m-xylene and 1,2,4-trimethylbenzene transformations on mordenites. influence of the exchange by various cations

Cartraud, P.; Cointot, A.; Dufour, M.; Gnep, N.S.; Guisnet, M.; Joly, G.; Tejada, Juan C.

doi:10.1016/s0166-9834(00)81330-5

“…An example is the change in the pore size of zeolite NaA (0.4 nm) upon cation exchange with potassium (0.3 nm) or calcium (0.5 nm) cations [20]. Likewise, the effective pore width of H-mordenite can be varied by post-synthetic ion exchange with large metal cations [129][130][131][132]. The density and strength of the catalytically active sites may, however, also be varied by this method [132].…”

Section: Ion Exchange and Pore Size Engineeringmentioning

confidence: 99%

Shape-Selective Catalysis in Zeolites

Weitkamp

¹

,

Puppe

²

1999

Catalysis and Zeolites

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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-

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“…Investigations of this kind have been reported, for example, for ZSM-5 and mordenite catalysts [152,153]. Investigations of this kind have been reported, for example, for ZSM-5 and mordenite catalysts [152,153].…”

Section: Controlled Modification Of the Pore Structurementioning

confidence: 99%

“…(152), it follows that the apparent point selectivity will approach unity as the ratio φ tends to zero. (152), it follows that the apparent point selectivity will approach unity as the ratio φ tends to zero.…”

Section: Type II Selectivitymentioning

confidence: 99%

“…(135) and (152) would have to be integrated over a range of conversions. (135) and (152) would have to be integrated over a range of conversions.…”

Section: Type II Selectivitymentioning

confidence: 99%

“…(152) and (153) may be derived for the case that both interphase and intraparticle concentration gradients occur, when instead of Eq. Relationships similar to Eqs.…”

Section: Type II Selectivitymentioning

confidence: 99%

See 2 more Smart Citations

Simultaneous Heat and Mass Transfer and Chemical Reaction

Dittmeyer

¹

,

Emig

²

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Mathematical Description Single Reactions (Conversion Problem) Pore Diffusion in an Isothermal Pellet Film and Pore Diffusion in an Isothermal Pellet Film and Pore Diffusion Together with Interphase Heat Transfer Film and Pore Diffusion Together with Interphase and Intraparticle Heat Transfer External Heat and Mass Transfer Use of Complex Rate Expressions Simple Reversible Reactions Simple Irreversible Reactions with L angmuir– H inshelwood‐Type Kinetics Simple Reversible Reactions with L angmuir– H inshelwood‐Type Kinetics Temperature Dependence and Reaction Order of Transport‐Limited Reactions Intraparticle Diffusion Interphase Mass Transfer Diagnostic Criteria and Experimental Methods for Estimating the Influence of Heat and Mass Transfer on the Effective Reaction Rate Experimental Criteria Theoretical Criteria Experimental Methods for Estimating the Influence of Heat and Mass Transfer Effects Multiple Reactions (Selectivity Problem) Type I Selectivity Type II Selectivity Type III Selectivity Mathematical Description of the Diffusional Transport F ick's Law with Constant Effective Diffusivities Bulk Diffusion and K nudsen Diffusion Pressure‐Driven Viscous Flow and Surface Diffusion M axwell– S tefan Equations and Related Models Bulk Diffusion, K nudsen Diffusion and Pressure‐Driven Viscous Flow Surface Diffusion Control of Selectivity in the Disproportionation of Ethylbenzene to Benzene and Diethylbenzenes on an HZSM ‐5 Catalyst by Utilizing Diffusion Effects Shape‐Selective Catalysis Microkinetics Macrokinetics Modeling of Shape Selectivity Effects Simplifying Assumptions Model Equations Simulation Results A Product Shape Selectivity (Unaffected by Other Factors) B Product Shape Selectivity and Reactant Diffusion Limitation (Combined Effect) C Product Shape Selectivity and Selective Adsorption (Combined Effect) D Product Shape Selectivity and Restricted Transition State Shape Selectivity (Combined Effect) Controlled Modification of the Pore Structure Concluding Remarks

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