MICROSCOPY Vol.46▶No.1 2011
â– Feature Articles: Applications of S/TEM Techniques to Chemistry of Catalysis

Electron Microscopic Study of Heterogeneous Catalysts with 80kV-1MV Accelerating Voltage

Kenta Yoshida, Shigeo Arai, Koh Saitoh and Nobuo Tanaka

Abstract: Platinum supported on titanium dioxide (Pt/TiO2) exhibits remarkably high activity towards the decomposition reaction of organic molecules. Recently the size of Pt clusters has been reduced to less than 1nm. In contrast, the size of TiO2 support particles has been kept at sub-micron sizes to ensure stability at high temperature. The surface has also been modified to form a heterogeneous nanostructure. Although these complex nanocatalysts can be visualized by transmission electron microscopy, switching between several accelerating voltages improves the reproducibility and reliability of the results. Here we report a progressive electron microscopy study of such heterogeneous catalysts using accelerating voltages of 80kV to 1MV. Switching voltages is also essential for estimating the beam effect when performing environmental transmission electron microscopy (ETEM). We present EM images of Pt/TiO2 photocatalysts by advanced ETEM taken over this range of accelerating voltages. In the 80keV TEM image, selective lattice imaging of the Pt nanoparticle was achieved. In addition, greater contrast was obtained in comparison with a conventional 200keV image. On the other hand, a 300keV accelerating voltage provided clearer lattice imaging of the TiO2 supporting particles. In the 1MeV TEM image, surface steps and defect structures of TiO2 were successfully visualized.

Key words: nanostructure, catalyst, in-situ, HRTEM, ETEM