Deficient copper decorated platinum nanoparticles for selective hydrogenation of chloronitrobenzene

Article abstract of DOI:10.1039/c7ta01587a

Two types of model Pt-Cu catalysts are designed and prepared to explore the contribution of the geometric and electronic effects from copper to the catalytic performance of Pt nanoparticles in the selective hydrogenation of p-chloronitrobenzene (p-CNB). One model Pt-Cu catalyst (called Cu/C-Pt) is Pt nanoparticles deposited on ultra-small copper particle-decorated activated carbon, and the other is copper particle-decorated Pt/C catalyst (called Pt/C-Cu). Cu/C-Pt catalyst has an activity lower than that of Pt/C, but the selectivity of the desired product p-chloroaniline (p-CAN) on the Cu/C-Pt catalyst is much higher than that on Pt/C. On the Pt/C-Cu catalyst, p-CNB cannot be completely converted into p-CAN. The dechlorination rates of p-CAN on Cu/C-Pt catalysts are three orders of magnitude lower than that on Pt/C. More interestingly, the dechlorination reaction of p-CAN on Pt/C-Cu cannot be observed. High resolution TEM images of our Pt-Cu catalysts show that Pt nanoparticles keep their crystalline structure after incorporation with copper. The dispersions of Pt in 2Pt/C, 5Cu/C-2Pt, and 2Pt/C-5Cu reach 0.106, 0.083 and 0.027, respectively (the numbers before Pt and Cu represent their percentages), revealing that Pt nanoparticles in Cu/C-Pt have a larger exposed surface than those in Pt/C-Cu. It can be deduced that copper mainly exerts an electronic effect on the catalytic performance of Pt nanoparticles in Cu/C-Pt. On the other hand, the geometric effect on Pt from copper in Pt/C-Cu leads to not only a low dispersion of Pt nanoparticles but a weak activity in catalytic hydrogenation of p-CNB and dechlorination of p-CAN. The interaction between Pt nanoparticles and Cu nanoparticles at room temperature is also discussed.

Full text of DOI:10.1039/c7ta01587a

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Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
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Journal Name
ARTICLE
Deficient Copper Decorated Platinum Nanoparticles for Selective
Hydrogenation of Chloronitrobenzene
Received 00th January 20xx,
Accepted 00th January 20xx
Xin Li,a,b Yue Wang,b Liqun Li,c Wenqing Huang,c Zicheng Xiao,a,* Pingfan Wu,a,* Wenbo Zhao,d
Wei Guo,d Peng Jiang,b,e* Minghui Liang,b,*
DOI: 10.1039/x0xx00000x
Two kinds of model Pt-Cu catalysts are designed and prepared to explore the contribution of geometric effect and
electronic effect from copper to the catalytic performance of Pt nanoparticles in the selective hydrogenation of p-
chloronitrobenzene (p-CNB). One model Pt-Cu catalyst (called Cu/C-Pt) is Pt nanoparticles depositing on ultra-small
copper particles decorated activated carbon, and another is copper particles decorated Pt/C catalyst (called Pt/C-Cu).
Cu/C-Pt catalyst has lower activity than Pt/C , but the selectivity of the desired product p-chloroaniline (p-CAN) on Cu/C-Pt
catalyst is much higher than that on Pt/C. Over Pt/C-Cu catalyst, p-CNB cannot be completely converted into p-CAN. The
dechlorination rates of p-CAN on Cu/C-Pt catalysts are three orders of magnitude lower than that on Pt/C. More
interestingly, the dechloronation reaction of p-CAN on Pt/C-Cu cannot be observed. High resolution TEM images of our
Pt-Cu catalysts show that Pt nanoparticles keep their crystalline structure after incorporation with copper. The dispersions
of Pt in 2Pt/C, 5Cu/C-2Pt, and 2Pt/C-5Cu reach 0.106, 0.083 and 0.027, respectively (the numbers before Pt and Cu
represent their percentages), revealing that Pt nanoparticles in Cu/C-Pt have much more exposed surface than that in
Pt/C-Cu. It can be deduced that copper mainly exerts electronic effect on the catalytic performance of Pt nanoparticles in
Cu/C-Pt . On the other hand, geometric effect on Pt from copper in Pt/C-Cu lead to not only the low dispersion of Pt
nanoparticles but its weak activity on catalytic hydrogenation of p-CNB and dechlorination of p-CAN. The interaction
between Pt nanoparticles and Cu nanoparticles at room temperature is also discussed.
