EFFECT OF AG-PROMOTION ON PD CATALYSTS BY XANES

Pd L-3 near-edge absorption measurements (XANES) were performed on fou r commercial acetylene hydrogenation catalyst samples, with and withou t the Ag promoter. The Pd L-3 edge XANES spectra showed that the Ag-pr omoted catalysts have relatively weaker absorption peaks and they foll ow the same order as the relative commercial performances of the four catalysts studied in terms of selectivity in ethylene purification, wh ich indicates that there are increases in the Pd d-band electron densi ties due to the addition of Ag. These results provide a reasonable exp lanation for the observed improvement in selectivity of the Ag-promote d acetylene hydrogenation catalysts. The Ag L-3 XANES spectra of the s upported Pd-Ag catalysts indicate the absence of a white-line feature which seems to suggest that the charge transferred from Ag to Pd may n ot be the d-type.