Coke formation in zeolite ZSM-5

Bibby, D.M.

doi:10.1016/0021-9517(86)90020-5

Cited by 225 publications

(82 citation statements)

References 9 publications

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“…The proportion of internal coke was estimated from the decrease in micropore volume compared with the starting zeolite, assuming a coke density of 1.22 g cm À 3 . The amount of external coke was calculated from the difference between the total and internal coke content 55 .…”

Section: Discussionmentioning

confidence: 99%

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

et al. 2014

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Deactivation due to coking limits the lifetime of zeolite catalysts in the production of chemicals and fuels. Superior performance can be achieved through hierarchically structuring the zeolite porosity, yet no relation has been established between the mesopore architecture and the catalyst lifetime. Here we introduce a top-down demetallation strategy to locate mesopores in different regions of MFI-type crystals with identical bulk porous and acidic properties. In contrast, well-established bottom-up strategies as carbon templating and seed silanization fail to yield materials with matching characteristics. Advanced characterization tools capable of accurately discriminating the mesopore size, distribution and connectivity are applied to corroborate the concept of mesopore quality. Positron annihilation lifetime spectroscopy proves powerful to quantify the global connectivity of the intracrystalline pore network, which, as demonstrated in the conversions of methanol or of propanal to hydrocarbons, is closely linked to the lifetime of zeolite catalysts. The findings emphasize the need to aptly tailor hierarchical materials for maximal catalytic advantage.

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Section: Discussionmentioning

confidence: 99%

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

et al. 2014

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“…However, considering there is a rapid mass transportation process during the reaction, the precursors of the external cokes are certain to be pre-activated inside the zeolite cavity/channels. Moreover, external cokes account for a great portion in the total coke amount, as reported by Bibby et al [37]. They noticed that in a MTH reaction, the coke volume had exceeded the concomitant decrease in void volume; therefore, there must have been coke deposited over the external zeolite surfaces.…”

Section: Introductionmentioning

confidence: 77%

“…Bulky coke contents, once formed within and spread over the zeolite porous system, invariably lead to a reduction in the number of catalytically active sites, and often a dramatic concomitant decrease in zeolite cavity volume and available surface area. As a result, the reaction process is interrupted with the mass transportation of reactant and product generation undesirably blocked [2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

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Advances in the study of coke formation over zeolite catalysts in the methanol-to-hydrocarbon process

et al. 2016

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Methanol-to-hydrocarbon (MTH) process over acidic zeolite catalysts has been widely utilised to yield many types of hydrocarbons, some of which are eventually converted into the highly dehydrogenated (graphitized) carbonaceous species (cokes). The coking process can be divided into two parallel pathways based on the accepted hydrocarbon pool theory. From extensive investigations, it is reasonable to conclude that inner zeollite cavity/channel reactions at acidic sites generate cokes. However, coke formation and accumulation over the zeolite external surfaces play a major role in reaction deactivation as they contribute a great portion to the total coke amount. Herein we have reviewed previous literatures and included some recent works from KOPRC in understanding the nature and mechanism of coke formation, particularly during an H-ZSM-5 catalysed MTH reaction. We specially conclude that rapid aromatics formation at the zeolite crystalite edges is the main reason for later stage coke accumulation on the zeolite external surfaces. Accordingly, the catalyst deactivation is in a great certain to arise at those edge areas due to having the earliest contact with the incoming methanol reactant. The final coke structure is therefore built up with layers of poly-aromatics, as the potential sp 2 carbons leading to pre-graphite structure. We have proposed a coke formation model particularly for the acidic catalyst, which we believe will be of assistance in understanding-and hence minimising-the coke formation mechanisms.

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“…O 2 plasmas are also good oxidizers, and can be generated in situ using a radio-frequency generator. The partial removal of coke from zeolite catalysts at low temperatures was demonstrated in the 1980s using an oxygen plasma [65]. Recent advances in the technique have seen oxygen plasmas generated at atmospheric pressures, with the complete removal of coke from Pt-Sn/Al 2 O 3 catalysts and H-ZSM-5 catalysts at near room temperature [62,63].…”

Section: Gaseous Reactants To Remove Ligands and To Regenerate Sitesmentioning

confidence: 99%

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

et al. 2018

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Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given.

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Coke formation in zeolite ZSM-5

Cited by 225 publications

References 9 publications

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

Advances in the study of coke formation over zeolite catalysts in the methanol-to-hydrocarbon process

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

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