Fundamental insights into sintering of Ag/γ-Al2O3 catalysts

Randall Meyer, John Lockemeyer, Donald Reinalda, Randy Yeates, Michael Lemanski, Matthew Neurock

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Ethylene oxide production continues to be one of the most important processes in the basic chemicals industry [1]. This reaction is typically catalyzed by silver particles supported on a-A12O3. One of the primary issues with respect to commercial practice is the short catalyst lifetimes as these catalysts readily deactivate with time due to a loss of active surface area via silver agglomeration on the support [2]. While various mechanisms have been proposed to describe Ag sintering in these materials, experimental studies suggest that metal particle growth follows Ostwald-Ripening kinetics and behavior rather than coalescence dominated sintering [3]. In this work, we have used first-principle density functional theoretical studies in order to explore the elementary surface diffusion processes necessary to describe Ostwald-Ripening over different alumina surfaces. In particular, we examine the adsorption and diffusion of various different potential mobile species including single Ag atoms, small Ag clusters, AgOH, AgCl, and Ag2O over various surface terminations of α-Al2O3(0001). In order to establish the influence of the working environment we specifically probe the adsorption and diffusion of the mobile Ag species on Al-terminated, O-terminated and various different hydroxylated α-Al2O3 surfaces. Experiments on hydroxylated surfaces indicate that the presence of water serves to lower barriers to diffusion for Ag atoms as compared to the oxygen terminated surface but decreases diffusion as compared to the more stable aluminum terminated surface. We have also examined the influence of adsorbed heteroatoms on the detachment of silver from large particles. It is seen that the presence of Cl lowers the barrier to Ag atom emission.

Original languageEnglish (US)
Title of host publication05AIChE
Subtitle of host publication2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings
PublisherAmerican Institute of Chemical Engineers
Number of pages1
ISBN (Print)0816909962, 9780816909964
StatePublished - Dec 1 2005
Event05AIChE: 2005 AIChE Annual Meeting and Fall Showcase - Cincinnati, OH, United States
Duration: Oct 30 2005Nov 4 2005

Publication series

NameAIChE Annual Meeting Conference Proceedings
Volume2005

Other

Other05AIChE: 2005 AIChE Annual Meeting and Fall Showcase
Country/TerritoryUnited States
CityCincinnati, OH
Period10/30/0511/4/05

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