Synthesis of the mixed oxide catalysts based upon the nickel-copper hydrotalcites of the type NixCu6-xCr2(OH)16(CO3)×4H2O

Abstract

High resolution TG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a chromium based series of Ni/Cu hydrotalcites of formulae NixCu6-xCr2(OH)(16)(CO3)center dot 4H(2)O where x varied from 6 to 0. The effect of increased Cu composition results in the increase of the endotherms and mass loss steps to higher temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps and that the interlayer carbonate anion is lost simultaneously with hydroxyl units. Differential scanning calorimetry was used to determine the heat flow steps for the thermal decomposition of the synthetic hydrotalcites. Hydrotalcites in which M2+ consist of Cu, Ni or Co form important precursors for mixed metal-oxide catalysts. The application of these mixed metal oxides is in the wet catalytic oxidation of low concentrations of retractable organics in water. Therefore, the thermal behaviour of synthetic hydrotalcites, NixCu6-xCr2(OH)(16)CO(3)center dot nH(2)O was studied by thermal analysis techniques in order to determine the correct temperatures for the synthesis of the mixed metal oxides.