Nitrogen doped carbon supported iron catalysts for highly selective production of 4,4′-diamino-2,2′-stilbenedisulfonic acid

Article abstract of DOI:10.1016/j.catcom.2019.105822

Nitrogen doped carbon supported iron catalysts were prepared from pyrolysis of a multidentate nitrogen ligand iron complex supported on chitosan at different temperature, and showed good performances in the reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid (DNS acid) to 4,4′-diamino-2,2′-stilbenedisulfonic acid (DSD acid) with hydrazine hydrate (N₂H₄·H₂O) as reductant. Characterization results revealed that the iron is mainly present in the form of Fe₂O₃ and metallic iron nanoparticles. The doped N atoms functionalized as anchoring sites to stabilize iron nanoparticles, which endows the catalysts with excellent activity and superior reusability.

Full text of DOI:10.1016/j.catcom.2019.105822

CatalysisCommunications132(2019)105822
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Catalysis Communications
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Short communication
Nitrogen doped carbon supported iron catalysts for highly selective
production of 4,4′-diamino-2,2′-stilbenedisulfonic acid
⁎
Pengwei Caoa, Hong-Yu Zhanga, Guohui Yina, Yuecheng Zhanga,b, , Jiquan Zhaoa,⁎
a School of Chemical Engineering and Technology, Hebei Provincial Key Lab of Green Chemical Technology & High Efficient Energy Saving, Hebei University of Technology,
Tianjin 300130, PR China
b National-Local Joint Engineering Laboratory for Energy Conservation of Chemical Process Integration and Resources Utilization, Hebei University of Technology, Tianjin
300130, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Nitrogen doped carbon supported iron catalysts were prepared from pyrolysis of a multidentate nitrogen ligand
iron complex supported on chitosan at different temperature, and showed good performances in the reduction of
4,4′-dinitrostilbene-2,2′-disulfonic acid (DNS acid) to 4,4′-diamino-2,2′-stilbenedisulfonic acid (DSD acid) with
hydrazine hydrate (N2H4·H2O) as reductant. Characterization results revealed that the iron is mainly present in
the form of Fe2O3 and metallic iron nanoparticles. The doped N atoms functionalized as anchoring sites to
stabilize iron nanoparticles, which endows the catalysts with excellent activity and superior reusability.
Iron nanoparticles
Nitrogen doped carbon
DSD acid
DNS acid
Hydrazine hydrate
1. Introduction
Therefore, it is promising to develop an efficient and sustainable iron
based catalyst for the conversion of DNS acid to DSD acid using
4,4′-Diamino-2,2′-stilbenedisulfonic acid (DSD acid) is an important
intermediate widely used for manufacturing dyes, pigments and fluor-
escent brightener [1–5]. Now, DSD acid is mainly produced from iron
powder reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid (DNS acid)
in China [1,2]. The reduction of DNS acid with iron powder can tolerate
co-existence of C]C double bond in the structure affording DSD acid
with high selectivity, but generate large amount of iron mud harmful to
environment. Therefore, efforts were made to develop alternative pro-
tocols to prepare DSD acid, such as electrochemical reduction [6] and
catalytic reduction of DNS acid using various reductants [2,7]. The
electrochemical reduction protocol encountered the bottleneck of low
current efficiency [6]. In 2012, Chen et al. reported the preparation and
the catalysis of gold nanoparticles supported on three metal oxides for
the reduction of DNS acid to DSD acid with H2, CO and HCO2Na as
reductants [2]. A selectivity higher than 94% was achieved over the
three Au NPs containing catalysts. However, the high cost of noble
metal based catalysts will become a big obstacle for the manufacture of
DSD acid belonging to a less expensive product.
N2H4·H2O as reductant.
Recently, nitrogen doped carbon supported metal catalysts have
attracted much attention due to their excellent activity and selectivity
in the reduction of nitro compounds with various hydrogen sources
[11–23]. The doped nitrogen could facilitate the transfer hydrogenation
of nitro compounds, due to the synergistic effect between the doped
nitrogen and the metal species in the catalysts as revealed by Beller
[15,16]. Beller [15] also found that the performance of a catalyst could
be controlled by the ligand in the complex and the support in the
preparation of the heterogeneous catalyst. The nitrogen numbers co-
ordinated to center metal in a complex is of great importance to give
highly active species in the prepared catalyst. Meanwhile, a suitable
match of a complex with a support is also important to afford a catalyst
with good performance.
