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

In situ ultraviolet Raman spectroscopy was used to follow the preparation o f Mo/H-ZSM5 catalysts by thermal treatment of a physical mixture of MoO3 an d H-ZSM5. The Raman spectra recorded from 300 to 1800 cm(-1) during the the rmal treatment showed that MoO3 spread over the zeolite support to form dis persed molybdenum oxide species. Curve-fitting analysis of the overall spec tral profile for the samples after treatment at 600 degreesC in O-2 showed the presence of three spectral components at 962. 868 and 815 cm(-1) The ba nd 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 tetr ahedrally coordinated monomers and the weaker band at 868 cm-l to bridging Mo-O-Mo groups of dimeric species. These last two assignments are not defin itive and may be due to other unique structures of oxides of molybdenum on the zeolite framework.