Abstract: The dispersion of VOx and MoOx on Al2O3 was investigated by means of in situ X-ray diffraction. For the VOx/Al2O3 catalyst prepared by the impregnation method, the precursor of (NH4)2［VO(C2O4)2］ dispersed uniformly on the support. (NH4)2［VO(C2O4)2］ began to decompose at 200 ℃, the decomposition finished at 400 ℃, and the obtained VOx species dispersed through the HxV2O5 phase. For the VOx/Al2O3 catalyst prepared by mechanical grinding, although there was an interaction between V2O5 and Al2O3, no obvious spontaneous dispersion phenomenon was observed; thus the dispersion of VOx was rather poor as compared with the impregnated catalyst. For the MoOx/Al2O3 catalysts prepared by impregnation and mechanical grinding, the MoO3 phase resulted from (NH4)6Mo2O24•4H2O decomposition was not completely the same, and the contents of (040) and (060) crystal planes were different.

Key words: in situ X-ray diffraction, vanadium oxide, molybdenum oxide, alumina, supported catalyst, dispersion