Two-dimensional porous γ-AlOOH and γ-Al2O3 nanosheets: Hydrothermal synthesis, formation mechanism and catalytic performance

Article abstract of DOI:10.1039/c5ra09772j

Novel two-dimensional (2D) γ-AlOOH porous nanosheets have been successfully prepared in a mixed system consisting of oleic acid (OA), dodecylamine (DDA), urea, and 1-octadecene. OA acted as a reaction reagent to form the Al-carboxyl precursor, DDA acted a

Full text of DOI:10.1039/c5ra09772j

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PAPER
Two-dimensional porous g-AlOOH and g-Al2O3
nanosheets: hydrothermal synthesis, formation
mechanism and catalytic performance†
Cite this: RSC Adv., 2015, 5, 71728
ab
Changyun Chen,a Qinpu Liu,a Yiwei Zhuo,b Dan Yuan,b Zhihui Daib
*
Suli Liu,
and Jianchun Baob
Novel two-dimensional (2D) g-AlOOH porous nanosheets have been successfully prepared in a mixed system
consisting of oleic acid (OA), dodecylamine (DDA), urea, and 1-octadecene. OA acted as a reaction reagent to
form the Al-carboxyl precursor, DDA acted as a soft template and induced the g-AlOOH sheet structure, and
urea acted as a porogen. Porous g-Al2O3 nanosheets were obtained by thermal decomposition of the g-
AlOOH. Furthermore, the obtained sheet-like g-Al2O3 was used as a support to prepare a monodisperse Ag/
g-Al2O3 nanocatalyst. This catalyst exhibited superior catalytic activity compared to g-Al2O3 nanosheets,
pure Ag nanocrystals (NCs) and Ag/amorphous Al2O3 for the hydrogenation of nitroaromatic compounds,
which can be explained by a higher concentration of Lewis type basic sites on sheet-like g-Al2O3 leading to
a higher concentration of nitrobenzene and more efficient hydrogenation.
Received 28th May 2015
Accepted 17th August 2015
DOI: 10.1039/c5ra09772j
www.rsc.org/advances
the literature contains few reports related to g-Al2O3 porous
nanostructures.
Introduction
Aromatic amines are important intermediates that have
been used in the production of dyes and analgesic drugs such as
acetaminophen. The primary process for the preparation of
aromatic amine involves the hydrogenation of nitroaromatics in
the presence of reducing agents (e.g., iron, sodium hydrosulte,
tin, or zinc) in ammonium hydroxide. The major drawback of
this method is the formation of a large number of by-products
that cannot be reused, which results in disposal issues.19
Catalytic hydrogenation by H2 is more ideal and involves the use
of expensive catalysts such as gold and platinum-group metals
supported on an oxide. The sole by-product of this approach is
water. Because of the limited reserves of noble metals such as
Au and PGMs, other metal catalysts for the catalytic hydroge-
nation reaction are needed.
Herein, we report the simple solvothermal synthesis of novel
g-AlOOH porous nanosheets in a mixed system consisting of
oleic acid (OA), dodecylamine (DDA), urea, and 1-octadecene
(ODE). Porous g-Al2O3 sheets were obtained by thermal
decomposition of g-AlOOH. Furthermore, Ag nanocrystals
(NCs), which are a relatively inexpensive and abundant metal,
were successfully supported on the porous g-Al2O3 to form an
Ag/g-Al2O3 composite. This catalyst exhibited good catalytic
action for the hydrogenation of nitroaromatics.
The morphology control of nanostructured materials has
attracted much interest because a close relationship exists
between the morphology of these materials and their proper-
ties.1–3 Because of their large specic surface areas, high
porosities, and low densities, porous materials are widely used
in electronics, photonics, catalysis, sensors, and as selectively
permeable membranes.3–5 For example, Wang et al. have
reported that mesoporous Co3O4 nanoakes exhibit excellent
electrochemical performance as anode materials in lithium-ion
batteries and as catalysts for the oxygen evolution reaction
under alkaline solutions.6 Xia et al. reported that inorganic
hollow mesoporous monodisperse MnO/C microspheres are
highly biocompatible and exhibit a high reversible specic
capacity of 700 mA h gꢀ1 at 0.1 A gꢀ1, and excellent cycling
stability with 94% capacity retention.7
As an important type of functional material, g-Al2O3 has
been used as an absorbent and catalyst carrier as well as to
reinforce ceramic composites.8–12 Currently, various morpho-
logic boehmite and g-Al2O3 nanomaterials, such as nano-
tubes,13 nanorods,14 nanoplatelets and nanowires,15 nanowire
bunches,16 microspheres,8 hollow microspheres,9 and ower-
like 3D nanoarchitectures,17,18 have been prepared. However,
aDepartment of Chemistry, Nanjing Xiaozhuang College, Nanjing 211171, P. R. China.