www.rsc.org/
metal to PGE catalysts’ performance, because the ratio of
metal to PGE, geometric effect and electronic effect are hard
to be tuned independently in the metal-PGE alloy or core-shell
Introduction
To controllably modify the catalytic performance of Pt group
elements (PGE, such as Pt, Ru and Rh) is an important issue
because of not only their extensive industrial application fields
but its great scientific interests.1-7 The added second non-Pt
group metal elements can act as an effective modifier for PGE
catalysts.8-12 Usually, the added metal incorporates with PGE in
the form of alloy or core-shell structure.13-17 The added metal
exerts the influence on the catalytic performance of PGE
catalysts in two ways, i.e. geometric effect and electronic
effect.18-20 However, it is difficult to know how much
contribution of geometric effect and electronic effect of added
structure. To know the role of geometric effect and electronic
effect in determining the catalytic performance of catalysts is
of great assistance in controllably modulating their
performance. It is thus necessary to develop newly structured
catalysts to explore the contribution of electronic effect and
geometric effect of added metal to PGE catalysts’ performance.
Chloroanilines (CANs) are important industrial intermediates,
which can be obtained by selective hydrogenation of
chloronitrobenzenes (CNBs) over PGE catalysts.21-24 One great
problem concerning this reaction is the dechlorination reaction,
particularly on CANs. Through metal-support interaction,
dechlorination reaction of CANs has been completely
suppressed on our previously reported catalyst of Pt
nanoparticles on partially reduced magnetic gamma-Fe2O3,
a.Institute of POM-based Materials, School of Materials and Chemical Engineering,
Hubei University of Technology, Wuhan, 430068, China, zichxiao@hotmail.com,
pingfanwu-111@163.com.
26
indicating that electronic effect can cause this result.25,
b.CAS Center for Excellence in Nanoscience, Key Laboratory of Nanosystem and
Hierarchical Fabrication, National Center for Nanoscience and Technology, No.11
Beiyitiao Zhongguancun, Beijing 100190, China. Email: pjiang@nanoctr.cn,
liangmh@nanoctr.cn, TEL: 861082545702
However, for the reported bimetallic (or multicomponent)
catalysts, such as Ru-Sn alloy, Ni-Pt-B alloy, Pt-Cu alloy, Pt-B
alloy and Pd@Pt core-shell nanoparticles, it is hard to attribute
the enhanced catalytic performance to electronic effect or
geometric effect.27-31
c. SINOPEC Beijing Research Institute of Chemical Industries, Beijing 100013, China.
d.National Research Centre for Geoanalysis, Beijing, 100037, China.
e. College of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, P. R. China.
Electronic Supplementary Information (ESI) available: STEM image of Cu(OH)2/C,
experimental details for the preparation of PVP-Metals samples, and ex-situ
treatment in the XPS apparatus. See DOI: 10.1039/x0xx00000x
To solve above problem, we developed two kinds of model
catalysts based on Pt nanoparticles for selective hydrogenation
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of p-chloronitrobenzene. One kind of Pt catalyst is Pt Table 1 the percentages of Cu and Pt in the catalyVsitesw Article Online
DOI: 10.1039/C7TA01587A
nanoparticles depositing on ultra-small copper nanoparticles
Catalyst
2Pt/C
2Cu/C-2Pt
5Cu/C-2Pt
10Cu/C-2Pt
20Cu/C-2Pt
2Pt/C-5Cu
Cu (wt.%)
Pt (wt.%)
decorated active carbon, and another is ultra-small copper
nanoparticles decorated Pt/C catalyst. The catalytic
performance and the characterization results of the catalysts
help us to know the role of geometric and electronic effect in
determining the catalytic performance of bimetallic catalysts.
