A Simple Method for Determining the Relative Significance of the Unimolecular and Bimolecular Pathways of Xylene Isomerization over HY Zeolites

Morin, S.; Gnep, N.S.; Guisnet, M.

doi:10.1006/jcat.1996.0091

Cited by 69 publications

(42 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A critical evaluation of published data [153] reveals that criterion (i) is useful for a discrimination between 10-and 12-membered ring zeolites, while it does not allow the ranking of zeolites with respect to their pore width in the individual classes of medium-and large-pore materials. Moreover, it has been repeatedly found that the para/ortho selectivity does not only depend on the pore width of a given structure, but also (especially for large pore zeolites) on its nsJnAJ ratio [171][172][173][174]. However, there seems to be valuable information on the pore architecture in the distribution of the trimethylbenzenes formed from meta-xylene in large-pore zeolites, as has been pointed out by Martens et al [163].…”

Section: Isomerization and Disproportionation Of Meta-xylenementioning

confidence: 89%

Shape-Selective Catalysis in Zeolites

Weitkamp

Puppe

1999

Catalysis and Zeolites

118

129

View full text Add to dashboard Cite

ScopeAmong the primary tasks of catalysis is the control of the selectivity in chemical reactions. In heterogeneously catalyzed reactions in zeolites and zeolite-related microporous solids, this can, inter alia, be achieved by exploiting the phenomenon of shape-selective catalysis. In a very simplified manner, shape-selective catalysis can be described as the combination of catalysis with the molecular sieve effect. Shape selectivity effects can occur, if the sizes and shapes of reactants, of products, of transition states or of reaction intermediates are similar to the dimensions of the pores and cavities of the zeolite.The first examples of shape-selective catalysis in zeolites were reported more than 35 years ago by Weisz and Frilette from the Mobil laboratories [1,2]. Since those days, research in the field of shape-selective catalysis has expanded both at universities and in industrial laboratories in an impressive manner. This has resulted in numerous examples of shape selectivity effects in the course of catalytic conversions over zeoli tic catalysts, which are nowadays no longer restricted to acid-catalyzed reactions as described in the early days. Rather, there are also examples for shape-selective catalysis on metals, on redox active sites, on basic guests in zeolites, and even for shape-selective photochemistry in a zeoli tic environment. Moreover, from the intensive research done in the field of shapeselective catalysis during the last decades, several large-scale commercial applications in the refining and the petrochemical industries have emerged, demonstrating the usefulness and importance of the phenomenon of shape-selective catalysis.In the past, numerous review papers on shape-selective catalysis, its principles and its commercial applications have been published [e. g., 3 -19]. In view of the vast amount of work that has been done in this field in recent years, it is obvious that a review on shape-selective catalysis cannot be exhaustive. Rather, the discussion has to be restricted to selected topics. In the present contribution, emphasis will be placed on a thorough discussion of the classical and of more recent principles of shape-selective catalysis and on how these principles can be used to rationalize the observed catalytic behavior in selected examples. In addition, it is the aim of the present contribution to discuss the available methods for tailoring the shape-selective properties of zeolite catalysts and for their characterization by catalytic methods. Finally, an attempt will be under-

show abstract

Section: Isomerization and Disproportionation Of Meta-xylenementioning

confidence: 89%

Shape-Selective Catalysis in Zeolites

Weitkamp

Puppe

1999

Catalysis and Zeolites

118

129

View full text Add to dashboard Cite

show abstract

“…Xylene isomerization occurs according to an acidic monofunctional mechanism, mono-or bimolecular depending on the porous characteristics of the acidic phase [2,[5][6][7]. Concerning ethylbenzene, the choice of catalyst depends on the target reaction.…”

Section: Location Through the Use Of Special Organic Templates Anothmentioning

confidence: 99%

How to Improve the Selectivity of Zeolitic Catalysts in C₈Aromatic Cut Isomerization

Guillon

Lacombe

Sozinho

et al. 2009

Oil & Gas Science and Technology - Rev. IFP

Self Cite

View full text Add to dashboard Cite

Résumé -Comment améliorer la sélectivité des catalyseurs zéolithiques en isomérisation de la coupe C 8 aromatique-Les catalyseurs utilisés dans les procédés d'isomérisation de la coupe C 8 aromatique (xylènes et éthylbenzène) sont généralement à base de platine supporté sur un support mixte liant/zéolithe. L'amélioration de ces catalyseurs consiste à augmenter la conversion de l'éthylbenzène, étape la plus difficile de cette transformation, en minimisant les réactions parasites secondaires telles que la dismutation et la désalkylation de l'éthylbenzène, l'ouverture de cycles naphténiques et le craquage consécutif des paraffines résultantes. Parmi les différentes approches qui ont été menées, la majorité concerne l'optimisation de la phase zéolithique. Sur les catalyseurs conventionnels à base de zéolithe mordénite, le gain en sélectivité reste limité et il semble donc plus judicieux d'explorer de nouvelles structures zéolithiques. Dans ce cadre, des résultats intéressants ont été obtenus sur des catalyseurs à base de zéolithe EU-1, qui présente la particularité de se sélectiver lors de la mise en régime et de travailler en bouche de pore après stabilisation. Ce concept de catalyse en bouche de pore a pu être étendu à d'autres structures zéolithiques monodimensionnelles à taille de pore intermédiaire, telles que la ZSM-22 ou la ferriérite. Par ailleurs, la sélectivité de la zéolithe EU-1 peut être optimisée en jouant sur la localisation des sites acides par utilisation de structurants organiques particuliers. Une autre approche a consisté à s'intéresser à l'ensemble du catalyseur (phases zéolithique et métallique, éventuellement associées à un support aluminique acide de type alumine chlorée), et à identifier les sites responsables des réactions de formation de paraffines. Les résultats montrent que le craquage des paraffines suit majoritairement un mécanisme bifonctionnel et, dans une moindre mesure, un mécanisme par hydrogénolyse, suggérant que la voie la plus prometteuse pour diminuer les pertes en paraffines est d'agir, en premier lieu, sur la zéolithe. Abstract -How to Improve the Selectivity of Zeolitic Catalysts in C 8 Aromatic Cut Isomerization

