ZINC-EXCHANGED Y-ZEOLITES STUDIED WITH CARBON-MONOXIDE AND XENON AS PROBES

The adsorption isotherms of carbon monoxide and xenon, as well as the Xe-129 NMR chemical shifts of xenon, in 55 and 74% zinc-exchanged Y zeolites with various pretreatment conditions, such as temperature of dehydration, oxidation and preloading with CO, have been measured. The sets of experimental data can be explained quantitatively with a unifying approach which considers localized adsorption of both CO and xenon on well defined adsorption sites consisting of two types of zinc cations in different environments, and sodium cations. The two different zinc cation sites are characterized by their individual adsorption constants and isosteric heats of CO adsorption (63 and 46 kJ mol-1) as well as by the Xe-129 NMR chemical shifts of the xenon atoms accommodated on them (185 and 135 ppm). The concentrations of these sites as a function of the degree of zinc exchange and pretreatment conditions were determined.