Oxidative dehydrogenation of propane with nitrous oxide over Fe–O–Al species occluded in ZSM-5: Reaction and deactivation mechanisms

Abstract

Fe-ZSM-5 was prepared via solid-state exchange method using ferrocene as iron precursor and applied as a model catalyst to investigate the reaction and deactivation mechanisms of the oxidative dehydrogenation of propane (ODHP) with nitrous oxide. Characterization results reveal that after severe calcination highly isolated Fe–O–Al species are the only exposed iron sites detectable, which account for ca. 60% of the total iron species in Fe-ZSM-5. Results from temperature-programmed experiments and in situ DRIFT spectroscopy suggest that the chemisorption of nitrous oxide on Fe–O–Al species leads to the formation of stable mono-oxygen species, which can react with gaseous propane to produce propylene with high selectivity. The accumulation of organic species in the catalyst is observed during the reaction, and the major organic species are determined to be alkylbenzenes. The accumulation rate and the specific constitution of alkylbenzenes are found to depend on the relative partial pressures of propane and nitrous oxide: lower N2O/C3H8 ratios result in formation of aromatics with smaller kinetic diameter, which are accumulated at a lower rate. This leads to lower deactivation rates and longer catalyst lifetimes. Remarkably, a superior stable propane conversion rate of ca. 13mmolgcat−1h−1 and a propylene production rate of ca. 6mmolgcat−1h−1 can be kept for >40h with a N2O/C3H8 ratio of 1:2.