Chenakin S P, Prada Silvy R, Kruse N
Université Libre de Bruxelles (ULB), Chimie Physique des Matériaux, CP243, Campus Plaine, B-1050 Bruxelles, Belgium.
J Phys Chem B. 2005 Aug 4;109(30):14611-8. doi: 10.1021/jp051944j.
The surface composition of Al(2)O(3), V(2)O(5), and aluminovanadate oxide, "V-Al-O", was studied by X-ray photoelectron spectroscopy (XPS), using Mg K(alpha) to reveal time-dependent irradiation damage of samples. Spectral parameters such as peak intensity and width and absolute and relative peak binding energies were evaluated along with the Auger parameter. Irradiation of Al(2)O(3) was found to cause partial dehydration of the surface hydroxide film, while sputter-cleaned alumina turned out to be resistant to X-rays. In V(2)O(5), a small fraction of V(4+) species was seen to form during X-ray exposure. X-ray induced damage in Al(2)O(3) and V(2)O(5) was compared to that caused by bombardment with 500 eV argon ions. The V-Al-O material which is used as a precursor of oxynitride catalysts for ammoxidation turned out to be most susceptible and could be damaged by low X-ray doses. An appreciable reduction from the V(5+) to the V(4+) formal oxidation state (the latter increases from 20 to 45% after 150 min time of exposure to Mg K(alpha) at 150 W) was found along with the decomposition of aluminum hydroxide which is believed to act as an amorphous support in this catalyst. Gas-phase analysis during X irradiation demonstrated desorption of oxygen and water molecules. X-ray induced damage is believed to be caused by electron-hole pair generation and Auger decay rather than by thermal effects since the sample surface temperature increased only slightly.
采用 Mg Kα 射线，通过 X 射线光电子能谱（XPS）研究了 Al₂O₃、V₂O₅ 和铝钒酸盐氧化物“V - Al - O”的表面组成，以揭示样品随时间变化的辐照损伤。评估了诸如峰强度、宽度以及绝对和相对峰结合能等光谱参数以及俄歇参数。发现 Al₂O₃ 的辐照会导致表面氢氧化物膜部分脱水，而溅射清洁后的氧化铝对 X 射线具有抗性。在 V₂O₅ 中，在 X 射线照射期间可观察到一小部分 V⁴⁺ 物种形成。将 Al₂O₃ 和 V₂O₅ 中 X 射线诱导的损伤与 500 eV 氩离子轰击所造成的损伤进行了比较。用作氨氧化氮氧化物催化剂前驱体的 V - Al - O 材料最易受到影响，低剂量 X 射线即可对其造成损伤。发现 V⁵⁺ 到 V⁴⁺ 的形式氧化态有明显降低（在 150 W 下暴露于 Mg Kα 150 分钟后，后者从 20% 增加到 45%），同时氢氧化铝分解，据信氢氧化铝在该催化剂中起无定形载体的作用。X 射线照射期间的气相分析表明有氧气和水分子解吸。由于样品表面温度仅略有升高，因此认为 X 射线诱导的损伤是由电子 - 空穴对的产生和俄歇衰变引起的，而非热效应。
