A platinum-based intermetallic phase with an early d-metal, Pt3Ti, has been synthesized in the form of nanoparticles (NPs) dispersed on silica (SiO2) supports. The organometallic Pt and Ti precursors, Pt(1,5-cyclooctadiene)Cl-2 and TiCl4(tetrahydrofuran)(2), were mixed with SiO2 and reduced by sodium naphthalide in tetrahydrofuran. Stoichiometric Pt3Ti NPs with an average particle size of 2.5 nm were formed on SiO2 (particle size: 20-200 nm) with an atomically disordered FCC-type structure (Fm (3) over barm; a = 0.39 nm). A high dispersivity of Pt3Ti NPs was achieved by adding excessive amounts of SiO2 relative to the Pt precursor. A 50-fold excess of SiO2 resulted in finely dispersed, SiO2-supported Pt3Ti NPs that contained 0.5 wt % Pt. The SiO2-supported Pt3Ti NPs showed a lower onset temperature of catalysis by 75 degrees C toward the oxidation reaction of CO than did SiO2-supported pure Pt NPs with the same particle size and Pt fraction, 0.5 wt %. The SiO2-supported Pt3Ti NPs also showed higher CO conversion than SiO2-supported pure Pt NPs even containing a 2-fold higher weight fraction of Pt. The SiO2-supported Pt3Ti NPs retained their stoichiometric composition after catalytic oxidation of CO at elevated temperatures, 325 degrees C. Pt3Ti NPs show promise as a catalytic center of purification catalysts for automobile exhaust due to their high catalytic activity toward CO oxidation with a low content of precious metals.