1. Isoprene and 1,3-pentadiene can be hydrogenated to olefins, without paraffin formation, on a palladium alloy containing 9.8% ruthenium. 2. The rate of 1,3-pentadiene hydrogenation is higher when hydrogen feed is by diffusion through the membrane catalyst than when the hydrogen is fed as part of a mixture with the hydrocarbon vapors. With the partial pressures of hydrogen and 1,3-pentadiene each greater than unity, the principal hydrogenation product is cis-2-pentene, with mixture hydrogen feed, and 1-pentene, with hydrogen feed through the membrane catalyst. 3. Although the rate of isoprene hydrogenation also increases as one passes from mixture to diffusion hydrogen feed, the effect is not as pronounced as in the 1,3-pentadiene hydrogenation. © 1981 Plenum Publishing Corporation.