Isomerization of n-butenes on A-type zeolites studied by infrared spectroscopy. Part 1.—n-butene adsorption on zeolites containing alkali and alkaline earth cations

Abstract

Adsorption of n-butenes on highly activated type A-zeolites containing alkali and alkaline earth cations is studied by infrared spectroscopy. The rate of adsorption is determined by the butene–zeolite interaction, depending on the dipole moment and the steric requirements of the butene molecules, and the occupancy of the cation sites.

The n-butenes are strongly physisorbed without fragmentation with preservation of the C[double bond, length as m-dash]C bond. The adsorption is accompanied by the appearance of forbidden i.r. fundamentals, small frequency shifts, a change in band intensities and a decrease in band widths. Narrow bands point to a largely restricted rotational freedom. The frequency shift of the C[double bond, length as m-dash]C band is cation sensitive and shows a direct polarizing power dependence. Under formation of a π-complex the butenes are attached to the cations in a “side on” mode. In the case of the alkali and alkaline earth forms isomerization is not affected. In the far infrared region phonon induced absorptions are observable.