N-doped graphitic carbon-improved Co-MoO3 catalysts on ordered mesoporous SBA-15 for chemoselective reduction of nitroarenes

Article abstract of DOI:10.1016/j.apcata.2018.04.024

Metallic Co-MoO₃ catalysts supported on ordered mesoporous SBA-15 were first prepared through in situ reaction of SBA-15-supported Co-Mo oxides with 1,10-phenanthroline. The resulting Co-MoO₃/NC@SBA-15 catalysts with N-doped carbon (NC) exhibited high catalytic activity and chemoselectivity for selective reduction of various functionalized nitroarenes to the corresponding arylamines in ethanol with hydrazine hydrate at near room temperature (30 °C). For reduction of all tested substrates (28 examples), the catalyst could afford a conversion of >99% and arylamine selectivity of >99%. The excellent catalytic performance of the Co-MoO₃/NC@SBA-15 was attributed to the Co-N_χ(C)-Mo active sites generated through the interaction between the surface Co-N_χ(C) and MoO₃ species, promoting the dissociation of hydrazine molecule into the active H* species for the reduction of nitro groups. After the seventh cycle for reduction of 4-methoxylnitrobenzene, the 2%Co-MoO₃/NC@SBA-15 showed little change in catalytic performance, textural properties, size and dispersion of metal species and valence states of elements, indicating high stability and recyclability.

Full text of DOI:10.1016/j.apcata.2018.04.024

AppliedCatalysisA,General559(2018)127–137
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
N-doped graphitic carbon-improved Co–MoO3 catalysts on ordered
mesoporous SBA-15 for chemoselective reduction of nitroarenes
Haigen Huanga, Xiangcheng Liangb, Xueguang Wanga,⁎, Yao Shenga, Chenju Chena, Xiujing Zoua,
Xionggang Lua,⁎
a
State Key Laboratory of Advanced Special Steel, School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
Sinopec Dalian Research Institute of Petroleum and Petrochemicals, Dalian 116041, Liaonin Province, China
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Cobalt
Molybdenum oxide
Nitroarene
Aromatic amine
Hydrazine
Metallic Co–MoO3 catalysts supported on ordered mesoporous SBA-15 were first prepared through in situ re-
action of SBA-15-supported Co–Mo oxides with 1,10-phenanthroline. The resulting Co–MoO3/NC@SBA-15
catalysts with N-doped carbon (NC) exhibited high catalytic activity and chemoselectivity for selective reduction
of various functionalized nitroarenes to the corresponding arylamines in ethanol with hydrazine hydrate at near
room temperature (30 °C). For reduction of all tested substrates (28 examples), the catalyst could afford a
conversion of > 99% and arylamine selectivity of > 99%. The excellent catalytic performance of the Co–MoO3/
NC@SBA-15 was attributed to the Co–Nχ(C)–Mo active sites generated through the interaction between the
surface Co–Nχ(C) and MoO3 species, promoting the dissociation of hydrazine molecule into the active H* species
for the reduction of nitro groups. After the seventh cycle for reduction of 4-methoxylnitrobenzene, the
2%Co–MoO3/NC@SBA-15 showed little change in catalytic performance, textural properties, size and dispersion
of metal species and valence states of elements, indicating high stability and recyclability.
1. Introduction
groups, but are not active. Besides, the high cost and limited availability
also prevent noble metal catalysts for industrial applications.
The selective reduction of nitro aromatics is one fundamental
transformation for the production of functional anilines, which are
important intermediates in the production of pharmaceuticals, agro-
chemicals, dyes, and pigments [1–3]. Traditional reduction routes using
reducing agents such as Fe and Zn, generate large amounts of waste
acids and residues, causing serious environmental problems [4]. The
catalytic reduction of nitro aromatics has been studied for the pro-
duction of anilines over transition metal-based catalysts using various
reducing agents like sodium borohydride [5,6], hydrosilanes [7], pi-
nacol [8], formic acid [9–11], hydrazine or hydrazine derivatives
[12,13], and molecular hydrogen [14,15]. From the standpoint of
atom-economical and environmentally-friendly chemistry, hetero-
geneous catalytic reduction with metal catalysts is accepted as a sus-
tainable and efficient process because of easy separation and catalyst
recycling. The noble metal catalysts based on Pt [16,17], Pd [18,19], Ru
[20,21], and Rh [22,23] are reported to be active for this transforma-
tion, however, in most cases the chemoselective reduction of nitro
group is poor when other reducible groups such as alkene, nitrile,
carbonyl, and halides exist in the benzene ring. Other noble metals like
Au [24,25] and Ag [26,27] are selective for the reduction of nitro
Non-noble transition metal materials including Co nanoparticles
[28–30], Co–Ni nanowires [31], mono-metallic or bimetallic oxides of
Co, Fe and Mo [32–34], Mo carbides [35], Mo sulfides [36,37], and Fe-
complexes [38,39] have been shown to be effective for the selective
reduction of nitro aromatics as catalysts or supports. However, the re-
ductions on these catalysts frequently require strict reaction conditions
(≥100 °C) and the aid of additives (acid, base and metal salts) [40,41].
The investigation results revealed that the activity and selectivity of
non-noble metal catalysts for the reduction of nitro groups depended
strongly on the catalyst preparation procedure, properties of metal and
supports, nature of reducing agent, etc.
Hydrazine hydrate (N2H4·H2O) has been widely used as a hydrogen
donor for a variety of catalytic reductions because it is abundant and
only produces N2 and water as by-products [42,43]. It is demonstrated
that transition metal oxides can facilitate the dissociation of HeN bond
of hydrazine into active hydrogen species (H*) for the reduction of nitro
groups [44–46]. Herein we have first developed ordered mesoporous
silica SBA-15-supported bimetallic Co–MoO3 catalyst (Co−MoO3/NC@
SBA-15) with N-doped graphite-like carbon (NC) by heat-treating SBA-
15-supported Co–Mo oxides (Co3O4−MoO3/SBA-15) with 1,10-
⁎
Corresponding authors.
