Adsorption and catalytic conversion of hydrocarbons on nanosized gold particles immobilized on alumina

Article abstract of DOI:10.1007/s11172-006-0111-8

Gold and nickel particles immobilized on alumina were prepared by the metal vapor synthesis and anionic adsorption methods. The dispersion of metals was determined by X-ray diffraction and transmission electron microscopy. The activity of nanoparticles, tested in model catalytic reactions of CCl ₄ addition to multiple bonds and allyl isomerization of allylbenzene, changes in a wide range (from 1 to 3000 (mole of product) (mole of Au) ^-1 h^-1) and is parallel to the chromatographically measured heats of adsorption of the corresponding unsaturated substrates. The heat of adsorption of unsaturated hydrocarbons can serve as a criterion for the efficiency of the gold-containing catalyst in olefin conversion.

Full text of DOI:10.1007/s11172-006-0111-8

2286
Russian Chemical Bulletin, International Edition, Vol. 54, No. 10, pp. 2286—2289, October, 2005
Adsorption and catalytic conversion of hydrocarbons on nanosized
gold particles immobilized on alumina
a
V. V. Smirnov,a S. N. Lanin,a A. Yu. Vasil´kov,b S. A. Nikolaev,a G. P. Murav´eva,
ꢀ
L. A. Tyurina,a and E. V. Vlasenkoa
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 932 8846. Eꢀmail: serge2000@rambler.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 5080. Eꢀmail: vasilkov@unislabs.com
Gold and nickel particles immobilized on alumina were prepared by the metal vapor
synthesis and anionic adsorption methods. The dispersion of metals was determined by Xꢀray
diffraction and transmission electron microscopy. The activity of nanoparticles, tested in
model catalytic reactions of CCl4 addition to multiple bonds and allyl isomerization of
allylbenzene, changes in a wide range (from 1 to 3000 (mole of product) (mole of Au)–1 h–1
)
and is parallel to the chromatographically measured heats of adsorption of the corresponding
unsaturated substrates. The heat of adsorption of unsaturated hydrocarbons can serve as a
criterion for the efficiency of the goldꢀcontaining catalyst in olefin conversion.
Key words: gold, alumina, adsorption of hydrocarbons, catalysis, metal vapor synthesis,
anionic adsorption, isomerization, addition, carbon tetrachloride.
lation. All distilled samples, except for olefins, were stored above
molecular sieves 4 Å (NaA).
Nanosized gold particles possess high catalytic activity
and selectivity.1—11 Gold nanoparticls immobilized on
oxide supports are highly active in the addition of carbon
tetrachloride to multiple bonds12 and in the allyl isomerꢀ
ization of olefins.13 Information on the strength and naꢀ
ture of interaction of nanoparticles with reactants is necꢀ
essary for an understanding of the mechanisms of isomerꢀ
ization and addition that occur on immobilized gold
nanoparticles. Therefore, data on the adsorption of reꢀ
agents and test molecules of different types are of great
interest.
Preparation of catalysts by the anionic adsorption and metal
vapor synthesis methods. Immobilized nanoꢀ and ultradispersed
particles were obtained by anionic adsorption and metal vapor
synthesis.12
Microspherical γꢀAl2O3 (IKTꢀ02ꢀ6M trade mark,
AO Katalizator, Russia) with a specific surface of 138 m2 g–1
was used as the support for nanoparticles. When the catalysts
were prepared by anionic adsorption, chloroauric acid hydrate
HAuCl4•xH2O (Aurat, TU 6ꢀ09ꢀ05ꢀ1075ꢀ89 trade mark) with
the weight content of Au 49.04%, distilled water, and a 0.1 M
solution of NaOH were used. A gold and/or nickel wire (l =
30 mm, d = 1.5 mm) was used as the metal source in the metal
vapor synthesis.
Determination of the average particle size by transmisꢀ
sion electron microscopy (TEM) and Xꢀray diffraction analysis.
Electronic microphotographs of organosols Au—Et3N,
Au—Ni—Et3N, and Ni—Et3N were obtained on a Jemꢀ100 inꢀ
strument with a resolution ability of 1—2 nm and an amplificaꢀ
tion of 1.5•105 times. In each case, data were processed using
the statistical method by 300 particles to determine the particle
size distribution.
In the present work, the heats of adsorption of carbon
tetrachloride, allylbenzene, and octꢀ1ꢀene on nanosized
particles of gold, nickel, and mixed samples Au + Ni were
measured by chromatography. To reveal the contribution
of alkyl chains, double bonds, and aromatic fragments of
substrate molecules, alkanes and simplest aromatic hyꢀ
drocarbons were chosen as test substances. The simplest
homologue of CCl4, viz, chloroform, was taken to eluciꢀ
date the contribution of the C—Cl bond to adsorption.
The Xꢀray diffraction study of the catalytic systems was carꢀ
ried out on a DRONꢀ3M diffractometer using filtered cobalt
radiation with a scan increment of 0.05° and the exposure to the
point from 10 to 50 s in the 2θ range from 38 to 48°.
The dispersion of immobilized particles was estimated from
the broadening of Xꢀray diffraction peaks. The size of gold crysꢀ
tallites was determined from the Debye—Scherrer formula. The
Experimental
Benzene (Aldrich, 98%), allylbenzene (Aldrich, 98%), and
octꢀ1ꢀene (Merck, 96%) were distilled over sodium. Haloꢀ
substituted hydrocarbons, ethanol, alkanes, and triethylamine
(all special purity grade, 98%) were used after drying and distilꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2215—2218, October, 2005.
1066ꢀ5285/05/5410ꢀ2286 © 2005 Springer Science+Business Media, Inc.

