Chemical composition optimization and characterization of the NiO/B 2O3-Al2O3 system as a catalyst for ethylene oligomerization

Article abstract of DOI:10.1134/S0023158410030134

The samples of the NiO/B₂O₃-Al₂O ₃ system with NiO contents from 0.48 to 38.30 wt % were synthesized by the impregnation of borate-containing alumina (20 wt % B₂O ₃). It was found that nickel oxide occurred in an X-ray amorphous state in the samples containing to 23.20 wt % NiO. At a NiO content of 4.86 wt % or higher, the support was blocked by the modifier to cause a decrease in the specific surface area from 234 to 176 m²/g and in the amount of acid sites from 409-424 to 333 μmol/g. An extremal character of the dependence of catalyst activity in ethylene oligomerization on NiO content was found with a maximum in the range of 4.86-9.31 wt %. Based on spectroscopic data, it was found that ethylene activation on the NiO/B₂O₃-Al ₂O₃ catalyst can be associated with the presence of Ni²⁺ cations, which chemically interact with the support. The catalyst containing 4.86 wt % NiO at 200°C, a pressure of 4 MPa, and an ethylene sup- ply rate of 1.1 h^-1 provided almost complete ethylene conversion at the yield of liquid oligomerization prod- ucts to 90.0 wt %; the total concentration of C⁸⁺ alkenes in these products was 89.0 wt %. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0023158410030134

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2010, Vol. 51, No. 3, pp. 404–409. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Lavrenov, E.A. Buluchevskii, M.A. Moiseenko, V.A. Drozdov, A.B. Arbuzov, T.I. Gulyaeva, V.A. Likholobov, V.K. Duplyakin, 2010, published in
Kinetika i Kataliz, 2010, Vol. 51, No. 3, pp. 423–428.
Chemical Composition Optimization and Characterization
of the NiO/B2O3–Al2O3 System
As a Catalyst for Ethylene Oligomerization
A. V. Lavrenov, E. A. Buluchevskii, M. A. Moiseenko, V. A. Drozdov, A. B. Arbuzov,
T. I. Gulyaeva, V. A. Likholobov, and V. K. Duplyakin
Institute of Hydrocarbon Processing, Siberian Branch, Russian Academy of Sciences, Omsk, 644040 Russia
eꢀmail: lavr@ihcp.oscsbras.ru
Received February 18, 2009
Abstract—The samples of the NiO/B2O3–Al2O3 system with NiO contents from 0.48 to 38.30 wt % were
synthesized by the impregnation of borateꢀcontaining alumina (20 wt % B2O3). It was found that nickel oxide
occurred in an Xꢀray amorphous state in the samples containing to 23.20 wt % NiO. At a NiO content of
4.86 wt % or higher, the support was blocked by the modifier to cause a decrease in the specific surface area
from 234 to 176 m2/g and in the amount of acid sites from 409–424 to 333
mol/g. An extremal character of
μ
the dependence of catalyst activity in ethylene oligomerization on NiO content was found with a maximum
in the range of 4.86–9.31 wt %. Based on spectroscopic data, it was found that ethylene activation on the
NiO/B2O3–Al2O3 catalyst can be associated with the presence of Ni2+ cations, which chemically interact
with the support. The catalyst containing 4.86 wt % NiO at 200 C, a pressure of 4 MPa, and an ethylene supꢀ
°
ply rate of 1.1 h–1 provided almost complete ethylene conversion at the yield of liquid oligomerization prodꢀ
ucts to 90.0 wt %; the total concentration of C8+ alkenes in these products was 89.0 wt %.
DOI: 10.1134/S0023158410030134
INTRODUCTION
of the reduction pretreatment of the catalyst, or
directly under the action of ethylene in the course of
oligomerization. The second and third steps involved
the reactions of 1ꢀbutene isomerization and the oligoꢀ
merization and cooligomerization of ethylene and
butenes at the acid sites. The disadvantages of wellꢀ
known nickelꢀcontaining catalysts for ethylene oligoꢀ
merization are complex preparation procedures, the
use of expensive acid supports, and, in the majority of
cases, low selectivity for the formation of liquid prodꢀ
ucts.
