Ethylene to 2-butene in a continuous gas phase reaction using silp-type cationic nickel catalysts

Article abstract of DOI:10.1002/cctc.201300636

Owing to shifting market demands, it is important to convert ethylene to propylene. One attractive way to achieve this conversion is the dimerization of ethylene to 1-butene, followed by isomerization to 2-butene and subsequent metathesis of 2-butene/ethylene olefin. Our contribution focuses on combining the first two steps. Herein, we report a highly selective tandem dimerization/isomerization of ethylene to 2-butene catalyzed by homogeneously dissolved cationic nickel complexes. These catalysts can be efficiently immobilized by using the supported ionic liquid phase technology. Such supported ionic liquid phase materials have been tested under continuous gas phase conditions and demonstrated attractive catalytic performance with respect to both catalyst stability and productivity after the optimization of support, ionic liquid, ligand, and process parameters. The limited thermal stability of the nickel complexes and olefin condensation at too low temperatures require a careful thermal management of the fixed-bed reactor. Copyright

Full text of DOI:10.1002/cctc.201300636

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DOI: 10.1002/cctc.201300636
Ethylene to 2-Butene in a Continuous Gas Phase Reaction
using SILP-Type Cationic Nickel Catalysts
[
a]
[a]
[b]
[a]
[b]
Judith Scholz, Veit Hager, Xinjiao Wang, Florian T. U. Kohler, Michelle Sternberg,
[a]
[c]
[b]
[a]
Marco Haumann,* Normen Szesni, Karsten Meyer, and Peter Wasserscheid*
Owing to shifting market demands, it is important to convert
ethylene to propylene. One attractive way to achieve this con-
version is the dimerization of ethylene to 1-butene, followed
by isomerization to 2-butene and subsequent metathesis of
the supported ionic liquid phase technology. Such supported
ionic liquid phase materials have been tested under continu-
ous gas phase conditions and demonstrated attractive catalytic
performance with respect to both catalyst stability and produc-
tivity after the optimization of support, ionic liquid, ligand, and
process parameters. The limited thermal stability of the nickel
complexes and olefin condensation at too low temperatures
require a careful thermal management of the fixed-bed reac-
tor.
2-butene/ethylene olefin. Our contribution focuses on combin-
ing the first two steps. Herein, we report a highly selective
tandem dimerization/isomerization of ethylene to 2-butene
catalyzed by homogeneously dissolved cationic nickel com-
plexes. These catalysts can be efficiently immobilized by using
Introduction
Propylene is the world’s second largest chemical commodity
(
after ethylene) with an annual production of 77 million tons in
010. Mainly driven by the increasing demand for polypropyl-
ene, the annual production of propylene is estimated to in-
Scheme 1. Conversion of ethylene to propylene through ethylene dimeriza-
tion, isomerization, and cross-metathesis.
2
[
1]
crease to 120 million tons in 2022. The demand for ethylene
[2]
is expected to increase at a minor rate in the same period.
Zeolites have been reported to catalyze the conversion of
ethylene to propylene via a carbenium ion mechanism, in
which the degree of oligomerization is controlled by the con-
Because today’s demand of both ethylene and propylene is
mainly met by using steam cracking, new on-purpose routes
to propylene are becoming important, such as propane dehy-
[
4,5]
fined space of the zeolite.
Multifunctional catalysts such as
[
3]
[6,7]
[8]
drogenation and methanol-to-propylene conversion. Another
promising route involves the dimerization of ethylene to
supported molybdenum,
tungsten oxide, tungsten hy-
[9]
[10,11]
dride, nickel ions loaded on MCM-41
have also been re-
1
-butene, followed by isomerization to 2-butene. Subsequent
ported. All these catalyst systems for the direct conversion of
ethylene to propylene are associated with varying degrees of
drawbacks, such as severe deactivation, low conversion, and/or
moderate propylene selectivity. Our latest attempts to realize
a cascade reaction such as dimerization/isomerization followed
by a metathesis reaction resulted in the development of new
nickel catalysts that enable the dimerization and isomerization
of ethylene to 2-butene with an exceptionally high selectivity.
Homogeneous nickel complexes are well-known oligomeri-
zation catalysts following a nickel hydride chain growth mech-
metathesis of 2-butene with ethylene would yield propylene.
These so-called ethylene-to-propylene conversion processes
(Scheme 1) have been reported in the literature, but no com-
mercial-scale process has been introduced yet.
