STATE, ACTIVATION, AND MIGRATION OF GALLIUM IN GA/H-MFI(SI,AL) PROPANE AROMATIZATION CATALYSTS

Several chemical, physical, and spectroscopic techniques were used to characterise the gallium-component in Ga/H-MFI(Si,Al) zeolitic propane aromatization catalysts, during their activation, stabilisation, and ageing with number of reaction-regeneration cycles. The initial gallium-modified catalysts prepared via ion exchange have a surface enriched in gallium as evidenced by X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy of alpha particles. The combination of reductive reaction and oxidative regeneration conditions leads to gallium migration and redistribution in the zeolite crystals, as well as to chemical change in the nature of the gallium species. Maximum activity and aromatics selectivity are observed when non-framework dispersed gallium-species have the highest concentration. They are associated with zeolite Bronsted acidic sites as bifunctional dual sites.