Measuring the Brønsted acid strength of zeolites – does it correlate with the O–H frequency shift probed by a weak base?

Areán, C. Otero; Delgado, M.; Nachtigall, Petr; Thang, Ho Viet; Rubeš, Miroslav; Bulánek, Roman; Eliášová, Pavla

doi:10.1039/c3cp54738h

Cited by 66 publications

(70 citation statements)

References 77 publications

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“…In the Co‐ and Zn‐containing materials, on the other hand, the HTI values are too low to account for the aromatics yield, which suggests another parallel pathway to aromatics formation. Co‐ and Zn‐exchanged zeolites were previously shown to have alkane dehydrogenation activity, and we speculate that this is also the case for the isomorphically substituted H‐CoAlPO‐5 and H‐ZnAlPO‐5 materials used in this study. Such activity could contribute to more rapid deactivation of the Co‐ and Zn‐containing catalysts.…”

Section: Resultssupporting

confidence: 70%

A Systematic Study of Isomorphically Substituted H‐MAlPO‐5 Materials for the Methanol‐to‐Hydrocarbons Reaction

et al. 2017

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Substituting metals for either aluminum or phosphorus in crystalline, microporous aluminophosphates creates Brønsted acid sites, which are well known to catalyze several key reactions, including the methanol to hydrocarbons (MTH) reaction. In this work, we synthesized a series of metal‐substituted aluminophosphates with AFI topology that differed primarily in their acid strength and that spanned a predicted range from high Brønsted acidity (H‐MgAlPO‐5, H‐CoAlPO‐5, and H‐ZnAlPO‐5) to medium acidity (H‐SAPO‐5) and low acidity (H‐TiAlPO‐5 and H‐ZrAlPO‐5). The synthesis was aimed to produce materials with homogenous properties (e.g. morphology, crystallite size, acid‐site density, and surface area) to isolate the influence of metal substitution. This was verified by extensive characterization. The materials were tested in the MTH reaction at 450 °C by using dimethyl ether (DME) as feed. A clear activity difference was found, for which the predicted stronger acids converted DME significantly faster than the medium and weak Brønsted acidic materials. Furthermore, the stronger Brønsted acids (Mg, Co and Zn) produced more light alkenes than the weaker acids. The weaker acids, especially H‐SAPO‐5, produced more aromatics and alkanes, which indicates that the relative rates of competing reactions change upon decreasing the acid strength.

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Section: Resultssupporting

confidence: 70%

A Systematic Study of Isomorphically Substituted H‐MAlPO‐5 Materials for the Methanol‐to‐Hydrocarbons Reaction

et al. 2017

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“…166 Further studies are necessary to investigate this topic. 166 Further studies are necessary to investigate this topic.…”

Section: Infrared Spectroscopymentioning

confidence: 99%

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

et al. 2015

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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.

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“…IR spectra and adsorption enthalpies. 116,117 Acid strength also seems to influence the relative reactivity of propene and benzene in the two isostructural AFI materials.…”

Section: Reactivity Indices From MDmentioning

confidence: 99%

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Wispelaere

Bailleul

Speybroeck

2016

Catal. Sci. Technol.

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Title: Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions Advanced ab initio molecular dynamics techniques enable study of the infl uence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on methylation reactions of benzene and propene, which are crucial reaction steps in the conversion of methanol into hydrocarbons. Our advanced simulations provide detailed insight into how operating conditions impact the competition of the concerted and stepwise methylation mechanism and thus the reaction kinetics. As featured in:See and mechanism of individual reaction steps at operating conditions. Herein we use state-of-the-art advanced ab initio molecular dynamics techniques to study the influence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on elementary reactions. Such advanced modeling techniques provide complementary insight to experimental knowledge as the impact of individual factors on the reaction mechanism and kinetics of zeolite-catalyzed reactions may be unraveled. We study key reaction steps in the conversion of methanol to hydrocarbons, namely benzene and propene methylation. These reactions may occur either in a concerted or stepwise fashion, i.e. methanol directly transfers its methyl group to a hydrocarbon or the reaction goes through a framework-bound methoxide intermediate. The DFT-based dynamical approach enables mimicking reaction conditions as close as possible and studying the competition between two methylation mechanisms in an integrated fashion. The reactions are studied in the unidirectional AFI-structured H-SSZ-24, H-SAPO-5 and TON-structured H-ZSM-22 materials. We show that varying the temperature, topology, acidity and number of protic molecules surrounding the active site may tune the reaction mechanism at the molecular level. Obtaining molecular control is crucial in optimizing current zeolite processes and designing emerging new technologies bearing alternative feedstocks.

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Measuring the Brønsted acid strength of zeolites – does it correlate with the O–H frequency shift probed by a weak base?

Cited by 66 publications

References 77 publications

A Systematic Study of Isomorphically Substituted H‐MAlPO‐5 Materials for the Methanol‐to‐Hydrocarbons Reaction

A Systematic Study of Isomorphically Substituted H‐MAlPO‐5 Materials for the Methanol‐to‐Hydrocarbons Reaction

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

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

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