Environmental electron microscopy (ETEM) for catalysts with a closed E-cell with carbon windows
ABSTRACT In a standard high-resolution electron microscope (Jeol 3010), an environmental sample holder designed by Jeol, has been used for in situ observations at the atomic scale of catalysts, during a chemical reaction. Experiments have been performed in H(2) and O(2) at a pressure up to 4 mbar at room temperature, and in the case of H(2), at various temperatures until 350 degrees C. For the first time, Au and Pd clusters supported on TiO(2) and amorphous carbon have been observed with a windows-cell environmental electron microscopy (ETEM) system, with the resolution of the (1 1 1) lattice fringes. Au clusters have been cleaned in H(2) and have got the equilibrium shape of the fcc crystals during annealing. The same Au particles can be observed during successive treatments under O(2) and H(2). For Pd clusters in situ exposed to O(2) , the adhesion has decreased.
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ABSTRACT: Transmission electron microscopy (TEM) has become an indispensable technique for studying heterogeneous catalysts. In particular, advancements of aberration-corrected electron optics and data acquisition schemes have made TEM capable of delivering images of catalysts with sub-Ångström resolution and single-atom sensitivity. Parallel developments of differentially pumped electron microscopes and of gas cells enable in situ observations of catalysts during the exposure to reactive gas environments at pressures of up to atmospheric levels and temperatures of up to several hundred centigrade. Here, we outline how to take advantage of the emerging state-of-the-art instrumentation and methodologies to study surface structures and dynamics to improve the understanding of structure-sensitive catalytic functionality. The concept of using low electron dose-rates in TEM in conjunction with in-line holography and aberration-correction at low voltage (80 kV) is introduced to allow maintaining atomic resolution and sensitivity during in situ observations of catalysts. Benefits are illustrated by exit wave reconstructions of TEM images of a nanocrystalline Co3O4 catalyst material acquired in situ during their exposure to either a reducing or oxidizing gas environment.Micron 10/2014; 68:176-185. DOI:10.1016/j.micron.2014.07.009