Hybrid polymer-immobilized palladium nanoparticles: Preparation and catalytic properties

Article abstract of DOI:10.1134/S0023158411020078

A new approach to the synthesis of mixed-type immobilized catalysts was developed: the frontal polymerization of a metal-containing monomer in the presence of a highly dispersed mineral support. The synthesis of an acrylamide complex of Pd(II) nitrate on the surface of SiO₂, Al ₂O₃, or C and its subsequent polymerization and reduction resulted in the formation of an organic-inorganic composite that included nanosized Pd particles stabilized by a polymer matrix and an inorganic support. The resulting hybrid nanocomposites are efficient and selective catalysts for the hydrogenation reactions of cyclohexene and alkene and acetylene alcohols.

Full text of DOI:10.1134/S0023158411020078

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2011, Vol. 52, No. 2, pp. 242–250. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.D. Golubeva, B.K. Dyusenalin, B.S. Selenova, S.I. Pomogailo, A.K. Zharmagambetova, G.I. Dzhardimalieva, A.D. Pomogailo, 2011, published in
Kinetika i Kataliz, 2011, Vol. 52, No. 2, pp. 250–258.
Hybrid PolymerꢀImmobilized Palladium Nanoparticles:
1
Preparation and Catalytic Properties
a
b
b
a
b
N. D. Golubeva , B. K. Dyusenalin , B. S. Selenova , S. I. Pomogailo , A. K. Zharmagambetova ,
a
a
G. I. Dzhardimalieva , and A. D. Pomogailo
a
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia
Sokol’skii Institute of Organic Catalysis and Electrochemistry, Academy of Sciences of Kazakhstan, Almaty, Kazakhstan
b
eꢀmail: dzhardim@icp.ac.ru, adpomog@icp.ac.ru
Received June 8, 2010
Abstract—A new approach to the synthesis of mixedꢀtype immobilized catalysts was developed: the frontal
polymerization of a metalꢀcontaining monomer in the presence of a highly dispersed mineral support. The
synthesis of an acrylamide complex of Pd(II) nitrate on the surface of SiO , Al O3, or C and its subsequent
2
2
polymerization and reduction resulted in the formation of an organic–inorganic composite that included
nanosized Pd particles stabilized by a polymer matrix and an inorganic support. The resulting hybrid nanoꢀ
composites are efficient and selective catalysts for the hydrogenation reactions of cyclohexene and alkene and
acetylene alcohols.
DOI: 10.1134/S0023158411020078
1
INTRODUCTION
Pd(II) nitrate and to evaluate their catalytic properties
in the hydrogenation reactions of unsaturated comꢀ
pounds. This procedure is a new approach to the
design of catalysts.
Materials containing nanometerꢀsized metal partiꢀ
cles exhibit unique physicochemical properties, and
they have been intensively studied in the last few years
[
2]. The use of these materials as catalysts is of particꢀ
ular interest because the fraction of surface atoms with
respect to the total number of atoms in a particle is
very high in these systems, and they catalytic properꢀ
ties can be controlled by varying the sizes of nanoparꢀ
ticles [3–5]. Zerovalent palladium complexes and purified in accordance with standard procedures.
nanoparticles are widely known as efficient and selecꢀ Methanol (chemically pure), PdCl 4H (chemiꢀ
EXPERIMENTAL
Chemicals
Benzene and diethyl ether (chemically pure) were
⋅
O
2
2
tive catalysts for many organic reactions, for example, cally pure), acrylamide (AAm) (99.0%; Fluka), and
alkene arylation [6, 7], cross coupling [8], and the toluene (chemically pure) were used without addiꢀ
hydrogenation of dienes, olefins [9, 10], and unsaturꢀ tional purification. Allyl alcohol (analytical grade;
ated alcohols [11]. The main problem consists in the 99%) from Reanal (Budapest) was distilled at atmoꢀ
aggregative instability of metal nanoparticles and their spheric pressure, and the main fraction with bp 96 С
°
tendency to agglomeration. Therefore, nanoparticles was collected. The acetylene alcohol 3,7,11,15ꢀtetꢀ
are immobilized on support surfaces (metal oxides, ramethylhexadecꢀ1ꢀynꢀ3ꢀol (C20) of chemically pure
zeolites, carbon, etc.) or stabilized by introducing grade was purified by double distillation, and its purity
ligands, including polymers of various types.
was monitored by chromatography. Concentrated
3
HNO (
ρ
= 1.18 g/cm ) was distilled at atmospheric
3
A promising method for the preparation of metal
polymers is polymerꢀmediated synthesis based on the
thermal polyꢀ and copolymerization of metalꢀconꢀ
taining monomers followed by the controlled therꢀ
molysis of the resulting products. This makes it possiꢀ
ble to in situ form metal nanoparticles and a stabilizing
polymer shell in a single step [12, 13]. The aim of this
work was to prepare polymerꢀimmobilized Pd nanoꢀ
particles in the presence of an inorganic support by the
frontal polymerization of an acrylamide complex of
pressure, and the main fraction with bp 110 was
°
С
taken. Silica gel 60 from Lancaster (220–240 mesh;
2
specific surface area Ssp = 240 m /g) and preactivated
(
8
by vacuum calcination at 450
°
С
) soot (Ssp =
2
2
50 m /g) and Al O (Ssp = 123 m /g) were used as
2 3
inorganic supports.
