Well-defined group IV supported catalysts: An efficient way to increase activities in the deperoxidation of cyclohexyl hydroperoxide with environmentally systems

Silica-supported (SiO)₃MOR (M=Ti, Zr, Hf; R=H, ^tBu) organometallic complexes of group 4, uniform in composition and in distribution, were synthesized via a molecular engineering approach of the construction of active sites. These catalysts were fully characterized by various methods including solid-state NMR, infrared spectroscopy and microanalysis. In the goal to develop environmentally friendly processes,these solids were used as catalysts for the deperoxidation of cyclohexyl hydroperoxide, an important step in the synthesis of adipic acid, a precursor of nylon 6-6. The best metal is titanium and its performances are far above those of calcined supported titanium catalysts previously reported in the patent litterature. The influence on the catalytic activity of the nature of the coordination sphere and more specifically the number of covalent bonds between titanium and the silica support were studied. The catalysis is mainly heterogeneous as shown by various experiments. A non-negligible amount of titanium is leached during the first stages of the reaction but after some recycles the reaction rate remains constant allowing to suggest that this catalyst should be a good candidate for heterogeneous deperoxidation of cyclohexyl hydroperoxide.