The formation of palladium hydride and carbide phases in palladium-based catalysts is a critical process that changes the catalytic performance and selectivity of the catalysts in important industrial reactions, such as the selective hydrogenation of alkynes or alkadienes. We present a comprehensive study of a 5 wt% carbon supported Pd nanoparticle (NP) catalyst in various environments by using in situ and operando X-ray absorption spectroscopy and diffraction, to determine the structure and evolution of palladium hydride and carbide phases, and their distribution throughout the NPs. We demonstrate how the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) spectra and X-ray powder diffraction (XRPD) patterns allows discrimination between the inner “core” and outer “shell” regions of the NP during hydride phase formation at different temperatures and under different hydrogen pressures, indicating that the amount of hydrogen in the shell region of the NP is lower than that in the core. For palladium carbide, advanced analysis of X-ray absorption near-edge structure (XANES) spectra allows the detection of Pd–C bonds with carbon-containing molecules adsorbed at the surface of the NPs. In addition, H/Pd and C/Pd stoichiometries of PdH_x and PdC_y phases were obtained by using theoretical modelling and fitting of XANES spectra. Finally, the collection of operando time-resolved XRPD patterns (with a time resolution of 5 s) allowed the detection, during the ethylene hydrogenation reaction, of periodic oscillations in the NPs core lattice parameter, which were in phase with the MS signal of ethane (product) and in antiphase with the MS signal of H₂ (reactant), highlighting an interesting direct structure–reactivity relationship. The presented studies show how a careful combination of X-ray absorption and diffraction can differentiate the structure of the core, shell and surface of the palladium NPs under working conditions and prove their relevant roles in catalysis.

中文翻译：

---

X射线衍射和吸收作用下加氢反应下碳载Pd纳米粒子的时间分辨操作研究

在基于钯的催化剂中氢化钯和碳化物相的形成是关键过程，其在重要的工业反应（例如炔烃或链二烯的选择性加氢）中改变了催化剂的催化性能和选择性。我们通过使用原位和操作方法，对各种环境中的5 wt％碳负载的Pd纳米粒子（NP）催化剂进行了全面的研究。X射线吸收光谱和衍射，以确定氢化钯和碳化物相的结构和演化，以及它们在整个NP中的分布。我们展示了如何同时分析扩展的X射线吸收精细结构（EXAFS）光谱和X射线粉末衍射（XRPD）模式，从而在氢化物相形成过程中区分NP的内部“核”和外部“壳”区域。在不同的温度和不同的氢气压力下，表明NP壳层中的氢含量低于核中的氢含量。对于碳化钯，通过对X射线吸收近边缘结构（XANES）光谱的高级分析，可以检测与NPs表面吸附的含碳分子之间的Pd–C键。此外，PdH的H / Pd和C / Pd化学计量比通过使用理论模型和XANES光谱的拟合获得_x和PdC _y相。最后，通过操作时间分辨的XRPD模式（时间分辨率为5 s）的收集，可以在乙烯加氢反应过程中检测到NPs核心晶格参数的周期性振荡，该振荡与乙烷的MS信号同相（产物）并与H ₂（反应物）的MS信号反相，突出显示了有趣的直接结构-反应性关系。提出的研究表明，精心组合的X射线吸收和衍射技术可以在工作条件下区分钯NP的核，壳和表面结构，并证明它们在催化中的相关作用。