1. The hydrogenation of cyclopentadiene, containing up to 25% of isoprene and 1.5% of 1,3-pentadiene, on a membrane catalyst composed of Pd alloy containing 9.8% Ru, proceeds at the same rate and selectivity in cyclopentene as does pure cyclopentadiene. 2. The relative adsorption coefficients of isoprene (0.6), 1,3-pentadiene (1.3), and cyclopentadiene (1) were determined. © 1981 Plenum Publishing Corporation.