A Chromium Hydroxide/MIL-101(Cr) MOF Composite Catalyst and Its Use for the Selective Isomerization of Glucose to Fructose

Article abstract of DOI:10.1002/anie.201712818

A metal–organic framework (MOF)-based catalyst, chromium hydroxide/MIL-101(Cr), was prepared by a one-pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL-101 accomplishes highly selective conversion of gluc

Full text of DOI:10.1002/anie.201712818

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Accepted Article
Title: A Chromium Hydroxide/MIL-101(Cr) Composite Catalyst and its
Use for Selective Glucose Isomerization to Fructose
Authors: Michael Tsapatsis, Qiang Guo, Limin Ren, Prashant Kumar,
Viktor J. Cybulskis, K. Andre Mkhoyan, and Mark E. Davis
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COMMUNICATION
A Chromium Hydroxide/MIL-101(Cr) Composite Catalyst and its
Use for Selective Glucose Isomerization to Fructose
Qiang Guo, Limin Ren*, Prashant Kumar, Viktor J. Cybulskis, K. Andre Mkhoyan, Mark E. Davis,
Michael Tsapatsis*
Abstract:
A
metal-organic framework (MOF)-based catalyst,
one-pot
alcohol, its performance was below that obtained by zeolite
[
34]
chromium hydroxide/MIL-101(Cr), was prepared by
a
catalysts, such as Sn-SPP.
Here, we demonstrate that a
synthesis method. The combination of chromium hydroxide particles
on and within Lewis acidic MIL-101 accomplishes highly selective
conversion of glucose to fructose in the presence of ethanol,
matching the performance of optimized Sn-containing Lewis acidic
zeolites. Differently from zeolites, NMR studies with isotopically
labeled molecules demonstrate that isomerization of glucose to
fructose on this catalyst, proceeds predominantly via a proton
transfer mechanism.
chromium hydroxide/MIL-101 catalyst can isomerize glucose to
fructose at glucose conversion and fructose yield comparable to
those obtained by optimized zeolite catalysts. We also show that
the isomerization mechanism is predominantly by proton-
transfer as in base-catalyzed isomerization, possibly due to
chromium hydroxide, while the ketalization reaction is catalyzed
by MIL-101. To our knowledge, this work is the first
demonstration of a base-like, proton-transfer dominated, high
yield catalytic route for fructose by glucose isomerization.
Metal-organic frameworks (MOFs) are a class of crystalline
materials with high surface areas and well-defined pore systems
[
1-7]
that hold promise for uses as adsorbents and membranes.
The ability to tune their composition also provides opportunities
in heterogeneous catalysis especially when bifunctional
catalysts are desirable, like in the catalysis of tandem
[
7-26]
reactions.
One such reaction is the isomerization of glucose
[
27-30]
to fructose in the presence of alcohols.
First proposed by
[
27]
Saravanamurugan et al., it has been shown to be a high-yield
route to fructose and a promising alternative to aqueous routes.
For instance, when glucose isomerization to fructose is
combined with fructose ketalization, increased fructose yields
beyond the equilibrium levels are achievable and the obtained
fructoside is readily hydrolyzed to fructose upon addition of
water (Scheme 1).
Scheme 1. Conversion of glucose to fructose in ethanol and water through
sequential reactions.
MOF catalysts have been explored for glucose isomerization
in water and recently their performance has approached that of
[
31-33]
the best zeolite catalysts (Sn-Beta).
Although a MOF-
derived catalyst has been explored for glucose isomerization in
[
a]
b]
Dr. Q. Guo, Dr. L. Ren, P. Kumar, Prof. K. A. Mkhoyan, Prof. M.
Tsapatsis
Department of Chemical Engineering and Materials Science
University of Minnesota
4
21 Washington Ave SE, Minneapolis, MN 55455 (USA)
E-mail: lren@umn.edu
tsapatsis@umn.edu
[
Dr. V. J. Cybulskis, Prof. M. E. Davis
Chemical Engineering
Figure 1. TEM images of materials prepared using 1.0 Cr: 0.8 BDC: 265 H
x GLY with x=1.6 (A), 1.3 (B), 1.0 (C) and 0.8 (D); XRD patterns (E) of
Simulated MIL-101, MIL-101-nano, MIL-101-[GLY], Cr(OH) -[GLY] and
Cr(OH) from JCPDS card No. 00-016-0817; Ar sorption isotherms (F) of MIL-
01-nano, MIL-101-[GLY] and a physical mixture of 83 wt% MIL-101-nano and
7 wt% Cr(OH) -[GLY].