Herein, nitrogen doped carbon supported iron catalysts (FeNC-T,
T = 700, 800, 900 °C) were prepared through pyrolysis a multidentate
nitrogen ligand iron complex Fe(phen)(pydic) absorbed on chitosan at
different temperature, and applied to the reduction of DNS acid to DSD
acid with N2H4·H2O. N2H4·H2O functionalized as hydrogen source en-
dows this strategy a green route to synthesis DSD acid. Characterization
results revealed that iron species mainly exist in the form of Fe2O3 and
metallic iron nanoparticles and anchor on the doped nitrogen atoms,
thus affording the catalysts good performances in application.
It is well known that hydrazine hydrate (N2H4·H2O) is a good hy-
drogen source for the reduction of nitro compounds to amines over iron
based catalysts [8–10], [14–16]. In principle, only nitrogen and water
are the byproducts in the reduction of nitro compounds with N2H4·H2O.
On the other hand, iron is non-toxic, cheap, and easily available.
⁎ Corresponding authors at: School of Chemical Engineering and Technology, Hebei Provincial Key Lab of Green Chemical Technology & High Efficient Energy
Saving, Hebei University of Technology, Tianjin 300130, PR China.
E-mail addresses: yczhang@hebut.edu.cn (Y. Zhang), zhaojq@hebut.edu.cn (J. Zhao).
https://doi.org/10.1016/j.catcom.2019.105822
Received 17 July 2019; Received in revised form 7 September 2019; Accepted 10 September 2019
Availableonline11September2019
1566-7367/©2019PublishedbyElsevierB.V.

P. Cao, et al.
CatalysisCommunications132(2019)105822
a* Fe(0)
# Fe2O3
& Fe3C
b
*
&
&
&
&
&
&
&
C 1s
N 1s
Fe2p
*
*
*
40
44
48
#
#
#
FeNC-900
FeNC-900
FeNC-800
FeNC-800
FeNC-700
70
FeNC-700
0
10
20
30
40
50
60
80
800
600 400
Binding energy(ev)
200
Pyridinic N
c
d
Fe-N
Pyrrolic N
Graphitic N
Fe2O3
Fe-N
satellite
Fe-N
Fe2O3
FeNC-900
FeNC-900
FeNC-800
FeNC-700
FeNC-800
FeNC-700
735
730
725
720
715
710
705
700
404
402
400
398
396
394
Binding energy(ev)
Binding energy(eV)
Fig. 1. (a) XRD patterns (b) XPS survey scan, (c) high resolution XPS analysis in N 1s region, and (d) detailed Fe 2p spectra of catalyst samples.
2. Experimental
binding energy 2p3/2 of Fe(III) species [29,30] The peak at 716.5 eV has
been identified as a satellite peak corresponding to Fe 2p3/2 [31]. The
peak at 712.8 is attributed to FeNx 2p3/2 [30] while the peaks at
723.2 eV and 725.7 eV are attributed to the binding energies 2p1/2 of
Fe2O3 and FeNx 2p1/2 [30].
The experimental procedures were given in Supplementary in-
formation.
(Fig. 1d). The separation of Fe (III) 2p3/2 and Fe (III) 2p1/2 is
13.2 eV, indicating the existence of Fe2O3 in the catalysts [13]. Com-
bined with the fitted N 1s XPS spectrum, we can conclude that partial
Fe species exist in the form of FeNx, which means iron coordinating
with doped nitrogen.
The morphologies and microstructures of catalyst FeNC-800 were
revealed by TEM. As shown in Fig. S1, the iron nanoparticles show a
homogeneous dispersion. Corresponding element mapping images in-
dicate a homogeneous dispersion of element C, N, and same location
area of FeNx and Fe2O3. The element mapping images in combination
with XPS analysis indicate that Fe2O3 species rooted in the FeNx species
to form iron nanoparticles, which is of great importance in determining
the catalysis of the catalysts due to synergistic effect between iron na-
noparticles and nitrogen doped carbon support [32,33].