In this work, we proposed the use of borateꢀconꢀ
taining alumina as an acid support for ethylene oligoꢀ
merization catalysts. We found previously [12] that
this support can serve as an efficient catalyst for the
oligomerization of butenes. In this case, the aims of
this study were to optimize the NiO content of the
NiO/B2O3–Al2O3 system in terms of catalytic activity,
to determine the effect of the NiO content on the texꢀ
ture and acid properties of the catalyst and on the
chemical state of nickel in this catalyst, and to examꢀ
ine the highly selective oligomerization of ethylene to
liquid С5+ alkenes on the NiO/B2O3–Al2O3 catalyst.
Ethylene oligomerization is usually performed to
synthesize ꢀolefins, which serve as raw materials for
α
the manufacture of copolymers, highꢀmolecularꢀ
weight alcohols, surfactants, industrial oils, and oil
additives [1, 2]. In the past 10–15 years, this process
has become a topic of considerable current research
because of the development of ethylene production
from natural gas [3]. As a result, ethylene oligomerizaꢀ
tion is currently an important step in gas to liquids
technologies. In this case, the improvement of cataꢀ
lysts for ethylene oligomerization is oriented to the
production of isoalkenes, which can be environmenꢀ
tally friendly fuel components, as target products. An
analysis of published data indicates that bifunctional
solid the most promising catalysts for ethylene converꢀ
sion into isoalkenes.
These catalysts are synthesized by the treatment of
acid supports with nickel salts followed by calcination.
Silica gel [4]; amorphous aluminosilicates [5]; zeolites
[6]; and sulfateꢀ, molybdateꢀ, and tungstateꢀcontainꢀ
ing alumina, zirconia, and titania [7–11] have been
studied as supports for nickel cations. From the results
of the studies of supported nickelꢀcontaining catalysts,
it follows that the oligomerization of ethylene on these
catalysts occurred in three main steps. At the first step,
EXPERIMENTAL
The borateꢀcontaining alumina was prepared by
ethylene dimerization to 1ꢀbutene occurred under the mixing commercial pseudoboehmite (Promyshlennye
action of Ni+ cations, which were formed in the course Katalizatory) with an aqueous solution of chemically
404

CHEMICAL COMPOSITION OPTIMIZATION AND CHARACTERIZATION
405
Table 1. Physicochemical properties of the samples of the NiO/B2O3–Al2O3 system
Texture characteristics
Acidity
μmol NH3/m2
NiO content,
wt %
S
sp, m2/g
V
pore, cm3/g
Da, nm
μmol NH3/g
0
234
231
232
213
205
190
176
0.58
0.53
0.53
0.49
0.45
0.42
0.26
9.9
9.2
9.1
9.2
8.9
8.8
5.8
409
412
–
1.7
1.8
–
0.93
1.87
4.86
9.30
14.40
38.30
424
385
382
333
2.0
1.9
2.0
1.9
pure orthoboric acid followed by drying at 150°С and thermalꢀconductivity detector. The adsorption of
calcination at 550°С for 15 h. The nominal boron ammonia was performed at 100°С. The desorption of
oxide content of the support was 20 wt %. Chemically ammonia was detected over the temperature range of
pure nickel nitrate was used to prepare the samples of 150–500°С at a heating rate of 10 K/min. The desorpꢀ
the NiO/B2O3–Al2O3 system. A fraction of the supꢀ tion was complete because of an additional exposure at
port with a particle size of 0.1–0.5 mm was impregꢀ 500°С for 30–60 min. Table 1 summarizes the physicꢀ
nated with an aqueous solution of nickel nitrate. After ochemical characteristics of the samples.
impregnating, the samples were dried at 150°С and
The catalyst samples were studied by IR spectrosꢀ
calcined at 500°С for 15 h. To vary the nickel oxide
copy using a Shimadzu IR Prestige 21 Fourier transꢀ
content of the catalyst, solutions with various concenꢀ
form spectrometer equipped with a vacuum cell. The
trations of nickel nitrate were used in combination
samples were formed as pellets 10–25 mg/cm2 in
with single or double impregnation. The concentraꢀ
thickness, placed in the measurement cell, and heated
tions of nickel oxide in the prepared catalyst samples
at 400°С and 7.5
10–5 Torr for 2 h. The spectra were
×
were determined by the complete dissolution of the
samples under the action of sulfuric acid followed by
the determination of nickel cations in solutions using
atomic absorption spectrometry on a Shimadzu AAꢀ
6300 instrument.
