Preparation of propylene and butylene dimers using palladium cyanide as catalyst

A process for the selective dimerization of propylene and/or n-butylenes which comprises steps for (a) contacting under mechanical agitation an olefin reactant selected from the group consisting of propylene, 1-butene, 2-butene, and mixtures thereof with a heterogeneous palladium cyanide catalyst at a temperature in the range from about 50.degree. C. to 150.degree. C., the quantity of said palladium cyanide being between about 0.01 and 10 percent by weight calculated on the weight of olefin reactant, to produce a reaction product solution containing olefin reactant dimers, and (b) recovering said dimers from said product solution.