Mechanisms of Hydrogen Exchange of Methane with H-Zeolite Y:  An ab Initio Embedded Cluster Study

and, James M. Vollmer; Truong, Thanh N.

doi:10.1021/jp0008445

Cited by 51 publications

(46 citation statements)

References 35 publications

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“…While several papers have reported quantum calculations concerning the energetics of hydrogen exchange between methane and zeolitic protons 19,20,21 , the use of quantum-chemical calculations to interpret the infrared spectrum of adsorbed CH 4 has not been previously described.…”

Section: Introductionmentioning

confidence: 99%

“…More commonly, however, only the electrostatic contribution of the zeolite lattice is included in the Hamiltonian for a cluster that is treated quantum mechanically. 21,32 One of the simplest and most accurate methods for including the electrostatic field of an infinite solid into the Hamiltonian of a cluster model is that developed by Stefanovich and…”

mentioning

confidence: 99%

“…33 The periodic-boundary, ab initio calculations for a purely siliceous zeolite framework. 21,34,35,36,37 The second set of charges is placed on a closed surface that encloses the quantum mechanically treated atoms. These charges, referred to as "surface" charges, are needed to reproduce the potential of the infinite crystal.…”

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confidence: 99%

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An Experimental and Density Functional Theory Study of the Interactions of CH₄ with H−ZSM-5

2001

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The interactions of methane with Brønsted acid sites in H-ZSM-5 were investigated both experimentally and theoretically. Diffuse reflectance infrared spectroscopy was used to acquire spectra for methane adsorbed on H-ZSM-5 at room temperature and at 77 K. Upon adsorption, the n 1 and n 3 vibrational bands of methane shift by -15 cm -1 and -23 cm -1 , respectively, and the vibrational band for OH groups associated with Brønsted acid sites shifts by -93 cm -1 . Quantum chemical calculations conducted at the DFT level of theory with a 6-31g**++ basis set show that the observed shifts for methane are attributable to the effects of the electrostatic field created by the atoms of the zeolite. To represent the influence of the zeolite on the adsorbed methane correctly, it is essential to take into account the effects of the Madelung field, as well as the local effects of the acid center. The calculated shift in the vibrational frequency of the bridging OH group lies within the range observed experimentally. However, the quantitative agreement of the calculated and observed shift is not as good as that seen for the bands of CH 4 .3

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Section: Introductionmentioning

confidence: 99%

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An Experimental and Density Functional Theory Study of the Interactions of CH₄ with H−ZSM-5

2001

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“…In the late 1960s Hogeveen and co-workers [8] reported an activation energy of 75 kJ mol À1 for the inverse reaction of dedeuteration of CH 3 D in HF/SbF 5 at high pressure (7 atm) over a temperature interval from À 10 8C to 258C. This apparent activation energy for the H/D exchange reaction between methane and D 2 SO 4 is also substantially higher than on zeolites (120 to 150 kJ mol À1 ) [9,28,29] and different sulfated zirconias (93 to 96 kJ mol À1 ). [27] Computational results: To better understand the isotope exchange process observed experimentally, we have also investigated the hydrogen exchange between sulfuric acid (1) and methane (3) According to the DFT calculations, methane forms a weak complex (4) with sulfuric acid (Figure 4).…”

Section: Resultsmentioning

confidence: 99%

Methane Activation and Oxidation in Sulfuric Acid

et al. 2002

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In a versatile modular scaffold system, gradient nonwovens of in situ crosslinked gelatin nanofibers (CGN), fabricated by reactive electrospinning, are laminated with perforated layers and nonwovens of thermoplastic non‐crosslinked biodegradable polyesters. The addition of glyoxal to a gelatin solution in a non‐toxic solvent mixture consisting of acetic acid, ethyl acetate, and water (5:3:2 w/w/w) enables the in situ crosslinking of gelatin nanofibers during electrospinning. The use of this fluorine‐free crosslinking system eliminates the need of post‐treatment crosslinking and purification steps typical for conventional CGN scaffolds. The slowly progressing crosslinking of the dissolved gelatin in the presence of glyoxal increases the viscosity of the gelatin solution during electrospinning so that the average diameter of the crosslinked gelatin nanofibers gradually increases from 90 to 680 nm. During the subsequent lamination process, alternating layers of CGN and polycaprolactone (PCL) nonwovens, produced by 3D microextrusion of micrometer‐sized PCL fibers, are bonded together upon heating above the PCL melting temperature. In contrast to the water‐soluble gelatin nanofibers and the comparatively weak CGN, the CGN/PCL/CGN layered biocomposites are water‐resistant and very robust. In such modular scaffold systems, strength, biodegradation rate, and biological functions can be controlled by varying the type, composition, fiber diameter, porosity, number, and sequence of the individual layers. The CGN/PCL multilayer biocomposites can be cut into any desired scaffold shape and attached to tissue by surgical sutures in order to suit the needs of individual patients.

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“…[33,24,[40][41][42] Much experimental work, often associated with theoretical calculations, has been published [24,[41][42][43][44] in relation to Scheme 2. The direct H/D exchange mechanism.…”

Section: Resultsmentioning

confidence: 99%

Room‐Temperature Alkane Reactivity in Zeolites: An H/D Exchange Study

Sido

Walspurger

Barbiche

et al. 2010

Chemistry A European J

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As evidenced by H/D exchange with acidic zeolites, isoalkanes react readily at room temperature whereas linear alkanes do not. The observed regioselectivity of the exchange process demonstrates that the main factor controlling the reaction is not the accessibility to the acid sites, but the intrinsic reactivity of the alkane. The mechanism is best rationalized by classic organic chemistry involving carbocationic intermediates including the Markovnikov rule.

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Mechanisms of Hydrogen Exchange of Methane with H-Zeolite Y: An ab Initio Embedded Cluster Study

Cited by 51 publications

References 35 publications

An Experimental and Density Functional Theory Study of the Interactions of CH₄ with H−ZSM-5

An Experimental and Density Functional Theory Study of the Interactions of CH₄ with H−ZSM-5

Methane Activation and Oxidation in Sulfuric Acid

Room‐Temperature Alkane Reactivity in Zeolites: An H/D Exchange Study

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Mechanisms of Hydrogen Exchange of Methane with H-Zeolite Y: An ab Initio Embedded Cluster Study

Cited by 51 publications

References 35 publications

An Experimental and Density Functional Theory Study of the Interactions of CH4 with H−ZSM-5

An Experimental and Density Functional Theory Study of the Interactions of CH4 with H−ZSM-5

Methane Activation and Oxidation in Sulfuric Acid

Room‐Temperature Alkane Reactivity in Zeolites: An H/D Exchange Study

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An Experimental and Density Functional Theory Study of the Interactions of CH₄ with H−ZSM-5

An Experimental and Density Functional Theory Study of the Interactions of CH₄ with H−ZSM-5