Bimetallic Platinum-Tin Nanoparticles on Hydrogenated Molybdenum Oxide for the Selective Hydrogenation of Functionalized Nitroarenes

Article abstract of DOI:10.1002/cctc.201700880

The hydrogenation of functionalized nitroarenes to the corresponding anilines is of great importance in the fine chemical industry and requires high-performance catalysts with a good activity and selectivity. Herein, hydrogenated MoO_x (H-MoO_x) supported bimetallic Pt-Sn (Pt-Sn/H-MoO_x) was developed to accomplish selective and efficient hydrogenation. In the case of 4-nitrostyrene, an outstanding selectivity to 4-vinylaniline (≈93 %) with a high turnover frequency (0.094 s^?1) was achieved under mild conditions (T=30 °C, P_H2 =1 atm). The metal–support interactions contributed to the efficient turnover on the ultrafine nanoparticles, and the atom-rearranged bimetallic Pt-Sn surface promoted the selectivity because of the preferred adsorption of the nitro group. The good efficiency for various functionalized nitroarenes further verified the promise of Pt-Sn/H-MoO_x in chemoselective hydrogenation.

Full text of DOI:10.1002/cctc.201700880

Accepted Article
Title: Bimetallic Pt-Sn nanoparticles on hydrogenated MoOx for the
selective hydrogenation of functionalized nitroarenes
Authors: Yijin Shu, Hang Cheong Chan, Lifang Xie, Zhangping Shi, Yi
Tang, and Qingsheng Gao
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ChemCatChem
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Bimetallic Pt-Sn nanoparticles on hydrogenated MoO for the
x
selective hydrogenation of functionalized nitroarenes
[
a]
[a]
[a]
[b]
[b]
[a]
Yijin Shu, Hang Cheong Chan, Lifang Xie, Zhangping Shi, Yi Tang, and Qingsheng Gao*
Abstract: Hydrogenating functionalized nitroarenes to the
corresponding anilines is of great importance in fine chemical
industry, which requires high-performance catalysts with good
Pt, Pd and Rh) with satisfied activity suffer seriously low
selectivity, because the undesired C=C hydrogenation is
kinetically and thermodynamically more favored than –NO .
2
[7]
activity and selectivity. Herein, hydrogenated MoO
x
(H-MoO
x
)
And, Au and Ag showing chemoselectivity for nitro group are
unfortunately prohibited by the poor activity, requiring high
supported bimetallic Pt-Sn (Pt-Sn/H-MoO was developed to
x
)
[
8-9]
accomplish selective and efficient hydrogenation. In the case of 4-
nitrostyrene, the outstanding selectivity of 4-vinylaniline (~ 93%) with
temperature or extreme H
2
pressure.
A feasible engineering is
desired to improve the both of activity and selectivity.
-
1
a high turnover frequency (0.094 s ) was achieved at a mild
Introducing other metal elements to construct bimetallic
o
[10-11]
condition (T = 30 C, PH2 = 1 atm.). The evidenced metal-support
catalysts is feasible to rearrange metal surface.
Because
interactions contributed to the efficient turnover on ultrafine
nanoparticles, and the atom-rearranged bimetallic Pt-Sn surface
promoted the selectivity owing to the preferred adsorption of nitro
group. The good efficiency for various functionalized nitroarenes
the isolation of active metal atoms will afford geometric and
electronic variation, bimetallic catalysts show the noticeable
enhancement in activity, selectivity and stability in comparison
[
10-11]
with their monometallic counterparts.
As one of the
further verified the promise of Pt-Sn/H-MoO
hydrogenation.
x
in chemoselective
promising bimetallic catalysts, Pt-Sn delivers the selectivity of
functionalized aniline in nitroarenes reduction, but the poor
activity, which might be associated with its inert supports (e.g.,
SiO
MSI).
leads to the varied catalytic turnover.
hydrogenated molybdenum oxides (H-MoO
2
and carbon) without effective metal-support interactions
[
12]
(
Noticeably, MSI arising from reducible oxides usually
Introduction
[13]
Very recently,
x
) with controlled H
Functionalized anilines, the valuable intermediates for
manufacturing dyes, pigments, pharmaceuticals and
agrochemicals, are usually produced via nitroarenes reduction.
doping and partial reduction emerge as promising supports or
additives, because the metallic band states can enhance the
[
1-
[14-15]
electronic interactions with loading metals.
