Selective hydrogenation of phenylacetylene into styrene on gold nanoparticles

Article abstract of DOI:10.1134/S0023158410020187

Gold nanoparticles (2-10 nm) supported on γ-Al₂O ₃ exhibit high activity and stability in the hydrogenation of phenylacetylene into styrene in the phenylacetylene-styrene mixture. The selectivity of the catalyst is particle size-depe

Full text of DOI:10.1134/S0023158410020187

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2010, Vol. 51, No. 2, pp. 288–292. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © S.A. Nikolaev, N.A. Permyakov, V.V. Smirnov, A.Yu. Vasil’kov, S.N. Lanin, 2010, published in Kinetika i Kataliz, 2010, Vol. 51, No. 2, pp. 305–309.
Selective Hydrogenation of Phenylacetylene
into Styrene on Gold Nanoparticles
†
S. A. Nikolaev, N. A. Permyakov, V. V. Smirnov , A. Yu. Vasil’kov, and S. N. Lanin
Faculty of Chemistry, Moscow State University, Moscow, 119992 Russia
eꢀmail: serge2000@rambler.ru
Received August 11, 2008
Abstract—Gold nanoparticles (2–10 nm) supported on ꢀAl O exhibit high activity and stability in the
γ
2 3
hydrogenation of phenylacetylene into styrene in the phenylacetylene–styrene mixture. The selectivity of the
catalyst is particle size–dependent: the styreneꢀtoꢀethylbenzene molar ratio in the reaction products
increases from 2 to 30 as the average gold particle size decreases from 8 to 2.5 nm. The selectivity of phenylꢀ
acetylene hydrogenation correlates with the selectivity of phenylacetylene adsorption on Au/
γ
ꢀAl O from
2 3
the phenylacetylene–styrene mixture.
DOI: 10.1134/S0023158410020187
†
2
The selective removal of acetylenic hydrocarbons area of Ssp = 138 m /g and a total pore volume of
3
from olefins, including the removal of phenylacetyꢀ 0.32 cm /g. Prior to use, ꢀAl O was calcined at
γ
2 3
lene from commercial styrene, is necessary for obtainꢀ 350
ing highꢀquality polymers [1, 2]. At present, this probꢀ
lem is solved by hydrogenation of acetylene derivatives
°
C for 3 h.
Catalysts were prepared using HAuCl4 ·
x
H O with
2
an Au content of 49.04 wt % (OAO Aurat, USSR
Specifications 6ꢀ09ꢀ05ꢀ1075ꢀ89), distilled water, and
a 0.1 M aqueous solution of NaOH.
in the presence of bimetallic catalysts containing
ultrafine Pd particles and some other metals, such as
Ag [3, 4]. However, although these systems are highly
active and selective, they are rapidly poisoned by byꢀ
products of the oligomerization of acetylene derivaꢀ
tives. Therefore, it is still a challenging problem to find
new approaches to the synthesis of highly efficient and
selective hydrogenation catalysts.
Preparation of Catalysts
γ
ꢀAl O ꢀsupported gold particles 2–10 nm in size
were formed using an anion adsorption procedure
14]. To obtain the Au/ ꢀAl O catalyst, the pH of the
2 3
[
γ
2
3
The high catalytic activity of Au nanoparticles in a
wide variety of processes [5–7] generates interest in
catalysis by goldꢀcontaining systems. It has recently
been found that gold nanocomposites are active in the
hydrogenation of 1,3ꢀbutadiene, acetylene, propyne,
and terminal olefins [8–13]. Therefore, it is of interest
to see whether gold nanoparticles are usable in the
selective hydrogenation of phenylacetylene in excess
styrene. The purpose of this work is to study the
dependence of the activity and selectivity of gold
nanoparticles on their size in the hydrogenation of
phenylacetylene into styrene.
aqueous solution of HAuCl4 was brought to 7.0 by
adding sodium hydroxide, an appropriate amount of
the support was added to the neutralized solution, and
the resulting suspension was stirred at 70 C for 1 h.
The catalyst precursor was separated from the mother
liquor, washed with distilled water, dried in air for
°
1
3
day, and calcined at 300 C in an inert atmosphere for
h. The resulting catalysts were stored in dry argon.
°
Determining the Composition and Structure
of Nanocomposites
The weight percentage of metals in the catalysts
EXPERIMENTAL
was determined by atomic absorption spectrometry on
a Hitachi 180ꢀ80 spectrometer. For analysis, the metꢀ
als were washed off the support with a solution of conꢀ
Chemicals
Phenylacetylene (Aldrich, no. 2086451,
and styrene (Aldrich, no. 2028515,
tilled from P2O5 in an argon atmosphere.
≥97%
)
centrated acids (HCl : HNO = 3 : 1). Electron microꢀ
3
≥
99.5%) were disꢀ graphs of nanocomposites were obtained by transmisꢀ
sion electron microscopy (TEM using an LEO912 AB
The support was microspherical
γ
ꢀAl O (AO OMEGA instrument with a resolving power of 0.2 nm.
2
3
Katalizator, IKTꢀ02ꢀ6M brand) with a specific surface For each sample, the size distribution of supported
particles was established by statistical processing of
data for 300 ones.
†
Deceased.
288

