Comparing alkene-mediated and formaldehyde-mediated diene formation routes in methanol-to-olefins catalysis in MFI and CHA

Kilburn, Lauren; DeLuca, Mykela; Hoffman, Alexander J.; Patel, Saumya; Hibbitts, David

doi:10.1016/j.jcat.2021.05.010

Cited by 17 publications

(34 citation statements)

References 99 publications

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“…6,7,13,16−24 HT pathways involving methanol disproportionation and its reactions with alkenes are inferred as the main sources of formaldehyde in the MTH transformation. 13,15,21,25,26 They are catalyzed by Brønsted acid sites (BAS), while HT from methanol to alkenes can be additionally promoted by aluminum-based Lewis acid sites (LAS). 13,15 However, the observation of formaldehyde along with carbon monoxide (CO) and hydrogen (H 2 ) upon passing methanol feed over BAS-free materials, such as silicalite, Na-ZSM-5, quartz, and silicon carbide, indicated that alternative pathways can also contribute to aldehyde production.…”

Section: Introductionmentioning

confidence: 99%

“…13,15,21,25,26 They are catalyzed by Brønsted acid sites (BAS), while HT from methanol to alkenes can be additionally promoted by aluminum-based Lewis acid sites (LAS). 13,15 However, the observation of formaldehyde along with carbon monoxide (CO) and hydrogen (H 2 ) upon passing methanol feed over BAS-free materials, such as silicalite, Na-ZSM-5, quartz, and silicon carbide, indicated that alternative pathways can also contribute to aldehyde production. 19,25 It was thereby speculated that structural defects in these materials can catalyze methanol disproportion or dehydrogenation.…”

Section: Introductionmentioning

confidence: 99%

“…It is widely accepted that PAHs grow through overalkylation and condensation of the arene HP species. , These processes proceed primarily via HT, comprising protonation and subsequent hydride transfer. ,− In the latter bimolecular step, hydride is transferred to surface-activated alkyl or carbenium ions from an aliphatic hydrocarbon or methanol. The hydride acceptors are thus transformed to more saturated (cyclo)alkanes, and the hydride donors, that is, unsaturated hydrocarbons and methanol, are converted to polyenes and formaldehyde, respectively .…”

Section: Introductionmentioning

confidence: 99%

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Impact of Nonzeolite-Catalyzed Formation of Formaldehyde on the Methanol-to-Hydrocarbons Conversion

et al. 2022

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Formaldehyde is an important intermediate that affects the catalyst performance in the methanol-to-hydrocarbons (MTH) conversion. In this study, photoelectron photoion coincidence spectroscopy was applied to elucidate the formation of this species in empty quartz and stainless steel reactors as well as over zeolite catalysts (ZSM-5 and BETA) and commonly used bed diluents (silicon carbide and quartz). The yields of formaldehyde in an empty stainless steel reactor and over the crude silicon carbide particles were found to be higher or comparable to those over the zeolite catalysts under similar reaction conditions. In the former two systems, formaldehyde is formed via methanol dehydrogenation, which is catalyzed by transition metals and yields hydrogen and carbon monoxide as the main byproducts. Thus produced formaldehyde is readily consumed in the MTH reaction, wherein its conversion is higher for the more acidic zeolites. The formaldehyde generated by the transition metal sites causes a decrease of the catalyst stability as well as a reduction of the propene-to-ethene ratio, as corroborated by catalytic tests exploring different contacting patterns between the ZSM-5 catalyst and stainless steel chips or silicon carbide particles. These results uncover an important role of methanol dehydrogenation in the MTH conversion, which is relevant for the laboratory testing of the zeolite catalysts and the industrial implementation of this technology.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impact of Nonzeolite-Catalyzed Formation of Formaldehyde on the Methanol-to-Hydrocarbons Conversion

et al. 2022

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“…Meanwhile, many studies have shown that formaldehyde was a key intermediate to form the early (or the first) ethene or propene in the induction period of MTO. , In addition, it was found that formaldehyde generated from methanol dehydrogenation could also react with propene and butene, viz., through the Prins reaction, forming dienes, such as butadiene and pentadiene. − Inspired by these observations, we propose that MCHs with a six-membered ring skeleton can be constructed through the (4 + 2) cycloaddition between an electron-rich conjugated diene like 1,3-butadiene and an electron-poor dienophile like propene; this is a typical Diels–Alder (D–A) reaction. , …”

Section: Resultsmentioning

confidence: 98%

“…In this regard, the possible routes for the construction of dienes, such as 1,3-butadiene and pentadiene, should then be clarified. Several recent studies were cognizant of the presence of formaldehyde in the reaction mixture of MTO in the induction stage, which could react with the early propene or butene to form 1,3-butadiene or pentadienes via the Prins reaction. − …”

Section: Resultsmentioning

confidence: 99%

Formation and Evolution of Methylcyclohexene in the Initial Period of Methanol to Olefins over H-ZSM-5

Fan

Wang

et al. 2022

ACS Catal.

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Identification of the reaction intermediates and probing into their evolution in the conversion of methanol to light olefins (MTO) are rather challenging but meaningful in unraveling the hydrocarbon pool (HCP) mechanism as well as in exploring more efficient catalysts in MTO. Hence, we would like to report a finding made in this regard that methylcyclohexene (MCH) is a crucial reaction intermediate in the initial period of MTO over H-ZSM-5 through various measures, including transient pulse experiment, 13C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR), gas chromatography–mass spectrometry (GC–MS), and density-functional theory (DFT) calculation. The early alkenes (mostly ethene and propene) produced in the induction stage can rapidly construct the long-chain alkenes through oligomerization and create dienes through the Prins reaction with formaldehyde from methanol dehydrogenation. After that, MCH is facilely formed via the Diels–Alder (D–A) reaction between dienes and monoenes. Compared with the oligomerization and cyclization of alkenes, the D–A reaction shows higher activity with a lower energy barrier in building larger molecule products. MCH is highly reactive and can be quickly transformed either into methylcyclopentene (MCP) via ring contraction or into methylbenzene (MB) via hydride transfer and deprotonations; the formation of MCP may take the priority over that of MB at a low temperature, as the former reaction needs a lower energy barrier. Accordingly, MCH acts as a bridge connecting MCP and MB and plays a vital role in the establishment of initial HCP in MTO. These findings should be helpful for an in-depth understanding of the MTO reaction mechanism and then benefit further research into MTO.

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Methanol to hydrocarbons conversion: Why dienes and monoenes contribute differently to catalyst deactivation?

Shi

Arora²,

Trahan³

et al. 2022

Chemical Engineering Journal

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Comparing alkene-mediated and formaldehyde-mediated diene formation routes in methanol-to-olefins catalysis in MFI and CHA

Cited by 17 publications

References 99 publications

Impact of Nonzeolite-Catalyzed Formation of Formaldehyde on the Methanol-to-Hydrocarbons Conversion

Impact of Nonzeolite-Catalyzed Formation of Formaldehyde on the Methanol-to-Hydrocarbons Conversion

Formation and Evolution of Methylcyclohexene in the Initial Period of Methanol to Olefins over H-ZSM-5

Methanol to hydrocarbons conversion: Why dienes and monoenes contribute differently to catalyst deactivation?

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