Au Nanoparticles Confined in SBA-15 as a Highly Efficient and Stable Catalyst for Hydrogenation of Quinoline to 1,2,3,4-Tetrahydroquinoline

Article abstract of DOI:10.1007/s10562-020-03190-3

Abstract: Au nanoparticles confined within the mesopores of the modified SBA-15 were obtained through adsorption-reduction method and firstly employed as chemoselective catalyst for quinoline hydrogenation. The effects of Au loadings, calcination temperature as well as structure of support on catalytic performances of Au catalysts were explored. The as-obtained 1.2percentAu@SBA-15-500 catalyst exhibited high activity, excellent selectivity towards 1,2,3,4-tetrahydroquinoline and extraordinary sintering-resistant property as high as 800?°C, which is sharp contrast to the 1.3percentAu/SiO₂-500 catalyst. It also showed good recyclability and versatility for quinoline derivatives. The observed properties were assigned to small-sized Au nanoparticles and mesopores of SBA-15. Our work provides a facile and promising approach to construct metal nanocatalysts with high catalytic performance by the use of mesoporous materials. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-020-03190-3

Catalysis Letters
https://doi.org/10.1007/s10562-020-03190-3
Au Nanoparticles Confned in SBA‑15 as a Highly Eꢀcient
and Stable Catalyst ꢁor Hydrogenation oꢁ Quinoline
to 1,2,3,4‑Tetrahydroquinoline
1
1
1
1
2
1
Jianbo Zhao · Haifeng Yuan · Xiaomei Qin · Kuan Tian · Yingfan Liu · Chengzhen Wei · Zhiqiang Zhang ·
3
3
Liming Zhou · Shaoming Fang
Received: 14 February 2020 / Accepted: 16 March 2020
Springer Science+Business Media, LLC, part of Springer Nature 2020
©
Abstract
Au nanoparticles confned within the mesopores oꢀ the modifed SBA-15 were obtained through adsorption-reduction method
and frstly employed as chemoselective catalyst ꢀor quinoline hydrogenation. The eꢁects oꢀ Au loadings, calcination tem-
perature as well as structure oꢀ support on catalytic perꢀormances oꢀ Au catalysts were explored. The as-obtained 1.2%Au@
SBA-15-500 catalyst exhibited high activity, excellent selectivity towards 1,2,3,4-tetrahydroquinoline and extraordinary
sintering-resistant property as high as 800 °C, which is sharp contrast to the 1.3%Au/SiO -500 catalyst. It also showed good
2
recyclability and versatility ꢀor quinoline derivatives. The observed properties were assigned to small-sized Au nanoparticles
and mesopores oꢀ SBA-15. Our work provides a ꢀacile and promising approach to construct metal nanocatalysts with high
catalytic perꢀormance by the use oꢀ mesoporous materials.
Graphic Abstract
Keywords Au nanocatalyst · SBA-15 · Quinoline · Selective hydrogenation
2
*
*
*
Jianbo Zhao
Henan Province Key Laboratory oꢀ New Opto-Electronic
Functional Materials, Anyang Normal University, Anyang,
Henan 455000, People’s Republic oꢀ China
zhaojianbo@zzuli.edu.cn
Liming Zhou
3
zlming1212@126.com
Henan Provincial Key Laboratory oꢀ Surꢀace
and Interꢀace Science, Zhengzhou University oꢀ Light
Industry, No. 136 oꢀ Science Road, Zhengzhou 450001,
People’s Republic oꢀ China
Shaoming Fang
mingꢀang@zzuli.edu.cn
1
School oꢀ Material and Chemical Engineering, Zhengzhou
University oꢀ Light Industry, No. 136 oꢀ Science Road,
Zhengzhou 450001, People’s Republic oꢀ China
Vol.:(0
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J. Zhao et al.
1
Introduction
temperature, specifc surꢀace area and porous structure oꢀ
support on the perꢀormances oꢀ Au catalysts were stud-
ied in detail. High activity, excellent selectivity towards
1,2,3,4-tetrahydroquinoline and especially outstanding
anti-sintering property were obtained over the as-prepared
Au catalyst. Its perꢀormances were ascribed to the appro-
priate sizes oꢀ Au nanoparticles, high specifc surꢀace area
and ordered mesopores oꢀ SBA-15.
