1-hexene oligomerization by fluorinated tin dioxide

Article abstract of DOI:10.1134/S0020168514050215

Fluorinated tin dioxide has been shown to exhibit catalytic activity for 1-hexene oligomerization. The physicochemical and functional properties of nanocrystalline fluorinated SnO₂ have been studied.

Full text of DOI:10.1134/S0020168514050215

ISSN 0020ꢀ1685, Inorganic Materials, 2014, Vol. 50, No. 5, pp. 479–481. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © L.L. Yurkova, S.A. Lermontov, A.N. Malkova, A.E. Baranchikov, V.K. Ivanov, 2014, published in Neorganicheskie Materialy, 2014, Vol. 50, No. 5,
pp. 518–521.
1ꢀHexene Oligomerization by Fluorinated Tin Dioxide
,
c
L. L. Yurkovaa, S. A. Lermontova, A. N. Malkovaa, A. E. Baranchikovb, and V. K. Ivanovb
aInstitute of Physiologically Active Compounds, Russian Academy of Sciences,
Severnyi proezd 1, Chernogolovka, Noginsk district, Moscow region, 142432 Russia
bKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
cMoscow State University, Moscow, 119899 Russia
eꢀmail: lermontov52@yandex.ru
Received November 12, 2013
Abstract—Fluorinated tin dioxide has been shown to exhibit catalytic activity for 1ꢀhexene oligomerization.
The physicochemical and functional properties of nanocrystalline fluorinated SnO2 have been studied.
DOI: 10.1134/S0020168514050215
INTRODUCTION
films feature high electrical conductivity and are used
in photoelectrochemical solar power converters [7].
The use of liquid mineral acids as industrial cataꢀ
lysts inevitable [1, 2] leads to the generation of a large
amount of waste. Moreover, such acids are highly
corrosive and toxic. For this reason, there is currently
great practical interest in the development of new
heterogeneous catalysts free of these drawbacks and
possessing high activity. Possible candidates include
sulfated metal oxides, which possess highly acidic
properties [3–5] due to the strong electron acceptor
2−
EXPERIMENTAL
The phase composition of the solid samples was
determined by Xꢀray diffraction on a Rigaku D/MAX
2500 diffractometer (Cu
K
radiation,
2 scan rate of
θ
α
2°/min). The crystallite size of the tin dioxide samples
was determined using the Scherrer formula, with
instrumental broadening taken into account.
Specific surface areas (S) were determined by lowꢀ
temperature nitrogen adsorption measurements with
an ATXꢀ06 analyzer (KATAKON, Russia). Prior to
effect of the
group. At the same time, M–O–S
SO4
bonds readily hydrolyze, which makes such catalysts
sensitive to the presence of moisture in the reaction
mixture.
measurements, the samples were outgassed at 200°C
in flowing dry helium for 30 min. The specific surface
of the powders was evaluated using Brunauer–
Emmett–Teller (BET) analysis (six points).
In this context, fluorinated oxide catalysts appear
sufficiently attractive because they are less susceptible
to hydrolysis and because the electron acceptor propꢀ
erties of the fluoride ion are at least comparable to
those of the sulfate ion.
1H NMR spectra in CDCl3 were measured on a
Bruker DPXꢀ200 spectrometer at 200 MHz, using tetꢀ
ramethylsilane as an external standard.
The activity of fluorinated acid catalysts has been
studied to date for a rather limited range of reactions.
In particular, a number of practically important proꢀ
cessers, such as dealkylation of aromatic compounds
and alkane isomerization, remain unexplored. Alkene
oligomerization, a promising process for the preparaꢀ
tion of liquid fuel from lower hydrocarbons, has only
been carried out on fluorinated alumina [6].
Mass spectra were obtained on a Finnigan
MATINCOS 50 quadrupole mass spectrometer
(direct insertion, 70ꢀeV electron impact ionization)
and a PerkinElmer Model Clarus 500 gas chromatoꢀ
graph/mass spectrometer (SEꢀ30 column).
Chromatographic analyses were carried out using
LHMꢀ2000 (1ꢀmꢀlong column, 3% Dexsil 300–
Chrom WꢀAW) and Kristallyuksꢀ4000M (ZBꢀ1 colꢀ
umn (Zebron) 100 m in length) chromatographs.
The objectives of this work were to prepare nanocꢀ
rystalline fluorinated tin dioxide, investigate its physiꢀ
cochemical properties, and assess its catalytic activity
for 1ꢀhexene oligomerization. Fluorinated tin dioxide
was chosen as the subject of this study because its sulꢀ
fated analog (SnO2/SO4) exhibited very high acidity
Thermogravimetric analysis (TGA) was performed
in the range 50–950°C using a PerkinElmer Model
PYRIS 6 TGA thermoanalytical system.
Xꢀray microanalysis was carried out on a Carl Zeiss
(exceeding that of sulfated alumina) and catalytic NVision 40 scanning electron microscope (SEM)
activity for isobutene, 1ꢀhexene, and cyclohexene oliꢀ equipped with an Oxford Instruments XꢀMax detector
gomerization [3]. Note that fluorinated tin dioxide and operated at an accelerating voltage of 20 kV.
479

