Enhanced low temperature performance of bimetallic Pd/Pt/SiO2(core)@Zr(shell) diesel oxidation catalysts

Abstract

In this study, the diesel oxidation performance of degreened (DG) and hydrothermally aged monometallic and bimetallic Pd/Pt/SiO2(core)@Zr(shell) catalysts with varying Pd/Pt molar ratios from 3/1–1/3 was evaluated. Pd/Pt(3/1)/SiO2 @Zr (DG) achieved 50% and 90% conversion of CO at 166 °C (T50), 169 °C (T90) and total hydrocarbons (THCs) at 198 °C (T50), 244 °C (T90). Decreasing the Pd/Pt molar ratio led to a decrease in the T50,90’s, with Pd/Pt(1/3)/SiO2 @Zr (DG) achieving T50,90’s at 153, 156 °C for CO and 171, 200 °C for THCs, respectively. Moreover, Pd/Pt(1/3)/SiO2@Zr showed enhanced hydrothermal stability. XRD and TEM showed that in the hydrothermally aged bimetallic catalysts, the fraction of Pd present as a Pt-Pd metallic alloy increased with Pt content. The enhanced low temperature performance of Pd/Pt(1/3)/SiO2@Zr compared to the other studied catalysts was attributed to Pd being primarily present in metallic form, despite being subjected to severe oxidizing conditions.