Catalytic studies with dealuminated Y zeolite. Part 1.—Catalyst characterisation and the disproportionation of ethylbenzene

Abstract

A series of highly crystalline, hydrothermally dealuminated Y zeolites has been prepared and further modified by extracting non-framework aluminium with Na₂H₂EDTA. The zeolites were comprehensively characterised using chemical analysis, X-ray diffraction, mid-infrared spectroscopy, ²⁷Al magic-angle-spinning nuclear magnetic resonance (²⁷Al MAS NMR), analysis of N₂ adsorption isotherms and temperature-programmed desorption of NH₃ to determined acid site concentrations. It is shown that aluminium from the framework resides in the micropores and freshly developed mesopores in a number of forms. Aluminium extraction with Na₂H₂EDTA increases both the pore volumes and the concentration of Brønsted acid sites, but leaves an average of five charge-balancing Al atoms per unit cell.

Catalytic studies of ethylbenzene disportionation at 473 K show that Brønsted acid sites are the seat of an activity which increases following Na₂H₂EDTA extraction. There is evidence, however, for a synergistic interaction between Brønsted acid sites and extrastructural hydroxo-aluminium species in unextracted catalysts to yield sites of higher activity than in extracted catalysts. The reaction is believed to proceed by a dealkylation/alkylation mechanism which accounts for minor yields of ethene, which is held responsible for coke formation and catalyst deactivation.