Low-loaded Pt-Pd Diesel Oxidation Catalyst: MnO_x Loading Effects

To reduce the content of Pt-group metals in a diesel oxidizing catalyst, the possibility of regulating the size of Pt and Pd nanoparticles as well as their microstructure by varying the amount (2.5–10 wt%) of the MnO_x modifying additive added to the Pt–Pd/Al₂O₃ catalyst has been studied. It was revealed that the as-prepared modified catalysts contain oxide clusters and single highly dispersed PtO_x/PdO_x nanoparticles, the cluster sizes dynamically changed under the electron beam during the registration of TEM images. Under reducing conditions (CO /250°C), PtO_x/PdO_x turn into metallic nanoparticles; their average size decreased (from 4.39 to 3.47 nm) with an increase in MnO_x content. It was found that the amount of reactive oxygen contained in PdO_x/PtO_x clusters and capable of interacting with CO at a temperature of 50–180 °C under TPR–CO conditions increases in proportion to the MnO_x content in the as-prepared catalysts. A similar trend characterized the ability of metal clusters and nanoparticles of Pt and/or Pd in the reduced MnO_x-modified samples to low-temperature oxidation with molecular oxygen. Both factors provide low light-off temperatures and low–temperature CO oxidation activity to Pt-Pd/MnO_x-Al₂O₃ catalysts.