E-mail addresses: wxg228@shu.edu.cn (X. Wang), luxg@shu.edu.cn (X. Lu).
https://doi.org/10.1016/j.apcata.2018.04.024
Received 9 February 2018; Received in revised form 17 April 2018; Accepted 20 April 2018
Availableonline22April2018
0926-860X/©2018PublishedbyElsevierB.V.

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
phenanthroline, which exhibited excellent activity and chemoselec-
tivity for the catalytic reduction of various substituted nitroarenes to
arylamines without any additive with N2H4·H2O. The influences of Co
contents, supports, organic carbon sources, reducing agents and reac-
tion conditions on the catalytic properties of the Co–MoO3/NC@SBA-15
were systematically investigated for the reduction of 4-methoxylni-
trobenzene as a model reaction. Furthermore, the reduction of various
substituted nitroarenes was examined and possible reduction me-
chanism was proposed over bimetallic Co–Mo catalyst.
and sonicated for 30 min, and then the solvent was evaporated under
stirring at 40 °C. The obtained solid was dried at 100 °C overnight, and
finally was treated in a flow of high-purity N2 (50 ml min−1) at 700 °C
for 2 h with a heating rate of 5 °C min−1 to form xCo−MoO3/NC@SBA-
15 or 2.0%Co/NC@SBA-15 catalysts.
2.0%Ni−MoO3/NC@SBA-15 and 2.0%Fe−MoO3/NC@SBA-15
catalysts were prepared by the same route, except that Ni(NO3)2⋅6H2O
and iron(III) acetylacetonate (Fe(C5H7O2)3) were used as Ni and Fe
sources, respectively.
MCM-41, γ-MA, CMK-3, AC, C3N4, CeO2, ZrO2, TiO2-supported
2.0%Co−MoO3/NC were prepared by the similar method, but CMK-3,
AC, C3N4-supported 2.0%Co3O4−MoO3 materials were calcined in N2
atmosphere at 400 °C for 6 h.
2.0%Pd/NC@SBA-15, 2.0%Pt/NC@SBA-15 and 2.0%Au/NC@SBA-
15 catalysts containing 2.0 wt% noble metals were prepared by the
same way to the 2.0%Co−MoO3/NC@SBA-15, except that Pd/SBA-15,
Pt/SBA-15 and Au/SBA-15 materials were prepared by the impregna-
tion route of SBA-15 with an aqueous solution of PdCl2, H2PtCl6, and
HAuCl4, respectively.
2.0%Co−MoO3/NC@SBA-15−B, M, and C catalysts were also
prepared through impregnating 2.0%Co3O4−MoO3/SBA-15 (1.0 g)
with water–ethanol solutions (40 mL) containing 2,2′-bipyridine
(1.2 g), 2-methylimidazole (1.2 g) and β-cyclodextrin (1.2 g) as organic
carbon precursors, respectively. The procedure was the same as that of
the 2.0%Co−MoO3/NC@SBA-15.
2. Experimental
2.1. Chemicals
Pluronic P123 (EO20PO70EO20, Mav = 5800) was purchased from
Aldrich. Other various chemicals of reagent grade such as Co
(NO3)2⋅6H2O, (NH4)6Mo7O24⋅4H2O, 1,10-phenanthroline monohydrate
(C12H8N2⋅H2O), and (NH4)6Mo7O24⋅4H2O and N2H4·H2O aqueous so-
lution (80 wt%) and so on, and commercial activated carbon (AC),
CeO2, ZrO2 and TiO2 as supports were from Sinopharm Chemical
Reagent Co., Ltd. SBA-15, MCM-41, mesoporous γ-Al2O3 (γ-MA) and
C3N4 supports were synthesized through the procedures reported in the
document [47–51]. Before use, all supports were treated in air or N2
atmosphere at 550 °C for 6 h to remove water and impurities.
2.2. Catalyst preparation
2.3. Catalyst characterization
The Co–MoO3/NC@SBA-15 catalysts were prepared by a facile two-
step impregnation method with water-ethanol solutions of metal ni-
trates and 1,10-phenanthroline, respectively, followed by pyrolysis and
reduction in N2 atmosphere (Scheme 1). Typically, the required
amounts of Co(NO3)2⋅6H2O and (NH4)6Mo7O24⋅4H2O were dissolved in
a mixed solution of water and ethanol (v/v = 1:3) (40 mL) at room
temperature. The SBA-15 powder (1.0 g) was added into the above
solutions under vigorous stirring, and then the suspension was con-
tinuously stirred to remove the solvent at 40 °C. The solids were dried at
100 °C overnight, and calcined in air at 400 °C for 6 h to produce the
xCo3O4–MoO3/SBA-15 materials with various Co mass percentages
(x = 0, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%), where the nominal Mo mass
percentage was set at 6.0%, which was proved to present the optimal
catalytic performance for the selective reduction of nitroarenes in the
preliminary experiments. The 2.0%Co3O4/SBA-15 material was also
prepared by the same way except use of (NH4)6Mo7O24⋅4H2O.
X-ray diffraction (XRD) patterns were collected with a Rigaku D/
MAX-2200 X-ray diffractometer using Cu Kα radiation (λ = 0.1542 nm)
operated at a voltage of 40 kV and a current of 40 mA.
N2 adsorption and desorption measurements were performed on a
Micromeritics ASAP 2020 Sorptometer at −196 °C. Before the analysis,
the sample was outgassed at 200 °C for 8 h. The specific surface area
(SBET) was calculated by the Brunauer–Emmett–Teller (BET) method in
the relative pressure (P/P0) range of 0.05−0.25. Pore size distribution
was
obtained
from
the
adsorption
branch
by
the
Barrett–Joyner–Halenda (BJH) method. The pore size (Dp) was read
from the maximum of the pore distribution curve. The pore volume (Vp)
was calculated from the adsorbed amount at P/P0 = 0.99.
Transmission electron microscopy (TEM) micrographs were taken
with a JEOL JEM-2010F field emission microscope operating at 200 kV.
The sample was prepared by drying an ethanolic dispersion of the well-
ground catalyst powder on a holey-carbon-coated copper grid.
