Abstract
The formation of O- radical over various metal oxides, its reactivity, and catalytic oxidations using O- as an oxidant have been described. It is confirmed by ESR, XPS, TPD etc. that O- radical can be generated through decomposition or charge transfer processes of O2, O2-, OH-, or N2O. Respective characters of O- on various metal oxides, that is, g-values of ESR spectra and desorption temperatures etc., were summarized. Among oxygen species such as O-, O-2 and O-3, O- radical shows the highest activity for stoichiometric oxidations of hydrocarbons and the order of reactivities has been clarified to be O->O-3>O-2 independent of metal oxides. Reaction schemes of O- radical with hydrocarbons have been proposed on the basis of the ESR, IR, and TPD observations and also been compared with those of O-2 and O-3. In the last section, catalytic oxidations of hydrocarbons by nitrous oxide, which decomposes readily and selectively to yield an O- radical on metal oxide surfaces, have been outlined, including new types of catalytic oxidations such as one-step conversions of methane into methanol, of alkanes into alkenes, and of benzene into phenol.
