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 ∞, 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.

Isosteric heats of adsorption of trichloroethylene (TCE) in a series of faujasite-type zeolites, siliceous faujasite, NaY (Si:Al ) 2.6), and NaX (Si:Al ) 1.2), have been studied by the combination of calorimetry and (N,V,T) Monte Carlo simulations, varying the sorbate loading up to ∼35 molecules per unit-cell. Excellent agreement is obtained between observed and calculated heats, confirming the applicability of our force field to the realm of unsaturated halocarbons for a large range of Si:Al ratio, cation content, and sorbate loading. The relative contributions of short-range and long-range interactions to the heat of adsorption are discussed, and the host/guest pair distribution functions (PDFs) from the MC simulations are analyzed in detail. At fixed loading, TCE heats of adsorption increase in the sequence of host basicity and cation content: siliceous faujasite: ∼40 kJ/mol < NaY: ∼55 kJ/mol < NaX: ∼80 kJ/mol (extrapolated to "zero" loading). Such a correlation is further elucidated from the host/guest PDFs by the enhancement of HTCE‚‚‚OZEO hydrogen bonding and ClTCE‚‚‚NaZEO electrostatic interactions from the siliceous faujasite to NaY and NaX. An increase in TCE loading gives rise to a systematic increase in adsorption heats (>10 kJ/mol); this is identified as of a predominantly dispersive nature arising from ClTCE‚‚‚ClTCE and HTCE‚‚‚ClTCE intermolecular interactions.