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Title: Mo-Fe catalysts supported on activated carbon for synthesis of liquid fuels by the Fischer-Tropsch process: effect of Mo addition on reducibility, activity, and hydrocarbon selectivity

Abstract

The effects of Mo loading (0-12 wt %) on the properties of activated-carbon- (AC-) supported Fe-Cu-K catalysts and their performance for Fischer-Tropsch synthesis are studied. Physicochemical properties studied include particle size, reducibility, and dispersion, and catalytic properties include activity, selectivity, and stability. Catalysts were characterized by N{sub 2} adsorption, energy-dispersive spectroscopy, X-ray diffraction (XRD), H{sub 2} temperature-programmed reduction (TPR), and CO chemisorption. Catalyst performance was studied at 310-320{sup o}C, 2.2 MPa, 3 Nl/g-cat/h, and H{sub 2}/CO = 0.9. Reaction results in a fixed-bed reactor show that addition of 6% Mo into the Fe-Cu-K/AC catalyst improves catalyst stability without sacrificing activity, but activity is suppressed dramatically on a 12% Mo-loaded catalyst. Detectable hydrocarbons of C{sub 1} to C{sub 34} are produced on the Fe-Cu-K/AC catalysts with or without Mo. However, the addition of Mo results in the production of more CH{sub 4} and less C{sub 5+} hydrocarbons. The Mo promoter greatly enhances secondary reactions of olefins, leading to a large amount of internal olefins (i.e., other than 1-olefins) in the product. TPR shows that a strong interaction between Fe and Mo oxides is present, and the extent of reduction of Fe is suppressed after addition of Mo to the Fe-Cu-K catalyst.more » CO-chemisorption and XRD studies show increased iron dispersion and decreased particle size of the iron carbide and iron oxide after the addition of Mo. Segregation of iron active sites, thereby preventing them from agglomerating, and a larger number of active sites on the 6% Mo catalyst are possible reasons for the improved stability and higher activity of Mo-promoted catalysts. 54 refs., 5 figs., 6 tabs.« less

Authors:
; ; ;  [1]
  1. West Virginia University, Morgantown, WV (United States). Department of Chemical Engineering
Publication Date:
OSTI Identifier:
20838250
Resource Type:
Journal Article
Resource Relation:
Journal Name: Energy and Fuels; Journal Volume: 20; Journal Issue: 6; Other Information: dady.dadyburjor@mail.wvu.edu
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; MOLYBDENUM; IRON; CATALYSTS; CATALYST SUPPORTS; ACTIVATED CARBON; FISCHER-TROPSCH SYNTHESIS; LIQUID FUELS; CATALYTIC EFFECTS; SPECIFICITY; PROMOTERS; STABILITY

