Catalytic oxidation of biomass-derived 5-hydroxymethylfurfural to 5-hydroxymethyl-2-furancarboxylic acid by Co-based MOFs

The selective oxidation of 5-hydroxymethylfurfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) has been investigated on Co-based MOF catalysts. ZIF-67 (ZIF, Zeolitic Imidazolate Framework), Co-BTC and Co-BTC-2mim were solvothermally synthesized by the association of cobalt with 2-methylimidazole (2-mim), 1,3,5-benzenetricarboxylic acid (H3BTC), or a mixture of the two linkers. Besides these, a novel core-shell Co3O4 @Co-BTC structure with a core of Co3O4 and Co-BTC on its outer layer has also been synthesized by a simple replacement of the cobalt nitrate precursor with Co3O4. Among the prepared materials the core-shell Co3O4 @Co-BTC catalyst afforded the proper catalytic features (i.e., specific density of the acid and base site combined with the high accessibility of the HMF molecules to the active Co sites) for a high selectivity to HMFCA (89%) at a HMF conversion (XHMF) of 79%, at 60 ℃ and after only 1 h, in the presence of t-BuOOH as oxidant and acetonitrile as solvent.