Low-loaded Pt-Pd Diesel Oxidation Catalyst: MnOx 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 MnOx 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 PtOx/PdOx nanoparticles, the cluster sizes dynamically changed under the electron beam during the registration of TEM images. Under reducing conditions (CO /250 degrees C), PtOx/PdOx turn into metallic nanoparticles; their average size decreased (from 4.39 to 3.47 nm) with an increase in MnOx content. It was found that the amount of reactive oxygen contained in PdOx/PtOx clusters and capable of interacting with CO at a temperature of 50-180 degrees C under TPR-CO conditions increases in proportion to the MnOx 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 MnOx-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/MnOx-Al2O3 catalysts.