-
1.65
1.84
1.96
1.83
1.63
1.62
1.31
6.32
8.47
18.12
4.44
Results and discussion
Table 2 the catalytic performance of the catalysts.
Two kinds of Pt-Cu catalysts were prepared as Scheme 1
depicted to explore the geometric effect and electronic effect
of copper on Pt nanoparticles. The soluble Cu(NH3)4(OH)2
aqueous solution was used as the precursor of metallic copper.
After evaporation of solution, it is difficult to observe Cu or
Cu(OH)2 nanoparticles for Cu/C in TEM images, indicating the
size of Cu or Cu(OH)2 nanoparticles are very small (Fig. S1, S2).
The STEM image (Fig. S3) of Cu(OH)2/C revealed that ultra-
small Cu(OH)2 nanoparticles evenly distributed on activated
carbon, which allowed randomly deposited Pt nanoparticles to
combine with Cu. The similar phenomenon has been reported
by us on ultra-small Ni(OH)2 nanoparticles over carbon.32 After
Pt colloid nanoparticles deposited on Cu/C derived from
Cu(OH)2/C, the Cu/C-Pt catalyst can be obtained. Another kind
of catalyst Pt/C-Cu was prepared by depositing Cu(OH)2 on the
Pt/C catalyst and reducing Cu(OH)2 by NaBH4 at room
temperature.
Time
（min） （×10-2）
Rate a
Selectivity (%)
Conversion
(%)
Catalyst
p-CAN
75.2
99.5
76.2
36.4
37.5
11.5
7.8
AN
20.5
0.5
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
2Pt/C
20
20
10
10
20
20
20
20
-
-
100
100
88.9
8.1
87.4
81.8
29.4
19.1
2Cu/C-2Pt
2Pt/Cb
1185
54
7.4
6.9
2.6
1.3
2Cu/C-2Ptc
5Cu/C-2Pt
10Cu/C-2Pt
20Cu/C-2Pt
2Pt/C-5Cu
18.9
Reaction conditions: temperature, 333 K; stirring rate, 700 rpm; the
pressure of hydrogen, 1 MPa; Pt in the catalyst, 0.019 mmol; the ratio of
substrate to catalyst (S/C), 100:1;
a, molCNBmolPt-1s-1;
b, the ratio of S/C, 8000:1;
c, the ratio of S/C, 4000:1
Above catalysts were tested for the catalytic hydrogenation
of p-chloronitrobenzene (p-CNB). As table 2 listed, Pt/C
The percentages of Cu and Pt in the prepared catalysts were catalyst and 2Cu/C-2Pt catalyst have very high activity for the
measured with ICP-AES as Table 1 listed. The numbers before hydrogenation of p-CNB. After 20 minutes reaction time, p-
copper or platinum represent the desired percentages.
CNB was completely consumed for both catalysts as the ratio
of substrate to catalyst (S/C) was 100:1. To distinguish the
difference in activity between Pt/C and 2Cu/C-2Pt, the ratios
of S/C were increased, and the activity of Pt/C was about 22
times of that of 2Cu/C-2Pt according to the test results.
However, the selectivity for p-CAN on Pt/C was lower than that
on 2Cu/C-2Pt, and the by-product aniline on Pt/C (20.5%) was
much higher than that on 2Cu/C-2Pt (0.5%). As the percentage
of copper increased for the Cu/C-Pt catalysts, the reaction rate
greatly decreased. For the nearly same percentages of Cu and
Pt, the reaction rate of 5Cu/C-2Pt was about 5.7 times as high
as that of 2Pt/C-5Cu, indicating the different structure of
5Cu/C-2Pt from 2Pt/C-5Cu.
