How does the balance of metal and acid functions on the benchmark Mo/ZSM-5 catalyst drive the Methane dehydroaromatization reaction?

Beuque, Antoine; Hu, Hao; Berrier, Élise; Sachse, Alexander; Paul, Jean‐François; Pinard, Ludovic

doi:10.1016/j.cattod.2022.06.001

Cited by 8 publications

(12 citation statements)

References 57 publications

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“…Both of these effects were reported in literature and can be attributed to the formation of bulk-like MoO 3 and Al extraction from the zeolite to form Al 2 (MoO 4 ) 3 phases, which were shown to preferably produce coke. 28,29 Furthermore, by normalizing the amount of benzene yield by the Mo loading, we observe a continuous decline of productivity at higher amounts of Mo. This can be explained by a decrease of Mo dispersion and stabilization by Al with increasing loading.…”

Section: Resultsmentioning

confidence: 66%

Accessibility of Reactants and Neighborhood of Mo Species during Methane Aromatization Uncovered by Operando NAP-XPS and MAS NMR

Peters,

Rieg,

Bartling

et al. 2023

ACS Catal.

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One-step nonoxidative methane dehydroaromatization is a facile process to generate aromatics and CO-free hydrogen. Despite their high activity and aromatics selectivity, Mo/HZSM-5 catalysts suffer from a continuous deactivation, hampering their application, yet the cause is intensively debated. Employing a combination of characterizations including, but not restricted to, high-resolution electron microscopy, operando NAP-XPS, and MAS NMR spectroscopy, we endeavored in this contribution to get deeper insight into the nature of active sites and origin of catalyst deactivation. Our results indicated (i) an irreversible reaction-induced MoO x particle sintering, (ii) reversible buildup/removal of coke species, (iii) no quantitative correlation between the deactivation rate and the presence/loss of Brønsted acid sites, and (iv) that coke accumulation occurs almost exclusively on Mo instead of Brønsted acid sites. Deactivation is explained by partial blocking of Mo species by coke, which diminishes the accessibility of methane to active sites and successive narrowing and/or blocking of pores hindering the diffusion of larger reaction products (e.g., naphthalene) to the outer surface. Active sites for aromatics formation are referred to as highly dispersed Mo species (mononuclear and tiny subnanometer oxy- and/or oxycarbidic Mo clusters) located inside the micropores on/or close to Brønsted sites.

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Section: Resultsmentioning

confidence: 66%

Accessibility of Reactants and Neighborhood of Mo Species during Methane Aromatization Uncovered by Operando NAP-XPS and MAS NMR

Peters,

Rieg,

Bartling

et al. 2023

ACS Catal.

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“…The occurrence of the 960-975 cm À1 band is ascribed to the existence of hydrated monomeric supported MoO x species, indicating the v(MoQO) stretching vibration. 33 These results indicate that molybdenum oxide is well associated with different Al sites within the MCM-22 zeolite modified with nano a-MoO 3 .…”

Section: Structural Analysismentioning

confidence: 74%

“…According to the results of EDS mapping, FT-IR and Raman spectroscopy, and NH 3 -TPD, the enhanced activity of the Mo(OA)-HMCM-22 catalyst is mainly attributed to there being more Mo species inside the channels of HMCM-22 associated with Brønsted acid sites, thus moderately reducing the density of acid centres and enhancing the overall accessibility of the acid centres. 33,42 The selectivity for different products is exhibited in Fig. 7c and Table 4.…”

Section: Mda Testingmentioning

confidence: 99%

Improving the methane aromatization activity and anti-carbon deposition on MCM-22 through nano α-MoO₃ modification

Hu¹,

Yang²,

Liu³

et al. 2023

New J. Chem.

