Effect of Ag-promotion on Pd catalysts by XANES

Pd L-3 near-edge absorption measurements (XANES) were performed on four commercial acetylene hydrogenation catalyst samples, with and without the Ag promoter. The Pd L-3 edge XANES spectra showed that the Ag-promoted catalysts have relatively weaker absorption peaks and they follow the same order as the relative commercial performances of the four catalysts studied in terms of selectivity in ethylene purification, which indicates that there are increases in the Pd d-band electron densities due to the addition of Ag. These results provide a reasonable explanation for the observed improvement in selectivity of the Ag-promoted acetylene hydrogenation catalysts. The Ag L-3 XANES spectra of the supported Pd-Ag catalysts indicate the absence of a white-line feature which seems to suggest that the charge transferred from Ag to Pd may not be the d-type.