Iron Oxide as a Catalyst for Nitroarene Hydrogenation: Important Role

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Iron Oxide as Catalyst for Nitroarenes Hydrogenation: the Important Role of Oxygen Vacancies Hongling Niu, Jinhui Lu, Jiajia Song, Lun Pan, Xiangwen Zhang, Li Wang, and Ji-Jun Zou Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00984 • Publication Date (Web): 01 May 2016 Downloaded from http://pubs.acs.org on May 22, 2016

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Industrial & Engineering Chemistry Research

1

Iron Oxide as Catalyst for Nitroarenes Hydrogenation: the

2

Important Role of Oxygen Vacancies

3

Hongling Niua,b, Jinhui Lua,b, JiaJia Songa,b, Lun Pana,b, Xiangwen Zhanga,b, Li Wanga,b,

4

Ji-Jun Zoua,b,*

5

a

6

of Chemical Engineering and Technology, Tianjin University, China

7

b

8

Tianjin 300072, China

9

*[email protected]; Tel. and fax: 86-22-27892340.

10

Key Laboratory for Green Chemical Technology of the Ministry of Education, School

Collaborative Innovative Center of Chemical Science and Engineering (Tianjin),

Abstract

11

Heterogeneous catalytic hydrogenation of nitroarenes is one of the most important

12

chemical transformations, and exploring earth-abundant catalyst is very attractive for

13

application. Herein, we studied the catalytic activity of several iron oxide catalysts with

14

similar structure and surface area. It is found that γ-Fe2O3, α-Fe2O3 and FeO show

15

obvious but a little limited activity, but the activity of used catalyst is increased in the

16

second run, especially for γ-Fe2O3. Characterization shows the Fe2O3 is partly reduced

17

with many oxygen vacancies produced on the surface, which accounts for the high

18

hydrogenation activity. Finally, Fe3O4 exhibits activity significantly higher than Fe2O3

19

and FeO, and 100% selectivity in the hydrogenation of nitroarenes to anilines. Also

20

Fe3O4 is easy to separate by magnetic field and shows excellent recycling stability.

21

KEYWORDS: heterogeneous catalysis, nitroarenes hydrogenation, oxygen vacancy,

22

iron oxide 1

ACS Paragon Plus Environment


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1

1. Introduction

2

Hydrogenation is one of the most valuable synthetic transformations, in petroleum

3

refining and processing and the manufacture of fine and bulk chemicals1−4. In particular,

4

the hydrogenation of substituted nitroarenes to the corresponding anilines is of great

5

importance because anilines are among the most important organic intermediates

6

necessary for the manufacture of many valuable products such as dyestuffs,

7

pharmaceuticals, and agricultural chemicals5,6. A significant number of investigations

8

have been devoted to creating new multifunctional catalysts for the efficient

9

hydrogenation of nitrobenzenes7,8. Indeed, aromatic nitro compounds can be

10

hydrogenated by Pt9, Pd10, Rh11 and Pd@Au12 catalysts. However, when the substrates

11

contain other reactive groups, such as ketones, aldehydes, alkenes or alkynes, the

12

selective reduction of -NO2 becomes particularly difficult7,13,14. Moreover, the high

13

price and limited availability of these precious metals have spurred interest in catalysts

14

with more earth-abundant alternatives.

15

Recently, an important breakthrough came from the group of Beller who disclosed a

16

heterogeneous Co3O4 and Fe2O3-based catalyst that could selectively hydrogenate nitro

17

compounds with a number of functional groups15,16. The formed CoNx(FeNx)/C centers

18

are regarded as the unique catalytic active sites. It is also reported that TaOxNy is an

19

efficient catalyst for the reduction of nitroarenes, where the doped nitrogen species and

20

oxygen vacancies are found to play the crucial roles in the reduction of nitrobenzenes17.

21

More recently, we reported oxygen-deficient tungsten oxide is a versatile and efficient

22

catalyst for the hydrogenation of nitroarenes and catalytic activity is closely related to 2


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1

the concentration of oxygen vacancies18,19. Actually, oxygen vacancies in metal oxide

2

act as shallow donors that can improve the electrical conductivity and donor density

3

and thus enhance the surface species (such as H2 and CO2) adsorption20, suggesting

4

great potential in H2 activation and subsequent hydrogenation. The presence of oxygen

5

vacancy also changes the manner of H2 dissociation, with one dissociated H atom

6

binding with a surface metal atom and the other with a bridge O atom18.

7

Encouraged by recent investigations on the use of iron-based catalysts15,21, we

8

investigated the hydrogenation performance of pure iron oxide materials to avoid the

9

effect of support materials. Our work suggests that oxygen vacancies play a crucial role

10

in the hydrogenation. In particular, Fe3O4 shows good activity and perfect selectivity

11

and stability in catalytic hydrogenation of nitroarenes.