X-ray photoelectron spectra (XPS) were obtained on an ESCALAB
250Xi spectrometer equipped with monochromatized Al Kα radiation
The prepared xCo3O4−MoO3/SBA-15 (1.0 g) or 2.0%Co3O4/SBA-15
powders (1.0 g) were suspended into a solution of water–ethanol (v/
v = 1:3) (40 mL) containing 1,10-phenanthroline monohydrate (1.2 g)
Scheme 1. General preparation procedure of Co−MoO3/NC@SBA-15.
128

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
(hν = 1486.6 eV). The spectra were calibrated using the binding energy
of C 1 s peak at 284.6 eV.
C and N deposition were observed to those for the 2.0%Co−MoO3/
NC@SBA-15. As for the 2.0%Co−MoO3/NC@SBA-15‒B, M, and C
catalysts obtained by different organic sources, differentiated amounts
of carbon and/or nitrogen deposition were achieved.
Fig. 1a illustrates the low-angle XRD patterns of the SBA-15-sup-
ported metal catalysts obtained by the pyrolysis of organic compounds.
All the samples exhibited one intense diffraction peak attributed to
(100) plane, similar to pure SBA-15 [47]. This result demonstrated that
the mesostructural ordering of SBA-15 was maintained in the process of
metal loading and in the coke deposition.
Raman measurements were taken at room temperature on
a
Renishaw 2000 Ramascope with an Ar+ ion laser (514.4 nm) as the
excitation source. Before each measurement was taken, the spectro-
meter was calibrated with a silicon wafer.
The factual amounts of metallic elements in the catalysts were
analyzed on a Perkin Elmer emission spectrometer by inductively
coupled plasma atomic emission spectrometry (ICP-AES). The analysis
of C and N elements was carried out on a Heraeus CHS elemental
analyzer.
The wide-angle XRD patterns of the SBA-15-supported metal cata-
lysts with deposited carbon and/or nitrogen are presented in Fig. 1b. In
the case of the xCo−MoO3/NC@SBA-15 (x = 0, 1.0%, 2.0%, 3.0%,
4.0%, 5.0%) catalysts, when the Co nominal content exceeded 2.0%,
there was a weak diffraction peak at 2θ = 44.2° corresponding to cubic
metallic Co (111) reflection (PDF 15–0806). This result demonstrated
that the Co oxides were reduced into metallic Co crystallites by H2 and
carbon species produced in the pyrolysis of organic compounds. The Co
peak intensity was strengthened, but the peak width became narrowed
with raising the Co content, indicating that the sizes of the Co crys-
tallites increased with the Co content. When the Co content was aug-
mented to 5.0 wt%, the average size of the Co crystallites was estimated
to be 8.3 nm from the line broadening of the Co (111) reflection. No Co
diffraction peak for the xCo−MoO3/NC@SBA-15 (x = 1.0%, 2.0%)
catalysts could be attributed to lower actual Co contents, which were
undetectable by XRD. For each sample, the diffraction peak corre-
sponding to Mo species did not occur, demonstrating that the Mo spe-
cies were highly dispersed in the SBA-15 framework. The carbon
structures in the NC-modified catalysts were analyzed by Raman
spectra (Fig. S1). The xCo−MoO3/NC@SBA-15 catalysts presented a
2.4. Catalytic reduction of nitro aromatics
The catalytic reduction of nitro aromatics was conducted in a 25 ml
Telfon-lined stainless steel autoclave with magnetic stirring. In a typical
process, 6 mmol nitroarene, and desired amounts of reducing agent and
solvents were introduced in the reactor. The autoclave was transferred
into a water bath at the set temperature with an accuracy of better than
0.2 °C for ∼0.5 h. Then, 10 mg catalyst was added into the reaction
mixture and started the reduction at a stirring rate of 450 rpm. After the
reaction, the catalyst was rapidly separated by filtration. n-Decane
(500 μL) as standard was added into the filtrate and was dried with
anhydrous Na2SO4. The products were analyzed by gas chromato-
graphy-mass spectrometry (GC–MS) (Shimadzu GCMS-QP2010 Plus)
and GC (Varian CP-3800) with a capillary column (column VF-1 ms,
15 m, 0.25 mm, 0.25 μm) and a flame ionization detector (FID).
3. Results and discussion
defect (D) band at ∼1356 cm−1 and
a graphite (G) band at
3.1. Catalyst characterization
∼1580 cm−1, which were attributed to the disordered graphitic carbon
and the graphitization degree, respectively [52,53]. As for the 2.0%
The actual contents of metals, C and N elements in the obtained
catalysts were determined in Table 1. All metal contents were always
lower than the nominal ones for the SBA-15-supported metal oxides, for
example, the factual contents of Co and Mo in the 2.0%Co−MoO3/
NC@SBA-15 were 1.1 wt% and 4.1 wt%, respectively. For the
xCo−MoO3/NC@SBA-15 catalysts, the real Co contents increased with
raising the initial ones for the xCo3O4−MoO3/SBA-15 materials.
Compared with the NC@SBA-15, both the xCo−MoO3/NC@SBA-15
and 2.0%Co/NC@SBA-15 catalysts exhibited much higher amounts of
carbon and nitrogen. This result demonstrated that the loadings of ei-
ther Co or Mo could promote the pyrolysis and condensation of phe-
nanthroline. However, both the amounts of carbon and the C/N molar
ratios in general increased with increasing the Co content. This result
suggested that the addition of Co benefited the deposition of carbon
more, and meanwhile, lowered the relative C/N gasification rate in the
pyrolysis of phenanthroline. In terms of the 2.0%Ni−MoO3/NC@SBA-
15 and 2.0%Fe−MoO3/NC@SBA-15 in Table 1, the similar amounts of
Ni−MoO3/NC@SBA-15,
2.0%Fe−MoO3/NC@SBA-15
and
the
2.0%Co−MoO3/NC@SBA-15−B, M, and C catalysts, almost the similar
things were observed for metal species and carbon species except a
weak diffraction peak of Ni (111) at ∼44° (PDF 04-0850).
