Activity of Cu–Al–Oxo Extra-Framework Clusters for Selective Methane Oxidation on Cu-Exchanged Zeolites
Insu Lee, Mal‐Soon Lee, Lei Tao, Takaaki Ikuno, Rachit Khare, Andreas Jentys, Thomas Huthwelker, Camelia N. Borca, Aleksandr Kalinko, Oliver Y. Gutiérrez, Niranjan Govind, John L. Fulton, Jian Zhi Hu, Vassiliki‐Alexandra Glezakou, Roger Rousseau, Maricruz Sanchez‐Sanchez, Johannes A. Lercher
Abstract
Cu-zeolites are able to directly convert methane to methanol via a three-step process using O 2 as oxidant. Among the different zeolite topologies, Cu-exchanged mordenite (MOR) shows the highest methanol yields, attributed to a preferential formation of active Cu-oxo species in its 8-MR pores. The presence of extraframework or partially detached Al species entrained in the micropores of MOR leads to the formation of nearly homotopic redox active Cu-Al-oxo nanoclusters with the ability to activate CH 4 . Studies of the activity of these sites together with characterization by This Cu-Al-oxo cluster shows an activity per Cu in methane oxidation significantly higher than of any previously reported active Cu-oxo species. In order to determine unambiguously the structure of the active Cu-Al-oxo cluster, we combine experimental XANES of Cu K-and L-edges, Cu K-edge HERFD-XANES, and Cu K-edge EXAFS with TDDFT and AIMD-assisted simulations. Our results provide evidence of a [Cu 2 AlO 3 ] 2+ cluster exchanged on MOR Al pairs that is able to oxidize up to two methane molecules per cluster at ambient pressure.