How the charge transfer in high performance oxidation catalysts controls activity and selectivity: noncontact measurement of Hall charge carrier mobilities and concentrations under reaction conditions

我们的目标是发展一种基于微波的非接触光谱方法，以研究在选定的氧化催化剂在反应条件下的动态电荷转移。测量微波霍尔效应以确定位于固定床流通式反应器中的催化剂中的电荷载体（电子、空穴、离子）的密度、迁移率和类型。通过改变反应温度、气相组成和气时空速（接触时间），考察了所选催化体系和反应，即磷酸钒和氧化钒催化剂上丙烷选择氧化制丙烯酸和正丁烷选择氧化制马来酸酐的催化活性和选择性与测定值的相关性。我们的目标是区分催化剂表面，表面下，并在散装和电荷载流子浓度和流动性之间的区别，并确定对催化性能的影响。为此，我们最近开发的微波腔微扰技术的原位表征的非均相催化剂是扩展到测量微波霍尔效应在一个静态磁场中的双峰谐振器。该装置将使用合适的单晶和粉末进行校准。结果进行了比较，并解释了原位光电子能谱和替代原位和非原位光谱技术，X射线衍射，热分析。此外，为了探测晶界和颗粒接触的影响并能够将结果与低频和DC测量结果进行比较，通过构造适当的谐振器，将迄今存在的在9GHz下的微波电导率测量扩展到1和20GHz之间的频率范围。

We are aiming at the development of a microwave-based noncontact spectroscopic method in order to study the dynamic charge transfer in selected oxidation catalysts under reaction conditions. The microwave Hall effect is to be measured to determine the density, mobility, and type of charge carriers (electron, hole, ion) in catalysts situated in a fixed bed flow-through reactor. By the variation of reaction temperature, gas phase composition, and gas hourly space velocity (contact time) the correlation of the measured values with the catalytic activity and selectivity is to be investigated for selected catalytic systems and reactions, i.e. the selective oxidation of propane to acrylic acid and n-butane to maleic anhydride on vanadium phosphate and oxide catalysts. Our goal is to discriminate between charge transfer on the catalyst surface, sub-surface, and in the bulk and to distinguish between charge carrier concentration and mobility and to identify the impact on the catalytic performance. For this purpose our recently developed microwave cavity perturbation technique for the in situ characterization of heterogeneous catalysts is to be extended to measure the microwave Hall effect in a bimodal resonator in a static magnetic field. The setup is to be calibrated with suitable single crystals and powders. The results are to be compared and explained by in situ photoelectron spectroscopy and alternative available in situ and ex situ spectroscopic techniques, X-ray diffractometry, and thermoanalysis. Moreover, the hitherto existing microwave conductivity measurement at 9 GHz is to be extended to the frequency range between 1 and 20 GHz by the construction of adequate resonators in order to probe the effect of grain boundaries and particle contacts and to be able to compare the results with low frequency and DC measurements.