12

2. Experimental section

13

2.1 Materials

14

Iron chloride hexahydrate (FeCl3·6H2O) and urea (99%) were obtained from Tianjin

15

Guangfu Fine Chemical Research Institute. Ethylene glycol was purchased from

16

Tianjin Jiangtian Chemical Technology Co., China. Tetrabutylammonium bromide

17

(98%) and tetrahydrofuran (99%) was obtained from Tianjin Xiensi Biochemistry

18

Technology Co. Ltd. 4-Chloronitrobenzene (99%), 4-nitrobenzaldehyde (99%), 4-

19

nitrobenzoic acid (99%), 4-nitrotoluene (99%), 4-nitrophenol and phenylacetylene

20

(99%) was purchased from J&K Chemical Co., China. Nitrobenzene (99%) was

21

obtained from Shanghai Crystal Pure Reagent Co., China. Analytical grade iron (II)

22

oxalate dehydrate (FeC2O4·2H2O) was purchased from Tianjin Kemiou Chemical 3



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1

Reagent Co. Ltd. All chemicals were used without further purification.

2

2.2 Synthesis of catalyst

3

Fe3O4, γ-Fe2O3 and α-Fe2O3 were synthesized according to literature 22. In a typical

4

procedure, 1.2 g of FeCl3·6H2O, 2.7 g of urea, and 7.2 g of tetrabutylammonium

5

bromide were stirred in 180 mL of ethylene glycol in a 250 mL round flask for 2 h at

6

room temperature. Then, the solution was refluxed at 195 °C for 30 min and the mixture

7

was cooled to room temperature. The green precipitate was collected by centrifugation，

8

washed with ethanol 4 times, and finally dried at 60 °C overnight. Finally, the

9

precipitates were calcined at 450 °C for 3 h in air with a heating rate of 5 °C/min to

10

obtain red α-Fe2O3 powders, and calcined at 450 °C for 3 h under N2 protection to obtain

11

black Fe3O4 powers, respectively. Furthermore, the as-obtained Fe3O4 was heated at

12

250 °C in air for 5 h to obtain red-brown γ-Fe2O3 powders. FeO catalyst was

13

synthesized by calcining FeC2O4·2H2O in a N2 gas stream at 650 °C for 1 h and further

14

reduced under a H2 gas stream at 750 °C for 15 min23.

15

2.3 Characterizations

16

X-ray diffraction (XRD) patterns were recorded with a Bruker D8 Focus operated at

17

40 kV and 40 mA equipped with a nickel-filtered Cu Kα radiation (λ=1.54056 A). SEM

18

images were obtained using a Hitachi S-4800 SEM. TEM and HRTEM images were

19

obtained using a JEM-2100Ftransmission electron microscope at 200 kV. X-ray

20

photoelectron spectroscopy (XPS) analysis were carried out on a Physical Electronics

21

PHI 1600 ESCA system operated at a pass energy of 187.85 eV for survey spectra with

22

an Al Kα X-ray source (E=1486.6 eV), and all the binding energies of the composing 4


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1

elements were referenced to the C1s peak at 284.6 eV arising from contamination

2

carbon. BET surface area was measured using N2 adsorption/desorption isotherm

3

measurements at -196°C on a Micrometrics TriStar 3000 equipment. Raman spectra

4

were obtained in a backscattering configuration at room temperature using a Renishaw

5

InVia reflex Raman spectrometer. A He-Ne laser at 633nm was used as the excitation

6

source. Oxygen storage capacity (OSC) measurements were carried out in a TGA-50

7

Instruments according to literature24. The samples were pretreated in Ar at 423 K for 1

8

h and then heated up to 473 K with heating rate of 5 K min-1. At this temperature, the

9

gas was switched to 5 vol % H2/Ar and maintained for 60 min to measure the weight

10

loss.

11

2.4 Catalytic hydrogenation

12

All hydrogenation reactions were tested in 100 mL autoclaves (PARR Instrument

13

Company). After 2 mmol of substrate, 0.15 g of catalyst and 20 mL water-THF (1:1)

14

solvent were mixed and sealed in, the autoclave was flushed with nitrogen twice at 50

15

bar and then pressurized to 30 bar hydrogen pressure. The autoclave was heated using

16

a surrounding oven, and the temperature was controlled using a PID temperature

17

controller. The reaction was conducted under mechanically agitation of 600 rpm.

