Structure-dependent catalytic properties of mesoporous cobalt oxides in furfural hydrogenation

As the development of noble metal free catalysts became important in the biomass conversion, catalytic hydrogenation of furfural (FAL) is investigated over ordered mesoporous cobalt oxide (m-Co3O4). When m-Co3O4 is reduced at 350 and 500 degrees C in hydrogen, the original crystal structure of Co3O4 is changed to CoO and Co, respectively. Here we examine the effect of the structure, porosity, and oxidation state of m-Co3O4 to identify catalytically active species for hydrogenation of FAL. Among cobalt oxide catalysts having different crystal structures and symmetry, m-CoO having p6mm symmetry exhibits the highest activity. In product selectivity, the CoO phase induces FAL hydrogenolysis by selective production of 2-methyl furan (MF), while the Co3O4 and Co phases promote preferential hydrogenation of side chain (carbonyl group) of FAL to furfuryl alcohol. Density functional theory calculations also reveal that the adsorption of FAL on CoO(111) is higher than Co(111). Overall, these studies demonstrate that Coo as the most active phase is responsible for the high FAL conversion and the distinct pathway of FAL to MF.