Performance and regeneration studies of Pd–Ag/Al₂O₃ catalysts for the selective hydrogenation of acetylene

The selective hydrogenation of acetylene is one process to remove traces of acetylene from steam cracker cuts during the production of ethylene. Current disadvantages of commercially used Pd–Ag/Al₂O₃ catalysts applied in the C₂-tail end-selective hydrogenation are relative short cycle time (fast deactivation) caused by green oil formation and deposition of coke. Long-term tests were performed in a laboratory reactor under typical industrial conditions to investigate the deactivation of those catalysts. It was found that the Pd–Ag/Al₂O₃ catalyst with the highest long-term stability contains a Ag/Pd-ratio in the bulk of 0.41 and the lowest concentration of silver. This low silver amount causes a higher dilution of the palladium surface area than the higher silver amount within the investigated catalysts. This was indicated by CO chemisorption experiments, X-ray photoelectron spectroscopy (XPS), electron probe micro analysis (EPMA), X-ray fluorescence spectroscopy (XRF) and through the investigation of hydrocarbons deposited on the catalyst surface. The same catalyst sample was subsequently regenerated and tested in the laboratory reactor with respect to its long-term stability. The regenerated samples have the same long-term stability as the fresh sample if the regeneration procedure includes a hydrogen treatment