2
O:
California Institute of Technology
Pasadena, CA 91125 (USA)
3
3
1
1
Supporting information for this article is given via a link at the end of
the document
3
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We observed that by increasing the amount of the amino
acid glycine (GLY) in a MIL-101 synthesis mixture, increased
101-nano are 20.2 %, 24.3 % and 24.9 %, respectively, after 24
h reactions at 100 C. Remarkably, 59.3 % yield of fructose was
o
amounts of co-precipitated Cr(OH)
Figures 1A-C show the results obtained from syntheses with
composition (molar ratio): 1.0 Cr: 0.8 terephthalic acid (BDC):
3
nanoparticles were obtained. obtained by using MIL-101-[GLY] at the same conditions.
Table 1. Comparison of glucose isomerization catalyzed by MOFs.
[
a]
[b]
Entry
Catalyst
Con/%
Product yield/%
Ref.
2
65 H
2
O: x GLY, where x=1.6, 1.3, and 1.0. We also determined
particles formed after the nucleation and initial
that the Cr(OH)
3
FRU
20.2
24.3
24.9
59.3
24.3
37.4
MAN
3.6
4.3
5
HMF
0.8
1.0
1.2
1.4
1.1
1.2
crystal growth of MIL-101, and that in the absence of BDC
linkers, nearly carbon-free particles are obtained which we call
1
2
3
4
5
6
MIL-101-HF
MIL-101
33.6
39.4
46.2
76.5
48.8
60.4
This work
This work
This work
This work
This work
This work
Cr(OH)
structure of Cr(OH)
Cr(OH) -[GLY] with the typical XRD of Cr(OH)
Figure 1E indicates that Cr(OH) -[GLY] is a nanocrystalline
material with distinct structure from Cr(OH) made by
When using the
O: 0.8 GLY, we obtained
particles attached to and
embedded in their periphery (Figure 1D). These Cr(OH)
particles could not be separated by repeated sonication and
washing. This Cr(OH) /MIL-101(Cr) material is denoted from
3
-[GLY] (Figure 1E, S1D and Table S1). The crystal
is not precisely known and a comparison of
provided in
3
3
3
MIL-101-nano
MIL-101-[GLY]
3
3
2.9
3.2
4.1
[
35]
precipitation at room temperature.
composition 1.0 Cr: 0.8 BDC: 265 H
MIL-101 crystals with Cr(OH)
3
Cr(OH) -[GLY]
2
3
Physical
3
[c]
mixture
[
[
34]
31]
3
7
8
9
NU-1000
derived oxide
52.5
22
23.4
21.6
-
-
-
-
Ref.
now on as MIL-101-[GLY]. We also prepared, for reference,
three other Cr-MIL-101 catalysts: MIL-101-HF, MIL-101 and
MIL-101-nano (Figure S1 and additional details for the materials
synthesis can be found in the Supporting Information). XRD data
of MIL-101-[GLY] show the characteristic reflections of MIL-101
MIL-101-SO
in water
3
H
Ref.
[
[
32]
33]
UiO-66 in water
Sn-Beta in water
31
59
~22
32
-
~6
-
Ref.
3
along with reflection attributed to Cr(OH) (Figure 1E and S1D).
10
9
Ref.
The broad Bragg reflections of the XRD pattern could be
attributed to the small particle size. TEM images show that the
particle size of MIL-101-[GLY] is around 80 nm, which is smaller
than that of the MIL-101 synthesized without glycine. The argon
adsorption isotherm of the MIL-101-[GLY] shows two uptake
o
Reaction conditions: 1 wt% glucose (0.036 g) in ethanol (3.564 g) at 100 C for
4 h, 0.013 wt% (based on Cr) catalyst. After quenching the reactor, 4.8 g of
2
o
deionized water was added to perform the hydrolysis at 100 C for 24 h.
[a] Glucose conversion. [b] FRU: fructose; MAN: mannose; HMF: 5-
steps around P/P
0
=0.1 and P/P
0
=0.2, which indicate the
hydroxymethylfurfural. [c] 83 wt% MIL-101-nano and 17 wt% Cr(OH) -[GLY].
