II International Symposium on Carbon for Catalysis ABSTRACTS

OP-I-2
PREPARATION OF CNF SUPPORTED COBALT CATALYSTS WITH HIGH
METAL LOADING BY DEPOSITION-PRECIPITATION
Yu Zhixin, Chen D., Fareid L.E., Rytter E. 1 , Moljord K. 1 , Holmen A.
Department of Chemical Engineering, Norwegian University of Science and Technology
(NTNU), N-7491 Trondheim, Norway
1 Statoil R&D, Postuttak, NO-7005 Trondheim, Norway
e-mail: zhixin.yu@chemeng.ntnu.no
Carbon nanofibers (CNFs) have been found to be an interesting support for a number of
catalytic reactions. Particularly, Bezemer et al. [1] have demonstrated that CNFs are
promising supports for Fischer-Tropsch (F-T) synthesis. F-T synthesis turnover rates on
cobalt catalysts are believed to be independent of cobalt dispersion and support. Therefore,
catalysts with high reaction rates require the synthesis of supported cobalt with high cobalt
concentrations and small particle sizes. Homogeneous deposition-precipitation (DP) has been
developed as a method for preparing highly loaded, highly dispersed metal/oxide catalysts,
but it has been scarcely used for the deposition of metal precursors on CNFs [2]. This has
been ascribed to the absence of a strong interaction between the support and metal precursor,
which is assumed indispensable for DP.
In this study, a series of 12, 20, 40 wt.% Co catalysts supported on oxidized CNFs have
been prepared by DP. Hydrolysis of urea at 363 K has been used to slowly increase the pH to
control the precipitation of cobalt nitrate precursors. The catalysts were calcined at 573 K in
flowing nitrogen, and characterized by TGA, XRD, TPR, BET, hydrogen chemisorption,
TEM, etc.
TGA analysis shows that the actual loadings of cobalt are lower than, but very close to
the nominal values, as shown in Table 1. Therefore, DP is suitable for the preparation of high
loading Co/CNF catalysts even though the interaction between the support and metal is low.
The difference between the nominal loading and the actual loading can be explained by the
formation of soluble Co-amine complexes at the deposition pH of around 7. Cobalt probably
nucleates as cobalt hydroxide and is anchored to the oxygen-containing groups of the CNFs.
After calcination, the XRD study shows that for all the catalysts, there are two cobalt
containing phases, CoO and Co 3 O 4 . The particle sizes calculated from the Scherrer equation
shows that all the catalysts have small particle sizes around 9 nm, even at the highest cobalt
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