Unconventional Rapid Synthesis of Layered Manganese Dioxide Nanostructures for Selective Oxidation of 5‑Hydroxymethylfurfural to 2,5-Diformylfuran

Nanostructured first row transition metal (Mn, Fe, Co, Ni, and Cu) oxides (TMOs) have shown promise as catalysts for creation of new and ransformative technologies for manufacturing value-added chemicals that are energy- and atom-efficient. Most of the synthesis routes to TMOs involve harsh reaction conditions or prolonged preparation times. Herein, we use potassium superoxide (KO₂), a commercially available stable salt of superoxide, as a viable oxidant for rapid but mild redox synthesis of birnessite type layered manganese dioxide (δ-MnO₂) nanomaterials. These δ-MnO₂ materials are synthesized in a fast (as fast as 5 min), ambient (room temperature), and convenient condition, employing a simple laboratory apparatus (grinding with mortar and pestle followed by washing with water). Characterization studies reveal a hierarchical porosity and sponge-like morphology for the δ-MnO₂ nanomaterial, whereas the surface area of the material is tunable as a function of the adopted synthetic aspects. The δ-MnO₂ materials deliver promising catalytic activity in the selective aerobic oxidation of 5-hydroxymethylfurfural alcohol (HMF) to 3,5-diformylfuran (DFF), an important probe reaction to transform biomass-derived feedstocks to useful chemicals. Density functional theory (DFT) is used to investigate the interaction of HMF with the catalyst surface and to chart out the energetics pathway of system relaxation, together showcasing various bond dissociations, intermediate steps, and rate limiting kinetics.