Physico-chemical characterization and framework topology of zeolite ZSM-20

Abstract

Zeolite ZSM-20 and its aluminium-free modification (prepared through dealumination of the parent sample with SiCl₄vapour) have been extensively characterized by physico-chemical methods, viz. X-ray powder diffraction, ²⁷Al and ²⁹Si m.a.s.n.m.r. spectroscopy, mid-infrared spectroscopy and thermal analysis. From the results, pronounced structural similarities between zeolite ZSM-20 and faujasite were deduced. Based on the information obtained, structural models for ZSM-20 were developed. Their simulated X-ray powder patterns were compared with the experimental ones. This led to a suggested framework topology of ZSM-20. Its pore system consists of supercages (also known in the faujasite structure) which are interconnected by circular 12-membered-ring windows to form large straight channels running along the c direction. The straight channels are interconnected through a two-dimensional pore system running parallel to a. The opening of the latter pores are also formed form 12-membered rings, but this time with an elliptical shape. The designation MTY is proposed for the framework topology of zeolite ZSM-20.