Kim Do Heui, Szanyi Janos, Kwak Ja Hun, Szailer Tamas, Hanson Jonathan, Wang Chong Min, Peden Charles H F
Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
J Phys Chem B. 2006 Jun 1;110(21):10441-8. doi: 10.1021/jp060119f.
Desulfation processes were investigated over sulfated Pt-BaO/Al2O3 with different barium loading (8 and 20 wt %) by using H2 temperature programmed reaction (TPRX), transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS), sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and in situ time-resolved X-ray diffraction (TR-XRD) techniques. Both sulfated samples (8 and 20 wt %) form sulfate species (primarily BaSO4) as evidenced by S K-edge XANES and in situ TR-XRD. However, the desulfation behavior is strongly dependent on the barium loading. Sulfated Pt-BaO8/Al2O3, consisting predominantly of surface BaO/BaCO3 species, displays more facile desulfation by H2 at lower temperatures than sulfated Pt-BaO20/Al2O3, a material containing primarily bulk BaO/BaCO3 species. Therefore, after desulfation with H2 up to 1073 K, the amount of the remaining sulfur species on the former, mostly as BaS, is much less than that on the latter. This suggests that the initial morphology differences between the two samples play a crucial role in determining the extent of desulfation and the temperature at which it occurs. It is concluded that the removal of sulfur is significantly easier at lower barium loading. This finding can potentially be important in developing more sulfur resistant LNT catalyst systems.
通过氢气程序升温反应（TPRX）、配有能谱仪（EDS）的透射电子显微镜（TEM）、硫K边X射线吸收近边光谱（XANES）以及原位时间分辨X射线衍射（TR-XRD）技术，对不同钡负载量（8 wt%和20 wt%）的硫酸化Pt-BaO/Al₂O₃上的脱硫过程进行了研究。S K边XANES和原位TR-XRD表明，两种硫酸化样品（8 wt%和20 wt%）均形成了硫酸盐物种（主要是BaSO₄）。然而，脱硫行为强烈依赖于钡负载量。主要由表面BaO/BaCO₃物种组成的硫酸化Pt-BaO₈/Al₂O₃，在较低温度下比主要含有体相BaO/BaCO₃物种的硫酸化Pt-BaO₂₀/Al₂O₃更容易被氢气脱硫。因此，在1073 K下用氢气脱硫后，前者上剩余的硫物种（大多为BaS）的量远少于后者。这表明两个样品之间的初始形态差异在决定脱硫程度及其发生温度方面起着关键作用。得出的结论是，在较低的钡负载量下，硫的去除明显更容易。这一发现对于开发更耐硫的LNT催化剂体系可能具有重要意义。