+
+
[a] Dr. J. Scholz, V. Hager, F. T. U. Kohler, Dr. M. Haumann,
Prof. Dr. P. Wasserscheid
Department of Chemical and Bioengineering, Reaction Engineering
University of Erlangen-Nuremberg
Egerlandstraße 3, 91058 Erlangen (Germany)
E-mail: marco.haumann@fau.de
[12]
anism. The competition between chain growth and termina-
tion via b-hydride elimination governs the product distribu-
[
13,14]
tion.
Neutral nickel complexes usually produce higher al-
peter.wasserscheid@crt.cbi.uni-erlangen.de
[15]
kenes in a relatively wide Schulz–Flory distribution, whereas
[
b] Dr. X. Wang, M. Sternberg, Prof. Dr. K. Meyer
Department of Chemistry and Pharmacy, Inorganic Chemistry
University of Erlangen-Nuremberg
[16]
small alkenes are mainly obtained with cationic catalysts.
Multidentate ligands such as P^O and P^N have been investi-
Egerlandstraße 1, 91058 Erlangen (Germany)
[17–21]
gated by several research groups.
Methallyl nickel com-
[c] Dr. N. Szesni
plexes, predominantly with phosphinocarboxylates as ligands,
demonstrated high activities at mild temperatures and low
Clariant Produkte (Deutschland) GmbH
Waldheimer Straße 13, 83052 Bruckmꢀhl (Germany)
[22]
+
ethylene pressures.
[
] These authors contributed equally to this work.
A comparison of catalytic results of neutral and analogous
cationic complexes showed that the latter demonstrated a dra-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300636.
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Results and Discussion
matic increase in activity with a lower selectivity toward linear
and higher alkenes. This behavior was ascribed to a loss of
chelate coordination of the P^O ligand under catalytic condi-
tions, which is necessary for a high selectivity toward linear
All dimerization experiments were performed in the continu-
ous laboratory rig with a fixed-bed reactor, as shown in
Figure 3. The first experiment was conducted with the catalyst
[
23]
1
-alkenes. In addition, the high electrophilicity of the cation-
ic nickel complexes facilitates the recoordination of product al-
kenes via the internal carbon atom of the double bond. The
subsequent b-hydride elimination results in the formation of
complex 1 at a cooling temperature of T =408C. The catalyst
c
achieved full conversion of ethylene at the beginning of the
reaction, a selectivity of 94% toward butenes and a selectivity
of more than 95% toward 2-butene within the butene fraction
[
24]
the isomerized internal alkene, as shown in Scheme 2.
(
Figure 4).
Within the first 10 h, the conversion decreased slowly. After
this period, a rapid decrease in conversion was observed. This
decrease in conversion was accompanied by an increase in se-
lectivity toward butene, whereas the isomerization activity of
1
-butene to 2-butene decreased, which is reflected in the se-
Scheme 2. Isomerization of 1-butene to 2-butene via recoordination of
formed 1-butene to the NiꢀP^O complex.
lectivity toward 2-butene within the butene fraction.
The unusual trend in the selectivity toward butenes stems
from the discontinuous removal of high-boiling alkenes in the
condenser (Figure 3). During the experiment, high-boiling by-
products accumulated in the condenser. With decreasing con-
version, these high-boiling byproducts were stripped out by
the gas flow, which results in lower selectivity toward butene.
To elucidate the reason for the decrease in catalytic activity,
the temperature at the top end of the fixed bed (Ttop) and the
temperature at the bottom end of the fixed bed (Tbottom) were
measured over time with two thermocouples (Figure 5). At the
beginning of the reaction, a significant increase in temperature
from Tinitial =408C to Ttop =598C was observed whereas Tbottom
increased to only 428C. After that, Ttop decreased quickly, ap-
Owing to their ionic nature, these nickel complexes can be
[
25–28]
dissolved in ionic liquids.
By dispersing these ionic liquid
catalyst solutions on a highly porous inorganic support, new
solid materials that can be handled like classical heteroge-
[
29,30]
neous catalysts are obtained.
