Promotional effect of ZrO2 and WO3 on bimetallic Pt-Pd diesel oxidation catalyst

Diesel oxidation catalysts Pt-Pd-(y)ZrO2-(z)WO3/CeZrOx-Al2O3 with total Pt & Pd loading of only 0.68 wt.% were prepared and investigated for oxidation activity and stability of CO, C3H6, and NO. Introduction of ZrO2 greatly improved low-temperature activities and retained stability especially for CO and C3H6 oxidation after treated at 800 degrees C. With the optimal loading amount of 6 wt% ZrO2, 2 wt% WO3 was introduced to the system and showed higher activity. Reaction temperature for 50% CO and C3H6 conversion declined to 160 and 181 degrees C, and the maximal NO conversion increased to 50%. By using XRD, TEM, CO chemisorption, XPS, and H-2-TPR analysis, it was found that ZrO2 could inhibit aggregation of Pt and Pd, improve metal dispersion, and increase surface-chemisorbed oxygen after high-temperature treatment, accounting for promoted performance. Also, there were more reducible oxide species in ZrO2-doped catalysts. ZrO2 could induce reduction of noble metal oxides and surface ceria by weakening Pt-O-Ce interaction, which increased the ability to dissociate H-2 and spillover effect of dissociated hydrogen to ceria. Doping WO3 increased metal dispersion of fresh samples and brought more Pt-0 species that were active sites for oxidation reactions. Thus, ZrO2 and WO3 could be effective additives for oxidation catalysts to synergistically improve their activities and thermal stability.

Automated summary

ZrO2 and WO3 additives were found to synergistically improve the activity and thermal stability of diesel oxidation catalysts, enhancing the oxidation reactions of CO, C3H6, and NO. ZrO2 improved metal dispersion and increased surface-chemisorbed oxygen, while WO3 increased active sites and metal dispersion in fresh samples.