MOR-to-MFI interzeolite transformations: Tuning of paired sites content towards the development of efficient MTH catalyst

Abstract

Interzeolite transformation is a rapidly developing method of zeolite synthesis, which allows a precise design of the active site structure. We report on the application of MOR to MFI interzeolite transformation (IZT) for the preparation of MFI zeolite with variable content of paired sites and the elucidation of their role in the MTH reaction. IZT procedure involved hydrothermal treatment of the reaction mixture containing mordenite zeolite as a source of silica and alumina, alkali, TPAOH, TPABr and water. Tuning of paired sites was achieved by variation of the content of water and alkali in the reaction mixture and the application of seeding. The results demonstrate that IZT procedure allows to tune paired sites content within 10–65 % without affecting other characteristics of MFI products, such as Si/Al ratio, crystal size, texture, acid sites type, content and strength, as well as the amount of EFAL species and the distribution of aluminum between channels and intersections of the MFI structure. The evaluation of MOR-to-MFI zeolites with different paired sites content in the MTH reaction pointed to significant effect of paired sites on the stability of catalytic activity with time on stream and on the propylene/ethylene selectivity.