Fig. 2 presents the TEM images of the SBA-15-supported metal
catalysts treated by phenanthroline. All the catalysts displayed distinct
one-dimensional channels, similar to pure SBA-15 [47]. This result
further confirmed that the ordered mesoporous structures were still
maintained in the catalysts, which were consistent with the XRD results
in Fig. 1. In the case of the xCo−MoO3/NC@SBA-15 (x = 0, 1.0%,
2.0%, 3.0%, 4.0%, 5.0%) and 2.0%Co/NC@SBA-15 (Fig. 2 a−g), it was
difficult to differentiate the boundaries of the Co particles when the
nominal metal contents were below 3.0 wt% because of the perturba-
tion of deposited graphitic carbon and high dispersion of metal parti-
cles. However, we could still identify that the sizes of Co particles in-
creased with raising the Co content, and were located mainly in the
Table 1
Actual composition of Co, Mo, C, and N elements in the prepared catalysts.
Sample
Co (wt%)
Mo (wt%)
C (wt%)
N (wt%)
C/N (mol/mol)
NC@SBA-15
MoO3/NC@SBA-15
−
−
−
0.6
7.4
0.2
2.0
2.5
2.4
2.2
2.0
1.8
2.1
2.5
2.3
0.3
0.4
−
3.5
4.3
5.6
6.2
6.8
8.3
9.3
7.1
6.4
7.2
7.7
6.1
−
4.9
4.5
4.1
4.3
4.1
3.8
−
4.4
4.3
5.3
5.1
4.5
1.0%Co−MoO3/NC@SBA-15
2.0%Co−MoO3/NC@SBA-15
3.0%Co−MoO3/NC@SBA-15
4.0%Co−MoO3/NC@SBA-15
5.0%Co−MoO3/NC@SBA-15
2.0%Co/NC@SBA-15
2.0%Ni−MoO3/NC@SBA-15
2.0%Fe−MoO3/NC@SBA-15
2.0%Co−MoO3/NC@SBA-15‒B
2.0%Co−MoO3/NC@SBA-15‒M
2.0%Co−MoO3/NC@SBA-15‒C
0.6
1.1
1.8
2.6
3.2
1.2
1.3
1.2
1.2
1.2
1.1
12.1
12.7
12.9
14.2
14.3
12.8
13.8
14.2
2.0
2.1
14.4
129

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Fig. 1. (a) Low-angle, and (b) wide-angle XRD patterns of the NC@SBA-15, xCo−MoO3/NC@SBA-15, 2%Co/NC@SBA-15, and other some SBA-15-supported metal
catalysts.
Fig. 2. Typical TEM images of the xCo−MoO3/NC@SBA-15: (a) x = 0%, (b) x = 1.0%, (c) x = 2.0%, (d) x = 3.0%, (e) x = 4.0%, (f) x = 5.0%, (g) 2.0%Co/NC@
SBA-15, (h) 2.0%Ni−MoO3/NC@SBA-15, and (i) 2.0%Fe−MoO3/NC@SBA-15.
130

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Fig. 3. (a) N2 sorption isotherms, and (b) BJH pore size distributions of the NC@SBA-15, xCo−MoO3/NC@SBA-15, 2.0%Co/NC@SBA-15 and other some SBA-15-
supported metal catalysts.
range of 7−10 nm at the Co content of 5.0 wt%. The 2.0%Ni−MoO3/
NC@SBA-15 and 2.0%Fe−MoO3/NC@SBA-15 catalysts in Fig. 2h and i
exhibited larger metal particles than the xCo−MoO3/NC@SBA-15. In
regard to the 2.0%Co−MoO3/NC@SBA-15−B, M, and C catalysts, al-
most the same TEM images (Fig. S2) were observed as that of
2.0%Co−MoO3/NC@SBA-15.
the XPS spectra of the Co 2p regions of the xCo−MoO3/NC@SBA-15
(x = 1.0%, 2.0%, 3.0%, 4.0%, 5.0%) and 2.0%Co/NC@SBA-15 cata-
lysts. All the samples exhibited a relatively symmetric Co 2p3/2 primary
peak at BE (binding energy) of 781.1
0.2 eV. The XRD patterns in
Fig. 1 showed that the xCo−MoO3/NC@SBA-15 catalysts contained
metallic Co crystallites. Nevertheless, it has been reported that the Co
2p3/2 BE was situated in the BE range of 777.7–778.1 eV for metallic Co
[54–57]. Thus, it could be judged that the surface Co−Nχ species were
generated with a strong interaction between the Co atoms and NC on
the surfaces of the Co particles, which gave rise to a lower electron
density at the Co sites [52–54]. Besides, the nature of the support and
the size or shape of metal particles might also exert a certain influence
on the binding energy of the metal elements [58,59].
The Mo 3d XPS spectra in Fig. 4b were given to reveal the valence
information on Mo element in the xCo−MoO3/NC@SBA-15 (x = 1.0%,
2.0%, 3.0%, 4.0%, and 5.0%) catalysts. In the case of the MoO3/NC@
SBA-15, a broadened Mo 3d5/2 XPS spectra were seen and could clearly
be deconvoluted into two curves peaked at BEs of 231.6 eV and
232.8 eV, which were attributed to the Mo5+ and Mo6+ oxidation
states, respectively [46,60,61]; however, upon addition of Co, the
xCo−MoO3/NC@SBA-15 showed only a relatively symmetric peak
corresponding to Mo6+ oxidation state for MoO3, the position of which
shifted to the lower binding energy of ∼232.4 eV. These results de-
monstrated that the presence of Co could suppress the MoO3 reduction,
and MoO3 species had a strong interaction with metal Co species.
The N 1 s XPS spectra of the xCo−MoO3/NC@SBA-15 and 2.0%Co/
NC@SBA-15 catalysts in Fig. 4c could be deconvoluted into three
curves peaked at the BEs of 398.4 eV, 399.4 eV and 401.0 eV, which
could be assigned to pyridine-type N, Co−Nx and/or pyrrolic-type N,
and graphite-type N, respectively [52,53]. In terms of the C 1 s XPS
spectra in Fig. 4d, only one strong peak was observed for both the
xCo−MoO3/NC@SBA-15 and Co/NC@SBA-15 catalysts, which was
attributed to C]C or CeC bonds from the pyrolysis of phenanthroline
and hydrocarbon residues adsorbed on the surface [52,53].
