Hydrocarbon and carbon monoxide oxidation catalysts having good catalytic activity, stability and improved physical durability were developed. Based on laboratory tests, these catalysts are predicted to be able to meet the Inter-Industry Emission Control Program HC and CO emission levels, and the durability goals, in vehicles in which HC, CO and NOx goals are achieved simultaneously. However, confirming vehicle tests must be made to validate these predictions.
The development of these catalysts has been aided by a mathematical model of the catalytic converter, and by some unique experimental techniques. These tools have been used to guide the development, and to evaluate the catalytic activity, the chemical stability, and the physical durability of the catalysts in laboratory tests.
These laboratory tests were complemented by several vehicle durability evaluations which have shown that although the IIEC goals were met initially, they were often exceeded after mileage accumulation. The principal causes for not meeting the goals have been catalyst loss due to inherently low catalyst attrition resistance and inter-particle abrasion caused by inadequate converter design. Improved converter designs and more attrition resistant catalysts have resulted in significant improvements in “on the road” durability of these systems.
Laboratory tests predict that some of these catalysts will meet IIEC HC and CO goals for more than 12,000 miles with leaded fuel (3.0 grms Pb/gal) and that a larger number will meet these goals for 50,000 miles with low leaded fuel (0.5 grms Pb/gal) or unleaded fuel. Although most vehicle testing is being done with unleaded fuel in order that acceptable converter and catalyst durability can be demonstrated, the ultimate economic choice for the optimized vehicle-fuel-system has not yet been made.