Highly Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Formylfuran Mediated by Surface Superoxo and Peroxo on Mo₃Cu₁/NH₂-SBA-15

Although thermocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-formylfuran (DFF) by O2 is an important reaction, achieving a high yield of DFF is still challenging. In this study, a series of MoxCuy/NH2-SBA-15 are prepared, and Mo3Cu1/NH2-SBA-15 exhibits the desirable catalytic reactivity with a complete conversion of HMF and high selectivity of 94.4% toward DFF. XPS and EPR analyses indicate that the abundant oxygen vacancies (Ov) and Cu(I) are the reactive sites for O2 activation. Quenching experiments and various characterizations reveal that superoxo (≡Cu(II)/Ov-OO•) on the surface of catalyst, instead of •OH and O2•–, are the primary oxidizing species to abstract H from HMF to RCH2-O•, accompanied by the formation of ≡Cu(II)/Ov-OOH peroxo. Meanwhile, the doped Mo(V/VI) further activates ≡Cu(II)/Ov-OOH peroxo to form ≡Mo-(η2-O2) peroxo, which significantly promotes the oxidation selectivity of RCH2-O• toward DFF via the H-abstraction pathway. This study provides new insight on selective thermal-oxidation of biomass-derived compounds to high-value-added chemicals via regulating reactive oxidizing species on the surface of catalysts.