Fig. 3 displays the N2 sorption isotherms and pore size distributions
of the obtained catalysts containing deposited carbon and/or nitrogen.
All the treated catalysts exhibited characteristic type IV isotherms with
H1 type hysteresis loops and narrow pore size distributions. This result
demonstrated that the mesoporous SBA-15 frameworks were not de-
stroyed after the treatment, as indicated in the XRD patterns in Fig. 1.
Table 2 lists the textural properties of the SBA-15-supported metal
catalysts. As a whole, the treated catalysts showed an obvious decrease
in specific surface area, pore volume, and pore size, compared with the
counterparts before the treatment (Table S1). This result indicated that
carbon and/or nitrogen was deposited inside the pores of the SBA-15, in
accordance with the results shown in Table 1. In addition, the higher
treatment temperature, reduction of the Co oxides, structural shrinkage
as well as plugging of pores of the support might also have a certain
effect on the textural parameters of the resulting catalysts. Due to
smaller amounts of carbon and/or nitrogen, the 2.0%Co−MoO3/NC@
SBA-15−B, M and C exhibited a bit larger surface areas, pore volumes
and pore sizes than the 2.0%Co−MoO3/NC@SBA-15.
XPS were applied to shed light on the chemical state of elements and
the interaction among surface species on the catalysts. Fig. 4a presents
Table 2
Textural properties of the prepared catalysts.
Sample
a0 (nm) SBET (m2/g) Vp (cm3/g) Dp (nm)
NC@SBA-15
MoO3/NC@SBA-15
11.0
10.7
10.3
10.2
10.2
10.2
10.2
10.6
10.3
10.3
10.5
10.5
467
365
332
330
289
250
245
349
299
357
387
463
0.72
0.53
0.43
0.39
0.35
0.29
0.25
0.46
0.37
0.50
0.55
0.69
7.5
6.5
6.3
5.6
5.6
5.6
5.6
6.5
5.6
5.5
7.6
7.6
1.0%Co−MoO3/NC@SBA-15
2.0%Co−MoO3/NC@SBA-15
3.0%Co−MoO3/NC@SBA-15
4.0%Co−MoO3/NC@SBA-15
5.0%Co−MoO3/NC@SBA-15
2.0%Co/NC@SBA-15
2.0%Ni−MoO3/NC@SBA-15
2.0%Fe−MoO3/NC@SBA-15
2.0%Co−MoO3/NC@SBA-15−B
2.0%Co−MoO3/NC@SBA-
15−M
As regards the 2.0%Ni−MoO3/NC@SBA-15 (Fig. S3) and 2.0%
Fe−MoO3/NC@SBA-15 catalysts (Fig. S4), the surface Ni−Nχ (Ni 2p3/
BE = 855.8 eV) and Fe−Nχ (Fe 2p3/2 BE = 711.1 eV) species with
2
strong interactions between the surface metal atoms and NC were
formed, similar to the Co element in the xCo−MoO3/NC@SBA-15 [60];
however, for the 2.0%Fe-MoO3/NC@SBA-15, the C 1 s showed another
weak feature at the BE of 288.8 eV corresponding to CeN]C bonds
[52,53], and the N 1s XPS spectra exhibited a new weak peak at the BE
of 405.0 eV corresponding to N-oxide [28]. The 2.0%Co−MoO3/NC@
2.0%Co−MoO3/NC@SBA-15−C
10.4
412
0.41
6.4
131

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Fig. 4. XPS spectra of the xCo−MoO3/NC@SBA-15 and Co/NC@SBA-15.
SBA-15‒B, M and C catalysts (Fig. S5−S7) were also characterized by
XPS. Compared with those with phenanthroline, the Mo 3d5/2 XPS
spectra were obviously different although the BEs of Co 2p3/2, N1s and
C 1s showed little change in the BE value. The 2.0%Co−MoO3/NC@
SBA-15‒M and C presented the Mo 3d5/2 XPS spectra with only one
curve peaked at ∼232.4 eV, similar to the 2.0%Co−MoO3/NC@SBA-
15; while the Mo 3d5/2 XPS spectra of 2.0%Co−MoO3/NC@SBA-15‒B
could be clearly fitted into three XPS curves at 232.5 eV, 231.4 eV and
228.0 eV, which could be assigned to Mo6+, Mo5+ and Mo2+ of Mo2C,
respectively [62,63]. These results implied that the addition of different
metals in the MoO3/NC@SBA-15 materials could exert differentiated
influence on the surface chemical properties of NC and the chemical
state of Mo species on the surface; and in turn, the organic precursors
used for NC also produced NC with differentiated surface chemical
characteristics and affected the chemical state of metal species. These
combined factors might improve the catalytic performance for various
organic reactions.
3.2. Catalytic reaction
4-methoxylnitrobenzene (4-MNB) was first used as a model com-
pound to conduct blank reaction experiments and to confirm the ex-
cellent catalytic performance of the xCo−MoO3/NC@SBA-15 catalysts
for the selective reduction of nitro aromatics with hydrazine hydrate.
Pure SBA-15, supported Co(Fe, Ni) oxides or Co(Fe, Ni) −Mo oxides
and NC@SBA-15 showed no activity for the reduction of 4-MNB in
various solvents like methanol, tetrahydrofuran (THF), toluene, ethyl
acetate, ethyl ether and dimethylformamide (DMF) in the range of
20−100 °C (Table S2); the fresh SBA-15-supported Co(Fe, Ni) and
metal−MoO3 catalysts obtained by H2 reduction at 600 °C and the
MoO3/SBA-15 exhibited a certain activity, for example, the conversions
of 4-MNB over the fresh 2.0%Co/SBA-15, 2.0%Co‒MoO3/SBA-15 and
MoO3/SBA-15 were ∼1%, ∼5% and ∼3% (Table S2), respectively,
under the given reaction conditions: 10 mg catalyst, 6 mmol 4-MNB,
36 mmol N2H4·H2O, 6 ml ethanol, 30 °C, 40 min. However, when they
132

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Table 3
while that for the 2.0%Co‒MoO3/NC@SBA-15 was up to 73%. On the
other hand, the catalysts with NC also showed much higher catalytic
activities than the fresh counterparts in the absence of NC by the H2
reduction. These results unambiguously revealed that it was the com-
prehensive synergistic effect among metal Co, MoO3 species and NC
that significantly improved the catalytic performance of the
xCo−MoO3/NC@SBA-15. The 2.0%Ni‒MoO3/NC@SBA-15 and 2.0%
Fe‒MoO3/NC@SBA-15 catalysts with similar porous structure and
amounts of NC exhibited the 4-MNB conversions of 37% and 34%, re-
spectively (entries 8 and 9 in Table 3), which were approximately one
half of the 2.0%Co−MoO3/NC@SBA-15 under the identical conditions.
