Promotional Effects of H2O Treatment on NO x Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NO x Trap Catalysts
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A simple liquid water treatment applied to fresh and thermally aged Pt(2 wt%)–BaO(20 wt%)/Al2O3 lean NO x trap catalysts at room temperature induces morphological and structural changes in the barium species as followed by XRD and TEM analysis. During the water treatment, liquid water sufficient to fill the catalyst pore volume is brought into contact with the samples. It was found that irrespective of the original barium chemical state (highly dispersed BaO or crystalline BaAl2O4), exposing the sample to this liquid water treatment promotes the formation of BaCO3 crystallites (about 15–25 nm of its size) without changing the Pt particle size. Such transformations of the barium species are found to significantly promote NO x uptake from 250 to 450 °C. The increase in the NO x uptake for the water-treated samples can be attributed to an enhanced Pt–Ba interaction through the redistribution of barium species. These results provide useful information for the regeneration of aged lean NO x trap catalysts since water is plentiful in the exhaust of diesel or lean-burn engines.
KeywordsPt–BaO/Al2O3 Lean NOx trap catalyst Water treatment BaAl2O4
Financial support was provided by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. The work was performed in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility and supported by the U.S. DOE, 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.