Citation Formats

Wenping Ma, Edwin L. Kugler, James Wright, and Dady B. Dadyburjor. Mo-Fe catalysts supported on activated carbon for synthesis of liquid fuels by the Fischer-Tropsch process: effect of Mo addition on reducibility, activity, and hydrocarbon selectivity. United States: N. p., 2006. Web.
Wenping Ma, Edwin L. Kugler, James Wright, & Dady B. Dadyburjor. Mo-Fe catalysts supported on activated carbon for synthesis of liquid fuels by the Fischer-Tropsch process: effect of Mo addition on reducibility, activity, and hydrocarbon selectivity. United States.
Wenping Ma, Edwin L. Kugler, James Wright, and Dady B. Dadyburjor. Fri . "Mo-Fe catalysts supported on activated carbon for synthesis of liquid fuels by the Fischer-Tropsch process: effect of Mo addition on reducibility, activity, and hydrocarbon selectivity". United States. doi:.
@article{osti_20838250,
title = {Mo-Fe catalysts supported on activated carbon for synthesis of liquid fuels by the Fischer-Tropsch process: effect of Mo addition on reducibility, activity, and hydrocarbon selectivity},
author = {Wenping Ma and Edwin L. Kugler and James Wright and Dady B. Dadyburjor},
abstractNote = {The effects of Mo loading (0-12 wt %) on the properties of activated-carbon- (AC-) supported Fe-Cu-K catalysts and their performance for Fischer-Tropsch synthesis are studied. Physicochemical properties studied include particle size, reducibility, and dispersion, and catalytic properties include activity, selectivity, and stability. Catalysts were characterized by N{sub 2} adsorption, energy-dispersive spectroscopy, X-ray diffraction (XRD), H{sub 2} temperature-programmed reduction (TPR), and CO chemisorption. Catalyst performance was studied at 310-320{sup o}C, 2.2 MPa, 3 Nl/g-cat/h, and H{sub 2}/CO = 0.9. Reaction results in a fixed-bed reactor show that addition of 6% Mo into the Fe-Cu-K/AC catalyst improves catalyst stability without sacrificing activity, but activity is suppressed dramatically on a 12% Mo-loaded catalyst. Detectable hydrocarbons of C{sub 1} to C{sub 34} are produced on the Fe-Cu-K/AC catalysts with or without Mo. However, the addition of Mo results in the production of more CH{sub 4} and less C{sub 5+} hydrocarbons. The Mo promoter greatly enhances secondary reactions of olefins, leading to a large amount of internal olefins (i.e., other than 1-olefins) in the product. TPR shows that a strong interaction between Fe and Mo oxides is present, and the extent of reduction of Fe is suppressed after addition of Mo to the Fe-Cu-K catalyst. CO-chemisorption and XRD studies show increased iron dispersion and decreased particle size of the iron carbide and iron oxide after the addition of Mo. Segregation of iron active sites, thereby preventing them from agglomerating, and a larger number of active sites on the 6% Mo catalyst are possible reasons for the improved stability and higher activity of Mo-promoted catalysts. 54 refs., 5 figs., 6 tabs.},
doi = {},
journal = {Energy and Fuels},
number = 6,
volume = 20,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The effect of potassium on the activity, selectivity, and distribution of products (hydrocarbons and oxygenates) was studied over iron catalysts supported on activated carbon (AC) for Fischer-Tropsch synthesis (FTS). This is part of a wider study on the incremental effects of components (including the support) of a multicomponent (Fe-Cu-Mo-K/AC) FTS catalyst. The range of potassium loading used was 0-2 wt%. A fixed-bed reactor was used under the conditions of 260-300{sup o}C, 300 psig, and 3 Nl/g cat/h, using syngas with a H{sub 2}/CO molar feed ratio of 0.9. Both FTS and water-gas shift activities increase after the addition of 0.9more » wt % potassium, whereas an opposite trend is observed with the addition of 2 wt % potassium. This is shown to be the result of interaction between the decrease of both the activation energy (E{sub a}) and the pre-exponental factor (k{sub 0}) with the amount of potassium promoter added. Detectable hydrocarbons up to C{sub 34} and oxygenates up to C{sub 5} are formed on the Fe/AC catalysts with or without potassium. The potassium promoter significantly suppresses formation of methane and methanol and shifts selectivities to higher-molecular-weight hydrocarbons (C{sub 5+}) and alcohols (C{sub 2}-C{sub 5}). Meanwhile, the potassium promoter changes paraffin and olefin distributions. At least for carbon numbers of 25 or less, increasing the K level to 0.9 wt % greatly decreases the amount of n-paraffins and internal olefins (i.e., those with the double bond in other than the terminal positions) and dramatically increases branched paraffins and 1-olefins, but a further increase in the K level shows little additional improvement. The addition of potassium changes the effect of temperature on the selectivity to oxygenates. In the absence of K, oxygenate selectivity decreases with temperature. However, when K is present, the selectivity is almost independent of the temperature. 71 refs., 13 figs., 3 tabs.« less
  • The kinetics of the gas-solid Fischer-Tropsch (FT) synthesis over a commercial Fe-Cu-K-SiO{sub 2} catalyst was studied in a continuous spinning basket reactor. Experimental conditions were varied as follows: reactor pressure of 0.8--3.2 MPa, H{sub 2}/CO feed ratio = 0.5--2.0, and a space velocity of 0.5--2.0 {times} 10{sup {minus}3} Nm{sup 3}/kg{sub cat} s at a constant temperature of 523 K. A new product distribution model for linear hydrocarbons is proposed. Deviations from conventional Anderson-Schulz-Flory distribution can be quantitatively described with an {alpha}-olefin readsorption product distribution model. The experimentally observed relatively high yield of methane, relatively low yield of ethene, and bothmore » the exponential decrease of the olefin-to-paraffin ratio and the change of the chain growth parameter with chain length can all be predicted from this new model. It combines a mechanistic model of olefin readsorption with kinetics of chain growth and termination on the same catalytic sites. The hydrocarbon formation is based on the surface carbide mechanism by CH{sub 2} insertion. The olefin readsorption rate depends on the chain length because of increasing physisorption strength on the catalyst surface and increasing solubility in FT wax with increasing chain length. Interfacial concentrations of reactive olefins near the gas-wax and wax-catalyst surface are used in the kinetic model. With optimization of three parameters per experimental product distribution, the olefin readsorption product distribution model proved to predict product selectivities accurately over the entire range of experimental conditions. The relative deviations are 10.1% and 9.1% for the selectivity to paraffins and olefins with n < 11, respectively.« less
  • In order to study the influence of the support on high dispersion catalysts used for the CO hydrogenation reaction, two catalysts, Fe/SiO{sub 2} and Fe/Al{sub 2}O{sub 3}, were prepared by the dry impregnation method. Selective chemisorption of CO, volumetric oxidation, and Moessbauer spectroscopy were used to determine the Fe species present as well as the metallic crystal size, the degree of dispersion, and the reduction percentage. The presence of small Fe{sup 0} crystallites with high dispersion was determined in both catalysts. Reaction rates were measured in a differential reactor and significant differences, about one order of magnitude less for themore » Al{sub 2}O{sub 3} than for the SiO{sub 2} supported catalysts, were found in the methane turnover frequencies. They are attributed to the interaction between the metal and the supports. The selectivity differences is also discussed in connection with distinct surface properties.« less