Promotional Effects of H2O Treatment on NOx Storage Over Fresh and Thermally Aged Pt–BaO/Al2O3 Lean NOx 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 NOx 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 NOx uptake from 250 to 450 °C. The increase in the NOx 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 NOx trap catalysts since water is plentiful in the exhaust of diesel or lean-burn engines.