The critical role of methanol pressure in controlling its transfer dehydrogenation and the corresponding effect on propylene-to-ethylene ratio during methanol-to-hydrocarbons catalysis on H-ZSM-5

Arora, Sukaran S.; Bhan, Aditya

doi:10.1016/j.jcat.2017.10.014

Cited by 55 publications

(65 citation statements)

References 62 publications

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“…With increasing the fly ash usage, the selectivities to ethylene and propylene of the as-synthesized catalysts decreased, in contrast, the selectivities to C5+ products increased. In the recently proposed "dual cycle" mechanism to explain the formation of ethylene and propylene, propylene and ethylene could be generated by the aromatic-based cycle, whereas, propylene mainly produced by the olefin-based cycle [33,34]. In this work, the propylene to ethylene ratio of selected samples were Figure 7a for instance, the grey area indicates weak acid, the light orange area indicates medium strong acid, and the light olive area indicates strong acid.…”

Section: Catalytic Tests Of As-synthesized Zsm-5 Catalystsmentioning

confidence: 73%

Synthesis of ZSM-5 Zeolite Using Coal Fly Ash as an Additive for the Methanol to Propylene (MTP) Reaction

et al. 2019

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Using ZSM-5 zeolites as catalysts for the methanol to propylene (MTP) reaction is being widely investigated and has been industrially applied. In this study, pure ZSM-5 zeolite was successfully synthesized by a direct hydrothermal method using the fly ash of coal gasification as an additional raw material. Various analysis methods such as X-ray diffraction, N2 sorption, scanning electron microscopy, and infrared spectroscopy, were employed to characterize the physicochemical properties of parent and modified zeolites. Then, the prepared ZSM-5 catalysts were tested in the MTP reaction. The results showed that pure ZSM-5 could be directly synthesized in the optimized conditions using fly ash as additional silicon and aluminum sources, and those ZSM-5 catalysts turned out to be candidate catalysts for the MTP reaction. Whereas their catalytic lifetimes were not good enough due to the strong acid sites and needed improving.

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Section: Catalytic Tests Of As-synthesized Zsm-5 Catalystsmentioning

confidence: 73%

Synthesis of ZSM-5 Zeolite Using Coal Fly Ash as an Additive for the Methanol to Propylene (MTP) Reaction

et al. 2019

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“…Unlike hydrogen transfer, the Prins reaction has not attracted much attention until recently. Earlier reports have, however, noted the possibility of Prins type reaction for the formation of dienes and aromatics without experimental evidence 20,24 . Comparing the isotope distribution allows now unequivocally establishing the importance of the two routes.…”

Section: Resultsmentioning

confidence: 95%

“…Having shown how HCHO participates in the formation of the first olefin, we investigate next its participation in the dual-cycle mechanism. Because HCHO is H-poor, incorporation into products must increase the selectivity to aromatic molecules 20,24 , and in turn the selectivity to ethene, formed in the aromatic cycle 20 . As the formation of aromatic molecules has been associated to deactivation of the zeolite catalysts, we hypothesize that the higher concentration of HCHO in the reacting mixture leads to faster deactivation of the catalyst 20 .…”

Section: Resultsmentioning

confidence: 99%

“…Theoretical calculations 15–17 and dedicated experiments 15,17,18 showed possible pathways forming the first C–C bond and first olefin from HCHO in a subtle interplay with Brønsted acid and extra-framework Al sites. Experimental observations of strong deactivation in presence of HCHO 19,20 and of the O-containing surface species, were attributed to reaction products of HCHO, strongly adsorbed on the zeolite acid sites 21–23 . While always being present during MTO conversion at least in very low concentrations, it promotes the formation of non-olefinic byproducts 24,25 and accelerates deactivation 19–21,26,27 .…”

Section: Introductionmentioning

confidence: 99%

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Critical role of formaldehyde during methanol conversion to hydrocarbons

et al. 2019

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Formaldehyde is an important intermediate product in the catalytic conversion of methanol to olefins (MTO). Here we show that formaldehyde is present during MTO with an average concentration of ~0.2 C% across the ZSM-5 catalyst bed up to a MeOH conversion of 70%. It condenses with acetic acid or methyl acetate, the carbonylation product of MeOH and DME, into unsaturated carboxylate or carboxylic acid, which decarboxylates into the first olefin. By tracing its reaction pathways of 13 C-labeled formaldehyde, it is shown that formaldehyde reacts with alkenes via Prins reaction into dienes and finally to aromatics. Because its rate is one order of magnitude higher than that of hydrogen transfer between alkenes on ZSM-5, the Prins reaction is concluded to be the major reaction route from formaldehyde to produce dienes and aromatics. In consequence, formaldehyde increases the yield of ethene by enhancing the contribution of aromatic cycle.

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“…15,17,18 Figure S15 shows spectra measured from methyl acetate injected into HZSM-5 crystals at various temperatures, demonstrating the sensitivity of the technique to the presence of surface carboxylate species. We therefore believe that under the reaction conditions employed here, a mechanism for direct carbon−carbon bond formation involving formalde-hyde 14,15,41,42 or methyl acetate 17,18 is not occurring. Once alkenes are formed, they may escape the zeolite or oligomerize.…”

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confidence: 90%

Elementary Steps in the Formation of Hydrocarbons from Surface Methoxy Groups in HZSM-5 Seen by Synchrotron Infrared Microspectroscopy

et al. 2019

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Synchrotron infrared microspectroscopy has identified with high temporal resolution (down to 0.25 s) the initial events occurring when methanol vapor is in contact with a crystal of zeolite HZSM-5. The first alkenes are generated directly from methoxy groups formed at the acid sites via their deprotonation. These alkenes can either desorb directly or oligomerize and cyclize to form dimethylcyclopentenyl cations. The oligomeric and dimethylcyclopentenyl cations are the first major components of the hydrocarbon pool that precede aromatic hydrocarbons and lead to indirect alkene formation. The technique observes these events in real time.

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The critical role of methanol pressure in controlling its transfer dehydrogenation and the corresponding effect on propylene-to-ethylene ratio during methanol-to-hydrocarbons catalysis on H-ZSM-5

Cited by 55 publications

References 62 publications

Synthesis of ZSM-5 Zeolite Using Coal Fly Ash as an Additive for the Methanol to Propylene (MTP) Reaction

Synthesis of ZSM-5 Zeolite Using Coal Fly Ash as an Additive for the Methanol to Propylene (MTP) Reaction

Critical role of formaldehyde during methanol conversion to hydrocarbons

Elementary Steps in the Formation of Hydrocarbons from Surface Methoxy Groups in HZSM-5 Seen by Synchrotron Infrared Microspectroscopy

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