A new perspective on catalytic dehydrogenation of ethylbenzene: the influence of side-reactions on catalytic performance

Abstract

eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. Takedown AbstractThe dehydrogenation of ethylbenzene to styrene is a highly important industrial reaction and the focus of significant research in order to optimise the selectivity to styrene and minimise catalyst deactivation. The reaction itself is a complex network of parallel and consecutive processes including cracking, steam-reforming and reverse water-gas shift (RWGS) in addition to dehydrogenation. The goal of this investigation is to decouple the major processes occurring and analyse how side-reactions affect both the equilibrium of ethylbenzene dehydrogenation and the surface chemistry of steam reforming activity over the reduced catalyst; and reverse water-gas shift reaction. Each of these processes plays a critical role in the observed catalytic activity.Notably, the presence of CO 2 evolved from the reduction of chromium by ethylbenzene and from the gasification of the deposited oxygen-functionalised coke results in the dehydrogenation reaction becoming partially oxidative, i.e. selectivity to styrene is enhanced by coupling of ethylbenzene dehydrogenation with the reverse water-gas shift reaction. Ethylbenzene cracking, coke gasification, steam-reforming and reverse water-gas-shift determine the relative quantities of CO 2 , CO, H 2 and H 2 O and hence affect the coupling of the reactions. Coke deposition during the cracking period lowers the catalyst acidity and may contribute to chromium reduction, hence diminishing the competition between acid and metal sites and favouring dehydrogenation activity.

Catalytic cracking of ethylbenzene as tar surrogate using pyrolysis chars from wastes

“…Based on the literature data dealing with ethylbenzene pyrolysis and tar cracking reactions, a set of reactions expected to be involved in the ethylbenzene decomposition has been identified. The styrene can be generated by the cracking reaction (R1) and the oxidative dehydrogenation of ethylbenzene "ODH" (R2) [71,72]. The ethylbenzene cracking reactions could also produce a wide range of molecules, such as toluene, benzene, ethylene, carbon dioxide or coke [73,74].…”

Structural changes in FeOx/γ-Al2O3 catalysts during ethylbenzene dehydrogenation

“…8 Elsewhere, the formation of CO in the direct dehydrogenation of ethylbenzene over CrO x /Al 2 O 3 has been demonstrated and its role in catalyst performance discussed. 12 In the system Needle, or whisker, like alumina morphologies have previously been identified in catalytic and related systems. For example MoO 3 has been observed to promote the growth of γ-Al 2 O 3 whiskers at temperatures above 850 °C 32 ; while the formation of alumina needles has been observed on FeCrAl foils after oxidation at 950 °C.…”

“…1), a change in the oxidation state of Fe was detected, which will have been caused by the reducing environment; molecular hydrogen will be present during reaction as a result of dehydrogenation, cracking, and thermal decomposition of ethylbenzene. 12 Thus with no steam or any other inert gas present and without any structural promoter to stabilize the Fe 3+ oxidation state, reduction of the oxide took place, i.e. Fe 2 O 3 (haematite) was transformed to Fe 3 O 4 (magnetite), which is generally accepted as being an inactive phase, 19 according to the following reaction:…”

“…Ethylbenzene dehydrogenation is the main route commercially employed in the production of styrene (Scheme 1). 12,13 This reaction is equilibrium limited and strongly endothermic, and under industrial conditions is normally carried out in fixed bed units operating in adiabatic mode. In the present study, a fluidised bed reactor (CREC Fluidized Riser Simulator) has been used, this reactor operates isothermally.…”

Second Youth of a Metal-Free Dehydrogenation Catalyst: When γ-Al2O3 Meets Coke Under Oxygen- and Steam-Free Conditions

“…In this contribution, we describe the straightforward preparation of durable dehydrogenation systems based on “coked or pre-coked γ-Al 2 O 3 trilobs” for the highly efficient and selective EB DDH to ST under steam- and oxygen-free environments. Although “coked Al 2 O 3 and coked mixed metal-oxide” have already received a great deal of attention as catalysts ,− in alkane DDH and ODH and great efforts have also been devoted to the study of nature of coke deposits and their beneficial effects in catalysis, ,,,− much less work has been addressed to unveil the real potentialities of these systems for the EB DDH under non-oxidative and industrially relevant conditions. Earlier evidence of the active role played by “coked metal oxides” in alkane DDH were anticipated in a Monsanto patent where the inventors first forecasted the non-innocent action of carbonaceous deposits on the process as well as their paramagnetic nature due to the presence of unpaired electrons, likely involved in the dehydrogenation path.…”