On the dynamic nature of Mo sites for methane dehydroaromatization

Abstract
The mechanism of methane activation on Mo/HZSM-5 is not yet fully understood, despite the great interest in methane dehydroaromatization (MDA) to replace aromatics production in oil refineries. It is difficult to assess the exact nature of the active site due to fast coking. By pre-carburizing Mo/HZSM-5 with carbon monoxide (CO), the MDA active site formation was isolated from coke formation. With this a clear C NMR signal solely from the active site and not obscured by coke was obtained, and it revealed two types of likely molecular Mo (oxy-)carbidic species in addition to the β-MoC nanoparticles often mentioned in the literature. Furthermore, separating the active site formation from coking by pre-carburization helped us examine how methane is activated on the catalytic site by carrying out MDA using isotopically labelled methane (CH). Carbon originating from the pre-formed carbide was incorporated into the main products of the reaction, ethylene and benzene, demonstrating the dynamic behavior of the (oxy-)carbidic active sites.

Citation
Vollmer I, van der Linden B, Ould-Chikh S, Aguilar-Tapia A, Yarulina I, et al. (2018) On the dynamic nature of Mo sites for methane dehydroaromatization. Chemical Science 9: 4801–4807. Available: http://dx.doi.org/10.1039/c8sc01263f.

Acknowledgements
We gratefully acknowledge the financial support from the Sabic- NWO CATC1CHEM CHIPP project. Thanks go to Dr Christoph Dittrich (SABIC), Dr Frank Mostert (SABIC) and Dr Xander Nijhuis (SABIC) as well as Prof. Emiel Hensen (TU Eindhoven) and Nikolay Kosinov (TU Eindhoven) for helpful discussion. We also acknowledge the BM26B DUBBLE beamline and the BM16 FAME-UHD beamline of the European Synchrotron Radiation Facility (ESRF), Grenoble, France for letting us use their facilities. Thanks also go to Maarten Gorseling (TU Delft) for performing GC-MS analysis. The FAME-UHD project is financially supported by the French "grand emprunt" EquipEx (EcoX, ANR- 10-EQPX-27-01), the CEA-CNRS CRG consortium and the INSU CNRS institute.

Publisher
Royal Society of Chemistry (RSC)

Journal
Chemical Science

DOI
10.1039/c8sc01263f

Additional Links
http://pubs.rsc.org/en/Content/ArticleLanding/2018/SC/C8SC01263F#!divAbstract

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