These supported ionic liquid
phase (SILP) catalysts have been used in various reactions,
[
31]
both in liquid and in gas phase contact. Owing to the ex-
tremely low volatility of ionic liquids, the SILP concept is ideally
[
32]
suited for continuous gas phase processes.
report on the use of different cationic nickel complexes
shown in Figure 1) immobilized in SILP systems (Figure 2) for
the gas phase dimerization and isomerization of ethylene to
Herein, we
(
proximating T , and T
increased slowly. At the same time
bottom
c
2
-butene.
at which Tbottom reached the maximum temperature (568C),
conversion decreased. The observed trend in temperature indi-
cates the deactivation of the catalyst by a migrating reaction/
deactivation front, as schematically depicted in Figure 6. This
migrating reaction/deactivation front started at the top end of
the fixed bed, at which ethylene reached the catalyst bed first.
Owing to the high catalytic activity of the nickel complex 1,
a full conversion of ethylene occurred in this uppermost layer
of the fixed bed. Thus, the major part of the reaction heat
The ionic liquid 3-ethyl-1-methylimidazolium tris(penta-
fluoroethyl)trifluorophosphate ([EMIM][FAP]) was chosen be-
cause of its low coordination strength toward the nickel cen-
[
33]
tral atom.
ꢀ
1
(
DH =ꢀ112.3 kJmol ) was released in this layer and a temper-
R
ature hot spot was formed, which resulted in the thermal de-
activation of complex 1. Owing to this catalyst deactivation,
the activity and thus the temperature in this layer decreased
and the reaction front migrated to the next layer of the cata-
lyst bed, which again induced an
Figure 1. Cationic methallyl nickel(II) complexes used herein.
increase in temperature and cat-
alyst deactivation. In this
manner, a reaction/deactivation
front migrated through the
entire fixed bed until it reached
the bottom.
The calculated average turn-
over frequency (TOF) of complex
1
in the region of full conversion
ꢀ
1
was 520 molbutene molNi
. With
the assumption that only a frac-
tion of the catalyst complexes is
Figure 2. Schematic representation of the SILP catalyst systems used herein.
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than the maximum temperature
of 598C measured in the dimeri-
zation experiment. This is true
for the precursor complex
1
only, not for the active NiꢀH
species. Because complex 1 dem-
onstrated good activity and se-
lectivity toward
2-butenes but lacked a long-
term stability, the following ex-
periments aimed at the improve-
ment in catalyst stability through
dilution and efficient heat re-
moval.
The first attempt to improve
the catalyst stability focused on
the prevention of hot spot for-
mation by decreasing the cata-
lytic activity of the SILP particles.
Therefore, the nickel loading wNi
of the SILP particles was de-
creased from 0.250 to 0.125 and
Figure 3. Flow scheme of the continuous gas phase dimerization rig.
0.083 wt%. The total amount of
Figure 5. Dimerization of ethylene to 2-butene: conversion of ethylene (
top (a), and Tbottom (c) versus time at T =408C. Conditions: SILP materi-
al includes complex 1, [EMIM][FAP], silica gel 100 (calcined at 6008C),
Ni =0.25 wt%, and aIL =30 vol%. Reaction conditions: T =408C,
P=0.1 MPa, t=8 s, volume flow of ethylene=23.1 NmLmin , and amount
of nickel=3.275 mg.
&
),
T
c
Figure 4. Dimerization of ethylene to 2-butene: conversion of ethylene (
selectivity toward butenes (1- and 2-butene; ~), and selectivity toward
2
&
),
w
c
-butene within the butene fraction (!) versus time. Conditions: SILP mate-
rial includes complex 1, [EMIM][FAP], silica gel 100 (calcined at 6008C),
Ni =0.25 wt%, and aIL =30 vol%. Reaction conditions: T =408C,
P=0.1 MPa, t=8 s, volume flow of ethylene=23.1 NmLmin , and amount
of nickel=3.275 mg.
ꢀ
1
w
c
ꢀ
1
nickel in the reactor was kept constant at 3.275 mg for each
experiment. Consequently, in experiments with lower nickel
loadings, the total amount of the used SILP catalyst was in-
creased. A plot of the conversion of ethylene and the corre-
sponding Tbottom versus reaction time is shown in Figure 7 (for
the position of Tbottom, see Figure 6). The decrease in the nickel
loading resulted in a lower hot spot temperature, but only in
a slight increase in catalyst lifetime.
active at a specific time, the real TOF should be much higher.