N-heterocyclic compounds including 1,2,3,4-tetraquino-
line have taken much interest because oꢀ their wide appli-
cation in fne chemical felds such as dyes, agrochemi-
cals and biological active molecules [1, 2]. Among the
synthetic strategies to acquire 1,2,3,4-tetraquinoline, the
quinoline hydrogenation is the most simple and powerꢀul
approach [3]. This kind oꢀ reaction was reported to pro-
ceed over homogeneous metal catalysts, such as Rh, Ru
and Ir [4–7]. Unꢀortunately, these catalytic systems usually
possessed some disadvantages such as the high cost oꢀ
ligands and catalysts, rigorous reaction conditions, espe-
cially the diꢂculties in recovering the rare and expensive
noble metal catalysts ꢀrom the reaction mixtures [3]. From
the standpoint oꢀ sustainable development, it is desirable
that the reaction is carried out over heterogeneous cata-
lysts under mild reaction conditions.
2 Experimental
2.1 Raw Materials
SBA-15 was purchased ꢀrom Nanjing XFNANO Mate-
rials Technology Company and chloroauric acid
(HAuCl4·3H2O, AR) was obtained ꢀrom Shanghai Chem-
ical Reagent Co., Ltd. 3-Amino-propyltrimethoxysilane
(APTES) (≥ 98.0%, AR), quinoline (≥ 99.5%, AR) were
provided ꢀrom Sigma-Aldrich and Shanghai Macklin Bio-
chemical Co., Ltd, respectively. NaBH4 (≥ 99.0%, AR)
was supplied ꢀrom Sinopharm Chemical Reagent Co., Ltd.
Other reagents were also analytical reagents.
In recent years, heterogeneous metal nanocatalysts
including Ru, Pd, Pt and Co have been developed ꢀor selec-
tive hydrogenation oꢀ quinoline compounds [8–15]. Many
oꢀ them exhibited good catalytic properties, even so, the
problem that oꢀten arises is that some catalytic systems
were carried out at drastic reaction conditions (> 120 °C
and/or 3.0 MPa H ) [8, 13–15]. It is notable that the N-het-
2
erocyclic compounds typically act as poisons ꢀor these
catalysts, which leads to the decrease and even loss oꢀ
catalytic activity [9, 11]. Owing to good catalytic perꢀor-
mances, especially extraordinary selectivity, heterogene-
ous gold catalysts have received more and more attention
in selective hydrogenations [16–23]. Furthermore, quino-
line compounds were ꢀound to be promoters and ꢀacilitate
2.2 Preparation of Au Nanocatalysts
The SBA-15 support was modiꢀication with APTES
according to our previous procedure [31]. In a 100 mL
three-necked ꢃask, 1.8 g oꢀ APTES was added dropwise
to 60 mL ethanol containing 1.0 g SBA-15 and the ꢀormed
mixture was stirred at 90 °C ꢀor 24.0 h. Once being fl-
trated and washed, the resulting solid was dried at 60 °C
ꢀor 10.0 h, denoted as SBA-15-APTES.
the activation oꢀ H in the Au-catalyzed hydrogenation
2
processes [22], which was in stark contrast with their poi-
soning action over traditional noble metal-based catalysts
[
9, 11, 22]. It is anticipated that the Au nanocatalysts can
The Au@SBA-15 catalysts were constructed by the
adsorption-reduction approach. Typically, 0.3 g SBA-15-
show the striking catalytic perꢀormance ꢀor hydrogena-
tion oꢀ quinoline, but the research about it has been rarely
reported [21, 22].
−
1
APTES was mixed with 10 mL 0.003 mol L HAuCl4
aqueous solution under stirring. Aꢀter 2.0 h, 1 mL cold
deionized water consisting oꢀ 0.008 g NaBH4 was added
slowly to the aꢀorementioned mixture and was stirred
ꢀor 2.0 h. The solid sample was recovered, washed and
dried under vacuum. Finally the pink Au catalyst was
obtained aꢀter being calcined under a ꢃow oꢀ air at 500 °C
ꢀor 3 h, designated as 1.2%Au@SBA-15-500. Likewise,
other SBA-15 supported Au catalysts were achieved by
modiꢀy Au loadings or calcination temperature, denoted
as X% Au@SBA-15-Y (X and Y represent the Au weight
loading and calcination temperature, respectively). The
SiO2-supported Au catalysts as reꢀerence catalysts were
also acquired according to the same procedure above.
