A Comparison of Conversion Efficiencies of Individual Hydrocarbon Species Across Pd- and Pt-Based Catalysts as a Function of Fuel-Air Ratio 982549

Individual hydrocarbon conversion efficiencies of engine-out emissions have been measured for four different catalyst formulations (Pd-only, trimetallic, Pd/Rh, and Pt/Rh) during stoichiometric and rich operation. The measurements were carried out as a function of fuel-air equivalence ratio (Φ) using a dynamometer-controlled 1993 Ford V8 engine and capillary gas chromatography. HC conversion efficiency was examined in terms of mass conversion efficiency and also using three new definitions of catalyst conversion efficiency. The efficiencies across the four catalysts show similar trends with Φ for almost all HC species. The catalyst efficiencies for alkanes, alkenes, and aromatic species decrease as Φ increases above stoichiometric: alkane efficiencies decrease faster than alkenes which in turn decrease faster than aromatics. All efficiencies fall to zero near Φ = 1.08 except those of MTBE and acetylene, which remain near 100%. The formaldehyde efficiency decreases from 92% at Φ = 1.0 to 78% at Φ= 1.068 for all Pd-based catalyst technologies