To determine the critical decomposition temperature of
complex 1, the NMR spectra of the complex dissolved in C D6
6
were measured while increasing the temperature of the solu-
tion stepwise from 25 to 608C in the presence of 1,5-cycloocta-
diene to imitate reaction conditions (see the Supporting Infor-
mation). Because no change in the NMR spectra could be ob-
served, it was assumed that the deactivation temperature of
complex 1 was higher than 608C and was thus also higher
A possible reason for this observation could be the higher
amount of the support (silica gel 100) in the reactor at lower
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by induced deactivation could
have counterbalanced the posi-
tive effect of a lower hot spot
temperature on catalyst stability.
A
clear correlation between
nickel loading and overall selec-
tivity toward butenes could not
be detected, and the overall
fraction of 2-butene within the
butenes remained unchanged
(
Table 1, entries 1–3).
Another attempt to improve
the stability of the catalytic
system consisted in increasing
the ionic liquid loading (a ) of
IL
the SILP catalyst. The goal was
to decrease the catalytic activity
by blocking the transport pores
inside the SILP particle while of-
Figure 6. Schematic representation of the reaction/deactivation front moving through the fixed SILP catalyst bed.
fering more ionic liquid for heat removal. The SILP catalysts
with an ionic liquid loading of 30, 60, and 90 vol% were tested
(
Table 1, entries 1, 4, and 5). As in the previous experiments,
the total amount of nickel in the reactor was kept constant at
.275 mg. A plot of the conversion of ethylene and Tbottom
3
versus reaction time is shown in Figure 8. A higher ionic liquid
loading resulted in increased catalyst lifetime, and the turnover
number (TON) increased linearly with the ionic liquid loading
(
Table 1, entries 1, 4, and 5). Given Tbottom, the maximum tem-
perature obtained decreased slightly with increasing ionic
liquid loading (568C for a =30 vol%, 548C for a =60 vol%,
IL
IL
and 538C for a =90 vol%), which indicates that the catalytic
IL
activity of the SILP particles was decreased. Higher ionic liquid
loadings resulted in a higher ionic liquid film thickness on the
surface of the silica support and a partial filling of the pores
combined with longer diffusion paths for the substrate ethyl-
ene. For this reason, the availability of ethylene within the
ionic liquid was lowered. Moreover, because the nickel loading
of the SILP particles was kept constant, the concentration of
complex 1 in the ionic liquid also decreased with increasing
Figure 7. Variation in wNi at an overall identical amount of Ni: ethylene con-
version ( ) and Tbottom (c) versus time: wNi =0.25 wt% ( ); wNi =0.125 wt%
*); wNi =0.083 wt% (~). Conditions: SILP material includes complex 1,
EMIM][FAP], silica gel 100 (calcined at 6008C), and aIL =30 vol%. Reaction
=408C, P=0.1 MPa, t=8 s, volume flow of ethyl-
&
&
(
[
conditions: T
ene=23.1 NmLmin , and amount of nickel=3.275 mg.
c
ꢀ
1
nickel loadings. Complex 1 is
sensitive not only to high tem-
peratures but also to air and
water.
Table 1. Variation in cooling temperature, Ni complex, Ni loading, and IL loading in the SILP-catalyzed dimeri-
zation/isomerization of ethylene to 2-butene along with overall selectivity toward butene (1-butene and
2
-butene), fraction of 2-butene in C4 products, and TON.
Entry
T
[8C]
c
Catalyst
w
[wt%]
Ni
a
IL
V˙
S
butenes
S
2-butene
TON
[molbutene molNi ]
ꢀ1
ꢀ1
Although the support was cal-
cined and dried in vacuum
before use, it presumably still
possessed a certain number of
hydrophilic surface groups and
traces of water adsorbed on its
surface. With a lower nickel load-
ing, the ratio of complex 1 to
these hydrophilic groups and
water traces increased, which re-
sulted in a partial deactivation of
the catalyst complex. The there-
[vol%]
[NmLmin
]
[wt%]
[wt%]
[a]
3
1
40
40
40
40
40
25
19
15
19
19
1
1
1
1
1
1
1
1
2
3
0.25
0.125
0.083
0.25
0.25
0.25
0.25
0.25
0.25
0.25
30
30
30
60
90
30
30
30
30
30
23.1
23.1
23.1
23.1
23.1
23.1
23.1
23.1
23.1
23.1
89.2
91.8
90.5
88.0
85.7
78.6
65.1
53.2
73.5
68.5
95.0
95.0
95.1
95.3
95.0
94.8
95.4
94.4
96.8
96.3
8.51ꢁ10
9.03ꢁ10
1.04ꢁ10
1.74ꢁ10
2.74ꢁ10
3.56ꢁ10
5.33ꢁ10
4.58ꢁ10
[
[
[
[
a]
a]
a]
a]
3
2
3
4
5
6
7
8
9
1
4
4
4
[b]
4
[
[
[
b]
b]
b]
[
4
4
4
3.47ꢁ10
9.77ꢁ10
b]
4
0
[a] Selectivity and TON calculated at a conversion of 50%; [b] Selectivity and TON calculated at a conversion of
9
5%.
