Characterization of Supported Catalytic Metallic Nanoparticles using Transmission Electron Microscopy

Abstract: In this project catalysts have been analyzed, in the sense of size and composition, using a Transmission Electron Microscope (TEM). This important class of substances are used to facilitate chemical reactions, in everything from specific molecular research to conversion car emissions which explains the importance of research. Nanoparticles of gold (Au) have been shown to have good catalytic performance. However, optimization in size is crucial due to the different facets present at different sizes. TEM has been used to image the catalysts, using contrast in different modes of operation to distinguish the gold from the carrier oxide which is there to prevent agglomeration of the gold. Sizes of the Au nanoparticles ranged from 5 to 16 nm without any agglomeration observed. Further, so called Molecular Imprinted Polymers, MIPs, were analyzed for their elemental content and to make sure no palladium (Pd) from the palladium containing molecules had reduced to metallic particles during polymerization. The results were promising in the sense that stable low levels of Pd without any metallic palladium were observed. TEM-modes used were different in how well they could distinguish the particles. Conventional imaging (CTEM) proved difficult since high scattering occurred from thicker oxide as well. While scanning TEM (STEM) was the preferred method due to the clearer results in its HAADF-mode (High Angle Annular Dark Field). Together with X-ray Energy Dispersive Spectroscopy (XEDS) STEM provided compelling images and elemental maps of where gold was found in the clusters. One could also pick certain points in the image to get local composition, useful for the MIP-analysis.