Effect of alkali metal promoters on natural manganese ore catalysts for the complete catalytic oxidation of o-xylene

A series of alkali metal doped natural manganese ore (NMO) catalysts were prepared by an impregnation method, and tested for the complete catalytic oxidation of o-xylene. The effects of alkali metal on the catalytic performance and structural properties of NMO were examined. Alkali metals were found to enhance the activity of NMO in the following order: Li < Na < Rb < K, Cs. The experimental results showed that NMO-K(Cs)-0.07 could convert o-xylene (0.055 vol.%) into CO2 and H2O at 240 °C, which was 60 °C lower than that of NMO. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) measurements revealed that the primary component of NMO and NMO-K-0.07 were MnO2. It was found that K2O was highly dispersed onto the NMO surface. The addition of K2O did not increase the BET surface area of the NMO. However, it resulted in the binding energy of the Mn 2p of NMO-K-0.07 shifted to a lower value. The results suggested that alkali metals act as electronic promoters, indicating that alkali metal doped NMO are promising catalyst candidates for the catalytic oxidation of VOCs.