0 and CoOx species were identified to synergistically boost the selective hydrogenation of HMF to DMF with a conversion of 100% and a selectivity of 92.2% under the optimum reaction conditions even using low-cost and nontoxic ethanol as the reaction medium. After five recycles, the HMF conversion still remained at 100%, and the DMF selectivity slightly decreased by merely 1.3%, indicating robust reusability and structure stability.