Preparation of Pd(NO3)2
⋅
2H O
2
The synthesis of Pd(II) nitrate was performed by
the interaction of freshly distilled concentrated nitric
acid with freshly precipitated palladium hydroxide
1
Communication no. 67 from the series Reactivity of MetalꢀConꢀ
taining Monomers. For communication no. 66, see [1].
242

HYBRID POLYMERꢀIMMOBILIZED PALLADIUM NANOPARTICLES
243
(
2.6 g, 1.84
×
10–2 mol), which was prepared by the part of the ampoule with the sample was immersed at
treatment of the complex salt Na PdCl (5.5 g, 1.84
1
×
a depth of 0.2 cm in a bath with a heat carrier (Wood
2
4
–2
0
mol) with sodium hydroxide.
alloy) at 80–100°С. The rate of reaction was evaluated
For Pd(NO3)2
.5; Pd, 39.9.
Found (%): N, 10.2; H, 1.4; Pd, 40.4.
IR spectrum of Pd(NO3)2 2H O (KBr pellet)
⋅
2H O anal. calcd. (%): N, 10.5; H, from the migration of the front of a colored zone.
2
1
Powdered polymer and hybrid nanocomposite prodꢀ
ucts were washed with methanol and ether and dried in
a vacuum at room temperature to constant weight.
⋅
2
⎯
1
(
cm ): 850, 1386 (NO ), 1650.
3
XPS (eV): Pd
3d5/2, 338.8; N 1s, 407.2; O 1s, 532.8.
Hydrogenation of Cyclohexene
and Unsaturated Alcohols
Preparation of Pd(CH =CHCONH ) (NO ) (PdAAm)
2
2 2
3 2
The experiments were performed in a glass batch
reactor as a longꢀnecked flask using isopropanol as a solꢀ
For the synthesis of PdAAm, we used a modified
procedure for the preparation of the acrylamide comꢀ
plexes of transition metal nitrates [14]. Palladium(II)
nitrate and acrylamide were mixed in a molar ratio of
–3
vent at a cyclohexene concentration from 4.72
×
10 to
–3
14.5
×
10 mol/l, a constant atmospheric pressure of
hydrogen, and a temperature of 20°С under condiꢀ
tions of intense stirring (300–400 shaking per minute).
The catalyst sample weight varied from 0.06 to 0.12 g.
Hydrogen was supplied to the reactor from a calibrated
receiver with a water lock. Before introducing cycloꢀ
hexene, the catalyst was treated with hydrogen for
1
: 5 in an inert atmosphere and ground to a pasteꢀlike
state; then, the mixture was washed with dry ether and
dried in a vacuum to constant weight.
For PdAAm anal. calcd. (%): C, 19.4; N, 15.0; H,
.7; Pd, 28.6.
2
Found (%): C, 20.1; N, 15.1; H, 3.5; Pd, 29.4.
1
5 min immediately in the reactor with stirring. The
⎯
1
IR spectrum (KBr pellet) (cm ): 3190 (NH,
428 (NH, as), 1665 (C=O), 1384 (NO3).
νs),
rate of reaction was calculated graphically from the
slope of the initial portions of the kinetic curves of
hydrogen consumption. In parallel experiments, the
discrepancy was no higher than 5%.
3
ν
Preparation of PdAAm on Inorganic Supports
The synthesis of PdAAm in the presence of SiO2,
The hydrogenation of allyl and acetylene alcohols
Al O , and C was performed in accordance with the was performed in a glass batch reactor using ethanol as
2
3
above procedure based on a 5–10 wt % Pd concentraꢀ a solvent (20 ml) at a substrate concentration of 2.2
×
–3
tion in a mixedꢀtype polymer + support catalyst. A 10 mol/l, a constant atmospheric pressure of hydroꢀ
mixture of the calculated amounts of Pd(II) nitrate, gen, and a temperature of 40°С under conditions of
acrylamide, and SiO (or Al O or C) was ground in an intense stirring (600–700 shaking per minute). The
2
2
3
agate mortar in a box with an inert atmosphere to a catalyst sample weight was 0.03 g. Hydrogen was supꢀ
pasteꢀlike state, washed with benzene and ether, and plied to the reactor from a gas meter, which was conꢀ
dried in a vacuum at 30
°С
for no shorter than 12 h. nected to an adapted calibrated receiver with a water
The concentrations of Pd, wt %: 5.2 (PdAAm/SiO ), lock. The catalyst was preliminarily treated with
2
8
.9 (PdAAm/Al O ), and 10.2 (PdAAm/C).
hydrogen for 30 min immediately in the reactor with
intense stirring; then, a substrate was introduced into
the reactor. The selectivity of the catalyst was evaluꢀ
ated as the fraction of the target product among all of
2
3
Preparation of Pd/C
The traditional Pd/C catalyst was prepared by the the reaction products at a specified degree of converꢀ
impregnation of AGꢀ3M activated carbon (
sion.
