Isomerization of n-butenes on type A zeolites studied by infrared spectroscopy. Part 2.—n-Butene isomerization on zeolites containing alkali metal and alkaline earth cations cocatalysed by sulphur dioxide

Abstract

The isomerization of n-butenes at room temperature cocatalysed by sulphur dioxide on type A zeolites containing various amounts of lithium, sodium, magnesium and calcium ions is studied by infrared spectroscopy. While zeolite NaA is inactive, on all other samples only n-butenes are formed. Quantitative evaluation of the dynamic infrared spectra gives information about the kinetics. With regard to n-butenes, the reaction is described well by a reversible first order equation; the order in sulphur dioxide is one, pointing to a direct intervention of the cocatalyst. Because of the lack of spectral evidence for hydroxyl groups and the linear dependence of the initial reaction rate on the charge/radius ratio, the cations are considered to be the active sites for isomerization. These findings, in conjunction with the kinetics and the distribution of reaction products, are in accordance with a concerted reaction mechanism.