Propane reactions over natural Todorokite

Abstract

This study reports results of propane transformation over the natural microporous manganese oxide, todorokite, and its hydrogen form (H-Todorokite), at the temperature range of 350°–550 °C. Both materials were fully characterized and their catalytic results were compared with results obtained with commercial Ultra-Stable-Y (USY), and steamed H-ZSM-5 zeolite catalysts. The natural todorokite sample shows appreciable dehydrogenation activity (propylene yield ∼8%, selectivity to propylene >31%), considerably higher compared to H-ZSM-5 zeolite. This is justified by the absence of strong acid sites and the presence of a large amount of ion-exchangeable cations, which induce the dehydrogenation capability of the material. The proton-exchanged form of todorokite, appears to act as a very efficient cracking catalyst (yield to methane and ethylene ∼40%, selectivity to cracking products >85%), due to the formation of a large number of framework Brønsted acid sites. The observed cracking capability of H-todorokite is superior to the activity of the commercial fluid catalytic cracking (FCC) USY catalyst, thus suggesting that the proton form of the mineral is a promising catalyst for the cracking of small alkanes.