The goal of this thesis is to develop synthesis methods for platinum and palladium based nanoparticles. We mainly focused on three synthesis pathways, i) Surface Organometallic Chemistry (SOMC), ii) metal organic chemical vapor deposition (MOCVD) and iii) a colloidal approach. Surface organometallic chemistry allowed the synthesis of silica supported nanoparticles with sizes of about 2 nm. The transfer of this methodology to cerium oxide has been carried out and allowed obtaining nanoparticles of less than 1.5 nm in diameter. Those researches had for purpose the synthesis of oxidation catalysts supported on ceria used for automotive pollution and paves the way for the surface organometallic chemistry on this oxide. By MOCVD, Pt nanoparticles from 4 to 6 nm were synthesized onto gas diffusion layers (GDL) for applications in fuel cell catalysis. Electrocatalysis results demonstrated the viability of this synthesis method and the efficiency of these catalysts for the Oxygen Reduction Reaction (ORR). For the same application, nanoparticles of Pt, Pd and Pt/Pd in various proportions were synthesized by the colloidal approach. These nanoparticles stabilized by octylsilane had a size ranging from 1.5 to 1.8 nm. For platinum, the influence of the organometallic precursor and temperature have been studied and synthesis without adding external reducing (H2) and from PtII precursor allowed obtaining stable nanoparticles of 1.2 nm. Their use for the ORR has shown interest to form alloys, the Pt/Pd 3:1 composition demonstrating an improvement by a factor of 1.4 compared to pure Pt
