An assessment of density functional methods for studying molecular adsorption in cluster models of zeolites

Zygmunt, Stan; Mueller, Rachel M.; Curtiss, Larry A.; Iton, Lennox E.

doi:10.1016/s0166-1280(98)90205-6

Cited by 74 publications

(69 citation statements)

References 49 publications

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“…The anharmonicities are large and from a one-dimensional calculations we have estimated an anharmonic downward shift of the zeolite OH stretch frequencies in the interval of 466 -551 cm Ϫ1 . Previous theoretical studies 13,17,31 have shown a protonated water molecule to be a transition state that connects two almost equivalent hydrogen-bonded minima with the activation energy being 15-26 kJ/mol. Such a low activation energy should be treated as a double-well potential.…”

Section: B Dynamicsmentioning

confidence: 99%

“…During the last decade, adsorption of water on zeolites has been extensively studied both experimentally [1][2][3][4][5][6][7][8] and theoretically [9][10][11][12][13][14][15][16][17][18][19][20] in order to understand the nature of the interaction of basic molecules with the Brøn-sted sites in the zeolites. The reaction can be studied by infrared spectroscopy because the frequencies of the vibrations of the zeolite hydroxyl group will change upon interaction with the water molecule.…”

Section: Introductionmentioning

confidence: 99%

“…Theoretical models have been made by representing the zeolite by clusters consisting of several tetrahedral atoms, [9][10][11][12][13][14][15][16][17] and a hydrogen-bonded water molecule was found to be a minimum on the potential energy surface and a protonated water molecule to be a transition state. The molecular dynamics of water in sodalite 18 and H-SAPO-34 ͑Refs.…”

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confidence: 99%

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Quantum chemical calculation of infrared spectra of acidic groups in chabazite in the presence of water

Mihaleva¹,

Santen

Jansen

2004

The Journal of Chemical Physics

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The changes in the spectra of the acidic group in chabazite are studied by quantum chemical calculations. The zeolite is modeled by two clusters consisting of eight tetrahedral atoms arranged in a ring and seven tetrahedral atoms coordinated around the zeolite OH group. The potential energy and dipole surfaces were constructed from the zeolite OH stretch, in-plane and out-of-plane bending coordinates, and the intermolecular stretch coordinate that corresponds to a movement of the water molecule as a whole. Both the anharmonicities of the potential energy and dipole were taken into account by calculation of the frequencies and intensities. The matrix elements of the vibrational Hamiltonian were calculated within the discrete variable representation basis set. We have assigned the experimentally observed frequencies at ϳ2900, ϳ2400, and ϳ1700 cm Ϫ1 to the strongly perturbed zeolite OH vibrations caused by the hydrogen bonding with the water molecule. The ABC triplet is a Fermi resonance of the zeolite OH stretch mode with the overtone of the in-plane bending ͑the A band͒ and the overtone of the out-of-plane bending ͑the C band͒. In the B band the stretch is also coupled with the second overtone of the out-of-plane bending. The frequencies at ϳ3700 and ϳ3550 cm Ϫ1 we have assigned to the OH stretch frequencies of a slightly perturbed water molecule.

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Section: B Dynamicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Quantum chemical calculation of infrared spectra of acidic groups in chabazite in the presence of water

Mihaleva¹,

Santen

Jansen

2004

The Journal of Chemical Physics

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“…Cluster calculations as described above have been shown to give good results for the interaction of molecules with zeolites. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In the calculations of the shifts of the frequency of the zeolite OH stretch vibration the anharmonicity has been included. This has been done by representing the potential energy in the 1-dimensional vibrational Hamiltonian by a polynomial:…”

Section: Computational Detailsmentioning

confidence: 99%

“…The adsorption of water and methanol has been studied both on clusters [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] representing a small part of the zeolite and in periodic calculations [19][20][21][22][23][24][25][26] including the zeolite crystal structure. The role of the zeolite structure on the activation of methanol has been studied in periodic approach but the conclusions are somewhat contradictory.…”

Section: Introductionmentioning

confidence: 99%

The heterogeneity of the hydroxyl groups in chabazite

Mihaleva

Santen

Jansen

2003

The Journal of Chemical Physics

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Two different clusters that have the topology of chabazite but different shapes have been used as a model for the Brønsted sites in chabazite. One of the clusters consists of eight tetrahedral atoms ͑8T͒ arranged in a ring and the other represents an intersection of two 8T rings. The adsorption of water and methanol on the two stable proton positions in chabazite has been studied using the B3LYP functional. The coordination of water and methanol with respect to the zeolite fragments were found to be similar, but with methanol situated closer to the acid site than water. The anharmonic zeolite OH stretch frequencies were found to be in the range of 2170-2500 cm Ϫ1 and 1457-2074 cm Ϫ1in the presence of water and methanol, respectively. As a measure of the acidity of the bridging hydroxyl groups in chabazite the shift of the zeolite OH stretch frequency upon adsorption has been used. We have found that the proton attached to the oxygen atom O 1 to be more acidic than the proton attached to the oxygen atom O 3 . Also, in the closed ring clusters the zeolite hydroxyl groups are more acidic than in the open clusters. This is not due to a steric effect as the orientation of the adsorbates with respect to the zeolite site is very similar for both clusters. The anharmonicities of the zeolite O-H bond account for about 40% in the redshift upon the adsorption of water or methanol.

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