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Thermal stability of zirconia as a catalyst support: Kinetics and modelling

Abstract : The textural changes of two zirconium dioxide powders, one containing only tetragonal crystallites and the other a mixture of monoclinic and tetragonal crystallites, were investigated. The crystallite size increase was followed by means of X-ray diffraction line broadening for powders annealed in a controlled gaseous atmosphere at 600 and 770°C, in order to establish the variations of its experimental rate versus partial pressures of water and oxygen. An accelerating influence of water vapour was observed for both powders. A model, based on a catalytic effect of water vapour, and involving six elementary steps, was proposed in order to calculate theoretical rates within the approximation of the rate-limiting step. The comparison between the experimental and theoretical rate laws attests to the validity of the model and defines the most probable rate-limiting step: tetragonal crystallite growth proceeds at a rate controlled either by adsorption (or desorption) of water molecules or diffusion of hydroxyl groups: monoclinic crystallite growth is controlled by the diffusion of zirconium ions.
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Alain Methivier, Michèle Pijolat. Thermal stability of zirconia as a catalyst support: Kinetics and modelling. Journal of Catalysis, Elsevier, 1993, 139, pp.329-337. ⟨10.1006/jcat.1993.1028⟩. ⟨emse-00610371⟩



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