XPS and 1H NMR study of thermally stabilized Rh/CeO2 catalysts submitted to reduction/oxidation treatments.
XPS and 1H NMR study of thermally stabilized Rh/CeO2 catalysts submitted to reduction/oxidation treatments.
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DOI：
10.1021/la0628118
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发表时间：
2007-03
期刊：
影响因子：
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通讯作者：
C. Force;E. Román;J. Guil;Jesús Sanz
中科院分区：
文献类型：
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作者：
C. Force;E. Román;J. Guil;Jesús Sanz
采用x射线光电子（XPS）和1H核磁共振（NMR）对Rh/CeO2催化剂进行了不同的H2还原、Ar+溅射和氧化处理。根据还原温度的不同，催化剂的还原分为两个阶段：在473 K以下，还原增加了OH和Ce3+的数量；在这个温度以上，还原性在支撑体表面产生氧空位。用体积法和微量热法研究了催化剂上的氢吸附，并用1H NMR谱法区分了金属上吸附的氢和载体上吸附的氢。根据1H NMR和TEM结果，估计了Rh/CeO2催化剂中的主要金属粒径（38 A）。研究了载体减少对金属吸附能力的影响，表明在金属-载体界面上形成氧空位增强了电子摄动，降低了金属颗粒对氢的吸附。对高、低比表面积载体催化剂的实验数据进行了比较，结果表明，在低比表面积的Rh/CeO2催化剂中，这两个过程都向更高的温度转移。
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.