On the adsorption of gaseous mixtures of hydrocarbons on high silica zeolites

An experimental study of the interactions of an equimolar binary gaseous mixture of toluene and n-hexane, model molecules of aromatic and aliphatic fuel-based pollutants, with two dealuminated high silica zeolites is here presented for the first time. Zeolites Y and ZSM-5 with diverse textural and surface properties were chosen as adsorbents, and the effects of their physicochemical features (predominantly the pore size architecture and silanol content) on sorption capacity were studied. The host-guest (i.e., sorbent-molecules) interactions were studied by FTIR and SS-NMR spectroscopies. IR optical adsorption isotherms of both toluene and n-hexane coadsorbed on the zeolites allowed the determination of the concentration of the adsorbed molecules. Variable temperature SS-NMR spectroscopy allowed the description of the mobility of the pollutant molecules when coadsorbed at the interface of the zeolites micropores. Finally, we describe how the proposed innovative approach can be of general use to determine the selectivity of adsorbent materials for a mixture of hydrocarbons.