Understanding the partial oxidation of propylene over silver catalysts: The effect of water and surface structure

Propylene oxidation over silver surfaces was investigated to develop an understanding of this important catalytic oxidation process. To determine the effects of surface reconstruction, water coadsorption, and support interactions, silver single crystal surfaces and supported/promoted silver materials were characterized using a combination of surface spectroscopies. On oxygen covered Ag(110), propylene combustion is observed. Disordered oxygen atoms are 10 times more active for combustion than oxygen embedded into the reconstructed O-Ag(110) surface. Oxygen adsorption on Ag(110) results in a 30% increase in the propylene and propylene oxide desorption activation energy. Coadsorption of water on O-Ag(110), forming OH groups, completely passivates propylene combustion and lowers the desorption activation energy of both propylene and propylene oxide. These results are consistent with the increased catalytic selectivity for propylene oxide production observed in the presence of water. Multilayer water coverages displace non-polar propylene resulting in an even lower desorption energy, while more polar propylene oxide and 2-propanol are not displaced. 2-propanol reacts with oxygen on Ag(110) forming acetone via an alkoxide intermediate, even in the presence of water multilayers. On silver supported on high surface area TiO...