Hydrocarbon conversion on Au nanoparticles
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 10, October, 2005
2287
strongest reflection at d = 0.235 from the [111] plane of Au was
chosen as an analytical reflection.
7.5•10–4 mol, the amount of CCl4 was 5.2•10–3 mol, 130 °C,
and the reaction time was 2 h.
Determination of the metal content in the catalytic systems.
The content of gold and nickel in the samples was determined by
the atomic absorption method on a Hitachi 180ꢀ80 spectromꢀ
eter. The metal was preliminarily washed from the support with
a solution of concentrated acids (HCl : HNO3 = 4 : 1). The
Chromatographic measurements and determination of the
heats of adsorption. Chromatographic measurements were carꢀ
ried out on a Tsvetꢀ100 chromatograph with a flameꢀionization
detector and a glass column (adsorbent weight 0.3 g, nitrogen as
carrier gas). Samples of test sorbates were introduced as a vaꢀ
por—air mixture.
sensitivity of the method was 5•10–6—5•10–5 g L–1
.
Determination of the catalytic activity in model catalytic reꢀ
actions. Catalytic experiments were carried out in sealed evacuꢀ
ated vessels with vigorous stirring in the kinetic regime of the
reaction.
Products were analyzed by the GLC and GCꢀMS methods.
A KristalLyuksꢀ4000 instrument with a packed column (l = 2 m,
d = 0.4 mm, SEꢀ30 phase, flameꢀionization detector, nitrogen
as carrier gas) was used for GLC. Analysis by GCꢀMS was
carried out on a Finnigan MAT112S instrument with an energy
of ionizing electrons of 75 eV using a capillary column (l = 50 m,
d = 0.1 mm, DBꢀ1 phase).
The activity of the catalysts in allylbenzene isomerization
((mole of product) (mole of Au)–1 h–1) was determined in stanꢀ
dard experiments: the weight of the sample (Au/γꢀAl2O3)
was 0.1 g, the metal amount in the weighed sample was
10–5—10–6 mol, the amount of allylbenzene was 7.5•10–4 mol,
the amount of benzene was 5.6•10–3 mol, the temperature was
170 °C, and the reaction time was 3 h.
The activity of the catalysts in CCl4 addition to the multiple
bond was determined in standard experiments: the weight of the
sample (Au/γꢀAl2O3) was 0.1 g, the metal amount in the
weighed sample was 10–5—10–6 mol, the amount of olefin was
Chromatographic data were processed using a MultiChrom
v.152m program (Ampersand Ltd). Retention times were meaꢀ
sured, and specific retention volumes were calculated from the
latter at different temperatures. Heats of adsorption (Q)14 were
calculated from the temperature dependence of the retention
volume. The error of determination of the retention times of the
adsorbates was 0.3%, and that for the heats of adsorption was
1 kJ mol–1
.
The temperature of adsorption measurements did not exꢀ
ceed 100 °C, which is much lower than the temperature interval
of catalytic allylbenzene isomerization (>170 °C) and CCl4 adꢀ
dition to the multiple bond of olefin (>130 °C).
Results and Discussion
The heats of adsorption determined by chromatoꢀ
graphy for the chosen test sorbates on the catalysts and
pure support are presented in Table 1 along with the
data on particle sizes and their activity in model reacꢀ
tions (1) and (2).
Table 1. Heats of adsorption of the sorbates (Q), the average diameter of metallic particles (d), and their catalytic
activity in model reactions
Parameter
γꢀAl2O3
M/γꢀAl2O3
Ni (0.3%)a
Au (0.4%)b
Au (0.55%)a Au (5%)b
Au (0.4%) + Ni (0.3%)a
Adsorbate
nꢀC6H14
nꢀC7H16
nꢀC8H18
CCl4
Q/kJ mol–1
27
32
37
45
48
30
49
51
39
26
27
31
34
49
46
28
48
50
42
26
51
55
60
44
49
27
49
71
75
43
53
57
61
46
49
28
48
68
68
40
39
42
45
48
49
27
47
55
66
23
61
64
66
47
50
35
50
79
90
52
CHCl3
C6H6
C6H5Me
C6H5All
Octꢀ1ꢀene
Isooctane
Particle
d/nm
—
0
50
03
03
23
3, 60 c
3100
30
Reaction
Activity/(mole of product) (mole of Au)–1 h–1
Isomerization
of C6H5All
Addition
to octꢀ1ꢀene
Addition
0
0
0
20
20
14
20
17
13
3
4
2
0
0
85
to C6H5All
a Prepared by the metal vapor synthesis.
b Prepared by the anionic adsorption method.
c Bimodal distribution.

