Design and use of nanostructured heterogeneous catalysts for the unsaturated alcohols selective oxidation

Since the discovery of the MCM-41 and FSM-16 in the early 1990`s of the last century, great and fascinating progress has been made in the design, preparation, characterisation and application of mesoporous silica materials. The mesoporous silica MCM-41 was successfully synthesized and used as the support to immobilize transition metals, such as nickel and ruthenium. High-surface-area supports like mesoporous silica afford highly dispersed metal oxide species which are the key parameter in the rather difficult liquid-phase oxidation of cyclohexene. The synthesized material has high specific surface area, narrow pore size distribution, and large pore with high wall thickness which is very suitable for using as support material. The transitional metals were effectively dispersed on MCM-41 by the direct synthesis method and kept the original 2D hexagonal mesostructure. The obtained nanostructured heterogeneous catalysts were characterized by N₂ adsorption, ultraviolet-visible, XPS and X-ray absorption spectroscopy. X-ray absorption spectroscopy showed the presence of Ru-O bonds, suggesting a higher number of oxidic species. The adopted procedure was simple, green and efficient for unsaturated alcohols oxidation, such as 1-buten-3-ol. The use of a clean oxidant such as H₂O₂, was an important feature of a green chemical reaction since it resulted only water as by-product. The nanostructured heterogeneous catalysts enabled a better accessibility of active sites to bulky substrate molecules, reflected in the high conversions and better selectivity.