Illuminating the Intrinsic Effect of Water Co-feeding on Methane Dehydroaromatization: A Comprehensive Study

Abstract
Among all catalytic natural gas valorization processes, methane dehydroaromatization (MDA) still has a great potential to be utilized at an industrial level. Although the use of Mo/H-ZSM-5 as an MDA catalyst was first reported almost three decades ago, the process is yet to be industrialized, because of its inherent challenges. In order to improve the overall catalytic performance and lifetime, the co-feeding of water constitutes a promising option, because of its abundance and nontoxicity. Although water’s (limited) positive influence on catalyst lifetime has earlier been exhibited, the exact course of action (like mechanism or the water effect on active sites) is yet to be established. To bridge this knowledge gap, in this work, we have performed an in-depth investigation to elucidate the effects of water co-feeding over a well-dispersed Mo/H-ZSM-5 catalyst by using an array of advanced characterization techniques (nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry–temperature-programmed oxidation/mass spectroscopy (TG-TPO/MS), scanning transmission electron microscopy (STEM), N2 physisorption, Raman spectroscopy, inductively coupled plasma–optical emission spectroscopy (ICP-OES)). Our results demonstrate that the addition of water results in the occurrence of steam reforming (of both coke and methane) in parallel to MDA. Moreover, the presence of water affects the reducibility of Mo sites, as corroborated with computational analysis to examine the state and locality of Mo sites under various water levels and transformation of the catalyst structure during deactivation. We anticipate that our comprehensive study of the structure–function relationship on Mo/H-ZSM-5 under humid MDA conditions will be beneficial for the development of future methane valorization technologies.

Citation
Çaǧlayan, M., Paioni, A. L., Dereli, B., Shterk, G., Hita, I., Abou-Hamad, E., … Gascon, J. (2021). Illuminating the Intrinsic Effect of Water Co-feeding on Methane Dehydroaromatization: A Comprehensive Study. ACS Catalysis, 11671–11684. doi:10.1021/acscatal.1c02763

Acknowledgements
Funding for this work was provided by King Abdullah University of Science and Technology (KAUST). The authors wish to acknowledge and thank Sandra Ramirez Cherbuy for the illustration (Scheme 1). Also, we would like to thank Dr. Jullian Vittenet for his support in ICP-OES analyses. A.D.C. acknowledges the financial supports of the start-up research grant from the Institute for Advanced Studies (IAS), Wuhan University (China). M.B. and A.L.P. acknowledge the TOPPUNT (No. 718.015.001) and a Middelgroot program (No.700.58.102) grant supports from NWO.

Publisher
American Chemical Society (ACS)

Journal
ACS Catalysis

DOI
10.1021/acscatal.1c02763

Additional Links
https://pubs.acs.org/doi/10.1021/acscatal.1c02763

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