show abstract

“…Moreover, it can be noticed that conversion passes through a maximum for all the reaction times studied, with an initial increase below 0.11 mmol/g, however it decreases subsequently. The initial increase in conversion with acidity can be explained easily, since transformation of m-xylene over Y-zeolite is enhanced with total acidity [1][2][3].…”

Section: Products Distributionmentioning

confidence: 99%

“…A convenient way to upgrade the low-valued m-xylene consists of its transformation to o-and p-xylene. In this context, the transformation of m-xylene has been studied over different types of zeolite catalysts [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The effect of Y-zeolite acidity on m-xylene transformation reactions

Al-Khattaf¹,

Iliyas²,

Al-Amer³

et al. 2005

Journal of Molecular Catalysis A: Chemical

View full text Add to dashboard Cite

m-Xylene transformation has been studied on as-prepared H-Y and a series of dealuminated Y zeolite catalysts. The conversion of m-xylene was found to increase initially with acidity, however, decreases subsequently. It has been proposed that the high concentration of acid sites in the H-Y catalyst increases paring reaction, in addition to the well-known isomerization and disproportionation pathways. A significant decrease was observed with respect to disproportionation/paring (D/Pa) ratio versus reaction temperature. This indicates that higher activation energy is required for paring as compared to disproportionation reaction. The p-xylene/o-xylene (P/O) was established to be independent of zeolite acidity. A higher coke deposition was found for the transformation of m-xylene over the parent H-Y as compared to the highly dealuminated USY zeolite. The formation of benzene and C 2 -C 4 gases were found to be proportional to zeolite acid concentration.Keywords: m-Xylene transformation, Y zeolite, isomerization, disproportionation, paring reaction. * Corresponding author. Tel.: +966-3-860-1429; Fax: +966-3-860-4234 E-mail address: skhattaf@kfupm.edu.sa 2 IntroductionXylenes are important starting materials for some industrial processes like the production of synthetic fibers, plasticizers and resins. The major sources of these aromatic hydrocarbons are the reforming and pyrolysis gasoline, which have a higher ratio of low-valued m-xylene. A convenient way to upgrade the low-valued m-xylene consists of its transformation to o-and p-xylene. In this context, the transformation of m-xylene has been studied over different types of zeolite catalysts [1][2][3][4][5][6][7][8].There is interest in ultrastable Y-type zeolites for m-xylene transformation, partly because of their increased chemical and thermal stability, with respect to other zeolites. Y-zeolite is made ultrastable by the removal of aluminum from the framework. The dealumination can be accomplished through the use of steam [9], acid leaching [10], or by chemical treatment with hexaflourosilicate or silicon tetrachloride [11][12][13]. However, the most common procedure is hydrothermal treatment at elevated temperatures under controlled atmosphere (steaming). The resulting material, USY (ultrastable Y) zeolites, being modified in the framework Si/Al ratio, structure and acidity, usually exhibits improved reactivity, selectivity and coking behavior for a catalytic reaction, which is of great interest to the petroleum industry. Several studies have been conducted on the effect of Y-zeolite acid properties on isomerization and disproportionation of m-xylene reactions [1,5,7]. However, studies correlating the intrinsic properties of Y-zeolite to other reaction pathways, apart from isomerization and disproportionation are somewhat limited. With this in mind, the present work reports the effect of acid properties of Y-zeolite on products selectivity and various reaction pathways during m-xylene transformation in a fluidizedbed reactor. As prepared H-Y zeolite ...

show abstract

A Simple Method for Determining the Relative Significance of the Unimolecular and Bimolecular Pathways of Xylene Isomerization over HY Zeolites

Cited by 69 publications

References 0 publications

Shape-Selective Catalysis in Zeolites

Shape-Selective Catalysis in Zeolites

How to Improve the Selectivity of Zeolitic Catalysts in C₈Aromatic Cut Isomerization

The effect of Y-zeolite acidity on m-xylene transformation reactions

Contact Info

Product

Resources

About

A Simple Method for Determining the Relative Significance of the Unimolecular and Bimolecular Pathways of Xylene Isomerization over HY Zeolites

Cited by 69 publications

References 0 publications

Shape-Selective Catalysis in Zeolites

Shape-Selective Catalysis in Zeolites

How to Improve the Selectivity of Zeolitic Catalysts in C8Aromatic Cut Isomerization

The effect of Y-zeolite acidity on m-xylene transformation reactions

Contact Info

Product

Resources

About

How to Improve the Selectivity of Zeolitic Catalysts in C₈Aromatic Cut Isomerization