Paper SS2-ThA2
Cesium Promotion in Styrene Epoxidation on Silver Catalysts

Thursday, October 23, 2008, 2:20 pm, Room 208

The promotion roles of cesium in styrene epoxidation on silver catalysts have been studied by means of temperature-program reaction spectroscopy (TPRS), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). The TPRS data have shown that the addition of 0.1 ML cesium can inhibit the secondary oxidation of styrene on Ag(111), and more significantly, switch the partial oxidation pathway from the production of phenylacetaldehyde and phenylketene to the production of styrene oxide on Ag(110). The XPS studies have revealed the formation of selective oxametallacycle intermediate and the reduced transformation of this intermediate to a combustion intermediate in the reaction on 0.1 ML cesium-covered silver surface, comparing with the reaction on the clean silver surface. No significant change of the C 1s and O 1s binding energies for certain intermediates was observed, suggesting that cesium does not play obvious electronic effect on the bonding of the intermediates. The STM studies have disclosed an interesting (1x2) reconstruction of the Ag(110) surface induced by cesium and a (3x5) surface oxide structure on the cesium-reconstructed Ag(110) surface. This (3x5)-ordered surface oxide is superimposed on the highly corrugated Ag(111) micro-facets. Our studies provide the insight into the microscopic origins of the structural effects of cesium in styrene epoxidation on silver catalysts.