Cluster and Periodic Calculations of the Ethene Protonation Reaction Catalyzed by theta-1 Zeolite: Influence of Method, Model Size, and Structural Constraints

Boronat, Mercè; Zicovich‐Wilson, Claudio M.; Viruela, Pedro M.; Corma, Avelino

doi:10.1002/1521-3765(20010316)7:6<1295::aid-chem1295>3.0.co;2-s

Cited by 29 publications

(42 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…269,270 Earlier theoretical papers often used very small clusters in which the topology of the material was not properly taken into account for reasons of computational expense. Either a cluster based model may be used in which part of the zeolite is cut out from the periodic structure or a periodic model in which the material is simulated using periodic boundary conditions.…”

Section: View Article Onlinementioning

confidence: 99%

Advances in theory and their application within the field of zeolite chemistry

et al. 2015

View full text Add to dashboard Cite

Zeolites are versatile and fascinating materials which are vital for a wide range of industries, due to their unique structural and chemical properties, which are the basis of applications in gas separation, ion exchange and catalysis. Given their economic impact, there is a powerful incentive for smart design of new materials with enhanced functionalities to obtain the best material for a given application. Over the last decades, theoretical modeling has matured to a level that model guided design has become within reach. Major hurdles have been overcome to reach this point and almost all contemporary methods in computational materials chemistry are actively used in the field of modeling zeolite chemistry and applications. Integration of complementary modeling approaches is necessary to obtain reliable predictions and rationalizations from theory. A close synergy between experimentalists and theoreticians has led to a deep understanding of the complexity of the system at hand, but also allowed the identification of shortcomings in current theoretical approaches. Inspired by the importance of zeolite characterization which can now be performed at the single atom and single molecule level from experiment, computational spectroscopy has grown in importance in the last decade. In this review most of the currently available modeling tools are introduced and illustrated on the most challenging problems in zeolite science. Directions for future model developments will be given.

show abstract

Section: View Article Onlinementioning

confidence: 99%

Advances in theory and their application within the field of zeolite chemistry

et al. 2015

View full text Add to dashboard Cite

show abstract

“…It is concluded from these works that there is a strong correlation between the local framework structure of the zeolite and the adsorbed state of methanol, 23 the stability of alkoxide complexes, 20 the chemisorption energy of ammonia 21,22 or the activation barrier for the H/D exchange in alkanes. 22 In previous work, 26,27 we have applied an alternative method that uses both the cluster and the periodic approaches. In a first step, the geometries of all minima and transition states involved in the reaction mechanisms considered are optimized using cluster models large enough to include all local or short-range interactions.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Local Geometry of Zeolite Active Sites and Olefin Size on the Stability of Alkoxide Intermediates

et al. 2001

Self Cite

View full text Add to dashboard Cite

The protonation of ethene, propene, 1-butene, and iso-butene by acidic theta-1 zeolite to give covalent alkoxide intermediates has been theoretically investigated by means of cluster and periodic calculations. The influence of the methodology used, of the olefin size and nature, of the cluster used to model the catalyst, of the degree of geometry relaxation around the active site, and of the long-range effects caused by the Madelung potential of the crystal has been analyzed. It has been found that the stability of alkoxide intermediates is very sensitive to the local geometry of the active site and to the nature of the carbon atom involved in the C-O bond, whereas the activation energy for the process is mainly influenced by the methodology used and by electrostatic effects, due to the carbocationic nature of the transition state. Finally, the question of whether the tert-butyl carbenium ion is a reaction intermediate or just a transition state in the iso-butene protonation process has been adressed by calculating the complete reaction mechanism at different theoretical levels. IntroductionAcidic zeolites are widely used in petroleum and chemical industries as solid catalysts for a number of commercially important hydrocarbon reactions due to their high activity, selectivity and thermal stability. 1,2 Their microporous structure provides a large internal surface and notable selectivity effects related both to diffusion of reactants and products inside the pore system and to steric constraints on transition states. For a long time, the mechanism of heterogeneous catalysis on zeolites was considered to be analogous to that of homogeneous reactions in gas phase or superacid media without any direct evidence. Following this, it was accepted that carbenium and carbonium ions were the intermediate species formed by interaction of hydrocarbon molecules with the zeolite Brønsted acid sites. 3,4 Experimental techniques for the in situ study of reactions on solids, such as variable temperature solid-state NMR 5,6 or IR 6-8 have been developed, and the direct observation of the Brønsted acid sites and their interaction with adsorbed molecules has become possible. As a consequence, it has been shown that simple carbenium ions are not stable within zeolite channels and that protonation of adsorbed olefins and alcohols results in formation of covalent alkoxide complexes. 5,[9][10] In agreement with these experimental observations, several quantum chemical studies 11-14 also indicate that protonation of olefins by Brønsted acid sites results in formation of very stable alkoxide complexes covalently bound to the catalyst surface, and that carbenium ion-like species are only the transition states through which these reactions proceed. However, the existence of free carbenium ions such as alkyl-substituted cyclopentenyl or indanyl cations in zeolites has been experimentally demonstrated, 5,15-16 whereas in the case of iso-butene protonation, for example, it is not completely clear whether the tert-butyl carbenium ion is a reactio...

