Direct Observation of Ni-Mo Bimetallic Catalyst Formation via Thermal Reduction of Nickel Molybdate Nanorods

We used in situ environmental transmission electron microscopy to image the formation of a Ni-Mo composite nanocatalyst via thermal reduction of NiMoO4 nanorods. Two clear structural changes were observed as the temperature was increased from 25 to 500 °C in the presence of H2(g): the first involved nucleation of nanoscale Ni-rich particles and the second involved general collapse of the remaining oxide phase along with substantial coarsening of the alloy particles. The activity of the catalyst toward alkaline hydrogen evolution was found to reach a maximum in a narrow range of reduction temperatures from 375 to 425 °C. This resulted in the formation of a mixed-phase product comprising sub-10 nm Ni0.9Mo0.1 particles embedded in a porous Mo-rich oxide matrix. Thus, the most active Ni-Mo catalyst apparently requires intimate contact between the alloy component and the oxide phase, lending support to a catalytic mechanism involving metallic and oxidized surface sites.