Study of Cs-promoted, {alpha}-alumina-supported silver, ethylene-epoxidation catalysts. II. Effects of aging

Journal Article · Thu Aug 01 04:00:00 EDT 1996 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1996.0258· OSTI ID:508440

Hoflund, G B ^[1]; Minahan, D M ^[2]

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1. Univ. of Florida, Gainesville, FL (United States)
2. Union Carbide Corp., South Charleston, WV (United States)

The aging effects of an {alpha}-alumina-supported Ag, ethylene epoxidation catalyst have been examined as a function of reaction time in a Berty backmix reactor. The catalyst was prepared by impregnation of commercial {alpha}-alumina pellets (1.3 m{sup 2}/g) in a Ag{sub 2}O/lactic acid solution and contained 13.87 wt% Ag and 420 ppm Cs by weight. The fresh and used catalysts have been characterized using scanning electron microscopy (SEM), ion scattering spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. With aging, the fresh catalyst becomes more active (percentage of conversion to ethylene oxide increases), and then the activity drops with increasing reaction time. Large changes are observed in the spectra obtained from these surfaces which are due primarily to morphological changes caused by sintering as observed in the SEM micrographs. The surface Cl content is increased at the support surface by adsorption of ethyl chloride, added in small amounts to the feed gas as a moderator, from the gas phase. The surface also becomes enriched in Na due to migration of the Na binder material to the surface where it associates with the Cl to from NaCl. The SEM micrographs indicate that both the Ag and alumina crystallites grow with age and that the large Ag crystallites do not interact with the aged alumina surface suggesting that the formation of NaCl plays a role in the sintering process. 12 refs., 5 figs.

• OSTI ID: 508440
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 162; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

10 SYNTHETIC FUELS
40 CHEMISTRY
ALUMINIUM OXIDES
AUGER ELECTRON SPECTROSCOPY
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CESIUM
ETHYLENE
ION SCATTERING ANALYSIS
OXIDATION
SCANNING ELECTRON MICROSCOPY
SILVER
SINTERING