Preparation and optimization of mixed iron cobalt oxide catalysts for conversion of synthesis gas to light olefins

Mirzaei, Ali Akbar; Habibpour, Razeieh; Kashi, Eslam

doi:10.1016/j.apcata.2005.08.033

Cited by 62 publications

(28 citation statements)

References 29 publications

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“…The molecular mass distribution of the hydrocarbons formed in the Fischer-Tropsch synthesis at Co/SiO 2 catalysts, which have been attracting increased interest [35][36][37][38][39][40], differs from the Anderson-Schulz-Flory distribution [7,9,16,20,30]. Such a distribution has a low content of the C 2 and sometimes of the C 3 hydrocarbons and shows an increase in the effective probability of chain growth with increase in its length for intermediates containing more than two or three carbon atoms.…”

Section: Resultsmentioning

confidence: 99%

Kinetic models of the molecular mass distribution of the products of the Fischer-Tropsch synthesis at cobalt catalysts

Yakubovich

Strizhak

2007

Theor Exp Chem

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Kinetic models were used to investigate the Fischer-Tropsch synthesis at increased pressures. The general mechanism proposed for the process at low and increased pressures was based on quantitative analysis of the products obtained with cobalt catalysts at pressures of 2.5-10 MPa using various kinetic models, the previously developed reference point method, and published data.The molecular mass distributions (MMD) of the hydrocarbons formed in the Fischer-Tropsch (FT) synthesis often differ from the Anderson-Schulz-Flory (ASF) distribution [1]. Various schemes have been proposed for the mechanism of the process to explain the deviations from the ASF distribution [2][3][4][5][6][7][8][9]. On the basis of such schemes mathematical models establishing a relationship between the concentrations of the individual products and the carbon number were derived. As kinetic coefficients they contain the probabilities or functions of the probabilities that the reactions occur with the participation of intermediates. They are models of the selectivity, but they make it possible to calculate the absolute rates of all stages of the kinetic scheme, starting from the rate of transformation of CO or H 2 [2]. A whole series of reasons for the deviations from the ASF distribution have been discussed in the literature.The reduced or increased methane content of the products is explained by the fact that the C 1 and C 2+ hydrocarbons are formed at different centers on the surface of the catalyst [10] or as a result of reactions leading to termination of the chain [1]. The deviation from the ASF distribution is sometimes attributed to increase in the probability of growth of the chain of C-C bonds (a) according to Herington scheme [11] with increase in the carbon number [1].The molecular mass distributions of the hydrocarbons often take the form of concave curves with a clearly defined kink [1,12,13]. Anderson approximated such distributions by two straight lines with different slopes in relation to the abscissa axis [13]. The existence of two probabilities of chain growth in the Fischer-Tropsch synthesis (usually a 1 < a 2 ) was thus mentioned first in this paper. Later Huff and Sutterfield [12] proposed an equation describing such distributions. This equation was obtained on the basis of the idea that the experimental molecular mass distributions represent the superimposition of the distributions of the a 1 -and a 2 -hydrocarbons.Initially the existence of two values for the probability of chain growth was explained by the fact that the growth of the C-C bonds takes place at different centers of the catalyst [12, 14]. However, subsequent data indicated that the two values of a arise as a result of simultaneous growth of the chain by two different mechanisms through two types of intermediates [9,[15][16][17][18]. The distributions of the hydrocarbons formed at Fe catalysts usually obey the Huff-Sutterfield equation [1,[11][12][13].(Here, they can often be approximated with sufficient accuracy by two straight lines.) The distributions o...

