Kinetics of the isomerization of but-1-ene on nahy zeolites studied by infrared spectroscopy

Abstract

The kinetics of but-1-ene isomerization on zeolite with an oligomer was studied by infrared spectroscopy. The product of butene oligomerization is catalytically inactive in but-1-ene isomerization. OH groups vibrating at 3640 cm–1 which remain in the zeolite are responsible for the reaction of the zeolite with the oligomer. However, their catalytic activity is very low, because they are not easily accessible to reagent molecules (the oligomer blocks the zeolite channels). At temperatures > 390 K partial decomposition of the oligomer takes place, the accessibility of the OH groups vibrating at 3640 cm–1 improves and the zeolite can again catalyse the isomerization. The kinetics of but-1-ene isomerization was also studied at low temperatures. Under these conditions butene oligomerization is avoided and all OH groups vibrating at 3640 cm–1 can participate in the reaction. Over a series of NaHY zeolites the catalytic activity increases with degree of exchange and decreases with the amount of pyridine adsorbed. The acid strength of the OH groups vibrating at 3640 cm–1 changes in the same direction thus indicating that there is a correlation between the acid strength of the groups and their catalytic activity.