Enhanced Oxidation of Glucose to Formic Acid under Mild Conditions Using an Oxygen-Deficient MnOx-Based Catalyst and a Novel Catalyst Regeneration Strategy

The oxidation of renewable biomass to formic acid using molecular oxygen over heterogeneous catalysts poses challenges due to harsh reaction conditions, limited O2 activation, and dissolved catalyst recovery issues. In this study, a novel approach utilizing a vitamin C-assisted and segmented calcination method was introduced to synthesize mesoporous MnOx materials with increased oxygen vacancy concentration for the oxidation of biomass-derived glucose to formic acid. The catalyst demonstrated a remarkable formic acid yield of 69.56% with O2 as the oxidant under mild conditions at 140 °C for 1 h. Furthermore, a simple precipitation method was developed to recover dissolved MnOx catalysts using MgO to adjust the pH of the solution for catalyst collection. The recovered MnOx with Mg2+-intercalated birnessite-like structures could be used again without any other regeneration treatment. Experimental results indicated that both the initially prepared MnOx and the catalysts obtained through the MgO-assisted precipitation method exhibited high concentrations of oxygen vacancies, significantly enhancing the oxidative activity of glucose. This study provides valuable insights into the activation of molecular oxygen at low temperatures for biomass oxidation and the recovery of heterogeneous catalysts prone to dissolution, thereby opening new avenues for sustainable biomass oxidation processes.