Adsorption of butenes on NaY and dehydroxylated Y zeolites studies by infrared spectroscopy

Abstract

Butene molecules adsorbed on NaY and dehydroxylated Y zeolites are bonded to electrophilic acid sites (Na⁺ ions or Lewis-acid sites) by their π electrons. The interaction of butene molecules with Lewis-acid sites results in an increase in the extinction coefficient of the band for the antisymmetric stretching vibration of the CH₃ group thus indicating an increased polarization of the C—H bond. The rates of desorption of the butenes from NaY or dehydroxylated zeolites increase in the sequence but-1-ene < cis-but-2-ene < trans-but-2-ene. These differences are explained by considering the steric factor. At low pressures the maximum butene content in Y zeolites is 3 molecules per supercage.