Promoting effects of Re and Cs on silver catalyst in ethylene epoxidation

The study of ethylene epoxidation on promoted silver catalysts has been an active field in recent years. Alkali metals, boron, thallium, antimony, etc., are often incorporated into practical Ag/[alpha]-Al[sub 2]O[sub 3] catalysts in order to improve the selectivity of ethylene oxide. In recent work, it has been found that both Re and Cs added to Ag/[alpha]-Al[sub 2]O[sub 3] can increase the selectivity greatly, but no further information about the function of promoters was given. The authors have recently reported that the Re-promoted electrolytic silver catalyst appears to have a higher selectivity for ethylene epoxidation, and have investigated the function of Re. Most investigators had been concerned with the nature of promoters in ethylene epoxidation. The promoting effects of alkali and alkaline earth metal compounds were studied by Lambert and co-workers, and Campbell with surface science techniques. Most of these experiments were carried out on single Ag crystals. The present work describes the promoting effects of adding Re and Cs to electrolytic silver, on ethylene epoxidation and the adsorption of oxygen on the sample surface. The nature of Re and Cs promoters is also reported. 21 refs., 3 figs., 1 tab.