METHOD OF PRODUCING NANOSTRUCTURED IRON-BASED CATALYSTS FOR CONVERTING SYNGAS TO LIGHT OLEFINS

Abstract

The present invention relates to a method of preparing a nano-sized, iron-based catalyst, the method comprising: mixing a solution containing an iron salt with a surfactant to form a mixture; adding a basic salt solution comprising a salt of element selected from the group consisting of: alkali metals, alkaline earth metals, transition metals of groups 3 to 7 and 9 to 11 of the Periodic Table of Elements, lanthanides, and combinations of elements thereof, to the mixture to form a precipitate; and calcining said precipitate to form the iron-based catalyst, said iron-based catalyst at least partially comprising said element of said basic salt. The present invention also relates to a nano-sized, iron-based catalyst prepared by the above method and a process for the production of light olefins using the nano-sized, iron-based catalyst.

Claims

1. A method of preparing a nano-sized, iron-based catalyst, the method comprising: i) mixing a solution containing an iron salt with a surfactant to form a mixture; ii) adding a basic salt solution comprising a salt of element selected from the group consisting of: alkali metals, alkaline earth metals, transition metals of groups 3 to 7 and 9 to 11 of the Periodic Table of Elements, lanthanides, and combinations of elements thereof, to the mixture to form a precipitate; and iii) calcining said precipitate to form the iron-based catalyst, said iron-based catalyst at least partially comprising said element of said basic salt.

2. The method of claim 1, wherein the basic salt solution comprises hydroxide, carbonate, or bicarbonate anions, or wherein the basic salt comprises an alkali metal or an alkali earth metal.

3. (canceled)

4. The method of claim 2, wherein the basic salt is sodium hydroxide, lithium hydroxide, potassium hydroxide, cesium hydroxide, or combinations thereof.

5. The method of claim 1, wherein the adding step comprises providing a molar ratio of elemental iron to the element of the basic salt of from 1:2 to 1:10.

6. The method of claim 1, wherein the solution of step (i) comprises at least one or more additional salts of a transition metal independently selected from groups 3 to 7 and 9 to 11 of the Periodic Table of Elements.

7. The method of claim 6, wherein the transition metal is Ni, Mn, Mg, Ca, La, Co, Li, K, Ce, or a combination thereof, or wherein the transition metal salt comprises an anion selected from the group consisting of hydroxide, carbonate, bicarbonate, nitrate, nitrite, chloride, fluoride, bromide, iodide, phosphate, pyrophosphate, perchlorate, and mixtures thereof.

8.-9. (canceled)

10. The method of claim 6, wherein the solution of step i) comprises a molar ratio of elemental transition metal to iron of from 1:8 to 1:100.

11. The method of claim 1, wherein the adding step (ii) further comprises introducing a silicate to the mixture and precipitating said Fe-based catalyst in the presence of the silicate to thereby form a silicate-supported Fe-based catalyst.

12. The method of claim 11, wherein the silicate comprises one or more alkoxy groups of 2 to 5 carbon atoms.

13. (canceled)

14. The method of claim 11, wherein the adding step comprises providing a molar ratio of elemental iron to said silicate of from 1:5 to 1:15.

15. The method of claim 1, wherein the precipitated mixture obtained from step ii) is not washed before calcination, or wherein the iron salt is an iron (II) or iron(III) salt, or wherein the iron salt comprises an anion selected from the group consisting of nitrate, chloride, fluoride, bromide, iodide, phosphate, pyrophosphate and perchlorate.

16.-18. (canceled)

19. The method of claim 1, wherein the surfactant is an ionic surfactant.

20.-21. (canceled)

22. The method of claim 1, wherein the molar ratio of iron to the surfactant is 1:0.5 to 1:2, or wherein the calcining step is carried out at a temperature of 400° C. to 600° C. for 1 hour to 3 hours.

23. (canceled)

24. A nano-sized, iron-based catalyst comprising: a) 5-99 wt. % of iron; and b) 1-50 wt. % of an oxide of a metal selected from the group consisting of: alkali metals, alkaline earth metals, transition metals of groups 3 to 7 and 9 to 11 of the Periodic Table of Elements, and lanthanides, wherein said metal is not iron, based on a total weight of the nano-sized catalyst, wherein said nano-sized catalyst has a diameter of 2 nm to 50 nm.