The rich valence
2]
Non-catalytic processes, including either Béchamp (with
Fe/HCl as reducing system) or sulfide reduction (with H S or
states of Mo (+6, +5, +4, +3, and +2) further ensure the
2
manipulated electronic MSI
hydrogenation.
toward efficient catalytic
NaSH as reducing agent), are employed for the reduction, which
however produce a large amount of waste and cause serious
environmental problems. Catalytic systems using renewable
[16]
Herein, a rational combination of bimetallic nanocatalysts
with interactive metal-oxide supports is introduced to promote
the both of activity and selectivity for nitroarenes hydrogenation.
As shown in Scheme 1, H-MoO xx nanorods (NRs) supported Pt
[
3]
[
4-5]
2
and green reagents, e.g., H , provide feasible alternatives.
When other reducible groups, such as C=C, C≡C, C-X (X: Cl, Br
and I), C=N and C≡N, are present in the same molecule, the
catalytic reduction of nitro group in a selective manner remains
the great challenge. Particularly, the C=C bond is more
reactive than the nitro group, resulting in difficulty to selectively
(
Pt/H-MoO
fabricated, in which the H
nanoparticles (NPs) enables the controlled H-doping into parent
MoO . The MSI on H-MoO supports results in the decreasing
x
)
and Pt-Sn (Pt
m x
Sn100-m/H-MoO ) are one-step
2
spillover from as-formed Pt or Pt-Sn
[
6]
3
x
[
3]
reduce nitro in its presence. Meanwhile, the activity is another
important criterion, which is however sacrificed to ensure the
selectivity. It is challenging to explore efficient catalysts with both
good selectivity and high activity. The Pt-group catalysts (e.g.,
size of Pt NPs with increasing temperature during reduction, and
the controlled introduction of Sn gradually rearrange Pt atoms on
their bimetallic surface. The hydrogenation of 4-nitrostyrene (4-
NS) to 4-vinylaniline (4-VA), holding the great challenge in
chemoselective nitroarenes hydrogenation, is studied as the
probe reaction. Combining the MSI associated with H-MoO
the atom-rearranged bimetallic surface, the optimal Pt40Sn60/H-
MoO delivers an efficient and selective hydrogenation of 4-NS
to 4-VA, performing among the best of current metal-based
catalysts.
x
and
[
a]
Y. J. Shu, H. C. Chan, L. F. Xie, and Prof. & Dr. Q. S. Gao
Department of Chemistry, College of Chemistry and Materials
Science
x
Jinan University
No. 601 Huangpu Avenue West, 510632 Guangzhou, P. R. China
E-mail: tqsgao@jnu.edu.cn
[
b]
Z. P. Shi and Prof. & Dr. Y. Tang
Department of Chemistry, Shanghai Key Laboratory of Molecular
Catalysis and Innovative Materials and Laboratory of Advanced
Materials
Fudan University
No. 220 Handan Road, 200433 Shanghai, P. R. China
Supporting information for this article is given via a link at the end of
the document.
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Scheme 1. Schematic illustration for the fabrication of Pt/H-MoO
x
and Pt-
x
Sn/H-MoO composites. T denotes for temperature.
Results and Discussion
The MoO
3
NRs, derived from Mo
3
O10(C
6
H
8 2
N) ·2H
2
O
via
calcination under air flow (Figures S1–S3 in Supporting
Information), are used as the reducible supports for Pt and Pt-Sn.
