An environmental cell high resolution electron microscope (EHREM) has been developed for in situ studies of dynamic chemical reactions on the atomic scale. It allows access to metastable intermediate phases of catalysts and to sequences of reversible microstructural and chemical development associated with the activation, deactivation and poisoning of a catalyst. Materials transported through air can be restored or recreated and samples damaged, e.g. by dehydration, by the usual vacuum environment in a conventional electron microscope can be preserved. A Philips C M30 HRTEM/STEM system has been extensively modified in our laboratory to add facilities for in situ gas-solid reaction studies in controlled atmospheres of gas or vapor at pressures of 0 -50 mbar, instead of the regular TEM high vacuum environment. The integrated new environmental cell capability is combined with t he original 0.23 nm TEM resolution, STEM imaging (bright field/annular dark field) and chemical and crystallographic microanalyses. Regular sample holders are used and include hot stages to > 1000°C. Examples of applications include direct studies of dynam ic reactions with supported metal particle catalysts, the generation of defects and structural changes in practical complex oxide catalyst systems under operating conditions and carbon microstructures.
Heterogeneous gas‐solid catalyst reactions occur on the atomic scale and there is increasing evidence single atoms and very small clusters can act as primary active sites in chemical reactions. Aberration corrected environmental scanning transmission electron microscope (AC ESTEM) has been developed for novel studies of nanoparticle catalysts with Angstrom (0.1 nm) resolution in gas. It extends high vacuum analyses with full analytical facilities and unrestricted high angle annular dark field (HAADF) imaging of single atoms, small clusters and nanoparticles in dynamic in‐situ experiments with controlled gas reaction environments at initial operating temperatures up to > 500 °C.
Advances in atomic resolution in situ environmental transmission electron microscopy for direct probing of gas-solid reactions, including at very high temperatures (approximately 2000 degrees C) are described. In addition, recent developments of dynamic real time in situ studies at the Angstrom level using a hot stage in an aberration corrected environment are presented. In situ data from Pt/Pd nanoparticles on carbon with the corresponding FFT/optical diffractogram illustrate an achieved resolution of 0.11 nm at 500 degrees C and higher in a double aberration corrected TEM/STEM instrument employing a wider gap objective pole piece. The new results open up opportunities for dynamic studies of materials in an aberration corrected environment.
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