The thermal analysis of intermediate catalyst speꢀ
cies (after drying at 150°С) was performed on a
Netzsch STA 449 C instrument in an atmosphere of air
over the temperature range of 20–800°С at a heating
rate of 10 K/min. The phase composition of the samꢀ
ples was studied on a Bruker D8 Xꢀray diffractometer
measured at room temperature over the wavenumber
range of 1000–4000 cm–1 (with a resolution of 4 cm–1)
with the accumulation and averaging of the results of
50 measurements. The IR spectra of adsorbed CO
were obtained in an analogous manner at a gas presꢀ
sure of 10 Torr in the cell. The diffuse reflectance specꢀ
tra were recorded on a Shimadzu UVꢀ2501PC specꢀ
trophotometer with an ISRꢀ240A attachment with
reference to the parent support over the wavenumber
range of 11000–54000 cm–1.
using Cu
the range of
K
radiation. The samples were scanned over
2
The oligomerization of ethylene was performed in
α
θ
angles of 5°–80° with a scan step of a flow reactor with a fixed catalyst bed at temperatures
react) of 150, 180, and 200°С and pressures ( react) of
0.1° and a counting time of 3 s at each point. Identifiꢀ
(
T
P
cation was performed using the ICDD PDFꢀ2 2006 1.0 and 4.0 MPa and an ethylene supply rate of 1.1 h–1.
Release database. The texture characteristics of cataꢀ The catalyst sample (4–8 g) with a particle size of 0.1–
lyst samples (specific surface area Ssp, pore volume 0.5 mm was placed in the reactor and activated in a
Vpore, and average pore diameter Da) were determined flow of dry air at 500°С for 1 h before the onset of testꢀ
from data on the lowꢀtemperature (77.4 K) adsorption ing. A methane–ethylene mixture with an ethylene
of nitrogen, which was studied on an ASAPꢀ2020M weight fraction of 30.54 wt % and chromatographiꢀ
analyzer (Micromeritics). The value of Ssp was estiꢀ cally pure ethylene were used as raw materials. The
mated by the BET method from an adsorption isoꢀ hydrocarbon compositions of the product mixtures
therm in the range of 0.05–0.30 of equilibrium relative formed in the oligomerization process were analyzed
nitrogen vapor values. The values of Vpore were deterꢀ online using a Tsvetꢀ800 gas chromatograph equipped
mined from the adsorption of nitrogen at an equilibꢀ with a DBꢀ1 capillary column and a flameꢀionization
rium relative nitrogen vapor value of 0.990. The averꢀ detector. The recording and treatment of chromatoꢀ
age pore diameter was calculated from the expression grams was performed using the Multichrom computer
D
a = 4Vpore
/
Ssp. The level of the acid properties of the system. The conversion of ethylene (
Х
) was calculated
samples was estimated from data on the temperatureꢀ from the equation
programmed desorption (TPD) of ammonia on an
AutoChemꢀ2920 instrument (Micromeritics) with a
X = 100(Wine −Wperod)/Wine,
(1)
KINETICS AND CATALYSIS Vol. 51
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2010

406
LAVRENOV et al.
not considerably change the specific surface area
(231–234 m2/g), pore volume (0.53–0.58 cm3/g), and
average pore diameter (9.1–9.9 nm) of the catalyst, as
compared with the initial support. Starting from a NiO
concentration of 4.86 wt %, the support was blocked
with the modifier, and this blocking was enhanced
with NiO content and accompanied by a decrease in
the specific surface area of the catalyst to 176 m2/g, in
the pore volume to 0.26 cm3/g, and in the average pore
diameter to 5.8 nm as a nickel oxide weight fraction of
38.30 wt % was reached.
