Promoter-Induced Morphological Changes of Ag Catalysts for Ethylene Epoxidation
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The combination of high-throughput reactor experiments and scanning electron microscopy analysis of promoted Ag catalysts provides critical insights into mechanistic and morphological changes. In particular, catalysts promoted with Cu, Cd, Au, Pt, and Re were analyzed to understand the morphological effects of these promoters on the Ag particles. Cu increases the sintering of Ag particles, while Cd and Re were found to alter the Ag particle sizes into a trimodal distribution. However, contrasting effects of Re and Cd were found on the catalyst activity. Cd-Ag catalysts exhibited a 5-fold increase in the ethylene conversion for a variety of Cd loadings, compared to unpromoted Ag. Moderate increases in conversion and selectivity were seen with the addition of 25 ppm Re, while further Re impregnation led to decreases in ethylene conversion and ethylene oxide selectivity. Au and Pt block surface Ag sites by nucleating as separate particles on the silver surface. In doing so, they reduce the activity of the catalyst, but also reduce the sintering of the Ag particles. © 2009 American Chemical Society.
author list (cited authors)
Dellamorte, J. C., Lauterbach, J., & Barteau, M. A.