(628a) Interactions between CO2 and Cl Modifiers on Ag Catalyzed Ethylene Epoxidation

Ethylene epoxidation is a critical reaction in the chemical industry, yielding ethylene oxide (EO) by catalytically converting ethylene and oxygen using a highly engineered silver (Ag) catalyst. This process is inherently influenced by the presence of carbon dioxide (CO₂) and chlorine (Cl) under industrial reaction conditions. CO₂ arises due to the thermodynamic tendency of ethylene and EO to undergo combustion, necessitating low per-pass ethylene conversion (typically 10-15%), consequently requiring process stream recycling. Residual CO₂ in the recycle stream has been shown to significantly impact catalytic activity. Meanwhile, Cl plays a pivotal role as a promoter in enhancing selectivity.

While there have been studies focusing on the effects of CO₂ and Cl on promoted Ag catalysts and in surface science, the understanding of how these components influence the epoxidation mechanism on the unpromoted, supported Ag catalyst remains limited. To address this knowledge gap, we utilize alumina-supported Ag nanoparticles, synthesized colloidally within relevant size ranges, to dissect the independent and concurrent effects of CO₂ and Cl on reaction rates and selectivity.

Our research employs kinetic analysis to determine modified activation barriers and reaction orders in the presence of CO₂ and Cl. Additionally, in-situ UV-VIS spectroscopy with high temporal resolution is used to monitor the rate of change in features associated with Ag and Ag-O. By combining kinetic analysis with in-situ structural measurements, we develop a comprehensive framework elucidating how CO­₂ and Cl act synergistically and individually to influence overall reactivity.