CO and NO Co-Oxidation in PdCu Catalysts

Newly developed diesel engines operate at lower temperatures and can simultaneously reduce NOx, particulate matter, and fuel consumption. However, typical catalytic converters use platinum-palladium alloys, which aren't active enough to meet EPA emission regulations at low temperatures due to the inhibition caused by the competitive adsorption between CO and NO. Thus, excess fuel must be burned in the engine to increase the exhaust temperature before entering the DOC. Since CO binds to the active sites more strongly than NO, the Pt-Pd catalyst bed must also be long enough for sufficient NO conversion. Finding a catalyst that co-oxidizes CO and NO at low temperatures with minimal inhibition effects will maximize fuel economy and lower the required costly precious metal loading for the DOC. Using density functional theory (DFT) and descriptor-based microkinetic modeling, alloys of coinage metals (copper, gold, and silver) with at least one oxophilic component were identified as potential candidates. Further computational screening of Pd and Pt alloyed with Cu or Ag was used to determine PdCu alloys as the most promising for inhibition-free, low-temperature CO oxidation in the presence of NO. By flowing gasses through a bench-scale reactor, we evaluated the performance of the PdCu, PdPt, and PdCu+PdPt alloys. The findings indicate the PdCu catalyst has the potential to improve PdPt at reduced temperatures.