ON THE ROLE OF GALLIUM FOR THE AROMATIZATION OF LOWER PARAFFINS WITH GA-PROMOTED ZSM-5 CATALYSTS

H-ZSM-5 showed a high selectivity of propane and low selectivity of aromatic hydrocarbons in butane conversion at 450-degrees-C, whereas Ga-supportd ZSM-5 (Ga-ZSM-5) showed higher selectivities of aromatic hydrocarbons and hydrogen. A small amount of oxygen in the feed promoted butane conversion to aromatic hydrocarbons on H-ZSM-5. Hybrid catalysts composed of the physical mixture of Ga/Al2O3 and H-ZSM-5 showed comparable activities and aromatic selectivities to those of the Ga-supported ZSM-5 zeolite (Ga-ZSM-5). Hydrogen was adsorbed quickly on the Ga-ZSM-5 and on the hybrid catalyst at 400-degrees-C and the adsorbed hydrogen was desorbed at around 450-degrees-C during the temperature programmed desorption experiment from both catalysts. However, little hydrogen was adsorbed on H-ZSM-5 and was desorbed from it. It was pointed out that the supported Ga promoted the zeolite-catalyzed aromatization of lower paraffins by promoting hydrogen desorption via the ''reverse spillover'' effect.