4
3
2
1
According to ammonia TPD data, the introduction
of NiO did not change the strength of surface acid sites
on the catalyst surface. As in borateꢀcontaining aluꢀ
mina, the main amount of ammonia was desorbed in
the temperature range of 150–350°С with a maximum
at 250–260°С. This suggests that the average level of
acid properties in the NiO/B2O3–Al2O3 system was
retained; this level was sufficient for the occurrence of
the oligomerization conversion of butenes. An
increase in the NiO content to 4.86 wt % did almost
not change the total amount of catalyst acid sites,
20
30
40
2
50
, deg
60
70
θ
Fig. 1. Diffraction patterns of catalyst samples with various
NiO contents: ( ) 0 (parent support), ( ) 4.86, ( ) 23.20,
and ( ) 38.30 wt %.
1
2
3
4
e
e
where
and
are the weight fractions of ethylꢀ
Wprod
Win
ene (%) in the initial and product mixtures, respecꢀ
tively. The yields of individual groups of oligomerizaꢀ
tion products (Y) were taken equal to the total weight
fractions of corresponding components (%) in the
product mixture. The composition of oligomerization
products was determined by normalizing the peak
areas of corresponding hydrocarbon groups to 100%.
which was 409–424 mol/g (Table 1). As the weight
µ
fraction of NiO in the system was further increased to
38.30 wt %, the total amount of acid sites decreased to
333 mol/g. At the same time, the total amount of
µ
acid sites per unit surface area of the catalyst was
almost independent of the presence of essentially difꢀ
ferent amounts of supported NiO and varied over the
range of 1.7–2.0
mol NH3/m2. This unambiguously
µ
suggests that, in this case, the TPD of ammonia could
not detect changes in the chemical nature of catalyst
surface upon the addition of the modifier and a priori
leveled the obvious difference between the acid propꢀ
erties of borateꢀcontaining alumina and nickel oxide.
RESULTS AND DISCUSSION
The thermal analysis of bulk nickel nitrate and
intermediate catalyst species, which were obtained by
supporting nickel nitrate on borateꢀcontaining aluꢀ
mina with drying at 150°С, demonstrated that the salt
From the experimental IRꢀspectroscopic data
(Fig. 2), it follows that the ion exchange of acid
hydroxyl groups like –B–OH on the support surface
(absorption bands at 3687 and 3700 cm–1) for nickel
cations occurred on the treatment of the support with
a solution of nickel nitrate, and the degree of this
exchange depended on the added amount of the modꢀ
ifier. The absorption of these groups was not observed
as the NiO content of the catalyst reached 4.9 wt % or
higher. Thus, in the course of catalyst formation,
nickel cations chemically bound to the support surface
were formed. It is likely that these cations occurred in
a complex anionic environment including not only
oxygen atoms but also boron atoms. The occurrence of
this interaction was also supported by the results
obtained by the IR spectroscopy of CO (Fig. 3) and
diffuse reflectance spectroscopy (Fig. 4).
underwent almost complete decomposition to 500°С
.
Therefore, the production of final catalyst samples in
the course of longꢀterm (15 h) calcination at 500°С
should really result in the formation of NiO on the surꢀ
face of borateꢀcontaining alumina preimpregnated
with a solution of nickel oxide. However, Xꢀray difꢀ
fraction analysis did not allow us to detect nickel oxide
phases in the samples containing to 23.20 wt % NiO
(Fig. 1). As well as the initial support, these samples
were Xꢀray amorphous. It is likely that, in the given
range of concentrations, nickel oxide occurred in a
highly dispersed state with a particle size smaller than
3.0 nm on the surface of borateꢀcontaining alumina;
the interaction with the support was responsible for
this state. Only in the sample containing 38.30 wt %
NiO, the presence of a cubic nickel oxide phase with a
particle size of about 21.4 nm in terms of coherentꢀ
scattering regions was detected.
