Supported MnOx on high surface area SiO2 (300 m(2)/g) catalysts were succes
sfully used in ethylbenzene oxidative dehydrogenation. X-ray diffraction an
d X-ray photoelectron spectroscopy were employed to characterize the struct
ure 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 chang
es in the crystalline structure and dispersion of supported MnOx were relat
ed to the precursor/support interaction and the conditions used during cata
lyst preparation. A possible mechanism for ethylbenzene conversion to styre
ne on MnOx/SiO2 catalysts is proposed, where lattice oxygen from crystallin
e MnO2 can be used in the oxidation or oxidative dehydrogenation processes.
The high selectivity in styrene (at 723 K, 24% conversion with 76% selecti
vity 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.