Methane Oxidation to Methanol Catalyzed by Cu-oxo Clusters Stabilized in NU-1000 Metal-organic Framework

Ikuno, T.; Zheng, J.; Vjunov, A.; Sanchez-Sanchez, M.; Ortuño, M. A.; Pahls, D. R.; Fulton, J. L.; Camaioni, D. M.; Li, Z.; Ray, D.; Mehdi, B. L.; Browning, N. D.; Farha, O. K.; Hupp, J. T.; Cramer, C. J.; Gagliardi, L.; Lercher, J. A.
J. Am. Chem. Soc. 2017, 139, 10294 (doi:10.1021/jacs.7b02936).

Copper oxide clusters synthesized via atomic layer deposition on the nodes of the metal-organic framework NU- 1000 are active for oxidation of methane to methanol under mild reaction conditions. Analysis of chemical reactivity, in situ X-ray absorption spectroscopy, and density functional theory calculations are used to determine structure/activity relations in the Cu-NU-1000 catalytic system. The Cu-loaded MOF contained Cu as clusters of a few atoms each. The Cu was present at ambient conditions as a mixture of ~15% Cu⁺ and ~85% Cu²⁺. The oxidation of methane on Cu-NU-1000 was accompanied by the reduction of 9% Cu in the catalyst from Cu²⁺ to Cu⁺. The products, methanol, dimethyl ether and CO₂, were desorbed with the passage of 10% water/He at 135 ^oC, giving a carbon selectivity for methane to methanol of 45-60%. Cu-NU-1000 is an interesting first-generation of MOF-based selective methane oxidation catalysts stabilizing Cu oxo-clusters.