This results in a series of rod-like catalysts after reduction
(
Figure S4 and Table S1 in Supporting Information). The H-
MoO supported Pt and Pt-Sn received at varied temperature (T)
are denoted as Pt/H-MoO -T and Pt -T,
respectively. The hydrogen temperature-programmed reduction
-TPR) was conducted to confirm the reduction of Pt and Pt-
x
x
m x
Sn100-m/H-MoO
(H
2
o
3
Sn below 300 C on MoO (Figure 1a). It’s obvious that the
introduction of Sn increases the temperature for Pt reduction,
implying the formation of bimetallic phases. A considerable H-
doping into MoO
consumption around 300 C, which is obviously lower than that
3 2
support is further indicated by the H
o
Figure 1. (a) H -TPR profiles of MoO , Pt/MoO and Pt-Sn/MoO . NH -TPD
profiles of (b) Pt/H-MoO obtained via re dd uction at varied temperature, and (c)
x
Pt Sn100-m/H-MoO -400 with different Sn cc ontent.
m x
2
3
3
3
3
o
of bare MoO
3
(> 480 C). The easier H-doping is associated with
surface.
the H spillover from as-form Pt or Pt-Sn NPs to MoO
2
3
The chemisorbed hydrogen molecules can dissociate at Pt or Pt-
Sn sites to highly active hydrogen atoms, which migrate to the
[
17]
displayed in Figure 2a, all the as-obtained Pt/H-MoO
x
show the
surface of MoO
doping into MoO
spectra (UV-vis DRS), which show the new adsorption at 400 ~
00 nm after reduction (Figure S5 in Supporting Information).
Furthermore, the acidity of the above samples was analyzed by
NH temperature-programmed desorption (NH -TPD). As shown
in Figure 1b, the amount of NH desorbed from the parent MoO
nanorods is negligible, indicating the low density of acidic sites.
3
, and further diffuse into the bulk.
The H-
o
characteristic diffraction peaks of Pt(111) and Pt(200) at 39.8
3
can be confirmed by UV–vis diffuse reflection
o
and 46.2 , respectively. Beside the peaks of H-MoO
x
at 2θ =
-300 also presents others
, which disappear after further
reduction at 400 ~ 600 C. Obviously, the H-doping into MoO is
enhanced by heating. As the Pt loading is cut down to the one-
tenth (i.e. 0.15 wt% Pt), a deep reduction of MoO to MoO at
only 400 C is observed (Figure S6 in Supporting Information),
implying the promoted -spillover on smaller Pt NPs.
o
o [18]
3
8.0 and 42.7 ,
Pt/H-MoO
x
6
associated with residual MoO
3
o
3
3
3
3
3
3
2
o
After the reduction at higher temperature, the signal for NH
desorption on Pt/H-MoO obviously increases (e.g., Pt/H-MoO
3
H
2
x
x
-
Interestingly, the peaks of Pt(111) and Pt(200) becoming broad
and weak with increasing temperature, suggest the decreasing
Pt size. This is further evidenced by TEM observation (Figure S7
in Supporting Information). Such unexpected decrease of Pt size
4
00, -500, and 600), consistent with the acidic sites arising from
[
15]
the enhanced H-doping in H-MoO
NH desoprtion at high temperature should be ascribed to the
3
x
.
Particularly, the emerging
Lewis acidic sites. By contrast, introducing Sn to construct
bimetallic Pt-Sn only generates a slight enhancement in surface
acidity (Figure 1c).
Accordingly, the structural variation relying on reduction
temperature is investigated by X-ray diffraction (XRD). As
should be ascribed to the strong interactions with H-MoO
x
[
19-20]
supports,
which are gradually doped by hydrogen upon
heating. The further interpretation will be included in the
following discussion of X-ray photoelectron spectroscopy (XPS).
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x
Figure 2. XRD patterns of (a) Pt/H-MoO obtained at varied temperature for
o
m x
reduction and (b) Pt Sn100-m/H-MoO reduced at 400 C.
Figure 4. XPS spectra of (a) Mo 3d an dd (b) Pt 4f in Pt/H-MoO
x
received after
reduction at different temperature. XPS profiles of (c) Mo 3d, (d) Pt 4f and (e)
Sn 3d for Pt40Sn60/H-MoO
x x
-400 and Pt/ HH -MoO -400.
o
After a reduction at 300 C, the Mo 3d profiles can be
deconvoluted into four peaks, ascribed to the Mo 3d5/2 and 3d3/2
Figure 3. TEM and HR-TEM images, and the corresponding particle-size
distribution of (a) 1.4%Pt/H-MoO -400 and (b) 2.7%Pt40Sn60/H-MoO -400 (Pt
loading: 1.4 wt%). (c) EDS pattern and (d) HAADF-STEM images of
Pt40Sn60/H-MoO -400, as well as the corresponding elemental mapping.
x
x
6+
5+
[21]
of Mo and Mo species.
