Multiscale Approaches for Modeling Hydrocarbon Conversion Reactions in Zeolites

Hansen, Niels; Keil, Frerich J.

doi:10.1002/cite.201200201

Cited by 8 publications

(7 citation statements)

References 65 publications

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“…Of course such an approach has its limits and it is obvious that future modeling techniques will have to focus more and more on a multiscale modeling approach. 12,[201][202][203][204] Still the examples shown herein already constitute a major step forwards as it has been shown that the reaction at the active site can be modelled with very good accuracy, provided the mechanism is known.…”

Section: Chemical Accuracy For Enthalpy Barriers and Kinetic Accuracy...mentioning

confidence: 79%

First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study

et al. 2014

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To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous catalysis. Herein, we review current computational procedures to determine chemical kinetics from first principles, thus by using no experimental input and by modeling the catalyst and reacting species at the molecular level. Therefore, we use the methanol-to-olefin (MTO) process as a case study to illustrate the various theoretical concepts. This process is a showcase example where rational design of the catalyst was for a long time performed on the basis of trial and error, due to insufficient knowledge of the mechanism. For theoreticians the MTO process is particularly challenging as the catalyst has an inherent supramolecular nature, for which not only the Brønsted acidic site is important but also organic species, trapped in the zeolite pores, must be essentially present during active catalyst operation. All these aspects give rise to specific challenges for theoretical modeling. It is shown that present computational techniques have matured to a level where accurate enthalpy barriers and rate constants can be predicted for reactions occurring at a single active site. The comparison with experimental data such as apparent kinetic data for well-defined elementary reactions has become feasible as current computational techniques also allow predicting adsorption enthalpies with reasonable accuracy. Real catalysts are truly heterogeneous in a space- and time-like manner. Future theory developments should focus on extending our view towards phenomena occurring at longer length and time scales and integrating information from various scales towards a unified understanding of the catalyst. Within this respect molecular dynamics methods complemented with additional techniques to simulate rare events are now gradually making their entrance within zeolite catalysis. Recent applications have already given a flavor of the benefit of such techniques to simulate chemical reactions in complex molecular environments.

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Section: Chemical Accuracy For Enthalpy Barriers and Kinetic Accuracy...mentioning

confidence: 79%

First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study

et al. 2014

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“…In this very recent work [95], the authors have achieved chemical accuracy of ± 2 kcal/mol for predicted ethene methylation activation barriers. Other applications of such multi-scale QM/QM schemes have been reported by Hansen and Keil [97]. Although such QM/QM schemes may be too computationally expensive for routine use, they could potentially be used to benchmark more cost-effective approaches [95].…”

Section: Subtractive Schemesmentioning

confidence: 97%

Impact of long-range electrostatic and dispersive interactions on theoretical predictions of adsorption and catalysis in zeolites

et al. 2018

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In this paper, we review the importance of long-range zeolite framework interactions in theoretical predictions for a variety of zeolite-catalyzed processes, and we show why such interactions must be determined accurately in order to reproduce experimentally measured adsorption and activation energies. We begin with an overview of the different strategies that have been used to account for long-range coulombic and dispersive interactions of zeolite framework atoms with species adsorbed at an active site. These methods include full periodic-DFT calculations and multi-layer hybrid techniques. Electrostatic interactions are observed to have a more significant impact than dispersive interactions on the geometries of ion-pair transition states and adsorbed species. Stabilization of the TS relative to reactant complexes is also dictated by electrostatic interactions. Dispersion effects are found to significantly stabilize both transition and reactant states for adsorbed species, especially those which have dimensions that provide good fits within the zeolite pore or cavity. We also show that the relevance of particular active site configurations can be missed, if the effects of long-range interactions are neglected. As a case in point, we demonstrate that a site previously considered inactive for ethane dehydrogenation, [GaH 2 ] + may in fact be more active than previously thought, when the impact of long-range interactions on the predicted activation energy is taken into account. Finally, the use of hybrid quantum mechanics/molecular mechanics approaches on extended, finite zeolite clusters has emerged as an accurate, highly cost-effective, and versatile alternative towards overcoming some of the present-day limitations of periodic calculations.

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“…Some interesting reviews appeared also recently on multiscale modeling of hydrocarbon conversion processes, which might be interesting for more in depth reading. 367,368 Swisher et al performed a theoretical simulation of n-alkane cracking in zeolites using an innovative combination of various theoretical methods. 369 The apparent rate constants for cracking of C3-C6 species were determined by separating the intrinsic kinetics of the alkane cracking from the thermodynamics of the adsorption step.…”

Section: Applications Using Zeolites: Selective Case Studiesmentioning

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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Multiscale Approaches for Modeling Hydrocarbon Conversion Reactions in Zeolites

Cited by 8 publications

References 65 publications

First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study

First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study

Impact of long-range electrostatic and dispersive interactions on theoretical predictions of adsorption and catalysis in zeolites

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

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