Palladium nanoparticles supported on nitrogen-functionalized active carbon: A stable and highly efficient catalyst for the selective hydrogenation of nitroarenes

Article abstract of DOI:10.1002/cctc.201301037

Nitrogen-functionalized active carbon-supported ultrasmall Pd nanoparticles were conveniently prepared by using a postloading method. The Pd catalyst was highly active and selective for the hydrogenation of nitroarenes at room temperature under ambient pressure. Reducible groups such as ketone, carboxylic acid, and ester were not hydrogenated, and the corresponding anilines were obtained quantitatively. The Pd catalyst demonstrated high stability and could be reused 10 times without the loss of catalytic performance. Be active, be fit! A facile method to prepare nitrogen-functionalized active carbon (NAC) has been described. The small-sized Pd nanoparticles are supported on NAC by using a postloading method. The representative catalyst Pd@NAC-800 demonstrated high activity and selectivity for the selective hydrogenation of nitroarenes under mild reaction conditions.

Full text of DOI:10.1002/cctc.201301037

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DOI: 10.1002/cctc.201301037
Palladium Nanoparticles Supported on Nitrogen-
Functionalized Active Carbon: A Stable and Highly
Efficient Catalyst for the Selective Hydrogenation of
Nitroarenes
[a, c]
[a, c]
[a]
[a, c]
[a]
[a, b]
Zelong Li,
Jinlei Li,
Jianhua Liu, Zelun Zhao,
Chungu Xia,* and Fuwei Li*
Nitrogen-functionalized active carbon-supported ultrasmall Pd
nanoparticles were conveniently prepared by using a postload-
ing method. The Pd catalyst was highly active and selective for
the hydrogenation of nitroarenes at room temperature under
ambient pressure. Reducible groups such as ketone, carboxylic
acid, and ester were not hydrogenated, and the corresponding
anilines were obtained quantitatively. The Pd catalyst demon-
strated high stability and could be reused 10 times without
the loss of catalytic performance.
Introduction
The hydrogenation of organic compounds is synthetically
selectivity for the hydrogenation of nitro compounds with H2
as a hydrogen source is highly desirable.
[
1]
important both in the laboratory and in industry, and the re-
duction of nitroarenes to anilines is widely used in industrial
processes because functionalized anilines are industrially im-
portant intermediates for fine chemicals such as agrochemicals,
Pd/C catalysts with good chemical stability are widely used
in many chemical processes, especially involving H , such as
2
[10]
hydrogenation, dehydrogenation, and hydrogenolysis.
The
[
2]
pharmaceuticals, and dyestuffs. The classical methods for the
hydrogenation of nitroarenes use various transition-metal cata-
catalytic activity of PdNPs supported on carbon materials is
highly dependent on the nature of surface functional groups
present on the support, which can affect the particle size dis-
[
3]
[4]
[5]
lysts, such as Pt, Pd, and Ru. However, with these highly
active supported metal catalysts, it is difficult to avoid side re-
actions, particularly if the nitro substrates with other reducible
groups are used. To solve this problem, other metal catalysts
[11]
persion and chemical state of PdNPs. The particle size has
a significant effect on hydrogenation reactions. Previous stud-
ies have revealed that the formation of weak hydrogen bonds
on the surface is the key factor for the hydrogenation to occur,
and the accessibility of these H atoms is found to be the origin
of the high activity of particles due to their nanoscale dimen-
[
6]
[7]
[8]
(
Au, Ag, and Cu ) were developed for the selective hydro-
genation of nitroarenes; however, the activity of such metal
catalysts was not always high and the reaction conditions were
harsh. In addition, the use of other hydrogen sources as stoi-
chiometric reducing agents could result in high selectivity but
[12]
sions. In addition, the chemical state of PdNPs has a signifi-
cant effect on the catalytic performance of Pd/C catalysts and
the oxide state and even the near-surface composition of
PdNPs can be altered, rendering the stabilization of Pd in the
most suitable oxidation state difficult in hydrogenation
[
9]
a large amount of wastes was produced. From a sustainable
point of view, the development of efficient and recyclable sup-
ported Pd nanoparticle (PdNP) catalysts with high activity and
[13]
reactions.