S
=
2
5
00 m /g) with an aqueous solution of Н PdCl4,
2
which was prepared by boiling a mixture of palladium
chloride, water, and concentrated hydrochloric acid
for 2 h followed by reduction with NaBH4 at 40°С and
additional heating at 80°С for 15 min. Then, the cataꢀ
lyst was filtered off, washed with distilled water, and
Analysis for Allyl Alcohol and Its Hydrogenation
and Isomerization Products
The analysis was performed on a Kristall 2000M
dried at 110°С for 3–5 h. The Pd content was 5 wt %. chromatograph with a flameꢀionization detector
under isothermal conditions using a multipurpose
copper capillary column for organic compounds 50 m
in length and 0.20 mm in an inner diameter. The colꢀ
Frontal Polymerization of PdAAm and PdAAm
on Inorganic Supports
umn temperature was 90
; helium served as a carrier gas;
PdAAm or PdAAm on a support were pressed as pelꢀ the injected sample volume was 0.2 l. The samples of
lets 0.5–0.8 cm in diameter and 1.2–1.5 cm in height a liquid reaction mixture were taken two or three times
°С, and the injector chamber
To perform frontal polymerization, the samples of temperature was 180 С
°
μ
3
with a density of 1.45
±
0.02 g/cm and placed in a in the course of an experiment with the use of a samꢀ
glass ampoule. To initiate polymerization, the bottom pler.
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2011

244
GOLUBEVA et al.
Table 1. Elemental composition of the acrylamide complexes of Pd(II) nitrate and relative concentrations of various elements
in them according to XPS data
Elemental composition, wt % (found/calculated)
Relative concentration, at %
Complex
C
H
N
Pd
C
O
N
Pd
Pd(NO3)2
PdAAm
–
1.4/1.5
3.5/2.7
–
10.2/10.5
40.4/39.9
29.4/28.6
5.2
–
68
27
57
14
21
19
6
10.5
2
20.1/19.4
15.1/15.0
52
16
83
PdAAm/SiO2
PdAAm/C
–
–
–
–
0.7
0.2
–
10.2
2.8
Analysis of Catalysts
The specific surface areas of inorganic supports and
polymer hybrid compositions and the pose sizes were
determined from nitrogen adsorption at 77 K by a volꢀ
umetric method using an AUTOSORBꢀ1 instrument
The elemental composition of samples was deterꢀ
mined by organic microanalysis and flameless atomic
absorption spectrometry on a Saturn instrument. The
Xꢀray diffraction of powders was studied on DRON
UMꢀ2 and Philips PW 1050 diffractometers using
(
Quantachrome, United States).
Cu
K
radiation ( = 1.54184 Å). The IR absorption
λ
α
RESULTS AND DISCUSSION
Synthesis of Pd(CH =CHCONH )(NO ) (PdAAm)
spectra were measured on a Specord 75 IR spectroꢀ
photometer; the samples were pressed as pellets
with KBr.
2
2
3 2
An ESꢀ2401 spectrometer with a magnesium
anode was used to obtain XPS spectra. The Xꢀray tube
power was 200 W; the pressure in the analyzer chamber
The acrylamide complex of Pd(II) nitrate was synꢀ
thesized by the replacement of crystal water in the
metal nitrate crystal hydrate by acrylamide molecules.
Table 1 summarizes the results of the elemental analyꢀ
sis and spectroscopic characteristics of the resulting
complex.
–6
was 10 Pa, and the analyzer energy was 50 eV. The
spectrometer was calibrated using the Au f7/2 line
84 eV). The binding energy (BE) corresponding to
4
(
the C 1s electron line in an alkyl group was taken equal
to 285.0 eV. The BE determination accuracy was 0.1–
The IRꢀspectroscopic data suggest that the metal
atom was coordinated through the oxygen atoms of the
0.2 eV.
The electronꢀmicroscopic studies were performed carbonyl group of the AAm ligand: the bands of CO
⎯
1
on a JEOL transmission electron microscope (TEM)
with an accelerating voltage of 100 kV.
vibrations (1665 cm ) were shifted to the longꢀwaveꢀ
length region, as in analogous transition metal comꢀ
plexes [15]. This was supported by shifts in the C 1
s
(
5
BE = 288.3 eV), N 1
31.6 eV) lines in XPS spectra toward the highꢀenergy
s
(BE = 399.8 eV), and O 1
s (BE =
N 1
s
Pd 3d
region by 0.5, 0.7, and 0.5 eV, respectively. Bands due
to the stretching vibrations of the nitrate ion at
1
2
3
384 cm⎯ (NO ) were also detected in the IR spectra
1
1
3
of complexes. The presence of a lowꢀintensity line
with BE = 337.2 eV in the Pd d5/2 XPS spectrum and
an increase in the intensity of a line with BE = 285.7 eV
may be explained by additional coordination of the
3
π
metal atom with respect to the double bond of the
ligand. Such examples frequently occur in the case of
Pd alkene complexes [16]. In the surface layer, the
Pd/N and O/N atomic ratios are 0.11 and 1.4, respecꢀ
tively (Table 1), and the intensity of a line with BE =
3
96 400 404 408 412 332 336 340 344 348
BE, eV
407.2 eV in the N 1s spectrum is 10% of the integrated
intensity of the entire spectrum. This observation
quantitatively correlates with the intensity of a line
with BE = 338.8 eV in the Pd 3d5/2 spectrum (Fig. 1)
and suggests the shielding of Pd atoms by AAm groups.
