Low-Temperature Methane Activation Reaction Pathways over Mechanochemically-Generated Ce⁴⁺/Cu⁺ Interfacial Sites

Methane is a valuable resource and its valorization is an important challenge in heterogeneous catalysis. Here it is shown that CeO₂/CuO composite prepared by ball milling activates methane at a temperature as low as 250 °C. In contrast to conventionally prepared catalysts, the formation of partial oxidation products such as methanol and formaldehyde is also observed. Through an in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and operando Near Edge X-Ray Absorption Fine Structure Spectroscopy (NEXAFS) approach, it can be established that this unusual reactivity can be attributed to the presence of Ce⁴⁺/Cu⁺ interfaces generated through a redox exchange between Ce³⁺ and Cu²⁺ atoms facilitated by the mechanical energy supplied during milling. DFT modeling of the electronic properties confirms the existence of a charge transfer mechanism. These results demonstrate the effectiveness and distinctiveness of the mechanical approach in creating unique and resilient interfaces thereby enabling the optimization and refining of CeO₂/CuO catalysts in methane activation reactions.