Selective hydrogenation of acetylene in the presence of ethylene on K+-β-zeolite supported Pd and PdAg catalysts

The selective hydrogenation of acetylene in the presence of ethylene has been studied on K+ exchanged β-zeolite supported Pd and PdAg catalysts. Results from batch reactor studies with Fourier transform infrared spectroscopy (FTIR) have shown that the K+-β-zeolite support is more selective than the Al2O3 or Na+-β-zeolite supports toward the hydrogenation of acetylene. The rate and equilibrium constants for Pd/K+-β-zeolite and PdAg/K+-β-zeolite were determined using a Langmuir–Hinshelwood model. The selectivity of the PdAg bimetallic catalyst is twice of that of the Pd catalyst. Results from flow reactor studies show that the PdAg/K+-β-zeolite catalyst has higher selectivity but lower activity toward acetylene hydrogenation than the Pd/K+-β-zeolite catalyst. The selectivity to the undesirable ethane by-product is inhibited on the bimetallic catalyst. Extended X-ray absorption fine structure (EXAFS) studies and transmission electron microscope (TEM) analysis confirm the formation of Pd–Ag bimetallic bonds in the PdAg/K+-β-zeolite catalyst.

The K+-β-zeolite supported Pd and PdAg catalysts have been synthesized and evaluated using both FTIR batch reactor and flow reactor. The bimetallic PdAg catalyst shows much higher selectivity but lower activity for acetylene hydrogenation in presence of ethylene than the Pd monometallic catalyst. The novel K+-β-zeolite support led to an increase in selectivity due to the preferential adsorption of acetylene over ethylene. This support is superior to the γ-Al2O3 and Na+-β-zeolite used in our previous studies. Figure optionsDownload as PowerPoint slide