Co/Si02 catalyst

Fig. 11. The loss of carbon rapidly increases with the increase of temperature. Heating of the catalysts in open air for 30 minutes at 973 K leads to the total elimination of carbon from the surface. The gasification of amorphous carbon proceeds more rapidly than that of filaments. The tubules obtained after oxidation of carbon-deposited catalysts during 30 minutes at 873 K are almost free from amorphous carbon. The process of gasification of nanotubules on the surface of the catalyst is easier in comparison with the oxidation of nanotubes containing soot obtained by the arc-discharge method[28, 29]. This can be easily explained, in agreement with Ref [30], by the surface activation of oxygen of the gaseous phase on Co-Si02 catalyst.

One way in which cobalt dispersion can be increased is the addition of an organic compound to the cobalt nitrate prior to calcination. Previous work in this area is summarized in Table 1.1. The data are complex, but there are a number of factors that affect the nature of the catalyst prepared. One of these is the cobalt loading. Preparation of catalysts containing low levels of cobalt tends to lead to high concentrations of cobalt-support compounds. For example, Mochizuki et al. [37] used x-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) to identify cobalt silicate-like species in their 5% Co/Si02 catalysts modified with nitrilotriacetic acid (NTA). The nature of the support also has... 

Zhang Y., Liu Y., Yang G., Sun S., and Tsubaki N. 2007. Effect of impregnation solvent on Co/Si02 catalyst with bimodal sized cobalt particles. Appl. Catal. A Gen. 321 79-85. 

Mochizuki T., Hara T., Koizumi N., and Yamada M. 2007. Surface structure and Fischer-Tropsch synthesis activity of highly active Co/Si02 catalysts prepared from the impregnating solution modified with some chelating agents. Appl. Catal. A Gen. 317 97-104. 

The kinetic methodology used by The University of Kentucky Center for Applied Energy Research (CAER) for analyzing the kinetic data has been reported elsewhere [10,12,17], Using the same approach, we obtained the kinetic parameters for the reduced air calcined 15% Co/Si02 and 25% Co/Si02 catalysts (see Table 3.1). 

The activation energies of the 15% Co/Si02 and 25% Co/Si02 catalysts were calculated to be 85.9 and 93.7 kJ/mol, respectively. These values are in agreement with the value of 86 kJ/mol in a study on Co/Zr/Si02by Chang et al. [22] and are consistent with several studies of Co-based catalysts [23,24],... 

In this study, four other kinetic models with or without water inhibition from references [11,13,20,25] plus the CAER model are used to lit the experimental results of the 15% Co/Si02 catalyst. The kinetic parameter values obtained based on the same analysis method along with MARR values are listed in Table 3.2. 

A comparison of catalyst activity and selectivities to hydrocarbon and C02 over the reduced air calcined and nitric oxide calcined 15% Co/Si02 catalysts is shown in Figures 3.1 through 3.4 and Table 3.3. Initial CO conversion at an SV of 10 Nl/g-cat/h over the reduced air calcined sample was 33%, but was significantly... 

Figure 3.4 and Table 3.3 show that C02 selectivity over the 15% Co/Si02 catalyst is quite low, less than 0.4% regardless of the calcination procedure used, indicating a small extent of the water-gas shift (WGS) reaction over the catalysts. However, as shown in Table 3.3, a slightly lower average C02 selectivity was observed over the NO calcined 15% Co/Si02 catalyst compared to the air calcined one (0.19 vs. 0.29%), another indication that the NO calcination benefited FTS performance. 

Bian, G.-Z., Fujishita, N., Mochizuki, T., Ning, W.-S., and Yamada, M. 2003. Investigations on the structural changes of two Co/Si02 catalysts by performing Fischer-Tropsch synthesis. Appl. Catal. A 252 251-60. 

Barbier, A., Tuel, A., Arcon, I., Kodre, A., and Martin, G. A. 2001. Characterization and catalytic behavior of Co/Si02 catalysts Influence of dispersion in the Fischer-Tropsch reaction. J. Catal. 200 106-16. 

Preparation of Highly Active Co/Si02 Catalyst with Chelating Agents for Fischer-Tropsch Synthesis Role of Chelating Agents... 

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