25. The iron-based catalyst of claim 24, wherein said metal is present in an amount of 4-50 wt. % based on the total weight of the catalyst, or wherein a weight ratio of the transition metal to iron is 1:5 to 1:200, or wherein the nano-sized catalyst adopts a spinel crystalline phase.

26. (canceled)

27. The iron based catalyst of claim 25, wherein a formula of the spinel phase catalyst is FeM.sub.2O.sub.4.

28. The iron-based catalyst of claim 24, wherein the catalyst further comprises a transition metal selected from groups 3-7 and 9-11 of the Periodic Table of Elements, or wherein the catalyst further comprises a SiO.sub.2 matrix, or wherein the catalyst further comprises an oxide of a halogen.

29.-31. (canceled)

32. The iron catalyst of claim 28, wherein the oxide of the halogen is present in an amount of about 0.1-50 wt. % based on the weight of catalyst.

33. iron-based catalyst prepared according to the method of claim 1, wherein the catalyst comprises: a) 5-99 wt. % of iron; and b) 1-50 wt. % of an oxide of a metal selected from the group consisting of: alkali metals, alkaline earth metals, transition metals of groups 3 to 7 and 9 to 11 of the Periodic Table of Elements, and lanthanides, wherein said metal is not iron, based on a total weight of the nano-sized catalyst, and wherein said nano-sized catalyst has a diameter of 2 nm to 50 nm.

34. A process for the production of light olefins, the process comprising the steps of: i) heating the catalyst of claim 24 in the presence of a gas comprising one or more oxides of carbon and hydrogen to activate said catalyst; and ii) contacting said activated catalyst of step (i) with a gas stream comprising one or more oxides of carbon and hydrogen to partially or fully convert said one or more oxides of carbon to said light olefins, said light olefins comprising between 2 to 4 carbon atoms, wherein methane is substantially absent from said light olefins, or constitutes less than 20% of said light olefins.

35. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0096] The accompanying figures, together with the description below are incorporated in and form part of the specification. These figures serve to illustrate various embodiments and to explain various principles and advantages in accordance with a present embodiment.

[0097] FIG. 1 is a flowchart illustrating the method of preparing the sodium-promoted nano-sized, iron based catalyst as described herein.

[0098] FIGS. 2a and 2b are transmission electron micrographs of the iron-sodium catalyst prepared by precipitation of Fe(NO.sub.3).sub.3 with NaOH. FIG. 1a shows a macro rod-like structure of the iron sodium catalyst while FIG. 1b is a close-up of the Fe nanoparticles. The macro structure is composed of smaller Fe nanoparticles of about 4-5 nm in size.

[0099] FIG. 3 shows the X-ray diffraction patterns of iron-sodium prepared through two methods. The peaks of the spinel phase of the FeNa catalyst are indicated by (*). The first method involved preparation of the catalyst at room temperature with no aging (top line) while the second method involved preparation of the catalyst at a temperature of 70° C. and left to age for 16 hours (bottom line). Catalysts prepared without aging (first method) exhibit peaks of both the spinel and haematite phases, indicating that the catalyst is formed with mixed hematite and spinel phases; while catalysts prepared with aging (second method) exhibit peaks of the spinel phase, indicating that the spinel phase is dominant. This demonstrates that it is possible to selectively form the spinel phase through preparation at higher temperature and aging.

[0100] FIG. 4 is an extended X-ray absorption fine structure (EXAFS) spectrum of the iron-sodium catalyst. The spectrum of the FeNa catalyst prepared by methods described herein shows that the Fe—Fe coordination peak is lacking a shoulder typically seen in the spectra of Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4, as indicated by the arrow. This implies that the phase of the FeNa spectrum is neither common haematite nor magnetite.

[0101] FIGS. 5a-5d are energy dispersive X-ray spectroscopy (EDS) map of the iron-sodium catalyst. The maps show a good dispersion of iron, bromine, sodium and oxygen. The EDS map of oxygen is also provided as a reference for the distribution of the elements.

[0102] FIG. 6 is a X-ray photoelectron spectrum (XPS) of the peak corresponding to bromine in the iron-sodium catalyst. The binding energy of suggests that bromine is present in the form of the bromate ion is present.

[0103] FIGS. 7a-7e are energy dispersive spectroscopy (EDS) maps of an iron-sodium-manganese catalyst showing the dispersion of iron, sodium and manganese. The map of oxygen is provided as a reference for the distribution of the elements.

