450717 Physical Properties Controlling Heterogeneous Catalyst Stability in Supercritical Water
We examined the stabilities of noble and transition metals, metal oxide catalyst supports, and transition metal carbides and nitrides. The catalysts were tested in both batch and flow conditions and the SCW density was varied from 0-0.5g/mL to observe the influence of the solvent properties on stability. The composition and structure of the fresh catalyst samples were characterized using x-ray diffraction, N2 physisorption, and electron microscopy techniques and then characterized again after exposure to the SCW environment. The aqueous and gaseous compositions exiting the flow reactor were analyzed using inductively coupled plasma atomic emission spectroscopy and gas chromatography, respectively. Overall, the experimentally observed hydrothermal stabilities agreed with trends predicted in the thermodynamic models. In addition, we found that the oxidative or reductive strength of the reaction substrate will influence the dissolution rate and maximum solubility of the catalyst. These results provide design criteria for creating high-stability catalysts for hydrothermal applications.
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