Isomerization of 1-Butene to 2-Butene Catalyzed by Metal-Organic Frameworks

Article abstract of DOI:10.1021/acs.organomet.9b00599

MIL-100 and MIL-101 were synthesized and evacuated to generate a series of heterogeneous catalysts for isomerization of 1-butene. Their crystal structures and pore properties were characterized by PXRD and nitrogen adsorption-desorption techniques. These catalysts showed high catalytic activity for isomerization of 1-butene and high selectivities for 2-butene at room temperature. Moreover, the MIL-101 (Cr) catalyst evacuated at 200 °C exhibited the largest BET surface area of 2759 m² g^-1. At the same time, conversion of 1-butene and the highest selectivity to 2-butene were up to 93.38% and 98.08%, respectively. This work indicated that MOFs containing coordinatively unsaturated metal sites might be promising catalysts for olefin isomerization under mild conditions.

Full text of DOI:10.1021/acs.organomet.9b00599

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Isomerization of 1‑Butene to 2‑Butene Catalyzed by Metal−Organic
Frameworks
,
†
,†,‡
†
†
†
‡
Donghai Sheng,* Ying Zhang,*
Qingxiang Song, Guang Xu, Dandan Peng, Heqian Hou,
‡
‡
†
Ronggui Xie, Dongming Shan, and Pengxiao Liu
†
‡
The State Key Laboratory of Heavy Oil Processing and Department of Materials Science and Engineering, China University of
Petroleum, Changping District, Beijing 102249, P. R. China
*
S Supporting Information
ABSTRACT: MIL-100 and MIL-101 were synthesized and
evacuated to generate a series of heterogeneous catalysts for
isomerization of 1-butene. Their crystal structures and pore
properties were characterized by PXRD and nitrogen
adsorption−desorption techniques. These catalysts showed
high catalytic activity for isomerization of 1-butene and high
selectivities for 2-butene at room temperature. Moreover, the
MIL-101 (Cr) catalyst evacuated at 200 °C exhibited the
2
−1
largest BET surface area of 2759 m g . At the same time,
conversion of 1-butene and the highest selectivity to 2-butene
were up to 93.38% and 98.08%, respectively. This work
indicated that MOFs containing coordinatively unsaturated
metal sites might be promising catalysts for olefin isomerization
under mild conditions.
INTRODUCTION
resulting in the reduction of catalytic activity or even
deactivation. Highly active, recyclable, and environmentally
friendly catalysts for butene isomerization under mild reaction
conditions are extremely desirable but challenging.
■
7
As environmental requirements have become more stringent,
methyl tert-butyl ether (MTBE) has been banned as a gasoline
additive in some developed countries and regions due to
1
Metal−organic frameworks (MOFs) are a new family of
crystalline porous materials formed by self-assembly of organic
ligands and metal ions. Due to their special periodic structures,
large specific surface areas, high porosity, and unique
adsorption properties, they have been widely applied in
contamination of groundwater as a carcinogen. Isooctane is
regarded as an ideal alternative component with a high octane
number. At present, in industry isooctane is obtained through
alkylation of butene with isobutane. Because the alkylation of
2
-butene or isobutene with isobutane produces isooctane with
8
storage, adsorption, electrochemistry, and catalysis. In
a higher octane number, 1-butene is usually isomerized to 2-
butene or isobutene, which is then alkylated with isobutane to
obtain isooctane.
The isomerization of 1-butene has attracted wide interest
from the perspectives of commercial demand and catalytic
issues. A large amount of catalysts have been reported for the
particular, some MOFs possess coordinatively unsaturated
metal sites (CUS), which are evenly and stably distributed due
to the crystalline nature of MOFs. These CUS can interact
with guest molecules in adsorption and catalysis and serve as
catalytic active sites. As far as we know, it has not been
reported that MOFs with CUS are used as catalysts in olefin
isomerization.
2
3
reaction, such as liquid and solid acids, metal halide, and
zeolite molecular sieves. They are all acidic catalysts with
4
In this paper, two common types of MOFs with zeolite-type
architecture, i.e., MIL-100 (Fe and Cr) and MIL-101 (Fe and
Cr) have been used to catalyze the isomerization of 1-butene.
The MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr) are
heated under vacuum to produce high content of CUS. The
CUS-containing MIL-100 (Fe and Cr) and MIL-101 (Fe and
Cr) can isomerize 1-butene to 2-butene and isobutene almost
completely at room temperature and 10 atm, and the
selectivity to 2-butene is as high as 98%. Furthermore, the
different acid centers, acid types, acid intensity, and
distribution of acidic sites. Generally, the butene isomer-
5
ization reaction is carried out following a single molecule
6
carbon cation mechanism, and reaction conditions are harsh,
requiring high temperature and high pressure.
Additionally, liquid and solid acid catalysts have obvious
disadvantages such as serious corrosion of equipment, difficulty
in recovery, and large environmental pollution. Metal halide
catalysts are sensitive to water in the feedstream and the
presence of water can lead to halogen elution, thereby
decreasing the catalytic activity. For widely used zeolite
molecular sieve catalysts, carbon deposition is a major concern
Received: August 31, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00599
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Article
MIL-101 (Cr) catalyst can be recycled at least four times
maintaining most of its original catalytic activity. Finally, the
catalytic mechanism for the isomerization of 1-butene to 2-
9
butene is discussed.
RESULTS AND DISCUSSION
■
Characterization of the Catalysts. For the as-synthesized
MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr), inorganic
metal ions and organic ligands are coordinatively bonded to
each other to form network structures with abundant pores,
and these pores are occupied by free water molecules, bound
water molecules, and F− or OH− counteranions. After the
removal of the guest molecules, MIL-100 (Fe and Cr) has two
types of mesoporous cages with free internal diameters of 2.5
and 2.9 nm, respectively. The large cage has a window opening
of 0.86 nm × 0.86 nm and the small cage has a window
10
opening of 0.55 nm × 0.55 nm. MIL-101 (Fe and Cr)
possess two larger mesoporous cages with free internal
diameters of 2.9 and 3.4 nm and window openings of 1.2
10
nm × 1.2 and 1.6 nm × 1.6 nm, respectively.
The structural units of MIL-100 (Fe and Cr) and MIL-101
(
Fe and Cr) are μ -oxo-centered trimers of Fe (III) or Cr (III)
3
octahedra. At the end of the octahedron of per trimer, there are
−
−
two bound H O molecules and one F or OH group. The
2
free water molecules located in pores can be easily removed by
heating under vacuum below 100 °C, while the terminal bound
water molecules can be removed at more than 100 °C under
11
vacuum, forming a lot of CUS in the structure.
Figure 1. (A) PXRD patterns of the as-synthesized (a) MIL-100 (Fe),
(b) MIL-101 (Fe), (c) MIL-100 (Cr), and (d) MIL-101 (Cr). (B)
PXRD patterns of (a) MIL-100 (Fe) evacuated at 250 °C, (b) MIL-
The powder X-ray diffraction (PXRD) patterns of the as-
syntheszied MIL-100 (Fe), MIL-101 (Fe), MIL-100 (Cr), and
MIL-101 (Cr) were consistent with the simulated data
reported in the literature (Figure 1A and Figure S1),
confirming the pure phase. Fourier transformation infrared
spectra (FT-IR) characterization results showed the presence
of the characteristic vibration bands of carboxylic groups in the
MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr) frameworks
at 1630 and 1400 cm− in Figure S3, confirming that the
carboxylic groups were coordinated to the metal ions in the
frameworks. Large bands around 3500 cm− also confirmed the
presence of an amount of water molecules in the four samples.
In order to give a reference for the choice of treatment
temperature to remove water molecules in the pore channels
and thus expose CUS, thermal gravimetric analysis (TGA) of
MIL-101 (Fe and Cr) and MIL-101 (Fe and Cr) was
performed in nitrogen atmosphere. TGA results revealed that
there were weight losses from approximately 40−150 °C for
the as-synthesized samples, which could be attributed to the
release of the guest water molecules. Another weight loss from
approximately 350−550 °C was due to decomposition of the
101 (Fe) evacuated at 200 °C, (c) MIL-100 (Cr) evacuated at 250
°
C, and (d) MIL-101 (Cr) evacuated at 200 °C.