[0104] FIGS. 8a-8e are electron dispersive spectroscopy maps of an iron-sodium-nickel catalyst which shows the dispersion of iron, bromine, sodium and nickel. The map of oxygen is provided as a reference for the distribution of the elements.

[0105] FIG. 9 is a transmission electron micrograph of an iron-sodium nanoparticle catalyst dispersed in a 90 wt. % silica matrix.

[0106] FIG. 10 shows the X-ray diffraction (XRD) diffraction patterns of FeNa in comparison to the simulated pattern of FeNa.sub.2O.sub.4.

EXAMPLES

[0107] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

[0108] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

[0109] The following acronyms and symbols have the following meanings

[0110] GHSV: Gas hourly space velocity

[0111] TOS: Time on Stream

[0112] LO: Light Olefins

[0113] O: Olefins

[0114] P: Paraffin

[0115] CNT: Carbon Nanotubes

[0116] CNF: Carbon Nanofibres

Example 1—Preparation of Na-Promoted Fe Catalyst

[0117] Na-promoted Fe catalyst (FeNa) was prepared by mixing 10.81 g of Fe(NO.sub.3).sub.3.9H.sub.2O with 10 g cetyl trimethyl ammonium bromide (CTAB) in 400 ml deionized H.sub.2O to form a homogenous solution. 4 g of NaOH in 80 ml deionized H.sub.2O was subsequently used to precipitate the iron in the solution. The suspension was allowed to age at room temperature for 5 min. before collection of the precipitate via centrifugation. No washing of the precipitate was performed in order to allow the Na to remain as a promoter. The precipitate was then dried in air before calcination at 550° C. for 2 h. This yields a FeNa catalyst with a Na promotion of about 10 wt. %.

[0118] The FeNa catalyst was transferred to a fixed bed reactor and reduced in flowing H.sub.2. A protocol flowing syngas in the ratio H.sub.2/CO=1, 10 bar and 290° C. for 24 h was used to activate the catalyst. Finally, an induction period was observed by tracking the performance of the catalyst at 370° C. and 20 bar in flowing syngas with H.sub.2/CO=1 at a space velocity of 2,000 ml/g.Math.h. Upon reaching a high activity (>90 C mol. % CO conversion), the temperature and/or H.sub.2/CO ratio may be tuned to maximize light olefin yield.

[0119] FIG. 2 shows the TEM images of the FeNa catalyst prepared herein, where the nanoparticles are clustered to form rod like features (FIG. 2a). Individual particles of the rod-like features can be seen in FIG. 2b. FIG. 3 shows the X-ray diffraction patterns of the FeNa catalyst. The major phase is a spinel phase that is based on iron. Follow-up studies with EXAFS indicate a phase with a missing Fe—Fe coordination peak when compared with spectra of Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4, shown in FIG. 4. This suggests a formation of an iron-based phase that is neither common haematite nor magnetite.

[0120] The composition of the FeNa catalyst was identified using EDS and the resulting color maps show a uniform dispersion of the elements in the catalyst, as shown in FIG. 5. FIG. 6 shows the XPS spectrum of FeNa for Br, where the binding energy suggests that Br is present in the catalyst in the bromate form and can be reduced to bromide during the reduction process in H.sub.2. The reduced bromide form is believed to be able to facilitate Fe.sub.5C.sub.2 formation, when the catalyst is used in a Fischer-Tropsch reaction.

[0121] Table 1 shows the performance of FeNa during the induction period at 370° C., 20 bar, H.sub.2/CO=1 and gas hourly space velocity (GHSV) of 2,000 ml/g.Math.h. Data in Table 1 demonstrates that the catalyst allows low selectivity to CH.sub.4 while allowing a high selectivity to C.sub.2-C.sub.4 light olefins. An optimal induction allows the catalyst to achieve high activity while maintaining a high selectivity to light olefins.

TABLE-US-00001 TABLE 1 Performance of FeNa, FeNa—Ni and FeNa—Mn during catalyst induction at 370° C., 20 bar, H.sub.2/CO = 1 and GHSV of 2,000 ml/g.h. Hydrocarbon Distribution Light O/ (C %) (O + P) LO Conv. CH.sub.4 CO.sub.2 C2- (C %) Yield Catalyst (C %) (C %) (C %) CH.sub.4 C4 C5+ C2 C3 C4 (C %) FeNa 58 7 45 18 47 35 67 90 84 12 FeNa—Ni 56 73 44 18 51 31 69 91 81 13 FeNa—Mn 59 6 44 17 51 32 71 92 86 14

[0122] Table 2 shows the performance of the FeNa catalyst at 350° C., 20 bar, H.sub.2/CO=1 and GHSV of 2000 ml/g.Math.h. The selectivity to CH.sub.4 is minimized, while activity is maximized close to full CO conversion. A considerable fraction of C2-C4 is also obtained with high olefinicity. The FeNa catalyst allows olefin selectivity is also reasonably well-maintained to offer good light olefin yield per pass.

