The reactivity of catalyst particles can be radically enhanced by decreasing their size down to the nanometer range. The nanostructure of a catalyst can have an enormous and positive influence on the reaction rate, for example strong structure sensitivity was observed for methane reforming and ammonia synthesis, and it is therefore crucial that catalysts preserve their nanostructures under operational conditions. Fundamental understanding of the relation between the catalytic activity and the morphology of the nanoparticle, their crystallinity and crystallite size, is required to improve the catalysts and assess the optimum conditions of operation. A powerful and suitable technique to resolve these relations is simultaneous small and wide angle X-ray scattering coupled with mass spectroscopy measurements, performed in situ at conditions comparable to large scale processes. A new heater setup for an in situ cell, accommodated in a laboratory SAXS/WAXS camera, has been developed and a sample gas system has been designed and installed. A mass spectrometer has been implemented to monitor the chemical reactions during the in situ experiments. The heater permits experiments in a temperature range from 298 - 1073 K. The heater performance was tested and it was shown that no temperature calibration is needed. The applicability of the new setup, to study nanostructured materials, was successfully demonstrated using anatase TiO2 nanorods. Heating experiments on the nanorods were performed in a temperature range from 298 - 1023 K. Correlated crystallite and particle growth due to sintering were observed after the decomposition of the surfactant. Furthermore transformations from rod to spherical particle shape were observed. In situ reduction experiments of a Ni/MgAl2O4 catalyst were performed. The Ni/NiO particles in a fresh catalyst sample showed a Ni/NiO core shell structure. The Ni lattice parameter decreased during the reduction due to the release of stress between the Ni core and the NiO shell. Ni particles sintered during heating in hydrogen after the reduction of the NiO shell. Dry reforming experiments were performed over a Ru/MgAl2O4. The catalyst showed a high sintering stability and no catalyst deactivation was observed. The results presented in this thesis emphasize the advantage of the simultaneous SAXS/W AXS laboratory setup to study nanostructured materials and catalysts in situ.
|Place of Publication||Kgs. Lyngby, Denmark|
|Publisher||Department of Energy Conversion and Storage, Technical University of Denmark|
|Number of pages||187|
|Publication status||Published - Apr 2011|
Kehres, J. (2011). Dynamical properties of nano-structured catalysts for methane conversion: an in situ scattering study. Kgs. Lyngby, Denmark: Department of Energy Conversion and Storage, Technical University of Denmark.