Porous ternary Fe-based catalysts for the oxidative dehydrogenation of ethylbenzene in the presence (absence) of carbon dioxide

Abstract

Porous ternary Fe-based catalysts were characterized and their catalytic properties through the oxidative dehydrogenation of ethylbenzene in the presence (ODH) or absence (DH) of carbon dioxide were investigated. The catalysts were characterized by X-ray diffraction (XRD), chemical analyses, thermoprogrammed reduction (TPR), physisorption measurements, Raman spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray spectrometry (SEM-EDX). The kinetic modeling of reverse water gas shift reaction (RWGS) and the effects of reaction parameters, such as reaction temperature and CO₂/H₂ ratio on the catalytic activity, were also investigated. The addition of Zn, La, Mg or Ni promoters to a porous Fe-based solid greatly enhanced the ODH reaction, whereas that of the RWGS is favoured by Ni promotion. The CO₂/H₂ = 1 ratio and temperature of 850 K were the best conditions for RWGS occurrence. The implications of these conditions on catalyst application for ODH and DH reactions were discussed. Ethylbenzene conversions were too low due to the decreased textural properties of some catalysts as well as the selectivity to styrene is inhibited. A porous FeAlZn catalyst exhibited higher catalytic performance than the other ternary solids in terms of the ethylbenzene dehydrogenation and resistance against deactivation, whereas low RGWS conversions were observed under the abovementioned conditions.