CHARACTERIZATION OF UNSUPPORTED MOLYBDENUM OXIDE COBALT OXIDE CATALYSTS

Study of the thermal decomposition of mixtures of ammonium heptamolybd ate (AM) and Co(NO3)2.6H2O by TGA and DTA show that small amounts of C o (up to 5 mol % expressed as Co3O4) did not alter the way in which AM decomposed. Larger amounts of Co (10-90 mol% as Co3O4) reduced the nu mber of steps from three to one, and in addition the transformation of Co3O4 to CoO was observed at c. 920-degrees-C. Endothermic peaks in D TA at 744-806-degrees-C, due to sublimation of MoO3, disappeared at hi gher Co contents. Samples containing 5, 10 and 30 mol % Co as Co3O4 sh owed exothermic peaks at 242-290-degrees-C due to formation of CoMoO4. The activation energies for the decompositions were calculated using the Coats-Redfern method from the TG results. XRD patterns of the samp les calcined at 500-degrees-C indicated the formation of CoMoO4 for Mo O3-30 mol % Co3O4, while those containing higher contents of Co3O4 (> 50 mol %) gave the typical XRD pattern of Co3O4. These results were co nfirmed by IR and TPR analyses. XPS analysis showed the presence of Mo (VI) in MoO3, but it was reduced to Mo(V) in the mixed samples. The bi nding energies for Mo 3d5/2 and Co 2p3/2 levels confirmed the formatio n of CoMoO4 in the sample MoO3-30 mol % Co3O4.