A one-step process was developed to prepare catalysts with monodispersed Pt nanocrystals on Fe3O4, based on leaching of the intermetallic compounds Al76.5-xFe23.5Ptx (at%: x = 0, 0.05, 0.5, 1) with an aqueous 10 wt% NaOH solution. In this process, the intermetallic Al13Fe4 lattice acts as a platform in which Pt atoms can be homogeneously dispersed, and also serves as a precursor for subsequent leaching. Compared with conventional preparation methods, including impregnation and coprecipitation, this one-step process eliminates the need for thermal treatments such as high temperature calcination and/or reduction, thus minimizing the sintering or crystal grain growth problems caused by these treatments. Consequently, the materials derived from Al76Fe23.5Pt0.5 exhibit high catalytic performance during CO oxidation and the CO-PROX reaction due to the monodispersed Pt nanocrystals in the porous or nanoparticle Fe3O4 matrix.