Zabilska Anna, Clark Adam H, Ferri Davide, Nachtegaal Maarten, Kröcher Oliver, Safonova Olga V
Paul Scherrer Institute, 5232 Villigen, Switzerland.
École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
Phys Chem Chem Phys. 2022 Sep 21;24(36):21916-21926. doi: 10.1039/d2cp02721f.
X-ray absorption spectroscopy (XAS) is a powerful technique for the investigation of heterogeneous catalysts and electrocatalysts. The obtained XAS spectra are usually interpreted from the point of view of the investigated chemical processes, thereby sometimes omitting the fact that intense X-ray irradiation may induce additional transformations in metal speciation and, thus, in the corresponding XAS spectra. In this work, we report on X-ray induced photochemical reduction of vanadium in supported vanadia (VO) catalysts under reaction conditions, detected at a synchrotron beamline. While this process was not observed in an inert atmosphere and in the presence of water vapor, it occurred at room temperature in the presence of a reducing agent (ethanol or hydrogen) alone or mixed with oxygen. Temperature programmed experiments have shown that X-ray induced reduction of VO species appeared very clear at 30-100 °C but was not detected at higher temperatures, where the thermocatalytic ethanol oxidative hydrogenation (ODH) takes place. Similar to other studies on X-ray induced effects, we suggest approaches, which can help to mitigate vanadium photoreduction, including defocusing of the X-ray beam and attenuation of the X-ray beam intensity by filters. To recognize beam damage under / conditions, we suggest performing X-ray beam switching (on and off) tests at different beam intensities under conditions.
X射线吸收光谱（XAS）是研究多相催化剂和电催化剂的一种强大技术。所获得的XAS光谱通常从所研究的化学过程的角度进行解释，从而有时忽略了强烈的X射线辐照可能会在金属形态以及相应的XAS光谱中诱导额外转变这一事实。在这项工作中，我们报告了在反应条件下，在同步加速器光束线上检测到的负载型氧化钒（VO）催化剂中钒的X射线诱导光化学还原。虽然在惰性气氛和有水蒸气存在的情况下未观察到这一过程，但在单独存在还原剂（乙醇或氢气）或与氧气混合的情况下，它在室温下发生。程序升温实验表明，X射线诱导的VO物种还原在30 - 100°C时非常明显，但在发生热催化乙醇氧化脱氢（ODH）的较高温度下未检测到。与其他关于X射线诱导效应的研究类似，我们提出了一些有助于减轻钒光还原的方法，包括使X射线束散焦以及通过滤光片衰减X射线束强度。为了识别/条件下的光束损伤，我们建议在条件下不同光束强度下进行X射线束切换（开和关）测试。
