Olivine catalytic activity

An answer to the first question was suggested by Lancet and Anders (1970). The principal meteoritic phases stable above 350-400 K (olivine, pyroxene, Fe, FeS) are not effective catalysts for the Fischer-Tropsch reaction, whereas the phases forming below this temperature (hydrated silicates, magnetite) are. P hough metallic iron is often regarded as a catalyst for this synthesis, the catalytically active phase actually is a thin coating of FCjO formed on the surface of the metal (Anderson, 1956)]. Thus CO may have survived metastably until catalysts became available by reactions such as ... 

Fig. 12. Fischer-Tropsch reaction at 1 atm is first-order in CO, with an activation energy of 27 kcal/ mole (Lancet, 1972). Rate in a flow system is 10 times faster than in the static system used here. Dashed line shows extrapolation to solar nebula, assuming that the rate is proportional to (PcoIIPhj) . Reaction proceeds at an undetectable rate when the Bruderheim L6 chondrite is used as a catalyst. Apparently the high-temperature minerals in this meteorite (olivine, orthopyroxene, troilite, and nickel-iron) do not catalyze the hydrogenation of CO. Thus CO can survive in the solar nebula down to 400 K, when catalytically active minerals first from (Fig. 1 and 10)...

Olivine activity, or more specifically olivine activation, depends on its iron oxide content [76, 77]. Iron can be present either in the olivine crystalline structure or free at different oxidation states depending on levels of high-temperature pretreatment and exposure to the reducing/oxidizing conditions in the gasifier. How this is able to account for catalytic activity in biomass gasification has been well documented [78]. 

Calcined dolomites are the most widely used nonmetallic catalysts for tar conversion in biomass gasification processes.626-631 They are relatively inexpensive and are considered disposable. However, they are not very robust and quickly undergo attrition in fluidized-bed reactors. Consequently, dolomites find most use in fixed-bed catalytic reactors. Tar conversion efficiency is high when calcined dolomites are operated at high temperatures (900°C) with steam. Olivine, another naturally occurring mineral, has also demonstrated tar conversion activity similar to that of calcined dolomite. Olivine is a much more... 

The impregnation method conditions of Ni and Ni-CaO supported olivine catalyst have great influence in the system and catalytic behaviour. The temperature of impregnation affects the interaction between the metal and the support, whereas the calcination temperature allows obtaining catalytic stable species. The parameters selection on physicochemical basis allow obtaining an active catalyst. The presence of small amounts of calcium in Ni/olivine catalysts improves the conversion of CH4 and the selectivity of H2 in the reaction, independently of die presence or absence of H2 and CO. 

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