Because the substrate p-CNB was not completely consumed
for 5Cu/C-2Pt, 10Cu/C-2Pt, 20Cu/C-2Pt and 2Pt/C-5Cu, the
reaction time was extended to 480 minutes to study the
difference in the catalytic performance of the catalysts. As
listed in table 3, p-CNB can be converted into p-CAN and AN on
the catalysts of 5Cu/C-2Pt and 10Cu/C-2Pt in the 480 minutes
reaction time. However, only 65% of p-CNB on 20Cu/C-2Pt
and 2Pt/C-5Cu can be hydrogenated into p-CAN in so long
reaction time. It is worth noticing that the selectivity of
produced AN on all Pt-Cu catalysts is very small, indicating the
low activities of these catalysts toward the dechlorination
reaction of p-CAN.
Scheme 1 the preparation route of two model catalysts Cu/C-
Pt and Pt/C-Cu.
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To prove this point, p-CAN was used as the substrate for
ARTICLE
The excellent performance of the Pt-Cu cataVlyieswtsArtiinclsepOinrleinde
DOI: 10.1039/C7TA01587A
hydrogenation dechlorination reaction on these catalysts. As us to explore the catalysts’ structure. The XRD patterns of the
table 4 shows, the dechlorination reaction rate on Pt/C is catalysts are shown in Fig. 1. As a result of the low percentages
fastest, reaching 8400 μmolCANmolPt-1s-1. But that on 2Cu/C-2Pt, of Pt in the catalysts, the diffraction peaks of metallic Pt
5Cu/C-2Pt and 10Cu/C-2Pt can only be 6.8, 15.5 and 7.4 cannot be observed. However, the diffraction peaks of copper
μmolCANmolPt-1s-1, respectively, which have three orders of nanoparticles can be clearly observed, particularly for 20Cu/C-
magnitude lower than that of Pt/C. More interestingly, the 2Pt. These results revealed that copper in the catalysts are of
dechlorination of p-CAN on 20Cu/C-2Pt and 2Pt/C-5Cu hardly metallic state, which was produced from Cu(OH)2 by reducing
occurred, even if the reaction time was extended to 960 with NaBH4 at room temperature.
minutes. These results reveal that copper has a great influence
on the Pt nanoparticles’ catalytic performance.
The Cu/C-Pt catalyst’s stability in the hydrogenation of p-
CNB was also tested. The 2Cu/C-2Pt catalyst was tested for 8
times for catalytic hydrogenation of p-CNB. With the same
Cu(111)
PDF card No. 04-0836
reaction conditions as that in table 2, all of the conversions of
Cu(200)
p-CNB reached 100%, and the selectivity of p-CAN was larger
than 99.5% in 20 minutes reaction time for every batch.
Cu(220)
20Cu/C-2Pt
10Cu/C-2Pt
5Cu/C-2Pt
2Cu/C-2Pt
2Pt/C-5Cu
Table 3 the catalytic performance of the catalysts in longer
time
2Pt/C
C
Time
（min） （×10-2）
Rate a
Selectivity (%)
Conversion
(%)
30
40
50
60
70
80
Catalyst
p-CAN
99.2
99.6
99.6
95.5
87.7
AN
0.8
0.4
0.4
<0.1
<0.1
2 Theta (deg)
2Cu/C-2Pt
5Cu/C-2Pt
10Cu/C-2Pt
20Cu/C-2Pt
2Pt/C-5Cu
480
480
480
480
480
-
-
-
100
100
100
65.5
Fig. 1 The XRD patterns of the catalysts.
0.23
0.23
65.1
Reaction conditions: temperature, 333 K; stirring rate, 700 rpm; the
pressure of hydrogen, 1 MPa; Pt in the catalyst, 0.019 mmol; the ratio of
S/C, 100:1;
a, molCNBmolPt-1s-1;
Table 4 the hydrogenation dechlorination of p-CAN on the
catalysts
Time
（min）
Conversion
(%)
Catalyst
Rate a
2Pt/C
270
270
270
270
270
960
270
960
8400
6.8
15.5
7.4
0
0
0
55.3
0.1
0.3
0.1
0
0
0
2Cu/C-2Pt
5Cu/C-2Pt
10Cu/C-2Pt
20Cu/C-2Pt
20Cu/C-2Pt
2Pt/C-5Cu
2Pt/C-5Cu
0
0
Reaction conditions: temperature, 333 K; stirring rate, 700 rpm; the
pressure of hydrogen, 1 MPa; Pt in the catalyst, 0.019 mmol; the ratio of
S/C, 100:1;
Fig. 2 the HRTEM images of (a) 2Pt/C, (b) 2Cu/C-2Pt (c) 5Cu/C-
2Pt, (d) 10Cu/C-2Pt, (e) 20Cu/C-2Pt and (f) 2Pt/C-5Cu. The
insets are the enlarged images of Pt nanoparticles.
