Supporting information

Iron ore as precursor for preparation of carbon-encapsulated χ-Fe5C2 catalyst

for Fischer-Tropsch synthesis

Sebastián Pérez, Fanor Mondragón, and Andrés Moreno

Química de Recursos Energéticos y Medio Ambiente, Instituto de Química, Facultad de Ciencias

Exactas y Naturales, Universidad de Antioquia, UdeA, Calle 70 No. 52 - 21, Medellín, Antioquia

050010, Colombia.

Figure S1 shows the characterization of the iron ore by XRD. The XRD pattern shows that it was

composed mainly of three phase goethite (FeOOH, ICDS: 71808), siderite (FeCO3, ICDS:

100678) and hematite (Fe2O3, ICDS: 161286), additionally the iron ore has an aluminosilicate

phase, (ICDS: 20593).

1

10 20 30 40 50 60

b)

Inte

nsity

(a.u

.) Yobs Ycalc Yobs-Ycalc

Aluminosilicate

a)

30 32 34 36 38

0

200

400

Inte

nsity

(a.u

.)

2

Fe2O3FeCO3

2

FeO(OH)

Figure S1. (a) XRD pattern for the iron ore with Rietveld refinement for the iron ore, (b)

magnification for the main peaks. (Blue) goethite (ICSD # 100678), (red) siderite (ICSD #

71808), and (green) hematite (ICSD # 161286).

Table S1. Quantification by Rietveld refinement and TGA of the phases present in the iron ore

Phase Hematite (%)

Goethite (%)

Siderite (%)

Aluminosilicate (%)

Iron (II) oxalate (%)

Iron ore by XRD (%) 31.11 37.88 18.14 12.87 -

Approximate quantification by TGA

Iron ore (%) 32.2 40.3 14.7 12.9 --

PRE-H2O 27.0 45.4 14.7 12.9 --

PRE-OA NA a 0 0 NA a 75.2

PRE-Ox - - - - 100

a The sum of hematite and aluminosilicate corresponding to 24.8 %, Do not was possible to determine these percentages by TGA.

2

Example of quantification using the TGA analysis.

The first event of temperature between 200 - 400 ° C for CAT-H2O can be assigned to the

decomposition of the goethite. [1].

2 FeO(OH )(s)→Fe2 O3(s)+H 2 O(g )(1)

According to the TGA 4.6 % of mass is loss as water (Figure 2), he following procedure was

used to determine the goethite content.

% FeO (OH )=4.6 g H 2 O100 gore

× 2 mol FeO (OH )1mol H 2O

× 88.852 gFeO (OH )1mol FeO (OH )

×1mol H2 O

18.0153 g H2O× 100

¿45.4 % FeO (OH ).

3

100 200 300 400 500 600

60

80

100

Wei

ght (

%)

Temperature (°C)

300 340 350 360 380

Figure S2. Thermogravimetric analysis for solids obtained from the modified iron ore, CAT-

OA, under CO atmosphere for 4h and at different temperatures.

The carburization profiles of the samples are shown in Figure S3. A higher CO2 signal is

observed at 350°C for the PRE-OA sample compared to PRE-H2O and PRE-Ox materials. In

agreement with the CO-TPR-MS, these results indicate that the oxalates prepared from the iron

ore react at lower temperatures compared with the iron ore that was treated only with water. It

must be noted that in the isothermal region, the signal for CO2 was present, indicating the

formation of iron carbides and carbonaceous material.

100 200 300

25 350 °C

CO

2 S

igna

(a.u

)

T (°C)

2 °C/min

40 80 120 160 200 240

Isotherm for 4 h 350 °C

PRE-OA

PRE-H2O

Time (min)

PRE-Ox

4

Figure S3: Signal for 44 amu of CO2 during the process of carburization at 350 °C using 90% CO + 10 % N2.

Figura S4.. Adsorption-desorption isotherms for the catalysts.

Tabla S2. Textural parameters of the catalysts.