3
existence of two different windows in the framework, and the
pore size distribution reflects two kinds of pore sizes centered at
Figure 2 compares the structure (as revealed by ADF-
STEM) and corresponding isomerization performance of MIL-
101-[GLY], MIL-101-nano and Cr(OH) -[GLY] catalysts. The
3
ADF-STEM images of MIL-101-[GLY] match well with the
corresponding atomic structure models when viewed along
different directions (Figure S3). The bright contrast features
[
36]
2
.2 and 2.9 nm. Its BET equivalent surface area is lower than
2
that of the nano-sized MIL-101 (MIL-101-nano) (2609 m /g
versus 3661 m /g) due to the presence of Cr(OH) . The surface
3
area (2970 m /g) of a physical mixture (ratio determined by Cr
content calibration with MIL-101-[GLY], Table S1) of MIL-101-
2
2
(
3
Figure 2A, B) in the images are Cr(OH) nanoparticles grown
3
nano (83 wt%) and Cr(OH) -[GLY] (17 wt%) is comparable to
both on and inside the outer parts of MIL-101 crystals. In the
presence of MIL-101-[GLY], about 60 % yield of fructose was
obtained at 76.5 % glucose conversion after 24 h of reaction
that of the MIL-101-[GLY] (Figure 1F). IR spectra of deuterated
acetonitrile adsorbed on MIL-101-[GLY] exhibit two bands at
-1
-1
2
260 and 2311 cm (Figure S2). The band at 2260 cm can be
(
Figure 2C). The profile of fructose yield vs glucose conversion
assigned to the physisorbed deuterated acetonitrile and the
-1
on MIL-101-[GLY] is very similar to that from optimized Sn-
containing zeolites (Figure S4A). In 24 h, we obtained 1.2, 0.91,
and 0.71 gfructose/gcatalyst using MIL-101-[GLY], Sn-MWW and Sn-
SPP, respectively. No further glucose conversion and fructose
production was observed once the catalyst was removed from
the reaction media (Figure S5). The recycling of MIL-101-[GLY]
shows an initial loss in activity after the first cycle followed by
minor losses up to four cycles. Fructose selectivity remains
stable (Figure S4B). The XRD patterns (Figure S6A) and TEM
images (Figure S6C) of the reused catalyst, after the 4th run, are
very similar to those of the fresh catalyst. Moreover, the
band at 2311 cm arises from the deuterated acetonitrile
[
21, 37]
adsorption on Lewis acid sites.
With increasing temperature,
-1
-1
the band at 2260 cm vanished while the band at 2311 cm
remained unchanged indicating that the MIL-101-[GLY] shows
strong Lewis acidity.
MIL-101-[GLY] was used as the catalyst for glucose
isomerization/fructose ketalization in ethanol followed by
fructoside hydrolysis in water (Scheme 1) and its performance
was compared to that of several other MIL-101 materials. In the
first step of this approach (first introduced in ref.27), glucose is
isomerized to fructose and fructose reacts with ethanol to give a
mixture of fructose and ethyl fructoside. Then, water is added
and hydrolysis of the fructoside yields fructose. Table 1 shows
glucose conversion and product yield from different MOF
catalysts. The fructose yields on MIL-101-HF, MIL-101 and MIL-
structure of the MIL-101 crystal and Cr(OH)
3
are intact as
confirmed by ADF-STEM (Figure S7). These results indicate that
MIL-101-[GLY] microstructure is stable under the reaction
conditions. The loss of activity could be attributed to irreversible
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adsorption of reaction byproducts that partially block the pores.
Consistently, Figure S6B shows a small decrease in the Ar-
sorption isotherms corroborating this hypothesis.
The glucose isomerization mechanism on MIL-101-[GLY]
was studied by determining the isotopic identity at C1 position of
1
3
the produced fructose with C-NMR spectroscopy (Scheme S1).
13
1
3
The reactions were performed in CD OD with [ C1, H2]-
1
3
glucose (glucose with C enrichment at C1 position and natural
abundance hydrogen at C2 position, denoted as G1 in Scheme
1
3
2
13
S1) or in CH
3
OH with [ C1, H2]-glucose (glucose with
C
enrichment at C1 position and deuterium enrichment at C2
position, denoted as G2 in Scheme S1). NMR spectra of
hydrolyzed products from G1 and G2 are shown in Figures 3A
and B, respectively. Figure 3A shows one strong resonance
(
[
(
Singlet I) at 63.84 ppm, which is ascribed to C1 of the
1
3
1
C1, H1]-fructose (β-pyranose configuration), and a triplet
Triplet II) at 63.73 ppm, 63.51 ppm and 63.29 ppm that results
1
3
13
2
from C1-D J coupling of the [ C1, H1]-fructose (β-pyranose
configuration).
