Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions

Article abstract of DOI:10.1016/S1872-2067(19)63276-6

An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors and α-Fe₂O₃ as a support. The catalyst with Pt content as low as 0.2 wt% exhibits high activities, chemoselectivi

Full text of DOI:10.1016/S1872-2067(19)63276-6

Chinese Journal of Catalysis 40 (2019) 214–222
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Synergism of Pt nanoparticles and iron oxide support for
chemoselective hydrogenation of nitroarenes under mild conditions
Pei Jing a, Tao Gan a, Hui Qi b, Bin Zheng a, Xuefeng Chu c, Guiyang Yu a, Wenfu Yan a, Yongcun Zou a,
Wenxiang Zhang a,*, Gang Liu a,#
a State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, Jilin, China
b The Second Hospital of Jilin University, Changchun 130041, Jilin, China
c Provincial Key Laboratory of Architectural Electricity & Comprehensive Energy Saving, School of Electrical and Electronic Information Engineering, Jilin
Jianzhu University, Changchun 130118, Jilin, China
A R T I C L E I N F O
A B S T R A C T
Article history:
An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with
colloid Pt precursors and α-Fe2O3 as a support. The catalyst with Pt content as low as 0.2 wt% ex-
hibits high activities, chemoselectivities and stability in the hydrogenation of nitrobenzene and a
Received 18 December 2018
Accepted 20 December 2018
Published 5 February 2019
–1
variety of niroarenes. The conversion of nitrobenzene can reach 3170 mol
h
molPt–1 under mild
conv
conditions (30 °C, 5 bar), which is much higher than that of commercial Pt/C catalyst and many
reported catalysts under similar reaction conditions. The spatial separation of the active sites for H2
dissociation and hydrogenation should be responsible for the high chemoselectivity, which de-
creases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles.
The unique surface properties of α-Fe2O3 play an important role in the reaction process. It provides
active sites for hydrogen spillover and reactant adsorption, and ultimately completes the hydro-
genation of the nitro group on the catalyst surface.
Keywords:
Supported Pt catalyst
Iron oxide
Nitroarene hydrogenation
Chemoselectivity
Noble metal catalysis
© 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
an example, nitro groups and other reducible groups (e.g., C=C,
C=O, –X, etc.) can be simultaneously hydrogenated over Pt met-
Pt-group metals supported on oxides or carbon are of great
importance in many industrial chemical processes as hetero-
geneous catalysts [1–3]. They usually exhibit high efficiency in
both oxidation and reduction reactions [4–7]. However, large
scale application of Pt-based catalysts is still limited by their
high cost [8–11]. Moreover, active Pt sites cannot discriminate
the differences of functional groups, causing a low catalytic
selectivity [12–14]. Take the hydrogenation of nitroarenes as
al active sites [15–18]. Some solutions for improving the selec-
tivity include adding metal salts or organic compounds as addi-
tives, or loading a less active component (e.g., Au, Ag, etc.)
[19–23]. The role of additives is to avoid the accumulation of
hazardous aromatic hydroxylamines or lower the flat adsorp-
tion of nitroarenes with the benzene ring to decrease a simul-
taneous exposure of the reducible groups toward the active
sites. However, most of them are at the cost of catalytic activity,
* Corresponding author. Tel: +86-431-85155390; Fax: +86-431-88499140; E-mail: zhwenx@jlu.edu.cn
# Corresponding author. Tel: +86-431-85155390; Fax: +86-431-88499140; E-mail: lgang@jlu.edu.cn
This work was supported by the National Natural Science Foundation of China (21473073, 21473074), ‘‘13th Five-Year’’ Science and Technology
Research of the Education Department of Jilin Province (2016403), the Development Project of Science and Technology of Jilin Province
(20170101171JC, 20180201068SF), and the Open Project of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (201703).
DOI: S1872-2067(19)63276-6 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 40, No. 2, February 2019

Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
215
and additional metal salts also face with the post-processing
and new environmental problems.
Hexachloroplatinic(IV) acid hexahydrate, Fe(NO3)3·9H2O,
Ce(NO3)3·6H2O and sodium carbonate were purchased from
Sinopharm Chemical Reagent Co., Ltd. Sodium hydroxide was
obtained from Beijing Chemical Work. Titania P25 (TiO2) was
purchased from Evonik Degussa (ca. 50 m2/g, anatase ca. 80%
and rutile ca. 20%). Magnesium oxide (MgO) was obtained
from Tianjin Fuchen Chemical Reagents Factory. Alumina ox-
ides (γ-Al2O3) were purchased from Longkou Chemical Paking
Co., Ltd. All chemical reagents used in the experiment were of
commercially available analytical grade, which were used
without further purification.
Recent research shows that rational design of Pt-group cen-
ters and/or proper regulating the environment around Pt sites
could obtain highly chemoselective catalysts for hydrogenation
of nitroarenes [24–29]. For example, Zhang’s group [24] re-
ported that the catalyst with single-atom and pseu-
do-single-atom Pt supported on FeOx exhibits high activity and
chemoselectivity for hydrogenation of functional nitroarenes.
Corma et al. [25] showed that the chemoselectivity can be sig-
nificantly improved by generating nanosized Pt with special
exposed crystal faces on the surface of a TiO2 support. Qu and
his coworkers [26] used porous CeO2 nanorods supported
sub-nanometric Pd clusters as catalysts to improve chemose-
lectivity. However, practical applications of these catalysts still
face great challenges due to the dependence of activity on the
amount of Pt loading [28]. Reducing the Pt sites within the cat-
alysts has a significantly negative effect on the catalytic activity.
Moreover, the aggregation of Pt nanoparticles and stability of
the oxide supports under strong reduction atmosphere also
deserve concern.
