AuPd@Mesoporous SiO2: Synthesis and selectivity in catalytic hydrogenation/hydrodechlorination of p-chloronitrobenzene

Article abstract of DOI:10.1166/jnn.2017.13990

AuPd nanoparticles (NPs) protected by tetradecyl trimethyl ammonium bromide (TTAB) were coated with SiO₂ through hydrolysis of tetraethylorthosilicate (TEOS). The as-synthesized AuPd@SiO₂ core-shell NPs were calcined in air at 500°C to remove TTAB and open up mesopores within the SiO₂ shells. The obtained Au-PdO@m-SiO₂ NPs were reduced by H₂ at 300°C to obtain AuPd@m-SiO₂ NPs with AuPd NP cores (diameter: ～3 nm) and SiO₂ shells (thickness: ～18 nm). Results from relevant characterization indicated that these SiO₂-protected core-shell NPs were highly stable during calcination and subsequent reduction. Au@m-SiO₂, Au₁₀Pd@m-SiO₂, Au₅Pd@m-SiO₂, AuPd₅@m-SiO₂, AuPd₁₀@m-SiO₂, and Pd@m-SiO₂ NPs with similar core sizes and shell thicknesses were also synthesized. These samples were tested in the catalytic hydrogenation of p-chloronitrobenzene. The activity and selectivity were found to be tunable, depending on the composition of the bimetallic alloys. AuPd@m-SiO₂ NPs with a 1/1 molar ratio of Au/Pd showed the highest selectivity for the hydrodechlorination of p-chloronitrobenzene.

Full text of DOI:10.1166/jnn.2017.13990

Article
Journal of
Nanoscience and Nanotechnology
Vol. 17, 3744–3750, 2017
Copyright © 2017 American Scientific Publishers
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Printed in the United States of America
AuPd@Mesoporous SiO2: Synthesis and Selectivity in
Catalytic Hydrogenation/Hydrodechlorination of
p-Chloronitrobenzene
Guangming Yang1ꢀ2, Hongbo Yu1, Jianfeng Zhang2, Hongfeng Yin1, Zhen Ma3ꢀ∗, and Shenghu Zhou1ꢀ4ꢀ∗
1Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, P. R. China
2Department of Materials Science and Chemical Engineering, Ningbo University, Ningbo, Zhejiang 315211, P. R. China
3Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, P. R. China
4School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, P. R. China
AuPd nanoparticles (NPs) protected by tetradecyl trimethyl ammonium bromide (TTAB) were coated
with SiO2 through hydrolysis of tetraethylorthosilicate (TEOS). The as-synthesized AuPd@SiO2
ꢀ
core–shell NPs were calcined in air at 500 C to remove TTAB and open up mesopores within the
SiO2 shells. The obtained Au–PdO@m-SiO2 NPs were reduced by H2 at 300 ꢀC to obtain AuPd@m-
SiO2 NPs with AuPd NP cores (diameter: ∼3 nm) and SiO2 shells (thickness: ∼18 nm). Results
from relevant characterization indicated that these SiO2-protected core–shell NPs were highly
stable during calcination and subsequent reduction. Au@m-SiO2, Au10Pd@m-SiO2, Au5Pd@m-
IP: 185.14.195.210 On: Mon, 30 Jul 2018 23:59:45
SiO2, AuPd5@m-SiO2, AuPd10@m-SiO2, and Pd@m-SiO NPs with similar core sizes and shell
Copyright: American Scientifi2c Publishers
thicknesses were also synthesized. These samples were tested in the catalytic hydrogenation of
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p-chloronitrobenzene. The activity and selectivity were found to be tunable, depending on the com-
position of the bimetallic alloys. AuPd@m-SiO2 NPs with a 1/1 molar ratio of Au/Pd showed the
highest selectivity for the hydrodechlorination of p-chloronitrobenzene.
Keywords: AuPd Alloy, Core–Shell, Mesoporous SiO2, Nanoparticles, Thermal Stability.
