Adsorption of propene on NaX zeolite exchanged with Zn2+ and Cu2+

Adsorption of C3H6 has been carried out thermogravimetrically on M2+X zeolites (M2+=Zn2+ or Cu2+) exchanged at different degrees. The Gibbs energy change, the isosteric heat and the differential entropy change of C3H6 adsorbed at intervals of 20 K between 303 and 363 K are investigated. Analysis of the Gibbs energy change curves reveals particularly the character energetically heterogeneous of NaX and Zn(x)X samples with respect to the C3H6 adsorption. Evaluation of the isosteric heat shows that these adsorbents present strong adsorptive centre-adsorbate interactions, in contrast to Cu(x)X where it is noted the predominance of attractive adsorbate-adsorbate interactions. Examination of differential entropy change shows that for NaX and Zn(23)X zeolites, the adsorbed phase is in a state strongly localized, at least at low concentrations of zeolitic propene, whereas the adsorbed molecules, in the case of Zn(62)X, have a restricted 2D translational motion, throughout the entire coverage range. For Cu(x)X samples, the mobility of the adsorbed phase decreases with increasing adsorbate loading. (C) 1999 Elsevier Science B.V. All rights reserved.