Iron Catalysts For Fischer-Tropsch Synthesis Research Articles

Fischer-Tropsch synthesis A measure of the contribution of hydrogenolysis using a doubly promoted iron catalyst in a continuous stirred tank reactor

Hydrogenolysis of a high carbon number alkane, octacosane, does not occur to a significant extent either under Fischer-Tropsch Synthesis (FTS) conditions nor under a 8 atm hydrogen (1 atm=1.01325 × 10 5 Pa) at 262°C using a carbided doubly-promoted fused-iron catalyst manufactured by United Catalyst, Inc. (C-73). Thus, the data show that the higher carbon number alkanes used in continuous stirred tank reactor studies do not undergo hydrogenolysis at a significant rate in comparison to the rate of hydrocarbon synthesis. This finding suggests that the two or more alphas needed for the Anderson-Schulz-Flory (ASF) plot for promoted iron FTS catalysts cannot be explained by the hydrogenolysis of higher hydrocarbons.

Binder/support effects on the activity and selectivity of iron catalysts in the Fischer-Tropsch synthesis

This paper reports on the influence of silica and alumina binders (supports) on the activity and product selectivity of precipitated iron catalyst for Fischer-Tropsch synthesis (FTS) that was studied in a fixed bed reactor at 1.5-3.0 MPa and 220-250{degrees} C, using synthesis gas with H{sub 2}/CO = 1 M feed ratio. Both the FTS and the water gas shift activity decreased with increasing support content. The catalyst deactivation rate decreased with catalysts containing 24 and 100 g of SiO{sub 2} per 100 g of Fe. Secondary reaction (olefin hydrogenation and isomerization) increased with increasing silica content. Hydrocarbon selectivities improved (less gaseous hydrocarbons) with the addition of support, except for the catalyst containing 24 SiO{sub 2}/100Fe. The results were interpreted in terms of interactions between potassium and/or iron with supports.

Promoter effects on precipitated iron catalysts for Fischer-Tropsch synthesis

The effects of potassium and copper promotion on the activity and selectivity of precipitated iron catalysts for Fischer--Tropsch synthesis (FTS) were studied in a fixed bed reactor at 1.48 MPa and 235--265{degrees} C using synthesis gas with a H{sub 2}/CO = 1 molar feed ratio. It was found that both potassium and copper increase the catalyst activity for FTS and the water gas shift reaction. Potassium promotion ({approximately} 0.2--1 wt %) results in an increase in the average molecular weight of hydrocarbon products and suppression of secondary reactions (olefin hydrogenation and isomerization of 1-alkenes to 2-alkenes). Copper promotion ({approximately} 3 wt %) has a similar effect on the hydrocarbon distribution, but it enhances slightly the secondary reactions. The activity of doubly promoted (100 Fe/3 Cu/{ital x}K, {ital x} = 0.2 or 0.5) catalysts was higher than that of singly promoted catalysts and was independent of potassium loading, whereas their selectivity behavior was strongly influenced by their potassium loading. Product selectivities on the 100 Fe/3 Cu/0.2 K catalyst were similar to those of the 100 Fe/3 Cu catalyst, whereas selectivities of the 100 Fe/3 Cu/0.5 K catalyst were similar to those obtained in tests with the 100 Fe/0.5 K catalyst.