With further reduction at higher
o
4+
x
temperature (400 ~ 600 C), the species of Mo emerges,
consistent with the enhanced reduction of MoO upon heating.
The corresponding evolution was observed in Pt 4f (Figure 4b).
The Pt/H-MoO -300 shows a doublet at 71.3 and 74.7 eV,
associated with the 4f7/2 and 4f5/2 of metallic Pt.
3
Furthermore, the introduction of Sn also leads to structural
variation (Figure 2b). In comparison with Pt/H-MoO , only the
peaks for H-MoO are detected by XRD in a series of Pt
/H-MoO , and those for Pt-Sn alloys are absent, suggesting the
ultra-small NPs. This can be further verified by TEM
investigation, taking Pt/H-MoO and Pt40Sn60/H-MoO for
comparison (Figures 3a and 3b). The average size of Pt in
x
[22]
x
With the
x
m
Sn100-
increasing reduction temperature, such peaks are obviously
m
x
shifted to higher binding energy, indicating the positively
δ+
x
charged Pt (Pt ) due to their interactions with H-MoO .
x
x
According to the previous experimental discovery and theoretical
[16]
3
calculation, the effective H-doping and reduction of MoO can
1
2
0
.4%Pt/H-MoO
.7%Pt40Sn60/H-MoO
.5 nm. In their HRTEM images, the characteristic lattices of Pt
and
(insets of Figures 3a and 3b), respectively.
The attached energy dispersive spectra (EDS) also identify the
loading of the corresponding metals on H-MoO supports (Figure
c and Figure S8 in Supporting Information). The high-angle
annular dark-field scanning transmission electron microscopy
HAADF-STEM, Figure 3d) displays the uniform distribution of
Mo, O, Pt and Sn in Pt40Sn60/H-MoO -400, identifying the well-
dispersed Pt–Sn NPs on H-MoO supports. To further ensure
x
is about 6.0
± 0.5 nm, while that in
lead to the metallic band configuration, which promotes the MSI
with loading metals. It’s remarkable that such interactions can be
x
(Pt: 1.4 wt%) is obviously reduced to 3.5 ±
varied by controlling the reduction degree in H-MoO
x
supports.
and Pt-Sn alloy are well observed on 1.4%Pt/H-MoO
.7%Pt40Sn60/H-MoO
x
Owing to such electronic interactions gradually enhanced by H-
2
x
[19-20]
doping,
the size of Pt will decrease as the temperature
increases during reduction (c.f. Figure 2a).
When Sn is introduced, negligible variation is observed in
the binding energy of Pt and Mo (Figure 4c and 4d). Both of
x
3
1
.4%Pt/H-MoO
x
-400 and 2.7%Pt 44 0Sn60/H-MoO
x
-400 present the
(
δ+
positive Pt species. In addition, the Sn in 2.7%Pt40Sn60/H-
0
x
MoO
oxidized species (Figure 4e). Meanwhile, the strong electronic
interactions associated with H-MoO are still obvious in
bimetallic Pt-Sn/H-MoO , as indicated by the blue-shift owing to
x
-400 is mainly represented by Sn , as well as some
x
the presence of both Pt and Sn on metal NPs, the linear
scanning EDS analysis was conducted on a slightly larger Pt-Sn
NPs (Figure S9 in Supporting Information). The correlative
distribution of Pt and Sn along Pt-Sn particles indicates the
formation of bimetallic Pt-Sn NPs.
x
x
H-doping in their Pt 4f XPS profiles (Figure S10 in Supporting
Information). As a result, the size of Pt-Sn NPs decreases with
the increasing temperature in reduction (Figure S11 in
Supporting Information), consistent with the situation of Pt/H-
XPS was carried out to study the chemical state of elements
in Pt/H-MoO
x
and Pt
m
Sn100-m/H-MoO
x
. Figures 4a and 4b display
, respectively.
