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.
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