18

Reactant solution was withdrawn at intervals and centrifuged for analysis. Reaction

19

intermediate

20

chromatography/5975N mass spectrometry (GC/MS) equipped with HP-5 capillary

21

column (30 m × 0.5 mm). Quantitative analysis was made by Agilent 7890A gas

22

chromatography equipped with FID detector and AT-SE-54 capillary column (50m ×

and

product

were

identified

using

5


Agilent

6890N

gas


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1

0.32 mm). The carbon balance was estimated using cyclohexane as internal standard

2

substance is > 99%, also the carbon deposited on used catalyst is less than 0.8% as

3

determined by thermo gravimetric analysis.

4

3. Results and Discussion

5

3.1. Structure of iron oxide

6

The XRD patterns in Figure 1 show that the synthesized Fe3O4, γ-Fe2O3, α-Fe2O3

7

and FeO are monoclinic phase, the diffraction peaks match well with those of Fe3O4

8

(Magnetite, JCPDS 19-0629), γ-Fe2O3 (Maghemite, JCPDS 39-1346), α-Fe2O3

9

(Hematite, JCPDS 33-0664) and FeO (Wustite, JCPDS 06-0615), respectively. The

10

averaged particle size was calculated according to Scherrer equation by using

11

parameters reported in literature25 is 18, 24, 25 and 34 nm for Fe3O4, γ-Fe2O3, α-Fe2O3

12

and FeO, respectively. From XRD it is hard to discriminate γ-Fe2O3 and Fe3O4, so

13

Raman spectra were recorded for these samples. Figure 2 shows the Raman spectra of

14

these oxides is agreed with reported results26,27, indicative the high purity of the

15

synthesized oxides. Specifically, Fe3O4 shows a characteristic peak at 660 cm-1 but α-

16

Fe2O3 and γ-Fe2O3 do not have this one.

17 18

6


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311

220

200

104 110

214 300

018

116

024

FeO 113

012

used FeO

-Fe2O3

440

422 511

400

311 222

200

210

111

used -Fe2O3

-Fe2O3

440

511

422

400

200

311 222

used -Fe2O3 111

Intensity (a.u.)

used Fe3O4 Fe3O4

20

30

2

40

50

60

70

2Theta (degree)

1

Figure 1. XRD patterns of fresh and used iron oxides. 660

used Fe3O4

Intensituy (a.u.)

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111

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Fe3O4 used -Fe2O3

215 280

-Fe2O3

298 230

414 499

614

used -Fe2O3 -Fe2O3

200 3 4

400

600

-1

800

1000

Wavenumber (cm ) Figure 2. Raman spectra of fresh and used iron oxides.

5

Figure 3 shows the SEM, TEM and HRTEM images of as-prepared iron oxides. SEM

6

images show Fe3O4, γ-Fe2O3 and α-Fe2O3 have similar flowerlike architectures with 7



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1

approximately 4 μm diameter and FeO is particle of several micrometers. TEM images

2

show the nanopetals of the flowerlike architecture are built by many nanoparticles

3

ranging from 15 to 25 nm, which is consistent with the XRD result. HRTEM images in

4

the insets of Figure 3 show Fe3O4, γ-Fe2O3, α-Fe2O3 and FeO is exposed with 311, 311,

5

110, and 200 plane, respectively. The BET surface area of the synthesized Fe3O4, γ-

6

Fe2O3, α-Fe2O3 and FeO are 73.2, 85.4, 80.3 and 32.9 m2/g, respectively.

7 8 9

Figure 3. SEM, TEM and HRTEM images of iron oxides. 3.2 Hydrogenation activity and surface change of iron oxides 8


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1

We tested the activity of γ-Fe2O3, α-Fe2O3 and FeO for hydrogenation of

2

nitrobenzene. Figure 4a shows that γ-Fe2O3, α-Fe2O3 and FeO all exhibit some activity,

3

although the activity is not very high. Among the three catalysts, γ-Fe2O3 performs best,

4

with the conversion reaching 15% in 10 h. Surprisingly Fe3O4 is much more active in

5

the hydrogenation of nitrobenzene, with almost 100% conversion in 6 h. 25

100

a)

Fe2O3 Fe2O3

15

60

10

40

5

20

2nd run

2

4

8

10

Time (h)

6 -2

0.5

b)

2

4

6

8

10

1st run 2nd run

2.5

0.4

2.0

0.3

1.5

0.2

1.0

0.1

0.5

0.0

7

6

-2

1st run 0

-Fe2O3

FeO

Conversion (%)

80

FeO Fe3O4

-Fe2O3

Normalized activity (g·mmol·m )

Conversion (%)

20


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Fe3O4

0.0

8

Figure 4. Catalytic performance of Fe2O3, FeO and Fe3O4. (a) Conversion of

9

nitrobenzene at 150 °C, (b) Normalized activity.