E-mail: niuniu_410@126.com
bJiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials
Science, Nanjing Normal University, Nanjing 210023, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra09772j
Experimental section
Materials
Aluminum isopropoxide, urea, heptane, and absolute alcohol
were purchased from Sinopharm Chemical Reagent Co. Ltd
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(Shanghai, China). The DDA (>98%) and ODE (>90%) were kV. The high resolution transmission electron microscopy
purchased from Alfa Aesar. All of the reagents were used as (HRTEM) images were recorded on a JEOL-2100F apparatus at an
received without further purication.
accelerating voltage of 200 kV. Nitrogen adsorption isotherms were
obtained using an ASAP 2000 instrument (Micromeritics. Nor-
cross, GA). The FT-IR spectrum were measured on a Nexus 670 FT-
IR spectrometer. Thermal gravimetric analysis (TGA) was carried
out on a Perkin-Elmer Diamond TG/DTA thermal analyzer with a
Typical synthesis of 2D g-AlOOH nanosheets
In a typical synthesis, aluminum isopropoxide (2 mmol), urea (3
mmol), DDA (5 mL), OA (3 mL), and ODE (10 mL) were added to
35 mL Teon lined autoclave. Then, it was seaꢀle1d and carefully
heating rate of 10 ꢁC minꢀ1 and a owing N2 of 50 mL minꢀ1
.
ꢁ
ꢁ
heated to 180 C at a heating rate of 4 C min in the electric
oven. Aer 24 h, the autoclave was air-cooled to room temper-
ature. The resultant colloidal product was ltered off, washed
with heptane and absolute ethanol for several times, and then
Results and discussion
The purity and crystallinity of the as-prepared samples were
examined by powder X-ray diffraction (XRD). Fig. 1A shows the
XRD pattern of a sample prepared under typical conditions. The
diffraction peaks at 10 < 2q < 80ꢁ were indexed as reections of
the (020), (120), (031), and (051) planes of orthorhombic g-
AlOOH.20,21 Additional diffraction peaks are indicated with
asterisks; they most likely result from the incorporation of DDA
molecules into neighboring g-AlOOH layers (dened as g-
AlOOH$cDDA), which is consistent with previously reported
results.16,17 Fig. 1B shows a typical diffraction pattern of g-
ꢁ
dried under vacuum at 60 C for 6 h, obtaining the g-AlOOH
ꢁ
sheet. This sample was calcined at 600 C for 1 h at a heating
rate of 2 C minꢀ1, generating the g-Al2O3 sheet.
ꢁ
Synthesis of Ag/g-Al2O3 (Ag 5 wt%) composite
First, the prepared g-Al2O3 was added to an aqueous solution of
silver nitrate. A Na2CO3 solution was then added dropwise into
the aforementioned solution to precipitate the silver ions, which
resulted in the formation of the composite of Ag2CO3 and g-Al2O3.
The composite was dried at 60 ꢁC and subsequently calcined in a
muffle furnace at 400 ꢁC for 1 h to yield the Ag/g-Al2O3 composite.
ꢁ
AlOOH obtained by calcining g-AlOOH$cDDA in air at 300 C
for 1 h. All the diffraction peaks were assigned to the standard
values of g-AlOOH (JCPDS card no. 21-1307). Fig. 1C shows the
XRD patterꢁn of g-Al2O3 obtained by calcining g-AlOOH$cDDA in
air at 600 C for 1 h. All the peaks were indexed to the cubic
structure of g-Al2O3, and these peaks are in good agreement
with the standard values (JCPDS card no. 10-425). No charac-
teristic peaks corresponding to impurities were observed in any
of the patterns, indicating the high purity of the products.
