Transformations of but-1-ene molecules adsorbed in NaHY zeolites studied by infrared spectroscopy

Abstract

The transformations of but-1-ene molecules adsorbed on NaY and NaHY zeolites with various degrees of cation exchange were studied by i.r. spectroscopy. But-1-ene adsorbed on NaY and NaHY zeolites with a low degree of cation exchange is adsorbed on Na⁺ ions. In the case at NaHY zeolites with degrees of cation exchange higher than 40% the but-1-ene molecules form a hydrogen-bond with the 3640 cm^–1 OH groups. The hydrogen-bonded but-1-ene molecules isomerize, the products of this reaction, cis-but-2-ene and trans-but-ene, being also hydrogen-bonded to the 3640 cm^–1 OH groups. Butenes adsorbed on NaHY zeolites undergo slow oligomerization which was found to be catalysed by the 3640 cm^–1 OH groups. The concentration and acid strength of the OH groups influence the oligomerization rate. Butene trimers are formed in zeolite supercages. The product of butene oligomerization is not stable at higher temperatures. Above 373 K the oligomer decomposes and some disproportionation takes place. Gaseous alkanes are formed and a hydrogen-deficient diene residue remains on the catalyst.