Adsorption microcalorimetry of probe molecules of different size to characterize the microporosity of pillared clays

Three pillared clays (PILC) prepared from different soil deposits, viz from Benavila and Porto Santo (Portugal), and from the Wyoming Volclay SPV-200 material were used as adsorbents. The adsorption of molecules of different size and shape, namely n-hexane, toluene, and 1,3,5-trimethylbenzene (mesitylene), followed by microcalorimetry was used to assess the microporosity of the samples. Information on the micropore capacity of each adsorbate on each PILC, the presence of cavities, and the separation between the pillars, was obtained from the adsorption results. The correlation of the packing densities of the adsorbates inside the micropores of the samples with the values for well known zeolites allowed to estimate the size of cavities and channels, which can be useful for potential applications of these materials in adsorption and catalysis. From the analysis of the differential calorimetric isotherms, q(st.sigma)-n(sigma), it was concluded that strong acid sites are present on the pillars, their density being the same in the three PILC. (C) 2002 Elsevier Science B.V. All rights reserved.