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Title: Determination of structure and acidity scales in zeolite systems by ab initio and pseudopotential calculations

Abstract

SCF ab initio calculations at the 6-31G level have been used to investigate the structure of several aggregates simulating some of the proton donor sites within faujasite-type zeolites. The Si(OH)/sub 4/, H/sub 3/SiOHAlH/sub 3/, and (OH)/sub 3/SiOHAl(OH)/sub 3/ clusters have been successively examined. Deprotonation energies and charge distribution are determined at a higher level by using a 6-31G basis set augmented with polarization and diffuse functions. The results are compared with values obtained by using pseudopotential methods. The small differences between the two sets of results demonstrate that comparable accuracy should be expected from both procedures. Finally, deprotonation energies of (OH)/sub 3/T/sub 1/OHT/sub 2/(OH)/sub 3/ aggregates (T/sub 1/, T/sub 2/ = AlSi, BSi, GaSi; AlGe, BGe, GaGe) are calculated by using pseudopotential methods and compared with the results given by the semiempirical MNDO method. In some cases ab initio SCF calculations were also performed. The results confirm that the inclusion of boron atom lowers the acidity as already demonstrated by experimental investigation. The effects due to the inclusion of Ga are discussed and compared to available experimental data.

Authors:
; ;
Publication Date:
Research Org.:
Universite Pierre et Marie Curie, Paris (France)
OSTI Identifier:
5994467
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Phys. Chem.; (United States); Journal Volume: 92:23
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALUMINIUM HYDRIDES; STRUCTURAL CHEMICAL ANALYSIS; BORON HYDROXIDES; GERMANIUM HYDROXIDES; SILANES; SILICON HYDROXIDES; BOND ANGLE; BOND LENGTHS; CATALYSIS; CATALYSTS; COMPLEXES; CRYSTAL STRUCTURE; HYDROGEN TRANSFER; PH VALUE; POTENTIALS; SELF-CONSISTENT FIELD; THEORETICAL DATA; ZEOLITES; ALUMINIUM COMPOUNDS; BORON COMPOUNDS; DATA; DIMENSIONS; GERMANIUM COMPOUNDS; HYDRIDES; HYDROGEN COMPOUNDS; HYDROXIDES; INFORMATION; INORGANIC ION EXCHANGERS; ION EXCHANGE MATERIALS; LENGTH; MATERIALS; MINERALS; NUMERICAL DATA; ORGANIC COMPOUNDS; ORGANIC SILICON COMPOUNDS; OXYGEN COMPOUNDS; SILICON COMPOUNDS; 400201* - Chemical & Physicochemical Properties

