Photo-Fenton-induced selective dehydrogenative coupling of methanol into ethylene glycol over iron species-anchored TiO2 nanorods

Abstract

It is fascinating yet extremely challenging to cleave inert aliphatic C(sp³)–H bonds to form carbon–carbon (C–C) bonds directly under environmentally friendly conditions. Due to the highly complex bonds of organic molecules and the low reactivity of C(sp³)–H bonds, the selective activation of an inert C–H bond is typically difficult. Derived from various carbon resources, methanol (which has versatile chemical bonds) can serve as a superior renewable one-carbon feedstock for the large-scale production of fine chemicals. Herein, we choose methanol as a model molecule of aliphatic alcohols and demonstrate that inert aliphatic C–H bonds can be selectively fractured to form hydroxymethyl radicals (˙CH₂OH) by hydroxyl radicals (˙OH) from the photo-Fenton reaction over iron species-anchored TiO₂ nanorods (TiO₂/FeO_x nanorods). Subsequently, ethylene glycol is generated through C–C coupling of the hydroxymethyl radicals (˙CH₂OH). Benefiting from the synergistic effect of the Fenton and photocatalytic mechanisms, the dehydrogenative C–C coupling of methanol is highly efficient with TiO₂/FeO_x nanorods as photocatalysts, with the formation rate of ethylene glycol up to 37.8 mmol h⁻¹, selectivity higher than 78% and the methanol conversion rate up to 95.5 mmol h⁻¹. This work efficiently utilizes methanol and offers an atomically economical and green methodology for the selective functionalization of an inert aliphatic C(sp³)–H bond.