MoO
x
. These well confirm the strong MSI for both Pt and Pt-Sn
supports.
the profiles of Mo 3d and Pt 4f on 1.4%Pt/H-MoO
x
on the interactive H-MoO
x
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Figure 6. (a) Product distribution ove rr 2.7%Pt40Sn60/H-MoO
wt%). (b) Cycling catalytic test of 4-NS hydrogenation over 2.7%Pt40Sn60/H-
MoO -400, Reaction condition: 1 mmol oo f 4-NS, catalyst (Pt : 4-NS = 0.002),
H2 = 1 atm, 30 mL of EtOH, 30 C, 1 h oo ur.
x
-400 (Pt: 1.4
x
o
P
o
3
00 ~ 600 C (Figure S12 in Supporting Information). Among
them, the 2.7%Pt40Sn60/H-MoO -400 remarkably fulfils the high
selectivity as well as the good activity. And the relatively low
selectivity on Pt-Sn/H-MoO -600 should be ascribed to easy
hydrogenation of 4-NS on ultrafine and positively-charged Pt-Sn
NPs, in which function groups show negligible difference in their
adsorption or activation on highly active metals. By contrast,
x
Figure 5. (a) Schematic illustration for the hydrogenation of 4-NS, and the
performance over (b) 1.4%Pt/H-MoO
temperature and (c) Pt Sn100-m/H-MoO -400 (fixed Pt loading of 1.4 wt%) with
varied Sn/Pt ratio. Reaction condition: 1 mmol of 4-NS, catalyst (Pt : 4-NS =
x
received at different reduction
x
m
x
o
0
.002), PH2 = 1 atm, 30 mL of EtOH, 30 C, 1 hour.
2
although Pt/SiO and Pt/C show high activity, they suffer the
obvious decrement as Sn is introduced (Table S2 in Supporting
The hydrogenation of 4-nitrostyrolene (4-NS) to 4-
Information), suggesting that the MSI associated with H-MoO
also contributes to the high activity on Pt-Sn.
x
vinylaniline (4-VA) was employed as the probing reaction for the
above catalysts. The typical hydrogenation routes are shown in
Figure 5a. The desired 4-VA is obtained via the direct
hydrogenation of nitro group, while the C=C hydrogenation
Figure 6a gives the details of product distribution on
o
x 2
Pt40Sn60/H-MoO -400. With a mild condition (30 C, 1 bar H ),
[
23]
the main product is the desired 4-VA, and by-products of 4-ENB
and 4-EA are kept at a low level. Almost complete conversion of
results in the undesired 4-ethylnitrobenzene (4-ENB).
The
partially-hydrogenated products of 4-VA and 4-ENB can be
further hydrogenated to 4-ethylaniline (4-EA). Figure 5b presents
4-NS is observed after 120 minutes, reaching the maximum
yield of desired 4-VA. At this point, the 4-VA selectivity is as high
as 90%. Remarkably, such selective performance is superior to
that of previously reported metal and bimetal catalysts, e.g.,
the activity of Pt/H-MoO
catalyst reduction. With the temperature increasing from 300 to
x
relying on the temperature adopted for
o
6
00 C, the Pt/H-MoO
conversion. Unfortunately, the poor selectivity of 4-VA is
delivered by the above Pt/H-MoO , as low as ~ 40% on Pt/H-
-300, -400, and -500. And no 4-VA is detected on Pt/H-
-600. Thus, an enhancement on selectivity is essentially
x
shows an obvious improvement in 4-NS
[
22]
[24]
Pt/Ti-WO
x
[
(sel.: 66%), Pt@MFI zeolite
(sel.: 80%) and
23]
RhIn/SiO
2
(sel.: 84%). Noticeably, higher temperature (e.g.,
2
pressure (10 ~20 bar) is usually required to reach
x
o
8
0 C) or H
MoO
MoO
x
[
22,24]
the good activity,
which can be easily accomplished by a
mild reaction (30 C, 1 bar H ) on Pt40Sn60/H-MoO . In addition,
the Pt40Sn60/H-MoO -400 exhibits good stability. In the
x
o
2
x
demanded.