show abstract

“…Los primeros estudios realizados, empleando el modelo de agregado molecular y utilizando modelos sencillos de catalizador (uno o tres sitios tetraédricos), sugerían que las especies alcóxidas se encontraban como especies intermediarias estables [26,85]. Sin embargo, empleando cálculos tipo periódico, se obtiene que estas especies tipo alcoxidas pueden llegar a ser tan inestables como los hidrocarburos protonados [86][87][88][89]. Estos resultados obtenidos con el modelo periódico, indican que los efectos estéricos generados por el resto la geometría del cristal en la zeolita juegan un papel importante y la estabilización de los complejos adsorbidos es muy sensible a la geometría local del sitio activo.…”

Section: ¿Puede Un Modelo De Agregado Molecular Describir Correctamente Las Interacciones Zeolita-adsorbato?unclassified

“…Estos resultados obtenidos con el modelo periódico, indican que los efectos estéricos generados por el resto la geometría del cristal en la zeolita juegan un papel importante y la estabilización de los complejos adsorbidos es muy sensible a la geometría local del sitio activo. Por tanto, en la interacción entre la estructura de una zeolita-substrato, el efecto de los átomos que rodean al sitio activo (primeros vecinos), así como las contribuciones electrostáticas del cristal [88] son muy importantes para la estabilización del estado de transición.…”

Section: ¿Puede Un Modelo De Agregado Molecular Describir Correctamente Las Interacciones Zeolita-adsorbato?unclassified

“…Para éste estudio realizado, ellos emplean un modelo de dos anillos completos de la zeolita mordenita para el modelo de cúmulo y comparan los resultados con los obtenidos del modelo periódico, obteniendo energías de activación y de los estados los absorbidos muy similares entre sí. Adicionalmente, si se emplea la teoría de funcionales de la densidad (DFT), en el modelo mejorado de agregado molecular, se obtiene una descripción del sistema de reacción comparable con un cálculo al nivel de teoría MP2 [82][83][84][85][86][87][88][89][90].…”

Section: ¿Puede Un Modelo De Agregado Molecular Describir Correctamente Las Interacciones Zeolita-adsorbato?unclassified

See 1 more Smart Citation

Estudio teórico de la reactividad de catalizadores modelo representativos de la zeolita HZSM-5

Hernández

View full text Add to dashboard Cite

Le doy las gracias al Prof. Marcelo Galván por darme la oportunidad de pertenecer a su grupo de investigación para realizar mi trabajo de doctorado y por compartir sus valiosos conocimientos y experiencia profesional conmigo, factores que me ayudaron en el correcto desarrollo de esta investigación, pero sobre todo por su valiosa amistad y por su apoyo incondicional.Gracias al Instituto Mexicano del Petróleo y a CONACYT, por el apoyo económico recibido durante la realización de esta investigación. Gracias a los Drs.Salvador Cruz e Isidoro García por el apoyo en la obtención de la Beca IMP.Gracias a los profesores Ricardo Gómez, Rubicelia Vargas, Miguel Castro y al Dr. Badhin Gómez, no solo por su importante contribución y enriquecimiento al trabajo a través de su revisión, sino también por su paciencia y compresión durante ésta.I thank to Prof. Pratim Chattaraj for his contribution to this work and for sharing his time and knowledge with me.Also thanks to Prof. Guy Marin, from the University of Gent in Belgium, for the granted facilities to be able to culminate this work. As well as, I am thankful to him and to Professor Marie-Françoise Reyniers by the valuable discussions and their right commentaries about my research that enriched it, during the time that I stayed in the Laboratory.Son muchas las personas a las que tengo que agradecer, y no terminaría esta lista, en verdad agradezco profundamente a todos aquellos que de alguna forma contribuyeron en la realización y el desarrollo de este trabajo y a mis amigos que confiaron en mí.

show abstract

Cluster and Periodic Calculations of the Ethene Protonation Reaction Catalyzed by theta-1 Zeolite: Influence of Method, Model Size, and Structural Constraints

Cited by 29 publications

References 34 publications

Advances in theory and their application within the field of zeolite chemistry

Advances in theory and their application within the field of zeolite chemistry

Influence of the Local Geometry of Zeolite Active Sites and Olefin Size on the Stability of Alkoxide Intermediates

Estudio teórico de la reactividad de catalizadores modelo representativos de la zeolita HZSM-5

Contact Info

Product

Resources

About