Innovative operando HERFD-XAS characterization of diluted Cs promoters on Ag/alpha-Al2O3 as catalysts for ethylene epoxidation

Silver-based nanoparticle catalysts supported on alpha alumina are widely used for ethylene oxide production. Caesium alkali promoters, such as Cs oxide and Cs rhenate, are essential for improving selectivity. However, the molecular and electronic details of Cs species remain unknown. X-ray absorption spectroscopy with high-energy resolution fluorescence detection offers a powerful means to characterize highly diluted Cs species. By studying Cs oxide and Cs rhenate formulations under reaction conditions relevant to EO synthesis, we can determine for the first time the atomic structure of Cs species and possibly their interactions with silver surfaces. Gaining fundamental insights into the states of Cs promoters will enable the design of more effective EO catalysts.