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In this study, the durability characteristics of three catalyst systems were evaluated. One system was a conventional platinum-rhodium catalyst. The second was a catalyst formulated with palladium and rhodium as the active components. The third system was a catalyst with palladium as the only active metal. These catalysts were evaluated for emissions performance after aging on two durability schedules. The first was a “3-step” aging schedule which is characterized by three distinct temperature steps from 440°C to 775°C. The second schedule involved steady state aging at 440°C. These aging schedules were set up on water-brake engine dynamometers. After low temperature aging, the palladium containing catalysts did not perform as well as the platinum-rhodium catalysts. After 400 hours aging at 440°C, the palladium catalysts had a steady state CO/NOx conversion efficiency of 77% while the platinum rhodium catalyst had a CO/NOx conversion of 95%.

A study was conducted to determine the effects of various factors on the performance characteristics of aged monolithic catalytic converters. The factors that were evaluated were catalyst volume, converter configuration (number of elements), catalyst supplier, “washcoat technology”, rhodium loading, platinum loading, and palladium loading. This study was also designed to evaluate the interactions among the various factors. To improve the efficiency of the study a 2-level fractional factorial experiment was designed using the Taguchi method. That made it possible to study the effects of the seven main factors and six interactions by evaluating only 16 different samples. The study helped sort the factors that had significant effects and helped quantify their effect on catalyst performance. This paper details the methodology used to design the experiment and analyze the results.