Raman spectroscopic study of MoO3/γ‐Al2O3 and CoO(or NiO)‐MoO3/γ‐Al2O3 oxide catalysts prepared by different methods

Abstract

AbstractRaman spectroscopy has been used to characterize various MoO3/γ‐Al2O3 and CoO (or NiO)‐MoO3/γ‐Al2O3 catalysts containing 12 wt% MoO3 and 3 wt% CoO (or NiO) prepared by different methods. No significant differences between samples prepared by the wet impregnation and the pore volume method could be observed in molybdena‐supported catalysts; in these samples the majority of Mo is present as isolated distorted MoO42− tetrahedra due probably to a low coverage of the alumina surface (SBET=240 m2 g−1). Addition of NiO to the molybdena‐supported catalysts seems to cause only a slight increase in the distortion and interaction between MoO42− species. In contrast, CoO addition to the molybdena‐supported catalysts changes considerably the spectra features, suggesting that the Mo species are highly distorted, presumably in different surroundings on the alumina surface, due to the strong interaction of Co with Mo species. However, simultaneous impregnation of both MoO3 and CoO or NiO results in a more regular arrangement of Mo species and an increase in formation of polymeric Mo species, particularly with Co‐containing catalyst, where a relative higher degree of polymeric aggregation may occur.