1. INTRODUCTION
for a reaction to take place. Usually the oxide shell is SiO2
because the sol–gel chemistry of SiO2 is well established
and SiO2 has better thermal stability than TiO2 and ZrO2.15
Although some papers have reported the preparation
and catalytic application of metal@oxide core–shell NPs,
it would be desirable to prepare alloy@oxide core–
shell NPs. Bimetallic NPs have attracted much atten-
tion because of their unique optical,16–18 magnetic,19ꢀ20
and catalytic properties.21–23 In particular, supported AuPd
NPs are useful for catalyzing many reactions such as
CO oxidation,24ꢀ25 combustion of methane,26 combus-
tion of tolune,27ꢀ28 photocatalytic degradation of antibi-
otic levofloxacin,29 direct synthesis of H2O2 from H2
and O2,30ꢀ31 selective oxidation of alcohols,32–34 aerobic
oxidation of clclohexane,35 H2 generation from formic
acid,36 and partial reduction of organic substrates.37–42
However, the synthesis and catalytic application of
AuPd@oxide core–shell NPs have been barely reported.
In a recent work, Torimoto et al. developed a new method
to coat AuPd NPs with In2O3 coatings, and studied the
Conventional supported catalysts are prepared by support-
ing active components (e.g., metals, metal oxides) onto
solid supports via methods such as impregnation, colloidal
deposition, and deposition-precipitation. These catalysts
are easy to prepare and have many choices of active com-
ponents and supports, thus they can be tailored to satisfy
the specific needs in different reactions. However, the ther-
mal stability of supported noble metal catalysts remains
to be an issue because metal nanoparticles (NPs) tend to
agglomerate/sinter under elevated temperatures. To tackle
this problem, metal@oxide core–shell catalysts have been
developed.1–8 A core–shell particle can be regarded as a
nanoreactor in which the metal NP within the shell can
provide catalytically active centers and the oxide shell can
not only host the metal NP but also protect it against ther-
mal sintering.9–14 The oxide shell should be porous, oth-
erwise the reactants cannot diffuse into the “nanoreactor”
∗Authors to whom correspondence should be addressed.
3744
J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 6
1533-4880/2017/17/3744/007
doi:10.1166/jnn.2017.13990

Yang et al.
AuPd@Mesoporous SiO2: Synthesis and Selectivity in Catalytic Hydrogenation/Hydrodechlorination of p-CNB
performance of the catalysts in electrocatalytic oxidation
of ethanol.43
2. EXPERIMENTAL DETAILS
2.1. Chemicals
We previously developed PdNi@m-SiO2,44 Pd–
NiO@m-SiO2,44 PtNi@m-SiO2,45 and Pt–NiO@m-SiO2,45
and tested their catalytic performance in the hydro-
genation of p-chloronitrobenzene. The hydrogenation of
p-chloronitrobenzene (p-CNB) may yield p-chloroaniline
(p-CAN), p-aminophenol (p-AP), and aniline (AN),
depending on the nature of catalysts and reaction con-
ditions (Fig. 1).44 Most references report the partial
hydrogenation of p-CNB to p-CAN,44–53 because p-CAN
is a useful chemical intermediate, whereas a few ref-
erences focus on the hydrodechlorination of p-CNB to
AN,54 because hydrodechlorination is an important topic
in environmental catalysis. The influence of support on
the selectivity of Pd catalysts in gas-phase hydrogenation
of p-CNB was also reported.55 It was found that while
Pd/ZnO favored the formation of p-CAN, Pd/SiO2 favored
the formation of p-AN.
Potassium tetrachloropalladate(II) (K2PdCl4ꢁ, gold
chloride solution (23.5–23.8%), sodium borohydride
(NaBH4, 98%), aqueous ammonia solution (25–28%),
tetraethylorthosilicate (TEOS, AR), and tetradecyl
trimethyl ammonium bromide (TTAB, AR) were pur-
chased from Aladdin. p-Chloronitrobenzene (p-CNB, AR)
was purchased from Shanghai Chemical Reagent
Company.
