The hydrogenation of phenylacetone to cyclohexylacetone, in which the aromatic ring is selectively reduced in preference to the carbonyl group, has been achieved with chemoselectivities exceeding 90%. The catalyst (precatalyst) used to achieve this transformation comprises PVP-stabilized Rh nanoparticles dispersed in water with some phosphine ligand additives. Phosphine ligands with different steric and electronic properties and polarities were investigated for this purpose, and several clear trends were observed, showing the potential of well-defined phosphine ligands as modifiers in nanocatalysis.