Low-temperature catalytic oxidation of benzene over nanocrystalline Cu–Mn composite oxides by facile sol–gel synthesis

A series of nanocrystalline copper–manganese oxides (denoted as Cu 3−x Mn x , x = 0, 1, 1.5, 2, 2.5, 3, where x means the molar ratio of Cu and Mn) were successfully prepared by a facile citric acid sol–gel method. The combination of Cu 2+ and Mn 3+ is intensified and enhanced interface effects generated, which is beneficial for the catalytic oxidation of benzene. A series of analyses, such as X-Ray Diffraction (XRD), N 2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature programmed reduction (H 2 -TPR), were employed to further investigate the structural properties of the catalysts. An optimal Mn/Cu ratio of 2 forms CuMn 2 O 4 spinels. CuMn 2 with CuMn 2 O 4 spinel structure presents a larger specific surface area, smaller pore diameter as well as more lattice oxygen species, exhibiting remarkable activity and stability for the catalytic oxidation of benzene. On account of these factors, CuMn 2 possesses better low temperature reducibility and shows the best catalytic performance with 90% benzene conversion at 186 °C. The enhanced catalytic activity of CuMn 2 is attributed to the stabilization of CuMn 2 O 4 active phases and the intensive synergistic effect between Cu–Mn oxides. To prove the effect of CuMn 2 O 4 spinel structure on catalytic performance, a CuO/Mn 2 O 3 mixed catalyst (molar ratio 1 : 1) was prepared and applied to benzene oxidation ( T 90% = 198 °C), which indicates that the spinel structure has an encouraging effect on benzene catalysis. The catalytic properties of single copper oxide and manganese trioxide were also tested, the results show that CuMn 2 O 4 has a crucial role in facilitating electronic transmission and mobility of the lattice oxygen.