AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM11
Direct Observation of Propylene Transformation Chemistry on and in the Pores of Silver Exchanged Faujasite Catalyst

Tuesday, October 26, 1999, 11:40 am, Room 607

Session: Model Catalysts
Presenter: S. Sambasivan, Brookhaven National Laboratory
Authors: S. Sambasivan, Brookhaven National Laboratory
D.A. Fischer, National Institute of Standards and Technology
A. Kuperman, Dow Chemical Company
B.M. DeKoven, Intevac Inc.
Correspondent: Click to Email
For the first time Near-Edge Soft X-ray Absorption Spectroscopy Fine Structure (NEXAFS) electron yield (surface sensitive about 50 Å) 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 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 @pi@ *intensity which begins 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 small of carbon 1s to @pi@ * intensity but a strong @sigma@ * intensity indicating a formation of a sigma complex which is stable up to 250 K. A very small adsorption of propylene was observed on a zeolite with similar cage structure, high Si/Al ratio and no silver loading. The difference in the nature propylene adsorption in the bulk and surface of Ag/LZY-52 is discussed with respect to the difference in acidity and the size of the Ag particles in the surface and bulk zeolite. The NEXAFS technique is demonstrated as a practical new probe of molecular level reaction chemistry in catalyst materials.