Investigation of a Nanoporous Gold / TiO 2 Catalyst by Electron Microscopy and Tomography
- PDF / 3,437,702 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 38 Downloads / 230 Views
Investigation of a Nanoporous Gold / TiO2 Catalyst by Electron Microscopy and Tomography Kristian Frank1, Andre Wichmann2, Arne Wittstock2, Marcus Bäumer2, Lutz Mädler3 and Andreas Rosenauer1. 1
Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany 2 Institute of Applied and Physical Chemistry, University of Bremen, Leobener Str. NW2, 28359 Bremen, Germany 3 IWT Foundation Institute of Materials Science, University of Bremen, Badgassteiner Str. 3, 28359 Bremen, Germany ABSTRACT Nanoporous gold is a material with many possible applications e.g. in catalysts, sensors and electrode materials. We studied the functionalization of the nanoporous gold with TiO2 particles. Aiming at the low temperature oxidation of CO, the nanoporous gold can be coated with TiO2 in order to enhance catalytic activity. Structure and distribution of the TiO2 on the gold surface are important structural features, which were investigated by transmission electron microscopy. The preparation of the porous gold was tested with focused ion beam - preparation, conventional Ar+ ion beam preparation of nanoporous gold embedded in epoxy and ultramicrotome preparation of nanoporous gold embedded in epoxy. Considering the beam damage on the structure and the contamination of the surface, ultramicrotome preparation turned out to be the best solution. It was shown, that the gold ligaments are abundantly covered by approximately 5 nm TiO2 particles. The determination of the largest lattice fringe distance in high resolution mode revealed that the crystalline nanoparticles consist of the anatase phase. The spatial Ti distribution was measured with energy filtered transmission electron microscopy. Scanning transmission electron microscopy tomography was applied to reconstruct the three-dimensional structure of the gold coated with TiO2 particles. INTRODUCTION Gold, usually known for its inertness, can be prepared as a nanoporous bulk material (figure 1a)) showing catalytic properties. A particular advantage of this catalytic material is the stable monolithic structure, combining mechanical strength, thermal and electrical conductivity and a reproducible porosity due to self-organization during the preparation by corrosion (leaching of Ag in an Ag-rich AuAg alloy). This can lead to many possible applications e.g. in catalysts, sensors and electrode materials [1]. As gold cannot dissociate oxygen, the oxidation capability of the material can be enhanced with e.g. TiO2 particles [2]. In the temperature range above 60 °C the CO to CO2 conversion of the TiO2 coated sample is increased by more than one order of magnitude compared with the pure nanoporous gold (figure 1b)). For the understanding of the catalytic behavior knowledge of the distribution of the TiO2 inside the volume is important. In order to dissociate the oxygen and supply the reaction at the gold ligaments with active oxygen
the TiO2 particles should be homogeneously distributed with average distances to each other in the order of magnitude of tenth of nm
Data Loading...
