Effects of coke formation on the acidity of ZSM-5

Mclellan, G.D.; Howe, Russell F.; Parker, L.M.; Bibby, D.M.

doi:10.1016/0021-9517(86)90373-8

Cited by 55 publications

(14 citation statements)

References 6 publications

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“…Looking first at the total coke content, this appears to increase linearly with time on stream until methanol breakthrough, after which a levelling off in the rate of coke accumulation is seen. Similar observations have been made by McLellan et al [79]. This can be explained if the rate of deactivation is assumed to be proportional to the degree of methanol conversion, as suggested by Janssens [20] (see section 4.5 below).…”

Section: Zsm-22supporting

confidence: 76%

A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

et al. 2017

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Catalyst deactivation during the methanol-to-hydrocarbons (MTH) reaction was investigated using five different commercially prepared microporous catalysts, including Mordenite, ZSM-22, ZSM-5, zeolite Beta and SAPO-34. The reaction was carried out in a fixed bed reactor at a constant feed rate per gram of catalyst. Deactivated and partially deactivated catalysts were obtained at increasing reaction times. The whole of the catalyst beds were characterized using nitrogen adsorption, thermogravimetric analysis, a dissolution-extraction protocol, and UV-Raman spectroscopy, focusing primarily on methods suitable for the quantification of the coke. The results illustrate that topology is the dominant parameter that influences not only catalyst lifetime and product distribution, but also the nature of the species causing the deactivation. For all catalyst topologies, when the entire catalyst bed is examined together, the micropore volume and BET surface area decrease more rapidly than total coke from TGA increases at short reaction times. In the materials with the more restricted access to the internal voids, such as ZSM-22 and SAPO-34, the loss of activity is to a large extent due to species which are soluble in dichloromethane and give rise to distinct features in the Raman spectra. For the Mordenite and Beta catalysts, which have larger pores comprising three dimensional networks, and to some extent for the ZSM-5 catalyst employed, the accumulation of more coke species which are insoluble in dichloromethane, presumably on the external surface of the zeolite crystals, is observed. This is linked to the appearance of more pronounced D and G bands in the Raman spectra, indicative of extended carbon species.

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Section: Zsm-22supporting

confidence: 76%

A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

et al. 2017

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“…With increasing acidity and higher reaction temperatures, the formation of larger aromatic compounds is evident. [13,[34][35][36] However, the absorption bands formed above 600 nm cannot be assigned to even more extended aromatic compounds occluded within the microporous network of H-ZSM-5 because the size of the carbonaceous compounds would go beyond the size that is topographically allowed by the H-ZSM-5 crystal structure. Under these reac- tion conditions, the fast formation of large coke species might induce pore blocking.…”

Section: Samplementioning

confidence: 99%

“…Here, the formation of larger coke species slows down, pore blockages diminish, and a change in the cokeformation pattern becomes evident. [27,34,35,38] Extensive studies indicated that the crystal framework that surrounds the HCP active species influences the fundamental reaction kinetics of the conversion. Here, crucial parameters such as framework topology and composition are strongly combined with the size, shape, and orientation of the hydrocarbons formed.…”

Section: Samplementioning

confidence: 99%

Coke Formation during the Methanol‐to‐Olefin Conversion: In Situ Microspectroscopy on Individual H‐ZSM‐5 Crystals with Different Brønsted Acidity

Kornatowski

Olsbye

et al. 2011

Chemistry A European J

255

228

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Coke formation during the methanol-to-olefin (MTO) conversion has been studied at the single-particle level with in situ UV/Vis and confocal fluorescence microscopy. For this purpose, large H-ZSM-5 crystals differing in their Si/Al molar ratio have been investigated. During MTO, performed at 623 and 773 K, three major UV/Vis bands assigned to different carbonaceous deposits and their precursors are observed. The absorption at 420 nm, assigned to methyl-substituted aromatic compounds, initiates the buildup of the optically active coke species. With time-on-stream, these carbonaceous compounds expand in size, resulting in the gradual development of a second absorption band at around 500 nm. An additional broad absorption band in the 600 nm region indicates the enhanced formation of extended carbonaceous compounds that form as the reaction temperature is raised. Overall, the rate of coke formation decreases with decreasing aluminum content. Analysis of the reaction kinetics indicates that an increased Brønsted acid site density facilitates the formation of larger coke species and enhances their formation rate. The use of multiple excitation wavelengths in confocal fluorescence microscopy enables the localization of coke compounds with different molecular dimensions in an individual H-ZSM-5 crystal. It demonstrates that small coke species evenly spread throughout the entire H-ZSM-5 crystal, whereas extended coke deposits primarily form near the crystal edges and surfaces. Polarization-dependent UV/Vis spectroscopy measurements illustrate that extended coke species are predominantly formed in the straight channels of H-ZSM-5. In addition, at higher temperatures, fast deactivation leads to the formation of large aromatic compounds within channel intersections and at the external zeolite surface, where the lack of spatial restrictions allows the formation of graphite-like coke.

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“…This also has effects on activity and product selectivity of the catalysts. As expected, the formed coke in the aromatization processes to be considered have been studied a lot in the area of effect of acidity on activity as well as deactivation [70,71]. As stated previously, the distribution of Al ions in ZSM-5 catalysts, which determines the number and strength of acid sites, controls the catalysts activity in various reactions [72].…”

Section: Acidity Of Catalystmentioning

confidence: 77%

An overview on the effects of metal promoters and acidity of ZSM-5 in performance of the aromatization of liquid hydrocarbons

Sharifi¹,

Halladj

Royaee³

2020

Reviews on Advanced Materials Science

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AbstractThe use of liquid hydrocarbons, such as FCC naphtha, having olefin components makes an adverse impact on our environment. To deal with the problem, one could convert those lethal components, including olefin and paraffin structures, into aromatic compounds under aromatization processes. To this aim, generally zeolite catalysts, especially the ZSM-5 sample, are utilized to facilitate the aromatization processes. According to the general knowledge in this field, such parameters as the metal promoter and the amount of acidity of catalyst affect the performance of zeolite catalysts. In this paper, with the aim of getting acquainted with the conditions to form the desirable products under the best performance of the zeolites, numerous published papers were reviewed.

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Effects of coke formation on the acidity of ZSM-5

Cited by 55 publications

References 6 publications

A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

Coke Formation during the Methanol‐to‐Olefin Conversion: In Situ Microspectroscopy on Individual H‐ZSM‐5 Crystals with Different Brønsted Acidity

An overview on the effects of metal promoters and acidity of ZSM-5 in performance of the aromatization of liquid hydrocarbons

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