This result could be mainly attributed to the altered nature of metal. In
addition, the sizes of metal particles and the interactions among metal
species and NC might also influence the catalytic performance. As for
the 2.0%Co−MoO3/NC@SBA-15‒B, M and C catalysts (entries 10−12
in Table 3), their catalytic activities were significantly lower than that
of the 2.0%Co−MoO3/NC@SBA-15. This result might be attributed to
the differentiated surface properties resulted from different amounts of
deposited carbon or nitrogen.
Catalytic performance of various supported catalysts for selective reduction of
4‒methoxylnitrobenzene to 4-methoxylanilinea.
Entry
Catalyst
Conv. (%)
Sel. (%)
1
2
3
4
5
6
7
8
9
MoO3/NC@SBA-15
7
> 99
> 99
> 99
> 99
> 99
> 99
96
> 99
> 99
> 99
1.0%Co‒MoO3/NC@SBA-15
2.0%Co‒MoO3/NC@SBA-15
3.0%Co‒MoO3/NC@SBA-15
4.0%Co‒MoO3/NC@SBA-15
5.0%Co‒MoO3/NC@SBA-15
2.0%Co/NC@SBA-15
2.0%Ni‒MoO3/NC@SBA-15
2.0%Fe‒MoO3/NC@SBA-15
2.0%Co‒MoO3/NC@SBA-
15‒B
52
73
70
64
62
4
38
34
14
10
The 2.0%Co−MoO3 catalysts on various supports including MCM-
41, γ-MA, CMK-3, AC, C3N4, CeO2, ZrO2 and TiO2, which were treated
with phenanthroline at 700 °C in a flow of N2, were tested for the se-
lective reduction of 4-MNB, and the results are listed in entries 13−20
in Table 3. It was clear that the catalytic activities of these supported
2.0%Co‒MoO3/NC catalysts were apparently different, and were all
much lower than that of the 2.0%Co−MoO3/NC@SBA-15. These re-
sults showed that the nature and porous structure of the support
strongly affected the catalytic performance of supported Co−MoO3.
Among all the tested catalysts, the SBA-15 supported 2.0%Co−MoO3
by phenanthroline was optimal for the selective reduction of 4-MNB.
Supported noble metal catalysts such as Pd, Pt and Au have been
widely accepted to be the most effective for the selective reduction of
nitro compounds. Therefore, the SBA-15 supported Pd, Pt and Au cat-
alysts prepared by phenanthroline were also listed in entries 21−23 of
Table 3 for comparison. It was clearly found that their catalytic activ-
ities were much lower than those of the xCo−MoO3/NC@SBA-15 cat-
alysts by our method.
The selective reduction of 4-MNB was further applied as a model
reaction to optimize the reaction conditions over the 2.0% Co‒MoO3/
NC@SBA-15 including types of reducing agents, temperature, con-
centrations of hydrazine hydrate and substrate, and types and amounts
of solvents, and the reduction results are listed in Table 4. It could be
seen that the 2.0%Co‒MoO3/NC@SBA-15 was less active with mole-
cular hydrogen (entry 1), sodium borohydride (entry 2), formic acid
and formic acid derivatives (entries 3−5), but exhibited significantly
high catalytic activity with hydrazine hydrate (entry 6). In the tem-
perature range of 20−100 °C (entries 6−11), the 4-MNB conversion
always increased with elevating the reaction temperature, and the 4-
MBA selectivity was kept at > 99%. When the temperature was ele-
vated to 100 °C, 4-MNB could be rapidly transformed into the 4-MBA
within a very short time (5 min) with no change of selectivity. The
amount of hydrazine in the reaction mixture exerted a significant in-
fluence on the catalytic activity of the 2.0%Co‒MoO3/NC@SBA-15. The
4-MNB conversion increased with increasing the content of hydrazine
and tended to be stable when the substrate/hydrazine molar ratio
reached 1 : 6 (entries 6, 12−15), while the 4-MBA selectivity showed
unchanged at > 99%. The reaction results without solvent and in var-
ious solvents in entries 6 and 16−25 revealed that the use of organic
solvents could in general improve the catalytic activity and selectivity
of the 2.0%Co‒MoO3/NC@SBA-15; and in 4-MNB ethanol solution at 4-
MNB/ethanol = 1:1 (mmol/mL), the catalyst showed the highest 4-
MNB conversion (entries 6, 16−19). It was found that all the catalytic
reductions of 4-MNB over the 2.0%Co‒MoO3/NC@SBA-15 could pro-
ceed to the end with a 4-MBA selectivity of > 99% by prolonging re-
action time. Note that there were no by-product including hydro-
xylamine, nitroso, azoxy and azo compounds found in the products for
11
12
13
2.0%Co‒MoO3/NC@SBA-
15‒M
2.0%Co‒MoO3/NC@SBA-
15‒C
2.0%Co‒MoO3/NC@MCM-
41
2.0%Co‒MoO3/NC@γ-MA
2.0%Co‒MoO3/NC@CMK-3
2.0%Co‒MoO3/NC@AC
2.0%Co‒MoO3/NC@C3N4
2.0%Co‒MoO3/NC@ZrO2
2.0%Co‒MoO3/NC@CeO2
2.0%Co‒MoO3/NC@TiO2
2.0%Pd/NC@SBA-15
2.0%Pt/NC@SBA-15
2.0%Au/NC@SBA-15
11
7
> 99
> 99
> 99
36
14
15
16
17
18
19
20
21
22
23
34
8
4
12
11
13
25
9
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
8
8
a
Reaction conditions: 10 mg catalyst, 6 mmol 4-MNB, 36 mmol N2H4·H2O,
6 ml ethanol, 30 °C, 40 min.
were exposed to ambient atmosphere for more than 24 h, the metal and
metal−MoO3 catalysts were almost completely deactivated for the 4-
MNB reduction due to the surface oxidization of metallic particles
(Table S2). These results demonstrated that both metal atoms and MoO3
species were active to some extent, and the synergism between Co and
MoO3 species improved the catalytic performance of the xCo−MoO3/
SBA-15 for the reduction of 4-MNB.