Compositional aspects of iron Fischer-Tropsch catalysts: An XPS/reaction study

The catalytic and compositional behaviors of prereduced and unreduced iron catalysts for Fischer-Tropsch synthesis were investigated. Catalytic behavior was evaluated by measuring rates of hydrocarbon formation in a 3:1 H 2:CO mixture at 1 atm and 250 °C. Iron phases which evolved near the catalyst surfaces were characterized by X-ray photoelectron spectroscopy, and bulk phases present following reaction were determined by Mössbauer spectroscopy. At low conversion levels the prereduced catalyst was gradually converted to iron carbide with no significant oxide phase formed. Synthesis activities increased initially with the formation of active surface carbon, but eventually lost some activity due to graphitic carbon formation. At higher conversions, the prereduced catalyst showed some formation of surface oxide phases and an inhibition of the synthesis rate due to water adsorption. Surface carbon accumulation was also suppressed under these conditions. Unreduced Fe 2O 3 showed no initial synthesis activity, but underwent a gradual activation to become even more active than the prereduced catalyst. The oxide catalyst was eventually completely reduced to Fe 3O 4, and any metallic phase formed was rapidly converted to iron carbide. Compared to reduced materials, the oxide catalyst accumulated considerably less surface carbon and showed no loss of activity for reaction times up to 48 h. XPS analysis suggests that Fe 3O 4 is active for synthesis.

Supported iron catalysts in Fischer-Tropsch synthesis: influence of the preparation method

Trois techniques differentes sont utilisees pour l'introduction de fer dans un melange de silice et d'alumine: l'impregnation par mouillage, l'echange d'ion et la coprecipitation au cours de la gelification du melange silice-alumine. Des essais de selectivite et de stabilite sont realises pour la synthese de Fischer-Tropsch

Characterization of a promoted precipitated iron catalyst for Fischer-Tropsch synthesis

A commercial precipitated catalyst for Fischer-Tropsch synthesis has been characterized by temperature-programmed techniques, carbon monoxide chemisorption, X-ray photoelectron spectroscopy, X-ray diffraction and Mössbauer spectroscopy. The catalyst consists of non-porous iron particles with a diameter close to 10 nm. Textural promotion, i.e. maintenance of the particle diameter during exposure to reaction conditions, is achieved by the coverage of the iron particles by silica islands. Upon exposure of the fresh catalyst to hydrogen at 493 K according to the manufacturer's specifications 20% of the iron is reduced to the metallic state. Only 3% of the iron atoms are exposed to the gas phase. After more than 200 h exposure to reaction conditions similar to industrial ones, the iron phase consists of more than 75% non-stoichiometric iron carbides with Fe 2.23C as the overall composition. The remaining iron atoms are either oxidized or present as carbides which show paramagnetic relaxation at 80 K. The iron atoms at the interface of the iron particles are oxidized. The pores of the catalyst pellets, i.e. the voids between the iron particles, are completely filled with liquid hydrocarbons during steady-state operation under industrial conditions.

Manganese-oxide-supported iron Fischer-Tropsch synthesis catalysts: Physical and catalytic characterization

It has been claimed that catalysts containing iron and manganese are especially selective for production of low molecular weight olefins in the Fischer-Tropsch (FT) synthesis. In this study a new system, manganese-oxide-supported iron, Fe MnO , was prepared, subjected to various calcination and reduction treatments, and then employed as a FT catalyst. Reaction studies were run with approximately 1 1 : CO H 2 feed at 515 and 540 K and 7.8 and 14.8 bar pressure. Although low conversions were employed, the synthesis rate decreased strongly with increasing conversion. Compared to conventional Fe catalysts, the Fe MnO was more active for water-gas shift and less selective for methane and alcohols, especially at higher conversions, lower temperature, and higher pressure. Olefin selectivity was high, hydrogen chemisorption was depressed, and secondary hydrogenation was not apparent. In general it is concluded that the manganese-supported iron does promote FT selectivity for low molecular weight olefins, but at the expense of high CO 2 formation.

Characterization of a fused iron catalyst for Fischer-Tropsch synthesis by in situ laser Raman spectroscopy

In situ laser Raman spectroscopy was used to characterize an alkali-promoted fused iron catalyst. Studies with adsorbed H 2 and CO revealed the presence of FeH and FeC bonds. Bands for adsorbed CO were also detected, indicating adsorption on Fe° and Fe n+ sites. Coexistence of Fe° Fe -carbide and Fe-oxide phases at the surface is proposed.

