Adsorption of Aromatics in Zeolites ZSM-5: A Thermodynamic−Calorimetric Study Based on the Model of Adsorption on Heterogeneous Adsorption Sites

On the basis of new experimental and theoretical findings, a revised version of the three-site model of collective localized adsorption, proposed originally by Lee and Chiang, is presented. Following the new findings, it is assumed, that benzene molecules filling channel intersections may be adsorbed in two different configurational states. That model leads to predicting, for the first time, the two steps observed on the isotherms of benzene adsorption at higher temperatures. The steps are due to cooperative redistributions of molecules adsorbed on various sites. That model allows also obtaining a quantitative simultaneous fit of both adsorption isotherms and the corresponding isosteric heats of adsorption. The estimated parameters of gas−solid interactions on various sites increase in the sequence predicted by computer simulations of one molecule adsorption.