Monitoring of molybdenum H-ZSM5 catalyst preparation by in situ ultraviolet Raman spectroscopy

In situ ultraviolet Raman spectroscopy was used to follow the preparation of Mo/H-ZSM5 catalysts by thermal treatment of a physical mixture of MoO₃ and H-ZSM5. The Raman spectra recorded from 300 to 1800 cm^–1 during the thermal treatment showed that MoO₃ spread over the zeolite support to form dispersed molybdenum oxide species. Curve-fitting analysis of the overall spectral profile for the samples after treatment at 600°C in O₂ showed the presence of three spectral components at 962, 868 and 815 cm^–1. The band at 815 cm^–1 was assigned to the zeolite support. The most intense band at 962 cm^–1 could be attributed to terminal Mo=O groups of isolated tetrahedrally coordinated monomers and the weaker band at 868 cm^–1 to bridging Mo–O–Mo groups of dimeric species. These last two assignments are not definitive and may be due to other unique structures of oxides of molybdenum on the zeolite framework.