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

Silica-supported molybdenum oxide catalysts have been prepared by liquid an d 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 calcinat ion of the absorbed molybdenum complexes, the supported molybdenum oxides w ere characterized by combining Fourier-transform infrared and Raman spectro scopy. 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 convent ional impregnation method using ammonium heptamolybdate. It is concluded th at the molecular designed dispersion method results in a better grafting (m ore Si-O-Mo bonds) and thus a stronger metal oxide-support interaction than the conventional impregnation methods.