N-doped carbon materials have recently attracted research
interest because of their remarkable performance as catalytic
[
a] Dr. Z. Li, Dr. J. Li, Dr. J. Liu, Dr. Z. Zhao, Prof. Dr. C. Xia, Prof. Dr. F. Li
State Key Laboratory for Oxo Synthesis and Selective Oxidation
Lanzhou Institute of Chemical Physics
Chinese Academy of Sciences
Lanzhou, Gansu 730000 (P.R. China)
Fax: (+86)931-4968129
[14]
supports.
Doping with the electron-rich N atoms could
modify the surface structure of carbon materials, with in-
[15]
creased p-binding ability and improved basicity.
The N
doping of carbon materials could realize the high dispersion of
PdNPs and stabilize the small-sized PdNPs on the carbon sup-
port, and small-sized PdNPs and the synergistic effect of the N
species could accelerate the selective hydrogenation of phe-
E-mail: cgxia@licp.cas.cn
fuweili@licp.cas.cn
[b] Prof. Dr. F. Li
[11b]
[16]
Suzhou Institute of Nano-Tech and Nano-Bionics
Chinese Academy of Sciences
Suzhou, Jiangsu 215123 (P.R. China)
nol
and quinoline. It has also been reported that the Pd/
N-functionalized carbon nanotube catalyst showed good sta-
bility because of the structural and electronic promoting effect
[
c] Dr. Z. Li, Dr. J. Li, Dr. Z. Zhao
University of Chinese Academy of Sciences
Beijing 100049 (P.R. China)
[12a]
of the N-functionalized carbon nanotube support.
Our
study has demonstrated that the N species as electron donors
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in the carbon support could increase the electron intensity of
the support for stabilizing the small-sized PdNPs, affect the oxi-
dation state of Pd, and promote the selective hydrogenation
[
17]
activities.
Herein, the commercially available and cheap active carbon
was initially functionalized with melamine at different tempera-
tures to yield the corresponding N-hybrid carbon supports
(NAC-T, in which NAC represents N-functionalized active
carbon and T represents treatment temperature), which could
be ideal supports for the postloading of PdNPs to prepare the
NAC-supported PdNPs (Pd@NAC-T). The catalytic activity and
stability of the resultant Pd@NAC-T were investigated in the
hydrogenation of nitro compounds under ambient reaction
conditions.
Results and Discussion
NAC-600, NAC-700, and NAC-800 were initially prepared by
heat treatment of the resultant mixture of commercially avail-
able active carbon and melamine through wet impregnation at
the corresponding temperature. Element analysis characteriza-
tions reveal that the N content of NAC-600, NAC-700, and
NAC-800 decrease significantly with the increase in heating
temperature (Table 1). The melamine molecules can be self-
Table 1. N content and N dopant state of NAC-600, NAC-700, and NAC-
800.
[
a]
[b]
Sample N content Content of different N species relative to total N
[
%]
Quaternary N
Pyrrolic N
Pyridinic N
NAC-600 18.56
NAC-700 11.02
NAC-800 7.25
0.27
0.30
0.33
0.24
0.18
0.14
0.49
0.52
0.53
Figure 1. N1s XPS spectra of a) NAC-600, b) NAC-700, and c) NAC-800.
[a] Determined from element analysis; [b] Determined from XPS analysis.
