A novel approach to the selective hydrogenation of acetylene involves a short contact time reactor. A thin Pd/gamma-Al2O3 catalytic membrane (about 5 mum thick) was observed to be void of minor defects. Forcing a dilute C2H2/H-2/Ar mixture through the layer produced high conversions coupled with high selectivity at high temperatures. The selectivity was observed to increase with temperature. A gas-dispersion model with derived kinetics was employed to explain the results. A solution to the corresponding coupled nonlinear differential equations resulted in a Peclet number of 64.5 and a contact time of 9.5 x 10(-3) s through the reactor at 100degreesC. A critical thickness is predicted to exist for a maximum in ethylene concentration. A value of 2.5 mum at 200degreesC is representative. Lastly, permeability experiments agree with modeling results to show that Knudsen diffusion is absent despite a narrow pore-size distribution.