Effect of Preparation Conditions on Ag Catalysts for Ethylene Epoxidation

Abstract

The effect of calcination of silver catalysts supported on foamed monoliths was examined for the epoxidation of ethylene. Previous results suggested that calcination at 673 K for 3 h would give a maximum conversion. Further study revealed that calcination for [3 h reduced the catalyst surface area and therefore the conversion seen in reactor studies. This phenomenon has been attributed to sintering, with the migration of Ag from mesopores of the catalysts to macropore regions and the eventual formation of a Ag film covering the walls of the macropores. Studies of the metal loading showed that a tradeoff exists between metal loading and calcination time. Increasing the amount of silver can have a detrimental effect on catalysts calcined for 12 h, however the opposite trend, an increased conversion with higher loadings, was observed for catalysts calcined for 2 h. These results imply that the sintering of Ag can play a dramatic effect on catalyst design for optimum performance.

Gas-phase epoxidation of butadiene: Effect of the concentration and distribution of cesium on the properties of the Ag/α-Al2O3 catalyst

“…From the EDRS data, it thus follows that the heating of the samples modifies the silver surface at low Cs concentrations. This agrees with the earlier reported XRD studies of silver [20][21][22].…”

Biosynthesized Ag/α-Al2O3 catalyst for ethylene epoxidation: the influence of silver precursors

“…7c), the peak at 248 C could be attributed to the nucleophilic oxygen species desorbing from regular surface and the peak at 323 C to electrophilic oxygen species desorbing from imperfect or defect regions of the silver surface. [42][43][44] The desorption peak at 403 C was referred to oxygen species desorbing from the subsurface of silver. 45 And it was believed that nucleophilic oxygen species located on the regular surface of silver was responsible for promoting the adsorption of C 2 H 4 on Ag surface, 21 and the electrophilic oxygen species adsorbed on the silver defects surface could attack the carbon-carbon double bond of ethylene to produce EO.…”

A Deep Investigation of the Thermal Decomposition Process of Supported Silver Catalysts

“…From previous studies it is clear that properties of the final catalysts are significantly dependent on both the silver precursor and the preparation method employed. 8,9 Metallic silver catalysts can be prepared by reduction of a variety of precursors including its oxide, [10][11][12] nitrate, 9,13 oxalate, 14,15 lactate, 16 and other salts (e.g. silver neodecanoate 12 ).…”