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 O 2 at the gas−micropore interface of a FeAlPO 4 -5 sieve has been studied by time-resolved FT-IR spectroscopy. Measurements using the rapid-scan method revealed that the final products, HCO 2 - ···Fe and H 2 O, emerge with a rise time of 4 s (250 K) by decomposition of the two-electron-transfer intermediate, HO 2 CH 2 OH. 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 HCO 2 H + H 2 O on the millisecond and second time scale. Formaldehyde was observed as minor two-electron oxidation product. The fast rise of the HO 2 CH 2 OH intermediate strongly suggests that it is formed by direct coupling of HOO and CH 2 OH 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 CH 3 OH and O 2 at LMCT-excited framework Fe centers.