Purification of normal α-olefins by removal of dienes has been demonstrated previously in our laboratories by π-complexation using Ag+ ion-exchanged zeolite (Ag−Y) or AgNO3/SiO2 sorbent. Although Ag−Y could purify 1-butene/1,3-butadiene effectively, the purification performance was degraded by H2 and/or H2S poisoning. A new sorbent for 1-butene/1,3-butadiene purification was developed in this study by ion-exchange of Cu2+ cations into Y-zeolite followed by reduction of Cu2+ to Cu+. The performance of the Cu+-zeolite, Cu(I)−Y or Cu−Y, was found to be superior to that of Ag−Y. Cu−Y exhibited higher diene/olefin separation factors than Ag−Y by approximately an order of magnitude. Furthermore, unlike Ag−Y, exposure to H2S/H2 at 120 °C had virtually no effect on 1,3-butadiene/1-butene adsorption, indicating the excellent poisoning resistance of Cu−Y. XPS and EPR analyses showed that half of the Cu2+ cations in Cu−Y underwent autoreduction to Cu+ either in vacuo or in He, resulting in the same purification capability with Cu−Y obtained by reduction with CO.