10

Although the bulk crystal structure of used γ-Fe2O3 is not changed as verified by

11

XRD analysis (Figure 1), it is noted that the red-brown γ-Fe2O3 changes to black,

12

indicating the surface of γ-Fe2O3 particles is partly reduced during the reaction. On the 9



1

contrary, α-Fe2O3 and FeO are relatively stable and still remain its original color after

2

the reaction, and XRD also confirms the bulk crystal structures of them are not changed

3

(Figure 1). Actually, FeO is hardly reduced at temperature below 350 °C28. Moreover,

4

the Fe 3p XPS spectra in Figure 5 shows that some surface Fe3+ ions in Fe2O3 have been

5

reduced to Fe2+. Fe2+ makes up 18% and 12% of Fe element in the used γ-Fe2O3 and α-

6

Fe2O3, respectively. This clearly shows that the surface of Fe2O3 is partly reduced in

7

the hydrogenation reaction, and γ-Fe2O3 is easier to be reduced than α-Fe2O3. In

8

particular, XPS spectrum shows Fe3O4 is easier to reduce, with the percentage of Fe2+

9

increasing from 32.3% to 47.6%. -Fe2O3

a)

used -Fe2O3

b)

3+

64

62

60

3+

Fe 81.8%

Intensity (a.u.)

Intensity (a.u.)

Fe

58

56

54

52

50

2+

Fe 18.2%

64

62

60

10

56

54

52

50

used -Fe2O3

d)

-Fe2O3

c)

58

Binding energy (eV)

Binding energy (eV)

3+

Fe 87.7%

3+

Intensity (a.u.)

Fe

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 34

64

11

62

60

58

56

54

52

2+

Fe 12.3%

64

50

Binding energy (eV)

62

60

58

56

Binding energy (eV)

10


54

52

50

Page 11 of 34

e)

Fe3O4

f)

used Fe3O4

Intensity (a.u.)

3+

2+

Fe 32.3%

64

62

60

58

56

3+

Fe 52.4%

Intensity (a.u.)

Fe 67.7%

54

52

2+

Fe 47.6%

50

64

62

60

58

56

54

52

50

Binding energy (eV)

Binding energy (eV)

1

FeO

g)

h)

used FeO

2+

Fe

2+

Fe

Intensity (a.u.)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


64

62

60

58

56

54

52

64

50

62

2

60

58

56

54

52

50

Binding energy (eV)

Binding energy (eV)

Figure 5. Fitted Fe 3p XPS spectra of fresh and used iron oxides.

3 4

Oxygen storage capacity (OSC) is a widely used method to evaluate the reducible

5

capability of oxides24. Table 1 shows the loss weight in H2 at 473 K is associated with

6

total oxygen storage at this temperature, in the order of Fe3O4 > γ-Fe2O3 > α-Fe2O3 >

7

FeO. Interestingly, this is not only consistent with the reduction degree catalyst after

8

the reaction but also agrees with the catalytic activity of hydrogenation. Table 1. Oxygen storage capacity of iron oxides

9

Sample

SBET[m2 g-1]

Loss weight[%]

OSC[μmol O m-2]

Fe3O4

73.2

0.0913

0.768

γ-Fe2O3

85.4

0.0625

0.457

α-Fe2O3

80.3

0.0512

0.398

11



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FeO

32.9

0.0193

Page 12 of 34

0.366

1 2

3.3 Formation of oxygen vacancies and its effect on hydrogenation

3

It should be noted that, the reduction of Fe2O3 may produce some Fe3O4 on the

4

surface, and Fe3O4 may produces some FeO nanoparticles that can not be detected by

5

XRD analysis. However, in Raman spectra (Figure 2) there is no any peak referring to

6

Fe3O4 are found on the used Fe2O3, and the used Fe3O4 does not show additional peaks

7

except the characteristic peak at 660 cm-1. This result excludes the formation of

8

separated reduced phase in the used catalyst. Therefore, it can be safely said that the

9

reduction of catalyst surface during the catalytic reaction neither changes the bulk

10

structure nor produces new surface phase. It is most likely that the reduction cause the

11

formation of oxygen vacancies via the process of 2Fe3+ + O2− + H2 → 2Fe2+ + VO +

12

H2O, wherein O2 − is lattice oxygen and VO is oxygen vacancy. The formation of

13

vacancies may cause the slight change of the local structure. Actually, the XRD patterns

14

of used catalyst are shifted slightly relatively to the fresh counterpart. Table 2 shows

15

the lattice parameters of the used catalysts are increased to some degree, suggesting the

16

formation of lattice distortion caused by oxygen vacancies. Table 2. Lattice parameters of fresh and used iron oxides

17

sample

a (Å)

b (Å)

Fe3O4

8.387

8.387

8.387

used Fe3O4

8.396

8.396

8.396

γ-Fe2O3

8.373

8.373

8.373

used γ-Fe2O3

8.393

8.393

8.393

α-Fe2O3

5.038

5.038

13.790

12


c (Å)

