Study on the Effect of Precious Metal Loading and Pt/Pd Ratio on Gaseous Pollutant Emissions from Diesel Engines

This study systematically investigated the influence of catalyst formulation parameters (precious metal loading and Pt/Pd ratio) in diesel oxidation catalysts (DOCs)+catalyzed diesel particulate filter (CDPF)+selective catalytic reduction (SCR) on gaseous pollutant emissions from diesel engines. Results indicate that under varying conditions, the impact of catalyst formulation on DOC system performance—such as temperature rise characteristics, pressure drop, and brake specific fuel consumption (BSFC)—remains limited. Notably, exhaust temperature exerts a decisive influence on carbon monoxide (CO) and hydrocarbon (HC) conversion efficiency, significantly outweighing the impact of exhaust flow rate. Increasing precious metal loading and Pt proportion markedly optimizes CO and HC ignition characteristics by lowering ignition temperatures. However, under high-load conditions, conversion efficiencies across different catalyst formulations tend to converge. Specifically, under low-load conditions, a competitive adsorption mechanism between CO and HC causes HC conversion efficiency to exhibit an inverse trend relative to CO. Furthermore, higher precious metal loading and Pt content significantly enhance the catalyst’s NO2 formation capacity at equilibrium temperatures, while higher Pd content contributes to improved thermal stability. Higher precious metal loading and Pt content increase nitrogen oxides (NOx) conversion efficiency. CDPF possesses the ability to further oxidize NO.