Entries 1−7 in Table 3 summaries the catalytic activities and se-
lectivities of the xCo−MoO3/NC@SBA-15 (x = 0, 1.0%, 2.0%, 3.0%,
4.0%, 5.0%) and 2.0%Co/NC@SBA-15 for the reduction of 4-MNB to 4-
methoxylaniline (4-MBA) in ethanol at 30 °C. All these catalysts ex-
hibited certain activities and high selectivities to 4-MBA. The 4-MNB
conversions increased with enhancing the Co content, and presented
the maximum value of 73% at the nominal Co content of 2.0 wt%. As
the Co content was further raised, the 4-MNB conversion began to de-
cline, and became 62% at the Co content of 5 wt%. This result might be
caused by the increase in the sizes of Co crystallites with the Co content.
Note that the activities of the Co-containing catalysts with NC showed
little change for this reaction after exposed to ambient atmosphere for
more than three months. These results implied that unlike those on the
xCo‒MoO3/SBA-15 and Co/SBA-15, the surface metal Co atoms on the
xCo−MoO3/NC@SBA-15 were highly stable, or in other words, the
presence of NC could inhibit the surface oxidation of Co particles with
air. It has been known that both the xCo−MoO3/NC@SBA-15 and
2%Co/NC@SBA-15 had similar mesoporous structure and large
amounts of NC. Upon combination of Co in the MoO3/NC@SBA-15, the
catalytic activity was steeply enhanced by a factor of more than 10 for
the 4-MNB reduction, for instance, the 4-MNB conversions were 7% and
4% for the MoO3/NC@SBA-15 and 2%Co/NC@SBA-15, respectively,
133

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Table 4
Effect of reaction conditions on the catalytic performance of 2%Co−MoO3/NC@SBA-15 for selective reduction of 4-methoxylnitrobenzene to 4-methoxylanilinea.
Entry
reducing agent
T (oC)
Solvent (mL)
Conv. (%)b
Sel. (%)
1
2
3
4
5
6
7
8
H2 (6 MPa)
NaBH4 (6 equiv.)
30
30
30
30
30
30
20
40
50
80
100
30
30
30
30
30
30
30
30
30
30
30
30
30
30
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
ethanol (6 m L)
no solvent
ethanol (2 mL)
ethanol (4 mL)
ethanol (8 mL)
methanol (6 mL)
THF (6 m L)
toluene (6 m L)
ethylacetate (6 m L)
ethyl ether (6 m L)
DMF (6 m L)
< 1
< 1
< 1
3
4
73
30
> 99 (45 min)
> 99 (35 min)
> 99 (20 min)
> 99 (5 min)
−
−
−
HCOOH (6 equiv.)
HCOOK (6 equiv.)
HCOOH-Et3N (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (0 equiv.)
N2H4⋅H2O (2 equiv.)
N2H4⋅H2O (4 equiv.)
N2H4⋅H2O (8 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
N2H4⋅H2O (6 equiv.)
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
−
> 99
> 99
> 99
73
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
0
23
49
75
12
18
53
61
50
48
34
26
41
15
a
b
Reaction conditions: 10 mg catalyst, 6 mmol 4-MNB, 40 min. Actual required reaction time for full conversion of 4-MNB in parenthesis.
Mo elements within the detectable limitation by ICP-AES. After the
cycle finished, the contents of Co and Mo in the spent catalysts were
1.1 wt% and 4.2 wt%, which were almost identical to those (1.1 wt%
and 4.1%) before the reaction, as shown in Table 1. These results in-
dicated that there was no leaching of metal elements in the reduction of
nitro groups. The characterization results in Fig. 6 revealed that the
textural properties (312 m2 −1, 0.39 cm3, 5.6 nm), size and dispersion
g
of metal species, and valence states of elements exhibited little change
after the cycle reaction of 4-MNB.
Transition metal nanoparticles (Co, Ni, Fe), molybdenum carbide
and molybdenum nitride have been reported to exhibit excellent cata-
lytic properties for the decomposition of hydrazine to H2 and N2
[44,64,65]. It was known in Table 3 that SBA-15 supported metal Co
and MoO3 catalysts with NC had certain catalytic properties, and fur-
thermore, the combination effect among metal Co, MoO3 species and
NC greatly improved the catalytic activity of the xCo−MoO3/NC@SBA-
15 for the selective reduction of 4-MNB with hydrazine. Therefore, it
was reasonably proposed that the intimate interaction between the
surface Co−Nχ(C) and MoO3 species led to the formation of
Co−Nχ(C)−Mo active sites. The hydrazine molecules were adsorbed
on the Co−Nχ(C) −Mo sites and were dissociated into active H* spe-
cies, which were reacted with the adjacent nitro compounds adsorbed
on the catalyst surface, as described in our previous study [46]. In the
selective reduction of 4-MNB to 4-MBA as a model reaction over all the
xCo−MoO3/NC@SBA-15 catalysts, nitroso, hydroxylamine and azo
compounds were not found in the products. Designed separate reactions
revealed that nitrosobenzene and phenylhydroxylamine could smoothly
be transformed into aniline in the ethanol solution of hydrazine hydrate
over the 2.0%Co−MoO3/NC@SBA-15 at 30 °C, while the reduction of
either azoxybenzene or azobenzene was quite slow under the identical
conditions. These results indicated that the selective reduction of ni-
troarenes to arylamines over the xCo−MoO3/NC@SBA-15 catalysts
Fig. 5. Reusable profiles of the 2.0%Co−MoO3/NC@SBA-15 catalyst for the
selective reduction of 4-methoxylnitrobenzene to 4-methoxylaniline. Reaction
conditions: 30 mg catalyst, 18 mmol 4-MNB, 108 mmol N2H4·H2O, 18 ml
ethanol, 30 °C, 45 min in the first cycle; the catalyst/4-MNB ratio was kept
unchanged in the following cycles.
the 4-MNB reduction with hydrazine over the 2.0%Co‒MoO3/NC@
SBA-15 except in the absence of no solvent.
