AROMATIZATION OF PROPANE OVER GALLIUM-CONTAINING H-ZSM-5 ZEOLITES - INFLUENCE OF THE PREPARATION METHOD ON THE PRODUCT SELECTIVITY AND THE CATALYTIC STABILITY

Three types of gallium-containing H-ZSM-5 zeolites were prepared in order to compare the catalytic stabilities during propane aromatization. The gallium was introduced into the zeolite in three different ways: isomorphous substitution of aluminum by gallium, impregnation of H-(Al)ZSM-5 with a GaCl3 or a Ga(NO3)3 solution, and physically mixing Ga2O3 powder with a H-(Al)ZSM-5 zeolite. In all cases, addition of 0.6 Ga/unit cell or more enlarged the aromatics selectivity from about 35 C-% to 60 C-%, while the activity remained almost unaffected. A negative side effect was an enhanced rate of deactivation by coke formation, which was most severe for the Ga/H(Al)ZSM-5 catalyst prepared via impregnation or physical mixing, as the gallium is located on the outer surface of the zeolite particles in these samples.