Supported MnOx on high surface area SiO2 (300 m(2)/g) catalysts were successfully used in ethylbenzene oxidative dehydrogenation. X-ray diffraction and X-ray photoelectron spectroscopy were employed to characterize the structure of fresh and used MnOx/SiO2 catalysts. The MnOx catalysts were prepared using the pore volume impregnation method, with MnO2 loading varying from 0.7 wt % (Mn/Si = 0.005, atomic ratio) to 30 wt % (Mn/Si = 0.14). The changes in the crystalline structure and dispersion of supported MnOx were related to the precursor/support interaction and the conditions used during catalyst preparation. A possible mechanism for ethylbenzene conversion to styrene on MnOx/SiO2 catalysts is proposed, where lattice oxygen from crystalline MnO2 can be used in the oxidation or oxidative dehydrogenation processes. The high selectivity in styrene (at 723 K, 24% conversion with 76% selectivity in styrene) was related to the high concentration in the MaO(2) phase from the MnOx/SiO2 catalysts. The formation of the Mn3O4 phase, observed on the used catalysts, supports the proposed mechanism. These findings are of potential use for industrial applications, particularly in optimization of various oxidative dehydrogenation processes.