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|Author(s):||S Sambasivan; Daniel A. Fischer; B M. DeKoven; A Kuperman;|
|Title:||Direct Observations of Propylene and Silver Transformations on the Surface and in the Pores of Silver Y Zeolites|
|Published:||December 01, 2000|
|Abstract:||Near-Edge Soft X-ray Absorption Spectroscopy Fine Structure (NEXAFS) electron yield (surface sensitive about 50 ) and fluorescence yield (bulk sensitive) have been applied simultaneously to characterize the adsorbed state of propylene in the surface and the bulk of the silver exchanged faujasite (LZY-52) catalyst. This technique is a non-destructive, element specific, and a direct probe of the bonding and concentration of the adsorbed species, and reactive intermediates on a highly complex zeolite catalyst. Propylene adsorption on Ag/LZY-52 faujasite at 125 K showed that a bulk adsorbed state was a weakly interacting gas-phase like species with a highly intense carbon 1s to p* signal which begin to desorb upon heating from 150 K to 300 K. On the other hand the propylene adsorbed on the surface forms a strongly chemisorbed intermediate with a weak carbon 1s to p* transition but a strong s* transition indicating a formation of a sigma complex which is stable up to 250 K. Very little propylene was adsorbed on a zeolite with the same framework structure, high Si/Al ratio and no silver loading. The difference in propylene adsorption in the bulk and on the surface of Ag/LZY-52 is explained by the difference in acidity and the size of the Ag particles on the surface of the zeolite and in the bulk. It is demonstrated that NEXAFS is a powerful new molecular probe of elementary reaction steps in heterogeneous catalysis.|
|Research Areas:||Ceramics, Characterization|