A Pd/gamma-Al2O3 membrane supported on a macroporous alpha-Al2O3 tube was prepared by sol-gel processing and used in the partial hydrogenation of acetylene and 1,3-butadiene. The average pore diameter of the Pd/gamma-Al2O3 membrane was 3.6 nm. The gases were separated by Knudsen diffusion. The activity and selectivity of the Pd/gamma-Al2O3 membrane was compared to that of Pd/gamma-Al2O3 catalysts used in a conventional packed bed reactor. The highest selectivity to the partially hydrogenated products occurred when the reactant was premixed with H-2 and was passed through the membrane wall.