A cyclic process for the purification of a diolefin hydrocarbon stream produced in a naphtha steam cracker to produce a high quality diolefin hydrocarbon stream having extremely low levels of acetylene over an extended period because of the ability to readily cyclically regenerate catalyst contained in an off-line selective hydrogenation reaction zone. The spent or partially spent catalyst is contacted with a stream containing naphtha and hydrogen to restore at least a portion of the fresh catalyst activity by the extraction of polymer compounds therefrom.