TABLE-US-00002 TABLE 1 Performance of the FeNa catalyst at 350° C., 20 bar, H.sub.2/CO = 1 and GHSV of 2,000 ml/g.h. Hydrocarbon Light Distribution O/(O + P) LO TOS Conv. CH.sub.4 CO.sub.2 (C %) (C %) Yield (h) (C %) (C %) (C %) CH.sub.4 C2-C4 C5+ C2 C3 C4 (C %) 64 97 5 40 15 48 37 58 89 84 22

[0123] Table 3 shows the performance comparison of the FeNa catalyst prepared by the described method (first row) with other reported catalysts with Na promotion (second to fourth row). The comparative catalysts were prepared by conventional impregnation of carbon-based supports with Fe catalysts with Na promotion followed by reduction in a H.sub.2 environment before syngas reaction, without calcination. Comparisons are made with comparative catalysts which comprise the highest sodium promotion available. It can be seen that the FeNa catalyst prepared by the methods described herein exhibits high syngas conversion activity and olefinicity compared with other catalysts.

TABLE-US-00003 TABLE 3 Performance comparison of FeNa catalyst with other Na-promoted catalysts in the art. Hydrocarbon Light Distribution O/(O + P) LO CO.sub.2 (C %) (C %) Yield Catalyst Conv.(C %) (C %) CH.sub.4 C2-C4 C5+ C2 C3 C4 (C %) FeNa 92 43 20 49 31 59 89 83 20 Fe(Na + S)/CNF* 98 53 10 60 30 ← 62 .fwdarw. 19 Fe—24Na/CNT** 71 14 7 22 72 N.A. 78 N.A 10 Fe/CNT(0.5)*** 51 38 4 20 76 ← 85 .fwdarw. 5

Example 2—Preparation of a Mn-Promoted FeNa Catalyst

[0124] Mn promoted FeNa (FeNa—Mn) catalyst was prepared by mixing 9.73 g of Fe(NO.sub.3).sub.3.9H.sub.2O and 0.67 g of Mn(NO.sub.3).sub.2.4H.sub.2O with 10 g CTAB in 400 ml deionized H.sub.2O to form a well-mixed solution. 4 g of NaOH in 80 ml deionized H.sub.2O was subsequently used to precipitate the iron in the solution. The suspension was allowed to age at room temperature for 5 min. before collection of the precipitate via centrifugation. No washing of the precipate was performed in order to allow the Na to remain as a promoter. The precipitate was then dried in air before calcination at 550° C. for 2 h. This results in a FeNa—Mn catalyst with a Na promotion of about 10 wt. % and an Fe to Mn ratio of about 9.

[0125] The FeNa—Mn catalyst was transferred to a fixed bed reactor and reduced in flowing H.sub.2. A protocol flowing syngas in the ratio H.sub.2/CO=1, 10 bar and 290° C. for 24 h was used to activate the catalyst. Finally, an induction period was observed by tracking the performance of the catalyst at 370° C. and 20 bar in flowing syngas with H.sub.2/CO=1 at a space velocity of 2,000 ml/g.Math.h. Upon reaching a high activity (>90 C mol. % CO conversion), the temperature and/or H.sub.2/CO ratio may be tuned to maximize light olefin yield.

[0126] FIG. 7 show the EDS identification and mapping of the constituent elements in the FeNa—Mn catalyst. The images show a well dispersed and uniform distribution of Fe, Na and Mn, as well as the oxygen content present in oxide form. Table 1 shows the performance of FeNa—Mn when compared with FeNa. The Mn promotion decreases the selectivity to CH.sub.4 and C5+, while further improving the C2-C4 hydrocarbon selectivity and olefinicity.

