Halocarbon adsorption in nanoporous materials: A combined calorimetric and Monte Carlo study of trichloroethylene (TCE) in faujasite-type zeolites

摘要

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. [References: 28]