Energetics of Ammonia Sorption in Alkali Metal Exchanged Analogues of Linde Type X Zeolites

Abstract

The parent zeolite NaX was prepared from hydrogel system 3.6 Na2O:3 SiO2:Al2O3:144 H2O at 368 K for 8 h under static condition. Postsynthesis modification was carried out using the conventional ion-exchange technique to obtain different ion-exchanged forms. The parent as well as exchanged samples were characterized by chemical analysis, IR, SEM, powder XRD, and low temperature nitrogen sorption. The ammonia sorption isotherms in parent NaX (Si/Al = 1.15) and its modified forms with a nearly equal degree of exchange by K+, Rb+, and Cs+ cations have been measured in the temperature range of 303−453 K up to 500 Torr. The equilibrium sorption uptake at 50 Torr and especially at temperatures above 363 K was found to follow the sequence NaX > NaK(53)X > NaRb(53)X > NaCs(58)X. The analysis of the ammonia sorption data in terms of different isotherm equations revealed satisfactory representation by Langmuir, Dubinin, BET, and Sips equations and statistical models of Langmuir and Volmer. However, the Freundlich eq...