Fig. 1. XPS spectra of (
with Pd(NO ) , ( ) PdAAm after polymerization, and
) the same after cyclohexene hydrogenation.
1) acrylamide complex monomer
2
3
2
(3
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HYBRID POLYMERꢀIMMOBILIZED PALLADIUM NANOPARTICLES
245
Frontal Polymerization of PdAAm in the Absence
and Presence of an Inorganic Support
As found previously [15, 17], the acrylamide comꢀ
plexes of metal nitrates can effectively undergo polyꢀ
merization in a condensed state in the frontal mode,
that is, under conditions when monomer conversion
into a polymer begins in a local reaction zone and
layerꢀbyꢀlayer propagates over the entire volume. The
reaction occurs under the mildest conditions known
for processes of this kind, namely, at atmospheric presꢀ
sure and thermal initiation (without the use of chemiꢀ
cal initiators and activators). Under conditions of the
steadyꢀstate propagation of a thermal wave, polymerꢀ
ization occurs in a narrow temperature range. The
heat released in the reaction zone is transferred to the
heating zone, where the substance is heated because of
thermal conductivity; the temperature increases to a
value at which the reaction comes into play; that is, the
propagation of a polymerization front occurs. The
reaction is initiated by the generation of a shortꢀtime
Fig. 2. Electron micrograph of polyꢀPdAAm/SiO (magꢀ
2
nification of 125000×).
of nanosized Pd particles 4–8 nm in diameter and
their aggregates of size 10–20 nm stabilized by a polyꢀ
mer matrix (Fig. 2).
(
~15 s) thermal agitation (“ignition”) at the end porꢀ
tion of a glass ampoule, where the sample of PdAAm
monomer or its mixture with a mineral filler pressed as
a cylinder is placed. In this case, the appearance and
As was expected, the action of fillers (SiO , Al O ,
2
2
3
=
propagation of a melting zone (firstꢀorder phase tranꢀ and C) on the autowave polymerization mode (
w
sition) and a color change from light brown to dark 0.024 cm/s) manifested itself as the fact that the polyꢀ
brown and black are observed (the rate of reaction is merization front acquired signs of spatiotemporal staꢀ
monitored using the migration of the boundary of this bilization, which, what is more important, was also
zone). Kinetic studies suggest the high rate of frontal reached at high degrees of filling (75 wt %).
polymerization of the acrylamide complex of Pd(II)
The Xꢀray diffraction patterns of the resulting samꢀ
(
w = 0.038 cm/s), the ignition temperature of which
ples exhibited broad diffraction peaks in a
from 36 to 85 , which correspond to crystalline Pd
Fig. 3). Diffuse diffraction peaks and broadened lines
2
θ
range0
(
80–100°С) is much lower than the corresponding
°
°
characteristics of AAm complexes with the nitrates of
Co(II), Ni(II), etc. (170–180 ) [15].
(
°С
suggest an ultradisperse state of particles (Table 2).
The resulting nanocomposites typically have a
microporous structure with a pore size of several
nanometers to 20 nm and a uniform pore size distribuꢀ
tion (Fig. 4). Note the fact that the specific surface area
of mixedꢀtype supports decreased after the frontal polyꢀ
merization of PdAAm on their surfaces, although it was
greater than Ssp of the PdAAm polymerization product
in the absence of an inorganic support (Table 3). Thus,
the resulting hybrid nanocomposites had a sufficiently
developed surface and pore structure to provide the
accessibility of the active centers of a catalyst to
At higher ignition temperatures (150–170°С), the
ejection of reaction mass from the glass tube and a
change to the combustion mode (!) were observed; this
was likely due to the formation of highly dispersed
pyrophoric palladium particles. According to XPS
d
data, the main line in the Pd 3 5
/2
spectrum of the
polymerization product corresponded to BE =
0
3
36.5 eV, which is higher than BE in Pd (<336.0 eV).
This can be explained by the formation of highly disꢀ
0
δ
+
persed Pd and Pd particles [10, 18]. It is likely that
an increase in the BE of the main line in the N 1 specꢀ
s
trum to 401.7 eV was due to the occurrence of polymer
chain cyclization reactions with the formation of
imide groups [19].