Muestra BET (m2/g) Vp (cm3/g) Dp (nm)

CAT-H2O 42 0.11 10.4

CAT-OA 84 0.15 7.0

CAT-Ox 70 0.36 20.4

5

0 20 40 60 80 1000

20

40

60

80

100

0 20 40 60 80 1000

20

40

60

80

100

0 20 40 60 80 1000

20

40

60

80

100

S (%

)

Time (h)

a) CAT-H2O CO2

CH4

C2-C4

C+5

CO2

CH4

C2-C4

C+5

CO2

CH4

C2-C4

C+5

S (%

)

Time (h)

b) CAT-OA

e)

Time (h)

c) CAT-Ox d)

0 5 10 15 20 25 300

2

4

6

8

10

12

5 10 15 20 25

-4.0

-3.5

-3.0

-2.5

-2.0

ln (W

n/n)

Carbon number (n)

CAT-H2O,

CAT-ACAT-Ox

Carbon number (n)

C-m

ol (%

)

Figure S5. (a, b, c) hydrocarbon product selectivity graphs, (d, e) hydrocarbon distribution (CO2

free), ASF plot and chain growth probability between 50 - 100 of time on stream. The sum of C 1

- C30 products were 96 %, 92 % and 84 % for CAT-H2O CAT-OA and CAT-Ox respectively.

6

60 70 80 90 1000

20

40

60

80320 °C

Xco

(%)

Time on stream (h)

300 °C

Figure S6. Stability of CAT-OA at HTFT, test for 25 hours, GHSV 24 NL gcat-1 h-1.

The rate of reaction can be determined using the followed equation [2].

−rCO=FCO

0 XCO

W cat(S1)

Where W cat cat is the mass of catalyst and FCO0 is the inlet molar CO flow rate. Experimental rate

constant (k) values are determined for every data point from the rate data using of Equation S1

by assuming the PCO and PH2 dependencies. Values of PCO and PH2 are simple averages of the inlet

and outlet partial pressures of each gas [3].

k=−rCO

PC O−0.05 PH 2

0.6 (S2)

Activation energy and pre-exponential factor are regressed from k versus T data using the

Arrhenius relationship, (Equation S3).

7

k=A e−E A /RT (S3)

From the activity data in Table S5 for the CAT-OA catalyst and using the above equations an

apparent activation energy (Eap) of 54.7 kJ/mol is estimated, which is too low as compared to

those reported in the scientific literature (70-130 kJ/mol) [2]. This discrepancy could be due to

the fact that the activity data (iron-time-yield, FTY) which indicates the number of CO

molecules converted to hydrocarbons per gram of iron per second, explicitly excluding carbon

dioxide selectivity, does not consider the contribution of the water-gas shift reaction (WGS).

In this regard, Huff and Satterfield [4] have proposed a FTS rate equation where an inhibition

effect of water involved in the WGS reaction is considered on a fused iron catalyst, based on a

carbide mechanism as well as the enol/carbide mechanism. The results for higher CO conversion

deviate substantially because the FTS reaction highly depend on the hydrogen formed by the

WGS as the carbon monoxide conversion increases. Thus, the overall FTS reaction rate is highly

affected by the rate/extent of the WGS reaction at high FTS conversions. Therefore, in our case,

the estimation of an apparent activation energy is not adequate, because at these conditions the

WGS and other secondary reactions as readsorption of olefins play an important role. For the

adequate determination of an apparent activation energy it is more convenient to use activity data

obtained at low CO conversion [2].

Figure S7 shows the Mössbauer spectra for CAT-ox and CAT-OA obtained at 295 K. The

Mössbauer spectra shows a superposition of the three-sextets of the Fe sites, corresponding to the

8

spectrum of χ- Fe5C2 crystallography sites. The parameters obtained are in accord with the

reported in the scientific literature for the iron carbide [5]

Figure S7. Mössbauer spectra at 295 K, (a) CAT-Ox and (b) CAT-OA.

Table S3. Mössbauer parameters obtained for the iron carbide.

Site

χ-Fe5C2

CAT-Ox

I (8f) II (8f) III (4e) Fe

Hhf (T) 20.91 18.83 10.08 -

δ (mm/s) 0.18 0.05 0.16 -

EQ (mm/s) 0.01 0.16 0.02 -

Area (%) 36.3 32.1 31.7 -

CAT-OA

Hhf (KOe) 21.36 17.64 10.07 0.75

δ (mm/s) 0.15 0.02 0.19 0.63

9

EQ (mm/s) 0.01 0.10 0.03 -

Area (%) 30.56 26.19 38.45 4.80

Hhf: hyperfine magnetic field; δ: isomer shift (all the isomer shifts are referred to α-Fe at 295K); EQ: quadrupole shift.