x
Bimetallic Pt-Sn NPs were constructed to improve the
selectivity of 4-VA, in which a moderated reduction at 400 C
was adopted. The introduction of Sn visibly increases the 4-VA
selectivity from 44% to a maximum of 93%, with the Sn/Pt molar
ratio from 0 to 1.5 (Figure 5c). And, no obvious variation in 4-NS
o
consecutive 6 cycle operation, negligible decrease in activity and
selectivity is observed (Figure 6b).
The promotion of 4-NS hydrogenation is obviously
associated with H-MoO
experimental discovery and theoretical calculation,
effective H-doping into MoO can lead to the large density states
within band gap, showing the strong MSI with loading metals.
x
support. According to the previous
[
16]
the
conversion is observed on these Pt
promoted selectivity by bimetallic Pt-Sn is further confirmed on
Pt that is reduced at varied temperature, i.e.,
m x
Sn100-m/H-MoO . The
3
m
Sn100-m/H-MoO
x
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Pt
m
Sn100-m/H-MoO
x
is rationally contributed by Pt and Pt-Sn,
x
respectively. On Pt/H-MoO -400, two broad peaks located at 150
o
o
~
250 C and 300 ~ 400 C are clearly observed, which can be
ascribed to the linear (α) and bridge (β) modes of CO
[
25]
chemisorption, respectively. After the introduction of Sn, the β
peak obviously decreases, indicating the diminishing bridge
[
26-27]
adsorption of CO on bimetallic NPs.
This variation indicates
the formation of bimetallic surface, in which Pt sites isolated by
Sn atoms don’t prefer the bridge CO adsorption. In this way, the
different configuration of 4-NS on Pt and Pt-Sn surface should
be taken into account for the varied hydrogenation selectivity. In
general, π adsorption mode is energetically favoured for an
[
22 3,28]
alkenyl moiety on Pt and Rh.
As for 4-NS, it’s further
demonstrated that both of vinyl moiety and aromatic ring were
[
23,29]
bound to Pt-group metals,
requiring the 4-NS activation on
neighbor metal atoms in the view of Balandin multiplet theory.
By contrast, only nitro group was adsorbed on metal towards
[
23]
nitro hydrogenation,
i.e., the activation on single metal-site.
Due to the isolated Pt atoms on bimetallic Pt-Sn surface, the
adsorption of vinyl moiety on multiple Pt atoms will be resitrictied,
while, the activation of nitro group on single Pt site is
insusceptible (Figure 7c). Meanwhile, the oxytropic Sn atoms
possessing strong interactions with nitro group also facilitate the
[
30]
preferential adsorption and activation. Therefore, the selective
hydrogenation is promoted on bimetallic Pt-Sn surface.
Furthermore, our Pt40Sn60/H-MoO
in a sense as a universal catalyst for nitroarenes hydrogenation
Table 1). The results clearly confirm that the chemoselective
x
-400 can be considered
(
hydrogenation of nitro group can be performed in the presence
of various groups like olefins, ha ll ogens and carboxylic acid. For
nitrobenzene, a selectivity of desired aniline as high as 91% is
observed (entry 1, Table 1), in which the by-products of
phenylhydroxylamine and azobenzene are negligible. Similar
with the reduction of 4-NS, the selective hydrogenation of 3-NS
to 3-VA (sel.: 80%) is also achieved at a mild condition (entry 2,
Table 1). In the case of halogenated nitrobenzenes (entries 3 ~
Figure 7. Schematic illustration for the hydrogenation of 4-NS over (a) Pt/H-
MoO
x x 3 x
and (c) Pt-Sn/H-MoO , and (b) CO-PTD profiles of MoO , Pt/H-MoO
and Pt-Sn/H-MoO
x
.
