CONVERSION OF METHANE TO BENZENE OVER TRANSITION-METAL ION ZSM-5 ZEOLITES - II - CATALYST CHARACTERIZATION BY X-RAY PHOTOELECTRON-SPECTROSCOPY

X-ray photoelectron spectroscopy (XPS) has been used to determine the state of the transition metal ions (V, Cr, Fe, W, and Mo) on impregnat ed and ion-exchanged H-ZSM-5 zeolites that are active for the catalyti c conversion of methane to benzene at 750 degrees C. During an inducti on period, transition metal suboxides are formed on all of the impregn ated catalysts except Mo/H-ZSM-5 for which Mo2C is formed. Ion-exchang ed samples became more active after treatment with CO at 500 degrees C . For the Fe/H-ZSM-5 sample, this treatment resulted in the migration of the metal to the external surface of the zeolite and the formation of an iron oxide phase. (C) 1998 Academic Press.