Table 2. Results of the XPS, XRD, and TEM analysis of polyꢀ
mer hybrid nanocomposites based on PdAAm
The previously developed approach to the preparaꢀ
tion of nanocomposite materials using frontal polyꢀ
merization [20] is of interest for the development of
polymerꢀimmobilized catalysts of the mixed (hybrid)
metal nanoparticles–polymer–inorganic support
type. Indeed, the preparation of an acrylamide comꢀ
plex of Pd(II) on the surface of a mineral support and
its subsequent polymerization resulted in the formaꢀ
tion of a polymer–inorganic composite. According to
electronꢀmicroscopic data, this composite consisted
Pd 3d5/2 XPS
spectrum, eV
Particle size
of Pd, nm
Nanocomposite
PdAAm
336.5, 338.9
337.6, 338.9
–
3.9
PdAAm/SiO2
3.6–4.0
PdAAm/Al O3
4
8
2
PdAAm/C
338.5, 341.3
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246
GOLUBEVA et al.
6
5
4
3
2
1
00
00
00
00
00
00
0
6
00
00
4
0.05
(
a)
(b)
5
2
1.6
2
0.6
400
24.5
300
200
100
0
40.15
46.6
68
8
0.3
6
8.35
2
0
40
60
c)
80
100
θ, deg
20
40
60
80
100
2θ, deg
2
3
9
(
500
400
300
200
100
0
67.3
45.65
2
8.8
7
9.2
2
0
40
60
80
θ, deg
2
Fig. 3. Diffraction patterns of PdAAm/SiO samples prepared at (a) 115 and (b) 130°C and (c) a PdAAm/Al O sample.
2 3
2
reagents and their high activity in the test catalytic
reactions.
The test nanocomposites retained catalytic activity
in repeatedly performed reaction cycles, and the
occurrence of the nanocomposites in an immobilized
form makes it possible to separate them from the reacꢀ
tion medium and to use them repeatedly; what is very
Catalytic Properties of the PdAAm on Inorganic
Supports in the Reaction of Cyclohexene Hydrogenation important, intermediates formed on the catalyst can
be studied using various physicochemical techniques.
In some cases, even an increase in activity was
observed in the repeated use; that is, the soꢀcalled
development of a catalyst occurred, which is characꢀ
teristic of many immobilized systems. In particular,
this phenomenon was demonstrated recently using the
polymer clusters of rhodium as an example [21].
The test systems exhibited a sufficiently high activꢀ
ity in the model reaction of cyclohexene hydrogenaꢀ
tion. Thus, under comparable conditions, the initial
rate of reaction on the polyꢀPdAAm/Al O catalyst
2
3
was higher by a factor of almost 2 than that on standard
Pd/C (Table 4, Fig. 5).
The catalytic properties of the test composites are
Table 3. Specific surface areas and pore sizes for polymer hyꢀ affected by the conditions of formation of Pd nanoꢀ
brid nanocomposites based on PdAAm
particles, for example, the use of various frontal polyꢀ
merization conditions in an inert atmosphere or postꢀ
thermal treatment at 100–150°С in a reducing atmoꢀ
sphere of hydrogen (Fig. 6). Thus, as the temperature
of the reductive treatment of nanocomposites was
increased, the rate of cyclohexene hydrogenation on
them decreased. Analogous behaviors were also
Pore volꢀ Average pore
ume, cm /g radius, Å
2
Sample
Ssp, m /g
3
polyꢀPdAAm
SiO2
18.2
238.7
146.8
123.6
60.2
0.10
0.41
0.28
–
113.2
34.3
37.8
–
observed in catalytic systems based on both SiO and
2
polyꢀPdAAm/SiO2
Al O
Al O (Table 4). It is most likely that the reason for the
2
3
decrease in the rate of reaction is the agglomeration of
Pd particles at relatively high nanocomposite treatꢀ
ment temperatures.
2
3
polyꢀPdAAm/Al O
0.17
55.0
2
3
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HYBRID POLYMERꢀIMMOBILIZED PALLADIUM NANOPARTICLES
247
Table 4. Initial rates of cyclohexene hydrogenation (w0) in the presence of hybrid polymerꢀimmobilized Pd nanoparticles
w0
,
(mol H ) (mol Pd)– min–1
1
2
Sample
Preparation conditions
cycle 1
cycle 2
cycle 3
polyꢀPdAAm/SiO2
FP
22.9
10.8
13.4
1.1
16.7
12.6
10.50
3.48
24.80
9.90
4.0
–
10.1
11.2
5.2
22.7
–
FP, 100
FP, 120
FP, 150
FP
°
°
°
C
C
C
polyꢀPdAAm/Al O
33.4
11.3
2.5
2
3
FP, 100
FP, 140
FP
°
C
C
°
4.3
–
polyꢀPdAAm/C
11.3
11.6
–
Pd/C
11.6
–
Note that, in polyꢀPdAAm after hydrogenation, reaction, which sometimes can even predominate over
the main fraction of Pd (90%) occurred in a zerovalent the main process. Therefore, isomerization should be
state (see Fig. 1) and its shielding by a polymer matrix suppressed to increase the yield of target products. In
decreased, as evidenced by an increase in the Pd conꢀ known examples, catalysts based on Pd nanoparticles
tent of the surface layer (from 1.5 at % in the starting encapsulated in polyelectrolyte multilayers [22] or
polymer complex to 4.3 at %). The polymer matrix dendrimers [23] were used for this purpose. The nanoꢀ
also underwent changes, which manifested themselves composites under consideration are active catalysts for
in a broadening of the N 1
s
spectrum.