SELECTIVE HYDROGENATION OF PHENYLACETYLENE INTO STYRENE
289
GasꢀPhase Hydrogenation
of Phenylacetylene–Styrene Mixtures
4ꢀml Pyrex reactor, which was heated to the preset
temperature in a tubular furnace. A liquid mixture
(
10 mol % phenylacetylene + 90 mol % styrene) was
C and was then fed into
styrene mixtures was carried out in a flow reactor. The the reactor. The GHSV of the organic mixture was varꢀ
The catalytic hydrogenation of phenylacetylene– heated in an evaporator to 150
°
–1
catalyst (1 g) was placed on a Schott filter built in a ied between 200 and 340 h and was calculated as
ρ
prodV
Vmol
prod
1
t
FGHSV
=
×
× ,
(
χ (C H ) ×102 + χ (C H ) ×104 + χ (C H ) ×106) m V
Cat Cat
t
8
6
t
8
8
t
8
10
where
ρ
= 0.9 g/ml is the density of the organic where m is the catalyst weight (g).
prod
fraction of the reaction products; Vprod is the accumuꢀ
The adsorption selectivity for the styrene–phenylꢀ
acetylene mixture was characterized by the selectivity
lated volume of organic products (ml); Vmol = 34.72 ×
3
1
0 ml/mol is the molar volume of the gas at 150
°
C;
=
coefficient
rected retention volume of the
α
=
Vr2
/
Vr1, where Vri is the specific corꢀ
21
VCat is the specific volume of the catalyst ( Cat
.885 ml/g for ꢀAl O );
h); (C H ),
fractions of phenylacetylene, styrene, and ethylbenꢀ
zene, respectively, in the organic mixture after ꢀhꢀ
V
i
th component (the
0
(
γ
t
is the accumulation time
(C H ), and (C H ) are the mole
2
3
components are numbered in the order of increasing
retention times).
χ
t
χ
t
χ
t
8
6
8
8
8
10
t
long passing of the reaction mixture through the cataꢀ
lyst bed; and mCat is the catalyst weight (g). Hydrogen
dried over solid KOH (1.25–1.29 ml/s) was fed into
the reactor along with the organic gas mixture. The
hydrogen/(styrene + phenylacetylene) molar ratio
ranged between 10 and 18. The reaction products were
analyzed by GLC on a KristallꢀLyuks 4000 chromatoꢀ
graph (50ꢀmꢀlong Thermon capillary column, conꢀ
RESULTS AND DISCUSSION
TEM Data
According to the literature [14], the anion adsorpꢀ
tion method makes it possible to obtain Au/
systems with immobilized gold nanoparticles 2–
0 nm in size. In the present work, catalysts with a gold
content of СAu = 0.018–1.8 wt % were prepared by this
method. The catalysts were lilac fine powders.
γ
ꢀAl O
2 3
2
stant temperature of 85 C, helium as the carrier gas,
°
flame ionization detector).
The phenylacetylene conversion
culated using the formula
Δ
(С H ) was calꢀ
8
6
Typical TEM images of the catalyst samples are
–1
Δ
(С H ) = (χ (С H ) –
8
χ
t
(С H ))
6
χ
(С H )
6
×
100%, shown in Figs. 1–3. The size of supported gold partiꢀ
8
6
0
6
8
0
8
cles (d(Au)) is 5–10 nm for the sample with an Au
content of 1.8 wt %, 3–5 nm for [Au] = 0.368 wt %,
and 2–3 nm for [Au] = 0.018 wt %. The particle size
where
χ (С H ) is the mole fraction of phenylacetyꢀ
0 8 6
lene in the organic mixture before the reaction.
The selectivity of the catalyst at 100% phenylacetꢀ
distribution maxima (d(Au)max) data are given in
ylene conversion ( 1
S
00) was calculated as
(С H ) + (С H )) .
–1
S100 = (С H )(
χ
t
χ
t
χ
t
8
8
8
6
8
10
Adsorption Measurements
Reactant adsorption was determined by GC from
corrected retention volume data for catalystꢀpacked
columns. Chromatographic measurements were carꢀ
ried out on a Kristall Lyuks 4000 chromatograph with
a flame ionization detector (column length of 20 mm,
inner diameter of 2 mm, oven temperature of 100 C).
°
Sorbate retention parameters, including the sorbate
retention time in the chromatographic column (tR) as
the time interval between the sample injection and
sorbate detection points, the retention time of a nearly
nonsorbable substance (methane) ( 0
t
), and the corꢀ
t0),
were determined at a carrier gas (helium) flow rate of
5 ml/min. Specific corrected retention volumes per
unit weight of the catalyst (Vr) were calculated as
rected retention time of the sorbate (t' ) = (tR
–
R
2
100 nm
Fig. 1. TEM image of the Au/
d(Au)max = 8 nm.
γ
ꢀAl O catalyst (1.8 wt %);
2 3
Vr = (t' – t0)/
m,
R
KINETICS AND CATALYSIS Vol. 51
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2010

