Cobalt cluster effects in zirconium promoted Co/SiO{sub 2} Fischer-Tropsch catalysts
- Univ. of Cape Town, Rondebosch (South Africa). Dept. of Chemical Engineering
The effect of zirconium addition to the catalyst formulation of Co/SiO{sub 2} Fischer-Tropsch catalysts was investigated. With increasing zirconium content the strong interaction between silica and cobalt is reduced and a somewhat weaker cobalt-zirconium interaction is observed. Therefore the degree of reduction of catalysts, which were reduced at 400 C for 16 h, increases strongly. The cobalt crystallite size increases with increasing zirconium content, leading to smaller cobalt metal surface areas for the freshly reduced catalyst. Cobalt particles can be found in clusters on the silica support. The size of cobalt clusters decreases and thus the number of cobalt particles within a cluster decreases with increasing zirconium content. At steady-state conditions the CO-conversion of the promoted catalyst in the Fischer-Tropsch synthesis increases with increasing zirconium content. The C{sub 5+}-selectivity and the secondary hydrogenation activity pass a maximum with increasing zirconium content. The observed changes in activity and selectivity are explained in terms of an increase in the amount of metallic cobalt available under reaction conditions, leading to an increased activity, and a decrease in the cobalt cluster size, which diminishes the probability for secondary reactions. Furthermore, it was concluded that secondary double bond isomerization can be catalyzed to some extent by zirconia.
- OSTI ID:
- 684570
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 185; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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