Web Release Date: January 19,
In Situ Time-Resolved Characterization of Ni-MoO2 Catalysts for the Water-Gas Shift Reaction
and
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, Department of Chemistry, University of Puerto Rico, Cayey, Puerto Rico 00736, Centro de Química, Instituto Venezolano de Investigaciones Cientificas, Apdo. 20632, Caracas 1020-A, Venezuela, and Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716
Received: October 5, 2007
In Final Form: October 31, 2007
Abstract:
Active catalysts for the water-gas shift (WGS, CO + H2O 
H2 + CO2) reaction were synthesized from
nickel molybdates (
-NiMoO4 and nH2O·NiMoO4) as precursors, and their structural transformations were
monitored 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/H2O
mixtures at high temperatures. The interaction of -NiMoO4 with the WGS reactants at 500 
C led to the
formation of a mixture of Ni (~24 nm particle size) and MoO2 (~10 nm particle size). These Ni-MoO2
systems displayed good catalytic activity at 350, 400, and 500 C. At 350 and 400 C, catalytic tests revealed
that the Ni-MoO2 system was much more active than isolated Ni (some activity) or isolated MoO2 (negligible
activity). Thus, cooperative interactions between the admetal and oxide support were probably responsible
for the high WGS activity of Ni-MoO2. In a second synthetic approach, the NiMoO4 hydrate was reduced
to a mixture of metallic Ni, NiO, and amorphous molybdenum oxide by direct reaction with H2 gas at 350
C. In the first pass of the water-gas shift reaction, MoO2 appeared gradually at 500 C with a concurrent
increase of the catalytic activity. For these catalysts, the particle size of Ni (~4 nm) was much smaller than
that of the MoO2 (~13 nm). These systems were found to be much more active WGS catalysts than Cu-MoO2, which in turn is superior to commercial low-temperature Cu-ZnO catalysts.
Download the full text: PDF | HTML