We treated MIL-101 (Fe) and MIL-101 (Cr) under vacuum
from 160 to 220 °C (Figure S2a,b) and found that when the
evacuation temperature was 200 °C, MIL-101 (Fe and Cr) had
the strongest diffraction peaks. However, when the evacuation
temperature was increased to 220 °C, the diffraction peak at 2θ
= 5.10° disappeared, indicating that the crystal structure was
destroyed. Therefore, the optimal evacuation temperatures for
MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr) were 250 and
200 °C, respectively. The PXRD of MIL-100 and MIL-101 (Fe
and Cr) evacuated under optimal temperatures were shown in
Figure 1B. The evacuated MIL-100 (Fe and Cr) and MIL-101
(Fe and Cr) samples maintained all the diffraction peaks for
the corresponding as-synthesized samples, showing that the
crystal structures were intact.
1
1
The nitrogen adsorption−desorption isotherms were meas-
ured for MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr)
evacuated under optimal temperatures at 77 K and shown in
Figure S5. All evacuated samples showed a typical type-I
isotherm with the presence of both micropores and mesopores.
As shown in Table S1, the MIL-100 (Fe) and MIL-100 (Cr)
−
−
whole framework and the departure of OH /F groups. The
moisture contents of MIL-100 (Fe and Cr) and MIL-101 (Fe
and Cr) were widely varied from 10% to 25% in Figure S4,
depending on the coordinating water molecules and laboratory
humidity. Based on the TGA, the appropriate evacuation
temperature range for the samples was 150−350 °C.
2
−1
displayed the BET areas of 1920 and 2340 m ·g and the pore
3
−1
volumes of 0.92 and 1.32 cm ·g , respectively. For MIL-101
12
According to the literature reports, when MIL-100 (Fe)
and MIL-100 (Cr) were evacuated from 150 to 250 °C, the
diffraction peaks and specific surface areas gradually became
strong. The higher evacuation temperature than 250 °C
resulted in the decrease of PXRD peak intensity and specific
surface areas. MIL-100 had the largest specific surface areas,
the strongest diffraction peaks, and thus the highest
crystallinity when the evacuation temperature was 250 °C.
(Fe) and MIL-101 (Cr), the BET areas were 2010 and 2759
2
−1
3
−1
m ·g , and the pore volumes were 1.09 and 1.98 cm ·g ,
respectively.
Isomerization of 1-Butene. The catalytic performances of
evacuated MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr) for
the isomerization of 1-butene were investigated. The
conversion percentage of 1-butene and the amounts of
isomerization products and selectivity of 2-butene were
B
DOI: 10.1021/acs.organomet.9b00599
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shown in Figure 2 and Figure S6 and Table S2. MIL-100 (Fe
and Cr) and MIL-101 (Fe and Cr) catalysts could catalyze the
faster reaction rates and higher conversion percentages of 1-
butene, but the same selectivities for 2-butene. The faster
reaction rate and higher conversion percentages were possibly
because more 1-butene molecules entered the catalyst pores at
high pressure, which greatly increased the concentration of 1-
butene as well as the contact chances between 1-butene and
CUS of catalysts. Additionally, the reaction pressure had little
effect on the catalytic selectivity, suggesting the same catalytic
mechanism was followed under 1 and 10 atm.
The equilibrium catalytic performances of the four MIL-100
Fe and Cr) and MIL-101 (Fe and Cr) catalysts at 24 h under
(
1
1
0 atm as well as other reported catalysts for isomerization of
-butene were listed in Table 1. For montmorillonite K10 and
H SO (3 M) catalysts, the conversion percentages of 1-butene
2
4
and the selectivity of 2-butene were 74.44% and 94.68% at 400
1
3
°
C, respectively. For the MeCl/BeO catalyst, the conversion
percentages of 1-butene and the selectivity of isobutylene were
9.20% and 76.20% at 430 °C, respectively. H-HPM-1
14
2
zeolites were used as catalysts and the conversion percentages
of 1-butene and the selectivity of isobutylene were 61.19% and
15
9
7.00% at 400 °C, respectively. Notably, the MOF catalysts
in this paper showed the conversion percentages of 1-butene
and selectivity of 2-butene over 92.00% and 91.00%,
respectively. Moreover, the MOFs catalysts were relatively
environmentally friendly and the reaction conditions were
mild.
