Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

Çağlayan, Mustafa; Paioni, Alessandra Lucini; Abou‐Hamad, Edy; Shterk, Genrikh; Pustovarenko, Alexey; Baldus, Marc; Chowdhury, Abhishek Dutta; Gascón, Jorge

doi:10.1002/anie.202007283

Cited by 38 publications

(18 citation statements)

References 64 publications

(81 reference statements)

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“…They were not the only group analyzing carbene formation on transition metal-loaded zeolites with computational approaches; many others 471,485−487 also studied these metal−carbene complexes in MDA with similar computational techniques. The most recent solid findings regarding carbenes in MDA were reported by Çaglayan et al 173,307 During the investigations on initial periods of MDA reaction with postreacted Mo/ZSM-5 catalysts, they detected methylene-based rigid spin systems through 2D 13 C− 1 H MAS solid-state NMR (ca. 42−45 ppm 13 C, and ca.…”

Section: Presence Of Carbenes In Nonoxidative Methane Aromatization/c...mentioning

confidence: 92%

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Gong

Çağlayan

et al. 2022

Chem. Rev.

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Zeolite chemistry and catalysis are expected to play a decisive role in the next decade(s) to build a more decentralized renewable feedstock-dependent sustainable society owing to the increased scrutiny over carbon emissions. Therefore, the lack of fundamental and mechanistic understanding of these processes is a critical “technical bottleneck” that must be eliminated to maximize economic value and minimize waste. We have identified, considering this objective, that the chemistry related to the first-generation reaction intermediates (i.e., carbocations, radicals, carbenes, ketenes, and carbanions) in zeolite chemistry and catalysis is highly underdeveloped or undervalued compared to other catalysis streams (e.g., homogeneous catalysis). This limitation can often be attributed to the technological restrictions to detect such “short-lived and highly reactive” intermediates at the interface (gas–solid/solid–liquid); however, the recent rise of sophisticated spectroscopic/analytical techniques (including under in situ/operando conditions) and modern data analysis methods collectively compete to unravel the impact of these organic intermediates. This comprehensive review summarizes the state-of-the-art first-generation organic reaction intermediates in zeolite chemistry and catalysis and evaluates their existing challenges and future prospects, to contribute significantly to the “circular carbon economy” initiatives.

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Section: Presence Of Carbenes In Nonoxidative Methane Aromatization/c...mentioning

confidence: 92%

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Gong

Çağlayan

et al. 2022

Chem. Rev.

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“…The Mo-loaded ZSM-5 samples present lower BET surface area, micropore surface area and volume, (see Table 1 and isotherms in Figure S2 in the Supplementary Materials) and a lower amount of total Brønsted acid sites (see Table 2) as compared to the parent zeolite. This fact could be related to the partial blocking of the zeolite microporosity by the MoO 3 particles and to the migration of the Mo species into the channels during the calcination step, as previously described [46,54,60], a migration that has been directly related to the presence of Brønsted acid sites [50,54,58,59,62,63,74]. As expected, the metal incorporation procedure has an important influence on the textural and acidic properties of the final catalysts, and the higher the metal dispersion according to PXRD and FESEM, the larger the reduction of micropore surface and BAS density, in good agreement with previous publications [49,69].…”

Section: Characterization Resultsmentioning

confidence: 61%

“…Although not essential for dehydroaromatization, as evidenced by Hensen [63], the BAS also enhance the conversion of the intermediates formed on the Mo-species into the desired aromatics [59,64,65]. Recent studies propose the contribution of a hydrocarbon pool mechanism to the MDA reaction [46][47][48]66,67], similar to the one described for the methanol-to-hydrocarbon (MTH) process.…”

Section: Introductionmentioning

confidence: 97%

“…Regarding the reaction mechanism and the active sites involved, it is widely accepted that methane is first activated on the Mo sites and that the reaction intermediates formed will further oligomerize, cyclate and dehydrogenate on the Brønsted acid sites [34,[43][44][45][46][47][48][49]. In the last few decades, a large effort has been made trying to identify the active species, as well as their formation and how these are affected by the physical-chemical properties of the zeolite used as support [50][51][52][53][54][55][56].…”