the hydrogenation of ally alcohol. As evidenced by
Thus, the resulting hybrid polymerꢀimmobilized experimental data (Table 5), they exhibited different
Pd nanoparticles exhibited high activity in the reacꢀ activities; however, both exhibited high selectivity in
tion of cyclohexene hydrogenation and retained it in this case. The main product of the hydrogenation of
repeated cycles. The catalytic properties of nanocomꢀ allyl alcohol is 1ꢀpropanol; propionaldehyde (allyl
posites depend on preparation conditions, which, eviꢀ alcohol isomerization product) was also identified in
dently, affect the size of formed Pd nanoparticles.
insignificant amounts (to 2% in the presence of polyꢀ
PdAAm/Al O and to 5% in the presence of polyꢀ
2
3
PdAAm/SiO ). Any other products were not detected.
It is likely that a higher rate of reaction on
2
Catalytic Properties of PolyꢀPdAAm Nanocomposites
on SiO and Al O in the Hydrogenation of Allyl Alcohol
2
2 3
PdAAm/SiO was due to its more developed surface
2
It is well known that substrate isomerization in the and specific features of substrate adsorption on this
hydrogenation of allyl alcohol is an undesirable side surface (see Table 3).
dVsp/dr
Volume of N2, cm3/g
10−
2
2.4
×
×
×
×
×
×
(a)
(b)
200
160
120
2
2
2
3
3
2.0
1.6
1.2
8.0
10−
1
1
10−
10−
2
8
0
0
10−
2
3
10−
4
3
4.0
0
0
0.2
0.4
0.6
0.8
1.0
10
100
1000
P/
P0
r, Å
Fig. 4. (a) Nitrogen adsorption–desorption isotherms and (b) differential pore radius (
r) distribution curves in polymer hybrid
nanocomposites: ( ) polyꢀPdAAm/SiO , ( ) polyꢀPdAAm/Al O , and ( ) polyꢀPdAAm.
1
2
3
2
2 3
KINETICS AND CATALYSIS Vol. 52
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2011

248
GOLUBEVA et al.
−
1
−1
5
−1 −1
w
, mol l s
w
×
10 , mol l s
2
2
1
1
5
3
3
2
2
1
1
5
0
0
1
1
5
0
5
0
5
5
0
5
2
3
2
3
4
0
2
4
6
8
10
Time, min
0
0.2
0.4
0.6
0.8
1.0
H conversion
2
Fig. 5. Hydrogen uptake kinetics in cyclohexene hydrogeꢀ
nation in the presence of ( ) polyꢀPdAAm/Al O ,
) polyꢀPdAAm/SiO , and ( ) Pd/C. Catalyst sample
weight, 0.05–0.10 g; temperature, 20 C; H2 pressure,
.1 MPa; solvent, isopropanol; and initial cyclohexene
amount, 6.9 mmol.
Fig. 6. Dependence of the rate of cyclohexene hydrogenaꢀ
1
tion on the H2 conversion in the presence of polyꢀ
2
3
(
2
3
PdAAm/SiO samples prepared under various conditions:
2
2
°
(
(
1
2
) frontal polymerization in a selfꢀgenerated atmosphere,
) frontal polymerization in a reductive atmosphere at
0
118–120
at 150 C. Catalyst sample weight, 0.10 g; temperature,
C; H pressure, 0.1 MPa; solvent, isopropanol; and iniꢀ
°C, (3) the same at 104–106°C, and (4) the same
°
20°
2
tial cyclohexene amount, 6.9 mmol.
The stability of catalysts was evaluated by performꢀ
ing the consecutive cycles of allyl alcohol hydrogenaꢀ
tion on the same sample (Fig. 7). The catalysts
retained high activity in repeated cycles; this is espeꢀ
as an example. The rate of its hydrogenation was much
lower than that of allyl alcohol (Fig. 8, Table 5); this
fact can be explained by diffusion limitations, which
hinder the access of the reactant to the active sites of
the catalyst.
cially characteristic of polyꢀPdAAm/SiO , the rate of
2
reaction on which decreased only after the tenth cycle.
It is likely that a pause of several hours (after sixth and
ninth cycles) in the process facilitated the equalizing
of the concentrations of all of the participants of the
process (solvent, products, and substrate) near active
sites, which resulted in an increase in the reaction rate.
