Active catalysts for the water-gas shift (WGS, CO + H
2O
![](/images/entities/rarr.gif)
H
2 + CO
2) reaction were synthesized fromnickel molybdates (
![](/images/gifchars/beta2.gif)
-NiMoO
4 and
nH
2O·NiMoO
4) as precursors, and their structural transformations weremonitored using in situ time-resolved X-ray diffraction and X-ray absorption near-edge spectroscopy. In general,the nickel molybdates were not stable and underwent partial reduction in the presence of CO or CO/H
2Omixtures at high temperatures. The interaction of
![](/images/gifchars/beta2.gif)
-NiMoO
4 with the WGS reactants at 500
![](/images/entities/deg.gif)
C led to theformation of a mixture of Ni (~24 nm particle size) and MoO
2 (~10 nm particle size). These Ni-MoO
2systems displayed good catalytic activity at 350, 400, and 500
![](/images/entities/deg.gif)
C. At 350 and 400
![](/images/entities/deg.gif)
C, catalytic tests revealedthat the Ni-MoO
2 system was much more active than isolated Ni (some activity) or isolated MoO
2 (negligibleactivity). Thus, cooperative interactions between the admetal and oxide support were probably responsiblefor the high WGS activity of Ni-MoO
2. In a second synthetic approach, the NiMoO
4 hydrate was reducedto a mixture of metallic Ni,
NiO, and amorphous molybdenum oxide by direct reaction with H
2 gas at 350
![](/images/entities/deg.gif)
C. In the first pass of the water-gas shift reaction, MoO
2 appeared gradually at 500
![](/images/entities/deg.gif)
C with a concurrentincrease of the catalytic activity. For these catalysts, the particle size of Ni (~4 nm) was much smaller thanthat of the MoO
2 (~13 nm). These systems were found to be much more active WGS catalysts than Cu-MoO
2, which in turn is superior to commercial low-temperature Cu-ZnO catalysts.