ZnCl2 supported on NaY zeolite by solid-state interaction under microwave irradiation and used as heterogeneous catalysts for high regioselective Diels–Alder reaction of myrcene and acrolein

Abstract

A novel catalyst preparation method is developed by solid-state interaction between ZnCl2 and NaY zeolite under microwave irradiation. The solid-state interaction is investigated by powder X-ray diffraction, FT-IR spectroscopy, and by testing the catalytic properties in the Diels–Alder reaction of myrcene and acrolein. XRD patterns indicate that ZnCl2 can disperse completely on the surface of NaY zeolite at the ZnCl2 loading less than 2.75 mmol g−1. FT-IR spectra of pyridine adsorption on catalyst show that Lewis acid sites are the predominant acid sites. The catalyst of ZnCl2/NaY prepared by the treatment of microwave irradiation is proved to be an effective heterogeneous catalyst for high regioselective Diels–Alder reaction of myrcene and acrolein. The catalytic activity and the regioselectivity of p/m strongly depend on the ZnCl2 loading. With an increase of the ZnCl2 loading up to 0.92 mmol g−1, the activity and selectivity increase a little. In this case, the active site is deduced from the zinc ion species formed by solid-state ion exchange. The Lewis acid sites are too weak to catalyze efficiently the Diels–Alder reaction. Keeping an increase of ZnCl2 loading from 0.92 mmol g−1 to 1.84 mmol g−1, the activity and the regioselctivity of p/m increased markedly due to the formation of new zinc ion species of –O–Zn–Cl as Lewis acid sites on NaY zeolite. The catalysts leached with a mixture solvent of acrolein and dichloromethane show little loss of catalytic activity and selectivity. Thanks to the possibility of simple and safe handling of the ZnCl2/NaY and to its easy separation from organic products, it becomes an alternative Lewis acid catalyst for the Diels–Alder reaction to homogeneous Lewis acids.