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A study of fuel conversion chemistry.

机译：燃料转化化学研究。

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摘要

Reforming of azabenzenes (C5H4XN) on (2 x 1)Pt(110) has been investigated spectroscopically under ultra-high vacuum conditions. By combining high-resolution electron energy loss spectroscopy (HREELS) and quantum mechanical calculations, pyridinium (C5H 5NH+), 2-fluoropyridinium and 3-fluoropyridinium (C 5H4FNH+) cations are identified. In addition, a spectroscopic method is developed to measure metal surface acidity/electronegativity (MSAE) of Pt(110).; A new species forms when pyridine and hydrogen coadsorb on Pt(110) at 140K. The new species has a HREEL spectrum that is consistent with the one expected for a pyridinium cation. At low coverage, the molecular plane of pyridine is parallel to the surface at 100K. At higher coverage, changes in the intensity of the in-plane versus out-of-plane vibrational modes show that adsorption phase transition occurs so that the molecular plane tilts with respect to the surface.; Fluoropyridinium cations (C5H4FNH+) could form when 2-fluoro or 3-fluoropyridine is adsorbed on a hydrogen-precovered Pt(110) surface. The ion concentration is much lower with the fluorinated pyridines than with pyridine as expected since the proton affinity of the substituted pyridines is much lower than that of pyridine. However, the trends in the data cannot be explained by simply considering the variations in the proton affinity. Instead the strength of the pairwise repulsions between adjacent cations on the Pt(110) surface also plays a key role in the stability of the cations.; Next the medium effect of ion stability was investigated by coadsorption of 3,5-dimethyl pyridine and hydrogen on Pt(110). The concentration of 3,5-dimethyl pyridinium ion is smaller than pyridinium ion, which contradicts the general brief of more basic nature of 3,5-dimethyl pyridine in gas phase and protic solvents. Instead Pt(110) acts like an aprotic solvent with high dielectric constant. When the aprotic medium has high dielectric constant, there is a reverse trend of basicity of 3,5-dimethyl pyridine and pyridine.; Finally, the stability of cations (C5H4XNH +) on Pt(110) at 140K was utilized to investigate the degree of proton transfer reaction on a hydrogen-precovered surface. Pyridine, 3-fluoropyridine and 2-fluoropyridine are chosen as indicators. The MSAE of Pt(110) in proton affinity scale has been determined to be 907 ± 4 kJ/mol using electron energy loss spectroscopy.
机译：在超高真空条件下，用光谱法研究了在（2 x 1）Pt（110）上重整氮杂苯（C 5 H 4 XN）的过程。通过结合高分辨率电子能量损失谱（HREELS）和量子力学计算，吡啶鎓（C 5 H 5 NH + ），2-鉴定了氟吡啶鎓和3-氟吡啶鎓（C 5 H 4 FNH + ）阳离子。另外，开发了一种光谱方法来测量Pt（110）的金属表面酸度/电负性（MSAE）。当吡啶和氢在140K下共吸附在Pt（110）上时，会形成一个新物种。新物种的HREEL光谱与预期的吡啶鎓阳离子相一致。在低覆盖率下，吡啶的分子平面在100K时平行于表面。在较高的覆盖率下，面内振动模式强度与面外振动模式的强度变化表明发生了吸附相变，因此分子平面相对于表面倾斜。当2-氟或3-氟吡啶被吸附在氢原子上的Pt上时，会形成氟吡啶鎓阳离子（C 5 H 4 FNH + ）。 110）表面。氟化吡啶的离子浓度比预期的要低得多，因为取代的吡啶的质子亲和力比吡啶的质子亲和力低得多。但是，仅通过考虑质子亲和力的变化就不能解释数据的趋势。相反，Pt（110）表面上相邻阳离子之间的成对排斥力的强度在阳离子的稳定性中也起着关键作用。接下来，通过在Pt（110）上共吸附3,5-二甲基吡啶和氢来研究离子稳定性的介质效应。 3，5-二甲基吡啶鎓离子的浓度小于吡啶鎓离子，这与在气相和质子溶剂中3，5-二甲基吡啶的更碱性的一般简要说明相反。相反，Pt（110）就像具有高介电常数的非质子溶剂。当非质子介质具有高介电常数时，存在3，5-二甲基吡啶和吡啶的碱性相反的趋势。最后，利用阳离子（C 5 H 4 XNH + ）在Pt（110）于140K时的稳定性研究了质子的程度。氢表面上的转移反应。选择吡啶，3-氟吡啶和2-氟吡啶作为指示剂。使用电子能量损失谱法，已确定质子亲和力级的Pt（110）的MSAE为907±4 kJ / mol。

著录项

  • 作者

    Lee, Ivan Chihang.;

  • 作者单位

    University of Illinois at Urbana-Champaign.;

  • 授予单位 University of Illinois at Urbana-Champaign.;
  • 学科 Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 203 p.
  • 总页数 203
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 化工过程（物理过程及物理化学过程）;
  • 关键词

  • 入库时间 2022-08-17 11:46:55

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