Catalytic Activity and Shape Selectivity of Methylation of Toluene over HZSM-5 Zeolite in an Integral Reactor.

隆夫, 増田; 浩敏, 溝田; 健治, 橋本

doi:10.1252/kakoronbunshu.20.170

Cited by 5 publications

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“…The activity and shape selectivity of zeolites are closely related to their acidic properties and diffusivities, which change with coke deposition (14)(15)(16)(17). Here, we will briefly explain how the shape selectivity is related to the above properties and will discuss about the change of it due to coke deposition.…”

Section: The Change Of Catalytic Properties Due To Coke Depositionmentioning

confidence: 99%

“…In this reaction, xylene isomers once produced inside the zeolite crystal diffuse to the outer surface of the crystal, and the shape selectivity is ascribed to the difference of the diffusivity among the isomers. Figure 4 shows typically the effect of the half of crystal size (L) on the relationship between methanol conversion and the selectivity toward para-xylene (17). The /c value represents the ratio of the acid amount outside crystal to that inside crystal.…”

Section: The Change Of Catalytic Properties Due To Coke Depositionmentioning

confidence: 99%

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Deactivation of Zeolite Catalysts by Coke

Masuda

Hashimoto

1996

ACS Symposium Series

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Zeolite catalysts are widely used in conversion processes of hydrocarbons, because of their high activity and shape selectivity. The conversion rate and the shape selectivity are closely related to intracrystalline diffusion rate and acidic properties of the zeolite catalyst. Carbonaceous materials called coke deposit on the catalyst during reactions, leading to changes in catalytic properties (diffusivity and acidic properties) as well as the reaction performance. This presentation reviews the mechanisms of the deactivation of zeolite catalysts caused by coke deposition from the following points of view. (1) Characterization of coke. Examination of the location of coke formation. (2) Relationship between the changes in acidic properties, and the acid strength and the acid amount. Prediction of the reduction of diffusion rate taking account of pore structure and molecular size. (3) Development of models for predicting the change in the activity and the shape selectivity.Zeolites are solid acid catalysts which are widely used in hydrocarbon processing, such as naphtha cracking, isomerization, dispropornation and alkylation. During reactions carbonaceous materials called coke deposit on the zeolite and reduces its activity and selectivity. Coke deposited not only covers the acid sites of the catalyst, but also blocks the pores, and restrain reactants from reaching the acid sites, leading to the decrease in the apparent reaction rate (1, 2). Here, we will mainly deal with the intracrystalline diffusivity of zeolites, and will discuss the relationship between it and the change in catalyst selectivity. THE PORE STRUCTURES OF ZEOLITES AND THE MODES OF COKE DEPOSITIONZeolites are composed of crystals of alumino silicate with the size of 0.1-5 micron. The pores of HY type zeolites consist of super cages and windows (0.74 nm). ZSM-

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Section: The Change Of Catalytic Properties Due To Coke Depositionmentioning

confidence: 99%

Section: The Change Of Catalytic Properties Due To Coke Depositionmentioning

confidence: 99%