In Situ Studies of Methane Activation Using Synchrotron-Based Techniques: Guiding the Conversion of C-H Bonds

Methane is a major component in natural gas, and its reforming or conversion to commodity chemicals (oxygenates, olefins, aromatics) has attracted a lot of attention. While many approaches have been explored, none to date has proven to be cost-effective. This highlights the need to identify catalytic materials that can activate and transform C-H bonds in a controlled manner. In simple terms, the lower the temperature for methane activation, the larger is the lifetime of CHx species and the greater is the probability of transforming them into high value chemicals. The rational design of advanced catalysts heavily relies on a basic understanding of all the essential elements in the transformation process, including the catalyst active sites and the associated reaction mechanism, making in situ characterization under working conditions necessary. In recent years, synchrotron-based characterization techniques such as ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), time-resolved X-ray diffraction (TR-XRD), X-ray absorption fine structure (XAFS), scanning transmission X-ray microscopy (STXM), and micro-X-ray diffraction computed tomography (XRD-CT) have substantially increased our fundamental knowledge of the chemical steps involved in methane conversion, showing when the hydrocarbon molecule is activated and when it reacts extensively with the metal and oxide components of a catalyst. This Perspective provides an overview of utilizing state-of-the-art in situ characterization tools under different reaction conditions. The benefits of applying these techniques to gain a deeper understanding of methane chemistry are discussed. At the end, the prospects of using in situ methods in future studies of methane activation/conversion are also examined.