In situ environmental transmission electron microscopy (ETEM) is a powerful tool for observing structural modifications taking place in heterogeneous catalysts under reaction conditions. However, to strengthen the link between catalyst structure and functionality, an operando measurement must be performed in which reaction kinetics and catalyst structure are simultaneously determined. To determine chemical kinetics for gas-phase catalysis, it is necessary to develop a reliable chemical engineering model to describe catalysis as well as heat and mass transport processes within the ETEM cell. Here, we establish a finite element model to determine the gas and temperature profiles during catalysis in an open-cell operando ETEM experiment. The model is applied to a SiO2-supported Ru catalyst performing CO oxidation. Good agreement is achieved between simulated compositions and those measured experimentally across a temperature range of 25 - 350 °C. In general, for lower conversions, the simulations show that the temperature and gas are relatively homogeneous within the hot zone of the TEM holder where the catalyst is located. The uniformity of gas and temperature indicates that the ETEM reactor system behavior approximates that of a continuously stirred tank reactor (CSTR). The large degree of gas-phase uniformity also allows one to estimate the catalytic conversion of reactants in the cell to within 10% using electron energy-loss spectroscopy. Moreover, the findings indicate that for reactant conversions below 35%, one can reliably evaluate the steady-state reaction rate of catalyst nanoparticles that are imaged on the TEM grid.

中文翻译：

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用于催化剂操作电子显微镜的化学动力学：催化反应过程中气体和温度分布的 3D 建模

原位环境透射电子显微镜 (ETEM) 是观察反应条件下多相催化剂中发生的结构变化的有力工具。然而，为了加强催化剂结构和功能之间的联系，必须进行操作测量，其中同时确定反应动力学和催化剂结构。为了确定气相催化的化学动力学，有必要开发一个可靠的化学工程模型来描述 ETEM 单元内的催化以及传热和传质过程。在这里，我们建立了一个有限元模型，以确定在开孔操作 ETEM 实验中催化过程中的气体和温度分布。该模型应用于执行 CO 氧化的 SiO2 负载的 Ru 催化剂。模拟成分与在 25 - 350 °C 的温度范围内通过实验测量的成分之间实现了良好的一致性。一般来说，对于较低的转化率，模拟显示温度和气体在催化剂所在的 TEM 支架的热区内相对均匀。气体和温度的均匀性表明 ETEM 反应器系统的行为接近于连续搅拌釜式反应器 (CSTR) 的行为。较大程度的气相均匀性还允许使用电子能量损失光谱法估计电池中反应物的催化转化率在 10% 以内。此外，研究结果表明，对于低于 35% 的反应物转化率，可以可靠地评估在 TEM 网格上成像的催化剂纳米颗粒的稳态反应速率。