On the basis of the above analysis, the NAC-T supports with
high N content could be interesting supports for the immobili-
zation of small-sized PdNPs; herein, 2 wt% PdNPs was loaded
onto the NCA-T supports to produce Pd@NAC-600, Pd@NAC-
700, and Pd@NAC-800. First, TEM and high-angle annular dark-
field scanning TEM (HAADF-STEM) were used to test the mor-
phology and distribution of the supported PdNPs (Figure 2, 1a,
2a, and 3a). The TEM images of Pd@NAC-T reveal that PdNPs
are finely and uniformly dispersed on the surface of NAC-T sup-
ports. However, the aggregation of PdNPs is not observed. The
HAADF-STEM images of Pd@NAC-T show that PdNPs appear as
white dots and are homogeneously dispersed on the surface
of NAC-T supports and all PdNPs are uniform in size and shape
(Figure 2, 1b, 2b, and 3b). Furthermore, the particle size distri-
butions of PdNPs for Pd@NAC-600, Pd@NAC-700, and
Pd@NAC-800 are quite similar (Figure 2, 1c, 2c, and 3c). The
high-resolution TEM (HRTEM) observations suggested that
PdNPs are highly crystalline and demonstrate well-resolved lat-
tices of approximately 0.23 nm identified as the d-spacing of
the (111) plane of face-centered cubic Pd (Figure 2, 3d). More-
over, the elemental mapping images of the representative cat-
condensed to carbon nitride after an appropriate thermal
treatment, and the resultant carbon nitride can be further de-
[
18]
composed at a high temperature (>5008C).
During our
preparation, carbon nitride could be formed on the surface of
active carbon and its further decomposition could be acceler-
ated at a higher reaction temperature, which could reduce the
N content of NAC-T. The N1s X-ray photoelectron spectroscopy
(XPS) spectra of NAC-600, NAC-700, and NAC-800 are shown in
Figure 1. The N1s spectra of these three samples can be well
fitted to three components: the peak at 398.5 eV can be as-
signed to the pyridinic N, the peak at 400 eV is attributed to
[
19]
pyrrolic N, and the peak at 401 eV is attributed to classical
graphitic-type quaternary N. Although the N content decreases
from 18.56 to 7.25 wt% with the increase in temperature, the
relative content of graphitic-type quaternary N increases but
the relative content of pyrrolic N decreases (Table 1). These var-
iations indicated that the carbon nitride species reconstructed
to form the proper ring system to fit the requirements of the
locally graphitized structure.
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alyst Pd@NAC-800 also confirm that the N and Pd atoms are
all homogeneously dispersed on the materials (Figure 2, 3e).
To further clarify the stabilizing role of the N-doped func-
tionalities, the original active carbon without N doping is used
as a support to prepare the corresponding supported PdNP
catalytic material (Pd@AC, 2 wt% Pd), as revealed in its TEM
and HAADF-STEM images (Figure 2, 4a), and most of the
PdNPs are distributed on the surface of active carbon. The par-
ticle size distribution of Pd@AC is larger than that of Pd@NAC-
T, and the PdNP aggregation in Pd@AC is observed. These dif-
ferences reveal that the N species can be a key factor in pre-
venting the aggregation of PdNPs and stabilizing the formed
PdNPs mainly on the surface of N-doped active carbon.
The XRD patterns of Pd@NAC-T show high-intensity (002)
and (100) diffraction peaks corresponding to the graphitic
carbon; however, the characteristic diffraction peaks of Pd are
not observed, which indicates that the supported PdNPs have
small particle sizes and are homogeneously dispersed on the
surface of the carbon matrix (Figure 3, 3a). The Pd XPS spectra
Figure 3. a) XRD patterns of Pd@NAC-T; Pd 3d XPS spectra of b) Pd@NAC-
600, c) Pd@NAC-700, and d) Pd@NAC-800.
of Pd@NAC-T show a doublet corresponding to Pd3d5 and
/2
0
Pd3d3/2. The Pd3d5/2 peak at 335.8 eV is attributed to Pd (met-
allic Pd), whereas the Pd3d peak at 337.8 eV is attributed to
3/2
2
+
[10]
0
Pd (PdO). According to the XPS data for Pd@NAC-T, Pd is
formed as the major phase on the surface of the support.
