The kinetics of reduction of a 10 wt %Fe₂O₃-MgAl₂O₄ spinel were investigated using XRD and time resolved Fe-K QXANES. The Rietveld refinement of the XRD pattern showed the replacement of Al with Fe in the spinel structure and the formation of MgFeAlO_x. The XANES pre-edge feature was employed to study the reduction kinetics during H₂-TPR (Temperature Programmed Reduction) up to 730°C. About 55% of the Fe³⁺ in MgFeAlO_x was reduced to Fe²⁺. A shrinking core model, which takes into account both solid-state diffusion via an oxygen diffusion coefficient, and gas-solid reaction through a reaction rate coefficient, was applied. The activation energy for chemical reaction showed a linear dependence on the conversion, increasing from 104 to 126 kJ/mol over the course of material reduction. The good accordance between the shrinking core model description and the experimental data indicates that XANES pre-edge features can be used to correlate changes in material structure and reaction kinetics. © 2017 American Institute of Chemical Engineers AIChE J, 2017

中文翻译：

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使用时间分辨的原位XAS从前缘特征洞察动力学

使用XRD和时间分辨的Fe-K QXANES研究了10 wt％Fe ₂ O ₃ -MgAl ₂ O ₄尖晶石的还原动力学。X射线衍射图的Rietveld细化表明尖晶石结构中的Al被Fe取代并形成MgFeAlO _x。XANES前缘特征用于研究H ₂ -TPR（温度程序控制的还原）在高达730°C的过程中的还原动力学。MgFeAlO _x中约55％的Fe ³⁺被还原为Fe ²⁺。应用了收缩核模型，该模型同时考虑了通过氧扩散系数的固态扩散和通过反应速率系数的气固反应。用于化学反应的活化能显示出对转化率的线性依赖性，在材料还原过程中从104增加到126 kJ / mol。收缩核模型描述与实验数据之间的良好一致性表明，XANES前缘特征可用于关联材料结构和反应动力学的变化。©2017美国化学工程师学会AIChE J，2017