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Issue 4, 2016
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The enhancement of the catalytic performance of CrOx/Al2O3 catalysts for ethylbenzene dehydrogenation through tailored coke deposition

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Abstract

In previous work we have shown that ethylbenzene dehydrogenation over CrOx/Al2O3 catalysts proceeds sequentially via cracking and then dehydrogenation reactions. The present work reports how tailored coke deposition on the catalyst surface can suppress undesired reactions such as cracking to benzene and coke during ethylbenzene dehydrogenation. Additionally, this approach also provides insights into the precursor molecules involved in the formation of carbonaceous deposits, hence providing further understanding of coke formation. Pre-coked catalysts were prepared by adsorbing the products of the ethylbenzene reaction (i.e., benzene, toluene, styrene, ethylene) as single components, in a flowing system at 600 °C over the fresh catalyst. The resulting pre-coked catalysts were then evaluated in the ethylbenzene dehydrogenation reaction and their performance compared with that of the catalyst without exposure to pre-treatment. Characterisation of pre-coked catalysts by elemental analysis, temperature-programmed oxidation (TPO), temperature-programmed desorption (TPD), Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that ethylene is the main coke precursor during ethylbenzene dehydrogenation and that ethylene-derived coke is associated with a reduction in selectivity to styrene as compared to the fresh catalyst. Coke deposited after pre-coking with aromatic molecules, and in particular with benzene, was beneficial for dehydrogenation activity, as shown by the increase in styrene selectivity relative to the fresh catalyst. This enhancement of dehydrogenation activity was correlated with deactivation of acid sites and the reduction of chromium from Cr(VI) to Cr(III) (active species for dehydrogenation) as a result of the pre-coking procedure.

Graphical abstract: The enhancement of the catalytic performance of CrOx/Al2O3 catalysts for ethylbenzene dehydrogenation through tailored coke deposition

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Publication details

The article was received on 22 Jul 2015, accepted on 02 Sep 2015 and first published on 16 Sep 2015


Article type: Paper
DOI: 10.1039/C5CY01157D
Author version available: Download Author version (PDF)
Citation: Catal. Sci. Technol., 2016,6, 1120-1133
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    The enhancement of the catalytic performance of CrOx/Al2O3 catalysts for ethylbenzene dehydrogenation through tailored coke deposition

    S. Gomez Sanz, L. McMillan, J. McGregor, J. A. Zeitler, N. Al-Yassir, S. Al-Khattaf and L. F. Gladden, Catal. Sci. Technol., 2016, 6, 1120
    DOI: 10.1039/C5CY01157D

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