As was found by chromatographic analysis, the triꢀ
ple bond of the С20 acetylene alcohol can be readily
reduced to a double bond (Fig. 9). The maximum
reaction rate was reached after 10 min (see Fig. 8);
then, it dramatically decreased. In this time, the acetꢀ
ylene alcohol was almost completely converted into
reaction products in the system with the participation
Catalytic Properties of PdAAm Nanocomposites on SiO2
and Al O in 3,7,11,15ꢀTetramethylhexadecꢀ1ꢀynꢀ3ꢀol
2
3
Hydrogenation
of polyꢀPdAAm/SiO . However, the process was nonꢀ
2
It is convenient to study steric effects on the selecꢀ selective. Simultaneously with the hydrogenation of
tivity of a catalytic reaction using the hydrogenation of the triple bond, the reduction of the double bond
a spatially hindered longꢀchain С20 acetylene alcohol occurred, so that both saturated 3,7,11,15ꢀtetramethꢀ
Table 5. Initial rates of and selectivities of the hydrogenation of allyl alcohol and 3,7,11,15ꢀtetramethylhexadecꢀ1ꢀynꢀ3ꢀol on
Pd hybrid polymerꢀimmobilized catalysts
Allyl alcohol
105, mol l–1 s–1
С20 acetylene alcohol
Catalyst
w
×
105, mol l–1 s–1
w
×
selectivity, %
selectivity, %
(
after 10 min)
polyꢀPdAAm/Al O
2
4.98
56.7
97.2
95.6
1.4
2.8
70
49.9
3
polyꢀPdAAm/SiO2
Note: Reaction conditions: alcohol concentration, 0.225 mol/l; catalyst sample weight, 0.03 g (1.41
pressure, 0.1 MPa; solvent, 20 ml of ethanol.
×
10–5 gꢀat Pd/g); temperature, 40°C;
KINETICS AND CATALYSIS Vol. 52
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2011

HYBRID POLYMERꢀIMMOBILIZED PALLADIUM NANOPARTICLES
249
4
−
1
−
1
5
−1 −1
w
×
10 , mol l s
w
×
10 , mol l s
3
2
2
.0
.5
.0
4
1
3
2
1
1
1.5
2
1
.0
.5
0
2
0
1
2
3
4
5
6
7
8
9 10 11 12 13
Cycle number
0
20
40
60
80
100
Time, min
Fig. 7. Consecutive hydrogenation of allyl alcohol portions
in the presence of ( ) polyꢀPdAAm/SiO and ( ) polyꢀ
PdAAm/Al O . Initial substrate amount, 2.58 mmol; catꢀ
Fig. 8. Time variation of the rate of 3,7,11,15ꢀtetramethylꢀ
1
2
hexadecꢀ1ꢀynꢀ3ꢀol hydrogenation on immobilized
2
(1) polyꢀPdAAm/SiO and (2) polyꢀPdAAm/Al O cataꢀ
2
3
2 2 3
lysts. Catalyst sample weight, 0.03 g; temperature, 40
H pressure, 0.1 MPa; and solvent, 20 ml of ethanol.
alyst sample weight, 0.03 g; solvent, 20 ml of ethanol; and
temperature, 40 C.
°C;
°
2
ylhexadecanꢀ1ꢀ3ꢀol and the corresponding olefin facilitated their separation from the reaction medium
alcohol were detected among the reaction products.
and repeated use and made it possible to study the
transformations of catalytic intermediates. The subseꢀ
quent studies will be oriented to the detection of size
effects (a study of the dependence of reaction rate and
selectivity on the size of palladium nanoparticles) and
A somewhat different behavior was observed upon
the hydrogenation of the С20 acetylene alcohol in the
presence of polyꢀPdAAm/Al O . Initially, it was
2
3
mainly converted into the corresponding olefin alcoꢀ
hol and the concentration of the saturated alcohol was
no higher than 8–10%. Only after 20 min when about
Composition of the reaction mixture, %
1
0% of the starting substrate remained in the reaction
100
mixture, the intense hydrogenation of the double bond
came into play with the formation of the aliphatic
alcohol. The selectivity of olefin alcohol formation
was 70% (Table 5). A comparison between Figs. 8 and
1
3
8
0
0
9
allowed us to conclude that the triple bond was rapꢀ
idly reduced to the double bond and the formation of
the saturated alcohol occurred very slowly ( = 0.1
mol l s ); that is, the double bond was hydrogeꢀ
nated more slowly than the triple bond by a factor of
–10. Currently, the mechanism of the selective
6
2
w
×
–5
–1 –1
10
40
7
action of the test hybrid polymerꢀimmobilized cataꢀ
lysts remains incompletely known, and it, as well as
catalytic process optimization, calls for further invesꢀ
tigation.
20
0
20
40
60
80
100 120 140
Time, min
Thus, we developed a procedure for the preparation
of mixedꢀtype polymerꢀimmobilized Pd nanoparticles
on the surface of supports. These nanoparticles are
efficient and selective catalysts for the hydrogenation
of unsaturated compounds. In the case of unsaturated
alcohols, the hydrogenation reaction path predomiꢀ
nates over isomerization. The test nanocomposites
retained catalytic activity in repeated cycles. The cirꢀ
cumstance that they occurred in an immobilized form
Fig. 9. Changes in the composition of the reaction mixture
during 3,7,11,15ꢀtetramethylhexadecꢀ1ꢀynꢀ3ꢀol hydrogeꢀ
nation in the presence of polyꢀPdAAm/SiO : (
ylene alcohol, (
1
) C20 acetꢀ
) the resulting ethylene alcohol, and
) the resulting saturated alcohol. Catalyst sample weight,
.03 g; temperature, 40 C; H pressure, 0.1 MPa; and iniꢀ
2
2
(
3
0
°
2
tial C20 content, 0.225 mol/l.
