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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Surface-Analytical Studies of Supported Vanadium Oxide Monolayer Catalysts
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Surface-Analytical Studies of Supported Vanadium Oxide Monolayer Catalysts

机译：负载型氧化钒单层催化剂的表面分析研究

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Supported vanadium oxide catalysts, consisting of surface vanadia species on Al2O3, ZrO_2, CeO_2, and Nb_2O_5 oxide supports, were investigated by X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) to elucidate the effect of calcination treatments as well as exposures to (nonmonochromatized) X-rays and He ions on the surface properties. It was found that calcination in air at 730 K of samples that had been previously calcined in air at 773 K and exposed to ambient atmosphere results in significant increases of the V intensity relative to the support signal both in XPS and ISS. This indicates that the surface vanadia species aggregate under the influence of moisture, but spread during calcination. The surface V(V) species were reduced to V(IV) upon extended exposure to X-rays of a nonmonochromatized source, which was accompanied by clustering as detected by ISS. Following a new methodology that avoids these effects by studying freshly calcined samples transferred without exposure to ambient atmosphere, without previous illumination by X-rays, and takes account of the abrasive effect of He ions by extrapolating the results of sputter series, it was found that in supported V_2O_5/ZrO_2, V_2O_5/CeO_2, and V_2O_5/Nb_2O_5 catalysts possessing a vanadia monolayer coverage or above, the supports are densely covered by two-dimensional surface vanadia species, and the underlying oxide support cations of Zr, Ce, or Nb are not exposed. For a supported V_2O_5/Al_2O_3 catalyst containing a monolayer surface coverage of vanadia, however, a slight exposure of the oxide support cation (Al~(3+)) was noted, which may originate from the much higher surface area of this support (Al_2O_3 Nb_2O_5, ZrO_2, and CeO)2) resulting in a higher curvature of the surfaces covered by the supported vanadia species. The current XPS and ISS surface studies confirm that supported vanadium oxide catalysts consist of close-packed monolayers of surface vanadia species.
机译：通过X射线光电子能谱（XPS）和离子散射能谱（ISS）研究了由Al2O3，ZrO_2，CeO_2和Nb_2O_5氧化物载体上的表面钒物种组成的负载型钒氧化物催化剂，以阐明煅烧处理的效果以及暴露于（非单色）X射线和He离子的表面性质。已发现先前在773 K的空气中煅烧并暴露于环境大气中的样品在730 K的空气中煅烧会导致相对于XPS和ISS中的支持信号而言，V强度显着增加。这表明表面钒物种在水分的影响下聚集，但在煅烧过程中扩散。长时间暴露于非单色光源的X射线后，表面V（V）物种被还原为V（IV），这伴随着ISS的聚类。通过研究一种新的方法来避免这些影响，方法是研究未经煅烧的样品，这些样品无需暴露在环境大气中，也无需事先通过X射线照射，并通过推断溅射序列的结果考虑了He离子的磨蚀作用，因此发现在具有钒单层覆盖率或更高的负载的V_2O_5 / ZrO_2，V_2O_5 / CeO_2和V_2O_5 / Nb_2O_5催化剂中，载体被二维表面钒物种密集地覆盖，并且下面的Zr，Ce或Nb氧化物载体阳离子为不暴露。但是，对于含有钒的单层表面覆盖的负载型V_2O_5 / Al_2O_3催化剂，注意到氧化物载体阳离子（Al〜（3+））的轻微暴露，这可能源于该载体（Al_2O_3）更高的表面积 Nb_2O_5，ZrO_2和CeO）2）导致被负载的钒物种覆盖的表面具有更高的曲率。当前的XPS和ISS表面研究证实，负载的钒氧化物催化剂由表面钒物种的密堆积单分子层组成。

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