Page 13 of 34

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used α-Fe2O3

5.042

5.042

13.801

FeO

4.310

4.310

4.310

used FeO

4.312

4.312

4.312

1

To see if the partly reduced surface has some effect on the hydrogenation activity,

2

we tested the activity of the used catalysts (Figure 4a). Interestingly, compared with the

3

fresh catalyst, the activity is increased 31.4% for γ-Fe2O3, 14.2% for α-Fe2O3 and 11.1%

4

for FeO, respectively. A comparison between γ-Fe2O3 and α-Fe2O3 shows that the

5

higher degree of reduction, the more improvement in the activity. We also calculated

6

the normalized activity to eliminate the effect of surface area (Figure 4b). It is noted

7

that γ-Fe2O3 shows slightly lower normalized activity than FeO in the first run, but

8

become more active in the second run. The improvement of hydrogenation activity is

9

more likely attributed to the presence of oxygen vacancies or Ov-Fe2+ pair in the lattice,

10

rather than the sole presence of Fe2+ ions. From the viewpoint of solid-state physics,

11

intrinsic defect centers such as oxygen vacancies are the most common defect in metal

12

oxides. The presence of O vacancies leads to an increase in the adsorption energy of H2

13

and substantially lowers the energy barrier associated with the cleavage of the H-H

14

bond19,29.

15

Fe3O4 is oxygen-deficient naturally and is composed of Fe3+ and Fe2+ in the

16

stoichiometry with the 33.3 % of Fe2+, and has very similar crystal structure to γ-Fe2O3.

17

So we can safely regard Fe3O4 as a highly reduced γ-Fe2O3 from surface to bulk. This

18

explains why it has very good performance even in the first run. Although its surface is

19

also reduced after the first run, the activity in the 2rd run does not increase significantly

20

(Figure 4), hinting that an optimal concentration of oxygen vacancies exists. It is also 13



1

noted that the catalyst is slightly aggregated after the reaction, as shown by the reduced

2

surface area of 65.0 m2/g.

3

3.4 Hydrogenation performance of Fe3O4

4

Considering the excellent performance of Fe3O4, we investigated it in more details

5

to show its potential in application. From the Figure 6a, almost 100% conversion is

6

obtained in 6 h at 150 °C, and at lower temperature (110, 120 and 135 °C) the activity

7

decreased correspondingly. In all temperature tested, the reaction follows the pseudo-

8

zero-order reaction kinetic, see the linear plot of conversion verse t (Figure 6a). From

9

the linear fit of the Arrhenius plot (ln k vs 1000/T) (Figure 6b), the apparent activation energy (Ea) is calculated to be 102.0 ±11 kJ/mol. 100

a -2

150C

-3

60 120C 40 20

Equation Adj. R-Square

-4

110C

-5

0 0

11

b)

135C

80

ln k

10

Conversion(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 34

5

10

15

20

y = a + b*x 0.97019

0.98084 Value

Intercept

0.01519

0.00275

135

Slope

0.03223

9.49147E-4

120

Intercept

120

Slope

150

Intercept

150

Slope

0.16281

0.00476

110

Intercept

0.01074

7.73335E-4

110

Slope

0.00513

2.1371E-4

0.01649

0.00172

0.01634

5.1026E-4

-0.00135

2.4

25

0.96727

Time/h

0.93669

Standard Error

135

0.00251

2.5

1000/T

2.6

2.7

12

Figure 6. (a) Catalytic activity of Fe3O4 at different temperature in nitrobenzene

13

hydrogenation (b) The Arrhenius plot.

14

Plentiful efforts have been devoted to chemoselective reduction of a nitro group to

15

amino group because it is very important for the synthesis of organic compounds,

16

especially the macromolecules of pharmaceutical intermediates. Fe3O4 also exhibits

17

good catalytic activity in the hydrogenation of several aromatic nitro compounds. When

18

prolonging the reaction time or increasing the reaction temperature, the conversion of 14


Page 15 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

the nitro compounds is in the range from 90 to 98% (Table 3). Moreover, Fe3O4

2

selectively hydrogenates the nitro to amino groups whereas all the other groups (CHO,

3

OH, Cl, CH3, COOH) on the same benzene ring are well-retained. This shows that

4

Fe3O4 is a very good catalyst for selective hydrogenation of substituted nitroarenes.

5

Table 3. Activity of Fe3O4 in the hydrogenation of substituted nitroarenes.

