Oxygen-dependent catalytic activity of mesoporous MnCO₃-based catalysts for highly effective benzene oxidation

The catalytic activities of mesoporous MnCO3-based catalysts synthesized with a simple precipitation method were investigated for the oxidation of benzene. The calcination temperature was confirmed to have significant influences on physicochemical structure and catalytic performance of samples. MnCO3-based catalysts prepared at the calcination temperature below 400 degrees C showed higher activity for benzene oxidation compared with manganese oxides (Mn5O8, MnxOy and MnO2), which was mainly ascribed to abundant reactive oxygen species, large specific surface areas and rich oxygen vacancies. The optimal MnCO3-300 with good durability and strong water resistance ability achieved 90% benzene conversion at 184 degrees C. In situ DRIFTS spectra results suggested that both lattice oxygen and adsorbed oxygen could participate in the benzene oxidation. The possible reaction pathway of benzene oxidized into CO2 and H2O was involved with phenolate, benzoquinone, maleic anhydride, maleate and acetate intermediates, where the transformation from phenolate to benzoquinone was identified as the rate-limiting step.