Comparing the isomerization performances of the four
MOFs catalysts (Table S2), we found that the Fe-containing
MOFs had higher conversion of 1-butene, while the Cr-
containing MOFs had better selectivity of 2-butene. For the
two MOFs containing the same metal, MIL-101 (Fe or Cr)
had slightly higher conversion percentage of 1-butene and
slightly better selectivity of 2-butene than MIL-100 (Fe or Cr).
However, the influence of the pore structure was relatively
small compared with the metal nature, indicating that the pores
of MIL-100 (Fe and Cr) were already sufficiently large to
expose sufficient metal sites to isomerize 1-butene.
Figure 2. Conversion percentage of 1-butene and the amounts of
isomerization products (A) at 1 atm and (B) at 10 atm based on the
catalyst MIL-101 (Cr). (a) Plot of amount of isobutylene vs reaction
time. (b) Plot of amount of 2-butene vs reaction time. (c) Conversion
percentage of 1-butene vs reaction time. Reaction conditions: 1-
butene (wt % = 10%, 17.82 mmol) in n-hexane 15 mL (10 g), catalyst
3
μmol, N atmospere, reaction time 24 h, temperature 25 °C, [Al]/
2
[
Cr] = 500, GC measurement.
In order to further comfirm the effect of metal active site
exposure on catalytic performance, MIL-101 (Cr) was
evacuated at 100, 200, and 220 °C. The conversion percentage
of 1-butene, the amounts of isomerization products, and the
selectivity of 2-butene are shown in Table 2. When the vacuum
temperature was as low as 100 °C, the active sites were not
sufficiently exposed and the conversion percentage of 1-butene
was only 53.19%. However, when the high vacuum temper-
ature was 220 °C, the structure was destroyed resulting in the
low conversion percentage of 24.29%. The optimal evacuation
temperature for MIL-100 (Cr) was 250 °C, at which MIL-101
conversion of 1-butene to 2-butene or isobutene, and had good
conversion and high selectivity under 1 atm. As the reaction
time was increased, the conversion percentage of 1-butene and
the amounts of isomerization products were increased, and
then the equilibrium was reached at 24 h. The equilibrium
conversion percentages of 1-butene ranged from 12.96% to
3
8.78% under 1 atm, while the equilibrium conversion
percentages under 10 atm and under nitrogen atmosphere
ranged from 92.31% to 95.57%. The selectivities of 2-butene
were in the range of 73.20−100%. Therefore, under 10 atm the
MIL-100 (Fe and Cr) and MIL-101 (Fe and Cr) catalysts had
a
Table 1. Conversion Percentage of 1-Butene, Amounts of Isomerization Products, and Selectivity to 2-Butene or Isobutylene
entry
catalysts
pressure (atm) temperature (°C) 2-butene (mmol) isobutene (mmol) conversion percentage (%)
selectivity (%)
1
2
3
4
5
6
7
MIL-100 (Fe)
MIL-101 (Fe)
MIL-100 (Cr)
MIL-101 (Cr)
K10/H SO (3 M)
10 atm
10 atm
10 atm
10 atm
1 atm
25
25
25
25
400
430
400
15.47
15.84
16.00
16.32
−
1.39
1.19
0.45
0.32
−
94.61
95.57
92.31
93.38
74.44
29.20
61.19
91.76 (2-butene)
93.01 (2-butene)
97.26 (2-butene)
98.08 (2-butene)
94.68 (2-butene)
76.20 (isobutylene)
97.00 (isobutylene)
2
4
MeCl/BeO
H-HPM-1 zeolites
1 atm
1 atm
−
−
−
−
a
Reaction conditions: MIL-100 (Fe and Cr) activated at 250 °C, MIL-101 (Fe and Cr) activated at 200 °C, 1-butene (w% = 10%, 17.82 mmol) in
n-hexane 15 mL (10 g), catalyst 3 μmol, N atmospere, reaction time 24 h, pressure 10 atm, and temperature 25 °C, [Al]/[Fe] = 500 or [Al]/[Cr]
=
2
500, GC measurement.
