Catalytic nanoparticles are typically immobilized on beads to avoid particle aggregation that decreases surface area and reduces catalytic activity. However, flow through bead-based columns goes around the beads, and slow diffusion into pores can sometimes limit reaction rates (see the accompanying figure). In contrast, when nanoparticles are adsorbed in porous membranes, convective flow can bring reactants to catalytic sites to avoid diffusion limitations. We have recently used simple layer-by-layer adsorption of nanoparticle/polyelectrolyte films in porous supports to prepare catalytic membranes as shown below, and these materials are remarkably effective catalysts in the reduction of p-nitrophenolate to p-aminophenolate. Even with a solution flux that corresponds to a residence time in the membrane of only 6 msec, 99% conversion of p-nitrophenolate to p-aminophenolate occurs. This work recently appeared in Nano Letters. To see SEM images of the nanoparticle- membranes click here. This work has been supported by the U.S. Department of Energy Office of Basic Energy Sciences. 