STUDY OF CS-PROMOTED, ALPHA-ALUMINA-SUPPORTED SILVER, ETHYLENE EPOXIDATION CATALYSTS .3. CHARACTERIZATION OF CS-PROMOTED AND NONPROMOTED CATALYSTS

A nonpromoted Ag/alpha-Al2O3 catalyst and a Ag/alpha-Al2O3 catalyst pr omoted with 420 ppm Cs used for ethylene epoxidation were studied usin g scanning electron microscopy (SEM), ion scattering spectroscopy (ISS ), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). SEM, ISS, XPS, and AES data indicate that the Cs-promoted catalyst consists of a thin fi lm of Ag covering most of the support surface. Both a thin film and sm all Ag clusters exist on the nonpromoted catalyst, but the alumina is only partially covered. ISS and SIMS depth profiling data taken from t he promoted catalyst indicate that most of the Cs lies beneath the sur face although a small amount is present at the surface. The surface ch aracterization data suggest that the Cs coats the support material dur ing the preparation and acts as a binder between the Ag and the suppor t resulting in a larger Ag coverage of the alpha-alumina. Total oxidat ion of ethylene and ethylene oxide occur primarily on the alumina surf ace. The enhancement in selectivity toward ethylene epoxidation may re sult from the fact that Cs addition results in the thin Ag film coveri ng the alumina. (C) 1997 Academic Press.