Methane‐to‐Methanol on Mononuclear Copper(II) Sites Supported on Al <sub>2</sub> O <sub>3</sub> : Structure of Active Sites from Electron Paramagnetic Resonance**
Jordan Meyet, Anton Ashuiev, Gina Noh, Mark A. Newton, Daniel Klose, Keith Searles, Alexander P. van Bavel, Andrew D. Horton, Gunnar Jeschke, Jeroen A. van Bokhoven, Christophe Copéret
Abstract
Abstract The selective conversion of methane to methanol remains one of the holy grails of chemistry, where Cu‐exchanged zeolites have been shown promote this reaction under stepwise conditions. Over the years, several active sites have been proposed, ranging from mono‐, di‐ to trimeric Cu II . Herein, we report the formation of well‐dispersed monomeric Cu II species supported on alumina using surface organometallic chemistry and their reactivity towards the selective and stepwise conversion of methane to methanol. Extensive studies using various transition alumina supports combined with spectroscopic characterization, in particular electron paramagnetic resonance (EPR), show that the active sites are associated with specific facets, which are typically found in γ‐ and η‐alumina phase, and that their EPR signature can be attributed to species having a tri‐coordinated [(Al 2 O)CuIIO(OH)] − T‐shape geometry. Overall, the selective conversion of methane to methanol, a two‐electron process, involves two monomeric Cu II sites that play in concert.