Adsorption of Alkenes on Acidic Zeolites. Theoretical Study Based on the Electron Charge Density

In this work we studied the host–guest interactions between confined molecules and zeolites and their relationship with the energies involved in the reaction of methylation of benzene by methanol in H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT) methods and the quantum theory of atoms in molecules. Results show that the strength of the interactions related to adsorption and coadsorption processes is higher in the catalyst with the larger cavity; however, the confinement effects are higher in the smaller zeolite, explaining, from an electronic viewpoint, the reason why the stabilization energy is higher in H-ZSM-5 than in H-Beta. The confinement effects of the catalyst on the confined species for methanol adsorption, benzene coadsorption, and the formed intermediates dominate this stabilization. For the transition state (TS), the stability of the TS is achieved due to the stabilizing effect of the surrounding zeolite framework on the formed carbocationic species (CH3 +) which is higher in H-ZSM-5 than in H-Beta. In both TSs the methyl cation is multicoordinated forming the following H2O···CH3 +···CB concerted bonds. It is demonstrated that, through the electron density analysis, the criteria can be defined to discriminate between interactions related to the confinement effects and the reaction itself (adsorption, coadsorption, and bond-breaking and bond-forming processes) and, thus, to discriminate the relative contributions of the degree of confinement to the reaction energies for two zeolite catalysts with different topologies.

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“…We have employed similar QTAIM analysis in our previous works on the reaction of alkenes over acidic zeolite. [13][14]16…”

Section: Methods and Calculation Detailsmentioning

confidence: 99%

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

et al. 2018

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“…However, only a bond critical point between the proton of BAS and the middle point of the vinyl double bond (C 7 –C 8 ) can be found; thus, no individual H Z1 ···C bonds are found (see Figure and Table ). This is not an unexpected behavior since adsorption of light alkenes on a small zeolite model showed similar behavior . The topological properties at the BCP for the H Z1 ···πCC interaction show characteristics of closed-shell interactions, and it constitutes a clear indicator of the formation of the π-complex.…”

Section: Resultsmentioning

confidence: 61%

“…In previous studies of chemical reactions of interest in the zeolite chemistry, we demonstrated the usefulness of quantum theory of atoms in molecules (QTAIMs) analysis and the relevance of the information that can be obtained through the analysis of electron density distribution. − One of the advantages of the QTAIM methodology over other global measures of the interaction energy is that it allows one to decompose the interaction energy in contributions by an atom or a group of atoms, and because of which it was used in the analysis, design, and optimization of ligand molecules in the ligand/receptor recognition process . Similar analysis could be applied in the study of adsorbate–catalyst interactions, which makes it particularly useful for these catalytic systems where several interactions are found.…”

Section: Introductionmentioning

confidence: 97%

Confinement Effects in Protonation Reactions Catalyzed by Zeolites with Large Void Structures

et al. 2018

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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.

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“…We selected the reaction of ethylene dimerization over acidic zeolite as a case study. We have employed quantum chemistry methods similar to those in our previous works on the reaction of alkenes over acidic zeolite . The zeolite catalyst has been modeled by a widely used cluster, H 3 Si–OH–Al(–O–SiH 3 ) 3 , denoted T5–OH.…”

Section: Methods and Calculation Detailsmentioning

confidence: 99%

Laplacian of the electron density: a hole–lump interaction as a tool to study stereoelectronic control of chemical reactions

Zalazar

Peruchena

2013

J of Physical Organic Chem

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a In this work, we applied the theory of Atoms in Molecules to the study of carbocationic transition states involved in two different reaction mechanisms, using the proposed mechanism of ethylene dimerization over Brønsted-acid site of zeolite catalyst as a study case. We report the main results of the analysis of the Laplacian of electron density distribution and Bader's atomic charges to increase our understanding of stereoelectronic aspects of these chemical reactions. At B3LYP/6-31++G(d,p)//B3LYP/6-3G(d,p) level, our results show that the envelopes of Laplacian distribution provide valuable information about the relative orientation of the species involved in the reaction, their interaction with the catalyst surface, and its stability. The stabilization and formation of these transition states depend on the availability of electrons in the environment. Such availability plays a key role to stabilize the positive charge on the carbocationic center and, thus, to stabilize the formed carbocation. The analysis of envelopes of Laplacian could be used to study different organic and inorganic chemical reactions and provide new insights to increase our understanding of these chemical reactions.

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Adsorption of Alkenes on Acidic Zeolites. Theoretical Study Based on the Electron Charge Density

Cited by 13 publications

References 54 publications

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

Confinement Effects in Protonation Reactions Catalyzed by Zeolites with Large Void Structures

Laplacian of the electron density: a hole–lump interaction as a tool to study stereoelectronic control of chemical reactions

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