The hydrogenation of nitrobenzene is performed as the
model reaction, and the results are listed in Table 2. The hydro-
genation of a less polar substrate in more polar solvents is pre-
[20]
ferred. However, in the heterogeneous catalytic system, the
solvation of the reacting species and its effect on the overall
Figure 2. TEM, HAADF-STEM, and particle size distribution images of 1a–
c) Pd@NAC-600, 2a–c) Pd@NAC-700, and 3a–c) Pd@NAC-800; 3d) HRTEM
image of Pd@NAC-800; 3e) elemental mapping analysis of Pd@NAC-800;
[21]
reaction mechanism are not clearly understood. The effect
of solvents on the hydrogenation of nitrobenzene was initially
investigated with the representative catalyst Pd@NAC-800 at
4
a) TEM and HAADF-STEM images of Pd@AC.
room temperature under atmospheric pressure of H gas. The
2
solvent has a strong effect on the catalytic efficiency in the
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Table 2. Evaluation of different solvents and catalysts for the reduction
[
a]
of nitrobenzene.
[
b]
Entry
Catalyst
Solvent
Conv./select.
Yield
[%]
[%]
1
2
3
4
5
6
7
8
9
Pd@NAC-800
Pd@NAC-800
Pd@NAC-800
Pd@NAC-800
Pd@NAC-800
Pd@NAC-800
Pd@NAC-800
Pd@NAC-700
Pd@NAC-600
ethanol
89/>99
82/>99
28/>99
42/>99
66/>99
<5/>99
73/>99
68/>99
55/>99
41/>99
89
82
28
42
66
<5
73
68
55
41
methanol
acetonitrile
THF
water
xylene
dichloromethane
ethanol
ethanol
Scheme 1. a) Haber mechanism of the hydrogenation of nitrobenzene with
transition-metal catalysts; b) possible mechanism of the hydrogenation of
hydroxylamine.
[c]
1
0
Pd/C
ethanol
[
a] Reaction conditions: 1 mmol of nitrobenzene, 0.5 mol% Pd, 2 mL sol-
as hydroxylamine, because they can undergo strong exother-
vent, room temperature, t=1 h; [b] Determined from GC and GC–MS
analyses with toluene as an internal standard; [c] 5 wt% Pd/C (1 mol%
Pd was used in this reaction) was purchased from Alfa Aesar.
[24]
mic disproportionation and other side reactions.
We and
others have reported that the N species in the carbon support
could improve the catalytic activity and selectivity of cyclohex-
anone in the hydrogenation of phenol because doping with
the electron-rich N atoms modifies the surface structure of
carbon materials owing to the increased interaction between
phenol and the support via the hydrogen bond (ÀOH···N) and
the electron-donating effect of N species in N-doped carbon
materials could increase the electron density of the anchored
present catalytic system; methanol or ethanol can give, respec-
tively, 82 and 89% yields within 1 h (Table 2). Other solvents re-
gardless of their polarities, such as acetonitrile, THF, n-hexane,
and water, are significantly less effective, and no hydrogena-
tion occurs in xylene. Because of the toxicity of methanol, eth-
anol was herein selected as the optimal solvent.
[11b,17a]
Pd.
In addition, the liquid phase semihydrogenation of
phenylacetylene and the selective hydrogenation of quinoline
to 1,2,3,4-tetrahydroquinoline could achieve the high catalytic
activity and selectivity because N doping of the carbon materi-
al could increase the electron density of PdNPs supported on
Furthermore, Pd@NAC-600, Pd@NAC-700, and the commer-
cially available Pd/C catalysts were compared. The catalytic
performance of Pd@NAC-T was better than that of the com-
mercial Pd/C; the conversion of nitrobenzene with different
catalysts decreased in the following order: Pd@NAC-800>
Pd@NAC-700>Pd@NAC-600>Pd/C; and the turnover frequen-
cies of Pd@NAC-800, Pd@NAC-700, Pd@NAC-600, and Pd/C for
[16,25]
the carbon material.
In such a hydrogenation system, the
N species in the carbon support could play two roles: 1) It is
possible that the hydroxylamine molecule can interact with
the surface through the hydroxyl group to form ÀOH···N or À
OH···p interactions. Therefore, the adsorption of the hydroxyla-
mine molecule on the surface of the support could be facilitat-
ed because of the existence of N species. 2) The N species in
the carbon support could act as electron donors and change
the electron density of the carbon matrix and thus increase
the electron density of PdNPs. The hydrogenation of the hy-
droxylamine molecule could be accelerated (Scheme 1b).
