Initial Oxidation Activity of Noble Metal Automotive Exhaust Catalysts 730570
The use of relatively small catalytic converters containing alumina-supported platinum (Pt) and palladium (Pd) catalysts to control exhaust emissions of hydrocarbons (HC) and carbon monoxide (CO) was investigated in full-scale vehicle tests. Catalytic converters containing 70-80in3 of fresh catalyst were installed at two converter locations on the vehicle. Carburetion was richer than stoichiometric, with air-fuel ratios (A/F) comparable to those proposed for dual-catalyst systems containing an NOx reduction catalyst. The vehicle was equipped with exhaust manifold air injection. Homogeneous thermal reaction in the exhaust manifolds played a significant role in the overall control of HC and CO.
Four Pt catalysts, three Pd catalysts, and one Pt-Pd catalyst were prepared and evaluated. Total metal loadings were varied 0.01-0.07 troy oz.
Hydrocarbon conversion efficiencies varied 62-82%, measured over the 1975 cold-hot start weighted Federal Test Procedure. Corresponding CO conversions ranged 89-97%. Catalyst performance was best in the front converter location which produced higher bed temperatures. This performance difference was almost exclusively due to the effect of converter location on warmup emissions.
There were no large differences in the emission control capabilities of Pt versus Pd catalysts. These metals had equal initial oxidation activity. In this vehicle, it appeared that 0.04 troy oz of either Pt or Pd gave sufficient initial oxidation activity to reduce HC and CO emissions to the desired 1975-1976 federal emission limits.