3. Results and discussion
3.1. Catalyst characterization
XRD and XPS were performed to disclose the compositions and
valence states of as prepared catalysts. As shown in Fig. 1a, diffraction
peak located at 2θ of 26° is assigned to graphitic carbon [24], the ones
at 2θ of 35.6°, 44.7° are assigned to Fe2O3 [25,26] and metallic iron
[13,25,27], respectively. It is also found that with the pyrolysis tem-
perature raised to 900 °C, diffraction peaks of Fe3C is observed in the 2θ
range of 40 to 50°, indicating partial transformation of metallic iron into
Fe3C [27]. Pyrolysis at high temperature of an iron and carbon-con-
taining material led to reduction of iron species to metallic iron by
carbon, and the metallic iron was chemically extremely active to react
with other atoms such nitrogen and carbon to form FeNx or FeCx species
[27].
XPS survey scan spectra are shown in Fig. 1b, the signals of C, N,
and Fe are observed in the spectra of all the three samples. It is found
that the content of nitrogen decreases with the increase of pyrolysis
temperature, which is in consistent with elemental analysis (Table S1).
Careful deconvolution of N 1s spectra (Fig. 1c) reveals that surface
nitrogen species exist in the forms of graphitic N (401.3 eV), pyrrolic N
(400.4 eV), Fe-Nx N(399.3 eV) and pyridinic N (398.7 eV) [27,28]. The
contents of the four nitrogen species and the total nitrogen content in
the three catalysts were determined by XPS, and the results are listed in
Table S2. The total nitrogen content in the catalysts decreased with
increase of pyrolysis temperature in the preparation of catalysts.
Though the total nitrogen content in FeNC-800 is lower than that in
FeNC-700, the nitrogen content of Fe-Nx N in FeNC-800 (0.65%) is
higher than the ones in FeNC-700 (0.58%) and FeNC-900 (0.48%).
Deconvolution of Fe 2p spectra reveals peaks at the binding energies of
710.0 eV, 712.8 eV, 716.5 eV. The peak at 710.0 eV is ascribed to the
N2 adsorption-desorption analysis revealed that all catalysts display
type-IV isotherms (Fig. S2), indicating the presence of mesoporous
pores in the catalysts. As shown in Table S3, catalyst FeNC-800 has the
largest specific areas of 125.34 m2 g−1. Pyrolysis at temperature either
higher or lower than 800 °C would lead to decrease of specific areas of
the catalysts. Larger specific areas will endow more active species ex-
posing to reactants in catalytic run. Therefore, FeNC-800 will show
good performance compared to the other ones in the reductive con-
version of DNS acid to DSD acid with N2H4·H2O.
3.2. Catalytic performance
Preliminary experiments indicated that catalyst FeNC-800 gave best
results in the reduction of DNS acid to DSD acid with N2H4·H2O in water
among the three FeNC-T catalysts. Therefore, the effects of various
parameters including reaction temperature, amount of N2H4·H2O and
catalyst loading on the catalysis of FeNC-800 were investigated in water
by maintaining reaction time 5 h, and the results are given in
2

P. Cao, et al.
CatalysisCommunications132(2019)105822
Table 1
conversion
selectivity
Catalytic performances of different catalysts.
100
80
60
40
20
0
Entry
Catalyst
Conversion (%)a
Selectivity (%)a
1
2
3
FeNC-700
FeNC-800
FeNC-900
NC-800
99.8
99.9
99.9
59.8
99.9
83.1
84.1
78.6
–
4
5b
FeCl3/AC
45.0
Reaction conditions: DNS acid 0.5 mmol, methanol 2 mL, water 3 mL, hydrazine
hydrate 2.25 mmol, catalyst 50 mg (7 mol% Fe), reaction temperature 140 °C,
1 bar N2, reaction time 5 h.
a
Conversion and selectivity were determined by HPLC external standard
1
2
3
method.
b
FeCl3 15 mg, AC 30 mg, methanol 10 mL, DNS 0.5 mmol, hydrazine hydrate
Recycle times
2 mmol, reflux temperature, 5 h,1 bar N2.
Fig. 2. Recyclability of catalyst FeNC-800.
supplementary information (Table S4a–c). The suitable reaction tem-
perature, amount of N2H4·H2O and catalyst loading were determined to
be 140 °C, 4.5 equivalents N2H4·H2O to DNS acid and 7 mol%, respec-
tively. In this case the conversion of DNS acid reached close to100%,
with 80.3% selectivity of DSD acid. Herein, intermediate 4-amino-4′-
nitrodiphenylethylene-2,2′-disulfonic acid (ANSD acid), and some uni-
dentified oligomers were found in the reaction mixture, which led to
the decrease of the selectivity of DSD acid. No 4,4′-diaminobibenzyl-
2,2′-disulfonic acid (DAD acid) was detected in the reaction, indicating
that this protocol can tolerate co-existence of C]C double bond in DNS
acid. DAD acid is generally generated from over hydrogenation of DSD
acid in the hydrogenation of DNS acid to DSD acid, leading to decrease
of the selectivity of DSD acid [2].
