Catalyst cobalt/silica

Girardon J.-S., Constant-Griboval A., Gengembre L., Chemavskii P.A., and Khodakov A.Y. 2005. Optimisation of the pretreatment procedure in the design of cobalt silica supported Fischer Tropsch catalysts. Paper presented at the Gas-Fuel 05 Conference, Bruges, Belgium. 

Lapidus, A., Krylova, A., Kazanskii, V., Borovkov, V., and Zaitsev, A. 1991. Hydrocarbon synthesis from carbon monoxide and hydrogen on impregnated cobalt catalysts. Part I. Physico-chemical properties of 10% cobalt/alumina and 10% cobalt/ silica. Appl. Catal. 73 65-81. 

F-T Catalysts The patent literature is replete with recipes for the production of F-T catalysts, with most formulations being based on iron, cobalt, or ruthenium, typically with the addition of some pro-moter(s). Nickel is sometimes listed as a F-T catalyst, but nickel has too much hydrogenation activity and produces mainly methane. In practice, because of the cost of ruthenium, commercial plants use either cobalt-based or iron-based catalysts. Cobalt is usually deposited on a refractory oxide support, such as alumina, silica, titania, or zirconia. Iron is typically not supported and may be prepared by precipitation. 

Girardon, J.-S., Lermontov, A.S., Gengembre, L., Chernavskii, RA., Griboval-Constant, A., and Khodakov, A.Y. I if feet of cobalt precursor and pretreatment conditions on the structure and catalytic performance of cobalt silica-supported Fischer-Tropsch catalysts. Journal of Catalysis, 2005, 230, 339. 

Batista et al. performed ethanol steam reforming over cobalt/alumina and cobalt/ silica catalysts containing 8 and 18wt.% cobalt [201]. Even with a reaction temperature of400 °C, 70% conversion could be achieved. Methane was the main by-product, ethylene was only formed over samples containing 8 wt.% cobalt. Then a bed of an iron oxide/chromium oxide water-gas shift catalyst was switched behind the cobalt/ silica catalyst. The carbon monoxide was converted as expected, but also less methane was found in the product [202]. Even less carbon monoxide was formed when both catalysts were mixed. Sahoo et al. varied the cobalt content of the cobalt/alumina catalyst from 10 to 20 wt.%. The highest activity was determined for the sample containing 15 wt.% cobalt [203]. 

In order to provide the homogeneous catalyst deposition, silicas were treated with volatile cobalt(II), nickel(II), and iron(II) acetylacetonates at the moderate temperatures. At these conditions acetylacetonates of metals are chemisorbed on the silica surface due to reaction with surface silanol groups with eliminating one of ligands. 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

Proven, industrially used catalysts are mostly based on either iron or cobalt. Ruthenium is an active F-T catalyst but is too expensive for industrial use. Both Fe and Co are prepared by several techniques including both precipitation and impregnation of (e.g. alumina or silica) supports. The more noble Ni catalyst produces nearly exclusively methane and is used for the removal of trace of CO in H2. 

The work of Kikuchi et al. (123) with silica-supported catalysts also shows the high tendency of iron (370°-400°C), cobalt (330o-360°C) and nickel (330°-370°C) to catalyze fragmentation (of n-pentane) to methane. This work also showed that with cobalt and nickel, the extent of methane formation tended to decrease with increasing hydrogen partial pressure. Some data are listed in Table XII. 

Storsaeter S., Totdal B., Walmsley J.C., Tanem B.S., and Holmen A. 2005. Characterisation of alumina-, silica- and titania-supported cobalt Fischer-Tropsch catalysts. 7. Catal. 236 139-52. 

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