Ethylbenzene dehydrogenation on Fe2O3-Cr2O3-K2CO3 catalysts promoted with transitional metal oxides

The effect of titanium, vanadium and cerium oxides on the activity and selectivity of Fe2O3-based catalysts for ethylbenzene (EB) dehydrogenation reaction has been examined in an integral fixed bed reactor. For all single- or double-promoted catalysts, the selectivity to styrene was higher than that for the unpromoted catalyst. For the V2O5-promoted catalyst, an optimum content of 3 wt.% was found with respect to the selectivity to styrene. Moreover, by promoting the standard catalyst with a combination of TiO2/CeO2 up to 6 wt.%, the activation energy decreased by 10 kJ/mol. The physicochemical properties of the promoted Fe2O3-Cr2O3-K2CO3 catalysts were examined using N-2 adsorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. All catalysts were macroporous, 65-75% of pores having a radius larger than 150 A. No diffraction patterns specific to TiO2 or V2O5 were observed. A CeO2 crystalline phase was present in the single promoted catalyst and in the double promoted with TiO2 as well. The average size of crystals was 48.6 nm for single and 21.4 nm for the double one. The XPS results confirmed the better dispersion of CeO2 in the presence of TiO2. Based on experimental data several kinetic models were proposed and kinetic parameters were estimated using a non-linear least squares optimization procedure. The Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model with surface reaction rate-determining step better described the experimental data. (c) 2005 Elsevier B.V. All rights reserved.