Then, the substrate tolerance of present NAC supported
with small-sized PdNPs was also investigated. The optimized
Pd@NAC-800 demonstrated high catalytic activity for the hy-
drogenation of nitrobenzene with low catalyst loading and
high aniline yield (Table 3, entry 1). Substrates with electron-
donating groups also worked efficiently and gave excellent
yields of the corresponding amine products within 2 h (Table 3,
entries 2–5). The introduction of an ortho substituent onto the
phenyl ring could slow the hydrogenation, and good yields
could be readily obtained by increasing the reaction time to
4 h (Table 3, entries 6–8). The hydrogenation reactions of p-
and m-chloronitrobenzene were also performed with the corre-
sponding aniline, and 82 and 86% yields, respectively, were
obtained (Table 3, entries 9 and 10); in addition, the hydro-
dechlorination of aryl chloride was observed as a side reaction.
the hydrogenation of nitrobenzene are 178, 136, 110, and
À1
8
2 h , respectively. The catalytic differences could be attribut-
ed to the N dopant state in the support. The N content in our
catalyst support decreased along with the increase in pyrolysis
temperature; however, the relative content of pyridinic and
graphitic-type quaternary N increased. Owing to its electron-
donating properties, pyridinic N is considered to constitute the
main transition-metal-binding site in the metal–CN (N-doped
[
22]
carbon) catalyst. At the same time, the carbon nitride spe-
cies formed from melamine could further reconstruct to form
the proper ring system with the locally graphitized structure at
a higher temperature. All these could change the physico-
chemical and electronic properties of the NAC support and
PdNPs and thus improve the catalytic performance of
Pd@NAC-800.
The widely accepted mechanism of the hydrogenation of ni-
[23]
trobenzene was proposed by Haber in 1898 (Scheme 1).
First, the nitro group is reduced to a nitroso group, and then
a second equivalent of H atom can result in the formation of
hydroxylamine. Finally, aniline is obtained with the addition of
the third equivalent H atom. In these three steps, the major
challenge is to avoid the accumulation of intermediates, such
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[
a]
Table 3. Reduction of nitroarenes to anilines.
In addition, Pd@NAC-800 demonstrated high catalytic ac-
tivity for the hydrogenation of more steric 2-nitronaphtha-
lene and 2,4-dinitrotoluene with two nitro substituents
[
b]
Entry Reactant
t
Product
Conv./
select. [%] [%]
Yield
[h]
(
Table 3, entries 11 and 12).
The selective hydrogenation of nitrobenzene derivatives
1
2
3
2
2
2
>99/>99 99
that contained other reducible groups is a challenging task
in organic synthesis. The reducible carbonyl groups, such
as ester, carbonyl acid, and ketone, were inert in the pres-
ent catalytic system, and quantitative amine products were
obtained (Table 3, entries 13–16).
>99/>99 99(96)
>99/>99 99
Stability is the most important character for a good solid
catalyst in the solid–liquid reaction, particularly if the reac-
tant or the product has a strong coordination ability
toward the supported metal catalyst, which could possibly
accelerate the irreversible leaching of metal atoms from
the supports. The N-doped carbon materials could be an
4
5
6
2
2
4
>99/>99 99
>99/>99 99
>99/>99 99(95)
[17a,26]
excellent support for stabilizing PdNPs.
