Abstract
In the preparation of impregnated catalyst composed of alumina carrier and cobalt salt the mixture of alumina or alumina hydrate and cobalt salt is calcined at the temperature between 500°and 800°C. From the theoretical and practical viewpoints it is important to clarify the state of cobalt compounds in the prepared catalysts. In the present study it is shown that the formation of cobalt aluminate begins at temperature higher than 850°C, while at lower temperature the oxidation or reduction of cobalt oxide occur, as in the case Without alumina.
DTA or TGA measurement and high temperature X-ray analysis were carried out during the heating process for the mixture of α-Al2O3, γ-Al2O3 or Al2O3·3H2O and CoO, Co3O4 or Co(CH3COO)2·4H2O. The heated mixtures were chemically analysed to determine the amounts of Co2+ and Co3+.
From the results obtained it will be concluded that the main reaction is the oxidation below 800°C, the oxidation and the reduction are in equilibrium between 700°and 900°C, and the reduction and the solid-state reaction occur in parallel between 900°and 1100°C, then the latter reaction becomes predominant above 1050°C. The beginning temperature of the solid-sate reaction has been affected by the presence of water vapor, while the rate of reaction would be affected by the diameter of reactant particle formed at the reaction temperature by the decomposition of the starting materials.