2.2. Synthesis of TTAB-Capped AuPd NPs and
AuPd@SiO2 NPs
In a typical synthesis, an aqueous solution of K2PdCl4
(0.183 mL, 153.2 mM) and an aqueous solution of HAuCl4
(0.280 mL, 100 mM) were mixed with 90 ml of deionized
water in a 250 mL three-neck round-bottomed flask with
magnetic stirring at room temperature, and then 0.840 g
TTAB was added. The mixture was stirred for ∼10 min to
fully dissolve TTAB. An ice-cooled NaBH4 aqueous solu-
tion (5 mL, 0.53 M) was then injected using a syringe.
The tip of the syringe was maintained in the system to
release the gas generated during the reaction, and was then
removed to make a closed system. The solution was fur-
ther stirred at low speeds for 15 h at room temperature to
obtain AuPd NP colloids. The as-synthesized AuPd col-
loids (24 mL) were mixed with 120 mL of deionized water
in a 250 mL three-neck round-bottomed flask at room tem-
In the present work, a series of AuPd@m-SiO2 NPs with
different Au/Pd ratios were synthesized using a sol–gel
method, and were tested in the hydrogenation of p-CNB.
It was found that Au@m-SiO2, Au10Pd@m-SiO2, and
Au5Pd@m-SiO2 showed no activity or low activity for
this reaction, whereas AuPd@m-SiO2, AuPd5@m-SiO2,
AuPd10@m-SiO2, and Pd@m-SiO2 showed 100% conver-
sion under the reaction condition. Pd@m-SiO2 showed
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55.0% selectivity to AN and 42.0% selectivity to p-CAN,
whereas AuPd@m-SiO2 with a 1/1 Au/Pd ratio favored
dechlorination, showing 94.7% selectivity to AN. The data
indicate that the activity and selectivity are tunable in this
bimetallic catalyst system.
Copyright: American Scientific Publishers
perature with magnetic stirring. A few drops of ammonia
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solution (25–28 wt.%) were added to adjust the pH value
to 10.7, and then TEOS (600 ꢂL, 2.69 mmol) was added.
The resultant solution was stirred at low speeds for 2 h at
room temperature to obtain AuPd@SiO2 NP colloids. The
mixture was centrifuged, washed with ethanol twice and
ꢀ
water twice, and then dried at 100 C for 3 h.
NH2
2.3. Synthesis of Au–PdO@m-SiO2 and
AuPd@m-SiO2 NPs
PATH A
The dried AuPd@SiO2 NPs were grounded and calcined
in a muffle furnace at 500 C for 2 h to remove TTAB.
The resultant Au–PdO@m-SiO2 powders were reduced
by hꢀigh-purity H2 (30 mL/min) in a fixed bed reactor at
300 C for 2 h to obtain AuPd@m-SiO2 NPs.
ꢀ
NO2
NH2
Cl
p-CAN
PATH B
PATH C
NH2
AN
2.4. Synthesis of Other Core–Shell NPs
Cl
Au@m-SiO2,
Au10Pd@m-SiO2,
Au5Pd@m-SiO2,
p-CNB
AuPd5@m-SiO2, AuPd10@m-SiO2, and Pd@m-SiO2 NPs
were prepared by the similar method mentioned above.
In each synthesis with different ratios of Au/Pd, the
total molar number of the metal(s) was equal to that of
AuPd@m-SiO2.
OH
p-AP
2.5. Characterization
XRD patterns of samples were collected by a Bruker D8
Advance X-ray diffractometer with Cu Kꢃ radiation in the
Figure 1. Reaction network for the catalytic hydrogenation of p-CNB.
Reproduced with permission from [44], X. J. Zhang, et al., Catal. Lett.
145, 784 (2015). © 2015, Springer.
J. Nanosci. Nanotechnol. 17, 3744–3750, 2017
3745

AuPd@Mesoporous SiO2: Synthesis and Selectivity in Catalytic Hydrogenation/Hydrodechlorination of p-CNB
Yang et al.