[
38, 39]
Considering that the nuclear Overhauser
effect (NOE) leads to the enhancement of signals from H-
bearing carbons, relative to D-bearing carbons, the pronounced
presence of the triplet indicates considerable presence of
1
3
2
[
[
C1, H1]-fructose (fructose shown as II in Figure 3) along with
1
3
1
C1, H1]-fructose (fructose shown as I in Figure 3); suggesting
3
that glucose G1 in CD OD was isomerized to fructose in two
different ways over MIL-101-[GLY]: 1,2-intramolecular hydride
shift to give fructose I and proton transfer mechanisms to give
fructose II. Glucose isomerization proceeds primarily via the 1,2-
Figure 2. High-resolution ADF-STEM images and glucose (GLU)
isomerization to fructose (FRU) profiles for (A-C) MIL-101-[GLY], (D-F) MIL-
intramolecular hydride shift mechanism on Lewis acid sites like
1
01-nano, and (G-I) Cr(OH)
3
-[GLY]. Reaction conditions: 1 wt% glucose
o
[40-43]
(0.036 g) in ethanol (3.564 g) at 100 C, 0.013 wt% (based on Cr) catalyst.
in Sn-containing zeolites (Figure S9A)
and the proton
After quenching the reactor, 4.8 g of deionized water was added to perform
transfer mechanism proceeds over base catalyst like Na-ETS-4
o
the hydrolysis at 100 C for 24 h. Scale bars for (A, D) are 100 nm, (B, E) are
[43, 44]
(
Figure S9C).
20 nm, (G) is 10 nm and (H) is 2 nm.
The MIL-101-nano, which was synthesized with the addition
of benzoic acid as modulator shows a typical morphology of
MIL-101 crystal and has a similar size as the MIL-101-[GLY]
(
Figure 2D, E). However, only 24.9 % yield of fructose was
obtained at 46.2 % glucose conversion after 24 hrs of reaction
Figure 2F) when it was used as the catalyst. Nanosized
Cr(OH) -[GLY], prepared with the same procedure as that of the
(
3
MIL-101-[GLY] but without the addition of BDC, is composed of
thin layers (Figure 2G, H and Figure S8). As mentioned earlier,
the XRD pattern of Cr(OH)
other Cr(OH) materials exhibiting an extra broad peak centered
at ~17˚. This broad XRD peak could be due to the ~5.2 Å
spacing between Cr(OH) layers determined by ADF-STEM
Figure S8). Further studies are required to fully elucidate the
3
-GLY does not fully agree with that of
3
[
35]
13
Figure 3. C NMR spectra of hydrolyzed products (fructose region) obtained
13
1
13
2
3
3
after reactions of (A) D-[ C1; H2]-glucose (G1) in CD OD, (B) D-[ C1; H2]-
glucose (G2) in CH
C NMR of hydrolyzed products (fructose region) obtained after reactions of
C) unlabeled glucose in CD
(
3
OH on MIL-101-[GLY]. Inverse gated coupled quantitative
13
3 3
structure of Cr(OH) made in the presence of glycine. Cr(OH) -
2
(
3 2 5
OD and (D) D-[ H2]-glucose in C H OH on MIL-
[
GLY] provided similar low yield of fructose (Figure 2I) as MIL-
1
01-[GLY].
101-nano. The glucose conversion and fructose yield only
slightly increased when the physical mixture of MIL-101-nano
(
(
83 wt%) and Cr(OH)
Table 1, entry 6).
3
-[GLY] (17 wt%) was used as the catalyst
13
These results were further confirmed by the C-NMR
spectra of fructose, which were produced from G2 in CH OH
See Figure 3B, and compare with Figure S9B and Figure S9D).
3
(
The NMR experiments with isotopically labeled glucose that
are described next revealed a predominantly proton-transfer
mechanism for isomerization attributable to Cr(OH) with MIL-
01 contributing mainly to Lewis acid catalyzed ketalization and
to a lesser extent of Lewis acid catalyzed isomerization.
