NIR FT Raman spectroscopic studies of eta-Al2O3 and Mo/eta-Al2O3 catalysts

NIR FT Raman spectra excited at 1064 nm have been obtained from samples of Mo/eta-Al2O3 catalysts after treatment at 773 K in vacuum for 12 h. The samples were heated in quartz tubes which were sealed and transferred directly to the spectrometers without exposure to the ambient atmosphere, The broad background previously observed in the NIR FT Raman spectra of hydrated Mo/eta-alumina samples disappeared after the dehydration. Upon exposure to ambient air the broad background signal reappeared suggesting that the broad background feature can be attributed to surface hydroxyl groups present in the hydrated samples. Furthermore, it was observed that upon treating the eta-Al2O3 with water the broad background signal disappeared and the presence of bayerite (Al(OH)(3)) or boehmite (AlO(OH)) was detected depending on the experimental details. The identification of the various phases is supported by XRPD analysis. The overall conclusion is that the broad NIR FT Raman background can be attributed to surface hydroxyl groups in hydrated eta-Al2O3.