SILICA-SUPPORTED MOLYBDENA CATALYSTS - SURFACE-STRUCTURES, REDUCTION PATTERN, AND OXYGEN-CHEMISORPTION

The effects of preparation method, nature of the silica support, oxide loading (0.2-7.0 wt %), and pretreatment conditions on the reduction pattern of MoO3/SiO2 catalysts have been systematically investigated b y temperature-programmed reduction (TPR) measurements in the range 200 -1200 degrees C. Modeling of TPR spectra of silica-supported molybdena catalysts highlights the presence of several ''surface Mo-VI species' ' characterized by a different interaction strength with the underlyin g support, the formation of which is mostly controlled by pretreatment conditions and oxide loading. The reduction path of the above surface species has been probed by catalytic measurements in propane hydrogen olysis reaction. The oxide dispersion of MoO3/SiO2 catalysts and bulk MoO3 has been comparatively evaluated by high- and low temperature oxy gen chemisorption measurements. Evidence of a strong metal oxide suppo rt interaction depressing both the reducibility and oxygen chemisorpti on of low-loaded (<4 wt %) MoO3/SiO2 catalysts are provided. The effec ts of thermal treatments on the ''surface structures'', reduction patt ern, and chemisorption behavior of the MoO3/SiO2 system have been addr essed.