Characterization of Na+-β-zeolite supported Pd and PdAg bimetallic catalysts using EXAFS, TEM and flow reactor

Flow reactor studies of the selective hydrogenation of acetylene in the presence of ethylene have been performed on Na+ exchanged β-zeolite supported Pd, Ag and PdAg catalysts, as an extension of our previous batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40–51]. Results from flow reactor studies show that the PdAg/Na+-β-zeolite bimetallic catalyst has lower activity than Pd/Na+-β-zeolite monometallic catalyst, while Ag/Na+-β-zeolite does not show any activity for acetylene hydrogenation. However, the selectivity for the PdAg bimetallic catalyst is much higher than that for either the Pd catalyst or Ag catalyst. The selectivity to byproduct (ethane) is greatly inhibited on the PdAg bimetallic catalyst as well. The results from the current flow reactor studies confirmed the pervious results from batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40–51]. In addition, we used transmission electron microscope (TEM), extended X-ray absorption fine structure (EXAFS), and FTIR of CO adsorption to confirm the formation of Pd–Ag bimetallic alloy in the PdAg/Na+-β-zeolite catalyst.

Alloying Pd with Ag reduced the acetylene hydrogenation activity but increased the selectivity. The apparent activation energy of acetylene hydrogenation on Pd/Na+-β-zeolite and PdAg/Na+-β-zeolite were estimated to be 8 kcal/mol and 15.2 kcal/mol. The formation of PdAg bimetallic particles on the Na+-β-zeolite support was confirmed by TEM, EXAFS, and CO adsorption using FTIR spectroscopy.Figure optionsDownload as PowerPoint slide