COMBINED DRS-RS-EXAFS-XANES-TPR STUDY OF SUPPORTED CHROMIUM CATALYSTS
COMBINED DRS-RS-EXAFS-XANES-TPR STUDY OF SUPPORTED CHROMIUM CATALYSTS
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负载型铬催化剂的 DRS-RS-EXAFS-XANES-TPR 组合研究
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
E. Poels
中科院分区：
文献类型：
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作者：
B. Weckhuysen;R. Schoonheydt;J. Jehng;I. Wachs;S. Cho;R. Ryoo;S. Kijlstra;E. Poels
采用漫反射光谱（DRS）、拉曼光谱（RS）、X射线吸收光谱（EXAFS-XANES）和程序升温还原（TPR）等方法系统地研究了负载型铬催化剂（Cr/SiO2·Al 2 O3）的表面化学性质与载体组成（Si：Al比）和Cr氧化物负载量的关系。通过这些表征技术获得的所有结果的组合导致表面Cr的统一解释和一般图片。在水合表面上，Cr氧化物物种的分子结构取决于氧化物载体的等电点和Cr负载：更多聚合的Cr氧化物物种对应于更高的Cr负载和载体的二氧化硅含量。煅烧后，Cr氧化物物种通过与载体的表面羟基反应而锚定在表面上。在氧化铝上，反应从氧化铝上最碱性的OH基团开始。这表明锚定过程是一个酸碱反应。在煅烧的表面上，锚定的Cr氧化物物种的聚合和Cr2 O3簇的量随着二氧化硅含量和Cr负载量而增加。还原的Cr样品同时具有Cr 2+和Cr 3+，其相对浓度取决于载体和负载量：较低的Cr 2+：Cr 3+比率对应于载体的较高的Cr负载量和氧化铝含量。
The surface chemistry of supported chromium catalysts (Cr/SiO2· Al2O3) has been systematically investigated as a function of the support composition (Si:Al ratio) and the Cr oxide loading by a combination of diffuse reflectance spectroscopy (DRS), Raman spectroscopy (RS), X-ray Absorption spectroscopy (EXAFS–XANES) and temperature-programmed reduction (TPR). Combination of all the obtained results by these characterization techniques leads to a uniform interpretation and general picture of surface Cr. On hydrated surfaces, the molecular structure of the Cr oxide species depends on the isoelectric point of the oxide support and the Cr loading: more polymerized Cr oxide species correspond to higher Cr loading and silica content of the support. After calcination, the Cr oxide species are anchored onto the surface by reaction with surface hydroxy groups of the supports. On alumina the reaction starts with the most basic OH groups on alumina. This suggests that the anchoring process is an acid–base reaction. On calcined surfaces, the polymerization of the anchored Cr oxide species and the amount of Cr2O3 clusters increases with silica content and Cr loading. Reduced Cr samples possess both Cr2+ and Cr3+, the relative concentrations of which are support and loading dependent: lower Cr2+:Cr3+ ratios correspond to higher Cr loading and alumina content of the support.