Enhancing polyol/sugar cascade oxidation to formic acid with defect rich MnO2 catalysts

Abstract

AbstractOxidation of renewable polyol/sugar into formic acid using molecular O2over heterogeneous catalysts is still challenging due to the insufficient activation of both O2and organic substrates on coordination-saturated metal oxides. In this study, we develop a defective MnO2catalyst through a coordination number reduction strategy to enhance the aerobic oxidation of various polyols/sugars to formic acid. Compared to common MnO2, the tri-coordinated Mn in the defective MnO2catalyst displays the electronic reconstruction of surface oxygen charge state and rich surface oxygen vacancies. These oxygen vacancies create more Mnδ+Lewis acid site together with nearby oxygen as Lewis base sites. This combined structure behaves much like Frustrated Lewis pairs, serving to facilitate the activation of O2, as well as C–C and C–H bonds. As a result, the defective MnO2catalyst shows high catalytic activity (turnover frequency: 113.5 h−1) and formic acid yield (>80%) comparable to noble metal catalysts for glycerol oxidation. The catalytic system is further extended to the oxidation of other polyols/sugars to formic acid with excellent catalytic performance.