Manganese oxide octahedral molecular sieve (OMS-2) with cryptomelane structure synthesized by a solvent-free method was employed to oxidize gaseous elemental mercury (Hg-0) in coal combustion flue gas for the first time. Brunauer-Emmett-Teller (BET) surface area analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, H-2 temperature-programmed reduction (H-2-TPR) and X-ray photoelectron spectroscopy (XPS) measurement were employed to characterize the catalyst. The OMS-2 with large surface area and abundant pores presented excellent Hg-0 oxidation performance at a wide temperature range of 100-250 degrees C. At the optimal operating temperature of 150 degrees C, 93% Hg-0 oxidation efficiency was obtained under a gas hourly space velocity as high as 1,350,000 h(-1). Hg-0 oxidation on OMS-2 catalyst was supposed to follow the Mars-Maessen mechanism, where the gaseous Hg-0 was firstly adsorbed on the OMS-2 catalyst surface to form adsorbed Hg-0, and then the adsorbed Hg-0 was oxidized by the lattice oxygen over catalyst surface to form mercury oxide (HgO). Both HCl and NO in the flue gas promoted Hg-0 oxidation mainly due to the formation of active species like Cl*, NO2, which reacted with Hg-0 to form volatile mercury species. SO2 inhibited the Hg-0 oxidation by reducing the adsorbed HgO into gaseous Hg-0 or generating sulfate on the catalyst surface. Water vapor also played an inhibitive role in Hg-0 oxidation. However, the SO2 and H2O resistance of OMS-2 catalyst was much superior compared to other commercial catalysts, which makes it promising for industrial application. This knowledge is beneficial for developing economical and efficient Hg degrees oxidation catalysts for coal-fired power plants.