Effect of the Zeolite Cavity on the Mechanism of Dehydrogenation of Light Alkanes over Gallium-Containing Zeolites

Pereira, Márcio Soares; Silva, Alexander; Nascimento, Marco Antônio Chaer

doi:10.1021/jp201107x

Cited by 30 publications

(32 citation statements)

References 44 publications

(54 reference statements)

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“…Pereira et al [142] Pidko et al [ transition states relative to reactant complexes by long-range electrostatic interactions is observed to increase with the increasing ionic character of the complex. Such TS stabilization can be especially significant in the case that the reactant complexes preceding the ratelimiting TS cover all bare active sites within the zeolite.…”

Section: Model Detailsmentioning

confidence: 96%

“…[GaH 2 ] + sites have been observed experimentally in Ga/H-MFI using DRIFTS, XAFS and XANES experiments [138][139][140] under reaction conditions for ethane dehydrogenation. Extensive DFT calculations [141][142][143] carried out using small cluster models of [GaH 2 ] + (ranging from T3 to T22 clusters) have reported apparent activation energies for ethane dehydrogenation, ranging from 54 kcal/ mol to 65 kcal/mol. The authors of these studies note however, that all of the predicted activation barriers for ethane dehydrogenation on [GaH 2 ] + are significantly larger than the experimentally measured activation barrier of 39 kcal/mol for Ga 2 O 3 /H-MFI [144].…”

Section: Theoretical Predictions Of Active Site Structuresmentioning

confidence: 99%

“…However, none of the aforementioned studies accounted for the impact of long-range electrostatic and dispersion corrections due to the extended zeolite lattice. Consequently, the possibility that DFT-predicted activation barriers for ethane dehydrogenation on [GaH 2 ] + cations [141][142][143]145] were overestimated due to shortcomings of small cluster models used rather than due to the inherent inactivity of univalent cations was not investigated. To this end, we have assessed the impact of long-range interactions on light alkane dehydrogenation catalysis on [GaH 2 ] + .…”

Section: Theoretical Predictions Of Active Site Structuresmentioning

confidence: 99%

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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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Section: Model Detailsmentioning

confidence: 96%

Section: Theoretical Predictions Of Active Site Structuresmentioning

confidence: 99%

Section: Theoretical Predictions Of Active Site Structuresmentioning

confidence: 99%

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

et al. 2018

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“…Comparison with the energetics previously reported for isobutane dehydrogenation on Zn-and Ga-modified MFI catalysts with those calculated here for IE-Cu/BEA indicates that one may expect Cu/BEA to be less active for isobutane dehydrogenation, compared to these materials. 11,32 In summary, Cu-containing catalyst materials were synthesized to target specific catalytic functionalities, namely, metallic copper, copper oxide, Cu(I) zeolite, Cu(II) zeolite, and Brønsted acid sites. Experimental isobutane dehydrogenation reaction studies demonstrated that only the ionic Cu-zeolite catalysts activate C−H bonds in isobutane to produce H 2 under these conditions.…”

mentioning

confidence: 99%

Exploring Low-Temperature Dehydrogenation at Ionic Cu Sites in Beta Zeolite To Enable Alkane Recycle in Dimethyl Ether Homologation

et al. 2017

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Cu-based catalysts containing targeted functionalities including metallic Cu, oxidized Cu, ionic Cu, and Brønsted acid sites were synthesized and evaluated for isobutane dehydrogenation. Hydrogen productivities, combined with operando X-ray absorption spectroscopy, indicated that Cu(I) sites in Cu/BEA catalysts activate C−H bonds in isobutane. Computational analysis revealed that isobutane dehydrogenation at a Cu(I) site proceeds through a two-step mechanism with a maximum energy barrier of 159 kJ/mol. These results demonstrate that light alkanes can be reactivated on Cu/BEA, which may enable re-entry of these species into the chain-growth cycle of dimethyl ether homologation, thereby increasing gasoline-range (C 5+ ) hydrocarbon yield.

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“…However, it is important to take under consideration that dispersion interactions, which can play an important role in adsorption processes, are not well described with B3LYP. 39 Vol. 23, No.…”

Section: Methodsmentioning

confidence: 99%

Probing topological electronic effects in catalysis: thiophene adsorption on NiMoS and CoMoS clusters

Borges¹,

Silva²

2012

J. Braz. Chem. Soc.

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Um método teórico geral em duas etapas para estudar redistribuições eletrônicas em processos catalíticos é apresentado. Na primeira etapa, teoria do funcional da densidade (DFT) é usada para otimizar completamente duas geometrias: o aglomerado que representa o catalisador e o sistema aglomerado mais molécula adsorvida. Na segunda etapa, a densidade eletrônica molecular convergida é dividida em multipolos centrados em sítios atômicos obtidos segundo uma análise de multipolos distribuídos, que fornece informação topológica detalhada da redistribuição de carga do catalisador e da molécula, antes e depois da adsorção. Esta abordagem é aplicada para a adsorção de tiofeno sobre a borda metálica 10 -10 dos catalisadores Ni(Co)MoS e comparada com a mesma reação em MoS 2 não-substituído. Energias de adsorção, geometrias e a análise de multipolos calculada indicam uma fraca adsorção do tiofeno em ambas as situações. Um modelo coulombiano para a ligação química mostra que a magnitude da ligação metal-enxofre na superfície dos catalisadores de Ni(Co)MoS promovidos é consideravelmente menor do que em MoS 2 não substituído, desta forma confirmando a origem do aumento da atividade de hidrodessulfurização (HDS) nestes catalisadores.A general two-step theoretical approach to study electronic redistributions in catalytic processes is presented. In the first step, density functional theory (DFT) is used to fully optimize two geometries: the cluster representing the catalyst and the cluster plus adsorbed molecule system. In the second step, the converged electron density is divided into multipoles centered on atomic sites according to a distributed multipole analysis which provides detailed topological information on the charge redistribution of catalyst and molecule before and after adsorption. This approach is applied to thiophene adsorption on the 10 -10 metal edge of Ni(Co)MoS catalysts and compared to the same reaction on bare MoS 2 . Calculated adsorption energies, geometries and multipole analysis indicate weak thiophene chemisorption on both cases. A Coulombic bond model showed that surface metal-sulfur bond strengths in Ni(Co)MoS promoted catalysts are considerably smaller than in bare MoS 2 , thus confirming the origin of the enhancement of hydrodesulfurization (HDS) activity in these catalysts.

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Effect of the Zeolite Cavity on the Mechanism of Dehydrogenation of Light Alkanes over Gallium-Containing Zeolites

Cited by 30 publications

References 44 publications

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

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

Exploring Low-Temperature Dehydrogenation at Ionic Cu Sites in Beta Zeolite To Enable Alkane Recycle in Dimethyl Ether Homologation

Probing topological electronic effects in catalysis: thiophene adsorption on NiMoS and CoMoS clusters

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