Browsing by Author "Uytterhoeven, Jan B."

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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.
Location of Cations in Synthetic Zeolites-X and -Y: Part 6.—Influence of X-ray Irradiation on the Location of Exchangeable Cations
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Costenoble, Martin L.; Mortier, Wilfried J.; Uytterhoeven, Jan B.
The X-ray irradiation of a scries of Ca- and La-Y zeolites, pretreated at different temperatures results in the formation of oxides (CaO and La2O3) in the sodalite cage, and in a depopulation of the hexagonal prisms. The structures are similar for all (previously different) samples and cannot be distinguished statistically. The number of oxygens in the oxides largely exceeds the level of residual water and originates from the framework. The reversible mobility of the framework oxygens is postulated, considering the zeolite framework and cations merely as a “ mixed oxide".
Surface Probing of Synthetic Faujasites by Adsorption of Carbon Dioxide: Part 1.—Infra-red Study of Carbon Dioxide Adsorbed on Na-Ca-Y and Na-Mg-Y Zeolites
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (6), 1973) Jacobs, Peter A.; Cauwelaert, Franz H. van; Vansant, Etienne F.; Uytterhoeven, Jan B.
Infra-red spectroscopy of carbon dioxide adsorbed on Na-Ca(Mg)-Y faujasites is used to determine the distribution of Ca and Mg ions over the cation sites. Physisorption of CO2 provides a sensitive method for the detection of Ca2+ and Mg2+ in supercage positions. High temperature outgassing of the samples facilitates the migration of bivalent ions from positions in the supercage to the small cavities. Bivalent ions in the dehydrated Y samples are only present in the supercages when the degree of ion exchange is 46 to 48 % or higher. For high temperature chemisorption of CO2, the chemisorbed species are closely related to co-ordinated carbonate ions. The concentration of this species does not exceed 2 molecules per unit cell.
Thermal Stability of NH4-Chabazite
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (07), 1977) Beyer, Hermann K.; Jacobs, Peter A.; Uytterhoeven, Jan B.; Till, Ferenc
The thermal stability of NH4-chabazite has been examined by i.r. spectroscopy and thermal analysis combined with mass spectrometry. Dehydration occurs in two and deammoniation in four steps. Disregarding a very small water loss during deammoniation, dehydroxylation is completely separable from deammoniation and occurs in two distinct steps. Two OH stretching bands at 3540 and 3630 cm–1 appear during deammoniation and could be related to distinct ammonium ions having bending vibrations at 1420 and 1460 cm–1 respectively. The hydroxyls showing a band at 3540 cm–1 are formed at lower temperatures and are less thermostable than other hydroxyls.