Fundamental insights into sintering of Ag/γ-Al₂O₃ catalysts

Ethylene oxide production continues to be one of the most important processes in the basic chemicals industry. This reaction is typically catalyzed by silver particles supported on α-Al₂O₃. The adsorption and diffusion of various different potential mobile species were studied including single Ag atoms, small Ag clusters, AgOH, AgCl, and Ag₂O over various surface terminations of α-Al₂O₃(0001). To establish the influence of the working environment, the adsorption and diffusion of the mobile Ag species were probed on Al-terminated, O-terminated, and various different hydroxylated α-Al₂O₃ surfaces. The presence of water served to lower barriers to diffusion for Ag atoms as compared to the oxygen terminated surface but decreased diffusion as compared to the more stable aluminum terminated surface. The influence of adsorbed heteroatoms on the detachment of silver from large particles was examined. The presence of Cl lowered the barrier to Ag atom emission. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).