290
NIKOLAEV et al.
100 nm
100 nm
Fig. 2. TEM image of the Au/
γ
ꢀAl O catalyst (0.368 wt %);
Fig. 3. TEM image of the Au/
γ
ꢀAl O catalyst (0.018 wt %);
2
3
2 3
d(Au)max = 4 nm.
d(Au)max = 2.5 nm.
Table 1. These results are in good agreement with the
literature [14].
The catalytic hydrogenation of phenylacetylene
into styrene (reaction (I)) can be accompanied by the
total hydrogenation of the acetylene and olefin derivꢀ
atives (reactions (IIa) and (IIb)) to ethylbenzene and
by phenylacetylene oligomerization (reaction (III)).
The following reactions occur in the hydrogenation
of the phenylacetylene–styrene mixture [15]:
H2
C H −C≡CH ⎯⎯→C H −CH=CH
2
(I)
(IIa)
(IIb)
6
5
6
5
In the presence of the
γ
ꢀAl O support, at 150
°
C
2
3
H2
Δ
(C H ) = 4.7% 1 h after the beginning of the run
8
6
C H −C≡CH ⎯⎯→C H −CH −CH
3
6
5
6
5
2
(
Table 1). The reaction mixture at the outlet of the
H2
reactor contains ethylbenzene (1.8%), the phenylꢀ
acetylene content remains almost unchanged, and the
C H −CH=CH ⎯⎯→C H −CH −CH
3
6
5
2
6
5
2
C H −C≡CH ⎯ ⎯→ oligomers
.
(III) styrene content is lower by 1.7%. The formation of
6
5
Table 1. Structural properties of catalysts and the molar compositions of the reaction mixture before (*) and after passing it
through an Au/γꢀAl O catalyst bed at 150°C and 100% phenylacetylene conversion
2
3
Mixture composition, mol %
CAu, %
d
(Au)max, nm GHSV, h–1
tr, h
S100, %
χ
C H
8
χ
C H
8
χ
C H
8
6
8
10
0
.018
.368
2.5
4.0
230
205
0*
1
9.8
0
90.2
96.7
96.7
89.8
95.1
95.0
92.0
90.4
79.4
70.0
97.9
96.2
0
3.3
3.3
0
29.3
29.3
4
0
0
0*
10.2
0
0
2
4
.6
4.9
5.0
8.0
0
19.4
19.1
11.6
0
0
1.8
8.0
200
340
0*
9.6
0
0.5
20.6
30.0
0
3.8
2.3
4
0
0
0*
1
2.1
2.0
1.8
Note: CAu is the weight percent of gold,
d(Au)max is the maximum gold particle size for the catalyst, t is the reaction time, and S100 is the
r
selectivity of the catalyst at 100% phenylacetylene conversion.
KINETICS AND CATALYSIS Vol. 51
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2010

