Kinetic isotope effects and mechanism of biomimetic oxidation of methane and benzene on FeZSM-5 zeolite

Earlier, iron complexes stabilized in a ZSM-5 zeolite matrix have been shown to produce a new form of surface oxygen (called alpha-oxygen) upon decomposition of N2O. alpha-Oxygen exhibits a very high reactivity typical for oxygen of monooxygenases (MO) and mimics its unique ability in selective oxidation of hydrocarbons at room temperature. Kinetic isotope effect (KIE) measurements reported here reveal additional similarities between MO and the model. Depending on the temperature, the value of KIE for oxidation of methane with alpha-oxygen ranges from 1.9 to 5.5. For the oxidation of benzene the value of KIE is 1.0. This indicates that both biological and chemical oxidation of methane involves a rate limiting C-H bond cleavage, whereas the reaction with benzene is probably limited by the formation of an epoxy-type intermediate. The assumed structure of the active sites as well as some features of the oxidation mechanism allow one to consider FeZSM-5-N2O system as a new and successful model for methane monooxygenase.