Epitaxial palladium on tungsten film, which has a preferred (100) orientation, represents a rationally designed catalyst with a surface tailored to achieve high cis-semihydrogenation selectivity. Comparison with the Lindlar catalyst reveals improved cis selectivity and a much higher semihydrogenation selectivity. TEM studies provide evidence for bulk morphological changes of Pd foil that affect the selectivity of the hydrogenation reaction. Reactions on (111) and (110) Pd single crystals reveal a strong dependence of cis-selective semihydrogenation on the orientation of the metal, indicating surface structure sensitivity. Cyclic voltammetry is used to measure Pd foil surface areas and Pd foil was electrochemically roughened to alter its catalytic selectivity. © 1987, American Chemical Society. All rights reserved.