Application of XANES Spectra to Supported Catalysts
Application of XANES Spectra to Supported Catalysts
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XANES 光谱在负载型催化剂中的应用
DOI：
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发表时间：
1999
期刊：
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通讯作者：
S. Yoshida
中科院分区：
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作者：
Tsunehiro Tanaka;Takashi Yamamoto;Y. Kohno;T. Yoshida;S. Yoshida
XANES 光谱用于表征负载型催化剂的表面物质。对于低负载量负载在二氧化硅 (V2O5/SiO2) 上的氧化钒，将钒 K 边 XANES 光谱与真实样品的光谱进行比较，可以确定表面物质是 VO4 四面体，其中四个氧原子中的三个与二氧化硅载体连接。水分子的吸附很容易改变配位环境，表明水分子直接附着在钒原子上。 Pt硫酸化ZrO2铂颗粒被称为促进超酸性反应的催化剂，由铂金属颗粒核心和氧化铂表面层组成。利用Pt金属和α-PtO2的XANES光谱分析催化剂样品，得到α-PtO2的分数。 Fe、Mn硫酸化ZrO2催化剂中的Fe离子被认为是促进超酸性反应的催化剂，被发现以固溶体形式存在于ZrO2内部，并且这些离子不直接参与超酸性反应。 Mn离子是反应气体分子的吸附位点。 Fe K 边缘的原位 XANES 光谱在整个反应过程中没有变化，而 Mn K 边缘的原位 XANES 光谱受到反应气体引入的影响。沸石中的铕酰胺络合物是三价和二价Eu物质的混合物。 Eu二价物质是碱催化反应的活性物质。 Eu 二价物质的分数可以通过对 Eu L3 边缘的 XANES 光谱进行分析来确定。适用于 Pt XANES 光谱的分析可应用于 Rh/TiO2 在 Rh K 边缘的 XANES 光谱。在Rh/TiO2光催化剂的情况下，催化剂的反应活性随着Rh的负载量而变化。 Rh/TiO2 催化剂的 XANES 分析表明，表面铑物种是 Rh 金属和高度分散的 Rh2O3 的混合物，并且 Rh2O3 的分数随负载量的变化而变化。我们发现，即使在氢气存在下将催化剂加热到 673 K 后，Rh 原子在低负载量下仍以氧化物形式存在。
XANES spectroscopy is applied to the characterization of surface species of supported catalysts. In case of vanadium oxide supported on silica (V2O5/SiO2) at low loadings, comparison of the vanadium K-edge XANES spectrum with the spectra of the authentic samples allowed the determination that the surface species is a VO4 tetrahedron where three oxygen atoms of the four are linked to silica support. The coordination environment changed easily by adsorption of water molecules, indicating the direct attachment of water molecules to vanadium atoms. A platinum particle of Pt-sulfated ZrO2, known as a catalyst promoting super acidic reactions, consists of a core of platinum metal particle and surface layers of platinum oxide. The analysis of XANES spectrum of the catalyst sample by using those of Pt metal and α-PtO2 goves the fraction of α-PtO2. Fe ions in Fe, Mn-sulfated ZrO2 catalyst, knowing as a catalyst promoting super acidic reactions, were found to be present inside the ZrO2 as a solid solution and the ions does not directly participate in the super acidic reaction. Mn ions are the site of adsorption of reactant gas molecules. The in situ XANES spectra at Fe K-edge did not change throughout the reaction and those at Mn K-edge were affected by introduction of reaction gas. Europium amide complex in zeolite is a mixture of trivalent and divalent Eu species. Eu divalent species is an active species for abase-catalyzed reaction. The fraction of Eu divalent species could be determined by danalysis of XANES spectra of Eu L3-edge. The analysis applied to Pt XANES spectra can be applied to the XANES spectra of Rh/TiO2 at Rh K-edge. In the case of a Rh/TiO2 photocatalyst, the reactivity of the catalyst varies with the loading amount of Rh. XANES analysis of the Rh/TiO2 catalysts showed that surface rhodium species are a mixture of Rh metal and highly dispersed Rh2O3 and the fraction of Rh2O3 varies with the loading amount. We found that Rh atoms are present as an oxide form at low loadings even after heating the catalyst in the presence of hydrogen at 673 K.