M�ssbauer spectroscopy study of iron-based catalysts used in Fischer-Tropsch synthesis

Rao, K.R.P.M.; Huggins, Frank E.; Mahajan, Vikram; Huffman, G.P.; Rao, V. U. S.; Bhatt, B. L.; Bukur, Dragomir B.; Davis, Burtron H.; O’Brien, Robert

doi:10.1007/bf01491956

Cited by 61 publications

(28 citation statements)

References 5 publications

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“…Although the FTS reaction does not occur in the bulk phase of carbides, the carbides can have FTS-active sites on their surfaces. Thus, it is proposed that iron carbides are the main active phases for the FTS reaction [17,[39][40][41][42], and Figure 3a represents the effect of the changing distribution of iron phases on CO conversion for an unpromoted catalyst. The catalytic activity showed a gradual decrease with time and the deactivation rate was found to be 4.86 % per day.…”

Section: Resultsmentioning

confidence: 99%

Fischer–Tropsch Synthesis: Deactivation as a Function of Potassium Promoter Loading for Precipitated Iron Catalyst

et al. 2014

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The effect of potassium promoter loading (0, 0.5, 1.0 and 2.0 atomic ratio) on the performance of precipitated iron catalysts was investigated during FischerTropsch synthesis using a continuously stirred tank reactor. Characterization by temperature-programmed reduction with CO, Mössbauer effect spectroscopy, and transmission/ scanning transmission electron microscopy were used to study the effect of potassium promoter interactions on the carburization, phase transformation and carbon layer formation behavior of the catalysts. Under similar reaction conditions, all four catalysts exhibited similar initial CO conversions (*85 %), whereas stability was found to increase with potassium loading up to 0.5 % (atomic ratio related to the iron), and further increases in potassium led to decreased activity. Unpromoted and excessively K loaded (2.0K/100Fe) catalysts exhibited similar deactivation trends with time and followed essentially similar conversion levels with time-on-stream. The selectivity of various potassium promoted catalysts was found to increase the average molecular weight of hydrocarbon products with increasing potassium loading. The deactivation rate was related to carbon deposition which could embed the iron carbide particles. If not enough K is present, Fe carbides tend to oxidize with TOS; with excessive K-loading, carbon deposition/site blocking become problematic.

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Section: Resultsmentioning

confidence: 99%

Fischer–Tropsch Synthesis: Deactivation as a Function of Potassium Promoter Loading for Precipitated Iron Catalyst

et al. 2014

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“…Fe carbides, Fe oxide (especially Fe 3 O 4 ), Fe metal, or surface iron phases on Fe 3 O 4 have been proposed to be the active species for FT reaction by different researchers [9][10][11][12][13][14][15]. The kinds and the relative abundances of these phases depend on the varied activation procedures and different reaction conditions [16,17].…”

Section: Introductionmentioning

confidence: 99%

Novel precipitated iron Fischer–Tropsch catalysts with Fe3O4 coexisting with α-Fe2O3

Tian

Xiang

et al. 2005

Catal Lett

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The present study was undertaken to investigate the catalytic behavior of an industrial iron catalyst (Fe/Cu/K/SiO 2 ) prepared from ferrous sulfate precursor for Fischer-Tropsch (FT) synthesis, in which different amount of Fe 3 O 4 coexist with a-Fe 2 O 3 . The catalyst samples were characterized by BET, XRD, H 2 -TPR and Mo¨ssbauer effect spectroscopy (MES). The FT synthesis performance of the catalysts were carried out in a fixed bed reactor (FBR) under reaction conditions of 250°C, 1.5 MPa, 2.0 nL/gcat/h, and H 2 /CO=2/1 for 200 h. The results from XRD and MES for the catalyst samples of pre-and post-reduction indicate that more iron carbides form in the catalysts that have lower Fe 3 O 4 contents. H 2 -TPR for the catalysts displays that Fe 3 O 4 may facilitate the reduction of catalysts only when it was highly dispersed. FT reaction study in the FBR shows that the catalysts become more active with the decrease of Fe 3 O 4 contents in the catalysts. However, the catalyst with certain amount of highly dispersed Fe 3 O 4 exhibited high FT synthesis activity with CO conversion more than 75%. The catalyst also displayed much less olefins selectivity. A comparison of FTS performances of one of these catalysts with some known catalysts was also made in this paper.

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“…Synthesis gas can also be used as the activating reagent. Activation in synthesis gas is usually started at temperatures well below typical FTS reaction temperatures, and then the temperature is gradually increased to typical FTS reaction temperatures [9][10][11][12][13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Structural analysis of unpromoted Fe-based Fischer–Tropsch catalysts using X-ray absorption spectroscopy

O’Brien

Meitzner³

et al. 2001

Applied Catalysis A: General

104

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The structure of unpromoted precipitated Fe catalysts was determined by Mössbauer emission and X-ray absorption spectroscopies after use in the Fischer-Tropsch synthesis (FTS) reaction in well-mixed autoclave reactors for various periods of time. X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS) analysis, and Mössbauer spectroscopy showed consistent trends in the structural evolution of these catalysts during reaction. The nearly complete formation of Fe carbides during initial activation in CO was followed by their gradual re-oxidation to form Fe 3 O 4 with increasing time-on-stream. Fe 3 O 4 became the only detectable Fe compound after 450 h. The observed correlation between FTS rates and Fe carbide concentration, and the unexpected re-oxidation of the catalysts as CO conversion decreased, suggest that the deactivation of Fe catalysts in FTS reactions parallels the conversion of Fe carbides to Fe 3 O 4 . It appears that the CO activation steps responsible for replenishing carbidic surface species and for removing chemisorbed oxygen are selectively inhibited by deactivation of surface sites, leading to the oxidation of Fe carbide even in the presence of a reducing reactant mixture.

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M�ssbauer spectroscopy study of iron-based catalysts used in Fischer-Tropsch synthesis

Cited by 61 publications

References 5 publications

Fischer–Tropsch Synthesis: Deactivation as a Function of Potassium Promoter Loading for Precipitated Iron Catalyst

Fischer–Tropsch Synthesis: Deactivation as a Function of Potassium Promoter Loading for Precipitated Iron Catalyst

Novel precipitated iron Fischer–Tropsch catalysts with Fe3O4 coexisting with α-Fe2O3

Structural analysis of unpromoted Fe-based Fischer–Tropsch catalysts using X-ray absorption spectroscopy

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