An investigation of the adsorption of aromatic hydrocarbons in zeolite Na–Y by solid-state NMR spectroscopy

Zhu, Jianfeng; Trefiak, Nick; Woo, Tom K.; Huang, Yining

doi:10.1016/j.micromeso.2008.01.035

Cited by 18 publications

(9 citation statements)

References 48 publications

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“…This hypothesis was validated by the results of FTIR and Raman spectroscopies on xylene adsorption in FAUs that clearly showed the formation of a π‐complex between the xylene aromatic system and the alkali cations as well as additional CH⋅⋅⋅O contacts with the basic lattice . Whereas toluene and xylenes can only form π‐complexes with individual cations or form stacked aggregates at higher loadings, benzene becomes symmetrically aligned in the 12‐membered ring window of the supercage as a result of the formation of multiple van der Waals interactions between benzene C−H groups and the framework oxygens ,. Similarly, the specific alignment of ferrocene in NaY pores has been attributed to the concert effect of multiple weak van der Waals interactions between the cyclopentadienyl ligands and pore walls .…”

Section: Confinement‐induced Reactivity and Molecular Recognition Phementioning

confidence: 65%

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

Pidko

2018

ChemCatChem

104

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Zeolites have a broad spectrum of applications as robust microporous catalysts for various chemical transformations. The reactivity of zeolite catalysts can be tailored by introducing heteroatoms either into the framework or at the extraframework positions that gives rise to the formation of versatile Brønsted acid, Lewis acid and redox‐active catalytic sites. Understanding the nature and catalytic role of such sites is crucial for guiding the design of new and improved zeolite‐based catalysts. This work presents an overview of recent computational studies devoted to unravelling the molecular level details of catalytic transformations inside the zeolite pores. The role of modern computational chemistry in addressing the structural problem in zeolite catalysis, understanding reaction mechanisms and establishing structure‐activity relations is discussed. Special attention is devoted to such mechanistic phenomena as active site cooperativity, multifunctional catalysis as well as confinement‐induced and multisite reactivity commonly encountered in zeolite catalysis.

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Section: Confinement‐induced Reactivity and Molecular Recognition Phementioning

confidence: 65%

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

Pidko

2018

ChemCatChem

104

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“…This illustrates the importance of weak van der Waals interactions on the molecular recognition properties of zeolite materials. In spite of being quite weak separately, the formation of multiple interactions collectively manages to induce specific conformations of the adsorbed molecules and therefore determine their most active geometries. , …”

Section: Resultsmentioning

confidence: 99%

“…In spite of being quite weak separately, the formation of multiple interactions collectively manages to induce specific conformations of the adsorbed molecules and therefore determine their most active geometries. 69,70 As there is a proportional correlation between the rate of methanol conversion and the content of crystalline and microporous domains, the zeolite structure should be ideally completely formed. On the other hand, the application of zeolites from intermediate synthesis stages is promising for reactions involving bulky molecules, as they have a satisfactory number of catalytic sites combined with the required accessibility.…”

Section: Methodsmentioning

confidence: 99%

Evolution of Structure and Active Sites during the Synthesis of ZSM-5: From Amorphous to Fully Grown Structure

et al. 2019

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Lately, to considerably reduce the diffusion constraints in the catalysis performed by zeolites, there has been significant interest in syntheses of partially formed zeolites with extremely accessible active sites, named embryonic zeolites. Their preparation relies on stopping the crystallization of conventional micron-sized zeolites before the zeolites reach full-crystallization, as detected by X-ray diffraction. In this current study, ZSM-5 zeolites were synthesized by using the same starting batch without an organic template and different times, obtaining amorphous, ill-crystallized, and fully grown structures that were characterized by various physicochemical methods and used in two catalytic test reactions. Using this synthesis strategy, two significant features of zeolites in catalysis are highlighted: (1) the accessibility of their inner pores for reactants and (2) the confinement effect, that is, the ability of zeolites to stabilize transition states in some catalytic reactions. As the ZSM-5 was being formed, it had a decreased activity for glycerol condensation with acetone, indicating steric restrictions to the bulky product that has a kinetic diameter (0.63 nm) considerably higher than the zeolite micropores (0.51 × 0.54 nm). On the other hand, the catalytic activity for methanol dehydration to dimethyl ether was proportional to crystallinity, as dimethyl ether intermediates adsorb within the zeolite cavities that tend to reciprocally enhance interactions giving an optimal effect in the catalytic property.

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“…In addition, the selective adsorption on zeolites is commonly considered the most economical industrial process for molecular separation and a valid solution for depollution purposes. − The definition of the host–guest interactions occurring in confined space between porous solids and embedded hydrocarbons is an important task to improve adsorption properties of materials and is essential to optimize effective sorbents for contaminant removal from polluted water . More specifically, the adsorption of aromatic and alkane molecules on FAU and MFI zeolites has been extensively investigated as single-component, ,− whereas studies on competitive adsorption of an organic molecule mixture with different polarities and chain length from water and gas phase are limited. − On the other hand, understanding the competition of organic contaminants for a specific adsorbent is relevant from an environmental point of view in that, under real conditions, pollutants are generally present in groundwater as complex mixtures.…”

Section: Introductionmentioning

confidence: 99%

On the Adsorption of Gaseous Mixtures of Hydrocarbons on High Silica Zeolites

Sacchetto¹,

Olivera²,

Paul³

et al. 2017

J. Phys. Chem. C

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An experimental study of the interactions of an equimolar binary gaseous mixture of toluene and n-hexane, model molecules of aromatic and aliphatic fuel-based pollutants, with two dealuminated high silica zeolites is here presented for the first time. Zeolites Y and ZSM-5 with diverse textural and surface properties were chosen as adsorbents, and the effects of their physicochemical features (predominantly the pore size architecture and silanol content) on sorption capacity were studied. The host−guest (i.e., sorbent-molecules) interactions were studied by FTIR and SS-NMR spectroscopies. IR optical adsorption isotherms of both toluene and n-hexane coadsorbed on the zeolites allowed the determination of the concentration of the adsorbed molecules. Variable temperature SS-NMR spectroscopy allowed the description of the mobility of the pollutant molecules when coadsorbed at the interface of the zeolites micropores. Finally, we describe how the proposed innovative approach can be of general use to determine the selectivity of adsorbent materials for a mixture of hydrocarbons.

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An investigation of the adsorption of aromatic hydrocarbons in zeolite Na–Y by solid-state NMR spectroscopy

Cited by 18 publications

References 48 publications

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

Evolution of Structure and Active Sites during the Synthesis of ZSM-5: From Amorphous to Fully Grown Structure

On the Adsorption of Gaseous Mixtures of Hydrocarbons on High Silica Zeolites

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