Propylene dimerization over nickel-ion exchanged zeolites in the liquid phase

The possibility of the dimerization of propylene in the liquid phase over n ickel-ion exchanged zeolites (Ni-zeolites) modified by treatment with AlEt2 Cl to provide enhanced activity is studied. In order to determine the influence of the crystalline structure of zeolite s on their catalytic activity and the selection of the most active catalyst the zeolites of faujasite (NaX, NaY), eryonite and mordenite types with va rious structures and different cell sizes have been chosen. The samples of Ni-zeolites were prepared by ion exchange with nickel nitrate in a correspo nding zeolite. The treatment of these zeolites with AlEt2Cl leads to the fo rmation of active dimerization of propylene catalytic systems. The activity of these systems reaches the maximum at an Al/Ni weight ratio approximatel y equal to 10. It is assumed that the mechanism of propylene dimerization in the investiga ted catalysts is similar to the mechanism of olefin dimerization in Ziegler -Natta catalytic systems. The ESR results suggests Ni-ion participation in the formation of catalytically active species. The distinctions in the catalytic behaviour of the studied zeolites are con nected with their crystalline structure. It is probable that the dimerizati on process over Ni-zeolites of faujasite type goes on in the kinetic area, while in the case of Ni-eryonite and Ni-mordenite, diffusional breaking, wh ich decreases an activity of these catalysts, takes place. The diffractographic investigation demonstrates a partial destruction of th e crystalline structure of zeolite after the repeated treatment with AlEt2C l. The preservation of the crystalline structure from full decay presumably is the consequence of the exchanged reaction between the Ni-ion and proton - product of the interaction of Ni-zeolite with AlEt2Cl.