In this work, we attempt to carry out the strategy of spatial
separating the active sites to develop low cost and highly effi-
cient catalysts for chemoselective hydrogenation of ni-
troarenes. It is expected to introduce the participation of oxide
supports to enhance the utilization efficiency of Pt sites. This
strategy is mainly based on the H2-spillover mechanism. The
challenges for realizing this strategy include the efficiency of H2
dissociation over Pt centers, and the capacity of H diffusion and
reactants adsorption over oxide supports [30–32]. More im-
portant is the synergism of these performances over Pt and
oxide supports. Therefore, the fabrication of Pt sites and
choosing well-matched oxides supports are the key factors for
this strategy.
2.2. Preparation of oxide supports and Pt colloids
The precursor of the Fe2O3 support was prepared via a pre-
cipitation reaction of an aqueous solution of Fe(NO3)3·9H2O
with sodium carbonate. In a typical preparation, a Na2CO3
aqueous solution was obtained by dissolving 23 g of Na2CO3 in
100 mL of water. 100 mL of an aqueous solution containing 56
g of Fe(NO3)3·9H2O was added dropwise into above solution.
Then, additional aqueous solution of Na2CO3 (0.1 mol/L) was
added into the mixture until the pH value reached 9.0. After
aging for 2 h, the precursor was collected by filtration and
washing with distilled water. Finally, the Fe2O3 support was
obtained by calcining the precursor at 500 °C for 3 h. CeO2 was
prepared by thermal treating Ce(NO3)3·6H2O at 350 °C for 4 h.
Platinum colloids were prepared by a polyol reduction
method which was reported in our previous work [4,33]. Typi-
cally, 13.5 mL glycol solution of sodium hydroxide (0.34 mol/L)
and 30 mL glycol solution of H2PtCl6·6H2O (8.5 × 10–4 mol/L)
were mixed under vigorous stirring for 20 min, and then heat-
ed at 140 °C for 30 min under N2 flow.
2.3. Preparation of supported Pt catalysts
For achieving above goals, a colloid method is adopted to
prepare Pt active centers, which has been proved in our previ-
ous work that this method could effectively control the sizes
and the dispersion states of Pt particles [4,33]. Considering the
strong electron-withdrawing properties of nitro groups, several
metal oxides with Lewis-basic sites are screened as catalyst
supports, including Fe2O3, CeO2, Al2O3 MgO and TiO2. They
could generally provide large number of electron-rich sites to
interact with nitro groups [34,35]. Interestingly, Pt/Fe2O3 with
Pt-loading amount as low as 0.2 wt% exhibits high catalytic
activities and chemoselectivities in the hydrogenation of a va-
riety of nitroarenes. It should be noted that the catalytic tests
are carried out under quite mild reaction conditions (30 °C, 5
bar H2). Besides, both the Pt nanoparticles and Fe2O3 support
exhibit a high stability under the strong reduction atmosphere.
The highly efficient H2 dissociation over Pt nanoparticles (Pt0),
and the capacity of H diffusion and reactant adsorption over
α-phase Fe2O3 should be co-responsible for the excellent per-
formance of Pt/Fe2O3 catalysts.
All the oxides-supported Pt catalysts were prepared using a
colloidal deposition method. Taking Pt/Fe2O3 catalyst as an
example, a certain amount of Fe2O3 was added to the Pt col-
loids. After stirring for about 2 h at room temperature, the
mixture was heated at 80 °C for 12 h. Then, the resulting mix-
ture was filtered and washed several times with distilled water
and dried at 100 °C overnight. Before characterizations and
activity tests, the obtained solid was calcined in 20% O2/Ar at
200 °C for 2 h. The loading amount of Pt in Pt/Fe2O3 was tuned
by the content of Pt colloids in the mixture, and finally identi-
fied with an inductively coupled plasma atomic emission spec-
trometer (ICP). According to the ICP results, the samples were
denoted as 0.1 wt% Pt/Fe2O3, 0.2 wt% Pt/Fe2O3 and 0.5 wt%
Pt/Fe2O3. The preparation of other oxides-supported Pt cata-
lysts also used the above colloidal deposition method. The
loading amount of Pt was identified by ICP and shown in Table
1.
2.4. Characterizations
2. Experimental
Powder X-ray diffraction (XRD) patterns were recorded
2.1. Materials
with a Rigaku X-ray diffractometer using Cu Kα radiation (λ =

216
Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
used in this work, which can effectively exclude the influence of
Table 1
Hydrogenation of nitrobenzene over different supported Pt catalystsa.
mass transfer on the reactions. The reactants and products
were analyzed with a gas chromatograph (GC-112A, FID detec-
tor) equipped with an HP-5 column (30 m). In the recycling
experiments, the solid catalyst was separated by simple de-
cantation and directly used for the next cycle without any fur-
ther treatment.
Pt content b
(wt%)
Sel.
