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 MoO 3 /SiO 2 catalysts have been systematically investigated by temperature-programmed reduction (TPR) measurements in the range 200−1200 °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 underlying 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 hydrogenolysis reaction. The oxide dispersion of MoO 3 /SiO 2 catalysts and bulk MoO 3 has been comparatively evaluated by high- and low-temperature oxygen chemisorption measurements. Evidence of a strong metal oxide support interaction depressing both the reducibility and oxygen chemisorption of low-loaded (<4 wt %) MoO 3 /SiO 2 catalysts are provided. The effects of thermal treatments on the “surface structures”, reduction pattern, and chemisorption behavior of the MoO 3 /SiO 2 system have been addressed.