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Developing highly efficient catalysts for chemoselective oxidation of methane to methanol under mild conditions is a grand challenge. We report the successful design and synthesis of a heterogeneous single-site cobalt hydroxide catalyst Ce-UiO-Co(OH) supported by the nodes of a cerium metal–organic framework (Ce-UiO-66 MOF), which is efficient in partial methane oxidation using hydrogen peroxide at 80 °C, giving an extraordinarily high methanol yield of 2166 mmol gcat–1 in 99% selectivity with a turnover number of 3250. The Ce-UiO-Co catalyst is significantly more active and selective than its iso-structural zirconium analogue Zr-UiO-Co in methane to methanol conversion. Experimental and computational studies suggest the formation of the CoIII(η2-hydroperoxide) intermediate coordinating with one μ4-O– and two neutral carboxylate oxygens of Ce4+ oxo nodes within the pores of Ce-UiO-66, which undergoes σ-bond metathesis with the methane C–H bond in the turnover limiting step of the catalytic cycle. The significantly lower activation energy of Ce-UiO-Co than Zr-UiO-Co is due to the highly electron-deficient nature of the cobalt ion of the Co(η2-O2H) species supported by the Ce-UiO nodes, which promotes facile C–H activation of methane via σ-bond metathesis. This MOF-based catalyst design holds promise in developing molecular electrophilic abundant metal catalysts for chemoselective functionalization of saturated hydrocarbons.
Antil et al. (Wed,) studied this question.