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Figure 8. Variation in aIL: conversion of ethylene ( ) and Tbottom (c) versus
&
time. aIL =30 vol% (
material includes complex 1, [EMIM][FAP], silica gel 100 (calcined at 6008C),
and wNi =0.25 wt%. Reaction conditions: T =408C, P=0.1 MPa, t=8 s,
&
); aIL =60 vol% (*); aIL =90 vol% (~). Conditions: SILP
Figure 9. Variation in T
=258C (*); T
=198C (~); T
c
c
: conversion of ethylene versus time: T
c
=408C (
&
);
T
c
c
=158C (!). Conditions: SILP material includes
complex 1, [EMIM][FAP], silica gel 100 (calcined at 6008C), wNi =0.25 wt%,
and aIL =30 vol%. Reaction conditions: P=0.1 MPa, t=8 s, volume flow of
c
ꢀ
1
volume flow of ethylene=23.1 NmLmin , and amount of nick-
el=3.275 mg.
ꢀ1
ethylene=23.1 NmLmin , and amount of nickel=3.275 mg.
ionic liquid loading. Both the lower availability of ethylene and
the lower concentration of complex 1 in the ionic liquid result-
ed in the desired moderation of the catalytic activity and heat
formation in the SILP particles.
fraction of higher alkenes (mainly hexene and octene isomers)
increased (Table 1, entries 1 and 6–8). These higher alkenes
were isolated from the product gas stream with a condenser
installed downstream to the reactor (Figure 3). In this way, un-
wanted condensation of these higher-boiling products in other
parts of the test rig could be avoided. Regarding the produc-
tion of butenes per mole of nickel, the decreasing selectivity
toward butene counterbalances the increased catalyst lifetime
at low cooling temperatures. For this reason, the TON in-
Another reason for the increased catalyst lifetime could be
an improved thermal conductivity within the SILP particles, as
pores filled with ionic liquid conduct heat better than empty
pores. A higher thermal conductivity leads to a better distribu-
tion of the released reaction heat. The ionic liquid loading
demonstrated no effect on the isomerization activity of the
catalyst, whereas the selectivity toward butenes decreased
slightly with increasing ionic liquid loading (Table 1, entries 1,
ꢀ
1
creased to 53300 molbutene molNi with a decrease in T from 40
c
to 198C (Table 1, entry 7), whereas a decrease in T to 158C de-
c
ꢀ
1
creased the TON to 45800 molbutene molNi (Table 1, entry 8).
The probability of chain termination decreases at lower cool-
ing temperatures, and this triggers the production of a higher
share of hexenes and octenes. In addition, lower temperatures
lead to a higher solubility of the formed olefins in the ionic
liquid film and even partial condensation within the pores of
the SILP catalyst. The isomerization activity was unaffected by
the cooling temperature.
4, and 5). The decreased selectivity toward butenes can be due
to the longer diffusion paths at higher ionic liquid loadings.
Owing to longer diffusion paths, the formed butenes remain in
the ionic liquid for a longer time and the probability of consec-
utive reinsertion into complex 1 combined with the formation
of higher olefin increases.
Furthermore, the reaction temperature was decreased by de-
creasing T (Table 1, entries 1 and 6–8). The effect of decreasing
Because complex 1 was prone to temperature-induced deac-
tivation, a structural modification of the ligand was attempted
to increase complex stability. For cationic nickel complexes,
little is known about the details of the observed decomposi-
tion mechanism. Even in the case of neutral SHOP-type nickel
complexes (SHOP=Shell higher olefin process), only a few in-
vestigations concerning deactivation pathways have been pub-
lished. Gibson et al. proposed the formation of nickel dimers
induced by the coordination of the oxygen atom of a nickel
P^O entity to a second nickel center belonging to a 14-elec-
c
Tc on catalyst lifetime is illustrated in Figure 9. For the SILP cat-
alyst complex 1 tested at T =408C, the conversion of ethylene
c
decreased after 10 h; however, the same system revealed a sig-
nificantly increased catalyst lifetime when cooled at T =258C
c
under otherwise identical reaction conditions. The phase of
stable catalytic performance could be prolonged by more than
7
0 h in the latter case. By further decreasing T to 19 and 158C,
c
a stable phase of more than 120 and 130 h, respectively, could
be achieved. Because the increase in catalyst lifetime was only
[34]
marginal with a decrease in T from 19 to 158C, a further de-
tron Ni(P,O)R species. In addition, the formation of oxygen-
c
[35,36]
crease in T appeared unreasonable considering catalyst stabili-
stabilized dimers was demonstrated by Klabunde.
