The use of a platinum-cerium bimetallic fuel additive has been proposed as a cost-effective strategy for reducing particulate matter (PM) and NOx emissions from diesel-powered engines. Although previous studies have demonstrated that the use of platinum-cerium bimetallic fuel additive reduced emissions from diesel engines, there have been no reported investigations of how the use of these fuel-borne catalysts (FBCs) impact the chemical and physical properties of diesel PM emissions. The present study demonstrates that the use of a platinum-cerium bimetallic fuel additive has a significant impact on the detailed chemical composition and size distribution of PM emitted from a diesel engine. Tests were conducted to explore the impact of different fuel concentrations of the fuel-borne catalyst at different engine-operating conditions. These tests were performed with a medium-duty diesel engine that was not equipped with exhaust gas recirculation or a diesel particulate filter (DPF). The results demonstrated that the use of the additive significantly reduced the emissions Of PM2.5 and carbonaceous species. The reduction was 34% for the PM2.5 mass, 54% for the PM2.5 elemental carbon, and 23% for the PM2.5 organic carbon when 0.1 ppm Pt and 7.5 ppm Cc of the additive were used. Emissions of particle-phase metals originating from the additive had a significant contribution to particle matter emissions when 0.7 ppm Pt and 42 ppm Ce of the additive were used. The particle size distribution of platinum in the PM emissions was different from the size distribution of cerium. The cerium/platinum ratio in the PM2.5 diesel particle emissions ranged from 119 to 656, which was much higher than the ratio in the fuel additive that was 58.5 +/- 5.6, indicating a higher penetration of cerium through the engine.