Anderson phases as precursors of nickel–molybdenum–tungsten oxides

Abstract

Mixed Ni–Mo–W oxides have been prepared by decomposition at 873 K of Anderson-type [NiMo 6-x W x O 24 H 6 ](NH 4 ) 4 5H 2 O (x=0, 2, 3, 4, 6) heteropolyoxometallates. Thermal analysis of the precursors, X-ray diffraction and Raman spectroscopy on the mixed oxides were performed. X-Ray powder patterns, collected at the end of the thermal treatment, revealed that the final products are NiMoO 4 and MoO 3 for the x=0 composition, whereas for tungsten-containing materials the final products are Mo 1-x W x O 3 solid solutions, NiWO 4 and WO 3 , depending on the Mo/W atomic ratio. Raman spectra have confirmed the XRPD analysis, revealing the presence of a stable WO 3 -type phase at high molybdenum contents and a high structural stability of Mo 1-x W x O 3 solid solutions.