Mechanistic study of CH3OH+O2 photoredox reaction in a FeAlPO4 sieve by time-resolved FT-IR spectroscopy

The mechanism of the ligand-to-metal charge transfer (LMCT) induced reaction of methanol and 0, at the gas-micropore interface of a FeAIPO(4)-5 sieve has been studied by time-resolved FT-IR spectroscopy. Measurements using the rapid-scan method revealed that the final products, HCO2-...Fe and H2O, emerge with a rise time of 4 s (250 K) by decomposition of the two-electron-transfer intermediate, HO2CH2OH. Intermediacy of hydroxymethylhydroperoxide was established by direct detection by step-scan FT-IR spectroscopy on the 500 microsecond time scale and by monitoring of its photodissociation products HCO2H + H2O on the millisecond and second time scale. Formaldehyde was observed as minor two-electron oxidation product. The fast rise of the HO2CH2OH intermediate strongly suggests that it is formed by direct coupling of HOO and CH2OH radicals. This constitutes the most conclusive evidence yet for the formation of a hydroperoxy radical and hydroxymethyl radical as the primary one-electron-transfer products of the reaction of CH3OH and O-2 at LMCT-excited framework Fe centers.