Example 3—Preparation and Performance of Nickel-Promoted FeNa Catalyst

[0127] Ni promoted FeNa (FeNa—Ni) catalyst was prepared by mixing 10.70 g of Fe(NO.sub.3).sub.3.9H.sub.2O and 0.078 g Ni(NO.sub.3).sub.2.6H.sub.2O with 10 g CTAB in 400 ml deionized H.sub.2O to form a homogenous solution. 4 g of NaOH in 80 ml deionized H.sub.2O was subsequently used to precipitate the iron in the solution. The suspension was allowed to age at room temperature for 5 min. before collection of the precipitate via centrifugation. No washing of the precipitate was performed in order to allow the Na to remain as a promoter. The precipitate was then dried in air before calcination at 550° C. for 2 h. This results in a FeNa—Ni catalyst with a Na promotion of about 10 wt. % and an Fe to Ni ratio of about 99.

[0128] The FeNa—Ni catalyst was transferred to a fixed bed reactor and reduced in flowing H.sub.2. A protocol flowing syngas in the ratio H.sub.2/CO=1, 10 bar and 290° C. for 24 h was used to activate the catalyst. Finally, an induction period was observed by tracking the performance of the catalyst at 370° C. and 20 bar in flowing syngas with H.sub.2/CO=1 at a space velocity of 2,000 ml/g.Math.h. Upon reaching a high activity (>90 C mol. % CO conversion), the temperature and/or H.sub.2/CO ratio may be tuned to maximize light olefin yield.

[0129] FIG. 8 shows the EDS identification and mapping of the constituent atoms in the FeNa—Ni catalyst. The images show a well dispersed and uniform distribution of Fe, Na and Ni, as well as the oxygen content present in oxide form. Table 1 shows the reaction data of FeNa—Ni during induction at 370° C., 20 bar, H.sub.2/CO=1 and GHSV of 2,000 ml/g.Math.h. The addition of Ni is able to improve selectivity for the C2-C4 fraction at the expense of the C5+ fraction due to its propensity to form very short chain hydrocarbons and is mainly active for the methanation of CO and H.sub.2. This, combined with the olefinicity of the FeNa catalyst, is believed to allow a better selectivity for light olefins.

Example 4—Performance of FeNa Catalyst

[0130] A FeNa catalyst was prepared by mixing 10.81 g of Fe(NO.sub.3).sub.3.9H.sub.2O with 10 g CTAB in 400 ml deionized H.sub.2O to form a homogenous solution. 4 g of NaOH in 80 ml deionized H.sub.2O was subsequently used to precipitate the iron from the solution. The suspension was allowed to age at room temperature for 5 min. before collection of the precipitate via centrifugation. No washing of the precipitate was performed in order to allow the Na to remain as a promoter. The precipitate was then dried in air before calcination at 550° C. for 2 h. This results in a FeNa catalyst with a Na promotion of about 10 wt. %.

[0131] The FeNa catalyst was transferred to a fixed bed reactor and reduced in flowing H.sub.2. A protocol flowing syngas in the ratio H.sub.2/CO=1, 10 bar and 290° C. for 24 h was used to activate the catalyst. Finally, an induction period was observed by tracking the performance of the catalyst at 330° C. and 20 bar in flowing syngas with H.sub.2/CO=1 at a space velocity of 12,000 ml/g.Math.h. High activity of >78 C mol. % CO conversion can be achieved after 178 h, with no sign of deactivation.

[0132] Table 4 shows the performance of FeNa at 330° C., 20 bar, H2/CO=1 and GHSV of 12,000 ml/g.Math.h. Data in table 4 demonstrates that the catalyst becomes highly active, achieving about 80 C mol % CO conversion at high GHSV. The activity is maintained after 176 hours TOS.

TABLE-US-00004 TABLE 2 Performance of FeNa at 330° C., 20 bar, H.sub.2/CO = 1 and GHSV of 12,000 ml/g.h Hydrocarbon Light Distribution O/(O + P) LO TOS Conv. CH.sub.4 CO.sub.2 (C %) (C %) Yield (h) (C %) (C %) (C %) CH.sub.4 C2-C4 C5+ C2 C3 C4 (C %) 176 78 10 37 18 41 41 39 82 58 14

Example 5—Supported FeNa Catalyst

[0133] The supported FeNa (s-FeNa) catalyst was prepared by mixing 1.08 g of Fe(NO.sub.3).sub.3.9H.sub.2O with 1 g of CTAB in 40 ml deionized H.sub.2O to form a well-mixed solution. 0.4 g of NaOH in 8 ml deionized H.sub.2O was subsequently used to precipitate the iron in the solution. The suspension was allowed to age at room temperature for 5 min., after which 7.14 ml of tetraethyl orthosilicate (TEOS) in 92.86 ml ethanol was introduced drop-wise to the suspension to create the SiO.sub.2 support matrix. The final mixture was allowed to age for 12 h before collection of the precipitate via centrifugation. No washing of the precipitate was performed in order to allow the Na to remain as a promoter. The precipitate was then dried in air before calcination at 550° C. for 2 h. This results in an Fe-based catalyst with a Na promotion of about 1 wt. %.

