Physico-chemical study on the state of cobalt in a precipitated cobalt-aluminum oxide system

Abstract

The evolution of Co–Al (1 ∶ 1) hydroxycarbonate with a hydrotalcite-like structure during its consequent calcination in an inert gas flow and reduction in H₂ has been studied by means of X-ray diffraction, infrared spectroscopy, UV–VIS diffusive reflectance spectroscopy and magnetic susceptibility measurements. The oxidation of Co²⁺ species to Co³⁺ state during the calcination in the inert gas medium occurs simultaneously with the formation of a highly inverted anion-modified spinel-like structure. The samples reduced at 480 °C and 620 °C contain metallic cobalt particles. Ferromagnetic and paramagnetic contributions are distinguished and evaluated. The spontaneous magnetization of the sample reduced at 480 °C increases monotonously with the temperature in the range of 78–300 K. The correlation of the results with earlier data on physico-chemical and catalytic properties has been discussed.