Determining the topology of zeolites by adsorption microcalorimetry of organic molecules

Adsorption microcalorimetric studies of n-hexane, toluene, m-xylene and 1,3,5-trimethylbenzene on a bidimensional ten-member ring (MR) (ZSM-11), a unidirectional uniform 12-MR (SSZ-24), a constrained unidirectional (ZSM-12), a 12- and 8-MR (mordenite) and a 12- and 10-MR (CIT-1) zeolites have been carried out. It is shown that the adsorption of the four probe molecules followed by adsorption microcalorimetry allows the determination of the approximated micropore diameter. Comparison of the total uptake of each adsorbate can show the existence of micropore sets of different diameter. The variation of adsorption heat with uptake provides information on the surface chemistry allowing one to see if there is adsorption specificity or not. The packing molar densities inside the micropores give information on the particular micropore shape and the existence of cavities, lobes, etc. Finally, toluene or n-hexane post-adsorption experiments after preadsorption of a different adsorbate give information on the connectivities or crossing between sets of channels. (C) 1998 Elsevier Science B.V. All rights reserved.