C
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a
Table 2. Effects of the Cocatalyst and Activated Temperature on 1-Butene Isomerization for MIL-101 (Cr) Catalyst
entry
activated temperature (°C)
catalyst
Et AlCl
2
2-butene (mmol)
isobutene (mmol)
conversion percentage (%)
S2‑butene (%)
1
2
3
4
5
200
200
200
100
220
+
+
-
+
+
+
-
+
+
+
16.32
1.13
0.00
9.38
4.26
0.32
0.00
0.00
0.10
0.07
93.38
6.34
0.00
53.19
24.29
98.08
100.00
0.00
98.95
98.38
a
Reaction conditions: MIL-101 (Cr) activated at 200 °C, 1-butene (w% = 10%, 17.82 mmol) in n-hexane 15 mL (10 g), Catalyst 3 μmol, N2
atmospere, reaction time 24 h, pressure 10 atm, and temperature 25 °C, [Al]/[Cr] = 500, GC measurement, + : represent addition, -: represent not
addition.
(
Cr) presented the largest specific surface area, the highest
Discussionon Catalytic Mechanism for 1-Butene to 2-
butene. At present, it is generally believed that transition
metal complexes catalyze the isomerization of olefins with two
mechanisms, namely, metal hydride addition−elimination
crystallinity, and the highest catalytic activity.
When cocatalyst diethylaluminum chloride (Et AlCl) or
2
MIL-101 (Cr) catalyst was added separately (Table 2), there
was almost no catalytic activity. This suggested the cocatalyst
Et AlCl participated the isomerization reaction and assisted the
MIL-101 (Cr) catalyst for catalysis. The amount of cocatalyst
Et AlCl on the isomerization was further investigated. The
decrease of the ratio of [Al]/[Cr] to 100:1 and 10:1 resulted in
the greatly reduced conversion of 87.37% and 22.95%,
respectively. When the[Al]/[Cr] ratio was increased to
16
mechanism and π-allylic mechanism. For the metal hydride
2
addition−elimination mechanism, olefin is adsorbed to active
sites, hydrogen and metal are added to the hydrocarbon double
bond, and then the metal and the α-H are removed to change
the position of the double bond. For π-allylic mechanism,
olefin is adsorbed on active sites to produce a thermodynami-
cally unstable cyclopropyl transition state complex. Then α-H
of olefin transfers, and ring opens to form an olefin with the
position of double bond changed.
2
6
00:1, the conversion was 93.94% (Table S3), which was
only slightly higher than the corresponding conversion 93.38%
at the [Al]/[Cr] ratio of 500:1. So, the [Al]/[Cr] ratio of
5
00:1 was chosen considering the cost of catalyst and
Based on the results reported in the literature as well as our
catalytic results, we proposed a metal hydride addition−
elimination mechanism for isomerization of 1-butene in Figure
17
cocatalyst under the premise of high conversion.
We speculated that the ethyl anion of the Et AlCl was first
2
inserted into the CUS. Then, the ethylene was produced and
left, forming complex metal hydride, which was regarded as the
catalytically active center of the isomerization reaction (see the
following discussion on catalytic mechanism for detail). In
addition, cocatalyst might clean up impurities in the pores,
allowing more CUS to be exposed and improve catalytic
activity. Therefore, MOFs with CUS might be promising
catalysts for isomerization of olefins.
3
. First of all, guest molecules or ions in the pore channels of
MOFs were removed to produce CUS by heating under
vacuum, and the ethyl anions of the Et AlCl were inserted into
2
the CUS. Then, the removal of ethylenes from ethyl anions
resulted in the formation of complex metal hydrides, which
were the catalytically active centers of the isomerization
reaction. The complex metal hydrides were added to the
double bond of 1-butene, and then along with the elimination
of α-H anion of 1-butene and its addition to the metal center
to form new active sites, 2-butene was released.
