(223c) Redox Sites In H-Zeolites and Their Role In Alkane Cracking and Dehydrogenation

We will investigate the formation of redox sizes in high-silica H-zeolites (ZSM-5, beta and chabazite) by the reaction of the zeolite in oxygen (500°C) or in inert atmosphere (argon, at 700°C and above). Evidence for the formation of the redox sites will be established using the reaction of naphthalene in the zeolite to form stable radical cations. We will show that the high temperature treatment decomposes the Bronsted acid sites of the zeolite while the oxygen gas treatment has no clear effect on the acidity of the zeolites. Using propane cracking and propane dehydrogenation as probe reactions, we will show that these redox sites increase the rate of propane dehydrogenation relative to propane cracking reactions. These results clearly show that redox processes, along with acid chemistry, must be considered when investigating the mechanisms of hydrocarbon conversion in fluidized catalytic cracking units in refineries.