NGR STUDY OF IRON MOLYBDATES AND IRON-COBALT MOLYBDATES CATALYSTS

Iron molybdates FM and cobalt-iron molybdates CFxM (which means Co1-yFeyMoO4 with y=x/100 6≤x≤67), used as matrix of catalysts for propene mild oxidation, were studied by Mössbauer spectroscopy at 295 K and 4 K. All the spectra exhibit three Fe2+ doublets, two of them correspond to β-FeMoO4 and the third one to α-FeMoO4. Enhancement of quadrupole splittings of Fe2+ in the spectra of the CFxM catalysts is ascribed to the occurrence of a solid solution of either iron in CoMoO4 or cobalt in FeMoO4. In each spectrum at 295 K one or several Fe3+ doublets were present, which low temperature spectra allow to be assigned to Fe2(MoO4)3, small particles of Fe2O3, solid solution of Fe3+ in ferrous molybdates and even Fe2MoO4 in some cases. The behaviour of all the iron species of these solids during reduction by hydrogen is described. © 1990 J.C. Baltzer A.G. Scientific Publishing Company.