Quantifying the Hydration-Dependent Dynamics of Copper Migration and Activity in Zeolite Omega for the Partial Oxidation of Methane

• Published in: Angewandte Chemie International Edition p. e202407395
• Main Authors: Wieser, Johannes, Wardecki, Dariusz, Fischer, Jörg W A, Newton, Mark A, Dejoie, Catherine, Knorpp, Amy J, Jeschke, Gunnar, Rzepka, Przemyslaw, van Bokhoven, Jeroen A
• Format: Journal Article
• Language: English
• Published: Germany 13.08.2024
• Subjects: Methane; Copper active sites; neutron diffraction; epr spectroscopy; Anomalous X-ray Diffraction
• ISSN: 1521-3773

Copper-exchanged zeolite omega (Cu-omega) is a potent material for the selective conversion of methane-to-methanol (MtM) via the oxygen looping approach. However, its performance exhibits substantial variation depending on the operational conditions. Under an isothermal temperature regime, Cu-omega demonstrates subdued activity below 230 °C, but experiences a remarkable increase in activity at 290 °C. Applying a high-temperature activation protocol at 450 °C causes a rapid deactivation of the material. This behavioral divergence is investigated by combining reactivity studies, neutron and in situ high-resolution anomalous X-ray powder diffraction (HR-AXRPD), as well as electron paramagnetic resonance spectroscopy, to reveal that the migration of Cu throughout the framework is the primary cause of these behaviors, which in turn is governed by the degree of hydration of the system. This work suggests that control over the Cu migration throughout the zeolite framework may be harnessed to significantly increase the activity of Cu-omega by generating more active sites for the MtM conversion. These results underscore the power of in situ HR-AXRPD for unraveling the behavior of materials under reaction conditions and suggest that a re-evaluation of Cu-zeolites priorly deemed inactive for the MtM conversion across a broader range of conditions and looping protocols may be warranted.