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“…The dispersion of molybdenum in the carburized Mo/HZSM-5 material is critical for the preparation of active and stable catalyst. ,,,, The zeolites with low Si/Al ratio provide more anchoring sites, leading to a homogeneous dispersion of Mo, while a high silica content or high molybdenum loading results in the formation of MoO x clusters and weak linkage with the framework oxygen. ,,, The weak interaction between molybdenum and the support (zeolite) leads to molybdenum migration and aggregation during the pretreatment of the catalysts (high temperature) or during the MDA reaction. , In order to prepare well-dispersed metal containing catalysts, the balance between the molybdenum and the Si/Al ratio of the zeolite ( i.e. , Mo/Al molar ratio) must be considered carefully …”

Section: Methane Dehydroaromatization (Mda)mentioning

confidence: 99%

“…151,222 In order to prepare welldispersed metal containing catalysts, the balance between the molybdenum and the Si/Al ratio of the zeolite (i.e., Mo/Al molar ratio) must be considered carefully. 223 Recent reviews emphasize two disadvantages restricting the industrial development of the nonoxidative transformation of methane. 8,12,18,224 First, the MDA reaction is thermodynamically limited with a maximum of benzene conversion of 12.5% at 700 °C; thus the Mo/HZSM-5 catalysts shows low activity.…”

Section: Acs Catalysis Pubsacsorg/acscatalysismentioning

confidence: 99%

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

et al. 2022

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Natural gas, the cleanest fossil fuel, is an abundant source of methane and expected to play an increasingly important role in powering the world’s economic growth over the energy transition of the coming decades. Methane has the potential to be a CO2-free feedstock to cogenerate hydrogen (H2) and added value “building-blocks” chemicals (e.g., olefins and aromatics) for petrochemistry. In this review, the two processes (i) the oxidative coupling of methane (OCM) for production of ethylene and (ii) the nonoxidative methane dehydroaromatization (MDA) producing hydrogen and benzene are discussed. Both routes convert methane directly into valuable products, an advantage over the several-steps syngas route. The performances of various a variety of catalysts reported during the last 25 years for OCM (MnNaW, La2O3, Li-MgO, etc.) and MDA (M/HZSM-5, M/TNU-9, M/IM-5, M/ITQ-2, M@SiO2, M@CeO2, TaH/SiO2, GaN/SBA15, single-site M@HZSM-5, bimetallic M-M′/HZSM-5, core–shell structures, M/Zr(SO4)2 with M = Mo, Fe, Pt) under similar reaction conditions are compared. The major drawbacks and the strategies used to mitigate the main challenges related with the performance of the catalysts in both OCM and MDA reactions are critically revealed. For instance, the overoxidation in the OCM is mitigated by optimizing of the operating conditions, using alternative oxidants, and the application of membrane reactor technology are discussed. In the MDA reaction, the major issue is the catalyst deactivation by coke formation and migration and sintering of metallic active phases. Strategies for robust catalysts, methods for mild coke removal, pretreatment under reductive atmosphere are presented. Approaches to improve aromatics yields over coke production by addition of promoters or co-feed reactants to the MDA catalysts are also discussed.

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How does the balance of metal and acid functions on the benchmark Mo/ZSM-5 catalyst drive the Methane dehydroaromatization reaction?

Cited by 8 publications

References 57 publications

Accessibility of Reactants and Neighborhood of Mo Species during Methane Aromatization Uncovered by Operando NAP-XPS and MAS NMR

Accessibility of Reactants and Neighborhood of Mo Species during Methane Aromatization Uncovered by Operando NAP-XPS and MAS NMR

Improving the methane aromatization activity and anti-carbon deposition on MCM-22 through nano α-MoO₃ modification

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

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How does the balance of metal and acid functions on the benchmark Mo/ZSM-5 catalyst drive the Methane dehydroaromatization reaction?

Cited by 8 publications

References 57 publications

Accessibility of Reactants and Neighborhood of Mo Species during Methane Aromatization Uncovered by Operando NAP-XPS and MAS NMR

Accessibility of Reactants and Neighborhood of Mo Species during Methane Aromatization Uncovered by Operando NAP-XPS and MAS NMR

Improving the methane aromatization activity and anti-carbon deposition on MCM-22 through nano α-MoO3 modification

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

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Improving the methane aromatization activity and anti-carbon deposition on MCM-22 through nano α-MoO₃ modification