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Start date: 1980Subject: search.filters.subject.Adsorption

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    Cooperative Interactions and Two-dimensional Ordering in the Adsorption of HBr on KBr
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (06), 1981) Harrison, Lionel G; Koga, Yoshikata; Lassau, Troy
    Adsorption isotherms of HBr gas on high surface area KBr have markedly non-ideal shapes. These are analysed using a two-layer model with repulsive interactions between molecules in the first layer. An earlier report from this laboratory of a transition in the surface layer at 20 °C, induced by adsorption, is confirmed by these data. Likewise, an apparent restriction of first-layer adsorption to no more than 25% coverage seems to correlate with the previous report from this laboratory that a ‘two-dimensional compound’ K4Br3Cl is formed in surfaces partly exchanged with HCl. Heat of adsorption is 48.5 kJ mol–1(below transition) and 30.5 kJ mol–1(above transition); mean-field repulsion constant C is ca. 40 kJ mol–1; the transition has ΔHt= 18.0 kJ mol–1 and ΔSt= 59.0 J mol–1 K–1. The remarkably large magnitudes of some of these quantities are discussed in terms of a model for adsorption involving normal weak hydrogen bonding plus additional electrostatic interactions between the Br of adsorbed HBr and adjacent K+ ions. Thereby, interactions between admolecules become intermediate-range, rather than nearest neighbour, averaging C/12 ≈ 3–4 kJ mol–1.
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    Adsorption of Butenes on NaY and Dehydroxylated Y Zeolites Studies by Infrared Spectroscopy
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (06), 1981) Datka, Jerzy
    Butene molecules adsorbed on NaY and dehydroxylated Y zeolites are bonded to electrophilic acid sites (Na+ ions or Lewis-acid sites) by their π electrons. The interaction of butene molecules with Lewis-acid sites results in an increase in the extinction coefficient of the band for the antisymmetric stretching vibration of the CH3 group thus indicating an increased polarization of the C—H bond. The rates of desorption of the butenes from NaY or dehydroxylated zeolites increase in the sequence but-1-ene < cis-but-2-ene < trans-but-2-ene. These differences are explained by considering the steric factor. At low pressures the maximum butene content in Y zeolites is 3 molecules per supercage.