Section: Introductionmentioning

confidence: 99%

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Influence of Preparation Conditions on the Catalytic Performance of Mo/H-ZSM-5 for Methane Dehydroaromatization

et al. 2021

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Methane, the main component of natural gas, is an interesting source of chemicals and clean liquid fuels, and a promising alternative raw material to oil. Among the possible direct routes for methane conversion, its aromatization under non-oxidative conditions has received increasing attention, despite the low conversions obtained due to thermodynamic limitations, because of its high selectivity to benzene. Mo/H-ZSM-5, the first bifunctional zeolite-catalyst proposed for this reaction, is still considered as one of the most adequate and has been widely studied. Although the mono- or bifunctional nature of the MDA mechanism is still under debate, it is generally accepted that the Mo species activate the C-H bond in methane, producing the intermediates. These will aromatize on the Brønsted acid sites of the zeolite, whose pore dimensions will provide the shape selectivity needed for converting methane into benzene. An additional role of the zeolite’s Brønsted acid sites is to promote the dispersion of the Mo oxide precursor. Here, we show the influence of the different preparation steps—metal incorporation, calcination and activation of the Mo/ZSM-5- on the metal dispersion and, therefore, on the activity and selectivity of the final catalyst. Metal dispersion is enhanced when the samples are calcined under dynamic conditions (DC) and activated in N2, and the benefits are larger when the metal has been incorporated by solid state reaction (SSR), as observed by FESEM-BSE and H2-TPR. This leads to catalysts with higher activity, increased aromatic selectivity and improved stability towards deactivation.

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“…The analysis of the gas product shows that ethene dominates the light hydrocarbons before 60 min of reaction time (Supporting Information, Table S2). Although the initial C−C bond formation in the MDA is still unclear, [55] the observation of the proximity between olefins and acidic protons provides direct evidence for the further dehydrocyclization of olefins to aromatics on BAS in close proximity to Mo sites. New cross peak between Brønsted acidic protons (4.0 ppm) and aromatics (8.1 ppm) appears at 30 min of reaction time (Figure 5 b), which is absent in the spectrum with short mixing time (50 ms; Supporting Information, Figure S8).…”

Section: Resultsmentioning

confidence: 99%

Dual Active Sites on Molybdenum/ZSM‐5 Catalyst for Methane Dehydroaromatization: Insights from Solid‐State NMR Spectroscopy

Gao

Wang

et al. 2021

Angewandte Chemie

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Methane dehydroaromatization (MDA) on Mo/ZSM‐5 zeolite catalyst is promising for direct transformation of natural gas. Understanding the nature of active sites on Mo/ZSM‐5 is a challenge for applications. Herein, using 1H{95Mo} double‐resonance solid‐state NMR spectroscopy, we identify proximate dual active sites on Mo/ZSM‐5 catalyst by direct observation of internuclear spatial interaction between Brønsted acid site and Mo species in zeolite channels. The acidic proton–Mo spatial interaction is correlated with methane conversion and aromatics formation in the MDA process, an important factor in determining the catalyst activity and lifetime. The evolution of olefins and aromatics in Mo/ZSM‐5 channels is monitored by detecting their host–guest interactions with both active Mo sites and Brønsted acid sites via 1H{95Mo} double‐resonance and two‐dimensional 1H–1H correlation NMR spectroscopy, revealing the intermediate role of olefins in hydrocarbon pool process during the MDA reaction.

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Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

Cited by 38 publications

References 64 publications

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Influence of Preparation Conditions on the Catalytic Performance of Mo/H-ZSM-5 for Methane Dehydroaromatization

Dual Active Sites on Molybdenum/ZSM‐5 Catalyst for Methane Dehydroaromatization: Insights from Solid‐State NMR Spectroscopy

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