Fig. 2A–C show TEM and HRTEM images of g-AlOOH fabri-
cated under typical synthesis conditions. As shown in Fig. 2A,
g-AlOOH exhibits a sheet-like shape 20–32 nm wide and 280–
330 nm long. Fig. 2B reveals that the g-AlOOH sheet contains
Catalytic hydrogenation of nitroaromatics
The hydrogenation of nitroaromatic compounds was carried
out in a 200 mL stainless steel autoclave. For each reaction, the
nitroaromatic compound (0.5 g) in 100 mL of ethanol was
placed into an autoclave along with 0.10 g of the Ag/g-Al2O3
composite. o-Xylene was used as an internal standard for the
nal determination of the conversion yields. Aer the autoclave
was sealed, the air content was purged by ushing three times
with hydrogen. The autoclave was then pressurized with 2.0
MPa of hydrogen and heated to 140 ꢁC for 5 h. During the
reaction, the stirring rate was xed at 800 rpm (mechanical
stirring). At the end of the reaction, the autoclave was allowed to
naturally cool to ambient temperature and ushed two times
with nitrogen. The Ag/g-Al2O3 composite was separated by
centrifugation at 12 000 rpm, recovered, and washed with
ethanol (3 ꢂ 5 mL) for reuse. The combined organic phase was
dried over anhydrous Na2SO4 and evaporated under reduced
pressure. The reaction products and intermediates in the cata-
lytic hydrogenation experiment were identied using a GC/MS-
QP2010 (Shimadzu) instrument equipped with a DB-MS capil-
lary column by comparison to standard samples.
Characterization
The XRD patterns were recorded on a powder sample using a D/
max 2500VL/PC diffractometer (Japan) equipped with graphite
˚
monochromatized Cu Ka radiation (l ¼ 1.54060 A) in 2q ranging
from 10 to 85ꢁ. The corresponding work voltage and current were
40 kV and 100 mA, respectively. MDI Jade 5.0 soware was used to
manage the acquired diffraction data. The transmission electro-
chemical microscopy (TEM) images were obtained on a JEM-
Fig. 1 XRD patterns of (A) g-AlOOH prepared under typical condi-
tions, (B) g-AlOOH prepared by calcining g-AlOOH$gDDA at 300 ꢁC
for 1 h, and (C) g-Al2O3 prepared by calcining g-AlOOH at 600 ꢁC
200CX instrument (Japan) using an accelerating voltage of 200 for 1 h.
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Fig. 3 N2 absorption–desorption isothermal and pore-size distribu-
tion curves (inset) for the g-Al2O3 products.
Fig. 2 TEM ((A) and (B)) and HRTEM (C) images of g-AlOOH obtained
by calcining g-AlOOH$cDDA at 300 ꢁC for 1 h. TEM ((D) and (E)) and
HRTEM (F) images of g-Al2O3 obtained by calcining g-AlOOH$cDDA at
600 ꢁC for 1 h.
Fig. 4 FT-IR spectra of (A) g-AlOOH$cDDA and (B) g-Al2O3 obtained
by calcining g-AlOOH$cDDA at 600 ꢁC.
many holes approximately 3 nm in diameter. The HRTEM
image in Fig. 2C indicates that the sheets are assembled from
small particles approximately 4.5 nm in size. The lattice spacing
is ca. 0.24 nm, which is consistent with that of the (031) plane of
the g-AlOOH sample. Fig. 2D and E show TEM images of g-Al2O3
surface of obtained g-AlOOH sheets was capped by DDA and
OA.24 Fig. 4B shows the FT-IR spectrum of g-Al2O3, which was
obtained by calcining g-AlOOH$cDDA at 600 ꢁC for 1 h. The
intense band at 3446 cmꢀ1 and a weak band at 1637 cmꢀ1 were
observed; these bands are due to the stretching vibrations of the
OH groups in the hydroxide structure as well as those in phys-
ically adsorbed water. In addition, the intense bands at 810 and
590 cmꢀ1 represent the vibration mode of the AlO6 octahedra.
In comparison to the spectrum in Fig. 4A, that in Fig. 4B lacks
ꢁ
obtained by calcining g-AlOOH$cDDA at 600 C. The obtained
g-Al2O3 has the same morphology as its corresponding
precursor. The HRTEM image indicates that the lattice spacing
is 0.239 nm, which is consistent with that of the (311) plane of
the g-Al2O3 crystals (Fig. 2F). To the best of our knowledge,
these novel porous 2D g-AlOOH and g-Al2O3 nanostructures
have rarely been previously reported.22,23
Table 1 Summary of results from FT-IR spectrum
The specic surface area of the porous g-Al2O3 sheets was
measured, as shown in Fig. 3. The BET specic surface areas of
g-Al2O3 calculated on the basis of the N2 isotherms at 77 K were
determined to be as high as approximately 129 m2 gꢀ1. The
inset in Fig. 3 shows the pore size distribution curve, which
indicates that the pores in g-Al2O3 are approximately 2.8 nm in
diameter, which is close to the value (3.0 nm) obtained from
TEM analysis (Fig. 2E). These results indicate that the obtained
g-Al2O3 products possess good porous character.
