Metal-Organic Framework-Encaged Monomeric Cobalt(III) Hydroperoxides Enable Chemoselective Methane Oxidation to Methanol

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?, giving an extraordinarily high methanol yield of 2166 mmol g(cat)( -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 Co-III(eta(2)-hydroperoxide) intermediate coordinating with one mu(4)-O- and two neutral carboxylate oxygens of Ce4+ oxo nodes within the pores of Ce-UiO-66, which undergoes sigma-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(eta(2)-O2H) species supported by the Ce-UiO nodes, which promotes facile C-H activation of methane via sigma-bond metathesis. This MOF-based catalyst design holds promise in developing molecular electrophilic abundant metal catalysts for chemoselective functionalization of saturated hydrocarbons.

Automated summary

This article reports the development of a highly efficient catalyst for the selective oxidation of methane to methanol under mild conditions. The catalyst, a cobalt hydroxide supported by a cerium metal-organic framework, achieves a high methanol yield and selectivity using hydrogen peroxide as the oxidant. Experimental and computational studies provide insights into the active sites and catalytic mechanism of the catalyst.