REDUCIBILITY AND THERMAL-BEHAVIOR OF SOME ANDERSON PHASES

The thermal behaviour of the (NH4)3[M(III)Mo6O24H6] . 7H2O, Anderson p hases, where M is Al, Co, Fe has been analysed in N2, N2/O2 and N2/H-2 atmospheres using TG-DTA, TPR, and XRD techniques. Additional measure ments were made by IR, EPR and Mossbauer spectroscopies, and also by s canning electron microscopy. Similar studies were carried out on ammon ium heptamolybdate for comparative purposes. Molybdenum oxide and meta llic molybdate are the solid products of the thermal treatment in N2 a nd N2/O2 atmospheres. While M2(MoO4)3 is observed when M is Al and Fe, the beta-CoMoO4 binary oxide is stabilized under both experimental co nditions. The intermediate [(NH4)2O]0.8MoO3(H2O)0.3 phase is only obse rved when working in static air atmosphere at a very low heating rate. The temperature-programmed reduction (TPR) study permits the analysis of the different reduction steps of the Mo(VI) and M(III) is Fe, Co c omponents. Mo4O11, MoO2, Mo and MMoO4 (M is Co, Fe) are also observed. The formation of an Al-Mo reduced oxidic phase (related to MoO2) can be inferred for the Al compound.