Ethylbenzene dehydrogenation on Fe 2O 3-Cr 2O 3-K 2CO 3 catalysts promoted with transitional metal oxides

Abstract

The effect of titanium, vanadium and cerium oxides on the activity and selectivity of Fe 2O 3-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 V 2O 5-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 TiO 2/CeO 2 up to 6 wt.%, the activation energy decreased by 10 kJ/mol. The physicochemical properties of the promoted Fe 2O 3-Cr 2O 3-K 2CO 3 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 Å. No diffraction patterns specific to TiO 2 or V 2O 5 were observed. A CeO 2 crystalline phase was present in the single promoted catalyst and in the double promoted with TiO 2 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 CeO 2 in the presence of TiO 2. 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.