Halocarbon Adsorption in Nanoporous Materials:  A Combined Calorimetric and Monte Carlo Study of Trichloroethylene (TCE) in Faujasite-Type Zeolites

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.