As an important class oꢀ mesoporous material, SBA-
1
5 has the ordered adjustable channel size, high specifc
surꢀace area and remarkable thermal stability, which
provides an excellent support ꢀor the preparation oꢀ het-
erogeneous metal nanocatalysts [24–27]. For the above
reasons, Au based catalysts deposited on SBA-15 were
prepared and used in many transꢀormations [26–30], how-
ever, to our best knowledge, no such research was ꢀound
in the literature about them ꢀor selective hydrogenation
oꢀ quinoline compounds. Herein, the Au nanocatalysts
were synthesized using SBA-15 modifed with APTES as
a support and frstly employed ꢀor selective hydrogenation
oꢀ quinoline. The eꢁects oꢀ the gold loading, calcination
1
3

Au Nanoparticles Confned in SBA‑15 as a Highly Eꢀcient and Stable Catalyst ꢁor Hydrogenation…
2.3 Characterizations of Supports and Catalysts
The gold loadings were tested by Inductively Coupled
Plasma Atomic Emission Spectrometry (ICP-AES) (Vista-
MPX, Varian). N adsorption–desorption isotherms were
2
achieved ꢀrom a Micromeritics Tristar 3000 instrument.
The pore size distribution and the specifc surꢀace area were
obtained using the BJH and BET methods, respectively.
Power X-ray diꢁraction patterns (XRD) oꢀ samples were
measured on a Shimadzu XRD-6000 using Cu Ka radia-
tion operated at 40 kV and 30 mA. The TEM morphology
and size distribution oꢀ Au catalysts were acquired using
JEOL JEM-2100F transmission electron microscopy. X-ray
photoelectron spectroscopy (XPS) was obtained under ultra-
Fig. 1 N2 adsorption–desorption isotherms (A) and BJH pore size
distribution curves (B) oꢀ Au catalysts: (a) SBA-15, (b) 0.7%Au@
SBA-15-500, (c) 1.2%Au@SBA-15-500, (d) 2.4%Au@SBA-15-500,
−6
high vacuum (<10 Pa) on a Thermo Scientifc ESCALAB
2
50Xi spectrometer with an Al anode (Al Kα=1486.6 eV).
(
e) 1.2%Au@SBA-15-500 (used); (f) 1.3%Au/SiO -500
2
All spectra were determined at room temperature and the
binding energies (BE) were reꢀerred to 284.6 eV oꢀ the C
1
s peak.
The XRD patterns oꢀ samples were showed in Fig. 2.
The broad peak (2θ = 15°–30°) was ascribed to the amor-
phous silica [24, 29]. Aꢀter gold nanoparticles were intro-
duced, no apparent diꢁraction peaks assigned to Au were
ꢀound on the resultant Au catalysts probably because
oꢀ low Au loading and small-sized Au nanoparticles. It
indicated the as-prepared Au catalysts remained almost
the ordered structure oꢀ the SBA-15 host. The Au (111)
2
.4 Catalytic Hydrogenation Test
The quinoline hydrogenation was tested in a stainless steel
autoclave under magnetic stirring. In a typical run, 3.0 mL
oꢀ water, 60 μL oꢀ quinoline and 0.1 g oꢀ Au catalysts were
added to the autoclave. Aꢀter sealing, nitrogen was intro-
duced to remove air ꢀor several times and pressurized with
diꢁraction peak oꢀ the 1.2%Au/SiO -800 catalyst was
2
H oꢀ 2.0 MPa. And then the reactor was heated to 100 °C
narrower compared with the 1.3%Au/SiO -500 catalyst,
2
2
and remained at this temperature under stirring. The reaction
suggesting Au nanoparticles become larger aꢀter the calci-
nation at 800 °C. Oꢀ note, the diameter oꢀ Au nanoparticles
oꢀ Au catalysts cannot be correctly obtained ꢀrom the XRD
patterns because oꢀ the weak intensity oꢀ Au diꢁraction
peaks. Their diameters can be measured by TEM images
aꢀterwards.
mixture was cooled and then extracted with ethyl acetate
ꢀ
or 3 times when the reaction was completed. The result-
ant extract was measured by gas chromatography/mass
spectrometry.
