In the present work, we studied the protonation reaction of styrene inside the cavity of acidic H-Y zeolite. Density functional theory calculation using M06-2X functional and analysis of quantum theory of atoms in molecules are used to investigate the confinement effects of zeolite framework on species involved on the reaction. A detailed analysis of the topology of the electron density of interactions among reactants, transition state, and intermediate products with the cavity of H-Y zeolite is performed, extracting conclusions about adsorption, catalysis, and confinement effects. Identification and quantification of host−guest interactions between zeolite framework and styryl cation support the larger contribution of weak closed-shell interactions in stabilization of the formed carbenium ion. Our results clearly show that reaction energies for all formed species inside a zeolite with large void structure are also significantly governed by the confinement effects related to weak host−guest interactions. In other words, zeolite confinement effect is a crucial factor that may affect the catalytic activity even on zeolites with large pore size and void structure as H-Y.

No abstract

In this work, a theoretical study in conjunction with a spectroscopic analysis by FTIR were carried out in order to obtain molecular insights on the role of (CTA + )(≡SiO − ) ion pair into the catalytic activity of [CTA + ]-Si-MCM-41, the non-calcined form of Si-MCM-41. The reaction of transesterification of ethyl acetate with methanol was used as a model of transesterification of vegetal oils using the mesoporous heterogeneous catalyst. The theoretical study was performed in the framework of density functional theory (DFT) in order to provide new insights that could be helpful in the understanding of these chemical reactions on solid surfaces. It is found that the most favorable reaction mechanism is the dual site mechanism and that the presence of the (CTA + )(≡SiO − ) ionic pair is fundamental for the catalytic activity. The basic center of [CTA + ]-Si-MCM-41 catalyst polarizes the adsorbed methanol and the acid center polarizes the carbonyl of adsorbed ethyl acetate. Thus, this bifunctional catalytic site makes possible the concerted adsorption of both reactants at the pore mouth and generates a concerted transition state that gives rise to the beginning of the transesterification reaction and the formation of the unstable tetrahedral intermediate which will give rise to the products.

<p>En este trabajo se describe una propuesta didáctica novedosa desarrollada en el marco de ferias y muestras itinerantes de Ciencia y Tecnología. El objetivo general de la experiencia es desarrollar la cultura científica y contribuir al despertar de vocaciones científicas en niños. A través de la participación en este tipo actividades se abren nuevas oportunidades de comunicación desde la Universidad y los Centros de Investigación hacia la sociedad. Esto redunda en una mayor motivación tanto por parte de los alumnos como de los docentes y el equipo de trabajo involucrado.</p><p> </p>