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:AI = 1.2), have been studied by the combination of calorimetry and (N,V,T) Monte Carlo simulations, varying the sorbate loading up to similar 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: similar to 40 kJ/mol < NaY: similar to 55 kJ/mol < NaX: similar to 80 kJ/mol (extrapolated to "zero" loading). Such a correlation Is further elucidated from the host/guest PDFs by the enhancement of H(TCE)... O(ZEO) hydrogen bonding and Cl(TCE)... Na(ZEO) 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 Cl(TCE)... Cl(TCE) and H(TCE)... Cl(TCE) intermolecular interactions.