环境扫描透射电子显微镜原位揭示氢溢流促进TiO2体缺陷修复机理

环境扫描透射电子显微镜原位揭示氢溢流促进TiO₂体缺陷修复机理

夏怡泽，欧  阳，王  飞，袁文涛^*，杨杭生，张  泽，王  勇^*

（浙江大学电子显微镜中心，硅材料国家重点实验室，材料科学与工程学院，浙江 杭州 310027）

摘  要 负载型纳米催化剂的缺陷是决定其催化性能的一个关键因素。但由于缺少外场环境下原子尺度的缺陷动态结构信息，精确调控材料中的晶体缺陷依然极富挑战性。本工作利用原位球差校正环境扫描透射电子显微镜（ESTEM）研究了Pd-TiO₂催化剂中TiO₂载体结构在不同气氛下的动态演变，原位观察了TiO₂载体中纳米级空洞结构在600 ℃氢气气氛下的消失行为。结合H₂程序升温还原(H₂- TPR)、X射线衍射(XRD)、电子顺磁共振(EPR)和X射线光电子能谱(XPS)等谱学表征，揭示了氢气气氛下Pd-TiO₂催化剂的结构演变机制。研究发现，高温氢气环境下Pd-TiO₂表面的氢溢流导致TiO₂载体上产生了大量的氧空位（V_O）并被负价Pd离子稳定，高浓度V_O促进了TiO₂载体中离子扩散，极大促进了具有高表面能的纳米级空洞的消失。

关键词  原位电镜；环境扫描透射电镜；二氧化钛；晶体缺陷；氢溢流

中图分类号：TG115. 21⁺ 5.3；TQ426；O64 

文献标识码：A   doi:10.3969/j.issn.1000-6281.2022.04.002

In siturevealing the mechanism of hydrogen-spillover promoted bulk defects healing in TiO₂ via environmental scanning transmission electron microscopy

XIA Yi-ze, OU Yang, WANG Fei, YUAN Wen-tao^*, YANG Hang-sheng, ZHANG Ze, WANG Yong^*

(Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou Zhejiang 310027, China)

Abstract   Defect of supported nanocatalyst is a key factor to determine its catalytic performance. However, due to the lack of the dynamic structural information of defects at atomic scale under external environments, precisely tuning crystal defects in materials is still challenging. Herein, we investigated the dynamic structural evolution of TiO₂ supports of Pd-TiO₂ catalysts under different atmospheres via in situ spherical aberration environmental scanning transmission electron microscope (ESTEM). A nanoscale pore disappearing behavior was in situ observed in H₂ environment at 600 °C. Combined with H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD), electron paramagnetic resonance (EPR)and X-ray photoelectron spectroscopy (XPS)analyses, a hydrogen-spillover promoted structural evolution mechanism of Pd-TiO₂ catalysts in H₂ environment was proposed. The hydrogen spillover, occured at the Pd-TiO₂ surface at high temperature, promotes the formation of a large amount of oxygen vacancies (V_Os), which is then stabilized by negative Pd ions.The high concerntration of Vo promotes the diffusion of ions in the TiO₂ bulk phase, leading to the disappearance of nanoscale pores with high surface energy.

Keywords   In situelectron microscopy；environmental scanning transmission electron microscopy；titanium dioxide；crystal defect；hydrogen spillover

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