a, μ
molCANmolPt-1s-1;
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It is worth mentioning that our Pt-Cu catalysts were based
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DOI: 10.1039/C7TA01587A
on Pt nanoparticles; therefore the preparation of the catalysts
involved a big problem how Pt nanoparticles interact with
metallic copper at room temperature. The morphologies of
2Pt/C, 5Cu/C-2Pt and 2Pt/C-5Cu are shown in Fig.S4, S5 and S6,
respectively. The difference between Pt/C and Cu/C-Pt in
morphology is not remarkable. The Pt nanoparticles in the
catalysts were observed with high resolution transmission
electron microscopy (HRTEM) as Fig. 2 shows. For all of the
samples, the d-space lattices correspond to Pt(111) can be
clearly observed, revealing that Pt nanoparticles’ crystalline
structure did not significantly change whatever the way or the
amount copper was added.
Cu(111)
Cu(200)
Cu(220)
a: Cu-PVP
b:PtCu-PVP
c:Pt-PVP/Cu-PVP
d:Pt-PVP
30
40
50
60
70
80
2 Theta (deg)
Pt-L
b
Fig. 4 The XRD patterns of Pt-PVP, Cu-PVP, Pt-PVP-Cu-PVP and
PtCu-PVP.
Cu/Pt (wt.)= 0.054
To further reveal the structural information of Pt
nanoparticles, the STEM images and EDX patterns of the
catalysts were obtained as Fig. 3 shows. The white spots in Fig.
3a, 3c, 3e and 3f represented the nanoparticles containing Pt
element in 2Cu/C-2Pt, 5Cu/C-2Pt, 20Cu/C-2Pt, and 2Pt/C-5Cu,
respectively. The EDX patterns of these randomly selected
nanoparticles revealed that Pt and Cu co-existed in the
nanoparticles. However, the mass ratio of Cu to Pt in these
nanoparticles was as low as 0.05.
Cu-K
0
2
4
6
8
10
12
14
16
18
Position (nm)
Cu/Pt (wt.)=0.049
d
Pt-L
Cu-K
The formation of Pt-Cu alloy has been reported, but the
preparation temperature is usually much higher than room
temperature.33-35 The interaction between Pt nanoparticles
and Cu nanoparticles at room temperature was explored (the
experimental details can be seen in supporting information).
First we prepared PVP encapsulated Cu nanoparticles (Cu-PVP)
and Pt nanoparticles (Pt-PVP). The XRD patterns of Cu-PVP and
Pt-PVP can be seen in Fig. 4 (line a, d). The mixture of
Cu(NH3)4(OH)2 aqueous solution and Pt-PVP aqueous solution
being treated by NaBH4 at room temperature, the Pt-Cu alloy
formed as XRD pattern shown (line b, Fig. 4). However, mixing
Cu-PVP aqueous solution with Pt-PVP aqueous solution only
led to a weak Pt-Cu alloy being close to Pt (line c, Fig. 4). These
results implied that the diffusion of solid copper into Pt
nanoparticles at room temperature was difficult and that Pt-Cu
alloy can be easily produced by reducing cationic state of Cu
with NaBH4 on Pt nanoparticles at room temperature. On the
other hand, the diffraction peaks of Cu in line c were same as
that in line a (Cu-PVP), indicating that the diffusion of Pt into
Cu nanoparticles didn’t occur or this phenomenon was not
remarkable.