Substrate

NO2

Conversion

Selectivity

conditions

[%]

[%]

120°C, 15h

98

73.7

Product

NH2

COOH

COOH

NO 2

NH2

CH3

CH3

NO2

NH2

OH

OH

NO2

NH2

Cl

Reaction

150°C, 15h

95

100

150°C, 15h

91

100

150°C, 15h

98

100

150°C, 15h

90

100

Cl

15



NO2

NH2

150°C, 15h CHO

93

100

CHO

1

Furthermore, we tested the recycling performance of Fe3O4 and found it performs

2

very stably in the recycling experiment, with activity loss < 10% in five runs and

3

selectivity of almost 100% (Figure 7). In addition, the catalysts particles are easily

4

separated from liquid by an external magnetic field, which is very convenient to recycle

5

and reuse. 100

80

80

60

60

40

40

20

20

0

0 1

6 7 8

Selectivity (%)

100

Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 34

2

3

Time of runs

4

5

Figure 7. Recycling performance of Fe3O4 in nitrobenzene hydrogenation. 4. Conclusion

9

We reported oxygen-deficient iron oxide is very active catalyst for hydrogenation of

10

nitroarenes. Oxygen vacancies were found to play the critical roles in the hydrogenation

11

of nitroarenes. Specifically, Fe3O4 shows a high activity and gives 100 % selectivity in

12

the hydrogenation of nitroarenes to anilines, which provides an earth-abundant, easily

13

synthesized, and low cost catalyst for industrial application. This work emphasizes the

14

role of oxygen vacancy in hydrogenation and suggests many cheap metal oxides may 16


Page 17 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

be made as hydrogenation catalyst through defect engineering.

2

Acknowledgements

3

The authors appreciate the support from the National Natural Science Foundation of

4

China (U1462119).

5 6

References

7

(1) Kyriakou, G.; Boucher, M. B.; Jewell, A. D.; Lewis, E. A.; Lawton, T. J.; Baber, A.

8

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Geometries as a Strategy for Selective Heterogeneous Hydrogenations. Science 2012,

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(2) Studt, F.; Abild-Pedersen, F.; Bligaard, T.; Sørensen, R. Z.; Christensen, C. H.;

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Nørskov, J. K. Identification of Non-Precious Metal Alloy Catalysts for Selective

13

Hydrogenation of Acetylene. Science 2008, 320, 1320.

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Hydrogenation of Halonitrobenzenes. Ind. Eng. Chem. Res. 2014, 53, 4589.

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Solvent-Free Selective Hydrogenation of Nitrobenzene to Aniline: an Unexpected

8

Catalytic Activity of Ultrafine Pt Nanoparticles Deposited on Carbon Nanotubes. Green

9

Chem. 2010, 12, 1007.

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(10) Watt, J.; Cheong, S.; Toney, M. F.; Ingham, B.; Cookson, J.; Bishop, P. T.; Tilley,

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R. D. Ultrafast Growth of Highly Branched Palladium Nanostructures for Catalysis.

12

ACS Nano 2009, 4, 396.

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(11) Furukawa, S.; Yoshida, Y.; Komatsu, T. Chemoselective Hydrogenation of

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Nitrostyrene to Aminostyrene over Pd-and Rh-Based Intermetallic Compounds. ACS

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Catal. 2014, 4, 1441.

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(12) Zhao, R.; Gong, M.; Zhu, H.; Chen, Y.; Tang, Y.-W.; Lu, T.-H. Seed-Assisted

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Synthesis of Pd@Au Core-Shell Nanotetrapods and Their Optical and Catalytic

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Properties. Nanoscale 2014, 6, 9273.

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(13) Cárdenas-Lizana, F.; Gómez-Quero, S.; Hugon, A.; Delannoy, L.; Louis, C.; Keane,

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M. A. Pd-Promoted Selective Gas Phase Hydrogenation of p-Chloronitrobenzene over

21

Alumina Supported Au. J. Catal. 2009, 262, 235.

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(14) Pei, Y.; Zhou, G.; Luan, N.; Zong, B.-N.; Qiao, M.-H.; Tao, F.-F. Synthesis and 18


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Catalysis of Chemically Reduced Metal-Metalloid Amorphous Alloys. Chem. Soc. Rev.

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2012, 41, 8140.

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(15) Jagadeesh, R. V.; Surkus, A. E.; Junge, H.; Pohl, M. M.; Radnik, J.; Rabeah,

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J.;Huan, H.; Schünemann, V.; Brückner, A.; Beller, M. Nanoscale Fe2O3-Based

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Catalysts for Selective Hydrogenation of Nitroarenes to Anilines. Science 2013, 342,

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Surkus, A. E.; Rabeah, J.; Junge, K.; Junge, H.; Nielsen, M.; Brückner, A.; Beller, M.

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Heterogenized Cobalt Oxide Catalysts for Nitroarene Reduction by Pyrolysis of

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Molecularly Defined Complexes. Nat. Chem. 2013, 5, 537.