[0134] The s-FeNa catalyst was transferred to a fixed bed reactor and reduced in flowing H.sub.2. A protocol flowing syngas in the ratio H.sub.2/CO=1, 10 bar and 290° C. for 24 h was used to activate the catalyst. Finally, an induction period was observed by tracking the performance of the catalyst at 330° C. and 20 bar in flowing syngas with H.sub.2/CO=1 at a space velocity of 12,000 ml/g.Math.h. High activity of >74 C mol. % CO conversion is achieved after 442 h, with no sign of deactivation.

[0135] FIG. 9 shows the TEM of s-FeNa where the nanoparticles are dispersed throughout a SiO2 matrix. The matrix stabilizes the nanoparticles, resisting particulate migration and sintering. shows the performance of s-FeNa at 330° C., 20 bar, H2/CO=1 and GHSV of 12,000 ml/g.Math.h. The inclusion of the SiO.sub.2 support activity of the catalyst can be stable past 442 h while operating at 74 C mol. %, allowing a consistent yield of light olefins.

TABLE-US-00005 TABLE 5 Performance of s-FeNa at 330° C., 20 bar, H.sub.2/CO = 1 and GHSVof 12,000 ml/g.h. Hydrocarbon Light Distribution O/(O + P) LO TOS Conv. CH.sub.4 CO.sub.2 (C %) (C %) Yield (h) (C %) (C %) (C %) CH.sub.4 C2-C4 C5+ C2 C3 C4 (C %) 442 74 11 36 20 44 36 26 79 47 14

Example 6—Conversion of CO.SUB.2 .to Olefins

[0136] To determine the performance of the catalyst in the conversion of CO.sub.2 to olefins, the FeNa catalyst was prepared and calcined according to the methods described herein. The calcined FeNa catalyst was subsequently washed with DI water and pelletized at 40 kN. The pellet was sieved to obtain particles of 250-500 μm. Subsequently, 1 g of the FeNa catalyst was loaded to a fixed bed reactor for testing after mixing with silicon carbide at a volume ratio=1:1. Reduction was carried out at 580° C. for 6 hours in H.sub.2 and ambient pressure at a space velocity of 2000 ml/(g.Math.h). Activation was carried out at 300° C. for 4 hours in CO and H.sub.2 with H.sub.2/CO ratio=2 at 10 barg and a space velocity of 2000 ml/(g.Math.h). The CO.sub.2 reaction was carried out at 350° C. in CO.sub.2 and H.sub.2 with H.sub.2/CO.sub.2 ratio=3 at 15 barg and a space velocity of 5500 ml/(g.Math.h).

[0137] The catalytic performance of the FeNa catalyst for the conversion of CO.sub.2 to olefins was monitored and the relevant experimental data is presented in Table 6.

TABLE-US-00006 TABLE 6 Performance of the FeNa catalyst for CO2 to olefins reaction, with X(CO.sub.2) the conversion of CO.sub.2, S(CH.sub.4) and S(CO) are the selectivity towards CH.sub.4 and CO respectively Hydrocarbon X(CO.sub.2) S(CH.sub.4) S(CO) % of Olefins [mol C %] distribution [mol C %] TOS mol mol mol LO C2- C2- (h) C % C % C % Yield C2 C3 C4 C4 CH.sub.4 C4 C5+ 2 42 11 14 9.1 79 89 84 84.5 13 30 57 4 44 12 13 10.0 79 90 83 84.6 14 30 56 6 44 13 12 10.2 80 90 84 85.0 14 31 55 8 44 13 12 9.9 80 90 85 85.5 13.8 29.7 56.5 10 45 13 12 10.2 80 91 85 85.8 14.1 30.0 55.9 18 45 13 11 10.2 81 91 86 86.6 13.8 29.3 56.8 20.0 46 13 11 10.4 81 91 88 87.4 14.0 29.4 56.6 22.0 46 13 11 10.6 82 91 85 86.5 14.2 30.2 55.6 26.0 46 13 11 10.8 82 91 85 86.5 14.1 30.6 55.3

[0138] The results in Table 6 demonstrate that the FeNa catalyst prepared by the methods described herein can achieve a light olefin yield of 10.8% at a CO.sub.2 conversion of 46% with very high percentage of olefin in C2-C4 and relatively low CH.sub.4 and CO selectivity. Following these preliminary results, further optimization to improve the olefin yield may be performed.