Berke-
c
ty. In contrast, a lower T decreased the selectivity toward bu-
feld and Mecking investigated the deactivation of a neutral
nickel complex with a N^O ligand and demonstrated that the
deactivation occurs through the bimolecular elimination of an
alkane from the reaction of nickel alkyl species with nickel hy-
c
tenes significantly while having a positive effect on catalyst
stability. By decreasing T from 40 to 158C, the overall selectivi-
c
ty toward butenes decreased from 89.2 to 53.2 wt%. Thus, the
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[
37]
dride species. The formation of dimers is likewise conceiv-
able as deactivation mechanism for the used cationic nickel
complexes with P^O chelating ligands. To circumvent the pro-
posed dimer formation, the steric hindrance in the coordina-
tion sphere of the complex was increased by the introduction
of sterically more demanding moieties. Therefore, the methyl
group of complex 1 was replaced by a n-decyl group in com-
plex 2 and by a 2,6-methylphenyl group in complex 3
were dissolved and deposited as thin films of 3-ethyl-1-methyl-
imidazolium tris(pentafluoroethyl)trifluorophosphate ionic liq-
uids dispersed on porous silica gel 100. The obtained catalysts
are highly active and selective for the formation of 2-butene,
which makes them important for an ethylene-to-propylene
cascade reaction consisting of dimerization/isomerization and
metathesis. Owing to the high activity and the strong exother-
micity of the dimerization reaction, significant hot spot forma-
tion was observed inside the catalytic fixed bed containing the
SILP catalyst. These hot spots resulted in the deactivation and
decomposition of the temperature-sensitive nickel catalysts.
Engineering approaches have been tested to decrease the
temperature increase inside the catalyst bed. By decreasing
the cooling temperature to 198C, the catalyst lifetime could be
increased to 120 h time on stream, which correlated with
(Figure 1).
The effect of the ligand structure on the catalyst lifetime is
illustrated in Figure 10. The performance of all nickel com-
plexes has been compared while keeping the reaction condi-
tions and SILP compositions constant. Complex 2 was signifi-
cantly less stable than complex 1, whereas the catalyst lifetime
was doubled by using complex 3 with the 2,6-methylphenyl
ꢀ
1
ꢀ1
group. Complex 3 achieved a TON of 97700 molbutene molNi
.
a turnover number of more than 53300 molbutene molNi . At the
Complexes 2 and 3 demonstrated a slightly higher selectivity
toward butenes than did complex 1 (Table 1, entries 7, 9, and
same time, the lower reaction temperature led to an increased
formation of C4+ alkenes and to product condensation inside
the pores of the SILP catalyst. Further improvement in the cat-
alyst stability was achieved through ligand modification. With
complex 3, the overall turnover number could be increased to
10).
ꢀ
1
97700 molbutene molNi without any compromise on the selec-
tivity toward 2-butene.
Experimental Section
The synthesis of the cationic nickel complexes was performed
under nitrogen by using standard Schlenk techniques or in a nitro-
gen-filled glove box (MBRAUN, Germany). Methallylnickel chloride
dimer was purchased from Strem Chemicals (USA), and the (2-me-
thoxyphenyl)diphenylphosphine ligand of complex 1 was pur-
chased from Sigma–Aldrich. Detailed information on the used P^O
ligands is given in the Supporting Information.
All air- and moisture-sensitive experiments were performed under
nitrogen by using standard Schlenk techniques or in a nitrogen-
filled glove box (MBRAUN). Chlorodiphenylphosphine, n-butyllithi-
um (1.6m solution in hexane), N,N,N’,N’-tetramethylethylenedi-
amine, and N-methyl-2-pyrrolidinone that were protected under
argon were purchased from Acros and used as received.
