Force C, Roman E, Guil J M, Sanz J
Instituto de Ciencia de Materiales, CSIC, Cantoblanco, 28049 Madrid, Spain.
Langmuir. 2007 Apr 10;23(8):4569-74. doi: 10.1021/la0628118. Epub 2007 Mar 14.
Rh/CeO2 catalysts submitted to different H2 reduction, Ar+ sputtering, and oxidation treatments have been studied by X-ray photoelectron (XPS) and 1H nuclear magnetic resonance (NMR) spectroscopies. Depending on the reduction temperature, two stages have been identified in the reduction of the catalyst: below 473 K, reduction increases the amount of OH and Ce3+ species; above this temperature, reduction produces oxygen vacancies at the surface of the support. Volumetric and microcalorimetric techniques have been used to study hydrogen adsorption on the catalyst, and 1H NMR spectroscopy was used to differentiate hydrogen adsorbed on the metal from that adsorbed on the support. From 1H NMR and TEM results, the main metal particle size (38 A) in the Rh/CeO2 catalyst has been estimated. The influence of the support reduction on the metal adsorption capacity has also been investigated, showing that formation of oxygen vacancies at the metal-support interface enhances the electronic perturbation and decreases the hydrogen adsorption on metal particles. The comparison of data reported on catalysts of high and low surface area supports has shown that both processes are shifted to higher temperatures in the Rh/CeO2 catalyst of lower surface area.
通过X射线光电子能谱（XPS）和1H核磁共振（NMR）光谱对经过不同氢气还原、氩离子溅射和氧化处理的Rh/CeO2催化剂进行了研究。根据还原温度，在催化剂还原过程中确定了两个阶段：低于473K时，还原增加了OH和Ce3+物种的数量；高于此温度时，还原在载体表面产生氧空位。采用体积法和微量热法研究了氢气在催化剂上的吸附，并利用1H NMR光谱区分吸附在金属上的氢和吸附在载体上的氢。根据1H NMR和TEM结果，估算了Rh/CeO2催化剂中的主要金属粒径（38 Å）。还研究了载体还原对金属吸附容量的影响，结果表明在金属-载体界面形成氧空位会增强电子扰动并降低氢在金属颗粒上的吸附。对高比表面积和低比表面积载体催化剂所报道数据的比较表明，在低比表面积的Rh/CeO2催化剂中，这两个过程都向更高温度偏移。