(%)
Conv. (%)
Cycle 1 Cycle 2 Cycle 3
Entry Catalyst
1
2
3
4
5
6
None
Fe2O3
0
0
0.9
1.2
—
—
—
—
—
—
Pt/Fe2O3
Pt/CeO2
Pt/MgO
Pt/Al2O3
Pt/TiO2
0.2
0.4
0.3
0.5
0.2
100
100
88.5
74.3
45.5
99.7
85.2
—
—
—
99.2
35.3
—
—
—
>99
>99
>99
>99
>99
3. Results and discussion
7
The hydrogenation of nitrobenzene was carried out to
screen suitable oxide supports for supported Pt catalysts. Five
oxides, Fe2O3, CeO2, Al2O3, MgO and TiO2, were chosen based on
their the surface acid-base properties and reducibility [36]. All
the supported Pt catalysts were prepared by a colloid deposi-
tion method. For achieving the aim of low cost, the Pt contents
in these catalysts were controlled at 0.1 wt%-0.5 wt%. No Pt
diffraction peaks can be observed in the XRD patterns of these
supported Pt catalysts (Fig. 1 and Fig. S1). Table 1 shows the
catalytic performance of these catalysts in hydrogenation of
nitrobenzene. Without a catalyst or in the presence of the Fe2O3
support only, nearly no products can be detected (Table 1, en-
tries 1 and 2). Under the same reaction conditions, Pt/Fe2O3
and Pt/CeO2 exhibit obviously higher activities than Pt/MgO,
Pt/Al2O3 and Pt/TiO2. Compared with Pt/CeO2, Pt/Fe2O3 pos-
sesses the advantage of high stability under the reaction condi-
tions (Table 1, entries 3 and 4). It can be recovered from the
reaction mixture through simple filtration, and there is no ob-
vious change in conversion of nitrobenzene and selectivity to
aniline after five successive runs (Fig. 2A). It should be noted
that mass transfer can be excluded in the above tests. Because
of the bulk nature of these oxides (Fig. S2), the active sites are
nearly all located on the external surface of the supports. In
addition, the influence of stirring rate on the catalytic perfor-
mance was also investigated. The same reaction rates under
800 and 1000 r/min over the Pt/Fe2O3 catalyst further show
that mass transfer has little influence on the reaction (Fig. S3).
The different activities over these catalysts should be mainly
a
Reaction condition: T = 30 °C, P = 5 bar, mcat = 50 mg, 1 mmol nitro-
benzene, 15 mL of toluene as solvent, reaction time t = 2 h. b Identified
by ICP.
0.15418 nm) at 40 kV and 40 mA. Elemental analysis for Pt was
obtained using a PLASMA-SPEC(I) inductively coupled plasma
atomic emission spectrometer (ICP). Transmission electron
microscopy (TEM) images were obtained on a JEOL JEM-2010
electron microscope with an operating voltage of 200 kV.
Temperature-programmed reduction (TPR) was performed
using a Tianjin Xianquan TP-5079 adsorption analyzer. Before
detection, the catalysts were treated in an Ar (99.99%) flow at
120 °C for 30 min. After the sample was cooled down to 30 °C,
the flowing gas was switched to 5 vol% H2/Ar and the sample
was heated to 800 °C with a temperature ramp rate of 10
°C/min. N2 adsorption-desorption isotherms were measured at
–196 °C, using a Micromeritics ASAP 2010N analyzer. X-ray
photoelectron spectroscopy (XPS) was performed on a Thermo
ESCA LAB 250 system with Mg Kα source (1254.6 eV). Binding
energies were obtained by referencing to the C 1s binding en-
ergy of carbon (peak at 284.6 eV). In-situ diffuse reflectance
infrared Fourier transform spectroscopy (DRIFT) spectra were
recorded on a Nicolet 6700 spectrometer. Among them, in-situ
CO adsorption DRIFT measurement was carried out to investi-
gate the state of Pt. The samples were pretreated in N2 flow at
100 °C for 10 min. After the system was cooled to room tem-
perature, a background spectrum was collected. Then the sam-
ple was exposed to 1 vol% CO/Ar flow before recording the
spectra. In-situ DRIFT spectra of nitrobenzene adsorption and
hydrogenation were obtained as following. Firstly, the samples
were treated in 30 mL/min N2 flow at 100 °C for 10 min. Then,
the nitrobenzene gas was carried by N2 flow and introduced
into the sample cell for adsorption. In the hydrogenation
measurement, the mixture of hydrogen and the nitrobenzene
gases was simultaneously introduced into the sample cell, and
the spectra were in-situ recorded.
Fe2O3








d
c
b
a
2.5. Catalytic hydrogenation of nitroarenes
The liquid-phase hydrogenation reaction of nitroarenes was
performed in a magnetically stirred 50 mL stainless steel auto-
clave. A quantity of catalyst (50 mg) was added to the autoclave
containing nitroarene (1 mmol) and toluene (15 mL). Then, the
autoclave was flushed with 10 bar hydrogen five times. After
being sealed, the autoclave was charged with H2 until 5 bar and
then it was kept at 30 °C. A rotation rate of 1000 r/min was
20
30
40
50
60
70
2deg.)
Fig. 1. XRD patterns of 0.1 wt% Pt/Fe2O3 (a), 0.2 wt% Pt/Fe2O3 (b), 0.5
wt% Pt/Fe2O3 (c) and used 0.2 wt% Pt/Fe2O3 after five cycles (d).

Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
217
100
80
60
40
20
0
conversion
selectivity
A
B
100
80
60
40
20
0
0.5 wt% Pt/Fe2O3
0.2 wt% Pt/Fe2O3
0.1 wt% Pt/Fe2O3
5 wt% Pt/C
1
2
3
4
5
0
30 60 90 120 150 180 210 240 270 300
Run times
Time (min)
Fig. 2. (A) Recycling test over the 0.2 wt% Pt/Fe2O3 catalyst and (B) catalytic performance of Pt/Fe2O3 with different Pt contents and commercial Pt/C
catalyst. Reaction conditions: T = 30 °C, P = 5 bar, mcat = 50 mg, 1 mmol nitrobenzene, 15 mL of toluene as solvent.
due to the surface properties of the oxide supports, which will
be discussed below.
the uniform Pt nanoparticles highly dispersed on the surface of
Fe2O3 and playing the similar role in the reaction process. It can
be observed that the value over 0.5 wt% Pt/Fe2O3 is relatively
low (2063 molconv. h–1 molPt–1), showing that there is no linear
relationship between activity and the Pt loading. This result
Fig. 2B shows the catalytic activities of Pt/Fe2O3 with dif-
ferent Pt loadings. The conversion of nitrobenzene improves
with the increase of Pt contents. According to the initial reac-
tion rates of these catalysts, the activities are normalized by Pt
–1
loading, which is 2627, 3170 and 2063 molconv. h–1 molPt for
Table 2
Hydrogenation of different substituted nitroarenes over the 0.2 wt%
Pt/Fe2O3 and commercial Pt/C catalystsa.