In the case of borateꢀcontaining alumina, absorpꢀ
tion bands characteristic of adsorbed CO molecules
Data on the texture characteristics of the samples, were not detected. The samples containing 0.93 and
which are summarized in Table 1, indirectly demonꢀ 4.86 wt % NiO exhibited an absorption band at
strate the occurrence of interactions between nickel 2196 cm–1, which was shifted by 6 cm–1, as compared
oxide and borateꢀcontaining alumina at NiO concenꢀ with the absorption band at 2190 cm–1, which is typiꢀ
trations to 1.87 wt %. In this region, modification did cal of the case of nonstoichiometric NiO. The latter
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CHEMICAL COMPOSITION OPTIMIZATION AND CHARACTERIZATION
407
2190
3687
3700
5
4
3
5
4
3
2
1
2
1
2196
2150
2200
2250
3600
3700
Wavenumber, cm−
3800
1
Wavenumber, cm−
1
Fig. 2. IR spectra of catalyst samples with various NiO
contents: ( ) 38.30, ( ) 23.20, ( ) 4.86, ( ) 0.93, and
) 0 wt % (parent support).
Fig. 3. IR spectra of adsorbed CO for catalyst samples with
various NiO contents: ( ) 0 (parent support), ( ) 0.93, (
4.86, ( ) 23.20, and ( ) 38.30 wt %.
1
2
3
4
1
2
3)
(5
4
5
intensely manifested itself in the highꢀpercentage catꢀ data on the TPD of ammonia, the acid properties of
alyst samples containing 23.20 and 38.30 wt % NiO.
According to published data [13], these shifts are charꢀ
acteristic of supported systems containing nickel catꢀ
ions directly bound to an acid matrix (such as zeolite)
along with NiO.
the samples remained similar. Thus, it can be conꢀ
cluded that nickel cations of a certain chemical nature
were responsible for the formation of ethylene activaꢀ
tion sites. The results of catalytic tests in combination
with the above data on the IR spectroscopy of CO and
diffuse reflectance spectra allowed us to state that
these Ni2+ cations are those formed by the interaction
with the acid support—the borateꢀcontaining aluꢀ
mina. An increase in the concentration of these catꢀ
ions in the catalyst led to an increase in its activity in
ethylene oligomerization. The Ni2+ cations arranged
in the crystal lattice of NiO did not participate in ethꢀ
ylene activation; thus, the degree of ethylene converꢀ
sion dramatically decreased down to zero upon supꢀ
porting more than 14.40 wt % of the modifier, which
strongly blocked the support.
The diffuse reflectance spectra of bulk nickel oxide,
which was prepared by the thermal decomposition of
the nitrate salt, exhibited absorption bands at 13900,
23700, and 26300 cm–1, which are typical of Ni2+ catꢀ
ions in an octahedral coordination. Similar absorption
bands were observed in the catalyst sample with a maxꢀ
imum modifier concentration (38.30 wt %). The
appearance of absorption bands at 13100 and
14900 cm–1, which can also be attributed to Ni2+ catꢀ
ions in an octahedral coordination that are partially
bound to hydroxyl groups or interact with acid anions
[14] (likely, borate anions in this case), was characterꢀ
istic of lowꢀpercentage catalyst samples (0.93 and
4.86 wt % NiO).
The results of testing the samples under the severe
conditions of ethylene oligomerization with the use of
a methane–ethylene mixture (with a low concentraꢀ
tion of ethylene) and a low pressure of 1.0 MPa
(Fig. 5) demonstrated that the effect of the NiO conꢀ
tent on changes in the texture and acid properties of
the NiO/B2O3–Al2O3 system was radically different
from its effect on the catalytic activity of this system.
First, as expected based on published data, the presꢀ
ence of NiO in the system was of paramount imporꢀ
tance for the occurrence of ethylene oligomerization.
The initial borateꢀcontaining alumina was almost
inactive in ethylene conversion. Second, the depenꢀ
dence of the degree of ethylene conversion on the
nickel oxide content of the catalyst exhibited an extreꢀ
mal character with a maximum at 4.86–9.31 wt %
NiO. At a NiO content of 38.30 wt %, the catalyst was
inactive in the process of ethylene oligomerization, as
well as the initial support. In this case, according to
26300
23700
5
13900
13100
14900
4
3
2
1
15000
20000
25000
1
Wavenumber, cm−
Fig. 4. Diffuse reflectance spectra of catalyst samples with
various NiO contents: ( ) 0.93, ( ) 4.86, ( ) 38.30, ( ) 0
(parent support), and ( ) 100.00 wt % (bulk nickel oxide).