2ꢄ range from 10ꢀ to 90ꢀ. Transition electron microscopy
(TEM) images were obtained by JEOL 2100 transmission
electron microscope. The samples were made as follows:
a certain amount of catalysts was dispersed in ethanol
by ultrasonic treatment, and a drop of the solution was
dropped onto a carbon-coated copper grid that was sub-
sequently dried in air at room temperature. The actual
metal contents of the catalysts were obtained by a PE
Optima 2100DV inductive coupled plasma optical emis-
sion spectrometer (ICP-OES). Infrared (IR) spectra of the
NPs before and after treatments were recorded in the trans-
mission mode by a Bruker Tensor 27 spectrophotometer.
The thermal degradation property of the sample before
treatment was measured by a Pyris Diamond thermo gravi-
metric analyzer (TGA). The sample was heated from
50 to 500 ꢀC at a heating rate of 10 ꢀC/min under
flowing air (50 mL/min). Brunauer–Emmett–Teller (BET)
surface areas, pore size distributions, and the adsorp-
tion/desorption isotherms of the samples were measured
by N2 adsorption at 77 K, using a Micrometrics ASAP-
2020 M automatic specific surface area and porous physi-
cal adsorption analyzer.
and a thickness of ∼18 nm for SiO2 shells. Empty SiO2
NPs are rarely seen in Figures 2(b–h), but a few core–shell
NPs with multiple cores are found. In this study, the opti-
mal hydrolysis condition is found at a pH value of 10.7
and a TEOS/total metal molar ratio of 192/1. Empty SiO2
NPs are observed at lower pH values, and a large percent-
age of NPs with multiple cores are observed at higher pH
values. Moreover, higher TEOS/total metal ratios result in
thicker silica shells.
Figure 3 shows the TEM images of mesoporous core–
ꢀ
shell NPs obtained by removing tꢀhe TTAB at 500 C fol-
lowed by reduction in H2 at 300 C. The average particle
size of the metal cores and thickness of silica shells of
metal@m-SiO2 structures are nearly the same as those of
metal@SiO2 NPs (Fig. 4), demonstrating the high ther-
mal stability for these core–shell catalysts. The presence
of mesopores is illustrated in Figure 3(f) showing one
AuPd5@m-SiO2 NP.
Figure 5 shows the N2 adsorption–desorption isotherms
and pore size distribution of various metal@m-SiO2 NPs
with different Au/Pd ratios. Table I shows the BET sur-
face areas, pore volumes, and pore sizes of these samples.
These mesoporous core–shell NPs exhibit large BET sur-
face areas higher than 1000 m2/g and the average pore
sizes are identical (2.1 nm).
3. RESULTS AND DISCUSSION
Figure 2 shows the TEM images of various as-synthesized
NPs. The average particle size of TTAB-capped AuPd
NPs with a 1/1 ratio of Au/Pd is ∼2.5 nm, and the lat-
The creation of mesopores through calcination is due
to the removal of TTAB. The TGA curve of AuPd@SiO2
in Figure 6 suggests that the calcination at 500 ꢀC in
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tice spacing is 0.302 nm (Fig. 2(a)), consistent with the
air can completely remove TTAB, and FT-IR spectra for
Copyright: American Scientific Publishers
lattice spacing of AuPd (111) plane. The TEMDeimlivaegreesd by Ingenta
AuPd@SiO2 and AuPd@m-SiO2 in Figure 7 further con-
of Au@SiO2, Au10Pd@SiO2, Au5Pd@SiO2, AuPd@SiO2,
AuPd5@SiO2, AuPd10@SiO2, and Pd@SiO2 are shown in
Figures 2(b–h), respectively. AuPd@SiO2 in Figure 2(e)
shows an average particle size of 2.5 nm for AuPd cores
firm the removal of TTAB upon calcination in air.
Figure 8 shows the XRD patterns of various core–shell
NPs. The broad feature in the 2ꢄ range of 20ꢀ and 30ꢀ
corresponds to amorphous SiO2. PdO@m-SiO2 prepared
Figure 2. TEM images of core–shell NPs synthesized at the condition of a pH value of 10.7 and a TEOS/total metal molar ratio of 192/1. (a) TTAB-
capped AuPd NPs, and insert is HRTEM image of one NP showing a lattice spacing of 0.302 nm; (b) Au@SiO2; (c) Au10Pd@SiO2; (d) Au5Pd@SiO2;
(e) AuPd@SiO2; (f) AuPd5@SiO2; (g) AuPd10@SiO2; (h) Pd@SiO2.
