Abstract：
Iron is considered as attractive energy carrier in a carbon-free circular energy economy. The reduction of iron oxide is crucial for its applica-tion as a metal fuel as it determines the efficiency of the cycle. Temperature programmed reduction of α-Fe2O3 was monitored by complementary X-ray absorption spectroscopy (XAS) and diffraction (XRD) to obtain the phase composition with high time resolution. Synchrotron Mössbauer spectroscopy (SMS) was additionally employed due to its high sensitivity to the different iron species. Theoretical calculations of surface and bulk adsorption processes were performed to establish the potential reaction pathways and the corresponding energy barriers. A kinetic particle model was then developed to bridge the experimental data and theoretical calculations, which reproduced the reduction onset and behavior. The reduction process was found to be strongly dependent on the heating rate in terms of the reduction window and the observed intermediate species. We propose that a core-shell mechanism determines the reaction by forming an iron layer which subsequently hinders diffusion of water out of the porous particles leading to some unreduced FeO at high temperature. This study demonstrates the need for complementary methods for describing complex heterogeneous systems and overcoming the chemical sensitivity limitations of any single method.
摘要：
在无碳循环能源经济中，铁被认为是有吸引力的能源载体。氧化铁的还原对于其作为金属燃料的应用至关重要，因为它决定了循环的效率。通过互补X射线吸收光谱（XAS）和衍射（XRD）监测α-Fe2O3的程序升温还原，以获得具有高时间分辨率的相组成。由于同步加速器Mössbauer光谱（SMS）对不同铁物种的高灵敏度，因此还采用了该光谱。进行了表面和本体吸附过程的理论计算，以建立潜在的反应途径和相应的能障。然后建立了动力学粒子模型，以桥接实验数据和理论计算，再现了还原的开始和行为。发现还原过程在还原窗口和观察到的中间物种方面强烈依赖于加热速率。我们建议核-壳机制通过形成铁层来决定反应，铁层随后阻碍水从多孔颗粒中扩散出来，从而在高温下产生一些未还原的FeO。这项研究表明需要补充方法来描述复杂的异质系统并克服任何单一方法的化学灵敏度限制。
