Alpha oxygen - a unique oxidation active site from a quantum chemical viewpoint.

The alpha oxygen (also α-O, Fe(IV)O, and Fe(III)-O-˙) stabilized in zeolite matrices exhibits a unique reactivity. It is, for example, able to oxidize methane to methanol at room temperature. Such a high oxidation activity makes the alpha oxygen an extremely attractive species from the point of view of oxidation catalysis. The alpha oxygen can be prepared by splitting either N2O or O2 also at low temperatures over different transition metal cations stabilized in extra-framework cationic sites of zeolites in the form of either isolated cations or two cooperating cations forming distant binuclear cationic sites. The alpha oxygen was primarily defined by its reactivity, and up to now, experimental data concerning its structure are rather scarce. Quantum chemical calculations are used to interpret experimental data and thus yield significantly deeper insights into the preparation, structure, and reactivity of this otherwise omitted active species with enormous potential for applications. This review represents the first collection and systematic interpretation of experimental data and quantum chemical calculations to provide a complex description of the alpha oxygen and its structure, reactivity, and properties.