Figure 3 showed the FT-IR spectra oꢀ the samples.
SBA-15 exhibited two absorption bands at 3127 and
−
1
3
Results & Discussion
1636 cm ,which were related to stretching vibration
ν(OH) and deꢀormation vibration δ(OH) oꢀ Si–OH group,
−
1
3.1 Physicochemical Properties of Catalysts
respectively. Besides, the other strong peak at 1092 cm
was assigned to stretching vibration ν(Si–O) oꢀ Si–OH
group in Fig. 3a [31, 33]. Aꢀter the SBA-15 support treated
with APTES, these characteristic peaks oꢀ SBA-15 were
N adsorption–desorption isotherms and pore size distribu-
2
tion curves oꢀ SBA-15 and corresponding Au catalysts were
presented in Fig. 1, and their textural ꢀeatures and chemi-
cal compositions were listed Table 1. As seen ꢀrom Fig. 1,
−
1
retained, and the new peaks at 2923 and 1539 cm associ-
ated with stretching vibration oꢀ CH groups oꢀ pendant
2
with the exception oꢀ 1.3%Au/SiO , other samples displayed
propyl chain and bending vibration oꢀ NH groups were
2
2
Langmuir type-IV isotherms with H1 hysteresis loop, pos-
sessing a ꢀeature oꢀ mesoporous materials [29, 32]. The spe-
cifc surꢀace area and pore size oꢀ Au catalysts decreased
slightly with the increase oꢀ Au amounts. These results
indicated that Au nanoparticles entered the mesopores oꢀ
SBA-15, but the ordered mesoporous structure oꢀ SBA-15
remained unchanged.
observed, respectively [30]. These results showed the
APTES molecule was successꢀully graꢀted onto the sur-
ꢀace oꢀ SBA-15. For the 1.2%Au@SBA-15-500 catalyst,
the bending vibration oꢀ NH group disappeared probably
2
due to the calcination treatment [34]. The immobilization
oꢀ Au nanoparticles on SBA-15-APTES can be confrmed
by TEM and XPS characterizations
1
3

J. Zhao et al.
Table 1 Relevant
SBET (m2g−1
Vpore (cm3g−1
Catalyst
SBA-15
Au content
wt%)
)
)
dpore (nm)
physicochemical parameters oꢀ
support and catalysts
(
–
636.0
598.7
562.7
547.8
554.9
194.9
0.9
0.8
0.7
0.6
0.7
0.7
7.3
6.9
6.8
6.7
6.6
1.5
1
2
3
2
2
%Au@SBA-15-500
%Au@SBA-15-500
%Au@SBA-15-500
%Au@SBA-15-500(used)
0.7
1.2
2.4
1.2
1.3
%Au/SiO -500
2
4
Micromorphology & Surface Property
of Catalysts
Transmission electron microscopy (TEM) was conducted
to obtain average sizes and size distributions oꢀ Au cata-
lysts. It allowed us to ꢀollow how the size and structure oꢀ
Au nanoparticles change according to the Au loading and
calcination treatment. As seen ꢀrom Fig. 4a–c, the spherical
Au nanoparticles were dispersed within the mesopores oꢀ
the SBA-15 support, and the mean diameters oꢀ Au nano-
particles oꢀ 0.7%Au@SBA-15-500, 1.2%Au@SBA-15-500
and 2.4%Au@SBA-15-500 increased ꢀrom 3.3 ± 1.5 nm to
5
.2± 0.6 nm and 5.6± 1.1 nm with the Au loadings, respec-
tively. Oꢀ note, the Au nanoparticles oꢀ 1.2%Au@SBA-
1
5–800 showed no signifcant change in spite oꢀ the calcina-
tion temperature up to 800 °C (Fig. 4d). It ꢀurther confrmed
that Au nanoparticles were located inside the mesopores oꢀ
Fig. 2 XRD patterns oꢀ catalysts: (a) SBA-15; (b) 0.7%Au@SBA-
1
1
5-500; (c) 1.2%Au@SBA-15-500; (d) 2.4%Au@SBA-15-500; (e)
.3%Au/SiO -500; (f) 1.3%Au/SiO -800; (g) 1.2%Au@SBA-15-800;
SBA-15. In contrast, 1.3%Au/SiO -500 as a reꢀerence cat-
2
2
2
alyst possessed the comparable Au particle size with the
wider distribution 5.8± 2.6 nm (Fig. 4e), while the Au nano-
(
h) 1.2%Au@SBA-15-500 (used)
particles located on the surꢀace oꢀ SiO agglomerated and
2
increased sharply to 13.7 ± 6.3 nm aꢀter being calcined at
8
00 °C (Fig. 4ꢀ), which was also confrmed by XRD results.