KINETICS AND CATALYSIS Vol. 52
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2011

250
GOLUBEVA et al.
the use of nanocomposites based on other metals in
hydrogenation reactions.
Izv. Akad. Nauk SSSR, Ser. Khim., 1987, no. 10,
p. 2153.
1. Kidambi, S., Dai, J., Li, J., and Bruening, M.L., J. Am.
1
Chem. Soc., 2004, vol. 126, p. 2658.
2. Pomogailo, A.D., Dzhardimalieva, G.I., Rozenberg, A.S.,
ACKNOWLEDGMENTS
1
and Muraviev, D.N., J. Nanopart. Res., 2003, vol. 5, p. 497.
3. Dzhardimalieva, G.I., Pomogailo, A.D., Rozenberg, A.S.,
We are grateful to Cand. Sci. (Chem.) A.M. Lyaꢀ
khovich for the XPS analysis of the samples.
1
and Leonowicz, M., in Magnetic Nanoparticles
,
Gubin, S.P., Ed., Weinheim: WileyꢀVCH, 2009.
REFERENCES
14. Savost’yanov, V.S., Ponomarev, V.I., Pomogailo, A.D.,
Selenova, B.S., Ivleva, I.N., Starikov, A.G., and
Atovmyan, L.O., Izv. Akad. Nauk SSSR, Ser. Khim.
990, vol. 39, p. 726 [Bull. Acad. Sci. USSR, Div. Chem.
Sci. (Engl. Transl.), vol. 39. p. 674].
1
. Dzhardimalieva, G.I., Dorokhov, V.G., Golubeva, N.D.,
Pomogailo, S.I., Lyakhovich, A.M., Savchenko, V.I., and
Pomogailo, A.D., Izv. Akad. Nauk, Ser. Khim., 2009,
no. 10, p. 2007.
,
1
1
5. Pomogailo, A.D. and Dzhardimalieva, G.I., Vysokoꢀ
mol. Soed., Ser. A, 2004, vol. 46, p. 437 [Polym. Sci., Ser.
A: Polym. Phys. (Engl. Transl.), vol. 46, p. 250].
2
3
4
. Pomogailo, A.D. and Kestelman, V.N., Metallopolymer
Nanocomposites, Heidelberg: Springer, 2005.
. Pomogailo, A.D., Kinet. Katal., 2004, vol. 45, p. 67 16. Shi, T. and Elding, L.I., Inorg. Chem., 1998, vol. 37,
Kinet. Catal. (Engl. Transl.), vol. 45, p. 61].
p. 5544.
[
. Wohrle, D. and Pomogailo, A.D., Metal Complexes and 17. Dzhardimalieva, G.I., Pomogailo, A.D., and Volpert, V.A.,
Metals in Macromolecules, Weinheim: WileyꢀVCH,
003.
J. Inorg. Organomet. Polym., 2002, vol. 12, p. 1.
2
18. Okitsu, K., Yue, A., Tunabe, S., and Matsumoto, H.,
Bull. Chem. Soc. Jpn., 2002, vol. 75, p. 449.
19. Fortenberry, D.I. and Pojman, J.A., J. Polym. Sci.,
Part A: Polym. Chem., 2000, vol. 38, p. 1129.
0. Barelko, V.V., Pomogailo, A.D., Dzhardimalieva, G.I.,
Evstratova, S.I., Rozenberg, A.S., and Uflyand, I.E.,
Chaos, 1999, vol. 9, p. 342.
1. Pomogailo, S.I., Dorokhov, V.G., Lyakhovich, A.M.,
Mikhailova, S.S., Dzhardimalieva, G.I., and
Pomogailo, A.D., Kinet. Katal., 2006, vol. 47, p. 742
5
6
7
8
9
. Campelo, J.M., Luna, D., Luque, R., Marinas, J.M.,
and Romero, A.A., ChemSusChem, 2009, vol. 2, p. 18.
. Heck, R.F., Palladium Reagents in Organic Synthesis
,
2
New York: Academic, 1985.
. Andersson, C.M., Karabelas, K., and Hallberg, A.,
J. Org. Chem., 1985, vol. 50, p. 3891.
2
. Ogasawar, S. and Kato, S., J. Am. Chem. Soc., 2010,
vol. 132, p. 4608.
. Hirai, M., Yakaru, N.I., Seta, Y., and Hodosima, S.,
[Kinet. Catal. (Engl. Transl.), vol. 47, p. 719].
React. Funct. Polym., 1998, vol. 37, p. 121.
22. Kidambi, S., Dai, J., Li, J., and Bruening, M.L., J. Am.
Chem. Soc., 2004, vol. 126, p. 2658.
1
0. Belyi, A.A., Chigladze, L.G., Rusanov, A.L., Shalikiꢀ
ani, M.O., Tabidze, R.S., Gagarin, S.G., Shpiro, E.S., 23. Jiang, Y. and Gao, Q., J. Am. Chem. Soc., 2006,
Antoshin, G.V., Minachev, Kh.M., and Vol’pin, M.E.,
vol. 128, p. 716.
KINETICS AND CATALYSIS Vol. 52
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2011