in an absence of added hydrogen, passing a mixture comprising olefins and a hydrocarbon of from 2 to about 8 carbon atoms including at least one vinyl group, acetylenic impurities having the same or similar carbon content and, optionally, saturated hydrocarbon through a particulate bed of catalyst comprising predominantly a support material having high surface area on which is dispersed a metal oxide selected from the group consisting of copper oxide, silver oxide, gold oxide, palladium oxide, zinc oxide, and cadmium oxide;

converting a portion of said acetylenic impurities to their corresponding condensation products diynes while converting another portion of the acetylenic impurities to their corresponding olefins and thereby obtaining a purified effluent containing less of the acetylenic impurities as compared to said hydrocarbon mixture.