As indicated
in Figure 4d, Pd@NAC-800 demonstrated stable recyclabili-
ty upon filtration from the reaction mixture and washing
with ethanol. The catalyst could be used for 10 successive
cycles in the hydrogenation of nitrobenzene, and a yield of
7
8
9
4
4
97/>99 97
98/>99 98
9
8
9% was well maintained. After removal of the Pd@NAC-
00 catalyst, the Pd concentration in the reaction solution
was obtained to be less than 0.1 ppm by using inductively
coupled plasma atomic emission spectroscopy. Nitroben-
zene (1 mmol) was again added to the filtrate, and the
mixture was held at room temperature and 0.1 MPa H2
pressure. In this case, no reaction proceeded. These results
indicated that leaching of Pd into the liquid phase was
negligible and the observed catalysis was intrinsically het-
erogeneous. The separated Pd@NAC-800 catalyst after the
tenth reaction run was also examined by using TEM,
HAADF-STEM, and XPS. Compared with the images of the
fresh Pd@NAC-800 catalyst, TEM and HAADF-STEM images
of the recycled catalyst Pd@NAC-800 do not show any ob-
vious changes. The small-sized PdNPs are still homogene-
ously dispersed on the surface of the support, and the par-
ticle size distribution of the catalyst is 2.2Æ0.5 nm, which
is close to that of the fresh catalyst. Its Pd3d XPS data
[
[
c]
c]
3
3
>99/82
>99/86
82
86
10
11
8
>99/>99 99(95)
96/>99 96
1
2
3
12
10
1
>99/>99 99(94)
>99/>99 99(93)
>99/>99 99
0
reveal that Pd is still the main metal species and the obvi-
0
ous change in the Pd content is not detected. All these
analyses further indicated that the N incorporation on the
surface of the carbon support could efficiently stabilize
PdNPs and prevent their aggregation.
1
1
1
4
5
6
5
5
4
Conclusions
A series of N-functionalized active carbon (NAC) were con-
veniently prepared from the cheap active carbon and used
as supports of small-sized Pd nanoparticle catalysts. Of all
the catalysts, Pd@NAC-800 demonstrated high catalytic
performance and excellent chemoselectivity for the selec-
tive hydrogenation of nitro compounds to the correspond-
ing aniline derivatives. The N species could stabilize Pd
nanoparticles and prevent their aggregation; at the same
time, the N species and their state could accelerate the hy-
drogenation reaction. Moreover, the Pd@NAC-800 catalyst
>99/>99 99(95)
[a] Reaction conditions: 1 mmol of substrate, 0.5 mol% Pd, 2 mL ethanol,
room temperature unless otherwise indicated; [b] Yields were based on nitro-
arenes, which were determined from GC analysis with toluene as an internal
standard; values in parentheses are the yields of the isolated products;
[c] Aniline was generated as a byproduct.
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the H PdCl solution (2 mL). The mixture was stirred for 5 h at RT.
2
4
Then, an excess of NaBH aqueous solution (144 mg dissolved in
4
1
0 mL of deionized water) was added slowly to the suspension
mixture under ice bath conditions. The mixture was stirred for 1 h,
and then the corresponding supported PdNPs were separated
through filtration, washed sequentially with distilled water and ab-
solute ethanol several times, and dried at 808C overnight in
a vacuum oven to obtain Pd@NAC-800.
Pd@NAC-T-catalyzed hydrogenation of nitro compounds
Hydrogenation reactions were performed in a 50 mL Schlenk glass
tube equipped with a magnetic bar. The heterogeneous Pd cata-
lyst, substrate, and solvent were introduced into the tube, and
then it was vacuumed and purged with H thrice before it was fi-
2
nally pressurized with 0.1 MPa of H gas. Subsequently, the reac-
2
tion mixture was stirred at RT. After the completion of the reaction,
excess H was carefully released and the internal standard toluene
2
was added. The resultant product mixtures were analyzed with an
Agilent gas chromatograph. The recycle experiments were per-
formed with use of a 350 mL Schlenk glass tube, and the catalyst
was separated from the reaction mixture through filtration in the
fresh run.
Figure 4. a) HAADF-STEM, b) distribution of particle size, and c) Pd3d XPS
spectra of Pd@NAC-800 after 10 runs; d) recycle experimental data for
Pd@NAC-800. Reaction conditions: 5 mmol of nitrobenzene, 0.5 mol%
2
Pd@NAC-800, 5 mL of ethanol, room temperature, t=3 h, P=0.1 MPa H .
could be used 10 times without the loss of product yield. In-
vestigations on the preparation of other supported metallic or
heterometallic nanoparticle catalysts and their catalysis are on-
going in our laboratory.
