In CuY zeolites degassed at temperatures above 650 K cupric ions are reduced to some extent to cuprous ions.Evidence for this process of auto-reduction was taken from the decrease in weight of the sample, and the detection of a desorbing gas in a volumetric system. The latter was identified as oxygen. U.V. reflectance spectroscopy showed directly the decrease of the Cu2+ species upon outgassing and their increase after oxygen adsorption. Excitation spectra showed the presence of Cu+ ions after high temperature degassing. Infrared spectroscopic techniques showed that Lewis sites are also formed upon degassing. A mechanism is proposed that accounts for the observations. JACOBS, DE WILDE, SCHOONHEYDT, UYTTERHOEVEN A D BEYER 1229 sites.21 From the "quasi-equilibrium" amount of CO adsorbed on a Y zeolite with 24.3 Cu2+ per unit at least 6.5 Cu2+ ions are present initially in the supercages. This number of supercage cupric ions is also close to the number of Lewis sites present in this work after a 803 K dehydration if differences in ion-exchange level are taken into account.20* 22 It might well be therefore that the extent of reaction ( 6) is determined by the amount of supercage Cu2+ ions or by the amounts of " loosely held oxygen atoms '7. Evidence for " losely held oxygen atoms " in CuY zeolites is in the increase of oxygen mobility in CuY compared with 24
Publication costs assisted by the Katholieke Unlversiteit Leuven Conduction in hydrated zeolites is due to the movement of the supercage cations, while dielectric dispersions in the kilohertz region are ascribed to the cations in the sodalite units. The activation energies and entropies for conduction vary in the range 100-30 kJ mol-1 and -69 to 226 J mol-1 K-1, respectively, according to the type of cation and the cation-water ratio. The activation energies for cationic relaxation range from 100 to 58 kJ mol-1. A combination of these two techniques allows a study of the cationic distribution in mixed cationic zeolites. The stepwise dehydration down to 90 H20/unit cell does not affect the cationic distribution at low cation-water ratios but does to a limited extent at high cation-water ratios.. Below that hydration level the zeolites undergo the change from hydrated to dehydrated cationic distribution. Water molecules are highly polarized by the cations and no freezing in the sense of a sharp phase transition occurs upon cooling down to 200 K.
Publication costs assisted by the National Science Foundation (USA) and Diensten van het Wetenschapsbeleid (Belgium) Bis(ethylenediamine)copper(II) complexes were ion exchanged from aqueous solution into zeolites X and Y. In Y-type zeolites only the bis complex was observed, but in X-type zeolites mono(ethylenediamine)copper(II) and aquo complexes were also detected in varying amounts, depending on the preparation. Exchange from solutions with an en:Cu ratio of one gives zeolites which contain bis, mono, and aquo complexes. Their relative amounts depend on the preparation conditions, the exchange level, and the type of zeolite. Tris(ethylenediamine)copper(II) complexes were prepared by adsorption of ethylenediamine from the gas phase on dehydrated zeolites with small Cu(II) loadings. The three complexes have apparent axial symmetry. The analysis of the EPR and electronic spectra of the bis complex on the surface shows a small but significant increase of the covalent character of the out-of-plane orbitals with respect to the complexes in aqueous solution. The replacement of axially coordinated water molecules in solution by surface oxygens in zeolites is thought to be responsible for that effect.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.