Porous Cerium Dioxide for Catalytic Applications

Sammanfattning: Mesoporous cerium dioxide with high crystallinity has been synthesized and studied by TEM, SEM, nitrogen adsorption, PXRD, AFM, and SAXS. The catalytic properties of the materials have been investigated The results of the catalysis experiments were correlated with high resolution TEM investigations of the corresponding material, and it was found that the exposed crystallographic facets play an important role in the conversion of carbon monoxide to carbon dioxide. The specific surface area of the material is dependent of the dispersion of the precursor mixture when calcined. Increased dispersions result in increasing surface areas. Thin films of mesoporous cerium dioxide was prepared by dip-coating and spin-coating techniques onto various substrate surfaces and the appearance and adhesion were investigated A copper oxide phase was deposited onto mesoporous cerium dioxide by two impregnation methods, and the catalytic performance was investigated for the conversion of CO to CO2 and for CH4 to CO2. The powders were subjected to different calcination temperatures to determine how the catalytic conversion was affected when the specific surface area was reduced. The catalysts prepared by the two impregnation methods were compared to results from non-impregnated mesoporous ceria and also to previous results from nanostructured CuOx/CeO2 particles prepared by inert gas condensation (IGC). The impregnated catalyst had light-off curves that were similar to samples prepared by IGC, showing that the impregnation preparation is a cheaper, large scale process for manufacturing of a catalyst, which is as efficient as IGC-produced material. Macroporous three-dimensionally ordered materials (3-DOM) of zirconium dioxide and cerium dioxide were synthesized and characterized by TEM, SEM, PXRD and nitrogen adsorption. The synthesis developed here is based on chlorine salts dissolved in ethanol solution, which is a much easier and quicker method than the currently most common methods. Both materials were compared by SEM and TEM down to atomic level, showing large differences in crystallite sizes; 50 nm for ZrO2 and 5 nm for CeO2, even though the structures are closely related. The thermal stability of macroporous zirconia was investigated by SEM, XEDS, and PXRD showing a phase transformation from cubic to baddeleyite coincides with the removal of the impurity in the walls (chlorine from the precursor) present for samples calcined below 600°C.