Spectroscopic characterization of an MoOx layer on the surface of silica. An evaluation of the molecular designed dispersion method

Abstract

Silica-supported molybdenum oxide catalysts have been prepared by liquid and gas phase deposition, followed by calcination of the deposited molybdenyl acetylacetonato complex. Fourier-transform infrared spectroscopy indicated a hydrogen bonding anchorage mechanism for the liquid phase deposition and a two step reaction mechanism for the gas phase deposition. After calcination of the absorbed molybdenum complexes, the supported molybdenum oxides were characterized by combining Fourier-transform infrared and Raman spectroscopy. X-ray diffraction was used to probe the possible clustering towards crystallites. An evaluation of the molecular designed dispersion method has been made by comparing the deposited molybdena structures obtained by the designed dispersion of MoO₂(acac)₂ with catalysts prepared by the conventional impregnation method using ammonium heptamolybdate. It is concluded that the molecular designed dispersion method results in a better grafting (more Si–O–Mo bonds) and thus a stronger metal oxide–support interaction than the conventional impregnation methods.