Here, the triplet is again associated with fructose II but this time
corresponds to fructose made by 1,2-intramolecular hydride shift.
Moreover, if the two paths were contributing equally, the
spectrum of Figure 3B should have been the same as that of
Figure 3A. This is not the case, and we can infer that the proton
transfer mechanism is the dominant path when MIL-101-[GLY]
3
1
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COMMUNICATION
was used as the catalyst for glucose isomerization. All the
reference MIL-101 materials (MIL-101-HF, MIL-101 and MIL-
for glucose isomerization in ethanol was synthesized by adding
glycine in MIL-101 synthesis. A product distribution of 23.5 %
101-nano) show behavior similar to the pure Lewis acid catalysts, glucose, 59.3 % fructose and 2.9 % mannose can be obtained
while Cr(OH)
3
-[GLY] behaves like a base catalyst: fructose
over this catalyst, matching the fructose yields achievable by
optimized Sn-containing Lewis acidic zeolites.
produced via proton transfer is the dominant product with only
trace amount of fructose formed via the hydride shift mechanism
[
45]
(
Figure S10).
1
3
Acknowledgements
Inverse gated coupled quantitative
C-NMR, which
suppresses the NOE, was used to further assess the
contribution to fructose yield by the two different paths. The
integral of Singlet I, which arises from C1 signal of the non-
deuterated fructose was quantitated using the integral of Singlet
III from the C6 signal of both the non-deuterated fructose and
This work was supported as part of the Catalysis Center for
Energy Innovation, an Energy Frontier Research Center funded
by the U.S. Department of Energy, Office of Science, Basic
Energy Sciences under Award DE-SC0001004.
2
H1-fructose (one deuterium at C1 position). If glucose
isomerization to fructose proceeds solely via 1,2-intramolecular
hydride shift of unlabeled glucose or proton transfer of [ H2]-
Keywords: Catalysis • Chromium-hydroxide • Fructose •
2
Isomerization • Metal-organic frameworks
glucose (glucose with deuterium enrichment at C2 position) in
unlabeled alcohol, only non-deuterated fructose would be
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Figure 3C exhibits the NMR spectrum of the hydrolyzed
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corresponds to fructose that was produced via 1,2-
intramolecular hydride shift was ~20 % of that of Singlet III (all
integrals in Figure 3C were normalized using the integral of
Singlet I, and the integral of Singlet III was corrected by the
integral at 63.73 ppm due to its overlap with the peak at 63.29
ppm, whose integral is the same as that of the peak at 63.73
ppm as indicated by Figures 3A and 3B). Figure 3D shows the
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2
2
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integral of Singlet III in Figure 3D was normalized using the
integral of Singlet I). These results demonstrate that ~80 % of
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043.
We propose that the MIL-101-[GLY] catalyst converts
glucose in ethanol via a synergistic way and the proximity of
chromium hydroxide and Lewis acidic MIL-101 plays a vital role.
Specifically, glucose is isomerized to fructose mainly on
chromium hydroxide; then the produced fructose is transformed
to ethyl fructoside over Lewis acid sites. Therefore, chromium
hydroxide and the Lewis acid sites should be close enough to
efficiently catalyze the consecutive reactions of glucose
isomerization and fructose ketalization. Based on the proton-
transfer dominated isomerization, it appears that chromium
hydroxide acts as a base catalyst. Further studies including IR
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spectroscopy of adsorbed CO
2
on MIL-101-[GLY] should be
performed in the future to elucidate the type and strength of
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In conclusion, an efficient and reusable MOF-based catalyst
containing Lewis acid and base-like chromium hydroxide sites
2
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Cr(OH)
3
inter-grown with MIL-101 is
Qiang Guo, Limin Ren*, Prashant
demonstrated to be a highly selective
catalyst for glucose isomerization to
fructose. Although isomerization
proceeds mainly by a proton transfer
mechanism, the new catalyst matches
the performance of optimized Lewis
acid zeolites.
Kumar, Viktor J. Cybulskis, K. Andre
Mkhoyan, Mark E. Davis, Michael
Tsapatsis*
Page No. – Page No.
A Chromium Hydroxide/MIL-101(Cr)
Composite Catalyst and its Use for
Selective Glucose Isomerization to
Fructose
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Author(s), Corresponding Author(s)*
((Insert TOC Graphic here))
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Title
Text for Table of Contents
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