SELECTIVE HYDROGENATION OF PHENYLACETYLENE INTO STYRENE
291
Table 2. Correlation between the hydrogenation selectivity and selective adsorption of phenylacetylene from the reaction mixꢀ
ture on the Au/γꢀAl O catalysts
2
3
Catalyst
Parameter
Au(1.8%)/γꢀAl O3
2
Au(0.368%)/
γ
ꢀAl O3
2
Au(0.018%)/γꢀAl O
2 3
α
1.74
8.0
1.89
4.0
2.05
2.5
d(Au)max, nm
S
2.3
11.6
29.3
Note: α is the phenylacetyleneꢀtoꢀstyrene retention volume ratio, S is the hydrogenation selectivity after 4ꢀhꢀlong operation for various catꢀ
alysts at 100% phenylacetylene conversion, and (Au)max is the maximum gold particle size in the catalyst.
d
ethylbenzene can be due to the fact that ꢀAl O conꢀ alyst, which contains the smallest amount of metal
γ
2 3
tains traces of hydrogenationꢀactive iron and other and consists of the finest particles. Since the Au conꢀ
metals (according to specifications, IKTꢀ02ꢀ6M can tent of this catalyst is negligible (the upper estimate of
–
4
contain up to 10 wt % Fe).
the metal coverage of the support surface is a few
tenths of a percent), this result possibly indicates the
pronounced adsorption selectivity of the nanosized
gold particles toward phenylacetylene. Probably, the
adsorption factor contributes substantially to the
increase in the selectivity of hydrogenation with a
decrease in the gold particle sizes.
The data listed in Table 1 show that the Au/ ꢀAl O
catalysts containing 2ꢀ to 10ꢀnm gold particles are
highly active and stable in the gasꢀphase hydrogenaꢀ
tion of phenylacetylene in styrene at 150 C. At 100%
phenylacetylene conversion, the catalyst retains its
initial activity for at least 4 h.
γ
2 3
°
The styrene selectivity depends substantially on the
average size of the gold particles (Table 1). As the parꢀ
ticle size decreases from 8 to 2.5 nm, S100 increases by
a factor of 13. It is likely that, in the samples with a
lower metal content, the fraction of highꢀmultiplicity
reaction sites decreases (the number of substrate coorꢀ
dination points increases) with a decreasing particle
size. Let us consider this thesis in greater detail. The
species responsible for olefin formation in the hydroꢀ
genation of acetylene derivatives are intermediates
adsorbed on sites with a multiplicity of 1–2, irrespecꢀ
tive of the nature of the metal. On the one hand,
alkanes usually form on sites with a multiplicity of 3,
whereas oligomers form on sites with a multiplicity of
CONCLUSIONS
At 150
°
C, the Au/ ꢀAl O catalysts are active,
γ
2 3
highly selective, and stable in the hydrogenation of
phenylacetylene into styrene.
A size effect of gold particles has been revealed:
the styrene selectivity increases with a decreasing
Au/ ꢀAl O particle size.
The hydrogenation selectivity in the phenylacetyꢀ
lene/styrene pair correlates with the selectivity of
γ
2 3
adsorption of these compounds on Au/ ꢀAl O .
γ
2 3
ACKNOWLEDGEMENTS
This work was supported by the Russian Foundaꢀ
≥
4
[15]. On the other hand, the proportion of planes
(
faces) containing highꢀmultiplicity sites decreases
sharply as the particle size decreases [16]. Thus, the tion for Basic Research (project nos. 08ꢀ03ꢀ00389 and
smaller the Au particle size (and, accordingly, the conꢀ 06ꢀ03ꢀ33131) and the Federal Agency for Science and
tribution from the high multiplicity sites to the cataꢀ Innovation (state contract no. 02.513.11.3204).
lytic processes), the lesser the extent of total hydrogeꢀ
nation and the higher the target product (styrene) ident Council for Supporting Young Russian Scientists
selectivity.
(grant no. MLꢀ5703.2008.3).
Another factor that enhances the selectivity as the
S.A. Nikolaev thanks the Russian Federation Presꢀ
Au particle size decreases is the selective adsorption of
phenylacetylene from the phenylacetylene–styrene
mixture. An essential fact for the selective hydrogenaꢀ
tion of acetylenic compounds in the presence of ethylꢀ
enic compounds is that the latter bind less strongly to
palladiumꢀ and platinumꢀbased catalyst surfaces and
are readily replaced by acetylene homologues [15, 17,
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KINETICS AND CATALYSIS Vol. 51
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2010