0.1 wt% Pt/Fe2O3, 0.2 wt% Pt/Fe2O3 and 0.5 wt% Pt/Fe2O3,
respectively. It should be noted that such high activities are
obtained under quite mild reaction conditions (30 °C, 5 bar).
Compared with the literature results under the similar reaction
conditions, Pt/Fe2O3 exhibits obvious advantage (Table S1).
Compared with the commercial Pt/C catalyst, Pt/Fe2O3 also
possesses advantage. The conversion rate of nitrobenzene over
0.5 wt% Pt/Fe2O3 and 0.2 wt% Pt/Fe2O3 is also obviously
higher than Pt/C under the same reaction conditions (Fig. 2B).
It is known that the loading amount of Pt in the commercial
Pt/C catalyst is 5 wt%, much higher than that of Pt/Fe2O3.
In addition, it is found that Pt/Fe2O3 also displayed good
performance when extended to substituted nitroarenes. We
mainly focus on nitroarenes with reducible groups such as
–C=O, O=C–O and –X because they are with grand challenge for
the application of selective hydrogenation. Table 2 shows that
Pt/Fe2O3 exhibits high selectivity to the corresponding anilines.
Even for halonitrobenzene, Pt/Fe2O3 catalyst is also with rela-
tively high chemoselectivity. Previously, it has been reported
that most Pt-based catalysts suffer from the hydrogenolysis of
weak carbon-halogen bond [24]. In our case, the high
chemoselectivity should be mainly due to the spatial separation
of H2 dissociation and hydrogenation active sites. As for com-
mercial Pt/C catalyst, a relatively low chemoselectivity is de-
tected in the hydrogenation of substituted nitroarenes under
the same reaction conditions (Table 2). Moreover, a decrease of
chemoselectivity can also be observed over Pt/Fe2O3 when Pt
loading is larger than 1 wt%, which should be due to the in-
crease of contact possibility between Pt sites and reducible
functional group.
Time Conv. Sel.
(min) (%) (%)
Entry
1
Substrate
Product
120 96.2 >99
2
70 99.9 >99
180 95.3 96.8
130 96.2 >99
220 98.5 >99
180 98.1 78.6
150 98.3 89.7
3
4
5
6 b
7 b
a Reaction conditions: T = 30 °C, P = 5 bar, mcat = 50 mg, 1 mmol nitro-
benzene, 15 mL of toluene as solvent. b Commercial 5 wt% Pt/C as the
catalyst.
Comparing the nitrobenzene conversion rates normalized
by the Pt loading amount, it can be seen that these values are at
the same order of magnitude, which should mainly ascribe to

218
Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
could give strong support to our strategy that separating the
hydrogenation active sites from Pt to the supports. It is known
that the Pt loading of 0.5 wt% is also a low content value com-
pared with many literature and the contrast sample in this case.
Given that the Pt particles are the hydrogenation active sites,
region. As for the spatial separation of the active sites, enough
reaction area is needed, which could effectively reduce the
contact possibility between the reducible groups of nitroarenes
and Pt sites. Considering the largest molecule in the reactants is
about 6 Å, it can be speculated that Pt/Fe2O3 provides enough
spaces to achieve the spatial separation of H2 dissociation and
hydrogenation active sites. Besides, the TEM images of the
sample after five cycles are also shown in Fig. 3. Both the sizes
and dispersion states of Pt are almost the same as that of the
fresh one. No particle aggregation can be observed, suggesting
that Pt nanoparticles possess a high stability during the reac-
tion process.
Pt 4f XPS was measured to analyze the surface chemical
state of Pt nanoparticles (Fig. 4). Because of the detection limit,
Pt signals in low Pt-content samples are hard to detect, so 0.5
wt% Pt/Fe2O3 was used as the representative sample for test-
ing. Two main peaks centered at about 71.5 and 74.6 eV can be
observed, which are corresponding to the spin-orbit split dou-
blet of Pt 4f7/2 and Pt 4f5/2, respectively [33,37–39]. The binding
energy of this original peak center is consistent with the Pt0
electron binding energy. Although the spectra still could be
deconvoluted into the components of metal Pt (Pt0) and oxide
states Pt (Pt2+), the amount of oxide states Pt (Pt2+) is quite
limited. Metallic Pt should be the absolutely predominant one
in the sample.
Furthermore, in-situ DRIFT spectra of adsorbed CO at room
temperature were also recorded over the samples of 0.1 wt%
Pt/Fe2O3, 0.2 wt% Pt/Fe2O3 and 0.5 wt% Pt/Fe2O3 to confirm
the chemical state of Pt. It is known that vco > 2100 cm–1 is as-
signed to the linear adsorption of CO on oxide states Pt, while
vco < 2100 cm–1 is ascribed to CO adsorbed on metallic Pt
[40,41]. Fig. 5 shows that a relatively strong band at 2085 cm–1
appears in all three samples, which can be ascribed to CO ad-
sorbed on metallic Pt. This result confirms that Pt mainly pre-
sents as metallic state in Pt/Fe2O3, and a small amount of Pt2+
detected by Pt 4f XPS should be located at the interface be-
tween Pt nanoparticles and supports, which can be reflected
from the shoulder peak of CO adsorption. This metallic Pt pos-
sesses strong H2 dissociation ability. H2-TPR profiles show that
the reduction peaks corresponding to Fe3+ to Fe2+ shift signifi-
the average contribution of Pt would not decrease from 3170
–1
mol
h
molPt–1 (0.2 wt% Pt) to 2063 molconv. h–1 molPt–1 (0.5
conv.
wt% Pt). It would maintain such high conversion efficiency at
least in this loading range. The results in our case show that Pt
sites only serve as hydrogen dissociation centers. The hydro-
genation process should occur on the surface of Fe2O3 supports.
