Portnyagin A S, Golikov A P, Drozd V A, Avramenko V A
Department of Sorption Processes, Institute of Chemistry, Far Eastern Branch of Russian Academy of Sciences pr. 100-letiya Vladivostoka Vladivostok Russia
School of Natural Sciences, Far Eastern Federal University Sukhanova str 8. Vladivostok Russia.
RSC Adv. 2018 Jan 16;8(6):3286-3295. doi: 10.1039/c7ra09848k. eCollection 2018 Jan 12.
To date, kinetic computations have been carried out efficiently for a great variety of physico-chemical processes including crystallization, melting and solid-solid transitions. However, appropriate methods for the kinetic analysis of chemical reactions, especially multi-staged reactions, are currently lacking. Here we report on an alternative way of treating temperature-programmed reaction data using the reduction of iron(iii) oxide as an example. The main principle in the suggested approach is to take into account every stage of the studied process, resulting in a system of kinetic differential equations. Kinetic parameters (activation energy and preexponential factors) are optimized for each of the stages, and cubic splines are used to approximate the conversion functions that reflect changes in reaction-specific surface area throughout the process. The applicability of the suggested method has been tested on temperature-programmed reduction (TPR) data for iron(iii) oxide samples produced from the original FeO powder by annealing it at 600, 700 and 800 °C. Results of kinetic analysis obtained at different temperature regimes demonstrate the good stability and performance of the method. Peculiarities of iron(iii) oxide reduction have been revealed, depending on the stage and heating rate. The influence of material morphology on the reduction kinetics has been assessed by comparing preexponential factors corresponding to the first reduction stage. This approach allows a comparison of the structural characteristics of the materials based on the kinetic analysis of the TPR data. Using optimized conversion functions, the initial particle size distribution has been reproduced. Theoretically found particle size distribution was found to correlate well with the experimental distribution obtained laser diffraction.
迄今为止，动力学计算已有效地应用于包括结晶、熔化和固-固转变在内的各种物理化学过程。然而，目前缺乏适用于化学反应，尤其是多阶段反应动力学分析的方法。在此，我们以氧化铁的还原为例，报告一种处理程序升温反应数据的替代方法。所建议方法的主要原理是考虑所研究过程的每个阶段，从而得到一个动力学微分方程组。针对每个阶段优化动力学参数（活化能和指前因子），并使用三次样条函数来近似反映整个过程中反应比表面积变化的转化率函数。所建议方法的适用性已通过对由原始FeO粉末在600、700和800°C退火制备的氧化铁样品的程序升温还原（TPR）数据进行测试。在不同温度条件下获得的动力学分析结果表明该方法具有良好的稳定性和性能。已揭示了氧化铁还原的特性，这取决于阶段和升温速率。通过比较对应于第一还原阶段的指前因子，评估了材料形态对还原动力学的影响。这种方法允许基于TPR数据的动力学分析来比较材料的结构特征。使用优化的转化率函数，再现了初始粒度分布。理论上发现的粒度分布与通过激光衍射获得的实验分布具有良好的相关性。