A series of catalytic reactions and characterizations were carried out
to investigate the stability and reusability of the 2.0%Co−MoO3/NC@
SBA-15. The reaction conditions with a 4-MNB conversion of 70−75%
were used for the first reaction. The catalyst after every operation was
recovered by centrifugation, washing with ethanol, and drying at
100 °C. The results in Fig. 5 indicated that after the 7th cycling reaction,
the catalyst still retained the 4-MNB conversion of 70−75% and 4-MBA
selectivity of > 99%. The centrifugate after every run could not con-
tinue to react with hydrazine hydrate and did not contain the Co and
134

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Fig. 6. (a) N2 sorption isotherms and pore size distribution, (b) XRD patterns, (c) TEM image, and (d) Co 2p XPS spectra, of the spent 2.0%Co−MoO3/NC@SBA-15
catalyst for the selective reduction of 4-methoxylnitrobenzene.
should be performed mainly through the direct pathway rather than the
indirect pathway, namely, the nitro group was first converted into the
nitroso intermediate, and subsequently, rapidly to hydroxylamine in
two consecutive steps, followed by the final reduction to aniline.
Table 5 summaries 28 typical examples of selective reduction of
various functionalized nitroarenes to the corresponding anilines, which
indicated the generality of the 2.0%Co−MoO3/NC@SBA-15 catalyst
under the mild conditions. All the substituted nitroarenes with non-
reducible groups including -CH3, -CH3OH, CH3O-, -OH, -NH2, and F3C-,
(entries 1–6) were quantitatively reduced into the corresponding ani-
lines. It is well known that the dehalogenation frequently take place in
the selective reduction of halogen-substituted nitroarenes. However,
the examples of halogen (F, Cl, Br)-substituted nitroarenes could
smoothly be completed up to the end with no observable dehalogena-
tion (entries 7−12). Entries (13−20) in Table 5 displayed the reaction
results of some representative nitroarenes with other reducible func-
tional groups in the benzene rings such as carboxy, nitrile, amide,
sulphanilamide, ester, alkene, etc. It could be found that all these cited
reducible groups could be tolerated in the hydrogenation of nitro
groups. These results were different from supported noble catalysts
such as Pd, Pt, Rh, Ru, etc, over which the nitro group reduction pre-
sented poor selectivity when alkenyl groups were present in the same
molecule [21,66]. These results were likely attributed to the higher
reactivity of the nitro group than other reducible functional groups over
the Co−MoO3/NC@SBA-15 [46]. Note that dinitro groups in the ben-
zene rings could be completely reduced with a diamino group se-
lectivity of > 99% (entry 21,22). Finally, the selective reduction of
some heterocyclic nitroarenes containing N and S elements to the
amines was also confirmed to be feasible with an amine selectivity
of > 99% over the Co−MoO3/NC@SBA-15 catalysts (entries 23−28).
4. Conclusions
In summary, ordered mesoporous silica SBA-15 supported non-
noble metal Co−MoO3 catalysts (Co−MoO3/NC@SBA-15) with N-
doped graphitic carbon (NC) have been prepared by the two-step im-
pregnation route of metal nitrates and 1,10-phenanthroline. The
Co−MoO3/NC@SBA-15 catalysts possessed large specific area surfaces,
pore volumes and narrow pore size distributions, and metal Co, MoO3
species, N and C elements generated the strong synergistic action
among them. The catalysts exhibited high catalytic activity and che-
moselectivity of > 99% for various substituted nitroarenes to the cor-
responding arylamines with hydrazine hydrate, and could completely
proceed through to the end. The high catalytic performance of the
Co−MoO3/NC@SBA-15 could be likely due to the Co−Nχ(C)−Mo
active sites formed through the interaction between the surface
Co−Nχ(C) and MoO3 species, benefiting the dissociation of hydrazine
molecule into active H* species for the reduction of nitro groups.
Recycling tests indicated that the Co−MoO3/NC@SBA-15 was highly
stable for the selective reduction of nitroarenes.
Acknowledgements
This research was supported by National Basic Research Program of
135

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Table 5
Selective reduction of various substituted nitroarenes to anilines over the 2.0%Co−MoO3/NC@SBA-15a.
Entry
Substrate
Time (min)
Conv. (%)b
Sel. (%)
1
2
3
4
5
6
7
8
R = H
R = 2,4-Me
R = 4-CH2OH
R = 2-CH3; 5-OH
R = 3-NH2; 4-Me
R = 4-CF3
R = 2,3,4-F
R = 2-Me; 3-Cl
R = 2,4-Cl
R = 2-NH2; 4,5-Cl
R = 4-Br
R = 2-Br; 5-F
R = 3-COOH
R = 3-Cl; 4-NH2; 5-CN
R = 4-CH2CN
R = 4-CONH2
R = 4-SO2NH2
R = 4-CO2CH2CH3
60
60
60
90
75
50
50
50
60
120
60
60
60
80
60
60
60
60
80
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
9
10
11
12
13
14
15
16
17
18
19
20
60
80
> 99
> 99
> 99
21b
> 99b
22b,c
120
60
> 99
> 99
> 99
> 99
23
24
60
> 99
> 99
25
26
60
> 99
> 99
> 99
> 99
120
27
360
> 99
> 99
(continued on next page)
136

H. Huang et al.
AppliedCatalysisA,General559(2018)127–137
Table 5 (continued)
Entry
28
Substrate
Time (min)
150
Conv. (%)b
> 99
Sel. (%)
> 99
a
b
Reaction conditions: 10 mg catalyst, 6 mmol substrate, 36 mmol N2H4·H2O, 6 ml ethanol, 30 °C unless otherwise specified. Dinitro groups are converted into
c
diamino groups. Reaction temperature of 90 °C.
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