In the catalytic hydrogenation of a,(3-unsaturated aldehydes and ketones, highly selective allylic alcohol formation can be achieved by application of Au-0 nanocolloids dispersed in amide solvents. The polyvinylpyrrolidone protected Au-0 nanoparticles prefer C=O reduction over C=C saturation and act as chemoselective quasi homogeneous metal catalysts in the hydrogenation of trans-2-butenal (crotonaldehyde), 2-methyl-2-propenal (methacrolein), 4-methyl-3-penten-2-one (mesityl oxide) and 3-methyl-3-penten-2-one. An extensive solvent screening revealed the superiority of amides as media for both synthesis and application of the Au-0 nanocolloids. In comparison with the widely used alcohol solvents, amides offer enhanced colloidal stability for the Au-0 nanosol and increased hydrogenation chemoselectivity. Control over the Au cluster formation provided the opportunity to investigate the size-dependency of the catalytic performance and to determine the optimum gold cluster size for a maximization of the allylic alcohol yields. The most successful Auo clusters, with a typical diameter of 7 nm and synthesized in N,Ndimethylformamide, lead to a crotyl alcohol selectivity of 73% at 93% crotonaldehyde conversion and a 58% allylic alcohol yield in the hydrogenation of mesityl oxide at a molar substrate/Au catalyst ratio of 200. Analogous Pt-0 and Ru-0 sols are more active than the Auo nanosols, but substantially less chemoselective for allylic alcohols. The Auo nanocolloids can be recycled efficiently by ultrafiltration over custom-made, crosslinked polyimide membranes. In the recycling experiments the gold nanodispersion was well retained by the solvent-resistant ultrafiltration membranes and the performance of the colloidal gold catalyst was satisfactorily preserved in successive hydrogenation runs. (C) 2007 Elsevier B.V. All rights reserved.