Enhanced High Temperature Performance of MgAl2O4-Supported Pt–BaO Lean NOx Trap Catalysts
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The structural and chemical characteristics of Pt/BaO lean NOx trap (LNT) catalysts supported on γ-Al2O3 and MgAl2O4 are compared in this study. The Pt–BaO/MgAl2O4 sample shows relatively low NOx uptake at temperatures below 300 °C, and the temperature of maximum NOx uptake (Tmax) is shifted to 350 °C in comparison to that of Pt–BaO/Al2O3 (Tmax ~ 250 °C). More importantly, the NOx uptake over the MgAl2O4-supported catalyst at 350 °C is twice that of the alumina-based one. The shift toward the higher temperature NOx uptake is explained by the larger interfacial area between Pt and BaO, due to smaller Pt clusters as evidenced by TEM and Pt L3 EXAFS. In situ TR-XRD results demonstrate that the formation of a BaAl2O4 phase in the BaO/MgAl2O4 LNT catalyst occurs at a temperature about 100 °C higher than on BaO/Al2O3, which may also represent a beneficial attribute of the BaO/MgAl2O4 LNT with respect to catalyst stability.
KeywordsMagnesium aluminate LNT Pt cluster Barium oxide NOx
Financial support was provided by the U.S. Department of Energy (DOE), Office of Freedom Car and Vehicle Technologies. The authors thank Dr. Chongmin Wang for obtaining the TEM images. The work was performed in the Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility and supported by the U.S. DOE’s Office of Biological and Environmental Research. PNNL is a multi-program national laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.
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