Untitled

Smith, Luis J.; Davidson, Anne; Cheetham, Anthony K.

doi:10.1023/a:1019097019846

Cited by 131 publications

(165 citation statements)

References 10 publications

Supporting

Mentioning

134

Contrasting

Unclassified

Order By: Relevance

“…We have calculated anharmonic frequencies for the zeolite OH stretch vibration in the presence of water in the range of 2170-2500 cm Ϫ1 . The frequencies for the acid proton H 3 in the 8T ring are close to the experimental value 27 of 2403 cm Ϫ1 in the spectra of hydrated H-SSZ-13. The frequency for the same proton in the open 7T cluster is close to the experimental value 10,48,49 of The two proton position in the 8T ring and the open 7T cluster have different environments which affects the adsorption geometry of the complex with water and the OH stretch vibration frequencies.…”

Section: Watersupporting

confidence: 84%

“…The experimentally found 27 and theoretically predicted 18,20,[37][38][39][40] preferred positions for the acid protons in chabazite are oxygen atoms O 1 and O 3 . In the present study we will concentrate on them.…”

Section: A Zeolite Cluster Without Adsorbatementioning

confidence: 77%

“…An example of a zeolite with different hydroxyl groups is chabazite. In the IR spectra two different proton position are observed 27 with a difference in the OH stretch frequencies of 24 cm Ϫ1 . As there is only one possible Si→Al substitution the protons are bound to oxygen atoms from the same Al tetrahedron.…”

Section: Introductionmentioning

confidence: 97%

See 2 more Smart Citations

The heterogeneity of the hydroxyl groups in chabazite

Mihaleva

Santen

Jansen

2003

The Journal of Chemical Physics

View full text Add to dashboard Cite

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.

show abstract

Section: Watersupporting

confidence: 84%

Section: A Zeolite Cluster Without Adsorbatementioning

confidence: 77%

See 1 more Smart Citation

The heterogeneity of the hydroxyl groups in chabazite

Mihaleva

Santen

Jansen

2003

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…The value of the stretch frequency in the 8T ring is in a good agreement with the experimental frequency of 3579 cm Ϫ1 for chabazite. 22 The corresponding value in the 7T cluster is 60 cm Ϫ1 higher and falls in the interval where the OH stretch frequency of H-ZSM-5 ͑Ref. 4͒ and mordenite ͑Ref.…”

Section: Figmentioning

confidence: 95%

“…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. When water is adsorbed on H-ZSM-5, [1][2][3][4][5][6]21 HY, 7 H-MOR, 4 or chabazite 22 a triplet of bands appears at 2872-3000, 2403-2515, and 1700 cm Ϫ1 , known also as an ABC triplet. This triplet is accompanied by two peaks at 3700 and 3550 cm Ϫ1 .…”

Section: Introductionmentioning

confidence: 99%

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

View full text Add to dashboard Cite

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.

show abstract

Solids: Characterization by Powder DiffractionBased in part on the article Solids: Characterization by Powder Diffraction by Anthony K. Cheetham which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

Vogt

2005

Encyclopedia of Inorganic Chemistry

View full text Add to dashboard Cite

This review article covers recent developments in X‐ray and neutron powder diffraction with an emphasis on the complementary nature of these two condensed matter probes. After a short summary of the basics of X‐ray and neutron scattering, examples of ‘mesoscopic’ structure investigations (i.e. particle size, strain) are presented followed by state‐of‐the‐art combined neutron and X‐ray high‐resolution powder diffraction studies of ‘real’ catalysts. Neutron and X‐ray powder diffraction studies in magnetic fields are highlighted and the reemergence of the total scattering approach using pair‐distribution function (PDF) analysis within the context of ‘nanocrystallography’ is discussed. Modern examples of high‐pressure crystallography using X‐ray and neutrons are given. A short outlook considers future directions in light of nanoscience and new X‐ray and neutron sources.

show abstract

Untitled

Cited by 131 publications

References 10 publications

The heterogeneity of the hydroxyl groups in chabazite

The heterogeneity of the hydroxyl groups in chabazite

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

Solids: Characterization by Powder DiffractionBased in part on the article Solids: Characterization by Powder Diffraction by Anthony K. Cheetham which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

Contact Info

Product

Resources

About