Figure 10. Comparison of different cationic NiꢀP^O complexes in the dime-
rization/isomerization of ethylene: conversion of ethylene: complex 1 ( );
complex 2 (*); complex 3 (~). Conditions: SILP material includes [EMIM]-
FAP], silica gel 100 (calcined at 6008C), wNi =0.25 wt%, and aIL =30 vol%.
Reaction conditions: T =198C, P=0.1 MPa, t=8 s, volume flow of ethyle-
&
[
c
The dimerization experiments were performed with pure ethylene
ꢀ
1
ne=23.1 NmLmin , and amount of nickel=3.275 mg.
(3.0, purity 99.9%, Linde Gas AG, Germany). Helium (4.6, purity
9
9.996%, Linde Gas AG) was used for the inertization of the reac-
tor. [EMIM][FAP] (purity ꢁ99.0%, water content ꢂ100 ppm, halide
content ꢂ100 ppm, Merck KGaA, Germany) was used as an ionic
liquid for the SILP system. Silica gel 100 (Merck KGaA) was used as
a support material for the SILP system. Before use, the support ma-
terial was calcined under nitrogen according to the following
method: The partial dehydroxylation was performed by heating
In addition, the isomerization activity of complexes 2 and 3
increased slightly than that of complex 1. This result indicates
that the presence of a sterically more demanding group at the
oxygen atom of the P^O chelating ligand of complex 3 does
not hinder the reinsertion of 1-butene, a prerequisite for the
isomerization to 2-butene. The higher C4 selectivity indicates
that a simultaneous coordination of ethylene to the nickel–
butyl complex of 2 and 3 is disfavored, as such coordination
would be necessary for the formation of longer-chain olefins.
ꢀ
1
the material from RT to 1508C (heating rate: 48Cmin ). To avoid
sintering of the wet material by further heating, the temperature
was kept constant for 2 h to remove water slowly out of the pores.
Afterward, the support was heated up to 6008C (heating rate:
ꢀ1
4
8Cmin ). Before the material finally cooled down to RT, the tem-
perature of 6008C was maintained for another 12 h. The pretreated
material was evacuated overnight and eventually stored in a glove
box. The properties of silica gel 100 were determined with Quan-
tachrome’s Quadrasorb SI instrument and are summarized in
Table 2. Dry dichloromethane (water <0.004%, Merck KGaA) was
used as a solvent for the preparation of the SILP catalyst.
Conclusions
We report the immobilization of cationic nickel complexes on
supported ionic liquid phase (SILP) materials for the catalytic
dimerization of ethylene. The cationic nickel complexes used
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 162 – 169 167

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1
.4541) had a height of 285 mm, an inner diameter of 10 mm, and
Table 2. Properties of the support material silica gel 100.
a wall thickness of 6.5 mm. The fixation of the SILP catalyst was fa-
cilitated by a metal frit at the bottom end of the reactor. Because
the dimerization of ethylene is an exothermic reaction, the reactor
was cooled and the cooling temperature was adjusted with a cryo-
stat. The temperature within the catalyst bed was measured with
two thermocouples installed at the top end and the bottom end
of the catalyst bed. A condenser was installed downstream to the
reactor to prevent condensation of high-boiling products in other
parts of the test rig. The condenser was directly connected to the
tubular reactor. It consisted of a slant double wall pipe into which
the formed liquid product was brought by the gaseous volume
flow. Cooling of this pipe with a cryostat led to the condensation
of the longer-chain products and their accumulation at the bottom
end of the tube, whereas the short chain products left the con-
denser as gas via a branched connection at the upper end of the
tube. To avoid an overtopping, the condenser (V=15 mL) had to
be emptied from time to time. The mass of the liquid product was
determined, and the composition was analyzed in an off-line gas
chromatograph (GC).
Particle size
mm]
BET surface
area
BJH cumulative
pore volume
Average pore
diameter
[nm]
2
ꢀ1
3
ꢀ1
[
[m g
]
[cm g
]
70–200
346.2
0.972
10
1
The H NMR spectra were recorded on a JEOL 400 MHz spectrome-
ter operating at respective frequencies of 399.782 MHz with
13
a probe temperature of 238C. The C NMR spectra were recorded
on JEOL 400 MHz spectrometer operating at respective frequencies
of 100.525 MHz with a probe temperature of 238C. Chemical shifts
were reported relative to the peak for SiMe by using H (residual)
chemical shifts of the solvent as a secondary standard. The results
of elemental analysis and HRMS were obtained from the Analytical
Laboratories at the Friedrich Alexander University Erlangen Nꢂrn-
berg (Erlangen, Germany).
