Tailored pore-confined single-site iron(III) catalyst for selective CH4 oxidation to CH3OH or CH3CO2H using O2

Abstract

Abstract Direct oxidation of methane to valuable oxygenates like alcohols and acetic acid under mild conditions poses a significant challenge due to high C‒H bond dissociation energy, facile overoxidation to CO and CO2 and the intricacy of C−H activation/C−C coupling. In this work, we develop a multifunctional iron(III) dihydroxyl catalytic species immobilized within a metal-organic framework (MOF) for selective methane oxidation into methanol or acetic acid at different reaction conditions using O2. The active-site isolation of monomeric FeIII(OH)2 species at the MOF nodes, their confinement within the porous framework, and their electron-deficient nature facilitate chemoselective C‒H oxidation, yielding methanol or acetic acid with high productivities of $$38,592\,\upmu {{{\rm{mol}}}}_{{{{\rm{CH}}}}_{3}{{\rm{OH}}}}{{{{\rm{g}}}}_{{{\rm{Fe}}}}}^{-1}{{{\rm{h}}}}^{-1}$$ 38 , 592 μ mol CH 3 OH g Fe − 1 h − 1 and $$81,043\,\upmu {{{\rm{mol}}}}_{{{{\rm{CH}}}}_{3}{{{\rm{CO}}}}_{2}{{\rm{H}}}}{{{{\rm{g}}}}_{{{\rm{Fe}}}}}^{-1}{{{\rm{h}}}}^{-1}$$ 81 , 043 μ mol CH 3 CO 2 H g Fe − 1 h − 1 , respectively. Experiments and theoretical calculations suggest that methanol formation occurs via a FeIII-FeI-FeIII catalytic cycle, whereas CH3CO2H is produced via hydrocarboxylation of in-situ generated CH3OH with CO2 and H2, and direct CH4 carboxylation with CO2.