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

Alternatives to petroleum-derived fuels and chemicals are being sought in an effort to improve air quality and increase energy security through development of novel technologies for the production of synthetic fuels and chemicals using renewable energy sources such as biomass. In this context, ethanol is being considered as a potential alternative synthetic fuel to be used in automobiles or as a potential source of hydrogen for fuel cells as it can be produced from biomass. Renewable ethanol can also serve as a feedstock for the synthesis of a variety of industrial chemicals and polymers. Currently, ethanol is produced primarily by fermentation of biomass-derived sugars, especially those containing six carbons, whereas 5-carbon sugars and lignin, which are also present in the biomass, remain unusable. Gasification of biomass to syngas (CO + H2), followed by catalytic conversion of syngas, could produce ethanol in large quantities. However, the catalytic conversion of syngas to ethanol remains challenging,...

A Review of Recent Literature to Search for an Efficient Catalytic Process for the Conversion of Syngas to Ethanol

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.

Structural and magnetic properties, methods of synthesis, and applications of seven iron(III) oxide polymorphs, including rare beta, epsilon, amorphous, and high-pressure forms, are reviewed. Thermal transformations resulting in the formation of iron oxides are classified according to different parameters, and their mechanisms are discussed. 57Fe Mossbauer spectroscopy is presented as a powerful tool for the identification, distinction, and characterization of individual polymorphs. The advantages of Mossbauer spectroscopy are demonstrated with two examples related to the study of the thermally induced solid-state reactions of Fe2(SO4)3.

Iron(III) Oxides from Thermal ProcessesSynthesis, Structural and Magnetic Properties, Mössbauer Spectroscopy Characterization, and Applications†

http://iglesia.cchem.berkeley.edu/Publications/2010%20FTS%20Mechanism%20Ojeda.pdf

CO activation pathways and the mechanism of Fischer–Tropsch synthesis

Slurry phase Fischer−Tropsch synthesis (FTS) was conducted with two precipitated iron catalysts (100 Fe/3.6 Si/0.71 K and 100 Fe/4.4 Si/1.0 K, atomic percent relative to Fe) at 543 K, 1.31 MPa, and a synthesis gas (H2/CO = 0.7) space velocity of 3.1 normal L h-1 (g of Fe)-1. The impact of activation gas (CO, H2/CO = 0.7, or H2/CO = 0.1), temperature (543 or 573 K), and pressure (1.31 or 0.10 MPa) on the long-term (>500 h) activity and selectivity of the catalysts was explored. Pretreatment with CO under the conditions employed gave highly active and stable catalysts. Catalyst performance when synthesis gas activation was used was found to be dependent upon the partial pressure of hydrogen in the activating gas, with low hydrogen partial pressures resulting in the highest catalyst activity. X-ray diffraction results indicate that carbon monoxide activations and synthesis gas activations with low hydrogen partial pressure result in the formation of the carbides χ-Fe5C2 and e‘-Fe2.2C, while activation with s...

Activation Study of Precipitated Iron Fischer−Tropsch Catalysts†

Activity and selectivity of precipitated iron Fischer-Tropsch catalysts

The CO conversion rate and the product selectivities for the conversion of syngas typical of one derived from coal (H 2 /CO = 0.7) or natural gas (H 2 /CO = 1.7) are very similar over the range of 30–90% CO conversion levels. For CO conversions up to about 50%, the iron catalyst is as or more productive than a similar mass of supported cobalt catalyst. A supported iron catalyst may exhibit about two-thirds the productivity, on a gram Fe basis, as an unsupported catalyst. Furthermore, whereas the unsupported iron catalyst disintegrates within 24 h of synthesis, the supported catalyst retains its integrity during hundreds of hours of slurry phase operation. Silica based catalysts exhibited less disintegration in the CSTR than alumina based catalysts.

Activity, selectivity and attrition characteristics of supported iron Fischer–Tropsch catalysts

The effect of pretreatment, using hydrogen or carbon monoxide, on the activity and selectivity of a ruthenium promoted cobalt catalyst (Ru(0.20 wt%)/Co(10 wt%)/TiO2) during Fischer–Tropsch (FT) synthesis was studied in a continuous-stirred tank reactor (CSTR). The hydrogen reduced catalyst exhibited a high initial synthesis gas conversion (72.5%) and reached steady state after 40 h on stream, after which the catalyst deactivated slightly with time on stream. The carbon monoxide reduced catalyst reached steady state quickly and showed a lower activity and a good stability. Methane selectivity on the carbon monoxide reduced catalyst was 15–20% (carbon base), much higher than that on the hydrogen reduced catalyst (5–10%). Carbon monoxide regeneration increased the activity on the hydrogen reduced catalyst; however, it did not have significant effect on the carbon monoxide reduced catalyst.

Fischer–Tropsch synthesis. Effect of CO pretreatment on a ruthenium promoted Co/TiO2

The present study has shown that activation of a high surface area Fe2O3 catalyst in CO in a CSTR using tetralin as solvent results in an activity that is three times that of the material that is activated in H2 or directly in the syngas. Independent of the catalyst activation, similar methane and CO2 selectivities are obtained. This suggests that the active catalytic phase is the same for the three pretreatments. Since the particle size estimated by XRD shows a variation within 30%, the difference among the activities of the differently activated catalysts can be attributed to differences in the concentration of active sites on the catalyst surface rather than the extent of the surface.

Liguang Xu

Papers

Activation Study of Precipitated Iron Fischer−Tropsch Catalysts†

Activity and selectivity of precipitated iron Fischer-Tropsch catalysts

Activity, selectivity and attrition characteristics of supported iron Fischer–Tropsch catalysts

Fischer–Tropsch synthesis. Effect of CO pretreatment on a ruthenium promoted Co/TiO2

Fischer-tropsch synthesis: impact of pretreatment of ultrafine iron oxide upon catalyst structure and selectivity