Advanced X-ray Absorption Spectroscopy Analysis to Determine Structure-Activity Relationships for Cu-Zeolites in the Direct Conversion of Methane to Methanol

An industrial process for direct conversion of methane to methanol (DMTM) would revolutionize methane as feedstock for the chemical industry and it would be a cherished contribution to climate change mitigation. At the present stage, it is a rather remote perspective, but the search for the materials that would make it possible and economically viable, is very active. Cu-exchanged zeolites have been shown to cleave the C−H bond of methane at low temperatures (≤200 °C), and has been extensively studied for the stepwise DMTM conversion over the last decades. The determination of the speciation of CuxOy-species in zeolites and the understanding of their role in the reaction mechanism has been heavily debated. Lately, advanced X-ray absorption spectroscopy (XAS) analysis has been standing out as a powerful technique for investigating the behavior of Cu in zeolites. In this review we focus on the in situ and operando studies of changes in the electronic and structural properties of Cu, during the different steps of the DMTM conversion uncovered by XAS, which have led to new and insightful information about the complex behavior of Cu-zeolites in the DMTM process.