3746
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Yang et al.
AuPd@Mesoporous SiO2: Synthesis and Selectivity in Catalytic Hydrogenation/Hydrodechlorination of p-CNB
Figure 3. TEM images of NPs synthesized at the condition of a pH value of 10.7 and a TEOS/total metal molar ratio of 192/1 after 500 ꢀC calcination
and following 300 ꢀC H2 reduction. (a) Au@m-SiO2; (b) Au10Pd@m-SiO2; (c) Au5Pd@m-SiO2; (d) AuPd@m-SiO2; (e) AuPd5@m-SiO2; (f) details
of AuPd5@m-SiO2; (g) AuPd10@m-SiO2; (h) Pd@m-SiO2.
IP: 185.14.195.210 On: Mon, 30 Jul 2018 23:59:45
Copyright: American Scientific Publishers
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Figure 4. Size distribution of AuPd and AuPd5 NPs in different systems. (a) AuPd NPs capped with TTAB; (b) AuPd@SiO2; (c) AuPd@m-SiO2;
(d) AuPd5 NPs capped with TTAB; (e) AuPd5@SiO2; (f) AuPd5@m-SiO2.
Figure 5. N2 adsorption–desorption isotherms (left panel) and pore size distribution (right panel). (a) Au@m-SiO2; (b) Au10Pd@m-SiO2;
(c) Au5Pd@m-SiO2; (d) AuPd@m-SiO2; (e) AuPd5@m-SiO2; (f) AuPd10@m-SiO2; (g) Pd@m-SiO2.
J. Nanosci. Nanotechnol. 17, 3744–3750, 2017
3747

AuPd@Mesoporous SiO2: Synthesis and Selectivity in Catalytic Hydrogenation/Hydrodechlorination of p-CNB
Yang et al.
Table I. BET surface areas, pore volumes, and pore sizes of core–
shell NPs.
BET surface
area (m2/g)
Pore
Pore
size (nm)
Samples
volume (cm3/g)
Au@m-SiO2
1527
1308
1209
1153
1199
1178
1147
2ꢅ0
1ꢅ6
1ꢅ5
1ꢅ5
1ꢅ5
1ꢅ4
1ꢅ4
2ꢅ1
2ꢅ1
2ꢅ1
2ꢅ1
2ꢅ1
2ꢅ1
2ꢅ1
Au10Pd@m-SiO2
Au5Pd@m-SiO2
AuPd@m-SiO2
AuPd5@m-SiO2
AuPd10@m-SiO2
Pd@m-SiO2
ꢀ
by calcining Pd@m-SiO2 at 500 C shows a diffraction
peak at 2ꢄ = 33ꢅ8ꢀ, corresponding to the (101) plane of
PdOꢀ(Fig. 8(a)). PdO@m-SiO2 can be reduced in H2 at
300 C to form Pd@m-SiO2, as seen from a peak at 2ꢄ =
40ꢅ1ꢀ corresponding to the (111) plane of metallic Pd
(Fig. 8(b)). Au@m-SiO2 obtained by calcining Au@SiO2
at 500 ꢀC contains metallic Au, as seen from a peak
at 2ꢄ = 38ꢅ2ꢀ corresponding to the (111) plane of Au
(Fig. 8(c)). Figure 8(d) shows the XRD pattern of as-
synthesized AuPd@SiO2 (without calcination to remove
TTAB and open up mesopores). A very weak diffraction
at 2ꢄ = 39ꢅ1ꢀ of (111) plane of AuPd is present. The
XRD pattern of AuPd@m-SiO2 (prepared by calcining
Figure 7. FT-IR spectra. (a) AuPd@m-SiO2; (b) AuPd@SiO2. The
2853 and 2923 cm−1 peaks in spectrum b are ascribed to methylene group
in TTAB, which disappears in the calcined sample in spectrum a.
