Browsing by Author "Vedrine, Jacques C."

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Characterization of the Hydroxyls in Offretitc Zeolite
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Mirodatos, Claude; Abou-Kais, Antoine; Vedrine, Jacques C.; Barthomeuf, Denise
It is shown that three structural hydroxyl groups are generated in offretite upon cation exchange. The 3660 cm–1 OH groups are either not acidic or only slightly so and are probably located in the inaccessible hexagonal prism (O6H). The 3610 and 3550 cm–1 hydroxyls are acidic. Their strength increases at low cation content. The 3610 cm–1 groups are mainly located in the channel (O5H) while the low frequency groups are suggested to be in the cancrinite cage (O2H or O4H).
Electron paramagnetic resonance study of hydrogen atoms trapped in γ-irradiated Y type zeolites exchanged with different cations
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Abou-Kais, Antoine; Vedrine, Jacques C.; Massardier, Jean; Dalmai-Imelik, Gisele
H atoms trapped after the γ-irradiation at 77 K of Y type zeolites exchanged with different cations have been studied using e.p.r. spectroscopy. The H atom yield is dependent on the acidic structural OH group content and it is postulated that the mechanism of formation and trapping of H atoms follows the following equilibrium: [graphic omitted] The H atom yield is related to the acidity and mobility of the hydrogen of the hydrogen of the hydroxyl groups and to the trapping strength. The trapping strength of H atoms, characterized by the values of both the hyperfine coupling constant with respect to the free H atom, and the activation energy of recombination, is strongly dependent on the nature of the exchanged cation, and follows the sequence K > Na [double greater-than, compressed] Ca > La.
Study of Surface Atom Behaviour on Pt/SiO2 and Pt/Al2O3 Catalysts by Isotopic Exchange of Oxygen from CO2
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Ducarme, Valentin; Vedrine, Jacques C.
Isotopic exchange of oxygen from CO2 was used to study and characterize the lability of oxygen species at the surface of a catalyst. The catalysts were Pt supported on silica or alumina with several Pt loadings. Pt dispersion could be determined and was found to be in excellent agreement with oxygen-hydrogen titration and electron microscopy. Some surface oxygen species from the support and neighbouring Pt particles were made more labile. This indicates that interaction has occurred between Pt particles and the support, leading to more mobile surface oxygen which may be related to the spill-over effect.
X-ray Photoelectron Spectroscopy Study of Pd and Pt Ions in Type Y-Zeolite: Electron Transfer between Metal Aggregates and the Support as Evidenced by X-ray Photoelectron Spectroscopy and Electron Spin Resonance
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Vedrine, Jacques C.; Dufaux, Michel; Naccache, Claude; Imelik, Boris
Spectroscopic study by ESCA and e.s.r. techniques was performed for Pt and Pd ions in type Y-zeolites. Pt and Pd ions were found to be ionically bonded to lattice oxygen ions. Atomically dispersed PtO and Pd° were shown to give significant X.P.S. positive chemical shifts: +1.3 and + 1.4 eV for Pt 4/and Pd 3d lines, respectively. These shifts were assigned to smaller electron relaxation energy. Metal aggregates of small diameter < 20 A) and narrow size distribution were prepared in zeolite or on silica. The X.P.S. chemical shift was quite significant (—}-0.7eV) for Pt on zeolite support with respect to those (< +0.3 eV) for Pd on zeolite or Pt or Pd on silica support and did not depend on the particle size. Electron donor and electron acceptor properties of the materials were studied by following the e.s.r. formation of charge transfer complexes (radical ion) as a function of Pt or Pd loading. Pt aggregates were shown to form charge transfer complexes with Lewis acid sites and to increase electron donor properties of the zeolite no matter what the particle size. This increase was shown to arise from electron donation from the metal to the zeolite lattice. However, Pd aggregates were shown by e.s.r. not to give rise to significant electron transfer.