Chemical Reactions of Alkanes Catalysed by Zeolites

Furtado, E. A.; Nascimento, Marco Antônio Chaer

doi:10.1007/0-306-47667-3_3

Cited by 3 publications

(4 citation statements)

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“…All reactions were studied by using a T5 cluster with gallium dihydride to model the nonframework gallium (Figure ). A similar cluster (T5) was used in previous studies to model the zeolite framework. ,− We are quite aware of the limitations of this cluster model. Indeed, several approaches using embedding techniques, , periodic DFT calculations, , and different ONIOM , schemes have been described in the literature.…”

Section: Models and Computational Detailsmentioning

confidence: 99%

“…A DFT method was chosen because very reasonable results can be obtained at relatively low computational costs. The B3LYP functional has been largely used in other calculations, − including some with gallium atoms, , providing, among the presently available functionals, the best description of these reactions. The LACVP basis set has already been used in a previous work, and the use of the ECP caused an increase no greater than 2 kcal/mol in the computed energies, which is less than the limit of accuracy of the present level of theory.…”

Section: Models and Computational Detailsmentioning

confidence: 99%

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Theoretical Study on the Dehydrogenation Reaction of Alkanes Catalyzed by Zeolites Containing Nonframework Gallium Species

Pereira

Nascimento

2006

J. Phys. Chem. B

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The dehydrogenation reaction of light alkanes in gallium-containing zeolites was studied by using density functional theory (DFT) and a nonframework gallium species in the dihydridegallium ion form. Two different mechanisms were considered: a 3-step mechanism and a 1-step concerted mechanism. The reactions occurring through the 3-step mechanism showed smaller activation barriers than the ones following the concerted mechanism. However, the energy barrier for the 3-step mechanism seems to be more influenced by the size and type (linear or branched) of the hydrocarbon chain and demands major conformational rearrangement, which could be hampered by the zeolite framework, especially for larger and/or branched hydrocarbons. On the other hand, the concerted mechanism seems to be much less dependent on the substrates geometry. Therefore, the concerted mechanism could be preferential when dealing with larger and/or branched alkanes.

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Section: Models and Computational Detailsmentioning

confidence: 99%

Section: Models and Computational Detailsmentioning

confidence: 99%

Theoretical Study on the Dehydrogenation Reaction of Alkanes Catalyzed by Zeolites Containing Nonframework Gallium Species

Pereira

Nascimento

2006

J. Phys. Chem. B

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“…The conformational and dynamic behavior of adsorbed molecules within zeolites is fundamentally important because the behavior of this type can have a significant effect on the adsorption and diffusion properties of guest molecules as well as the subsequent chemistry within these systems. Detailed knowledge of the adsorption of n -alkanes in zeolites is of considerable practical interest in petrochemical applications, since zeolites are widely employed for acid-catalyzed reactions involving n -alkanes . Adsorption of n -alkanes in zeolites has been the subject of a large number of studies; − however, most of these studies are computational simulations .…”

Section: Introductionmentioning

confidence: 99%

Investigations of the Adsorption of n-Pentane in Several Representative Zeolites

2006

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We have examined the adsorption of n-pentane in several representative zeolites such as silicalite (MFI), ferrierite (FER), zeolite L (LTL), and faujasite zeolites with FAU structure including siliceous Y (Si-Y) and Na-Y by using FT-Raman spectroscopy in combination with thermogravimetric analysis (TGA) with particular attention being paid to the conformational and dynamic behavior of the guest molecule. The results indicate that the framework topology mainly dictates the conformation of n-pentane in a zeolite. For the zeolites with channel systems such as silicalite, ferrierite, and zeolite L, the population of the all-trans conformer increases upon loading, given that the geometry of the isomer fits better in the channel. When n-pentane is adsorbed in zeolites with a large cavity, such as Si-Y and Na-Y, the distribution of the all-trans (TT) and trans-gauche (TG) conformers is similar to that of pure liquid, suggesting that the large supercage in the framework imposes minimal effect on the conformational equilibrium. The dynamics of the guest molecule is, however, influenced significantly by the existence of cations. Adsorption of n-pentane in a siliceous framework such as silicalite and Si-Y results in extensive molecular motion at room temperature, the degree of which decreases with decreasing temperature. In zeolites ferrierite, L, and Na-Y, the presence of cations in the framework markedly hinders the overall molecular motion. The cations clearly play a role in the observed static disorder of the guest molecule in zeolite L. Important information regarding the location of the n-pentane molecules within silicalite and ferrierite is also obtained.

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“…Modern heterogeneous catalysis methodologies currently grant researchers the capacity to zoom in to nanoscale levels, investigate, and gain insights that are translatable to the macroscale performance. − These insights help to provide a greater understanding of the activity at the catalyst–reactant interface, and all of this fundamental knowledge helps to design more efficient catalysts. − A major component of such investigations is computational studies; however, computational results still diverge from those obtained experimentally. These deviations are especially noticeable when important results such as adsorption energies, desorption temperatures, measured coverages, vibrational frequencies, etc., are compared when obtained using these two avenues. − Such discrepancies are due to critical knowledge gaps in computational catalysis, with two of the major factors being (1) accurately capturing coverage effects and (2) accounting for multifaceted effects present on catalyst nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

Coverage- and Facet-Dependent Multiscale Modeling of O* and H* Adsorption on Pt Catalytic Nanoparticles

Omoniyi,

Hensley

2024

J. Phys. Chem. C

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Within computational heterogeneous catalysis, two critical factors exist�coverage and multifaceted effects�which are challenging to incorporate and contribute to differences between the results obtained from computational and experimental studies. Such disparities exist when significant adsorbate−adsorbate interactions are present, particularly when coupled with computationally limited facet sampling. Here, we designed a study to demonstrate the significance of coverage and facet effects on the predicted coverages for O* and H* on Pt nanoparticles. This is accomplished by employing multiscale modeling techniques using a three-pronged approach consisting of density functional theory (DFT), ab initio phase diagrams, and mean-field microkinetic models. Overall, adsorbate−adsorbate interactions are repulsive and far stronger for O*/Pt than for H*/Pt. For O* on Pt(111), repulsive interactions are both two-and three-body, but on Pt(100) and Pt(110), they are predominantly three-body. Through benchmarks to existing experimental literature, we demonstrate that experimentally observed coverages and desorption temperatures can be accurately estimated by computational models when the adsorbate−adsorbate interactions are included. Finally, by combining microkinetic models at the equilibrium limit with kubic harmonic interpolation, we model the impacts of the treatment of adsorbate−adsorbate interactions on the predicted O* and H* coverages over multifaceted Pt nanoparticles. Omitting adsorbate− adsorbate interactions over Pt nanoparticles leads to an overestimation of equilibrium coverages of the adsorbates (maximum of 0.29 and 0.11 ML for O* and H*, respectively) across a wide range of temperatures and pressures relevant to heterogeneous catalysis. Altogether, our work demonstrates that the inclusion of coverage and facet effects increases the accuracy of computational models for heterogeneous catalysts.

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Chemical Reactions of Alkanes Catalysed by Zeolites

Cited by 3 publications

References 58 publications

Theoretical Study on the Dehydrogenation Reaction of Alkanes Catalyzed by Zeolites Containing Nonframework Gallium Species

Theoretical Study on the Dehydrogenation Reaction of Alkanes Catalyzed by Zeolites Containing Nonframework Gallium Species

Investigations of the Adsorption of n-Pentane in Several Representative Zeolites

Coverage- and Facet-Dependent Multiscale Modeling of O* and H* Adsorption on Pt Catalytic Nanoparticles

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