Interactions of Toluene and n-Hexane on High Silica Zeolites: An Experimental and Computational Model Study

The knowledge of host-guest interactions occurring in confined space between porous solids and embedded molecules of different origin is an important task to improve adsorption properties of materials, thus extending their application fields. In this work, the interactions of toluene and n-hexane molecules (selected as models of organic pollutants coming from industrial waste of oil refineries and gas stations) on different dealuminated high silica zeolites were studied by means of both experimental and computational approaches. Zeolites with different textural and surface features were selected as adsorbents and the effect of their physicochemical properties (i.e., pore size architecture and type and amount of surface OH sites) on sorption capacity were studied. High silica Y and ZSM-5 zeolites (with a SiO2/Al2O3 ratio of 200 and 280, respectively) were selected as model sorbents. FTIR and SS-NMR spectroscopy were used to study the type and strength of the host-guest interactions between the molecules and the zeolite surface. Gravimetric analysis allowed the determination of the sorption capacity of both zeolites and their affinity to pollutants. The interactions between the silica surfaces and pollutants molecules computed at the DFT level, and supplemented by empirical formulation of dispersion energies, led to estimate the intensity of hydrogen bonding and cooperative van der Waals interactions.