The chemical states oꢀ the as-synthesized Au catalysts were
clarifed by XPS (Fig. 4h). For 1.3%Au/SiO -500, 0.7%Au@
2
SBA-15-500, 1.2%Au@SBA-15-500 and 2.4%Au@
SBA-15-500, the binding energies oꢀ Au 4ꢀ
were
/2
7
8
3.7–83.8 eV, which were characteristic oꢀ 4ꢀ oꢀ the Au
7/2
metallic [35, 36]. It indicated that Au existed in the state oꢀ
0
Au ꢀor the Au catalysts tested.
5
Catalytic Properties
The chemoselective hydrogenation oꢀ quinoline was
employed to study the catalytic perꢀormances oꢀ Au nano-
catalysts (Table 2). The plain SBA-15 support exhibited
the poor catalytic activity, but the as-prepared Au catalysts
delivered high activity and excellent selectivity under the
Fig. 3 FT-IR patterns oꢀ the samples: (a) SBA-15; (b) SBA-15
APTES; (c)1.2%Au@SBA-15-500
1
3

Au Nanoparticles Confned in SBA‑15 as a Highly Eꢀcient and Stable Catalyst ꢁor Hydrogenation…
Fig. 4 Representative TEM
images oꢀ Au catalysts: A
0
1
2
1
1
.7%Au@SBA-15-500; B
.2%Au@SBA-15-500; C
.4%Au@SBA-15-500; D
.2%Au@SBA-15-800; E
.3%Au/SiO -500; F 1.3%Au@
2
SiO -800; G 1.2%Au@SBA-
2
1
5-500 (used); The insets
show size distributions oꢀ Au
nanoparticles. H Au 4ꢀ XPS
spectra oꢀ typical Au catalysts:
(
a) 1.3%Au/SiO -500; (b)
2
0
1
2
.7%Au@SBA-15-500; (c)
.2%Au@SBA-15-500; (d)
.4%Au@SBA-15-500
same reaction conditions. Combined with our XPS results,
it showed that Au nanoparticles in the existence oꢀ metallic
state is catalytic active sites, in also accordance with the
previous report [37]. And then the inꢃuence oꢀ the Au load-
ing was investigated. The 1.2%Au@SBA-15-500 catalyst
showed the highest perꢀormances with 97.6% quinoline
conversion and 99.8% selectivity towards 1,2,3,4-tetrahy-
droquinoline among observed gold catalysts (Entry 2–4).
The adsorption and dissociation oꢀ hydrogen molecule is
usually thought to be the rate-determining step in metal
catalyzed-hydrogenation reactions [20, 21]. Small-sized Au
nanoparticles have more low-coordinated edge and corner
atoms, being considered to be catalytic active sites, and usu-
ally gave good activity. As shown in the results oꢀ XRD and
TEM, the 0.7%Au@SBA-15 catalyst has the smallest size oꢀ
Au nanoparticles. However, it exhibited lower activity than
the 1.2%Au@SBA-15 catalyst. It indicates that an appropri-
ate size oꢀ Au nanoparticles (about 5 nm) was required ꢀor
selective hydrogenation oꢀ quinoline. The smaller Au nano-
particles do not necessarily mean the higher activity. This
detailed reasons deserved to be explored in the ꢀuture. The
and high selectivity oꢀ 1,2,3,4-tetrahydroquinoline when
the reaction proceeded under the lower pressure oꢀ H or
2
at lower temperature (Entry 5–7). It showed that the 1.2%
Au@SBA-15-500 was indeed a high perꢀormance catalyst
ꢀor chemoselective hydrogenation oꢀ 1,2,3,4-quinoline.
