The process of the invention comprises contacting a hydrocarbon stream, comprising light olefins plus impurities such as acetylenes, in the absence of hydrogen with a supported copper catalyst, preferably CuO/alumina. The acetylene component undergoes a coupling reaction producing a diacetylene which can be more readily removed. Thus, the methylacetylene (MA) contaminant in liquid propylene yields at about 80.degree. C. and 3792 kPa (550 psig) a significant amount dimethyl diacetylene (2,4-hexadiyne). Surprisingly, very little cyclization products are present. The process is useful for purification of olefin feeds. It can be used alone or in combination with known purification methods such as catalytic distillation or selective hydrogenation.