The OA and DDA were used in the present reaction system.
Therefore, FT-IR spectrum and TGA/DTA characterizations were
carried out to determine if OA and DDA were present on the g-
AlOOH sheets. The FT-IR spectrum of AlOOH$cDDA is shown in
Fig. 4A. On the basis of the FT-IR spectrums (Table 1), the
The typical
Correspond to the
stretching mode
peaks (cmꢀ1
)
3328
3091
2920
2842
1616
1572
1477
1151
1074
738
–NH2
nAl–O–H
–CH3
–CH2
C]O
C–N
–COOH
dasAl–O–H
dsAl–O–H
–COOH
nAl–O
621
474
dAl–O
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the aforementioned peaks corresponding to the OA and DDA,
indicating decomposition of these organic molecules upon
calcination.
TGA/DTA curves were collected for AlOOH$cDDA and are
shown in Fig. 5. The TGA curve indicates a 1.2% weight loss in
the 25–110 ꢁC temperature range, with a slight endothermic
peak at approximately 107 ꢁC due to volatilization of physically
adsorbed water. The endothermic peak at approximately 280 ꢁC
in stage B is due to the removal of organic molecules (bidentate
carboxylate and DDA), with a total weight loss of 64.2%. Stage C
is due to the endothermic transformation of boehmite to the g–
Al2O3 transition phase at approximately 471 ꢁC, with a total
weight loss of 16.4%; this weight loss is consistent with the
theoretical weight loss from the transition of g-AlOOH to g-
Al2O3.
To gain insight into the formation mechanism of the sheet-
like nanostructures, the intermediates at different reaction
times were characterized by TEM. Fig. 6A–C show typical TEM
images of the samples obtained at 2 h, 6 h, and 12 h, respec-
tively. As shown in Fig. 6A, the brous structures form during
the initial stage. As the solvothermal time is increased to 6 h,
the bers begin to fuse and a sheet structure appears (Fig. 6B).
Aer 12 h of aging, well-dened porous nanosheets are formed
(Fig. 6C and S1†). On the basis of these results, the porous
sheets evolved from the brous particles.
Fig. 6 TEM images of g-AlOOH$cDDA obtained at (A) 2 h, (B) 6 h, and
(C) 12 h.
Al[(CH3)2CHO]3 + mH2O / AlOOH + mCH3CHOHCH3 (4)
or
What roles do OA and DDA play in the formation of the
porous sheets? According to previously reported studies, we
speculate that the formation process of boehmite involves
Al[(CH3)2CHO]3ꢀn(RCOO)n + mH2O / AlOOH + mROH (5)
First, OA (dened as RCOOH) reacts with aluminum alkoxide
substitution, dehydration or esterication and hydrolysis reac- to form an alcohol and an Al-carboxylate (eqn (1)). Scheme 1
tions.25 OA, which acts as a reactant, plays an important role in shows the proposed structure of the Al-carboxylate. This
the reaction. The basic steps are as follows:
Al(OH)(C17H33CO2)2 structure includes a carboxyl group as a
bidentate ligand that bridges two aluminum atoms to form a 2D
structure. The esterication or dehydration reactions subse-
quently occur at 180 ꢁC, resulting in the production of water
(eqn (2) and (3)). The resulting water promotes the hydrolysis
reaction to instantly generate AlOOH (eqn (4) and (5)).
[(CH3)2CHO]3Al + nRCOOH /
Al[(CH3)2CHO]3ꢀn(RCOO)n + (CH3)2CHOH (1)
(CH3)2CHOH / CH3CH]CH2 + H2O (2)
Yu25 reported that, during the synthesis of lamellar meso-
structured CoSe2-amine nanobelts, an amine with a linear
conguration acted as a so template, which led to the forma-
tion of mesostructured nanosheets and induced anisotropic
growth of 2D nanostructures. In the present case, when the DDA
reaches a certain concentration, it might aggregate to form
lamellar micelles. The brous Al-carboxylate precursor might
then be incorporated into the neighboring DDA layers. At longer
or
RCOOH + (CH3)2CHOH / RCOOCH(CH3)2 + H2O (3)
Fig.