480
YURKOVA et al.
Table 1. Specific surface area and crystallite size of the
SnO2/F catalyst
600
ered to 150
°
C
. The temperature in the reactor was then lowꢀ
°C, and the catalyst sample was exposed to
flowing dry air, which had been bubbled through pyriꢀ
dine (1 mL) until it completely vaporized.
Pyridineꢀsaturated samples weighing 30 to 40 mg
were placed in an alundum crucible under a dry pure
argon atmosphere, and the crucible was then heated at
a rate of 5°C/min in the range 50–950°C. The deviaꢀ
tion of the reading of the thermobalance from zero was
Heat treatment
Specificsurfacearea, Crystallite
temperature,
°
C
m2/g
size, nm
120
600
49
69
≈
2
7
within 0.025 mg in the range 50–950°C and less than
0.01 mg in the range 300–700
°C.
Catalyst acidity determination. The surface acidity
of the catalyst was determined by visually assessing
changes in the color of Hammett indicators [8]. A
weighed amount (0.2 g) of the starting catalyst was first
Catalyst synthesis. SnCl4 5H2O (50 g, 0.14 mol)
⋅
was dissolved in water (300 mL) and then 30% aqueꢀ
ous ammonia was added dropwise with stirring until
pH 10 was reached. The precipitate was washed with
water until the test for chloride was negative, and dried
calcined at a temperature of 600°C and then cooled in
flowing dry air. A weighed amount (0.2 mg) of an indiꢀ
cator (4ꢀnitrochlorobenzene, 2,4ꢀdinitrotoluene,
2,4,6ꢀtrinitrotoluene) was dissolved in sulfuryl chloꢀ
ride (2 mL) prepurified by distillation. Next, the indiꢀ
cator solution was added to the cooled catalyst, the
suspension was shaken for some time, and we visually
determined whether the color of the catalyst surface
changed (from white to yellow).
at 120°C for 2 h. After cooling, a weighed amount (4 g)
of the powder was added to 100 mL of an aqueous 2M
NH4F solution and the suspension was stirred for 1 h.
The product was filtered off and dried at 120
1ꢀHexene oligomerization. Prior to catalytic experꢀ
iments, the asꢀprepared catalyst was calcined at 600
°C for 2 h.
°C
in flowing dry air for 2 h and then cooled in a dry
atmosphere.
Catalytic activity was assessed as follows: The cataꢀ
lyst (1 g) was placed in a waterꢀcooled flask, 1ꢀhexene
(0.04 mol, 3.4 g, 5 mL) was added, and the mixture
was stirred at constant temperature. Samples of the
reaction mixture (0.2 mL) were taken at intervals for
analysis by NMR spectroscopy and chromatography.
The degree of conversion of the starting compound
RESULTS AND DISCUSSION
Physicochemical characterization of the catalyst.
Determination of the strength of acid centers (Hamꢀ
mett acidity function Н0) on the samples showed that
the acidity (Н0) of the catalyst obtained exceeded
1
⎯
16.04 (2,4,6ꢀtrinitrotoluene as an indicator).
was evaluated from H NMR spectra, and the oligoꢀ
mer content was determined by gas–liquid chromaꢀ
tography (GLC).
This estimate indicates that SnO2/F is a superacid
according to Olah’s definition (Н0 –11.93 [9]).
≤
Thermal desorption of pyridine. Catalyst samples
(0.1 g) were calcined in dry air in a tubular reactor at
The total density of acid centers on the catalyst surꢀ
face, determined using thermal desorption of pyriꢀ
dine, was 0.09 mgꢀequiv/g.
The types of acid centers present on the surface of
the fluorinated SnO2 were identified by IR spectrosꢀ
copy of adsorbed pyridine. Comparison of the present
IR spectra of adsorbed pyridine and spectra reported
previously clearly indicates that the surface of fluoriꢀ
nated tin dioxide has both Lewis and Brönsted acid
centers [3].
Catalyst
18–60°C
C6 + C12 + C18 + C24 + C30
+
+H
C4H9
+
CH
CH3
The total fluorine content of the samples was deterꢀ
mined by Xꢀray microanalysis. Heat treatment
+
C4H9
–H
(
600
orine by about a factor of 2 relative to the asꢀprepared
material. In particular, the Sn/F molar ratio was in
the asꢀprepared material and after annealing.
°C) was shown to reduce the mole fraction of fluꢀ
CH3
C4H9
CH2
CH3
C4H9
4
+
+
9
(1) +H
(2) –H
+
CH
CH
C4H9
–H
+
According to Xꢀray diffraction data, all of the fluꢀ
orinated tin dioxide samples consisted of singleꢀphase
cassiterite (PDF no. 41ꢀ1445), with no impurity
phases. Their diffraction peaks were strongly broadꢀ
ened, suggesting a small particle size of the fluorinated
tin dioxide. Using the Scherrer formula, the crystallite
CH
C4H9
1ꢀHexene oligomerization.
size of the SnO2 was estimated at
2 nm in the asꢀpreꢀ
INORGANIC MATERIALS Vol. 50
No. 5
2014

