XPS and TEM Studies on the Role of the Support and Alkali Promoter in Ru/MgO and Ru-Cs+/MgO Catalysts for Ammonia Synthesis
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- 作者：Yurii V. Larichev ; Boris L. Moroz ; Vladimir I. Zaikovskii ; Safar M. Yunusov ; Elena S. Kalyuzhnaya ; Vladimir B. Shur ; Valerii I. Bukhtiyarov
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：July 5, 2007
- 年：2007
- 卷：111
- 期：26
- 页码：9427 - 9436
- 全文大小：227K
- 年卷期：v.111,no.26(July 5, 2007)
- ISSN：1932-7455
文摘
The chemical state of ruthenium in the Ru/MgO and Ru-Cs+/MgO catalysts prepared by the incipient wetnesstechnique with the use of Ru(OH)Cl3 and Cs2CO3 as the catalyst and promoter precursors, respectively, ischaracterized by X-ray photoelectron spectroscopy (XPS). The influence of the final state effects (the differentialcharging and variations of the relaxation energy) on the binding energy of Ru 3d5/2 core level measured forsupported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parametersdetermined for the Ru/MgO and Ru-Cs+/MgO catalysts with the corresponding characteristics ofpolycrystalline Ru foil. High-resolution transmission electron microscopy (HRTEM) in combination withenergy dispersive X-ray (EDX) microanalysis reveals that Ru particles in the Ru-Cs+/MgO catalyst arecovered with an amorphous layer containing cesium. XPS data show that the layer subjected to the prolongedtreatment with H2 at 450 
C consists of cesium suboxide Cs2+XO. The shift of the Ru 3d5/2 binding energytoward lower values is found for the Ru-Cs+/MgO catalyst (279.7 eV) with respect to metallic Ru (280.2eV) and the Ru/MgO catalyst (280.5 eV). It is assumed that the shift results from a decrease in the workfunction of ruthenium under the action of Cs+ cations located on the Ru surface. The data obtained are usedto explain the sharp difference in the activities of the Ru/MgO and Ru-Cs+/MgO catalysts for ammoniasynthesis at 250-400 C.
C consists of cesium suboxide Cs2+XO. The shift of the Ru 3d5/2 binding energytoward lower values is found for the Ru-Cs+/MgO catalyst (279.7 eV) with respect to metallic Ru (280.2eV) and the Ru/MgO catalyst (280.5 eV). It is assumed that the shift results from a decrease in the workfunction of ruthenium under the action of Cs+ cations located on the Ru surface. The data obtained are usedto explain the sharp difference in the activities of the Ru/MgO and Ru-Cs+/MgO catalysts for ammoniasynthesis at 250-400 C.