5 DTA/TG curves related to the thermal analysis of the Scheme 1 Schematic of the structure of the linear macromolecule
AlOOH$cDDA nanostrips.
with a repeating Al(OH)(C18H33CO2)2 unit.
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times, brous AlOOH is formed by hydrolysis of the Al-
carboxylate precursor and gradually fuses to form sheet-like
AlOOH$cDDA.
The inuence of the mole ratio of OA and DDA on the
morphology of AlOOH was also studied. Only irregular particles
were obtained in the absence of OA (Fig. 7A). When the molar
ratio was nOA/nDDA ¼ 1/1, g-AlOOH exhibited a nger-like
morphology. The central section of the bers was fused
together, and sharp tips were still observed (marked with a
solid-line arrow in Fig. 7B). When the ratio of nOA/nDDA was
increased to 3/1, straw-like nanoarchitectures (Fig. 7C)
composed of 2D nanosheets with a diameter of approximately
8–15 nm were formed. In the absence of DDA, ber clusters
instead of sheets were generated (Fig. 7D). From these observed
morphologies of the products, a mole ratio of nOA/nDDA ¼ 2/3
(typical condition) was determined to be favorable for the
formation of sheet-like AlOOH. An increase in the amount of OA
was benecial for the formation of brous g-AlOOH. Xie
reported that a surfactant can tailor the lamellar structures
along a certain direction to obtain nanobelts, which is the so-
called molecule tailoring lamella mechanism.22 We believe OA
functions in a similar fashion in our system. In our reaction
system, OA not only acted as a reactant but also acted as a
breaking agent. Aer the formation of lamellar AlOOH, the
excess OA continued to interact with the hydrogen atom of the
hydroxyl to gradually break the hydrogen bonds. Apart from the
inuence of OA and DDA, we found that the type of carboxylic
acid have great impact on the formation of sheet-like g-AlOOH.
For example, when we used 6-aminocaproic acid, octanedioic
acid, and undecylenic acid instead of OA and kept other
conditions constant, it was found that the longer carbon chain
was more favorable for the formation of sheet-like AlOOH
(Fig. S2†). This process should result in splitting of the lamellar
structures to produce sheet-like nanostructures (Scheme 2).
Scheme 2 Redundant OA breaks the hydrogen bonds to split the
lamellar structure of AlOOH.
Porous nanomaterials were recently synthesized using
different methods. Gao26 prepared mesoporous g-alumina
through the scaffolding of pseudo-boehmite nanoparticles in
the presence of a nonionic surfactant, which acted as the
porogen. Li27 fabricated hollow ZnSe microspheres using N2
produced during the reaction as aggregation centers. The
formation of porous AlOOH in our case is due to the gas
released by urea. With a prolonged reaction time, urea decom-
posed to form ammonia and CO2 gas, which act as a porogen
(eqn (6)).
CO(NH2)2 + H2O / 2NH3 + CO2
(6)
Unlike the porous g-AlOOH products formed in the presence
of urea, the sample prepared in the absence of urea did not
exhibit a porous structure (Fig. 8).
A growth mechanism for AlOOH was proposed on the basis
of the aforementioned experiments and discussions; it is shown
in Scheme 3.
For the reduction of nitroaromatic compounds to corre-
sponding aromatic amines, most previous studies have focused
on traditional expensive supported metal catalysts, such as
platinum-group metal-based catalysts, which are deposited
onto the surface of commercial products.28,29 Less attention has
been devoted to the effects of inexpensive Ag NCs and nano-
structured g-Al2O3 as a support. In fact, metal NCs and metal
oxide supports are two major components of most heteroge-
neous catalysts. g-Al2O3 is an acid-based bifunctional support,
and we used sheet-like g-Al2O3 as a support for the deposition of
Ag NCs. The resulting Ag/sheet-like g-Al2O3 was successfully
used to catalyze the hydrogenation of nitro groups.
Fig. 7 TEM images of the samples obtained at 180 ꢁC for 24 h (A) in the
absence of OA. (B) Finger-like morphology with nOA/nDDA ¼ 1/1, (C)
straw-like morphology assembled by nanosheets with nOA/nDDA ¼ 3/1,
and (D) without DDA.
Fig. 8 TEM images of samples prepared without urea.
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Fig. 10 (A) Low-magnification and (B) high-magnification TEM images
of the Ag/g-Al2O3 nanocomposites.
Scheme 3 Schematic of the growth process of AlOOH.