1ꢀHEXENE OLIGOMERIZATION BY FLUORINATED TIN DIOXIDE
481
Table 2. Results of 1ꢀhexene oligomerization by fluorinatꢀ
ed tin dioxide, SnO2/F, annealed at 600
temperature, the С6 content decreases slightly and,
accordingly, the С12 and С18 contents increase. It is
worth pointing out that the sulfated tin dioxide syntheꢀ
sized previously showed a higher catalytic activity for
1ꢀhexene oligomerization [3] in comparison with the
fluorinated tin dioxide. In the case of SnO2/SO4, the
degree of conversion was 100% in 24 h at room temꢀ
perature.
°
C
Percent of C6–30
Reaction Percent
temperaꢀ converꢀ
Reaction
time, h
ture,
°C
sion
C6 C12 C18 C24 C30
2
24
1
18
18
40
60
20
30
31
31
–
–
–
–
1
–
0
74 15 10
70 17 12
65 19 13
CONCLUSIONS
1
0
It is shown that nanocrystalline fluorinated tin
dioxide is a superacid catalyst and promotes 1ꢀhexene
oligomerization and dimerization reactions.
1
3
0
ACKNOWLEDGMENTS
pared material and 7 nm in the material heatꢀtreated
at a temperature of 600 for 2 h (Table 1).
The specific surface areas of the powder before and
after annealing at 600
were 49 and 69 m2/g, respecꢀ
°
C
This work was supported by the Russian Foundaꢀ
tion for Basic Research, grant nos. 11ꢀ03ꢀ00981.
°
C
tively (Table 1), as determined by lowꢀtemperature
nitrogen adsorption measurements. From these data,
the particle sizes were estimated at 17 nm in the asꢀ
prepared material and 12 nm in the annealed material.
That the particle size evaluated from the lowꢀtemperꢀ
ature nitrogen adsorption data considerably exceeds
that inferred from the Xꢀray diffraction data suggests
that the particles were aggregated to a significant degree.
The observed increase in specific surface area upon heat
treatment was obviously due to the reduction in the
degree of aggregation of the powder particles.
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The hexeneꢀ1 oligomerization products were charꢀ
acterized by GLC, gas chromatography/mass specꢀ
1
trometry, and H NMR spectroscopy through comꢀ
parison of the signal of the CH2=CH–R group in the
parent 1ꢀhexene to that of the R–CH=CH–R' group
in the reaction products (Table 2).
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conversion of 1ꢀhexene in 24 h is 30% at room temperꢀ
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Translated by O. Tsarev
INORGANIC MATERIALS Vol. 50
No. 5 2014