The effect of Pt/Pd ratio on the oxidation activity and resistance to sulfur poisoning for Pt-Pd/BEA diesel oxidation catalysts with high siliceous content

This study investigates the effect of the Pt/Pd ratio on the oxidation activity and sulfur poisoning/regeneration of diesel oxidation catalysts (DOC) using beta zeolites with high siliceous content as support. Formation of Pt-Pd alloy leads to contraction of the cell lattice of Pt in the bimetallic catalysts, improving not only the sintering resistance of Pt but also retaining a high fraction of Pd in Pd2+ form. Moreover, the Pt-Pd alloy also improves the oxidation resistance of the particles, which enhances the activity of the catalysts for CO and C3H6 oxidation. Bimetallic catalysts also favor NO reduction at a lower temperature than the monometallic Pt although they showed lower values for the absolute conversion of NO due to a decrease in the total number of the Pt active sites. In addition, the bimetallic catalysts significantly improved the sulfur resistance as compared to the monometallic Pd catalyst. Moreover, the bimetallic catalysts could easily recover their activity for NO and C3H6 oxidation by thermal treatment either in lean conditions or in H2. The reduction with H2 was necessary to recover completely the activity of the CO and C3H8 oxidation.