AN EXAMINATION OF SUPPORTED SILVER: SAMPLE PREPARATION, OXYGEN ADSORPTION AND BIMETALLIC INFLUENCE

The preparation of highly dispersed silver on (eta)-Al(,2)O(,3), SiO(,2) and TiO(,2) is reported. Different precursors salts, AgNO(,3), AgO(,2)C(,2)H(,3), AgO(,2)C(,2)F(,3) and AgO(,3)C(,3)H(,5), supported on TiO(,2) showed no effect on the resulting particle size of the supported Ag crystallites. The effect of reduction on the particle size of 2wt% Ag/(eta)-Al(,2)O(,3), Ag/SiO(,2) and Ag/TiO(,2) samples was investigated. For Ag/(eta)-Al(,2)O(,3) and Ag/SiO(,2) samples, reduction with formaldehyde or hydrazine gave larger particles than a high temperature hydrogen reduction. The reduction procedure had no influence on the particle size of the Ag/TiO(,2) sample.;A 0.71wt% Ag/TiO(,2) sample was prepared using AgO(,3)C(,3)H(,5). Characterization of this sample showed a dispersion of 65% assuming a 1 Ag atom: 1 O(,2) atom ratio, arguing against a 2 Ag atom: 1 oxygen atom ratio. This sample also showed an enhanced oxygen adsorption at high pressures (800 Torr), which is discussed.;Adsorption of oxygen on 13.3% Ag/(eta)-Al(,2)O(,3) was monitored until no further pressure changes were observed (1800 minutes). A rapid initial O(,2) adsorption is followed by a slower adsorption which tapers off until no further adsorption occurs. Four models are considered to explain the observed adsorption pattern: cleaning of the surface, oxygen spillover onto the support, diffusion, and a change in surface morphology. Of these the latter model seems most reasonable.;Cobalt and silver were supported by successive impregnations onto (eta)-Al(,2)O(,3). These samples were characterized by chemisorption. The presence of cobalt had no detectable effect on ethylene epoxidation catalysis. Silver led to an increase in activity and wider product distribution while lowering the activation energy for carbon monoxide hydrogenation.