ملخص: The Gibbs energy change, isosteric heat and entropy of CO2, sorbed at intervals of approximately 30 K between 273 and 393 K in X-type zeolites exchanged with Zn2+ and Cu2+ cations to diVerent degrees, are investigated. The best fit of sorption isotherm data is obtained with the Langmuir model. The NaX zeolite revealed the highest sorption aYnity which decreases with increasing level of exchange. Analysis of the isosteric heat and diVerential entropy curves shows that the Zn(x)X samples present a heterogeneous profile, only at a greater extent of Zn2+ exchange and at low coverages. The most likely explanation of this is the appearance of Zn2+ in the supercages on sites II accessible to sorbed CO2. In contrast, the X zeolites containing Cu2+ cations do not exhibit an energetic heterogeneity at any exchange degree throughout the entire coverage range. Such a behaviour could be ascribed to the formation of inactive (CuMOMCu)2+ entities within zeolitic cavities. Furthermore, integral entropies of zeolitic CO2 are less than the entropy of liquid CO2, suggesting reduced freedom in the sorbed phase.

لغة: إنجليزية