Synthesis of stable, hydrophobic MCM-48/VOx catalysts using alkylchlorosilanes as coupling agents for the molecular designed dispersion of VO(acac)(2)

The use of dimethyldichlorosilane as a coupling agent for the grafting of V Ox structures on the MCM-48 surface produces a material that is simultaneou sly hydrophobic (immiscible with water) and very active (all V centers are accessible, even for water molecules). The VOx surface species are grafted by the molecular designed dispersion of VO(acac)(2) on the silylated surfac e, followed by a calcination in air at 450 degrees C. These hydrophobic MCM -48 supported VOx catalysts are thermally stable up to 500 degrees C. The g rafted VOx surface species are very resistant toward leaching-out in aqueou s media. Also, the structural and hydrothermal stability has improved enorm ously. The crystallinity of the materials does not decrease when the sample s are subjected to a hydrothermal treatment at 150 degrees C and 4.7 atm pr essure. A reaction mechanism is proposed and consolidated by FT-IR, Raman s pectroscopy, and UV-vis diffuse reflectance. Pore size distributions, water adsorption isotherms, and X-ray diffractograms confirm the structural stab ility of these materials.