The catalytic activity oꢀ Au nanocatalysts not only
depends on the sizes oꢀ Au nanoparticles but also the type
and structure oꢀ support [38, 39]. To elucidate the struc-
ture eꢀꢀect oꢀ support, 1.3%Au/SiO -500 was prepared
2
with microporous SiO as support and then employed in
2
the selective hydrogenation oꢀ quinolone. Apparently, the
1.2%Au@SBA-15-500 catalyst showed higher activity than
the 1.3%Au/SiO -500 catalyst (Entry 3–8). As shown in N
2
2
adsorption–desorption characterizations and TEM images
above, due to the higher surꢀace area oꢀ SBA-15, the Au
nanoparticles oꢀ 1.2%Au@SBA-15-500 and 1.3%Au/SiO -
2
500 had similar sizes, but the ꢀormer showed a narrow size
distribution. It in part accounted ꢀor the high activity oꢀ
1.2%Au@SBA-15-500. Besides, the ordered mesopore oꢀ
SBA-15 made quinoline more accessible to the surꢀace oꢀ Au
nanoparticles, which also endowed 1.2%Au@SBA-15-500
with high activity. In the chemoselective hydrogenation oꢀ
1
.2%Au@SBA-15-500 catalyst still delivered good activity
1
3

J. Zhao et al.
Table 2 Selective hydrogenation oꢀ quinoline over diꢁerent Au cata-
originated ꢀrom the adsorption and cleavage oꢀ H over the
2
lysts
surꢀace oꢀ Au nanoparticles, interacted with the adsorbed
quinoline and generated the 1,2,3,4-tetrahydroquinoline
product. This confguration adsorption oꢀ quinoline over the
surꢀace oꢀ as-prepared Au catalysts led to the high selectivity
towards 1,2,3,4-tetrahydroquinoline.
The eꢁect oꢀ calcination temperature on the catalytic
perꢀormances oꢀ Au catalysts was also explored. As seen
Conv./%a
Sel./%a
1
ꢀ
rom Fig. 5a, when the calcination temperature was 400 °C,
Entry
Cat
the as-obtained Au catalysts showed the low activity. It was
maybe related to the smaller size or chemical state oꢀ gold
nanoparticles. While it increased to 500 °C, the 1.2%Au@
SBA-15-800 catalyst aꢁorded the quinoline conversion oꢀ
97.5% and selectivity towards 1,2,3,4-tetrahydroquinoline oꢀ
99.8%. It was worth nothing that the Au catalysts still pos-
sessed high activity even aꢀter being treated at 800 °C. The
92.5% quinoline conversion and 98.3% selectivity towards
1,2,3,4-tetraquinoline were obtained. It was ascribed to the
similar mean sizes and size distribution oꢀ the 1.2%Au@
SBA-15-500 and 1.2%Au@SBA-15-800 catalysts, which
was confrmed by XRD and TEM results. To ꢀurther elu-
cidate the mechanism oꢀ outstanding anti-sintering prop-
erty oꢀ the 1.2%Au@SBA-15-500 catalyst, the Au catalysts
as a reꢀerence catalyst prepared ꢀrom the same procedure
2
1
2
3
4
SBA-15
8.9
51.3
97.5
96.2
91.1
73.6
86.2
76.2
42.3
92.3
99.8
98.7
98.7
97.3
98.1
93.7
57.7
7.7
0.2
1.3
1.4
2.7
1.9
6.3
0.7%Au@SBA-15-500
1.2%Au@SBA-15-500
2.4%Au@SBA-15-500
1.2%Au@SBA-15-500
1.2%Au@SBA-15-500
1.2%Au@SBA-15-500
b
5
c
6
d
7
8
1.3%Au/SiO -500
2
Reaction conditions: p(H )=2.0 MPa; T=100 °C; catalyst 0.1 g; qui-
2
noline 60 uL; water 3.0 mL; stirring speed=500 r/min; reaction time
4
h
a
The conversion oꢀ quinoline and selectivity towards 1,2,3,4-tetrahyd-
roquinoline were determined by GC and GC–MS
b
p(H )=1.5 MPa
2
with micropore SiO as a support was employed in the
2
c
p(H )=1.0 MPa