According to above results, a reaction mechanism concerning
H2 dissociation, nitroarene adsorption and hydrogenation is
proposed (Scheme 1). The Fe2O3 support provides adsorption
sites for the nitroarenes and should also function as the reac-
tion area for the hydrogenation.
To verify this hypothesis, a series of characterizations were
carried out to detect the physicochemical properties of
Pt/Fe2O3 and in-situ reaction process of nitroarene hydrogena-
tion over this catalyst. XRD patterns (Fig. 1) show that only
diffraction peaks assigned to α-Fe2O3 phase could be observed
on the patterns of both samples with different Pt contents and
the one after five cycles. It shows that α-Fe2O3 possesses a rela-
tively high stability. Both the reducibility of Pt colloids in the
preparation process and the strong reduction atmosphere in
the reaction process have little influence on the phase structure
of α-Fe2O3. No diffraction peaks assigned to Pt can be observed,
suggesting that Pt nanoparticles are highly dispersed on the
surface of α-Fe2O3.
TEM images further confirm the above results. Fig. 3b and
3c shows that almost all Pt particles in the Pt/Fe2O3 catalyst are
consistent with the size of Pt particles in the colloids (Fig. 3a).
The size of 3–4 nm is the most probable distribution of these
particles. It should be noted that Pt nanoparticles are highly
dispersed on the surface of the Fe2O3 support, which might be
correlated with the low loading amount. The shortest distance
between two Pt nanoparticles is about 12 nm in the detected
Fig. 3. TEM images of Pt colloids (a), 0.2 wt% Pt/Fe2O3 (b and c) and
used 0.2 wt% Pt/Fe2O3 after five cycles (d, e and f).
Scheme 1. Proposed reaction mechanism of H2 dissociation, adsorption
and hydrogenation of nitroarenes on the Pt/Fe2O3 catalyst.

Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
219
Pt 4f
O 1s
77
76
75
74
73
72
71
536
534
532
530
528
526
Binding energy (eV)
Binding energy (eV)
Fig. 4. Pt 4f and O 1s XPS spectra of 0.5 wt% Pt/Fe2O3.
cantly to the relatively low temperature in the presence of Pt
nanoparticles (Fig. 6). It decreases at least 120 °C compared
with that of pure Fe2O3 support. Increasing the Pt contents
could further decrease the reduction temperature. In addition,
the low reduction temperature and narrow reduction peak
could also show that Fe2O3 support possesses excellent hydro-
gen spillover capability. It could facilitate the diffusion of hy-
drogen on the surface of Fe2O3. In our case, the strong H2 disso-
ciation ability of Pt nanoparticles and hydrogen spillover capa-
bility of Fe2O3 support should be two important factors that
catalyze the hydrogenation reaction under mild conditions (30
°C, 5 bar).
For understanding the adsorption behavior and hydrogena-
tion of nitroarenes over the Pt/Fe2O3 catalyst, in-situ DRIFT
measurements were carried out. Nitrobenzene is introduced by
a N2 flow to the Fe2O3 support and 0.2 wt% Pt/Fe2O3. Two
bands appeared at 1531 and 1350 cm–1 could be attributed to
asymmetric stretching and symmetric stretching vibrations of
the nitro group, respectively [28]. There is no difference be-
tween Fe2O3 support and Pt/Fe2O3 (Fig. 7a and 7c), suggesting
that the nitro group mainly adsorbed on the surface of Fe2O3
support. Upon introducing H2 to 0.2wt% Pt/Fe2O3, a new broad
band can be observed at 1589–1620 cm–1 (Fig. 7d), which is
attributed to the vibrations of –NO and –NH2 species
[28,42,43]. This suggests that hydrogenation of nitrobenzene
occurs over 0.2 wt% Pt/Fe2O3. In contrast, when H2 is intro-
duced to the Fe2O3 support, no signal assigned to –NH2 species
can be observed (Fig. 7b). This is mainly due to the lack of H2
dissociation sites on the Fe2O3 support.
The strong nitrobenzene adsorption behavior for Fe2O3
should origin from the presence of oxygen vacancies. The O 1s
XPS spectrum (Fig. 4) indicates that a large amount of oxygen
vacancy (531 eV) is present on the surface of Pt/Fe2O3 [44,45].
These oxygen vacancies are electron-rich sites, which could
have a relatively strong interaction with nitro groups (strong
electron-withdrawing group). Correspondingly, a relatively
broad Fe 2p XPS peak (711 and 724.3 eV) can be observed (Fig.
S4). It shows that most of iron species on the surface of the
samples are present as a valence of +3, combining with a small
amount of iron species with a valence of +2 [10,46]. This prop-
erty should facilitate both the reactant adsorption and the hy-
d
c
c
b
a
b
a
2500
2400
2300
2200
2100
2000
1900
1800
100
200
300
400
500
600
700
800
Wavenumber (cm1)
Temperature (°C)
Fig. 5. In-situ DRIFT spectra of CO adsorbed on 0.1 wt% Pt/Fe2O3 (a),
Fig. 6. H2-TPR profiles of Fe2O3 (a), 0.1 wt% Pt/Fe2O3 (b), 0.2 wt%
0.2 wt% Pt/Fe2O3 (b) and 0.5 wt% Pt/Fe2O3 (c).
Pt/Fe2O3 (c) and 0.5 wt% Pt/Fe2O3 (d).