hydrogenation of p-chloronitrobenzene is in line with the
finding that Au/C showed no activity in the hydrogenation
of 2-chloronitrobenzene.56
On the other hand, AuPd@m-SiO2, AuPd5@m-SiO2,
AuPd10@m-SiO2, and Pd@m-SiO2 show 100% con-
version under the reaction conditions. The selectiv-
ity to AN obtained using different catalysts follows
the sequence of AuPd@m-SiO2 (94.7%) > AuPd5@m-
SiO2 (77.8%) > AuPd10@m-SiO2 (51.3%)∼Pd@m-SiO2
(55.0%). The selectivity to p-CAN obtained using dif-
ꢀ
AuPd@SiO2 in air at 500 C followed by reduction in H2
ꢀ
at 300 C) is shown in Figure 8(e). The AuPd alloy phase
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ferent catalysts follows the sequence of AuPd@m-SiO2
(3.3%) < AuPd5@m-SiO2 (20.2%) > AuPd10@m-SiO2
is maintained after calcination and reduction.
Copyright: American Scientific Publishers
Catalytic hydrogenation of p-chloronitrobenzene with
H2 using mesoporous core–shell NPs as catalysts was
tested using ethanol solvent with vigorous stirring at 50 ꢀC
and atmospheric pressure. Table II shows the actual load-
ings of Au and Pd in various mesoporous core–shell NPs,
as obtained by ICP. The weight of catalysts was adjusted
according to the actual metal loadings to keep the total
molar number of Au and Pd constant. Figure 1 shows
the reaction network,44 and Table III shows the catalytic
results. It is clear that Au@m-SiO2 and Au10Pd@m-SiO2
are not active at all. Au5Pd@m-SiO2 shows a low con-
version of 6.5%. The null activity of Au@m-SiO2 in the
Delivered by Ingenta
(44.0%)∼Pd@m-SiO2 (42.0%). The data indicate that the
selectivity is tunable and AuPd@m-SiO2 favors dechlori-
nation. Corbos and co-workers developed several PdAu/C
catalysts with Pd/Au weight percentage ratios of 10/90,
50/50, 75/25, and 100/0, respectively, and tested the cata-
lysts in the hydrogenation of 2-chloronitrobenzene.56 The
authors found that the selectivity to 2-CAN increased when
the Pd content of the catalyst was increased. The trend is
consistent with the trend seen in our current work. Addi-
tional theoretical work is still needed to understand the
e
d
c
b
a
AuPd(JCDPS 01-072-5376)
PdO(JCPDS 00-043-1024)
Pd(JCPDS 01-071-3757)
Au(JCPDS 01-071-3755)
20
40
60
80
2θ (degree)
Figure 8. XRD patterns of NPs. (a) PdO@m-SiO2; (b) Pd@m-SiO2;
Figure 6. TGA curve of AuPd@SiO2 NPs.
(c) Au@m-SiO2; (d) as-synthesized AuPd@SiO2; (e) AuPd@m-SiO2.
3748
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Yang et al.
AuPd@Mesoporous SiO2: Synthesis and Selectivity in Catalytic Hydrogenation/Hydrodechlorination of p-CNB
Table II. The real metal loadings of core–shell NPs as analyzed by
ICP-OES.
100% conversion and the selectivity to AN is 95.2%. In the
second cycle, the conversion is 99.8%, and the selectivity
to AN somehow decreases to 85.6%. In the third cycle,
the conversion is 99%, and the selectivity to AN remains
84.7%. For Pd@m-SiO2, the conversion is 100% and the
selectivity to AN is 55.6% under the reaction condition.
Both the conversion and selectivity to AN are constant in
three cycles. These data indicate that both catalysts are
recyclable.
Sample
Au content (wt.%)
Pd content (wt.%)
Au@m-SiO2
1ꢅ876
1ꢅ737
1ꢅ6235
0ꢅ9615
0ꢅ321
0ꢅ174
N/A
N/A
0ꢅ0875
0ꢅ1625
0ꢅ496
0ꢅ757
0ꢅ872
1ꢅ009
Au10Pd@m-SiO2
Au5Pd@m-SiO2
AuPd@m-SiO2
AuPd5@m-SiO2
AuPd10@m-SiO2
Pd@m-SiO2
4. CONCLUSIONS
Table III. Hydrogenation of p-CNB with H2 catalyzed by core–shell
MPs. The products are aniline (AN), p-chloroaniline (p-CAN), and
p-aminophenol (p-AP).