Instead of DSD acid, nitroso and hydroxylamine intermediates as
main products were detected over iron-free material NC-800, indicating
their necessity of iron species in the catalysts. It is known that ferric
trichloride in combination with active carbon (FeCl3/AC) was very
active in the reduction of nitro compounds with N2H4·H2O [34].
Therefore, the reaction was also carried out with FeCl3/AC as catalyst.
Though the conversion of DNS acid was near 100% in the presence of
FeCl3/AC, the selectivity towards DSD acid was only 45%. The results in
combination with the catalytic results of FeNC-800 indicated the great
importance of the texture properties of FeNC-800, and presence of sy-
nergistic effect between iron nanoparticles and nitrogen doped carbon
support in FeNC-800.
Efforts were made to improve the selectivity of DSD acid by per-
forming the reaction in organic solvents, but failed due to its poor so-
lubility of DNS acid in organic solvents. Thankfully, introduction of
appropriate amount of methanol into water could improve the reaction
in some degree (Table S5). Initially, the selectivity of DSD acid in-
creased with the introduction of methanol, and reached its maximum of
83.1% at methanol to water volume ratio of 2:3. Instead, further in-
crease of methanol content led to a decrease of the selectivity of DSD,
probably due to the low solubility of DNS in methanol. Therefore, the
suitable solvent is the mixture of methanol and water in volume ratio of
2:3. After the suitable solvent was gotten, the reaction time was eval-
uated and determined to be 5 h (Table S6).
Based on the above results, the optimized reaction conditions were
obtained, which were reaction temperature 140 °C, catalyst loading
7 mol%, 4.5 equivalents N2H4·H2O, methanol to water volume ratio of
2:3, and reaction time 5 h. In this case the yield of DSD acid reached
83.1%.
Finally, the reusability of FeNC-800 was examined for three recycles
(Fig. 2) and no obvious decrease in activity was found in the recycle
runs, indicating the excellent stability and reusability of FeNC-800
catalyst.
4. Conclusion
In summary, nitrogen doped carbon supported iron nanoparticles
were readily prepared through pyrolysis an iron complex Fe(phen)
(pydic) absorbed on chitosan. In these materials, the iron nanoparticles
anchor on the doped N atoms in the carbon matrix. These materials,
especially FeNC-800, as catalysts exhibited high activity and selectivity
in the reduction of DNS to DSD with N2H4·H2O, and had advantages of
easy recovery and good reusability, endowing this strategy a green and
sustainable route to synthesis DSD acid from DNS acid.
Acknowledgement
The catalysis of as prepared catalysts was compared under the op-
timized reaction conditions. As shown in Table 1, catalyst FeNC-800
showed best selectivity towards DSD acid, and catalyst FeNC-700 per-
formed slight worse compared to catalyst FeNC-800, but better than
catalyst FeNC-900. The selectivities of DSD acid over the three catalysts
were in agreement with the Fe-Nx N contents in FeNC-700 (0.58%),
We acknowledge the financial support from the National Natural
Science Foundation of China (Grant NO. 21776056) the Natural Science
Foundation of Hebei Province (CN) (Grant No. B2018202253).
Appendix A. Supplementary data
FeNC-800 (0.65%) and FeNC-900 (0.49%). The higher the Fe-Nx
N
content in the catalyst is, the higher selectivity of DSD acid is. This can
be ascribed to that the higher FeNx N content will lead more Fe2O3
nanoparticles formed, rooting in FeNx species. Fe2O3 nanoparticles
rooting in Fe-Nx species can be confirmed by element mapping images
(Fig. S1). Fe2O3 nanoparticles rooting in FeNx species are active species
in the reduction of DNS acid to DSD acid with N2H4·H2O. Therefore, the
catalyst FeNC-800 performed best among the three catalysts. The lar-
gest specific areas of FeNC-800 might be another reason that FeNC-800
showed best performance in the reaction. Besides, the poor perfor-
mance of FeNC-900 compared to FeNC-700 and FeNC-800 could be
partially ascribed to the transformation of iron species into Fe3C in
FeNC-900.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.catcom.2019.105822.
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