An in depth analysis of the pelleted automotive catalysts from the 1975 General Motors Certification Fleet led to the development of a useful catalyst poisoning model. By optimizing three variables: pore volume and pore size distribution, precious metals penetration, and surface area, it was possible to design a more poison resistant catalyst. The application of these ideas resulted in a second generation of catalysts, introduced in 1978, which were characterized by better performance and greater durability.In order to meet 1980 and 1981 emissions requirements, further improvements were required. To achieve this, two different variables were studied: geometric surface area and noble metal ratios. From the optimization of these added variables there evolved several new catalysts which, after extensive engine dynamometer and vehicle testing, were selected for use on General Motors vehicles.