Regeneration of supported palladium catalyst for selective hydrogenation of acetylene

The catalytic performance and the physicochemical characterization of a commercial palladium catalyst have been studied before and after regeneration treatments. The spent catalyst was in continuos operation by 7 years in a commercial ethylene purification plant. The industrial conditions used to regenerate the samples have shown to be a very efficient way to eliminate adsorbed hydrocarbons and to burn coke deposits. The results of catalytic activity test correlate very well with the free metal surface area (dispersion) obtained by hydrogen-oxygen titration cycles (HOTC) method. The regenerated sample has the 50% of the metal dispersion measured on fresh sample, nevertheless regenerated and fresh samples have almost the same catalytic activity. This fact is attributed to a high deactivation rate by coke deposition in fresh samples during the earliest moments of reaction. Finally, hydrocarbon polymeric species coating catalytic metal surface have important implications on selectivity. Coke deposits could promote hydrogen transference to acetylene and ethylene adsorbed molecules leading to a decrease in ethylene selectivity and an increase in ethylene loss.