Figure S8. TGA for oxalic acid

Evaluation of possible diffusional problems

To ensure that the reactor was operated in the absence of diffusional problems, reactions were

carried out with different catalyst loading, 50 mg and 100 mg, with different amount of quartz

sand to dilute the catalyst, 100 mg of catalyst with 1 and 2 grams of sand were used, without

finding significant differences in the conversion (Table S3). To obtain reliable data, the syngas

flow was changed every 25 hours.

10

Table S4. Reactions with different catalyst loading to ensure that the reactions were carried out

without difucionales problems, tests carried out with the iron ore modified CAT-OA.

Catalyst 50 mg Catalyst 100 mgGHSV (NL gcat

-1 h-1)F (mL/min) XCO (%) F (mL/min) XCO (%)

10 66.0 20 65.3 12

15 48.8 30 48.8 18

20 41.7 40 39.5 24

30 30.2 60 30.1 36

Table S5. Comparison of the CO conversion, FTS activity and selectivity of CAT-OA catalyst

with those found in the literature for Fe in FTS reactions.

CatalystGHSV

(NL∙gcat-1∙h-1)

XCO

(%)T

(°C) FTY* CH4 C5+ CO2 Ref.

CAT-OA

(Precursor, iron ore)

12 65.3 280 0.42 10 63 37 This work

18 48.8 280 0.50 11 61 34

24 39.6 280 0.56 11.8 61.7 31

36 30.2 280 0.68 15 55 27

24 71.0 300 0.87 17 50 42

24 78.3 320 0.93 22 45 45

CAT-H2O, (Precursor, iron ore)

12 46.5 280 0.36 11.7 62.4 30

CAT-Ox, (Precursor

12 88.8 280 0.42 9.2 66.0 42.3

11

(FeC2O4·2H2O)

Comercial-Fe2O3 12 88.3 280 0.41 9.1 62.8 41.3

Fe-MIL-88B 36 33.8 300 1.5 11.5 63.4 33.7

[6]Fe-MIL-88B-NH2/C

Fe3O4@Fe5C2

36 81.8 300 3.2 15.1 50.7 42.9

36 13.1 270 0.77 13.1 53.4 16

Fe2O3@MnO2, 9% 3 86 280 0.12 8.9 66.6 40.5

[7]Fe2O3@MnO2, 10 % 3 89.9 280 0.12 16.8 62.6 41.8

Fe2O3 (Mn-free) 3 98.9 280 0.13 16.8 47.4 43.9

Fe/g-C3N4, LUDOX, χ-Fe5C2

9 77.86 340 2.41 4.8 74.28 35.04[8]

Fe/g-C3N4, χ-Fe5C2 9 96.49 340 3.09 11.1 66.7 33.42

FNS (spheres) 3 70.47 280 0.05 7.72 64.23 39.36

[9]FNP (polyhedrons) 3 42.48 280 0.033 10.5 54.32 33.06

Fe (precipitated) 3 37.1 280 0.029 20.7 40.11 32.61

*FTY: molCO gFe-1 s-1 x 10-4

References

[1] S. Song, F. Jia, C. Peng, Surf. Rev. Lett. 21 (2014) 1450019.

[2] M.K. Albretsen, B. Huang, K. Keyvanloo, B.F. Woodfield, C.H. Bartholomew, M.D.

Argyle, W.C. Hecker, J. Nanomater. 2017 (2017).

[3] K.M. Brunner, PhD Thesis. Brigham Young University, (2012).

[4] G.A. Huff, C.N. Satterfield, Ind. Eng. Chem. Process Des. Dev. 23 (1984) 696–705.

[5] S.Y. Hong, D.H. Chun, J. Il Yang, H. Jung, H.T. Lee, S. Hong, S. Jang, J.T. Lim, C.S.

12

Kim, J.C. Park, Nanoscale 7 (2015) 16616–16620.

[6] B. An, K. Cheng, C. Wang, Y. Wang, W. Lin, ACS Catal. 6 (2016) 3610–3618.

[7] Y. Zhang, L. Ma, T. Wang, X. Li, Fuel 177 (2016) 197–205.

[8] H. Park, D.H. Youn, J.Y. Kim, W.Y. Kim, Y.H. Choi, Y.H. Lee, S.H. Choi, J.S. Lee,

ChemCatChem 7 (2015) 3488–3494.

[9] J. Tu, M. Ding, Y. Zhang, Y. Li, T. Wang, L. Ma, C. Wang, X. Li, Catal. Commun. 59

(2015) 211–215.

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