The recycling performance of MIL-101 (Cr) catalyst was
measured and shown in Table 3. The MIL-101 (Cr) catalyst
In order to confirm the isomerization mechanism of 1-
butene, we tried to separate the intermediates from the
reaction mixture and found that they were particularly sensitive
to air. For this reason, the reaction mixture was measured
through GC/MS and we found that the product contained
ethylene as shown in Figure S7. For the π-allylic mechanism, 1-
butene is adsorbed on CUS to produce a thermodynamically
unstable cyclopropyl transition state complex, and then α-H of
olefin transferred, ring-opened to form an olefin with the
position of double bond changed, and ethylene cannot be
produced during the reaction. Additionally, the MIL-101 (Cr)
Table 3. Catalytic Cycle Performance for MIL-101 (Cr)
Catalyst
a
number of
cycles
2-butene
(mmol)
iso-butene
(mmol)
conversion
percentage (%)
S2
‑butene
(%)
0
1
2
3
4
16.32
15.33
13.41
11.15
10.29
0.32
0.33
0.35
0.35
0.36
93.38
87.91
77.21
64.53
59.76
98.08
97.89
97.46
96.96
96.62
a
Reaction conditions: MIL-101 (Cr) activated at 200 °C, 1-butene (w
= 10%, 17.82 mmol) in n-hexane 15 mL (10 g), catalyst 3 μmol, N2
atmospere, reaction time 24 h, pressure 10 atm, and temperature 25
C, [Al]/[Cr] = 500, GC measurement.
%
catalyst was pretreated using LiAlH in n-hexane under stirring
4
°
for 30 min to catalyze the isomerization of 1-butene, showing
an equilibrium conversion of 23.96%. This result suggested
that metal hydride as active species did catalyze the
isomerization of 1-butene. Such metal hydride addition−
elimination mechanism for olefin isomerization has been
could be recycled at least four times maintaining >60.00% of
the initial conversion and >98.00% of the 2-butene selectivity.
However, the conversion percentage of 1-butene decreased
with an increasing number of cycles. This was possibly because
after the metal active center was alkylated by cocatalyst
17c
reported by Lehmkuhl and Tsienin.
In the paper, the
removal of propylenes from allyl anions resulted in the
formation of complex metal hydrides, which were the
catalytically active center for the isomerization reaction of
1,5-hexadiene at room temperature.
Et AlCl, the AlCl3 produced was decomposed to form
2
Al(OH) precipitate in contact with the water vapor in the
3
air, which covered the active sites and decreased the catalytic
activity.
D
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Figure 3. Proposed catalytic mechanism for 1-butene to 2-butene. Only one α-H atom of 1-butene is shown in the 1-butene molecule and all other
III
III
hydrogen atoms are omitted; M represents Cr or Fe .
CONCLUSION
room temperature. The reaction mixture was transferred to a
Teflon Autoclave and heated for 4 days at 220 °C. The
resulting green solid was washed with deionized water and hot
ethanol, and dried in vacuum at 100 °C. MIL-101 (Cr) was
■
In summary, we have prepared a series of MOF catalysts for 1-
butene isomerization by evacuating MIL-100 (Fe and Cr) and
MIL-101 (Fe and Cr) under optimal temperatures. MIL-100
Fe and Cr) and MIL-101 (Fe and Cr) catalysts can isomerize
-butene to 2-butene and isobutene almost completely at room
temperature and 10 atm with the conversion percentage of 1-
butene and selectivity of 2-butene above 92.00% and 91.00%,
respectively. In addition, the MOF catalysts are relatively
environmentally friendly and the reaction conditions are mild.
Furthermore, the MIL-101 (Cr) catalyst can be recycled at
least four times maintaining above 60.00% of the initial
conversion and above 98.00% of the 2-butene selectivity. This
work indicates that MOFs with CUS may be promising
isomerization catalysts for olefin.
2
0
hydrothermally synthesized according to the literature,
Cr(NO ·9H O (1 mmol, 400 mg), terephthalic acid (1
mmol, 166 mg), and HF (1 mmol, 0.02 mL) in deionized H O
2
(
1
)
3
3
2
(4.8 mL, 265 mmol) was stirred for 8 h at 220 °C. The
resulting green powder was washed with deionized water, and
dried at 100 °C in vacuum.