1
4
The synthesis of the cationic nickel complexes used herein was
performed according to the following method known from the lit-
erature (for detail, see the Supporting Information).
Before loading the tubular reactor with the SILP catalyst under
a permanent helium counterflow, the complete rig was flushed
with helium for 2 h to ensure an oxygen- and water-free atmo-
sphere. The reactor was brought to the desired reaction tempera-
ture either by heating or by cooling while maintaining a constant
[
38–40]
The P^O
ligand (2 equiv.) in dichloromethane (5 mL) was added to a solution
of methallylnickel chloride dimer in dry dichloromethane at a tem-
perature ranging from ꢀ10 to ꢀ208C. The resulting red-orange
suspension was stirred for 30 min, and then AgSbF (2 equiv.) in di-
ꢀ1
6
helium flow of 100 mLmin . As soon as the reaction temperature
chloromethane (5 mL) was added. The colorless AgCl precipitated
immediately and was filtered through Celite under argon. The clear
yellow solution was evaporated at ꢀ208C, and the residual solid
was washed with cold diethyl ether and n-pentane. The product
was dried in high vacuum at 08C and stored at ꢀ208C.
was reached, the temperature records of both thermocouples were
combined with the initiation of the reaction by turning of the
helium feed and starting to dose ethylene in the respective volu-
metric flow. At the same time, the GC was started for the analysis
of the product mixture.
Detailed information on the synthesis of the (2-(decyloxy)phenyl)di-
phenylphosphine (complex 2) and (2-(2,6-dimethylphenoxy)phe-
nyl)diphenylphosphine (complex 3) ligands as well as on the syn-
thesis of the cationic nickel complexes is given in the Supporting
Information.
After passing the condenser, the product flow was heated up to
1
208C to circumvent the condensation of possible longer-chain al-
kenes. The composition of the product flow was determined with
an online 7820A GC (Agilent Technology, USA). Each compound
was separated with the CP7531 wall-coated open tubular fused
silica column (50 mꢁ0.21 mm, Varian, USA). The products were an-
alyzed with a flame ionization detector. The obtained peaks were
automatically integrated with the Agilent EZChrom Elite software.
The equations for calculating conversion, selectivity, TOFs, and
TONs are given in the Supporting Information. The composition of
the liquid product in the condenser was analyzed in an off-line
For the preparation of the SILP catalyst, the cationic nickel catalyst
complex, ionic liquid, silica support, and dichloromethane were
mixed together under argon by using standard Schlenk tech-
niques. The relevant amount of the [EMIM][FAP] ionic liquid was
dissolved in dichloromethane (20 mL) with continuous stirring.
After complete dissolution of the ionic liquid, the nickel catalyst
complex was added, which produced a yellow solution. Finally, cal-
cined silica gel 100 was added to the solution and stirred for an-
other 10 min. The slurry medium was subsequently evaporated
3
900 GC (Varian) with a CP-Sil PONA CB column (50 mꢁ0.21 mm).
under vacuum to remove the dichloromethane and obtain a free- Acknowledgements
flowing powder. The amount of the ionic liquid and the silica sup-
port depended on the ionic liquid loading a and the nickel load-
IL
We gratefully acknowledge the funding of the German Research
ing w , respectively [see Eqs (1) and (2)].
Ni
Council (DFG), which, within the framework of its “Excellence Ini-
tiative,” supports the Cluster of Excellence “Engineering of Ad-
vanced Materials” (www.eam.uni-erlangen.de) at the University of
Erlangen-Nuremberg. We especially thank Dr. Nicola Taccardi for
assistance in the synthesis of the nickel complexes.
VIL
a ¼
ꢃ 100%
ꢃ 100%
ð1Þ
ð2Þ
IL
Vpore;total
mNi
wNi ¼ m
SiO2;total
The standard values were a =30 vol% and w =0.25 wt% corre-
IL
Ni
Keywords: gas phase reactions · ionic liquids · ligand effects ·
nickel · supported catalysts
sponding to an amount of 0.654 g of ionic liquid and 3.275 mg of
nickel for an amount of 1.310 g of silica support. The produced
SILP catalyst was introduced directly into the rig for catalyst test-
ing.
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Received: July 31, 2013
Published online on November 7, 2013
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 162 – 169 169