Abstract
This work reports the synthesis of Ni-clay catalysts by impregnation of Al-pillared saponite with various Ni salts, using several Ni loadings. The catalysts were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric and differential thermal analysis, nitrogen adsorption, temperature-programmed reduction studies, and ultraviolet–visible spectroscopy. All the solids displayed good structural properties. FTIR spectroscopy confirmed the total removal of the anionic precursors after calcination of the solids at 500 °C. The presence of NiO and NiAl 2O 4 in the nickel particles formed on the surface of the solids was demonstrated. Deconvolution of TPR curves allowed to identify three Ni-reduction effects, their temperature and relative intensity depended on the preparation of each sample. The catalytic behaviour of the solids for (Z)-cyclooctene epoxidation and cyclohexane oxidation by either iodosylbenzene (a model oxidant) or hydrogen peroxide (a clean oxidant) was studied. In the case of the epoxidation reactions, there was 100% selectivity for the epoxide. As for cyclohexane oxidation, only cyclohexanone was formed, whereas no cyclohexanol was detected. The use of radical scavengers indicated that the high-valent oxo-nickel species is responsible for the oxygen transfer between the oxidant and the substrates.
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