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(17) Su, Y.; Lang, J.; Li, L.; Guan, K.; Du, C.-F.; Peng, L.-M.; Han, D.; Wang, X.-J.

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Unexpected Catalytic Performance in Silent Tantalum Oxide through Nitridation and

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Defect Chemistry. J. Am. Chem. Soc. 2013, 135, 11433.

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(18) Song, J.; Huang, Z.-F.; Pan, L.; Zou, J.-J.; Zhang, X.-W.; Wang, Li. Oxygen-

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Deficient Tungsten Oxide as Versatile and Efficient Hydrogenation Catalyst. ACS Catal.

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2015, 5, 6594.

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(19) Lu, J.-H.; Song, J.-J.; Niu, H.-L.; Pan, L.; Zhang, X.-W.; Wang, L.; Zou, J.-J.

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Periodic Density Functional Theory Study of Ethylene Hydrogenation over Co3O4 (111)

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Surface: the Critical Role of Oxygen Vacancies. Appl. Surf. Sci. 2016, 371, 61.

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(20) Huang, Z.-F.; Song, J.; Pan, L.; Zhang, X.-W.; Wang, L.; Zou, J.-J. Tungsten

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Oxides for Photocatalysis, Electrochemistry, and Phototherapy. Adv. Mater. 2015, 27,

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5309. 19



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(21) MacNair, A. J.; Tran, M.; Nelson, J. E.; Sloan, G. U.; Ironmonger, A.; Thomas, S.

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P. Iron-Catalysed, General and Operationally Simple Formal Hydrogenation Using Fe

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(OTf)3 and NaBH4. Org. Biomol. Chem. 2014, 12, 5082.

4

(22) Zhong, L.-S.; Hu, J.-S.; Liang, H.-P.; Cao, A.-M.; Song, W.-G.; Wan, L.-J. Self-

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Assembled 3D Flowerlike Iron Oxide Nanostructures and Their Application in Water

6

Treatment. Adv. Mater. 2006, 18, 2426.

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Molten Salt Using FeO Catalyst. Sol. Energy 2002, 72, 243.

9

(24) Vilé, G.; Colussi, S.; Krumeich, F.; Trovarelli, A.; Pérez-Ramírez, J. Opposite Face

10

Sensitivity of CeO2 in Hydrogenation and Oxidation Catalysis. Angew. Chem., Int.

11

Ed. 2014, 53, 12069.

12

(25) Monshi, A.; Foroughi, M. R.; Monshi, M. R. Modified Scherrer Equation to

13

Estimate More Accurately Nano-Crystallite Size Using XRD. World J. Nano Sci. Eng.

14

2012, 2, 154.

15

(26) Xu, J.-S.; Zhu, Y.-J. Monodisperse Fe3O4 and γ-Fe2O3 Magnetic Mesoporous

16

Microspheres as Anode Materials for Lithium-Ion Batteries. ACS Appl. Mater.

17

Interfaces 2012, 4, 4752.

18

(27) De Faria, D. L. A.; Lopes, F. N. Heated Goethite and Natural Hematite: Can Raman

19

Spectroscopy Be Used to Differentiate Them? Vib. Spectrosc. 2007, 45, 117.

20

(28) Jozwiak, W. K.; Kaczmarek, E.; Maniecki, T. P.; Ignaczak, W.; Maniukiewicz, W.

21

Reduction Behavior of Iron Oxides in Hydrogen and Carbon Monoxide Atmospheres.

22

Appl. Catal., A 2007, 326, 17. 20


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1

(29) Vilé, G.; Bridier, B.; Wichert, J.; Pérez-Ramírez, J. Ceria in Hydrogenation

2

Catalysis: High Selectivity in the Conversion of Alkynes to Olefins. Angew. Chem., Int.

3

Ed. 2012, 51, 8620.

4 5

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Figure Captions

2

Figure 1. XRD patterns of fresh and used iron oxides.

3

Figure 2. Raman spectra of fresh and used iron oxides.

4

Figure 3. SEM, TEM and HRTEM images of iron oxides.

5


6


7


8


9


10

Figure 7. Recycling performance of Fe3O4 in nitrobenzene hydrogenation.

11 12

Table Captions

13

Table 1. Oxygen storage capacity of iron oxides.

14

Table 2. Lattice parameters of fresh and used iron oxides.

15


16 17

22


Page 22 of 34

311

220

200

104 110

214 300

018

116

024

FeO 113

012

used FeO

440

422 511

400

311 222

200

210

111


440

511

422

400

311 222

200

used -Fe2O3 111

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


111

Page 23 of 34

-Fe2O3

used Fe3O4 Fe3O4

20 1 2

30

40

50

60

70

2Theta (degree) Figure 1. XRD patterns of fresh and used iron oxides.

