Selective oxidation of glycerol to lactic acid catalyzed by MOF-74 (Cu/Co) derived Cu/Cu2O/CoO@C nanocomposites

In this study, Cu/Cu2O/CoO@C series nanocomposites were successfully prepared by pyrolyzing bimetallic MOF-74 (Cu/Co) precursor. The abundant unsaturated bimetallic sites and excellent stability of this precursor laid the foundation for the efficient catalytic conversion of glycerol to lactic acid. After pyrolysis at 550 °C for 2 h, the C skeleton structure was retained, and its high porosity provided abundant active sites for glycerol adsorption, ensuring high catalytic activity. It was confirmed by XRD, XPS and TEM that the active sites of the catalyst were Cu0, Cu+ and Co2+. The Cu/Cu2O/CoO@C (Cu/Co = 45/55) sample (V3) has a large specific surface area (160 m2/g), which is conducive to active site exposure and charge transport. HRTEM further reveals that the Cu (111), Cu2O (111) and CoO (200) crystal planes in V3 have the smallest lattice spacing, indicating that the density of active sites is the highest, which significantly enhances the adsorption capacity of glycerol. The unique Cu-Cu2O-CoO heterojunction structure formed in the sample promotes the synergy between the metal components and is also a key factor in improving the catalytic activity. Under the optimal reaction conditions (air atmosphere, 190 °C, 6 h), V3 exhibited excellent catalytic performance, i.e. glycerol conversion of 99.84% and lactic acid selectivity of 91.21%. Cyclic experiments showed that V3 showed good stability during the catalytic process. XRD and XPS showed that the crystal phase and valence state of V3 did not change significantly after the reaction.