Metal in the Middle Biphasic reaction mixtures allow the isolation of sensitive products, which can form in one solvent and then shift rapidly into another, protected from side reactions and interfering by-products. However, ensuring that catalysts remain in the proper phase can be challenging, and surfactants added to induce efficient mixing often prove difficult to separate from the product stream. Crossley et al. (p. 68 ; see the Perspective by Cole-Hamilton ) tackle these issues by preparing easily recoverable amphiphilic nanoparticles that simultaneously stabilize aqueous-organic emulsions and catalyze organic reactions. The particles combine hydrophobic nanotubes with hydrophilic oxides, causing them to accumulate at water-hydrocarbon interfaces. Depositing palladium on specific portions of the particles' surfaces thus localizes the metal in one or both phases, facilitating hydrogenation of several compounds of interest in biofuel refining.