Ab initio SCF–MO study of the topology of the charge distribution of acid sites of zeolites

Soscún, Humberto; Hernández, Javier; Castellano, Olga; Díaz, Gilberto; Hinchliffe, Alan

doi:10.1002/(sici)1097-461x(1998)70:4/5<951::aid-qua41>3.3.co;2-x

Cited by 2 publications

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“…25,43 The charge on the H atom and the oxygen atom of the Brønsted sites can be used to study the acidity. [44][45][46][47][48] A high charge on the H atom corresponds to a high acidity. [44][45][46][47][48] For all cluster models containing two Al atoms, the charge on Hb is higher than that on Ha.…”

Section: Resultsmentioning

confidence: 99%

“…[44][45][46][47][48] A high charge on the H atom corresponds to a high acidity. [44][45][46][47][48] For all cluster models containing two Al atoms, the charge on Hb is higher than that on Ha. This is consistent with previous analysis: the interaction between the oxygen atom of PdO and Ha is stronger than that between the oxygen atom of PdO and Hb.…”

Section: Resultsmentioning

confidence: 99%

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DFT Study of Structural and Electronic Properties of PdO/HZSM-5

Wang¹,

Liu²,

Fang³

et al. 2004

J. Phys. Chem. B

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A density functional theory (DFT) study has been conducted to investigate the structural and electronic properties of PdO/HZSM-5 and thereby the relationship between PdO and the acid sites of HZSM-5. Different cluster models of PdO/HZSM-5 based on experimental and theoretical works are presented. The study shows that the local structure of PdO supported on HZSM-5 is very similar to the four-coordinated square planar structure of bulk PdO. This is consistent with the reported EXAFS analysis in the literature. The average distances between the Pd and the four coordinated oxygen atoms obtained by DFT calculations with different cluster models are close to the reported experimental results. The analysis of the Mulliken population and the electron density difference of the cluster models shows that there exists a charge transfer from the four coordinated oxygen atoms to the Pd. The components of the frontier molecular orbital of these cluster models come mainly from the Pd and the four coordinated oxygen atoms. The DFT study confirms that the acid sites in HZSM-5 keep the PdO well dispersed due to the bond interaction between the acidic proton atom and the oxygen atom of PdO. In addition, after the formation of PdOH + , the acidity of HZSM-5 complex remains high or in some instances increases.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

DFT Study of Structural and Electronic Properties of PdO/HZSM-5

Wang¹,

Liu²,

Fang³

et al. 2004

J. Phys. Chem. B

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“…The B 1 OH model is similar to the B 1 cluster, where OH groups substitute the terminal H atoms of Si and Al ones. The B 2 model is a well‐know cluster 4, 12.…”

Section: Resultsmentioning

confidence: 99%

“…These zeolite acid sites were represented as H 3 Si(OH)AlH 3 (B 1 ), (OH) 3 Si(OH)Al(OH) 3 (B 1 OH), and the H 3 Si(OH)Al(OH) 2 OSiH 3 (B 2 ). Structural, electronic, and topologic properties of these isolated molecular species have been reported elsewhere 4.…”

Section: Introductionmentioning

confidence: 98%

Theoretical study of the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and Brönsted acid sites of zeolites

Soscún

Castellano

Hernández

et al. 2001

Int J of Quantum Chemistry

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ABSTRACT:The main interaction between thiophene and zeolites leads to the formation of a hydrogen bond between the S atom of thiophene and the OH group of zeolites, giving 1:1 stable molecular complexes. The present work reports a theoretical study about the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and a series of Brönsted acid sites of zeolites, modeled as the H 3 SiOHAlH 3 (B 1 ), (OH) 3 Si(OH)Al(OH) 3 (B 1 OH), and H 3 Si(OH)Al(OH) 2 OSiH 3 (B 2 ) clusters. The studied properties were calculated at a Hartree-Fock level with the standard 6-31+G(d,p) basis set. Additionally, electron correlation effects for geometric and vibrational properties were evaluated at second-order Møller-Plesset (MP2) and BLYP for B 1 -thiophene complex, whereas the BLYP technique was employed for the complexes of thiophene with B 1 OH and B2 clusters. Symmetry restriction was considered for structure calculations, being C 2v for thiophene, C s for zeolite clusters, and C s linear conformation for the complexes. It was found that these linear thiophene-zeolite complexes reproduce the tendencies in the experimental frequency shifts of the OH vibration mode from the adsorption of thiophene in ZSM5 zeolites. The topologic properties of the complexes give a pattern for the interaction of

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Ab initio SCF–MO study of the topology of the charge distribution of acid sites of zeolites

Cited by 2 publications

References 0 publications

DFT Study of Structural and Electronic Properties of PdO/HZSM-5

DFT Study of Structural and Electronic Properties of PdO/HZSM-5

Theoretical study of the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and Brönsted acid sites of zeolites

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