A recently developed, highly selective, CuSiO2 catalyst for the hydrogenation of unsaturated hydrocarbon contaminants in C-2 and C-3 alkene streams has been employed to remove alkynes from an industrial C-4 cracker stream. At a temperature of 320 degrees C and with approximately equal concentrations of H-2 and C-4 feed effectively all the contaminating alkynes and all the butadienes were hydrogenated selectively to butenes. No further hydrogenation of butenes to butanes was detected. The purified C-4-stream was successfully employed in a butene dimerization reaction catalyzed by a homogeneous, Ziegler-type nickel catalyst system [Ni(dithioacetylacetonato) (P(n)Bu(3)) Cl + diethylaluminiumchloride] . Prior to selective hydrogenation, alkynes present in the C-4 Stream had poisoned the nickel catalyst. After removing the contaminants dimerization proceeded with an activity (1480 turnovers/h) and product distribution in line with that observed using pure 1-butene feeds.