Publication Catalysis 2010
B. M. Vogelaar, A. D. van Langeveld, P. J. Kooyman, C. M. Lok, R. L. C. Bonne, J. A. Moulijn, Catal. Today 2010, 163, 20.
The formation of nickel and cobalt nanoparticles in hydrogenation catalysts and their stability against sintering during the redn. of the oxidic precursors were investigated. The morphol. of the catalysts was manipulated by varying the redn. conditions. The catalysts were characterized using temp. programmed redn. (TPR), hydrogen chemisorption, XPS, and high-resoln. transmission electron microscopy (HREM). The transformation of the oxidic precursor into the active phase was monitored using quasi in situ HREM, which proved to be an excellent technique to visualize the formation of metal nanoparticles. For the nickel catalyst the redn. temp. plays a crucial role, whereas time is more crit. for the cobalt catalyst.
The sintering rate of cobalt is considerably lower than that of nickel during redn. It is concluded that the activation energy for sintering is significantly higher for nickel than for cobalt. A model is proposed which depicts the structure of both types of catalysts in their oxidic and reduced state. TPR and XPS results indicate that the passivated catalysts contain approx. two oxygen atoms per surface Ni or Co atom.