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 Mo_xCu_y/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 (O_v) and Cu(I) are the reactive sites for O₂ activation. Quenching experiments and various characterizations reveal that superoxo (≡Cu(II)/O_v-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)/O_v-OOH peroxo. Meanwhile, the doped Mo(V/VI) further activates ≡Cu(II)/O_v-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.