Colloidal oxide synthesis is a new technique for the preparation of bimetallic supported particles which provides the opportunity to control particle size distribution and interaction between both metals. It consists in synthesizing in aqueous medium a sol of colloidal oxide Pd-Sn nanoparticles which is further deposited onto a porous support. In this work, this method has been applied to the preparation of Pd-Sn/Al2O3 dedicated to the selective hydrogenation of unsaturated hydrocarbons. Two synthesis routes, surface precipitation and surface adsorption, are described to demonstrate the potential of colloidal oxide chemistry to generate a bimetallic interaction in aqueous solution which is strengthened during the reduction step after deposition onto alumina. Sn-119 Mossbauer spectroscopy (Sn-119 MS) and transmission electron microscopy (TEM) were used to characterize the sols and the supported catalysts. This allowed us to determine the key parameters of colloidal oxide synthesis as far as formation of bimetallic PdxSny phases is concerned. (C) 2003 Elsevier Inc. All rights reserved.