(401f) Various Effects of CO2 in Pt-BaO/Al2O3 Lean NOx Trap Catalysts
The lean NOx trap (LNT) technology , also known as NOx adsorber and NOx storage/reduction catalysts, is considered as one of the promising solutions to reduce NOx emissions from lean burn engines, which is more economically favorable and environmentally benign. Although continuing research regarding NOx storage and regeneration steps is providing for a good understanding of LNT performance, the stability of the material against SO2 poisoning remains a critical issue. Our group  reported that the desulfation processes for sulfated Pt BaO/Al2O3 materials is different with varying barium loading and, moreover, more facile over the lower barium loading studied by a combination of the H2 temperature programmed reaction (TPRX), transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS), sulfur K-edge XANES (X-ray near-edge spectroscopy), and in situ TR-XRD (Time-resolved X-ray Diffraction) results. Since CO2 always exists in the engine exhaust, a question arise how CO2 affects the desulfation chemistry over LNT catalysts. In this presentation, we try to elucidate the role of CO2 in desulfation steps over Pt-BaO/Al2O3 with different barium loading by using the TR-XRD, H2 TPRX and XPS analysis. The results evidently demonstrate that the presence of CO2 promoted the removal of sulfur species, especially at low temperature below 500 °C, by suppressing the formation BaS and encouraging H2S desorption, thus resulting in the less residual sulfur after desulfation step, irrespective of BaSO4 species formed both barium species (surface or bulk). In addition, the role of CO2 during NOx desorption on BaO/Al2O3 catalyst was investigated by using NO2 TPD, TR-XRD and in situ Raman spectroscopy. It was demonstrated that CO2 clearly promotes the desorption of NO2 at lower temperature by inhibiting the formation of bulk type of barium nitrates.
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