0
2
4
6
8
10
12
14
16
Position (nm)
Pt-L
Cu/Pt (wt.) = 0.031
f
Cu-K
0
2
4
6
8
10
12
14
16
Position (nm)
Cu/Pt (wt.) = 0.05
h
Pt-L
Cu-K
0
2
4
6
8
10
12
Position (nm)
Fig. 3 The STEM images of (a) 2Cu/C-2Pt, (c) 5Cu/C-2Pt, (e)
20Cu/C-2Pt, and (g) 2Pt/C-5Cu; and the corresponding EDX
patterns concerning Pt and Cu for (b) 2Cu/C-2Pt (d) 5Cu/C-2Pt,
(f) 20Cu/C-2Pt, and (h) 2Pt/C-5Cu.
Though the ratios of Cu to Pt in our Pt-Cu catalysts are higher
than 0.7 according to the ICP-AES analysis results in Tab. 1, the
ratios of Cu to Pt in the Pt-Cu nanoparticles are much lower
(typically 0.05). This result can be interpreted that most of
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ARTICLE
copper dispersed on the surface of active carbon and did not
interact with Pt nanoparticles. In this circumstance, even if Pt-
Cu alloy can form in our Pt-Cu catalysts, the deficient Cu
cannot influence the crystalline structure of Pt nanoparticles
as we observed in Fig. 2. Additionally, Cu nanoparticles were
seldom observed for Cu/C or Cu/C-Pt composites in the TEM
images. The Cu nanoparticles in Cu/C-Pt can be occasionally
found (Fig. S7a). The Pt nanoparticles decorated Cu
nanoparticle is shown in Fig. S7b, revealing that the contact
between Cu and Pt did not cause the disappearance of Pt-
based nanoparticles.
View Article Online
DOI: 10.1039/C7TA01587A
Pt 4f5/2
71.4
Pt 4f7/2
10Cu/C-5Pt
5Pt/C-10Cu
71.6
10Pt/C
To know how copper interacted with Pt in the nanoparticles,
the exposed Pt surface in the nanoparticles were measured.
2Pt/C being used as the reference sample, the dispersion of Pt
nanoparticles in 5Cu/C-2Pt and 2Pt/C-5Cu were obtained with
pulsed hydrogen-oxygen titration. The dispersions of Pt
nanoparticles (ratios of H/Pt) in 2Pt/C, 5Cu/C-2Pt and 2Pt/C-
5Cu were 0.106, 0.083, and 0.027, respectively. The dispersion
of Pt nanoparticles for 5Cu/C-2Pt was close to that for 2Pt/C,
indicating that copper in 5Cu/C-2Pt had small influence on the
exposed surface of Pt nanoparticles’ surface. However, the
added copper led to the great decrease of exposed Pt surface
for 2Pt/C-5Cu, implying that the surface of Pt nanoparticles
was covered by copper. The great difference in dispersion of Pt
nanoparticles between 5Cu/C-2Pt and 2Pt/C-5Cu may be
caused by their different preparation methods (Scheme 1).
According to above results, the electronic effect from Cu to Pt
in Cu/C-Pt played a major role in determining the catalytic
performance of Pt nanoparticles, and geometric effect from Cu
to Pt in Pt/C-Cu led to Pt nanoparticles’ weak activity on
catalytic hydrogenation of p-CNB and dechlorination of p-CAN.
The electronic effect from Cu to Pt in the catalysts was
examined by measuring the binding energies of Pt in Pt-Cu
samples.
Because the binding energy of Pt can be influenced by the
adsorbed oxygen, our Pt-Cu catalysts and Pt/C catalyst were
treated by flowing hydrogen at room temperature before XPS
measurements. The binding energy of Pt4f7/2 in 10Cu/C-5Pt
and 5Pt/C-10Cu was about 71.4 eV, and that for Pt/C was
about 71.6 eV. If Pt/C was used as the reference sample, the
electronic transfer from Cu to Pt can be induced. The same
binding energy of Pt in Cu/C-Pt and Pt/C-Cu revealed that the
electronic interaction between Cu and Pt in both kinds of Pt-Cu
catalysts is nearly same. Therefore, in both kinds of Pt-Cu
catalysts, the electronic effect from Cu to Pt played the role in
modifying the catalysts’ performance. And in Pt/C-Cu, both
electronic effect and geometric effect from Cu to Pt led to the
low catalytic activity. However, geometric effect had a special
effect to completely inhibit the dechlorination of p-CAN at the
same Pt and Cu loading percentages.
