Calorimetric and computational studies of chlorocarbon adsorption in zeolites

Monte Carlo simulations on the adsorption of the two model chlorocarbons, chloroform and trichloroethylene, in three faujasite type zeolites, NaX, NaY, and siliceous faujasite (Si/Al = 1.2, 3.0, and infinity, respectively), are compared with the results of calorimetric measurements on the same systems. At low sorbate loadings, the heats of adsorption increase with increasing polarity of the zeolite host (siliceous faujasite < NaY < NaX), underlining the importance of the dipolar nature of the sorbates. For all six systems, quantitative agreement is found between the calculated and observed heats as a function of sorbate loading. Decomposition of the calculated heats into the short-range and long-range contributions shows that sorbate-sorbate interactions are important in all three hosts and lead to an increase in the adsorption heat with coverage in NaY and siliceous faujasite. The SIII' cations play a specific role in the case of zeolite NaX, where a cancellation between the short-range and electrostatic interactions leads to a heat of adsorption that is invariant with coverage.