Enhancement of the basic properties in FAU zeolites by impregnation with cesium hydroxide

Impregnation of FAU zeolites with seven cesium hydroxide atoms per unit cell improved their basic properties in toluene methylation without affecting the physical properties of the zeolite (framework, silicon/aluminium molar ratio, aluminium coordination, etc.). The enhancement was greater in the zeolites with good initial basic properties such as the cesium-exchanged zeolite. The effect of the impregnation was to first decrease the acid activity and then to increase the basic activity. The basic catalytic activity showed a maximum for a cesium content of 20CsOH/u.c. in the NaX zeolite. Higher contents of cesium hydroxide did not show catalytic activity due to the collapse of the FAU framework. Higher yields of basic methylation were achieved with a zeolite synthesised with occluded alkaline hydroxide (NaKX-I) without post-synthesis treatment. In this case, the cesium hydroxide content yielding the maximum catalytic activity was 15CsOH/u.c.