82
80
78
76
74
72
70
68
Binding energy (eV)
Fig. 5 The Pt 4f XPS spectra of 10Cu/C-5Pt, 5Pt/C-10Cu and
10Pt/C.
Experimental
Chemical Reagents
All of the reagents are of analytical grade without any further
purification procedures. H2PtCl6·6H2O, NH3·H2O (25%),
anhydrous ethanol, NaOH (≥96%), NaBH4 (98%), ethylene
glycol (≥99%), anhydrous methanol (≥99%) and acetone were
purchased from Sinopharm Chemical reagents Co. Ltd. PVP K-
30, biphenyl (99.5%), p-chloronitrobenzene (p-CNB,
99.5%),and p-chloroaniline (p-CAN, 99%) were supplied with
Aladdin reagents Co. Ltd. Anhydrous CuCl2 (99%) was obtained
from OurChem reagents Co. Ltd. The active carbon (super P)
was provided by Shenzhen Kejingzhida Company. High purity
hydrogen gas (99.999%) and argon gas (99.999%) were
supplied by Beijing Gas Company.
Catalysts preparation
Platinum colloid solution was prepared according to the
literature.36 Typically, 1 gram H2PtCl6·6H2O was dissolved in 50
ml ethylene glycol (EG), and about 50 ml NaOH EG solution
(0.25 M) was added into above solution under stirring in order
that the pH value was larger than 10. After 30 minutes stirring,
the mixed solution was treated at 160
℃ for 3 hours under
flowing argon gas to form dark-brown platinum colloid
solution (0.32 wt.%), which was ready for use after cooled
down to room temperature.
Cu(NH3)4(OH)2 aqueous solution was prepared as following
procedures: in a typical experiment, 0.126 gram anhydrous
CuCl2 was dissolved in 30 ml purified water (18 Mohm), then
20 ml NaOH aqueous solution (0.1 M) was added to form blue
precipitation Cu(OH)2, which was washed by water for three
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times to remove residue salt; Then the washed precipitation obtained on Tecnai G2 F20 U-TWIN. The X-ray diffraction
View Article Online
DOI: 10.1039/C7TA01587A
was added into 50 ml NH3·H2O to form dark-blue solution.
patterns were collected on an X-ray diffractometer (XRD,
Rigaku, D/MAX-TTRIII, 40 kV, 200 mA) with Cu Kα radiation (λ=
0.154178 nm). The X-ray photoelectron spectroscopy spectra
of the samples were measured on ESCALAB 250Xi equipped
with ex-situ treatment chamber, and the binding energy of C1s
(284.8 eV) was used as the reference to correct the measured
binding energies of the samples. The loading percentages of Cu
and Pt in the catalysts were measured by an inductively
coupled plasma atomic emission spectroscopy (ICP-AES,
Optima 7000DV). The dispersions of Pt in the catalysts were
measured on a chemisorption analyser (PCA 1200, Beijing
Builder Company) through pulsed hydrogen-oxygen titration.
Cu/C-Pt catalysts were prepared as following steps: 3 grams
active carbon was dispersed in 150 ml ethanol with ultrasonic
treatment, then above Cu(NH3)4(OH)2 aqueous solution with
desired volume was slowly added under stirring, and the
mixture was stirred for 1 hour, which was dried at 333 K to
form Cu(OH)2/C; The obtained Cu(OH)2/C was dispersed in 100
ml water, and 50 ml NaBH4 aqueous solution (0.27 M) was
drop wise added under flowing argon gas; After 2 hours
reaction time, the suspension was repeatedly washed by water
and separated with centrifuge, and the solid material Cu/C can
be obtained by freeze-drying treatment; Cu/C was dispersed in
100 ml EG, and 18.75 g Pt colloid solution was added at room
temperature under flowing argon gas, following 1 hour stirring Conclusions
treatment, and then 200 ml purified water was added and
stirred for 2 hours; after washed by water and freeze-dried
treatments, Cu/C-Pt catalyst can be obtained.
