Ca-Ag compounds in ethylene epoxidation reaction.

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Ethylene epoxidation is a critical industrial process demanding highly active and selective catalysts.
• Understanding catalyst behavior under reaction conditions is essential for developing improved catalytic systems.

Purpose of the Study:

• To systematically investigate the chemical behavior of Ca-Ag intermetallic compounds under ethylene epoxidation conditions.
• To correlate the atomic interactions and chemical nature of Ca-Ag compounds with their reactivity and catalytic performance.

Main Methods:

• Experimental study of Ca-Ag intermetallic compounds under ethylene epoxidation conditions.
• Surface characterization and analysis of oxidation products.
• First-principles calculations and chemical bonding analysis.

Main Results:

• Ag-rich Ca-Ag compounds (Ca2Ag7, CaAg2) oxidize to form fcc Ag and a Ca-based support.
• Ca-rich Ca-Ag compounds (CaAg, Ca5Ag3, Ca3Ag) exhibit bulk stability under harsh epoxidation conditions.
• Water vapor in the gas stream causes corrosion in the stable Ca-rich compounds.

Conclusions:

• The atomic interactions within Ca-Ag intermetallic compounds dictate their surface oxidation behavior and catalytic properties.
• Stable Ca-Ag compounds offer potential as supports or components in ethylene epoxidation catalysts, with considerations for water vapor presence.
• This study provides fundamental insights into structure-reactivity relationships for designing effective ethylene epoxidation catalysts.