Study of physisorption of carbon dioxide on NaA zeolite. Part 2.—Interpretation of infrared spectra from statistical models

Abstract

Two theoretical models are considered. The first is a model of energetically different sites, the second a model of the distribution of interacting molecules on energetically homogeneous cavities. The temperature dependence of distributions for adsorbed amounts comprising between 0.2 and 0.7 molecules per cavity are compared with the results of Part 1. The first model seems more adequate and an interaction calculation confirms the heterogeneity of the cavity. On the other hand, it does not permit precise determination of the multiplicity of the sites. We have thus been led to analyse other experimental data. Isotherms and adsorption heat curves deduced from infrared results show a good fit with results obtained by other authors for up to 4 molecules per cavity with the assumption that there are 1 and 6 sites of each type. The energy would be 57 and 50 kJ mol^–1, respectively, and the mean frequency of external vibration ca. 50 cm^–1.