Three-way catalysis with bimetallic supported Pd-Au catalysts: Gold as a poison and as a promotor

Three-way catalysts containing Au and/or Pd supported on either CeZrOx (CZ) or La2O3/Al2O3 (LA) were studied with respect to their performance in a model feed and characterized by various techniques (physisorption, CO chemisorption, TEM, XRD, XPS, XANES). A drastic support influence was found in both catalytic behavior and Pd-Au relation. While Au was a strong poison for all catalytic functions of Pd (oxidation, NO reduction) on LA, poisoning was much mitigated on CZ, rendering all Pd containing catalysts superior to a commercial reference. After ageing, the poisoning by Au was aggravated on LA. On CZ, Pd-rich bimetallic combinations retained better activity than Pd/CZ, which still outperformed the reference. As Au did not significantly contribute to propene oxidation and NO reduction, activity of Pd was markedly increased under a promoting influence of Au. Stabilization of Pd-II by ceria and delayed Pd-Au alloy formation are key features in the CZ-supported PdAu catalysts.