ChemInform Abstract: THE USE OF NITROUS OXIDE AS A SURFACE PROBE OF IRON CATALYSTS FOR FISCHER‐TROPSCH SYNTHESIS

Chemischer InformationsdienstVolume 15, Issue 49 Preparative Organic Chemistry ChemInform Abstract: THE USE OF NITROUS OXIDE AS A SURFACE PROBE OF IRON CATALYSTS FOR FISCHER-TROPSCH SYNTHESIS G. L. VOGLER, G. L. VOGLERSearch for more papers by this authorX.-Z. JIANG, X.-Z. JIANGSearch for more papers by this authorJ. A. DUMESIC, J. A. DUMESICSearch for more papers by this authorR. J. MADON, R. J. MADONSearch for more papers by this author G. L. VOGLER, G. L. VOGLERSearch for more papers by this authorX.-Z. JIANG, X.-Z. JIANGSearch for more papers by this authorJ. A. DUMESIC, J. A. DUMESICSearch for more papers by this authorR. J. MADON, R. J. MADONSearch for more papers by this author First published: December 4, 1984 https://doi.org/10.1002/chin.198449076AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue49December 4, 1984 RelatedInformation

The use of nitrous oxide as a surface probe of iron catalysts for Fischer-Tropsch synthesis

Nitrous oxide was used as a probe of the surface of iron-based samples for Fischer-Tropsch synthesis. Identities of the bulk iron phases present were determined by Mössbauer spectroscopy. Both unpromoted and potassium-promoted iron samples were treated for 48 h in H 2 CO (1:1) at atmospheric pressure and temperatures ranging from 493 to 553 K. Wax produced during this treatment was washed from the samples by oxygen-free toluene at 373 K. After 1 h of evacuation at 650 K, the sample was dosed with N 2O at 298 K. This molecule oxidized the surface, accompanied by the formation of gaseous N 2. The unpromoted samples displayed two distinct reactivities with N 2O depending on the temperature of the H 2 CO treatment. Iron carbide was formed by treatment at 543 K, and about 10% of the surface area reacted with N 2O to form N 2. In contrast, about 75% of the surface of the unpromoted sample treated at 508 K for 48 h in H 2 CO reacted with N 2O. This sample was composed of about 90% magnetite and 10% iron carbide. The high reactivity toward N 2O of the sample treated in H 2 CO at 508 K was attributed to reduced iron species on the surface, while the low reactivity of the sample treated at 543 K was interpreted as being due to coverage of the surface by carbon deposits. Potassium-promoted iron treated in H 2 CO at temperatures below 515 K reacts with about the same amount of N 2O as the corresponding unpromoted catalyst. The promoted sample consisted of about equal amounts of magnetite and iron carbide, indicating that the potassium promoter increased the rate of iron carbide formation compared to the unpromoted sample. When the promoted iron sample was treated at 543 K, the extent of N 2O reaction was greater than that for the corresponding unpromoted sample. This sample consisted of iron carbide. The increase in the extent of N 2O reaction with the promoted compared to the unpromoted catalyst equaled the amount of potassium in the catalyst. Potassium cations do not react with nitrous oxide. Instead, the promoter enhances the extent of reaction of this probe molecule with iron.

Investigation of supported iron Fischer-Tropsch synthesis catalysts by Mössbauer spectroscopy

The carburization of the iron in a 10% Fe on Al 2O 3 (Alon-C) catalyst has been followed by Mössbauer spectroscopy. The studies were made mostly at 270–285 °C and the catalyst was exposed to CO/H 2 and CO/He gas mixtures. The decarburization by H 2 was also studied. The principal carbides found are χ-carbide, Fe 2.5C, ε′-carbide, Fe 2.2C with a tendency for a preponderance of the latter at long reaction times. The carburization by CO is promoted by the presence of H 2, even in a small concentration. The promoting action of H 2 seems to be related to the ease of carburizing a particle with a well-reduced surface. Adding water to CO/H 2 slows the carburization rate without slowing the carbon deposition rate. Similar experiments with 10% Fe/SiO 2 (Cab-O-Sil) catalyst give similar results. Rates are somewhat reduced, but there is no qualitative change introduced by the different support.

Active surface of a fused iron catalyst in fischer-tropsch synthesis.

