Size effects in ethylene oxidation on silver catalysts. Influence of support and Cs promoter

• Published in: Applied catalysis. A, General General, 1995-05, Vol.126 (1), p.67-84
• Main Authors: Goncharova, S.N., Paukshtis, E.A., Bal'zhinimaev, B.S.
• Format: Article
• Language: English
• Subjects: Ethylene epoxidation; Ethylene π-complex; Silver catalyst; Silver particle size distribution; Size effect
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/0926-860X(95)00036-4

A new method for preparing supported silver catalysts with a narrow particle size distribution has been developed. For crystals with a diameter ranging from 100 to 1000 Å the dependencies of reaction rates on size have been studied for epoxidation and deep oxidation of ethylene. For particles 300–500 Å in size the reaction rate was found to increase sharply. The concentration of ethylene π-complexes with Ag + cations increased proportionally to the reaction rate. These π-complexes are assumed to be the only intermediates directing the reaction towards epoxidation. The ratio of the reaction rate to the concentration of π-complexes was found to remain constant within a wide range of Ag crystal sizes including bulk silver samples. The influence of the support (α-Al 2O 3, SiO 2) on the size effect relates to the secondary processes of ethylene oxide conversion. The factors that cause the catalytic size effect and the promoting effect of Cs are discussed.