Quantum chemical calculations of the physical characteristics of the hydroxyl groups of zeolites

Dubský, J. V.; Beran, S.; Bosáček, V.

doi:10.1016/0304-5102(79)85007-5

Cited by 35 publications

(8 citation statements)

References 20 publications

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“…42 Interestingly, we find the O1-site in FAU very close in energy to the O3-site, closer than in any previous computational study. 26,[43][44][45] The energy difference found here (1 kJ/mol) is in complete agreement with the experimental difference calculated from relative occupancy.…”

Section: Resultssupporting

confidence: 83%

Zeolite Structure and Reactivity by Combined Quantum-Chemical−Classical Calculations

et al. 1999

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Proton-energy differences, ammonia adsorption, and D/H-exchange barriers for methane at selected isolated Brønsted sites in zeolites FAU, MFI, BEA, ERI, and CHA are studied by combined quantum-chemicalclassical (QM/MM) calculations in an attempt to understand the factors that determine the reactivity at these Brønsted sites. The barrier of the D/H-exchange reaction for methane was found to correlate well with the calculated ammonia chemisorption energy, but even better with the O-Al-O angle of the free zeolite Brønsted site the reaction is taking place on, provided the Si-O-Al-O-Si moiety over which the reaction takes place is more or less collinear. The barrier is considerably higher if this collinearity is weaker, which may be explained by the necessity of costly backbone distortions to accommodate the geometrical requirements of the transition state. This is confirmed by similarly strong correlations with the O-Al-O angle change going from the free acid site to zeolite-ammonium ion bidentate structures, which may be thought of as a measure of the backbone distortion. A new measurement of the D/H-exchange barrier in BEA is also reported. It was found to be 88 ( 18 kJ/mol, lower than the experimental barriers in both FAU and MFI.

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Section: Resultssupporting

confidence: 83%

Zeolite Structure and Reactivity by Combined Quantum-Chemical−Classical Calculations

et al. 1999

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“…A few theoretical studies have investigated the question of proton siting in H-zeolite Y. [23][24][25] All studies are in agreement with our embedded cluster results, predicting the proton to be more stable at site O1 than O4 by: 51 kJ/mol, using CNDO/2 semiempirical method; 23 18.4 kJ/mol, performing lattice energy minimizations with shell model potentials; 24 and 54.1 kJ/mol, performing lattice energy minimizations with van Santen et al's potential parameters. 25 A recent neutron powder diffraction studies has been able to directly determine the positions and occupations of the proton sites in H-zeolite Y.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, we also examine the proton siting in H-zeolite Y in comparison to neutron and X-ray diffraction studies, 20-22 as well as theoretical studies. [23][24][25] …”

Section: Introductionmentioning

confidence: 99%

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

and

Truong

2000

J. Phys. Chem. B

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We present ab initio embedded cluster studies on the mechanism of hydrogen exchange of methane with H-Zeolite Y. We found that inclusion of the Madelung field stabilizes the formation of a carbonium-like transition state, and consequently reduces the reaction barrier by 17-23 kJ/mol, relative to the corresponding bare cluster predictions. Using the CCSD(T)/6-31G(d,p) level of theory, including zero-point energy (∼10 kJ/mol) and tunneling (1.6 kJ/mol) corrections, the activation energy is predicted to be 124 ( 5 and 137 ( 5 kJ/mol for hydrogen exchange from two different binding sites. These predictions agree well with the experimental estimate of 122-130 kJ/mol. We also found that it is necessary to include the Madelung potential to find preferrential proton siting at site O1 versus site O4, in agreement with experimental observation.

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“…However, it is in the field of the heterogeneous catalysis that the most important applications of these materials [3] can be found. In their protonated forms, zeolites are widely employed in the oil and petrochemical industries, in processes such as the conversion of alcohols to gasoline, catalytic cracking, isomerization and alkylation of hydrocarbons [3][4][5]. These chemical reactions most probably involve proton transfer from the acidic site of the zeolite to the organic substrate.…”

Section: Introductionmentioning

confidence: 99%

The Dehydrogenation Reaction of Light Alkanes Catalyzed by Zeolites

Furtado¹,

Milas²,

LINS³

et al. 2001

phys. stat. sol. (a)

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The several steps of the dehydrogenation reactions of ethane, propane and isobutane were studied by theoretical methods. Molecular dynamics simulation techniques have been used to study diffusion of the alkanes through the zeolite HZMS-5 framework. Adsorption energies were computed by the methods of molecular mechanics, molecular dynamics and Monte-Carlo. Molecular dynamics was also used to determine the preferred adsorption sites of the alkanes in silicalite and HZMS-5. The mechanism of the chemical reactions at the zeolite's acid site was investigated at the DFT(B3LYP) level of calculation using 6-31G ** and 6-311G ** basis sets, and 3 and 5 T cluster models to represent the zeolite. GIAO/B3LYP calculations were performed on the 3 and 5 T alkyalkoxides and the results were compared with experimental 13 C NMR data.

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Quantum chemical calculations of the physical characteristics of the hydroxyl groups of zeolites

Cited by 35 publications

References 20 publications

Zeolite Structure and Reactivity by Combined Quantum-Chemical−Classical Calculations

Zeolite Structure and Reactivity by Combined Quantum-Chemical−Classical Calculations

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

The Dehydrogenation Reaction of Light Alkanes Catalyzed by Zeolites

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