1
5
2
3
4
KINETICS AND CATALYSIS Vol. 51
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408
LAVRENOV et al.
, %
X
, %
Y
50
40
30
20
10
0
150°C
180°C
200°C
3
30
20
10
0
2
1
C1−C4
C5
−
C7
C8
C9+
Fig. 6. Yields of С –С products on the catalyst with a
nickel oxide content of 4.90 wt % depending on oligomerꢀ
ization temperature. Raw material: methane–ethylene
0
10
20
30
40
1
9+
NiO content, wt %
mixture;
P
= 4.0 MPa.
react
Fig. 5. Dependence of the degree of ethylene conversion
on the nickel oxide sample of the catalyst at various oligoꢀ
merization temperatures: (1) 150, (2) 180, and (3) 200°С
sure of 4.0 MPa in the reaction atmosphere. As a
result, we found that this catalyst can result in ethylene
conversion at a level of 99.6–99.9% with the yields of
С5+ liquid oligomerization products to 90.0 wt %; the
total concentration of С8+ alkenes in these products
was 89.0 wt % (Fig. 6). In this case, the yield of С1–С4
light gases can be no higher than 10 wt %.
(raw material: methane–ethylene mixture;
1.0 MPa).
P
=
react
Data summarized in Table 2 indicate that
butenes were the main products of ethylene converꢀ
sion under severe oligomerization conditions. The
nꢀ
weight fraction of nꢀbutenes in the total products was
as high as 73.8–75.5 wt %. Hexenes (18.8–20.2 wt %)
and С8 and С9+ alkenes were also formed in much
smaller amounts. For the process parameters of oligoꢀ
merization used in this case, the manifestations of the
acid function of the catalyst can be detected only
Thus, the experimental studies demonstrated that
the NiO/B2O3–Al2O3 system can be used as an active
and selective catalyst for ethylene oligomerization to
liquid С5+ alkenes. The range of 4.86–9.31 wt % was
determined for optimum NiO concentrations in the
catalyst. It was found that ethylene activation on the
NiO/B2O3–Al2O3 catalyst depends on the presence of
Ni2+ cations chemically bound to the catalyst surface.
The role of borateꢀcontaining alumina depends on its
acid properties. These properties are required for the
formation of specific Ni2+ cations. It is likely that these
cations are subsequently transformed into Ni+ cations,
which are the real sites of ethylene activation, as folꢀ
lows from previously performed studies. In addition,
the acid sites of the support are required for performꢀ
ing isomerization and oligomerization reactions for
the formation of С5+ highꢀmolecularꢀweight alkenes
based on the isomer composition of nꢀbutenes. In this
case, in accordance with thermodynamic data [15],
transꢀ2ꢀbutene was predominant; the fraction of cisꢀ2ꢀ
butene was intermediate, and the 1ꢀbutene content
was the lowest. Thus, these data suggest the occurꢀ
rence of the isomerization of 1ꢀbutene (the primary
product of ethylene conversion) to 2ꢀbutenes under
the action of the acid sites of the NiO/B2O3–Al2O3
system.
It is well known that an increase in the alkene conꢀ
tent of the starting raw material and the total pressure
of the reaction atmosphere facilitated the course of
oligomerization. Thus, at the final stage of this work,
we performed the oligomerization of pure ethylene on
a catalyst sample containing 4.86 wt % NiO at a presꢀ from ethylene.
Table 2. Composition of the products of ethylene oligomerization on the catalyst with a nickel oxide content of 4.90 wt % (raw
material: methane–ethylene mixture; Preact = 1.0 MPa)
Concentration, wt %
Treact, °С
1ꢀbutene
cisꢀ2ꢀbutene
transꢀ2ꢀbutene
С6
С8
С9+
150
180
200
9.2
11.0
10.3
24.6
25.4
24.0
41.5
39.1
39.5
18.8
18.5
20.2
5.5
5.6
5.1
0.4
0.3
0.9
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CHEMICAL COMPOSITION OPTIMIZATION AND CHARACTERIZATION
409
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KINETICS AND CATALYSIS Vol. 51
No. 3
2010