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, andCu) oxides (TMOs) have shown promise as catalysts for creation ofnew and ransformative technologies for manufacturing value-added chemicalsthat are energy- and atom-efficient. Most of the synthesis routesto TMOs involve harsh reaction conditions or prolonged preparationtimes. Herein, we use potassium superoxide (KO2), a commerciallyavailable stable salt of superoxide, as a viable oxidant for rapidbut mild redox synthesis of birnessite type layered manganese dioxide(& delta;-MnO2) nanomaterials. These & delta;-MnO2 materials are synthesized in a fast (as fast as 5 min), ambient(room temperature), and convenient condition, employing a simple laboratoryapparatus (grinding with mortar and pestle followed by washing withwater). Characterization studies reveal a hierarchical porosity andsponge-like morphology for the & delta;-MnO2 nanomaterial,whereas the surface area of the material is tunable as a functionof the adopted synthetic aspects. The & delta;-MnO2 materialsdeliver promising catalytic activity in the selective aerobic oxidationof 5-hydroxymethylfurfural alcohol (HMF) to 3,5-diformylfuran (DFF),an important probe reaction to transform biomass-derived feedstocksto useful chemicals. Density functional theory (DFT) is used to investigatethe interaction of HMF with the catalyst surface and to chart outthe energetics pathway of system relaxation, together showcasing variousbond dissociations, intermediate steps, and rate limiting kinetics.