A Systematic Experimental Investigation of Pd-Based Light-Off Catalysts

Close-coupled or manifold catalysts have been extensively employed to reduce emissions during cold start by achieving quick catalyst light-off. These catalysts must have good thermal durability, high intrinsic light-off activity and high HC/CO/NOx conversions at high temperature and flow conditions. A number of studies have been dedicated to engine control, manifold design and converter optimization to reduce cold start emissions. The current paper focuses on the effect of catalyst design parameters and their performance response to different engine operating conditions. Key design parameters such as catalyst formulation (CeO₂ vs. non CeO₂), precious metal loading and composition (Pd vs. Pd/Rh), washcoat loading, catalyst thermal mass, substrate properties and key application (in use) parameters such as catalyst aging, exhaust A/F ratio, A/F ratio modulation, exhaust temperature, temperature rise rate and exhaust flow rate were studied on engine dynamometers in a systematic manner. Optimized Pd light-off catalysts on 400cpsi/6.5, 600cpsi/3 and 900cpsi/2mil cordierite substrates were further examined at the manifold location for FTP-75 emission performance as a function of cold start A/F ratio to achieve the best emission results on a 1997 Nissan Altima.