hydrogenation oꢀ quinoline (Fig. 5b). The activity oꢀ the
2
d
T=80 °C
as-prepared Au catalyst frstly increased with the calcina-
tion temperature ꢀrom 400 °C to 500 °C. The 1.3%Au/SiO -
2
5
00 catalyst showed the good catalytic perꢀormance with
quinoline, the nitrogen-containing benzene ring preꢀerred to
adsorb on the surꢀace oꢀ Au nanoparticles due to the interac-
tion between Au and N, which is confrmed by the previous
report [22]. And then the resulting hydrogen species, which
76.2% conversion oꢀ 1,2,3,4-quinoline and 93.7% selectivity
towards 1,2,3,4-tarahydroquinoline. When the calcination
temperature increased to 800 °C, the catalytic activity oꢀ the
corresponding Au catalysts decreased drastically ꢀrom 73.6%
Fig. 5 The conversion and selectivity over a 1.2%Au@SBA-15 and b
3.0 mL; stirring speed=500 r/min; reaction time 4 h. The conversion
oꢀ quinoline and selectivity towards 1,2,3,4-tetrahydroquinoline were
determined by GC and GC–MS
1
.3%Au/SiO calcined at diꢁerent temperatures. Reaction conditions:
2
p(H )=2.0 MPa; T=100 °C; catalyst 0.1 g; quinoline 60 uL; water
2
1
3

Au Nanoparticles Confned in SBA‑15 as a Highly Eꢀcient and Stable Catalyst ꢁor Hydrogenation…
that oꢀ the one beꢀore reaction. According to XRD (Fig. 2h)
and TEM results (Fig. 4g), the average diameter and size
distribution oꢀ Au particles oꢀ the used 1.2%Au@SBA-15-
5
00 catalyst showed no obvious aggregation compared to
the ꢀresh one. Thereꢀore, the 1.2%Au@SBA-15-500 catalyst
was a stable and good recyclable catalyst ꢀor selective hydro-
genation oꢀ quinoline.
The general applicability oꢀ the 1.2%Au@SBA-15-500
catalyst ꢀor chemoselective hydrogenation oꢀ quinoline
derivatives was ꢀurther explored. As ꢀound ꢀrom Table 3,
good to excellent conversions (91.1–100.0%) and high selec-
tivities (78.7–100.0%) were obtained. It indicated that the
1
.2%Au@SBA-15-500 catalysts was highly active and selec-
tive ꢀor hydrogenation reactions oꢀ quinoline compounds.
Fig. 6 Recyclability oꢀ 1.2% Au@SBA-15-500 ꢀor selective hydro-
genation oꢀ quinoline. Reaction conditions: p(H )=2.0 MPa;
2
T=100 °C; catalyst 0.1 g; quinoline 60 uL; water 3.0 mL; stirring
speed=500 r/min; reaction time 4 h
6 Conclusion
In conclusion, we reported the synthesis, characterizations
oꢀ Au nanoparticles deposited on the modifed SBA-15
support and the frst use ꢀor the selective hydrogenation
oꢀ quinoline. The 1.2%Au@SBA-15-500 catalyst aꢁorded
to 22.4%. According to the XRD and TEM results, the Au
nanoparticles supported on SiO sintered and agglomerated
2
severely aꢀter the thermal treatment oꢀ 800 °C, resulting in
the obvious loss in the activity oꢀ 1.3%Au/SiO -800. For
2
9
7.6% conversion oꢀ quinoline and 99.8% selectivity towards
,2,3,4-tetrahydroquinoline under mild conditions. It pos-
the 1.2%Au@SBA-15-500 and 1.3%Au/SiO -500 catalysts,
2
1
the dramatic diꢁerence in anti-sintering property should be
associated with the structure oꢀ support. The confned eꢁect
oꢀ the ordered mesopore oꢀ SBA-15 can eꢂciently prevent
the agglomeration oꢀ Au nanoparticles and so aꢁord the as-
prepared Au catalysts with extraordinary sintering-resistant
property.