Procedure for Isomerization of 1-Butene. The reaction
was performed using a 300 mL stainless steel autoclave
equipped with a stirring bar (Figure S8) and 100 mL Schlenk
bottle, which were preheated at 150 °C in vacumm for 60 min
and then cooled to room temperature under nitrogen
atmosphere. The autoclave and the Schlenk bottle were
evacuated using a vacuum pump and backfilled with nitrogen
for three times, and then the nitrogen was released. A certain
amount of MOF catalyst (3 μmol, based on the number of
moles of SBU of MOF) was added to Schlenk bottle under
EXPERIMENTAL SECTION
■
(
Preparation of the MIL-100 (Fe and Cr) and MIL-101
Fe and Cr) Catalysts. MIL-100 (Fe) was prepared according
1
8
to the literature, MIL-100 (Fe) was hydrothermally prepared
from a mixture of Fe (5.0 mmol, 0.28 g), trimesic acid (3.35
nitrogen, and then the required amount of Et AlCl (0.9 M in
2
mmol, 0.70 g), HF (10.0 mmol, 0.20 g), and HNO (3 mmol,
.19 g) in deionized H O (25 mL). The reaction mixture was
3
toluene) cocatalyst was injected into the Schlenk bottle
through a dry syringe, and the mixture was stirred for 10
min under nitrogen atmosphere. Subsequently, a suspension of
0
2
stirred for 10 min, then transferred to a Teflon autoclave, and
heated at 150 °C for 12 h. The light orange solid product was
filtered, washed with deionized water, and further purified
using boiling water and hot ethanol for 5 h. The solid was
finally dried 36 h at 100 °C in vacuum. MIL-101 (Fe) was
MOF and Et AlCl was transferred into a stainless steel
2
autoclave through a dry syringe under nitrogen atmosphere.
Then, an ultradry solution of 1-butene in n-hexane (15 mL)
was injected into the autoclave through the feeding valve. The
nitrogen pressure was increased to 1 or 10 atm and kept
constant during the reaction at room temperature. After
finishing, the reaction steel autoclave was cooled down to −25
19
synthesized according to the literature, a mixture containing
FeCl ·6H O (2.45 mmol, 662.2 mg) and terephthalic acid
3
2
(
1.24 mmol, 206.0 mg) in DMF(15 mL). The reaction mixture
was transferred to an autoclave and heated at 110 °C for 20 h,
then slowly cooled to room temperature, and further purified
using boiling water and hot ethanol for 5 h. The solid was
dried 36 h at 100 °C in vacuum. MIL-100 (Cr) was obtained
according to the literature, CrO (5 mmol, 0.5 g), trimesic
acid (5 mmol, 1.05 g), and HF solution (5 mmol, 5 M, 1.0
mL) in deionized water (24 mL) was stirred for 10 min at
°
C by the condensing circulation pump, and then depressur-
ized. A small amount of reaction solution was taken out
through the feeding valve with a syringe and qualitatively
analyzed by GC/MS. All of above air- or moisture-sensitive
substances were protected and transferred via Schlenk
technique. The peak positions of the desired isomerization
10
3
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DOI: 10.1021/acs.organomet.9b00599
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Organometallics
Article
products of butene were shown at different retention times in
gas chromatography (Figure S7).
The amounts of products, the conversion percentage of 1-
butene, and the selectivity of 2-butene or isobutene were
calculated according to the following equation:
ACKNOWLEDGMENTS
■
We acknowledge the support of this work by National Natural
Science Foundation of China (Grant No. 21676296) and
National Key Research and Development Plan (Grant No.
2
016YFC0303704).
Ai
Atotal
ni =
× 17.82 mmol
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AUTHOR INFORMATION
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Corresponding Authors
E-mail: shengdonghai120@163.com (D.S.).
E-mail: y.zhang@cup.edu.cn (Y.Z.).
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DOI: 10.1021/acs.organomet.9b00599
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