PARAMETERS AFFECTING THE DISPERSION OF THE GALLIUM PHASE OF GALLIUM H-MFI AROMATIZATION CATALYSTS

The dispersion of the gallium phase of Ga-H-MFI aromatization catalysts can be controlled either during the introduction of gallium in the catalyst or by using hydrogen activation pretreatments. Incipient wetness impregnation of H-MFI with Ga(NO3)3 solution leads to the highest gallium dispersion compared with "wet" impregnation techniques at various pH. In every case, most of the gallium phase is found to be located closely to the outer surface of the zeolite grains as thin platelets from 5 to 400 nm in average size depending on the gallium introduction mode. Hydrogen activation treatment at 823 K induces gallium migration from gallium platelets to the zeolite micropores leading to a highly dispersed gallium phase located close to the acid sites.