Citation Formats

Kassab, E., Seiti, K., and Allavena, M. Determination of structure and acidity scales in zeolite systems by ab initio and pseudopotential calculations. United States: N. p., 1988. Web. doi:10.1021/j100334a043.
Kassab, E., Seiti, K., & Allavena, M. Determination of structure and acidity scales in zeolite systems by ab initio and pseudopotential calculations. United States. doi:10.1021/j100334a043.
Kassab, E., Seiti, K., and Allavena, M. Thu . "Determination of structure and acidity scales in zeolite systems by ab initio and pseudopotential calculations". United States. doi:10.1021/j100334a043.
@article{osti_5994467,
title = {Determination of structure and acidity scales in zeolite systems by ab initio and pseudopotential calculations},
author = {Kassab, E. and Seiti, K. and Allavena, M.},
abstractNote = {SCF ab initio calculations at the 6-31G level have been used to investigate the structure of several aggregates simulating some of the proton donor sites within faujasite-type zeolites. The Si(OH)/sub 4/, H/sub 3/SiOHAlH/sub 3/, and (OH)/sub 3/SiOHAl(OH)/sub 3/ clusters have been successively examined. Deprotonation energies and charge distribution are determined at a higher level by using a 6-31G basis set augmented with polarization and diffuse functions. The results are compared with values obtained by using pseudopotential methods. The small differences between the two sets of results demonstrate that comparable accuracy should be expected from both procedures. Finally, deprotonation energies of (OH)/sub 3/T/sub 1/OHT/sub 2/(OH)/sub 3/ aggregates (T/sub 1/, T/sub 2/ = AlSi, BSi, GaSi; AlGe, BGe, GaGe) are calculated by using pseudopotential methods and compared with the results given by the semiempirical MNDO method. In some cases ab initio SCF calculations were also performed. The results confirm that the inclusion of boron atom lowers the acidity as already demonstrated by experimental investigation. The effects due to the inclusion of Ga are discussed and compared to available experimental data.},
doi = {10.1021/j100334a043},
journal = {J. Phys. Chem.; (United States)},
number = ,
volume = 92:23,
place = {United States},
year = {Thu Nov 17 00:00:00 EST 1988},
month = {Thu Nov 17 00:00:00 EST 1988}
}
  • {ital Ab} {ital initio} pseudopotential calculations are performed for the electronic structure of the low-{ital T}{sub {ital c}} intermetallics LuNi{sub 2}B{sub 2}C and the related nonsuperconducting compound LuNiBC. Electronic structures of the two compounds are compared in great detail, especially in terms of the Fermi surfaces and the symmetry-decomposed density of states (DOS) near the Fermi level. The estimated electron-phonon coupling constant {lambda} (0.8--1.1) from the heat-capacity data as well as from the calculated DOS at {ital E}{sub {ital F}} indicates that {ital T}{sub {ital c}} of LuNi{sub 2}B{sub 2}C is reasonably well explained by the conventional Bardeen-Cooper-Schrieffer mechanism withmore » intermediate coupling strength. The relatively high {ital T}{sub {ital c}} arises from the large DOS at the Fermi level. Absence of superconductivity in LuNiBC may be understood to be due to the reduced DOS at {ital E}{sub {ital F}}. Unlike the high-{ital T}{sub {ital c}} cuprates, the low-{ital T}{sub {ital c}} LuNi{sub 2}B{sub 2}C does not have the half-filled {sigma}-antibonding bands and its electronic structure is almost three dimensional despite the layered atomic structure.« less
  • There is no abstract currently available for this item
  • Density functional calculations are performed on M{sub 3}(OH){sub 7}(H{sub 2}O){sub 6}{sup 2+} and M{sub 3}O(OH){sub 6}(H{sub 2}O){sub 6}{sup +} clusters for M {double_bond} Al, Cr(III), and Fe(III), allowing determination of the relative acidities of the {mu}{sub 3}-hydroxo and aquo functional groups. Contrary to previous predictions and rationalizations, {double_bond}Fe{sub 3}OH and {double_bond}Al{sub 3}OH groups have nearly the same intrinsic acidity, while {double_bond}Cr{sub 3}OH groups are significantly more acidic. The gas-phase acidity of the Fe{sub 3}OH site is in good agreement with the value predicted by the molecular mechanics model previously used to estimate the relative acidities of surface sites on ironmore » oxides. Acidities of aquo functional groups were also computed for Al and Cr. The {double_bond}AlOH{sub 2} site is more acidic than the {double_bond}Al{sub 3}OH site, whereas the {double_bond}Cr{sub 3}OH site is more acidic than the {double_bond}CrOH{sub 2} site. These findings predict that the surface charging behavior of chromium oxides/oxyhydroxides should be distinguishable from their Fe, Al counterparts. The calculations also provide insight into why the lepidocrocite/boehmite polymorph is not observed for CrOOH.« less
  • The {ital ab} {ital initio} pseudopotential method was used to study the boron diffusion and pairing process in crystalline silicon. The results show that substitutional B attracts interstitial Si with a binding energy of 1.1 {plus_minus} 0.1 eV. We show that B diffusion is significantly enhanced in the presence of the Si interstitial due to the substantial lowering of the migrational barrier through most likely a kick-out mechanism. The resulting mobile boron can also be trapped by another substitutional boron with a binding energy of 1.8 {plus_minus} 0.1 eV, forming an immobile and electrically inactive two-boron pair along a {l_angle}001{r_angle}more » direction. It is also found that the pairing of these two boron atoms involves the trapping of a Si interstitial. Alternatively, two B pairs that do not trap the Si interstitial were found to be energetically unfavorable. All of these findings are consistent with experimental results. {copyright} {ital 1996 The American Physical Society.}« less
  • Ab initio pseudopotential total-energy calculations on infinite monatomic chains of Au, Al, Ag, Pd, Rh, and Ru were performed within the local-density approximation. We used the frozen phonon approximation to study the stability of these chains as a function of strain. Within a window of strains the au, Al, Ag, Pd, and Rh linear chains are stable with respect to q=pi/a deformations. For large strains all the chains dimerize. All the chains exhibit at least one zero-strain zigzag stable equilibrium configuration, and Au, Al, and Rh zigzag chains exhibit two. The ideal strengths of the different chains were calculated. Themore » stability of the chains is discussed in connection with the electronic structure.« less