Instruments
Pd content and immobilization yield were obtained by using in-
ductively coupled plasma atomic emission spectroscopy. The
powder XRD measurements were performed with a PANalytical’s
Experimental Section
X’Pert PRO multipurpose diffractometer with Ni-filtered CuK radia-
a
tion (l=0.15046 nm) at RT and 2q=10.0–80.08. TEM and HRTEM
experiments were performed with a JEM-2010 transmission elec-
tron microscope operating at an accelerating voltage of 200 kV.
XPS analyses of the catalysts were performed on a Thermo Fisher
Scientific’s K-Alpha X-ray photoelectron spectrometer.
N-Functionalization of active carbon with melamine through
heat treatment
In general, active carbon (10 g) and melamine (10 g) were added
into a 250 mL round bottom flask containing ethanol (160 mL),
and the resultant mixture was heated to 808C to volatilize the sol-
vent under stirring. The solid mixture was loaded into the high-
temperature reactor, and the reactor was kept in the muffle fur-
nace; then, it was heated up to the targeted temperature (600,
NMR data for some of the products
À1
7
00, and 8008C; ramp rate: 38Cmin ) and held for 2 h. Finally, the
1
p-Toluidine: H NMR (400 MHz, CDCl ): d=7.04–6.85 (m, 2H), 6.59
3
reactor was cooled to RT and the N-doped active carbon materials
were obtained. Those carbon materials were labeled NAC-T (in
which T represented the treatment temperature in the muffle
furnace).
(
dd, J=14.1, 7.6 Hz, 2H), 3.66–3.45 (m, 2H), 2.23 ppm (s, 3H);
13
C NMR (100 MHz, CDCl ): d=143.8, 129.8, 127.8, 115.4, 20.5 ppm.
3
1
Benzene-1,2-diamine: H NMR (400 MHz, CDCl ): d=6.79–6.65 (m,
3
13
4
H), 3.36 ppm (s, 4H); C NMR (100 MHz, CDCl ): d=134.8, 120.3,
3
116.8 ppm.
Immobilization of PdNPs
1
An aqueous solution of H PdCl was initially prepared by mixing
Naphthalen-1-amine: H NMR (400 MHz, CDCl ): d=7.52–7.39 (m,
2
4
3
PdCl (0.34 g) and the HCl aqueous solution (20 mL, 10% v/v) with
4H), 7.36–7.30 (m, 1H), 7.19–7.06 (m, 2H), 6.94–6.63 (m, 2H),
2
13
stirring at RT until the salt dissolved homogeneously. Then, a certain
amount of the prepared NAC powder was impregnated with the
H PdCl solution and the mixture was stirred for 5 h at RT. Subse-
3.70 ppm (s, 2H); C NMR (100 MHz, CDCl ): d=143.6, 139.6, 130.5,
3
129.1, 128.9, 128.5, 127.7, 127.2, 118.7, 115.6 ppm.
2
4
1
quently, an excess of NaBH aqueous solution was added slowly to
Methyl 4-aminobenzoate: H NMR (400 MHz, CDCl ): d=8.04–7.75
4
3
1
3
the suspension mixture under ice bath conditions. Finally, the cor-
responding supported PdNPs were separated through filtration,
washed sequentially with distilled water and absolute ethanol sev-
eral times, and dried at 808C overnight in a vacuum oven to
obtain the corresponding PdNP catalysts (labeled as Pd@NAC-T).
The typical method for preparing Pd@NAC-800 was as follows:
NAC-800 (1 g) was mixed with deionized water (20 mL) containing
(m, 2H), 6.80–6.57 (m, 2H), 4.10 (s, 2H), 3.85 ppm (s, 3H); C NMR
(100 MHz, CDCl ): d=167.2, 150.9, 131.6, 119.6, 113.8, 51.6 ppm.
3
1
1-(4-Aminophenyl)ethanone: H NMR (400 MHz, CDCl ): d=7.86–
3
7.76 (m, 2H), 6.65–6.61 (m, 2H), 4.12 (s, 2H), 2.50 ppm (s, 3H);
13
C NMR (100 MHz, CDCl ): d=196.5, 151.3, 130.8, 126.8, 113.7,
3
26.1 ppm.
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2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1333 – 1339 1338

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Received: December 5, 2013
Published online on March 11, 2014
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2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1333 – 1339 1339