Browsing by Author "Schoonheydt, Robert A."

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    Cation motion in dehydrated, partially ca2+-exchanged zeolites
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (12), 1974) Schoonheydt, Robert A.; Wilde, Willy De
    Ionic conduction in dehydrated partially Ca2+-exchanged synthetic faujasites is due to Na+ ions on sites II. The mechanism is a vacancy diffusion. Activation energies lie in the range 38–59 kJ mol–1 and are mainly determined by the positive charge density in the hexagonal prisms and in the cubo-octahedra. Deep bed heating prior to the conduction experiments leads to an increase of the activation energy for migration of Na+ ions in X zeolites but not in Y zeolites. Two relaxations are observed. The low frequency relaxation is a Maxwell–Wagner effect. The high frequency relaxation is ascribed to the movement of Ca2+ ions on sites I and I′ between neighbouring sites. The activation energies for this relaxation range between 84 and 106 kJ mol–1. The electrical permittivities, uncorrected for pellet heterogeneity, are in the range 2.32–2.84.
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    Complexes of Ammonia and Ethylenediamine with Cu" on Zeolite A
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Schoonheydt, Robert A.; Peigneur, Paul; Uytterhoeven, Jan B.
    Adsorption of NH3 on a dehydrated CuA zeolite gives Cu(NH3)2+4 and a small amount of tetrahedrally coordinated CuII ions. These complexes are unstable and decompose by vacuum heating in the range 295–373 K to yield lattice-bonded CuII ions characterized by an e.p.r. signal with g‖= 2.3087, A‖= 0.015 09 cm–1, g⊥= 2.067 and A⊥= 0.000 96 cm–1. Above 373 K this signal transforms to g‖= 2.3715, A‖= 0.013 63 cm–1, g⊥= 2.062 and A⊥= 0.001 92 cm–1. Adsorption of ethylenediamine on a dehydrated CuA zeolite gives only Cu(en)2+, stable up to 473 K. However, in the presence of water, Cu(en)2+2 and Cu(en)2+3 can also be synthesized on the surface. The latter two complexes are unstable and decompose by vacuum heating to the mono-complex. Cu(en)2+ can also be loaded on NaA by ion-exchange from aqueous solution, but Cu(en)2+2 cannot, due to space requirements and the instability of the bis-complex in the supercages of zeolite A. First it is necessary to exchange the mono-complex and to synthesize the bis-complex in situ by adding large excesses of ethylenediamine to the aqueous suspension. The e.p.r. and reflectance spectra of the various complexes depend slightly but consistently on the environment in the supercages of zeolite A. Their analysis, however, shows that this does not induce major changes in the CuII—N bonding characteristics.