6, Table 1), the selectivity of the corresponding halogenated
anilines can be maintained at a high level (94 ~ 98%), with an
almost complete conversion of subtracts. No dehalogenation
products are detected after reaction, which are usually the by-
products on Pt mono-metal catalysts. As the good examples
for carboxyl functionalized nitroarenes, 3-nitrobenzoic and 4-
nitrobenzoic can be efficiently hydrogenated to the
corresponding animobenzoic acid (entries 7 and 8, Table 1),
showing the high selectivity >99%. These results well verify
Such interactions in Pt/H-MoO
doping and partial reduction in H-MoO
temperature in reduction. Thus, the Pt NPs on H-MoO
diminish in size (Figure 2a and S7 in Supporting Information),
and more importantly they are positively-charged due to the
charge redistribution on interfaces (Figure 4b). These variations
x
are enhanced by improving H-
, as a result of increasing
surface
x
[
12]
x
should be responsible for the superior activity on Pt/H-MoO
x
, as
shown in Figure 7a. In addition, the surface acidity of H-MoO
x
m
Pt Sn100-m/H-MoOx as
a
promising catalyst for the
supports should be noticed. The enhanced acidity due to H-
doping, espeically the emerging Lewis acidic sites confirmed by
chemoselective hydrogenation of nitroarenes.
3
NH -TPD (Figure 2b), will promote the adsorption of substract
with large π electrons. However, it doese not favor the selective
conversion to 4-VA.
Conclusions
Introducing Sn leads to the obvious improvement in
selectivity, probably due to the atom-rearranged bimetallic
surface. We conducted CO temperature-programmed desorption
x
In summary, bimetallic Pt-Sn catalyst loading on H-MoO was
developed for the chemoselective hydrogenation of
functionalized nitroarenes. Strong electronic interactions arising
from H-MoO supports were evidenced, which led to the efficient
x
hydrogenation on diminishing metal NPs with positive charge.
Via introducing Pt-Sn bimetallic catalysts, the highly selective
(
CO-TPD) to investigate the surface evolution after Sn
introduction (Figure 7b). Regarding the negligible CO desorption
on bare MoO , the visible CO adsorption on Pt/H-MoO and
3
x
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Chemical Reagent Co. Ltd (Shanghai, China). Hydrochloric acid was
purchased from Guangzhou Chemical Reagent Factory. H PtCl , SnCl ,
2 6 2
Table 1. Hydrogenation of various functionalized nitroarenes over Pt40Sn60/H-
[
a]
MoO
x
-400.
2
SiO , and CNT were purchased from Aladdin. All aqueous solutions were
prepared using ultrapure water (> 18 MΩ).
o
Catalyst preparation
Entry
Substrate
Product
T ( C) Conv. (%) Sel. (%)
Synthesis of MoO
according to our previous report : 2.48 g of ammonium heptamolybdate
((NH Mo O) was dissolved in 40 mL of distilled water, and then
.34 g of aniline was added in the above solution. Afterwards, 1 M HCl
aqueous solution was dropwise added with magnetic stirring at room
temperature until white precipitate appeared (pH 4~5). After stirring at
3 3
NRs: The synthesis of MoO NRs was conducted
[32]
NO
2
NH
2
[
b]
b]
4
)
6
7 2
O24·4H
1
2
30
30
92
98
91
80
3
NO
2
NH
2
[
50 °C in oil bath for 4 hours, the Mo
Finally, MoO NRs were harvested after calcining Mo
at 400 C for 2 hours under air flow.
Synthesis of Pt/H-MoO , Pt-Sn/H-MoO
and Pt-Sn/C catalysts: An impregnation method was introduced for the
3 6
O10(C H
8
N)
2 2
·2H O was received.