Various AuPd@m-SiO2 mesoporous core–shell NPs were
synthesized by a sol–gel method. They exhibited high sur-
face areas (>1000 m2/g) and mesopores (average pore
sizes ∼2.1 nm) due to the removal of TTAB tem-
plate by calcination. These materials were tested in the
hydrogenation of p-chloronitrobenzene. Au@m-SiO2 and
Au10Pd@m-SiO2 are not active at all under the reac-
tion condition. Au5Pd@m-SiO2 shows a low conversion
of 6.5%. AuPd@m-SiO2, AuPd5@m-SiO2, AuPd10@m-
SiO2, and Pd@m-SiO2 show 100% conversion. The selec-
tivity to aniline obtained using different catalysts follows
the sequence of AuPd@m-SiO2 (94.7%) > AuPd5@m-
SiO2 (77.8%) > AuPd10@m-SiO2 (51.3%)∼Pd@m-SiO2
(55.0%). In particular, AuPd@m-SiO2 with a 1/1 ratio of
Au/Pd exhibited enhanced hydrodechlorination selectivity.
This kind of materials could be potentially used in high
Selectivity (%)
Catalysts
Conv. (%)
AN
p-CAN
p-AP
Au@m-SiO2
0.0
0.0
6.5
100
100
100
100
0ꢅ0
0ꢅ0
3ꢅ5
94ꢅ7
77ꢅ8
51ꢅ3
55ꢅ0
0ꢅ0
0ꢅ0
49ꢅ4
3ꢅ3
20ꢅ2
44ꢅ0
42ꢅ0
0ꢅ0
0ꢅ0
47ꢅ1
2ꢅ0
2ꢅ0
3ꢅ7
Au10Pd@m-SiO2
Au5Pd@m-SiO2
AuPd@m-SiO2
AuPd5@m-SiO2
AuPd10@m-SiO2
Pd@m-SiO2
3ꢅ0
Note: Reaction conditions: atmospheric H2 pressure; reaction time (2.5 h);
ethanol (30 ml); reaction temperature (50 ꢀC); p-CNB (1 g); Au@m-SiO2
(2.008 g); Au10Pd@m-SiO2 (1.984 g); Au5Pd@m-SiO2 (1.957 g); AuPd@m-
SiO2 (2.0 g); AuPd5@m-SiO2 (2.178 g); AuPd10@m-SiO2 (2.097 g); Pd@m-SiO2
(2.008 g); speed of agitation (600 rpm).
IP: 185.14.195.210 On: Mon, 30 Jul 2018 23:59:45
temperature reactions due to the high thermal stability. In
Copyright: American Scientific Publishers
addition, they may be tested in other hydrogenation and
reasons for the change of selectivity as a function oDfePlidv/eArued by Ingenta
hydrodechlorination reactions because the selectivity can
ratios.
The recyclability of representative catalysts was also
be tuned as a function of alloy compositions.
studied. There was slight loss of catalysts after the separa-
tion of catalysts and the products, so the amount of reac-
tant (p-CNB) and solvent (ethanol) were adjusted to make
sure that the ratios of ethanol/p-CNB and catalyst/p-CNB
in the following cycles were kept the same as those in the
first cycle. As shown in Table IV, AuPd@m-SiO2 shows
Acknowledgments: This study was supported by
National Natural Science Foundation of China (NSFC,
21571183), Ningbo City International Coorperation Pro-
gram (Y40831DG05), the National Basic Research Pro-
gram of China (“973” program) (2013CB934800), and
Ningbo City Natural Science Foundation (2015A610056).
Table IV. Recyclability of typical catalysts in hydrogenation of p-CNB
with H2. The products are aniline (AN), p-chloroaniline (p-CAN), and
p-aminophenol (p-AP).
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