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Section: Resultsmentioning

confidence: 99%

Kinetic models of the molecular mass distribution of the products of the Fischer-Tropsch synthesis at cobalt catalysts

Yakubovich

Strizhak

2007

Theor Exp Chem

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“…In our previous studies [32][33][34][35][36][37][38][39][40] we demonstrated the importance of ageing time with respect to catalyst activity for the oxidation of CO by mixed copper manganese oxides and mixed copper zinc oxides. We have also studied the effect of ageing time on the performance of mixed iron cobalt oxide [41,42] and mixed cobalt manganese oxide [43] catalysts for FTS. The results of all of these investigations have shown that the ageing of the precipitates obtained by co-precipitation leads to phase changes toward forms that are more thermodynamically stable.…”

Section: Effect Of Preparation Conditionsmentioning

confidence: 99%

Preparation and operating conditions for cobalt cerium oxide catalysts used in the conversion of synthesis gas into light olefins

Mirzaei

Galavy

Beigbabaei

et al. 2007

JICS

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Cobalt cerium oxides, prepared using a co-precipitation procedure, were studied as catalysts for the conversion of synthesis gas to light olefins (C 2 -C 4 ). Specifically, we studied the effect of a range of preparation variables, including the molar ratio of the [Co]/[Ce] of the precipitation solution, ageing time and calcination temperature. In addition, the effects of supports and promoters on the catalysts' activity and selectivity and a range of reaction temperatures using synthesis gas with different H 2 /CO molar feed ratios were investigated. The catalyst containing a molar ratio of 80% Co and 20% Ce, aged for 2 h, supported with 15 wt% SiO 2 without any promoter, at an operating temperature of 450 ºC and an H 2 /CO feed ratio of 2/1 (GHSV = 4500 h -1 ), performed optimally for the conversion of synthesis gas to light olefins. The characterization of both the precursors and the calcined catalysts by powder X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller specific surface area measurements and thermal analysis methods, including TGA and DSC, show that all the preparation variables influenced the catalyst precursor structure.

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“…The broad product distribution of Fischer-Tropsch synthesis (FTS) has placed severe limitations on its attractiveness as a commercial operation [1], even the catalyst activity was found deviating from Anderson-Schulz-Flory (A-S-F) distribution [2]. Some iron-based catalysts have been reported for the selective synthesis of light olefins from CO hydrogenation [3][4][5][6][7]. Although transition metal modified iron-based catalysts were proved to improve the hydrocarbon distribution and promote the formation of C 2 -C 4 hydrocarbons to some extent [3], this also caused the increase of CH 4 or the decrease of olefin selectivity due to the acidity of the metal oxide.…”

Section: Introductionmentioning

confidence: 99%

Carbon modified Fe–Mn–K catalyst for the synthesis of light olefins from CO hydrogenation

Zhang

Fan

Zhao

et al. 2011

Reac Kinet Mech Cat

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A novel carbon modified Fe-Mn-K catalyst for light olefin synthesis from CO hydrogenation was prepared by the sol-gel method. The effect of carbon contents on the structure and performance of the catalysts was investigated. With the incorporation of carbon, the catalysts showed much different morphology from that prepared by co-precipitation. At the carbon contents between 0.23 and 6.66 wt%, the catalyst particles were around 10 nm while the carbon phase was amorphous. The activity test results indicated that the catalysts (Fe/Mn/K molar ratio = 60/20/1) with carbon modification showed high conversion of CO and selectivity to light olefins with low CH 4 selectivity. At the carbon content of 2.43 wt%, the total C 2 -C 4 content in all hydrocarbons and O/P (olefin/paraffin) in the C 2 -C 4 fraction was 49 wt% and 4.89, respectively. Furthermore, when the K content in the catalyst was reduced by half, the C 2 -C 4 olefin yield raised from 60 to 71 g/Nm 3 syngas. The formation of carbon provided a more hydrophobic surface, which inhibited the water gas shift reaction (WGSR) and caused a decrease in CO 2 selectivity. The dispersion of carbon favored the formation and stabilization of small particles, and promoted the production of light olefins via suppressing the chain propagation.

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Preparation and optimization of mixed iron cobalt oxide catalysts for conversion of synthesis gas to light olefins

Cited by 62 publications

References 29 publications

Kinetic models of the molecular mass distribution of the products of the Fischer-Tropsch synthesis at cobalt catalysts

Kinetic models of the molecular mass distribution of the products of the Fischer-Tropsch synthesis at cobalt catalysts

Preparation and operating conditions for cobalt cerium oxide catalysts used in the conversion of synthesis gas into light olefins

Carbon modified Fe–Mn–K catalyst for the synthesis of light olefins from CO hydrogenation

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