Speciation of Cu-Oxo Clusters in Ferrierite for Selective Oxidation of Methane to Methanol

Abstract

Cu-oxo nanoclusters in Cu-exchanged zeolites oxidize methane to methanol via a three-step process. Cu-exchanged ferrierite shows high reactivity to this selective oxidation at both ambient and elevated methane pressures. The active sites are dimeric Cu clusters located in the eight-membered channels of ferrierite, containing two oxygen atoms with different reactivities. Combining in situ ultraviolet-visible (UV-vis), X-ray absorption spectroscopy (XAS), and Raman spectroscopy, it is shown that the active site is a [Cu2O2]2+ cluster stabilized at pairs of negatively charged aluminum oxygen tetrahedra. This cluster is able to oxidize up to two methane molecules at elevated methane chemical potential.