Processes of ammonia adsorption in gallium zeolites as studied by microcalorimetry

Tn adsorption calorimetric studies, it is necessary to analyse the obtained calorimetric and volumetric data in relation to coverage or number of sites. For this purpose, procedures have been developed to relate quantitative measurements of heat Liberation to the different processes which are taking place as the amount of adsorbed ammonia increases, due to reversible and irreversible adsorption. In order to describe the relative contributions of these two phenomena (physical and chemical adsorption) to volumetric isotherms as well as to calorimetric thermograms, they have been modeled and chemisorption was separated from physisorption. Calorimetric and volumetric measurements performed on H-[Ga]-BEA and H-[Ga]-MFI zeolites have provided experimental data to validate the theoretical models. The acidity of the gallium samples has been compared with that of the corresponding aluminum samples. (C) 1998 Elsevier Science B.V.