A detailed study on the synthesis of Pt3Co intermetallic nanoparticles supported on ceria via preferential chemical vapor deposition was conducted, leading to a fundamental understanding of the deposition process and the Co-Pt alloying. This understanding helps us to develop a facile and scalable method for preferential adding of a metal on the surface of another metal already supported on an oxide which facilitates the design of novel structured nanoparticles. The fluidized flow reactor eliminated the deposition profile and resulted in Pt3Co nanoparticles uniformly and homogeneously distributed on ceria. The kinetic study of cobalt deposition on the platinum surface, in accordance with DFT calculations, demonstrates that the platinum surface catalyzes the deposition reaction; while the ceria surface is inert in the preferential deposition temperature window between 150 °C and 180 °C. The obtained sample was characterized by in situ XRD, HAADF-STEM, FT-IR, and XAS methods. The results indicate the formation of uniform Pt3Co nanoparticles with an average size of 1.1 nm. This sample showed superior catalytic activity in preferential oxidation of CO with an almost twice higher CO conversion rate and CO2 selectivity compared to a classically synthesized sample with successive impregnation.