3

23



660

used Fe3O4

Intensituy (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34

Fe3O4 used -Fe2O3

215 280

-Fe2O3

298 230

414 499

614


200 1 2

400

600

-1

800

1000

Wavenumber (cm ) Figure 2. Raman spectra of fresh and used iron oxides.

24


Page 25 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3


Figure 3. SEM, TEM and HRTEM images of iron oxides.

25



25

100

a)

Fe2O3 Fe2O3

15

60

10

40

5

20

2nd run

2

4

8

10

Time (h)

1 -2

0.5

b)

2

4

6

8

10

1st run 2nd run

2.5

0.4

2.0

0.3

1.5

0.2

1.0

0.1

0.5

0.0

2

6

-2

1st run 0

-Fe2O3

FeO

Conversion (%)

80

FeO Fe3O4

-Fe2O3


Conversion (%)

20


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 34

Fe3O4

0.0

3


4


5

26


Page 27 of 34

-Fe2O3

a)

used -Fe2O3

b)

3+

64

62

60

3+

Fe 81.8%

Intensity (a.u.)

Intensity (a.u.)

Fe

58

56

54

52

50

2+

Fe 18.2%

64

62

60

1

56

54

52

50

used -Fe2O3

d)

-Fe2O3

c)

58

Binding energy (eV)

Binding energy (eV)

3+

Fe 87.7%

3+

Intensity (a.u.)

Intensity (a.u.)

Fe

64

62

60

58

56

54

2

64

50

62

60

Fe3O4

58

56

52

50

3+

Fe 52.4%

Intensity (a.u.)

2+

Fe 32.3%

60

54

used Fe3O4

3+

62

56

f)

Fe 67.7%

64

58

Binding energy (eV)

e)

3

52

2+

Fe 12.3%

Binding energy (eV)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


54

52

50

2+

Fe 47.6%

64

62

60

58

56

54

Binding energy (eV)

Binding energy (eV)

27


52

50


FeO

g)

h)

used FeO

2+

Fe

64

1 2

2+

Fe

Intensity (a.u.)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 34

62

60

58

56

54

52

64

50

62

60

58

56

54

Binding energy (eV)

Binding energy (eV)


3

28


52

50

Page 29 of 34

100

a -2

150C

-3

ln k

60 120C 40 20

Equation Adj. R-Square

-4

110C

-5

0 0

1

b)

135C

80

Conversion(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5

10

15

20

y = a + b*x 0.97019

0.98084 Value

Intercept

0.01519

0.00275

135

Slope

0.03223

9.49147E-4

120

Intercept

120

Slope

150

Intercept

150

Slope

0.16281

0.00476

110

Intercept

0.01074

7.73335E-4

110

Slope

0.00513

2.1371E-4

0.01649

0.00172

0.01634

5.1026E-4

-0.00135

2.4

25

0.96727

Time/h

0.93669

Standard Error

135

0.00251

2.5

1000/T

2.6

2.7

2


3


4

29



100

80

80

60

60

40

40

20

20

0

0 1

1 2

Selectivity (%)

100

Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 34

2

3

Time of runs

4

5

Figure 7. Recycling performance of Fe3O4 in nitrobenzene hydrogenation.

3

30


Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Oxygen storage capacity of iron oxides.

1

Sample

SBET[m2 g-1]

Loss weight[%]

OSC[μmol O m-2]

Fe3O4

73.2

0.0913

0.768

γ-Fe2O3

85.4

0.0625

0.457

α-Fe2O3

80.3

0.0512

0.398

FeO

32.9

0.0193

0.366

2 3

31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 34

Table 2. Lattice parameters of fresh and used iron oxides.

1

sample

a (Å)

b (Å)

c (Å)

Fe3O4

8.387

8.387

8.387

used Fe3O4

8.396

8.396

8.396

γ-Fe2O3

8.373

8.373

8.373

used γ-Fe2O3

8.393

8.393

8.393

α-Fe2O3

5.038

5.038

13.790

used α-Fe2O3

5.042

5.042

13.801

FeO

4.310

4.310

4.310

used FeO

4.312

4.312

4.312

2 3

32


Page 33 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1



Substrate

NO2

Conversion

Selectivity

conditions

[%]

[%]

120°C, 15h

98

73.7

Product

NH2

COOH

COOH

NO 2

NH2

CH3

CH3

NO2

NH2

OH

OH

NO2

NH2

Cl

Cl

NO2

NH2

CHO

Reaction

150°C, 15h

95

100

150°C, 15h

91

100

150°C, 15h

98

100

150°C, 15h

90

100

150°C, 15h

93

100

CHO

2 3 33



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

For Table of Contents Only

2

34


Page 34 of 34

Iron Oxide as a Catalyst for Nitroarene Hydrogenation: Important Role

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