Example 7. Effect of Br Content on Catalyst Performance

[0139] To investigate the effect of bromine in the catalyst on the conversion of carbon dioxide, a batch of unwashed FeNa catalyst prepared by the methods described herein was tested first in CO Fischer Tropsch Olefin production until high conversion of CO was achieved. The catalyst was subsequently tested for the Fischer Tropsch conversion of CO2. The results are provided below in Table 7.

TABLE-US-00007 TABLE 7 Performance of FeNa catalyst for CO and CO.sub.2 Fischer Tropsch conversion. X(CO) S(CH4) S(CO2) LO GC TOS mol mol mol Yield OP ratio Hydrocarbon distribution run (hrs) C % C % C % (GC) C2 C3 C4 C2-C4 CH4 C2-C4 C5+ H.sub.2/CO 22 20 95 6 31 19.0 61 88 82 77.8 17 37 46 1 25 26 97.0 9 21 21 58 85 81 76.0 8 36 46 2 X(CO2) S(CH4) S(CO) LO GC TOS mol mol mol Yield OP ratio Hydrocarbon distribution run (hrs) C % C % C % (GC) C2 C3 C4 C2-C4 CH4 C2-C4 C5+ 49 70.4 39 12 25 11.2 78 91 88 86.0 18.8 44.3 36.9 Reduction: 600° C., 2 h 0 barg, SV = 12000 ml/(gh).sup.−1 Activation: 290° C., 24 h 10 barg. H.sub.2/CO ratio = 1. SV = 2000 ml/(gh).sup.−1 Reaction(CO): 370° C. 20 barg. H.sub.2/CO.sub.2 = 1. SV = 2000 ml/(gh).sup.−1 24 h 370° C. 20 barg. H.sub.2/CO.sub.2 = 2. SV = 2000 ml/(gh).sup.−1 6 h Reaction(CO.sub.2): 350° C. 15 barg. H.sub.2/CO.sub.2 = 3. SV = 5500 ml/(gh).sup.−1

[0140] It was found that the unwashed FeNa catalyst can achieve a light olefin yield of 11.2% after full activation with CO. The FeNa catalyst has a CO.sub.2 conversion of 39% with very high percentage of olefin in C2-C4 and maintained low CH.sub.4, but with slightly higher CO selectivity.

[0141] The result obtained by using the calcined, but unwashed FeNa catalyst for the conversion of CO followed by CO.sub.2 is similar to that of Example 6 which utilizes a calcined catalyst which is washed. It is believed that washing FeNa after calcination will help to remove excess Br. During CO reaction, water as the by-product from the reaction will also remove excess Br.

[0142] The similar result obtained above indicates that Br may be leeched by water which is formed as a by-product during the CO Fischer Tropsch reaction. This also suggests that Br plays a role during the initial activation of the catalyst but may not be required after the catalyst reaches steady state. From Table 7, LO yield was lower under CO.sub.2 flow, however considering the much lower conversion (39% CO.sub.2 conversion vs. 97% CO conversion), the FeNa catalyst is actually more selective to light olefins under CO2. Therefore by activation of unwashed FeNa catalyst via the CO reaction, the catalyst achieved good performance.

INDUSTRIAL APPLICABILITY

[0143] The method as described herein allows for a one-pot synthesis of a sodium-promoted nano-sized, iron-based catalyst which may be used in a Fisher-Tropsch process. In particular, the iron catalyst prepared by the method described herein can be used for the selective conversion of carbon monoxide and carbon dioxide to light olefins, with minimal hydrogenation to methane. Light olefins produced from the Fischer Tropsch reaction catalyzed by the Iron-sodium nano-sized catalyst prepared herein may subsequently be used as fuels and lubrication oils.

[0144] Further, the method of preparing a Na-promoted iron described herein can be conveniently scaled up for preparation of the selective FeNa catalyst at an industrial scale.