220
Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
modifying the catalysts with vanadium salts or organic thiol
compounds could effectively tune the adsorption and desorp-
tion behavior of the catalysts [19,20]. The role of vanadium
salts is to avoid accumulation of hazardous aromatic hydrox-
ylamines, while organic thiol compounds could avoid the flat
adsorption of nitroarenes via the benzene ring. Flat adsorption
would cause a simultaneous exposure of the reducible groups
toward the active sites. In our case, the suitable surface chemi-
cal state of α-Fe2O3 facilitates the adsorption of nitro group of
nitroarenes. The unique properties of α-Fe2O3 realize its high
performance cooperated with Pt nanoparticles for chemoselec-
tive hydrogenation of niroarenes.
1531
1589-1620
1350
d
c
b
a
4. Conclusions
3200
2800
2400
2000
1600
1200
Wavenumber (cm-1)
Pt/Fe2O3 prepared by a colloidal deposition method exhibits
high activity and chemoselectivity in hydrogenation of ni-
troarenes. Uniform Pt nanoparticles, mainly present as metallic
Pt0, highly disperse on the surface of the α-Fe2O3 support, facil-
itating the dissociation of H2. Stable α-Fe2O3 support possesses
the ability of selective adsorption of nitro group and diffusion
of hydrogen, providing the active sites for hydrogenation of
nitroarenes. The low contents of Pt lead to spatial separation of
the active sites for H2 dissociation and hydrogenation, which
effectively reduce the contact possibility between Pt and ni-
troarenes, avoiding the undesirable hydrogenation of other
reducible functional groups.
Fig. 7. In-situ DRIFT spectra of nitrobenzene adsorption over Fe2O3 (a)
and 0.2 wt% Pt/Fe2O3 (c); co-presence of nitrobenzene and H2: Fe2O3 (b)
and 0.2 wt% Pt/Fe2O3 (d).
drogen spillover.
It should be noted that the high stability of α-Fe2O3 under
the reduction condition is also a critical factor for Pt/Fe2O3 to
become an excellent catalyst. We had ever detected the per-
formance of ferrihydrite (Fe(OH, H2O) and composite iron ox-
ides co-presence of (Fe(OH, H2O) and α-Fe2O3 (Fig. S5). It is
well known that the presence of water could accelerate the
diffusion of hydrogen atoms across solid oxide surfaces. Alt-
hough the catalysts prepared with above two oxides exhibit a
little higher initial activity than α-Fe2O3 (Fig. S6), their poor
performance in the following reaction cycles shows that they
cannot become efficient catalysts (Fig. S7). As for the support of
α-Fe2O3, it exhibits not only relatively high activity but also high
stability in the hydrogenation of nitroarenes.
References
[1] E. Schmidt, A. Vargas, T. Mallat, A. Baiker, J. Am. Chem. Soc., 2009,
131, 12358–12367.
[2] W. Y. Cui, D. Xue, N. D. Tan, B. Zheng, M. J. Jia, W. X. Zhang, Chin. J.
Catal., 2018, 39, 1534–1542.
[3] J. J. Liu, S. H. Zou, J. C. Wu, H. Kobayashi, H. T. Zhao, J. Fan, Chin. J.
Catal., 2018, 39, 1081–1089.
Combined with the catalytic tests and characterization re-
sults, it can be confirmed that the supports play an important
role in the reaction process. The catalyst performance directly
correlates with their capability of reactant adsorption and hy-
drogen spillover. Reducible oxides have higher capability of
hydrogen spillover than irreducible oxide supports, which re-
flects on not only the spillover speed but also the migrated dis-
tance [30]. It should be the main reason that Al2O3- and
MgO-supported Pt catalysts exhibit low activities. The stability
of the supports under the reduction condition should also be
concerned. The poor recyclability of CeO2 and ferrihydrite
supported samples should be mainly due to the stability of the
oxide support in the presence of H2. Actually, both CeO2 and
ferrihydrite have higher reducibility than α-Fe2O3 because of
the high activity of surface oxygen species, but these active
species are easily damaged in the strong reduction atmosphere
of H2.
[4] B. Zheng, S. J. Wu, X. W. Yang, M. J. Jia, W. X. Zhang, G. Liu, ACS. Appl.
Mater. Inter., 2016, 8, 26683–26689.
[5] P. P. Ye, A. J. Gellman, J. Am. Chem. Soc., 2008, 130, 8518–8526.
[6] G. C. da Silva, M. R. Fernandes, E. A. Ticianelli, ACS. Catal., 2018, 8,
2081–2092.
[7] Z. J. Chen, J. Y. Chen, Y. W. Li, Chin. J. Catal., 2017, 38, 1108–1126.
[8] S. Anantharaj, P. E. Karthik, B. Subramanian, S. Kundu, ACS. Catal.,
2016, 6, 4660–4672.
[9] Y. L. Sui, S. B. Liu, T. F. Li, Q. X. Liu, T. Jiang, Y. F. Guo, J. L. Luo, J.
Catal., 2017, 353, 250–255.
[10] L. L. Geng, M. Zhang, W. X. Zhang, M. J. Jia, W. F. Yan, G. Liu, Catal.
Sci. Technol., 2015, 5, 3097–3102.
[11] R. V. Jagadeesh, A. E. Surkus, H. Junge, M-M. Pohl, J. Radnik, J.
Rabeah, H. Huan, V. Schünemann, A. Brückner, M. Beller, Science,
2013, 342, 1073–1076.
[12] Y. J. Shu, T. Chen, H. C. Chan, L. F. Xie, Q. S. Gao, Chem – Asian. J.,
2018, 13, 3737–3744.
[13] Q. M. Hu, S. Wang, Z. Gao, Y. Q. Li, Q. Zhang, Q. Xiang, Y. Qin, Appl.