The components and phase structure of the as-synthesized
Ag/g-Al2O3 nanocomposites were examined by powder XRD
(Fig. 9). Seven diffraction peaks were observed, which were
indexed to the (200) and (220) planes of the fcc phase of g-Al2O3
and the (111), (200), (220), (311), and (222) planes of the face-
centered cubic phase (fcc) of Ag. The microstructure features
of the Ag/g-Al2O3 nanocomposites were characterized by TEM
and HRTEM (Fig. 10). The TEM image (Fig. 10A) indicates that
the Ag NCs were well dispersed on the g-Al2O3 nanosheets, and
no aggregates were observed. The size of the Ag NCs was in the
10–12 nm range (inset of Fig. 10A). The HRTEM image (inset of
Fig. 10B) indicates a fringe of 0.239 nm, which agrees with the
spacing of the (111) facet of fcc Ag. These results demonstrate
that the obtained nanocomposites are composed of fcc g-Al2O3
and fcc Ag.
The catalytic hydrogenation of aromatic nitro compounds
was selected as a model reaction to evaluate the performance of
the Ag/g-Al2O3 nanocomposites. For comparison, the catalytic
performances of both bare g-Al2O3 nanosheets and pure Ag NCs
prepared under the same conditions as those used to prepare
the Ag/g-Al2O3 nanocomposites were also measured. The results
indicate that both the bare g-Al2O3 nanosheets and the pure Ag
NCs exhibit no catalytic activity. However, the Ag/sheet-like
g-Al2O3 nanocomposites exhibit high catalytic performance
under the same reaction conditions. To further learn the effect
of the support material, amorphous Al2O3 was employed as a
support for the deposition of Ag NCs with a diameter similar to
Table 2 The catalytic performances of Ag/g-Al2O3 nanocatalysta
Entry
NO2Ph–R
T (ꢁC)
Time (h)
Yield (%)
1
2
3
4
5
6
NO2Ph
NO2PhOH
NO2PhCHO
p-NO2PhCH3
o-NO2PhCH3
m-NO2PhCH3
140
140
140
140
140
140
5
5
5
5
5
5
86
82
85
99
42
49
a
Substrate (0.5 g), CH3CH2OH (75 mL), H2 (2 MPa), catalyst (0.1 g, Ag
loading ¼ 5 wt%), T ¼ 140 ꢁC, t ¼ 5 h, conversion was determined by
GC-MS.
that of Ag/sheet-like g-Al2O3. Ag/amorphous Al2O3 (Fig. S3†)
exhibited no catalytic activity toward p-nitrotoluene or p-nitro-
phenol. The experimental results are summarized in Table 2.
He and Satsuma et al.30,31 proposed a reaction mechanism for
the catalysis of the ethanol by Ag clusters supported on g-Al2O3.
Cooperation between the acid–base pair site on Al2O3 and the
coordinatively unsaturated Ag sites on the Ag clusters were
responsible for the highly chemoselective reduction of nitro-
aromatic compounds. We speculate that, in the present case,
the high catalytic activity of the Ag/sheet-like g-Al2O3 is due
primarily to the higher concentration of Lewis type basic sites
providing higher concentration of adsorbed electrondecient
nitrobenzene on the surface.30,31 Further studies on the catalytic
performances are under way.
Conclusions
In summary, a simple method to prepare novel 2D porous g-
AlOOH and g-Al2O3 nanosheets has been developed by using a
mixed system consisting of OA, DDA, urea, and ODE. Based on a
series of control experiments and characterizations, the
formation mechanism of boehmite involving substitution,
dehydration or esterication, hydrolysis and fusion is proposed.
The used urea is responsible for the formation of the pore
structure. The obtained sheet-like g-Al2O3 can be used as a
support to prepare a monodisperse Ag/g-Al2O3 nanocatalyst.
This catalyst exhibits good catalytic activity compared to bare g-
Al2O3 nanosheets, pure Ag NCs and Ag/amorphous Al2O3 for the
hydrogenation of nitroaromatic compounds. In the future, the
ndings of this work could be used to design novel selective
hydrogenation catalysts.
Fig. 9 XRD pattern of the synthesized Ag/g-Al2O3 nanocomposites.
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This work was supported by the NSFC (21471081, 21271105,
21175069, and 21171096), Research Fund for the Young Teacher
Project of Nanjing Xiaozhuang College (4051067). We appre-
ciate the nancial support from the PAPD of Jiangsu Higher
Education Institutions and the Program for Jiangsu Collabora-
tive Innovation Center of Biomedical Functional Materials.
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71734 | RSC Adv., 2015, 5, 71728–71734
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