3
3
O10(C
6
H
8
N) ·2H
2
2
O
o
NO
2
NH
2
x
x 2 2
, Pt/SiO , Pt-Sn/SiO Pt/C
[
b]
3
30
30
98
95
94
98
synthesis. Typically, supports (MoO SiO
6
impregnated with H PtCl or H PtCl -SnCl
3
,
2
,
or active carbon) were
solution, and then were
Cl
Cl
2
6
2
2
o
NO
2
NH
2
stirred at 80 C in oil bath until dried. The solids were reduced with a
stream of 5 vol% H /Ar at target temperature for 2 hours (H-MoO
2
x
[
b]
o
4
supported catalysts: 300 ~ 600 C; SiO and carbon supported catalysts:
2
o
4
00 C).
Br
Br
Physical characterization
SEM was taken on a ZEISS ULTRA55. TEM, HRTEM, EDS and
elemental mapping investigations were carried out with a JEOL JEM
2100F. XRD analysis was performed on Bruker D8 diffractometer using
Cu Kα radiation (λ = 1.54056 Å). XPS was processed on a Thermo
scientific (Escalab 250Xi), using C 1s (284.6 eV) as a reference. The
metal loading was determined by an inductively coupled plasma-atomic
emission spectroscopy (ICP-AES). The H -TPR, CO-TPD and NH -TPD
2 3
were conducted on a Quantachrome CHEMBET PULSAR TPR/TPD.
Catalytic performance measurement
NO
2
NH
2
[
[
b]
b]
30
>99
>99
98
95
5
Cl
Cl
NO
2
NH
2
30
6
Br
Br
NO
2
NH
2
The hydrogenation of nitroarenes were performed in 300 mL Parr 5500
series compact reactor which was assembled with Parr 4848 reactor
[
c]
7
60
60
>99
>99
>99
>99
controller. In a typical reaction, catalyst and nitroarenes (nPt : nnitroarenes
0.002) were dispersed into the 30 mL of ethanol. The reactor was sealed
and purged with H to remove the a ii r for 5 times, and then the reactor
=
HOOC
HOOC
HOOC
HOOC
NO
2
NH
2
2
[
d]
8
was heated to the desired temperature. And the products were analyzed
by Shimadzu HPLC-20 with a UV-detector. To calculate the turn-over
frequency (TOF), it is assumed that all of Pt contributes to catalytic
hydrogenation. The TOF value for 4-VA formation was determined by the
target product generated on per Pt per second.
[
a]
Reaction conditions: 1 mmol of substrate, 2.7%Pt40Sn60/H-MoO
substrate = 0.002), 30 mL of EtOH, PH2 = 1 bar. Reaction time: 6 hours,
hours, 2 hours.
x
-400 (Pt :
[b]
[c]
4
[
d]
hydrogenation with superior activity was accomplished. As a Acknowledgements
result, the Pt-Sn/H-MoO presents the selective hydrogenation of
-NS to 4-VA (TOF: 0.094 s , VA sel.: ~93%) at a mild condition
x
-
1
4
(
We appreciate the financial support from National Natural
Science Foundation of China (21433002 and 21373102),
Guangdong Natural Science Funds for Distinguished Young
Scholar (2015A030306014), Guangdong Program for Support of
Top-notch Young Professionals (2014TQ01N036), and Science
and Technology Program of Guangzhou (201707010268).
o
T = 30 C, PH2 = 1 atm.), performing among the best of ever
reported metal-based catalysts. Showing the efficiency for
various functionalized nitroarenes, our Pt-Sn/H-MoO is
promising in chemoselective hydrogenation. It is envisioned that
the precise control over the interfaces between bimetallic
catalysts and oxide supports would further boost the catalytic
x
[
31]
applications.
Keywords: bimetallic Pt-Sn, metal-support interactions,
hydrogenated
molybdenum
oxides,
chemoselective
hydrogenation, functionalized nitroarenes
Experimental Section
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Bimetallic Pt-Sn catalysts supported
Yijin Shu, Hang Cheong Chan, Lifang
Xie, Zhangping Shi, Yi Tang, and
Qingsheng Gao*
by hydrogenated MoO
MoO ) delivered both high selectivity
and activity for the selective
hydrogenation of functionalized
x
(Pt-Sn/H-
x
nitroarenes at a mild condition. The
atom-rearranged bimetallic Pt-Sn
surface and the electronic metal-
Page No. – Page No.
Bimetallic Pt-Sn nanoparticles on
support interactions with H-MoO
contributed to the remarkably
improved selectivity and activity,
respectively.
x
x
hydrogenated MoO for the selective
hydrogenation of functionalized
nitroarenes
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