Catal. B: Environ., 2017, 218, 591–599.
In addition, the adsorption behavior of the supports is an-
other important factor that affects the catalytic performance of
these catalysts. It is directly affected by the surface electronic
properties of the supports. Some literature has reported that
[14] M. W. Zhu, B. Huang, Q. Shao, Y. C. Pi, Y. Qian, X. Q. Huang,
ChemCatChem., 2018, 10, 3214–3218.
[15] W. Shi, B. S. Zhang, Y. M. Lin, Q. Wang, Q. Zhang, D. S. Su, ACS. Catal.,

Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
221
Graphical Abstract
Chin. J. Catal., 2019, 40: 214–222 doi: S1872-2067(19)63276-6
Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions
Pei Jing, Tao Gan, Hui Qi, Bin Zheng, Xuefeng Chu, Guiyang Yu, Wenfu Yan, Yongcun Zou, Wenxiang Zhang *, Gang Liu *
Jilin University; The Second Hospital of Jilin University; Jilin Jianzhu University
Pt/α-Fe2O3 with ultralow Pt loading amount could spatially separate the active sites for H2 dissociation and hydrogenation, leading to a
high chemoselectivity for hydrogenation of nitroarenes under mild reaction conditions.
L. Li, J. Y. Liu, J. H. Wang, G. F. Wang, D. S. Su, T. Zhang, Chem. Sci.,
2017, 8, 5126–5131.
[29] B. Zhang, H. Asakura, J. Zhang, J. G. Zhang, S. De, N. Yan, Angew.
Chem. Int. Ed., 2016, 55, 8319–8323.
2016, 6, 7844–7854.
[16] P. Lara, K. Philippot, Catal. Sci. Technol., 2014, 4, 2445–2465.
[17] G. Vilé, D. Albani, N. Almora-Barrios, N. López, J. Pérez-Ramírez,
ChemCatChem., 2016, 8, 21–33.
[30] W. Karim, C. Spreafico, A. Kleibert, J. Gobrecht, J. VandeVondele, Y.
Ekinci, J. A. van Bokhoven, Nature, 2017, 541, 68–71.
[31] L. R. Merte, G. Peng, R. Bechstein, F. Rieboldt, C. A. Farberow, L. C.
Grabow, W. Kudernatsch, S. Wendt, E. Laegsgaard, M. Mavrikakis,
F. Besenbacher, Science, 2012, 336, 889–893.
[18] J. Wang, Y. J. Zhang, J. Y. Diao, J. Y. Zhang, H. Y. Liu, D. S.Su, Chin. J.
Catal., 2018, 39, 79–87.
[19] K. Möbus, D. Wolf, H. Benischke, U. Dittmeier, K. Simon, U.
Packruhn, R. Jantke, S. Weidlich, C. Weber, B. S. Chen, Top. Catal.,
2010, 53, 1126–1131.
[32] R. Prins, Chem. Rev., 2012, 112, 2714–2738.
[20] M. Makosch, W-I. Lin, V. Bumbálek, J. Sá, J. W. Medlin, K.
Hungerbühler, J. A. van Bokhoven, ACS. Catal., 2012, 2,
2079–2081.
[21] K-i. Shimizu, Y. Miyamoto, A. Satsuma, J. Catal., 2010, 270, 86–94.
[22] K-i. Shimizu, Y. Miyamoto, T. Kawasaki, T. Tanji, Y. Tai, A. Satsuma,
J. Phys. Chem. C., 2009, 113, 17803–17810.
[23] T. Mitsudome, Y. Mikami, M. Matoba, T. Mizugaki, K. Jitsukawa, K.
Kaneda, Angew. Chem. Int. Ed., 2012, 51, 136–139.
[24] H. S. Wei, X. Y. Liu, A. Q. Wang, L. L. Zhang, B. T. Qiao, X. F. Yang, Y.
Q. Huang, S. Miao, J. Y. Liu, T. Zhang, Nat. Commun., 2014, 5,
5634–5641.
[33] B. Zheng, G. Liu, L. L. Geng, J. Y. Cui, S. J. Wu, P. Wu, M. J. Jia, W. F.
Yan, W. X. Zhang, Catal. Sci. Technol., 2016, 6, 1546–1554.
[34] A. Corma, P. Serna, H. Garcia, J. Am. Chem. Soc., 2007, 129,
6358–6359.
[35] M. Boronat, P. Concepcion, A. Corma, S. Gonzalez, F. Illas, P. Serna,
J. Am. Chem. Soc., 2007, 129, 16230–16237.
[36] J. L. Song, G. Y. Yu, X. Li, X. W. Yang, W. X. Zhang, W. F. Yan, G. Liu,
Chin. J. Catal., 2018, 39, 309–318.
[37] L. Q. Liu, F. Zhou, L. G. Wang, X. J. Qi, F. Shi, Y. Q. Deng, J. Catal.,
2010, 274, 1–10.
[38] Z. Z. Yang, N. Zhang, Y. Cao, M. C. Gong, M. Zhao, Y. Q. Chen, Catal.
Sci. Technol., 2014, 4, 3032–3043.
[25] A. Corma, P. Serna, P. Concepcion, J. J. Calvino, J. Am. Chem. Soc.,
2008, 130, 8748–8753.
[39] R. Ahmadi, M. K. Amini, J. C. Bennett, J. Catal., 2012, 292, 81–89.
[40] E. Ivanova, M. Mihaylov, F. Thibault-Starzyk, M. Daturi, K.
Hadjiivanov, J. Mol. Catal. A, 2007, 274, 179–184.
[41] S. Shen, X. L. Wang, Q. Ding, S. Q. Jin, Z. C. Feng, C. Li, Chin. J. Catal.,
2014, 35, 1900–1906.
