Enhancing the catalytic activity of aluminum oxide for permanganate oxidation of phenols by N-doping and hydration

Aluminum oxide is an excellent catalyst in organic synthesis and petrochemistry but requires good crystallinity. This study used a simple low-temperature pyrolysis method to successfully synthesize an amorphous N-doped aluminum oxide (N-AO_am, N-[Al(OH)₃]_0.47[Al₂O₃]_0.53) sample for catalytic KMnO₄ oxidation. N-AO_am reduced the activation energy of the reaction and increased the TOC removal by forming oligomers. From a combined analysis of probe test, electrochemical measurement and DFT calculations, it was revealed that both N doping and hydration could lead to a decrease in LUMO energy of the MnO₄⁻···AO complex, facilitating the electron transfer process to enhance the oxidizing capacity of KMnO₄. Finally, the universality of the KMnO₄/N-AO_am system for catalytic oxidation of various phenols was verified, with the establishment of a QSAR model by multiple linear regression and machine learning optimization. This study fundamentally reveals the key role of nitrogen doping on the basic catalyst alumina, helping the green and low-cost traditional oxidant KMnO₄ to be rebirthed.