Tao Franklin
Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS, USA.
Nat Protoc. 2025 Aug 27. doi: 10.1038/s41596-024-01092-x.
The surface chemistry of catalyst nanoparticles is crucial for understanding catalytic mechanisms of reactions significant for chemical transformation, energy conversion and environmental sustainability. To enable a high-vacuum X-ray photoelectron spectroscopy (XPS) system to characterize nanoparticle surfaces in liquid or gas phase using a differentially pumped energy analyzer, major and substantial modifications to the high-vacuum XPS instrumentation are required. In this protocol we describe a membrane-separated cell-based XPS approach that allows characterization of the surface of catalyst nanoparticles dispersed in a flowing liquid or gas (at 2 bar) without any instrumental modification to a high-vacuum X-ray photoelectron spectrometer. The cell features a double-layer graphene membrane that separates a catalyst and its reaction environment from the high-vacuum environment of the high-vacuum XPS system. The graphene membrane is assembled onto the pore of a modified SiN window of the cell, admitting an X-ray beam to excite subshell electrons of the catalyst surface atoms in liquid or gas and allowing excited electrons to transit to the high-vacuum environment for XPS analysis. This protocol describes how to create a pore in a SiN window, prepare and load graphene layers to seal the pore, assemble the sealed window onto a cell cap, introduce catalyst nanoparticles to the cell cap, install the cell cap to a cell body to form a complete cell, assemble the complete cell to the high-vacuum XPS system, flow liquid or gas through the cell and collect photoelectrons during catalysis or in vivo/in vitro biological processes performed at solid-liquid or solid-gas interfaces in the cell. Equipment and parts setup takes 2-5 d and data collection takes 12-24 h. This protocol examples the operando studies of C-C coupling on Ag nanoparticles performed in flowing liquid and CO oxidation on Ni/TiO nanoparticles in flowing mixture of 0.4 bar CO and 1.6 bar O.
催化剂纳米颗粒的表面化学对于理解对化学转化、能量转换和环境可持续性具有重要意义的反应的催化机制至关重要。为了使高真空X射线光电子能谱（XPS）系统能够使用差分抽气能量分析仪表征液相或气相中的纳米颗粒表面，需要对高真空XPS仪器进行重大且实质性的修改。在本方案中，我们描述了一种基于膜分离池的XPS方法，该方法可以表征分散在流动液体或气体（2巴）中的催化剂纳米颗粒的表面，而无需对高真空X射线光电子能谱仪进行任何仪器修改。该池具有双层石墨烯膜，可将催化剂及其反应环境与高真空XPS系统的高真空环境隔开。石墨烯膜组装在池的改性SiN窗口的孔上，允许X射线束激发液相或气相中催化剂表面原子的内层电子，并使激发电子传输到高真空环境中进行XPS分析。本方案描述了如何在SiN窗口中创建一个孔，制备并加载石墨烯层以密封该孔，将密封窗口组装到池盖上，将催化剂纳米颗粒引入池盖，将池盖安装到池体上以形成完整的池，将完整的池组装到高真空XPS系统上，使液体或气体流过池，并在池内固液或固气界面进行的催化过程或体内/体外生物过程中收集光电子。设备和部件设置需要2 - 5天，数据收集需要12 - 24小时。本方案举例说明了在流动液体中对银纳米颗粒上的C - C偶联以及在0.4巴CO和1.6巴O的流动混合物中对镍/二氧化钛纳米颗粒上的CO氧化进行的原位研究。
