A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H2O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differe...

Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review

Lower olefins are key building blocks for the manufacture of plastics, cosmetics, and drugs. Traditionally, olefins with two to four carbons are produced by steam cracking of crude oil-derived naphtha, but there is a pressing need for alternative feedstocks and processes in view of supply limitations and of environmental issues. Although the Fischer-Tropsch synthesis has long offered a means to convert coal, biomass, and natural gas into hydrocarbon derivatives through the intermediacy of synthesis gas (a mixture of molecular hydrogen and carbon monoxide), selectivity toward lower olefins tends to be low. We report on the conversion of synthesis gas to C(2) through C(4) olefins with selectivity up to 60 weight percent, using catalysts that constitute iron nanoparticles (promoted by sulfur plus sodium) homogeneously dispersed on weakly interactive α-alumina or carbon nanofiber supports.

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Supported Iron Nanoparticles as Catalysts for Sustainable Production of Lower Olefins

http://pubs.acs.org/doi/pdfplus/10.1021/cr500486u

Recent Developments in the Synthesis of Supported Catalysts

C2 to C4 olefins are traditionally produced from steam cracking of naphtha. The necessity for alternative production routes for these major commodity chemicals via non-oil-based processes has driven research in past times during the oil crises. Currently, there is a renewed interest in producing lower olefins from alternative feedstocks such as coal, natural gas, or biomass, in view of high oil prices, environmental regulations, and strategies to gain independence from oil imports. This review describes the major routes for the production of lower olefins from synthesis gas with an emphasis on a direct or single step process, the so-called FTO or Fischer–Tropsch to olefins process. The different catalysts for FTO are outlined and compared, and the key issues and requirements for future developments are highlighted. Iron-based catalysts are prevailing for FTO, and reproducible lower olefin selectivities of 50 wt % of hydrocarbons produced have been realized at CO conversions higher than 70% for 60 to 1000 ...

Catalysts for Production of Lower Olefins from Synthesis Gas: A Review

Iron-based Fischer–Tropsch catalysts, which are applied in the conversion of CO and H2 into longer hydrocarbon chains, are historically amongst the most intensively studied systems in heterogeneous catalysis. Despite this, fundamental understanding of the complex and dynamic chemistry of the iron–carbon–oxygen system and its implications for the rapid deactivation of the iron-based catalysts is still a developing field. Fischer–Tropsch catalysis is characterized by its multidisciplinary nature and therefore deals with a wide variety of fundamental chemical and physical problems. This critical review will summarize the current state of knowledge of the underlying mechanisms for the activation and eventual deactivation of iron-based Fischer–Tropsch catalysts and suggest systematic approaches for relating chemical identity to performance in next generation iron-based catalyst systems (210 references).

The renaissance of iron-based Fischer-Tropsch synthesis: on the multifaceted catalyst deactivation behaviour.

Activation of Precipitated Iron Fischer-Tropsch Synthesis Catalysts

The morphological transformations during activation of a commercial, precipitated and spray-dried, Fe2O3-CuO-K2O Fischer-Tropsch Catal.yst are studied. The Catal.yst is activated in a flowing (H2/CO = 0.7/1.0) mixture at 523 K and 543 K and subsequent reaction is carried out at 523 K. The activation temperature causes these Catal.ysts to exhibit significant differences in their Catal.ytic activity for CO hydrogenation. The solid-state phase transformations from the oxide phase (hematite) to the iron carbide are studied by high resolution transmission electron microscopy (HRTEM), X-ray diffraction and elemental analysis. The differing extents of formation of the carbide phase correlate well with the Catal.ytic activity of iron. HRTEM shows that as magnetite transforms into carbide, the crystals of magnetite break down into smaller crystallites of the carbide phase. Deposition of carbon on the surface causes the carbide crystallites to further separate from each other. Morphological transformations such as these determine the attrition of the Catal.yst and help provide clues to understanding the deactivation of iron Fischer-Tropsch Catalysts.

M. S. Harrington

Papers

Activation of Precipitated Iron Fischer-Tropsch Synthesis Catalysts

Carbide formation during activation of iron Fisher-Tropsch catalysts