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Russ.Chem.Bull., Int.Ed., Vol. 54, No. 10, October, 2005
Smirnov et al.
tion of all the substances under study coincide within the
experimental error with those obtained for the pure supꢀ
port. Thus, the nickel itself does not compete with the
support for sites of hydrocarbon adsorption. However,
being added into the composition of the mixed particles
(Au + Ni), nickel favors, most likely, the formation of
additional defects, which activate gold atoms. A possibilꢀ
ity of similar activation is indicated by literature data21 on
the bimetallic nanoparticles.
Let us attempt to compare the strength of adsorption
with the catalytic activity of the M/γꢀAl2O3 samples in
transformations of the corresponding unsaturated subꢀ
strates.
M = Au, Ni, Au + Ni; R = Ph, nꢀC5H11
Gold nanoparticles supported in approximately equal
amounts by the methods of anionic adsorption and metal
vapor synthesis possess similar adsorption properties. For
instance, the heats of adsorption on the catalysts, which
were obtained by anionic adsorption (0.4 wt.% Au) and
metal vapor synthesis (0.55 wt.% Au), are virtually
the same.
The heat of adsorption of allylbenzene on γꢀAl2O3,
which is catalytically inactive in reactions (1) and (2),
equals 51 kJ mol–1. The same values within the measureꢀ
ment error were obtained for Ni/γꢀAl2O3, which is also
catalytically inactive in these reactions. The increase in
the heat of adsorption of allylbenzene on all monoꢀ and
The heats of adsorption of alkanes on pure alumina
are somewhat lower than the published values.15,16 For
example, Q(nꢀC7H16) on γꢀAl2O3 is 32 kJ mol–1 (see
Table 1). The heats of adsorption of nꢀheptane on γꢀAl2O3
calculated from published data using extrapolation by the
additive scheme17 are 43.1 15 and 46.4 kJ mol–1 16
.
bimetallic goldꢀcontaining systems above 51 kJ mol–1
,
The data on adsorption of substances of other classes
agree with the known adsorption properties of γꢀAl2O3.
An increase in the basicity of the molecules upon the
introduction of alkyl or alkenyl substituents into the aroꢀ
matic ring determines a stronger adsorption of toluene
and allylbenzene as compared with unsubstituted benꢀ
zene. The lower (compared to that of octane) heat of
adsorption is caused by steric hindrance created by alkyl
substituents, which decrease the number of effective conꢀ
tacts of the methylene groups of alkane with active adꢀ
sorption sites of the surface.18,19
induces a measurable catalytic activity of these samples in
reactions (1) and (2). This activity changes in parallel to
the heat (see Table 1). A similar change in the catalytic
activity of M/γꢀAl2O3 (M = Au, Au + Ni) in the addition
of CCl4 to the multiple bond of C8H16 at different heats of
olefin adsorption is also observed for octꢀ1ꢀene.
Thus, the heats of adsorption can serve as indicators
of the activity of the goldꢀcontaining systems in the proꢀ
cesses including the step of activation of unsaturated comꢀ
pounds by the interaction with the metal.
Gold immobilization exerts no effect on the heats of
adsorption of chlorohydrocarbons, benzene, and toluene
but increases the heats for sorbates with long alkyl or
alkenyl groups, viz., alkanes, olefins, and isooctane (see
Table 1). Thus, the increase in the heat of adsorption
(∆Q), when small gold nanoparticles (average diameter
3 nm) appear on the support surface, is equal to 24, 23,
and 23 kJ mol–1 for hexane, heptane, and octane, respecꢀ
tively. For octꢀ1ꢀene containing both the methylene chain
and double bond, ∆Q = 36 kJ mol–1. The effect ∆Q of
alkanes is low for the samples with relatively large gold
crystallites (average diameter 23 nm). The probable exꢀ
planation of different adsorptions of alkanes on the
nanoparticles of different size is that the strong interacꢀ
tion between the metal and hydrocarbons occurs only
with special, coordinatively unsaturated metallic sites (verꢀ
tices, edges, cracks, and other "roughness").20 Undoubtꢀ
edly, the smaller is the size of the nanocluster, the higher
is the fraction of such strongly nonequilibrated areas on
the nanocluster surface .
The authors are grateful to the Ministry of Education
and Science of the Russian Federation for help in the
creation of the necessary instrumental basis for the work.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 05ꢀ03ꢀ33065)
and the Council on Grants of the President of the Russian
Federation (Program of State Support for the Leading
Scientific Schools of the Russian Federation, Grant
NSh 1275.2003.3).
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Received May 24, 2005;
in revised form October 19, 2005