[26] S. Zhang, C. R. Chang, Z. Q. Huang, J. Li, Z. M. Wu, Y. Y. Ma, Z. Y.
Zhang, Y. Wang, Y. Q. Qu, J. Am. Chem. Soc., 2016, 138, 2629–2637.
[27] L. Wang, E. J. Guan, J. Zhang, J. H. Yang, Y. H. Zhu, Y. Han, M. Yang, C.
Cen, G. Fu, B. C. Gates, F. S. Xiao, Nat. Commun., 2018, 9,
1362–1369.
[42] G. Richner, J. A. van Bokhoven, Y. M. Neuhold, M. Makosch, K.
[28] H. S. Wei, Y. J. Ren, A. Q. Wang, X. Y. Liu, X. Liu, L. L. Zhang, S. Miao,

222
Pei Jing et al. / Chinese Journal of Catalysis 40 (2019) 214–222
Hungerbuhler, Phys. Chem. Chem. Phys., 2011, 13, 12463–12471.
[45] S. Sultana, S. Mansingh, K. M. Parida, J. Mater. Chem. A., 2018, 6,
11377–11389.
[46] L. L. Geng, J. L. Song, B. Zheng, S. J. Wu, W. X. Zhang, M. J. Jia, G. Liu,
[43] S. Meijers, V. Ponec, J. Catal., 1996, 160, 1–9.
[44] D. Flak, Q. Chen, B. S. Mun, Z. Liu, M. Rękas, A. Braun, Appl. Surf. Sci.,
2018, 455, 1019–1028.
Chin. J. Catal., 2016, 37, 1451–1460.
铂纳米粒子与氧化铁载体协同作用促进芳香硝基化合物温和条件下选择加氢
景 培a, 甘 涛a, 戚 卉b, 郑 彬a, 初学峰c, 于贵阳a, 闫文付a, 邹永存a, 张文祥a,*, 刘 钢a,#
a吉林大学化学学院, 无机合成与制备化学国家重点实验室, 吉林长春130012
b吉林大学第二医院, 吉林长春130041
c吉林建筑大学电气与电子信息工程学院, 吉林省建筑电气综合节能重点实验室, 吉林长春130041
摘要: 负载型Pt基催化剂是一类重要的工业催化剂, 在很多还原和氧化反应中都表现出很高的催化活性, 但高昂的价格一
直制约着Pt基催化剂的大规模应用. 另外, Pt活性位点对有机化合物不同基团的区分性差, 通常造成目的产物的选择性较
低. 以人们熟知的芳香硝基化合物加氢为例, 当有其它易还原基团如C=C、C=O、–X等存在时, 在硝基加氢的同时, 这些基
团也不同程度地被还原. 在已报道的工作中, 通过合理设计Pt活性中心结构、改善Pt周围环境以及在反应中添加无机盐或
有机化合物等方法, 芳香硝基化合物加氢的选择性获得大幅提升, 但催化剂活性对Pt负载量的依赖性仍然很高, 降低催化
剂中的Pt活性位数量会显著降低催化剂活性. 此外, Pt纳米粒子在反应过程中的聚集以及氧化物载体在强还原气氛下的性
能变化等对催化剂的稳定性产生很大影响.
本文工作中我们尝试发挥载体在反应中的作用, 实现氢解离和反应物加氢活性中心在空间上分离, 从而降低Pt的负载
量. 工作思路主要是基于氢溢流的基本原理, 其难点在于高效氢解离活性中心的设计和载体的选择, 后者需满足活泼氢物
种的输运和硝基基团的有效吸附. 为了实现上述目标, 本文采用胶体法制备了3–4 nm的Pt粒子, 该方法可以有效地控制Pt
纳米粒子的尺寸以及在载体上的分散状态, 从而形成大量的Pt0活性位, 实现高效氢解离. 在充分考虑载体的氧化还原性和
表面碱性质(给电子能力)的基础上, 我们筛选了多种氧化物作为载体. 反应结果显示, Pt/α-Fe2O3在Pt负载量仅为0.2 wt%时
即表现出很高的芳香硝基化合物加氢催化活性和选择性, 并且该反应可在相当温和的条件(30 °C, 5 bar H2)下进行. 在经过
多次循环反应后, Pt纳米粒子的尺寸、分散状态以及α-Fe2O3载体的物相等均未发生变化, 催化剂表现出很高的稳定性.
Pt纳米粒子的高效氢解离能力是催化剂实现高活性的重要因素之一, 而α-Fe2O3的表面性质也同样发挥了重要作用, 其
表面一定数量的氧空位具有较强的给电子能力, 可以与具有较强吸电子能力的硝基基团作用, 实现反应物的高效吸附; 载
体表面适当的氧化还原性有利于活泼氢的输运, 在与Pt纳米粒子的协同作用下实现了温和条件下芳香硝基化合物的选择
性加氢. 本工作显著降低了Pt的使用量, 实现了非常温和条件下的稳定、高效加氢, 可为低成本Pt基催化剂的设计提供借鉴.
关键词: 负载型铂基催化剂; 氧化铁; 芳香硝基化合物加氢; 选择性; 贵金属催化
收稿日期: 2018-12-18. 接受日期: 2018-12-20. 出版日期: 2019-02-05.
*通讯联系人. 电话: (0431)85155390; 传真: (0431)88499140; 电子信箱: zhwenx@jlu.edu.cn
#通讯联系人. 电话: (0431)85155390; 传真: (0431)88499140; 电子信箱: lgang@jlu.edu.cn
基金来源: 国家自然科学基金(21473073, 21473074); 吉林省科技发展计划(20170101171JC, 20180201068SF); 吉林省教育厅“十
三五”科学技术研究项目(2016403); 无机合成和制备化学国家重点实验室开放项目(201703).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).