Utilization of carbon dioxide in oxidative dehydrogenation reactions

Abstract

Utilization of CO₂ as a feedstock for synthesis of chemicals is an alternate and most promising option for CO₂ abatement. In the present study, CO₂ has been utilized as a soft oxidant for oxidative dehydrogenation of ethylbenzene and <i style="mso-bidi-font-style: normal">n</i>-butane to the corresponding olefins. For this, TiO₂−ZrO₂ (TZ) mixed oxide-supported V₂O₅, CeO₂and V₂O₅–CeO₂catalysts has been synthesized, characterized and evaluated for the oxidative dehydrogenation reactions. The physicochemical characterization has been achieved by various techniques such as, powder X-ray diffraction, CO₂ and NH₃ temperature-preprogrammed desorption, temperature-preprogrammed reduction, X-ray photoelectron spectroscopy and BET surface area methods. XRD analysis of the samples calcined at 550 °C indicates that the impregnated active components are in a highly dispersed state on the support. XP spectra shows the existence of vanadium and cerium in V⁴⁺ and Ce⁴⁺/Ce³⁺ oxidation states, respectively. Among the various catalysts investigated, V₂O₅−CeO₂/TiO₂−ZrO₂ exhibits a high conversion and product selectivity for the oxidative dehydrogenation of ethyl benzene. On the other hand, a high conversion and selectivity in the oxidative dehydrogenation of <i style="mso-bidi-font-style: normal">n</i>-butane is noted over V₂O₅/SnO₂−ZrO₂ mixed oxide catalyst. The combined acid–base and redox properties of the catalysts play a major role in these reactions. In particular, the characterization studies reveal that mixed oxides show a high specific surface area, superior acid-base properties and better redox characteristics. All these properties enhance the catalytic performance of mixed oxide catalysts.