We have developed a new route to prepare deficient copper
decorated platinum nanoparticles for selective hydrogenation
of p-chloronitrobenzene. Two ways are used to incorporate
copper with platinum nanoparticles at room temperature; one
is depositing Pt nanoparticles on copper decorated active
carbon (Cu/C-Pt), and another is covering Pt nanoparticles on
active carbon with copper (Pt/C-Cu). After incorporating with
copper, the crystalline structure of Pt nanoparticles still
remains. For Cu/C-Pt, the exposed surface of Pt is close to that
of Pt/C, but most of the surface of Pt nanoparticles in Pt/C-Cu
is covered by copper. The contribution of the electronic effect
and geometric effect on the catalytic performance of Pt
nanoparticles is studied on the basis of two kinds of Pt-Cu
nanostructure. The catalytic activity of Cu/C-Pt is lower than
that of Pt/C for the selective hydrogenation of p-CNB, but the
selectivity of p-CAN is greatly enhanced. However, for Pt/C-Cu,
the catalytic activity of hydrogenation is very weak, and its
activity on the dechlorination of p-CAN is also very weak. In
Cu/C-Pt, the electronic effect from Cu to Pt plays a major role
in Pt nanoparticles’ catalytic performance; In Pt/C-Cu, the
surface geometry of Pt nanoparticles is greatly influenced by
copper, leading to their weak catalytic activity. The present
work is just the first step to explore the contribution of
electronic effect and geometric effect on the catalyst’s
performance, and much more work will be further proceeded
to explore how electronic effect and geometric effect play
their roles in modifying the catalytic performance of catalysts.
Pt/C catalyst (2 wt. %) can be obtained by adding 18.75 Pt
colloid solution into 100 ml EG with 3 g dispersed active
carbon, following the addition of 200 ml water, centrifugal
treatment and freeze-dried treatment.
Pt/C-Cu catalyst was prepared as following steps: 3 g Pt/C
catalyst (2%) was dispersed in 150 ml ethanol, and then
Cu(NH3)4(OH)2 aqueous solution with desired volume was
added, and the formed mixture was dried at 333 K to obtained
solid material; the solid material was further dispersed in 100
ml water, and 50 ml NaBH4 aqueous solution (0.27 M) was
drop wise added under flowing argon gas; After 2 hours
reaction time, the suspension was repeatedly washed by water
and separated with centrifuge, and the catalyst Pt/C-Cu can be
obtained by freeze-dried treatment.
Catalytic test
The catalytic reactions were executed in a 100 ml stainless
steel autoclave with an inside quartz vessel. Before catalytic
reactions, the catalysts were dispersed in 60 ml methanol, and
air in the autoclave was replaced by 1 MP hydrogen gas for 5
times, then the catalysts were pre-activated for 2 hours at 333
K in hydrogen. The reaction substrate p-CNB or p-CAN was
then added into the reaction system. All of the reactions were
carried out at 333 K under 1MPa hydrogen with the stirring
rate of 700 rpm. The products were detected by GC equipped
with the capillary column SE-54 (0.25 mm×30 m) and FID
detector. Biphenyl was added as inner standard substance
after reaction to avoid the influence on the reaction.
Acknowledgements
The authors acknowledge the grants from Beijing Municipal
Science and Technology Project (No.Z161100001116080),
Ministry of Land and Resources Special Fund for Research in
the Public Interests (No. 201311115), National Key Scientific
Instrument
and
Equipment
Development
Projects
(No.2014YQ090709), Major Project of the Ministry of Science
and Technology (No. 2016YFA0200904), and National Natural
Science Foundation (No. 21605030, 21271068, 21401050).
Characterizations
High resolution-transmission electron microscopy (HRTEM)
images, STEM images and elemental mapping results were
6 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry A
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DOI: 10.1039/C7TA01587A
Table of Content Entry
Two model Pt-Cu catalysts are designed to explore the contribution of electronic effect and
geometric effect on their catalytic performance.