Tailoring Facets of α-Mn2O3 Microcrystalline Catalysts for Enhanced Selective Oxidation of Glycerol to Glycolic Acid

Understanding and tuning the crystal-facet-dependent catalytic properties of catalysts are of great importance for the selective oxidation of polyols. Herein, a series of α-Mn2O3 catalysts with various morphologies (octahedron, truncated octahedron, and cube) are successfully synthesized for the enhanced selective oxidation of glycerol to glycolic acid. Our results show that the different catalytic performances of Mn2O3 catalysts with various morphologies originated from the chemical nature of the (001) and (111) facets. Multicharacterizations and density functional theory calculations revealed that the surface oxygen vacancies on the (001) facets are well correlated with the catalytic activity, and the C–H bond in oxygen-containing intermediates could be easily activated on the surface oxygen vacancies of the (001) facets, thus improving the catalytic activity. Moreover, the main role of (111) facets is to prevent the over-oxidation of glycolic acid products, leading to the improvement of glycolic acid selectivity. Consequently, the Mn2O3-truncated octahedron catalyst with both (001) and (111) facets shows high catalytic activity (0.87 mmol/(h m2)) and glycolic acid selectivity (52.6%) simultaneously. We anticipate that this work could give some suggestions for the design of highly efficient inexpensive catalysts in the glycerol oxidation system.