The following zeolite materials were used in this study: Ag 6 Na 46 Y, Ag 16 -Na 36 Y, and Ag 52 Y. These materials were prepared by ion-exchange of the sodium form of LZY-52 (UOP) using standard procedures. For the NEXAFS experiments the powder samples were pressed into aluminum studs (about 10 mm in diameter and 1 mm in depth). The pressed samples were heated resistively in a high vacuum chamber at about 350 C for 30 min to remove the preadsorbed water. Subsequently the faujasites (LZY-52) with and without Ag loading were cooled to 125 K and the NEXAFS spectrum was recorded prior to dosing with 100 L (100 s at 1Β΄10 Β±6 torr pressure) of propylene gas (ultra high purity grade). The X-ray absorption experiments (NEXAFS) at the carbon K-edge were carried out at the National Synchrotron Light Source U7A Beamline, which is equipped with a toroidal mirror spherical grating monochromator [30]. The incident photon energy resolution and intensity were 0.2 eV and 5Β΄10 10 photon/s respectively for an incident photon energy of 300 eV and a typical storage ring current of 500 mA. The monochromator energy resolution and photon energy was calibrated by comparing gas-phase carbon monoxide with electron-energy-loss reference data [31]. The carbon FY intensity was measured utilizing a differentially pumped, high-vacuum-compatible proportional counter filled with 200 torr of P-90 (90 % methane, 10 % argon) in an energy dispersive mode [32] to reduce background fluorescence from other elements. Electron yield measurements were made surface sensitive (probe depth of approximately 3Β±5 nm) by applying a negative bias of Β±100 V at the cone (entrance) of the channeltron. The sample was charge compensated using a low-energy electron flood gun. FY and EY data were normalized using the photo yield from a clean gold grid (I o yield). All NEXAFS data were recorded with the incoming photon beam normal to the sample surface.