sessed outstanding sintering-resistant property as high as
8
00 °C, broad substrate scope and good reusability. The
high specifc surꢀace area oꢀ SBA-15 and low Au loading
contribute to small-sized gold nanoparticles, and ordered
mesoporous oꢀ SBA-15 ꢀacilitate the mass transꢀer oꢀ sub-
strates during the reaction, leading to high activity oꢀ gold
nanocatalysts. This selective adsorption oꢀ the nitrogen-
containing benzene ring on the surꢀace oꢀ the Au catalysts
accounted ꢀor the high selectivity towards 1,2,3,4-tetrahyd-
roquinoline. The confnement oꢀ mesopores oꢀ SBA-15 can
eꢂciently prevent gold nanoparticles ꢀrom sintering at high
temperature. It opens a promising avenue to construct metal
nanocatalysts with high catalytic perꢀormance and especially
outstanding anti-sintering property by the use oꢀ mesoporous
materials.
The reusability oꢀ 1.2%Au@SBA-15-500 catalyst was
evaluated ꢀor the selective hydrogenation oꢀ quinoline. Aꢀter
the reaction ended, the 1.2%Au@SBA-15-500 catalyst was
recovered by centriꢀugation, washed with ethyl acetate, dried
and reused under the same reaction conditions. No signif-
cant decrease in activity and selectivity oꢀ 1.2%Au@SBA-
1
5-500 was ꢀound when it was reused ꢀor 6 runs, as shown
in Fig. 6. To disclose the mechanism oꢀ its good recyclabil-
ity, the used 1.2%Au@SBA-15-500 catalyst was tested by
series oꢀ characterizations. The Au amount oꢀ the catalyst
aꢀter reaction ꢀrom ICP-AES remained almost the same with
1
3

J. Zhao et al.
Table 3 Selective
hydrogenation oꢀ quinoline
derivatives over 1.2%Au@
SBA-15-500
Entry
1
Product
Conv. /% a
Sel. /% a
99.8
Substrate
9
7.5
1.1
2
96.5
9
3
4
97.3
96.1
100.0
85.8b
5
6
100.0
78.7c
99.5
9
6.0
Reaction conditions: p(H )=2.0 MPa; T=100 °C; catalyst 0.1 g; quinoline 60 uL; water 3.0 mL; stirring
2
speed=500 r/min; reaction time 4 h
a
The conv. oꢀ quinoline and sel. ꢀor the products were determined by GC and GC–MS
b
6
-Chloro-5,6,7,8-tetrahydroquinoline as the by-product were observed
c
6
-Methoxy-5,6,7,8-tetrahydroquinoline as the by-product were observed.
Acknowledgments This work was ꢀinancially supported by the
2. Wang T, Zhuo LG, Li Z, Chen F, Ding Z, He Y, Fan QH, Xiang
J, Yu ZX, Chan ASC (2011) Highly enantioselective hydrogena-
tion oꢀ quinolines using phosphineꢀree chiral cationic ruthenium
catalysts: scope, mechanism, and origin oꢀ Enantioselectivity. J
Am Chem Soc 133:9878–9891
National Natural Science Foundation oꢀ China (Grant Nos. 21576248,
2
1671178 and 21571159) and a research ꢀund ꢀrom the doctoral
program oꢀ Zhengzhou University oꢀ Light Industry (Grant No.
2
014BSJJ007). The authors honestly thank Yongꢀa Zhu in Tsinghua
University ꢀor good advices about XPS analysis.
3. Gong Y, Zhang P, Xu X, Li Y, Li H, Wang Y (2013) A novel
catalyst Pd@ompg-C N ꢀor highly chemoselective hydrogenation
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Alvarado Y, Busolo M, Lopez-Linares F (1999) Regioselective
homogeneous hydrogenation oꢀ quinoline by use oꢀ pyrazolyl
borate ligand and transition metal complexes as a precatalyst. J
Mol Catal A-Chem 14:2163–2167
Compliance with Ethical Standards
4
5
6
.
.
.
Conꢁlict oꢁ interest The authors declare that they have no conꢃict oꢀ
interest.
Kuwano R, Ikedaa R, Hirasadaa K (2015) Catalytic asymmet-
ric hydrogenation oꢀ quinoline carbocycles: unusual chemose-
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