| This dissertation was directed to studying catalyst sintering, which is an important form of catalyst deactivation. A better understanding of this phenomenon will be of great help in the applications of catalyst under high temperature, such as automotive emission control and catalytic combustion.; This work focuses on Pd based catalysts since they are the most likely candidates for close-coupled catalytic converters. While concentrating on Pd, Pt and Au catalysts were also studied in order to compare their sintering behaviors with that of Pd catalysts. A novel approach to prepare gold catalyst based on aqueous impregnation from a gold chloride precursor has been developed to prepare highly dispersed catalysts. These catalysts have low chloride content and excellent hydrothermal stability. The activity of these catalysts compares favorably with the most active catalysts prepared reported in the literature prepared by the deposition precipitation method.; Multiple techniques have been applied to measure the metal particle size in Pd/SCCa catalysts. Good agreement was obtained between various techniques, meaning that the analytical methods employed in our research (TEM, XRD, chemisorption and CO oxidation) are internally consistent and provide a reliable measure of the change in metal particle size and dispersion as a function of sintering time.; The kinetic study of Pd catalysts suggests that its sintering under study conditions proceeds by Ostwald ripening.; It is shown in this work that both sintering mechanisms can lead to log normal particle size distribution (PSD). In other words, PSD alone cannot be used alone to differentiate sintering mechanisms.; Various factors influencing support sintering were investigated. It was found that The BET surface area of support only has a limited effect on catalyst sintering. So does the metal loading of catalyst.; It was found that melting point, heat of sublimation or Tamman temperature are not the reliable indicators for sintering behavior, while the model of atomic weight is a promising one. |