Fischer-Tropsch synthesis on a fused iron catalyst has been investigated in both isothermal and temperature-programmed experiments. Rates of hydrocarbon formation increased proportionally with the increase in weight of the catalyst during synthesis. The carburization enhanced catalytic activity was almost completely retained despite repeated evacuations of the catalyst. The carburization was recognized as weakening the CO-Fe interaction and raising the surface concentration of the more weakly bound carbon species. From these points of view, it was concluded that the carburization of the fused iron catalyst contributed, not to the formation of the reaction intermediates, but to the development of the active surface for catalysis.

Effects of potassium promotion on the activity and selectivity of iron Fischer-Tropsch catalysts

A systematic study has been carried out of the effects of potassium promotion on the performance of alumina supported iron catalysts for Fischer-Tropsch synthesis. The results show that potassium promotion causes a decrease in Fe dispersion, an increase in the strength of CO chemisorption on reduced Fe, a decrease in the turnover frequency for total CO consumption, an increase in the average molecular weight and olefi to paraffin ratio of the products, and an increase in the water-gas-shift activity. The addition of potassium is also found to increase the rate of catalyst carburization. This process occurs more rapidly in a mixture of CO and H/sub 2/ than in CO alone.

On the time-dependent behavior of iron catalysts in Fischer-Tropsch synthesis

Iron, cobalt, and nickel behave differently during the Fischer-Tropsch synthesis. Iron catalytic activity is initially low and increases slowly to a maximum while the catalytic activity of Co and Ni is essentially constant throughout the process. Three explanations denoted as the carbide model, competition model, and the slow activation model, have been previously advanced to explain this behavior. A brief survey of these explanations is included herein, and experiments and described whose results should define the catalytic behavior. Failure of the slow activation model and the carbide model in explaining two of the four experiments is taken as sufficient reason to reject these two models. The different rates of C diffusion into the metals will satisfactorily explain the difference between Fe and the other Fischer-Tropsch catalysts. Results of competition between the carbidation rate and the Fischer-Tropsch rate for the different catalysts leads to the assumption that the competition model most closely describes catalytic behavior. (BLM)

Factors in sulfur poisoning of iron catalysts in Fischer-Tropsch synthesis

Poisoning of catalysts in the Fischer-Tropsch synthesis by sulfur compounds has been investigated at the U.S. Bureau of Mines as part of its program on the conversion of coal to liquid and gaseous fuels. The effects of alkali content, initial surface area, and particle size on the poisoning of fixed beds of reduced fused iron oxide catalysts are reported for synthesis tests with 1 H 2 + 1 CO gas containing 69 mg S as H 2S/m 3 at 21.4 atm. Chemisorption studies of CO at −195 °C and CO 2 at −78 °C on reduced catalysts on which H 2S was adsorbed indicate that sulfur chemisorbs on both metallic iron and on alkali promoter if present. However, the decrease in the moles of CO plus CO 2 chemisorbed was only 14 to 29% of the moles of H 2S chemisorbed on the catalyst. Alkali promoters increase both the activity of the catalyst and its resistance to poisoning. Addition of 0.51 g K 2O/100 g Fe to an alumina-promoted catalyst increased activity about sixfold and resistance to poisoning about fivefold. In the early and intermediate stages of poisoning, the selectivity was not significantly changed. The relative amounts of products in different boiling fractions and the concentrations of olefins and oxygenated molecules in these fractions remained essentially constant. Initial surface area of reduced catalysts was not an important factor in determining either activity or resistance to poisoning. Decreasing particle size from 6–8 mesh to 28–32 mesh (a fivefold increase in external area) increased the activity and the resistance to poisoning more than threefold. Apparently poisoning occurs in a thin active layer near the external surface of the particles. Previous work from this laboratory has shown the depth of this active layer to be about 0.1 mm. In three fixed-bed poisoning tests, the concentration of sulfur in the catalyst was determined as a function of bed length. Most of the sulfur was found in the inlet third of the catalyst.