Pt–Cu dual-site synergistic construction in lean NOx traps(LNTs)towards high NH3 selectivity

Abstract

The traditional NH3-SCR technology has some drawbacks since it requires an additional NH3 source; nevertheless, the LNT-SCR coupling system could efficiently use the byproduct (NH3) of the lean NOx traps (LNTs) as a NH3 source for the NH3-SCR catalyst to reduce NOx. Therefore, the regulation of NH3 selectivity in LNT to enhance NOx removal efficiency in LNT-SCR coupling system have been a prominent focus of research. As previously discovered, the LNT catalyst Cu(5)/Ba(5)/CeO2 demonstrated high NOx storage efficiency with low NOx removal and NH3 slip efficiencies; however, the Pt(1)/ZrO2 catalyst exhibited low NOx storage efficiency and high NH3 slip efficiency. In this study, a Pt–Cu dual-site LNT catalyst was prepared using the high-energy ball milling method with the aim of ensuring that the Cu and Pt sites can perform their respective roles in enhancing NOx removal efficiency and NH3 selectivity. The Pt(1)/ZrO2+Cu(5)/Ba(5)/CeO2 exhibited NOx storage and removal efficiencies of 98.8 % and 92.1 %, respectively, as well as the NH3 slip efficiency of 83.6 %. A comprehensive characterization was also conducted to analyze the effects of co-impregnation and high-energy ball milling methods on a Pt–Cu dual-site LNT catalyst. XPS, CO-DRIFTs, and HRTEM-EDS results demonstrated that the Pt and Cu in Pt(1)/ZrO2+Cu(5)/Ba(5)/CeO2 were less influenced compared to Pt(1)/Cu(5)/Ba(5)CeO2–ZrO2, resulting in relatively independent and aggregated reaction sites favoring the Pt and Cu sites in their respective roles and generating high concentrations of Ce3+ species and surface oxygen, which facilitated effective NOx storage. The exceptional NH3-generation capability displayed by the Pt(1)/ZrO2+Cu(5)/Ba(5)/CeO2 holds significant promise for NOx purification in the LNT-SCR coupling system.