Bimetallic Mo-Co/ZSM-5 and Mo-Ni/ZSM-5 catalysts for methane dehydroaromatization: A study of the effect of pretreatment and metal loadings on the catalytic behavior

• Published in: Applied catalysis. A, General Vol. 589; no. C; p. 117247
• Main Authors: Sridhar, Apoorva, Rahman, Mustafizur, Infantes-Molina, Antonia, Wylie, Benjamin J., Borcik, Collin G., Khatib, Sheima J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05-01-2020; Elsevier Science SA; Elsevier
• Subjects: 6 wt% Mo/HZSM-5; Additives; Aluminum; Benzene; Bimetals; Carburization (corrosion); Carburizing; Catalysts; Co-modified Mo catalysts; Methane; Methane dehydroaromatization; Molybdenum; Nickel; NMR; Nuclear magnetic resonance; Pretreatment; Reduction; Regeneration; Stability; Thermogravimetric analysis; Zeolites; Regeneration; Methane dehydroaromatization; 6 wt% Mo/HZSM-5; Benzene; Co-modified Mo catalysts
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2019.117247

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•ZSM5-supported Mo carbide catalysts modified with Co and Ni additives were more stable in methane dehydroaromatization.•A synergy is established between Mo and each additive, with increased benzene yield compared to an unmodified Mo catalyst.•Each additive presents an optimum loading for 6wt% Mo, resulting in the most stable catalyst (0.6 wt% Co and 0.2 wt% Ni).•The effect of the additives is only beneficial when the Mo carbide species are formed ex situ via previous carburization.•The additives interact with the Mo, decreasing its mobility and changing its reducibility.
Methane dehydroaromatization is studied using different loadings (0.2 wt%, 0.6 and 1 wt%) of Co and Ni additives on a 6 wt% Mo/ZSM-5 catalyst to evaluate the promoting effect of Ni and Co on reactivity and stability of the catalysts. A synergy between Mo and the additives is observed when combining a reduction/carburization pretreatment with an optimum additive loading: benzene yield and catalytic stability are both improved. The fresh and spent samples were characterized by X-Ray Diffraction, 27Al Magic-Angle Spinning Solid State Nuclear Magnetic Resonance Spectroscopy, Temperature-Programmed Reduction and Thermogravimetric Analysis. The results suggest that catalytic enhancement in precarburized Mo-Co and Mo-Ni samples is due to a combination of effects: extraction of Al from the ZSM-5 framework to form inactive Al2(MoO4)3 is reduced, interaction of Mo with the additives enhances the retention of Mo species within the zeolite channels, prevents Mo aggregation in reaction and modifies the reducibility of the Mo sites.