Phosphonate-Modified UiO-66 Br?nsted Acid Catalyst and Its Use in Dehydra-Decyclization of 2-Methyltetrahydrofuran to Pentadienes

Article abstract of DOI:10.1002/ange.202001332

Phosphorus-modified all-silica zeolites exhibit activity and selectivity in certain Br?nsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well-defined sites, we report the incorporation of Br?nsted acidity to metal–organic frameworks with the UiO-66 topology, achieved by attaching phosphonic acid to the 1,4-benzenedicarboxylate ligand and using it to form UiO-66-PO₃H₂ by post-synthesis modification. Characterization reveals that UiO-66-PO₃H₂ retains stability similar to UiO-66, and exhibits weak Br?nsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF). For the later reaction, the reported catalyst exhibits site-time yields and selectivity approaching that of phosphoric acid on all-silica zeolites. Using solid-state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.

Full text of DOI:10.1002/ange.202001332

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Titel: Phosphonate-modified UiO-66 Brønsted acid catalyst and its
use in dehydra-decyclization of 2-methyltetrahydrofuran to
pentadienes
Autoren: Matheus Dorneles de Mello, Gaurav Kumar, Tarnuma
Tabassum, Sheetal K Jain, Tso-Hsuan Chen, Stavros
Caratzoulas, Xinyu Li, Dionisios G. Vlachos, Songi-i Han,
Susannah Scott, Paul J. Dauenhauer, and Michael Tsapatsis
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Zitierweise: Angew. Chem. Int. Ed. 10.1002/anie.202001332
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Angewandte Chemie
10.1002/ange.202001332
RESEARCH ARTICLE
Phosphonate-modified UiO-66 Brønsted acid catalyst and its use
in dehydra-decyclization of 2-methyltetrahydrofuran to
pentadienes
[
a]
[a]
[b]
[b]
Matheus Dorneles de Mello , Gaurav Kumar , Tarnuma Tabassum , Sheetal K. Jain , Tso-Hsuan
[
c]
[c]
[a]
[c]
[b]
[b]
Chen , Stavros Caratzoulas , Xinyu Li , Dionisios G. Vlachos , Songi-I Han , Susannah L. Scott ,
[
a]
[a,d,e]
Paul Dauenhauer , and Michael Tsapatsis*
Abstract: Phosphorus-modified all-silica zeolites exhibit activity and
selectivity in certain Brønsted acid catalyzed reactions for biomass
conversion. In an effort to achieve similar performance with catalysts
having well-defined sites, we report the incorporation of Brønsted
acidity to metal-organic frameworks with the UiO-66 topology,
achieved by attaching phosphonic acid to the 1,4-
and dynamic nature of phosphoric acid species on these zeosils
under reaction conditions makes the identification and tuning of
the active sites challenging.[
14]
Functionalized MOF-derived solid acids have found
numerous applications in catalysis and separations.[16] For
example, MIL-101 (Cr) and UiO-66 (Zr) were functionalized with
sulfonic acid, introducing Brønsted acidity and making these
materials active for fructose dehydration.[17] Functionalized UiO-
benzenedicarboxylate ligand and using it to form UiO-66-PO
post-synthesis modification. Characterization reveals that UiO-66-
PO retains stability similar to UiO-66, and exhibits weak Brønsted
3 2
H by
6
6-CO
2
H and UiO-66-SO
3
H also showed enhanced selectivity
3 2
H
towards CO
2
/CH
4
separation.[18] The COOH moiety was
acidity, as demonstrated by titrations, alcohol dehydration, and
dehydra-decyclization of 2-methyl-tetrahydrofuran (2-MTHF). For the
later reaction, the reported catalyst exhibits site-time yields and
selectivity approaching that of phosphoric acid on all-silica zeolites.
Using solid-state NMR and deprotonation energy calculations, the
chemical environments of P and the corresponding acidities are
determined.
introduced into the framework of UiO-67 by C-H activation using
a rhodium catalyst. The resulting Brønsted acidity from the free
acid was active for an epoxide ring-opening reaction with high
selectivity.[19] Also, Farha and coworkers succeeded in
impregnating the Zr clusters of the MOF NU-1000 with H
applications in glucose dehydration.[20]
3 4
PO for
Inspired by the existing MOF-derived solid acids and with
our goal to prepare tunable materials with well-defined catalytic
sites that show high selectivity for acid-catalyzed reactions, we
investigated the synthesis of phosphonate-modified MOFs by
ligand functionalization and their activity for Brønsted acid-
catalyzed reactions. We report the installation of phosphonate
and phosphonic acid functionalities into benzene-1,4-dicarboxylic
Introduction
Phosphorus-based materials[1–12] are reported to have
Brønsted acidity and have been extensively studied as catalysts,
including for the catalytic upgrading of lignocellulosic biomass.
For example, niobium phosphate is a selective catalyst for
fructose dehydration to 5-hydroxymethylfurfural (HMF), exhibiting
3 2
acid (BDC) ligands and their use to form UiO-66-PO H by a post-
7
8.2% HMF selectivity at 58% fructose conversion.[13] Similarly,
synthesis modification (PSM) method while maintaining the
stability, crystallinity, and topology of the parent material. The
resulting P-sites were characterized by a combination of solid-
state NMR and deprotonation energy DFT calculations. Brønsted
acidity in the synthesized materials was probed using four acid-
catalyzed chemistries (dehydration of ethanol and isopropyl
alcohol (IPA), Hoffman elimination of tert-butylamine, and
dehydra-decyclization of 2-methyl-tetrahydrofuran (2-MTHF)).
The performance of P-modified MOFs for dehydra-decyclization
of 2-methyl-tetrahydrofuran was found to be comparable with
phosphoric acid supported on zeosils. To our knowledge, this is
the first demonstration of pendant phosphonic-acid in MOFs
functioning as a selective Brønsted-acid catalyst.
phosphoric acid supported on all-silica zeolites (zeosils) are
highly selective catalysts in the production of p-xylene from 2,5-
dimethyl furan (2,5-DMF) and ethylene.[14] Furthermore, we have
recently reported their utility for the tandem ring-opening and
dehydration (dehydra-decyclization) of tetrahydrofuran (THF) to
produce butadiene selectively.[15] However, the heterogeneous
[
a]
M.Dorneles de Mello, G.Kumar, Prof. P. Dauenhauer and Prof. M.
Tsapatsis*
Department of Chemical Engineering and Materials Science
University of Minnesota
421 Washington Ave SE, Minneapolis, MN, 55455 (USA)
E-mail: tsapatsis@jhu.edu
[b]
[c]
[d]
[e]
T. Tabassum, Dr. S.K. Jain, Prof. S. Han, Prof. S.L. Scott
Department of Chemical Engineering
University of California
Results and Discussion
2
2-(Diisopropylphosphonate)terephthalic acid (PO(OPr) -
10 Mesa Road, Santa Barbara, CA ,93106 (USA)
TPA) was synthesized and used in the PSM of UiO-66 to
incorporate P-O groups into the framework (P-UiO66-PSM). The
synthesis details of P-UiO66-PSM are described in the
Supporting Information (Section S1). The introduction of different
functional groups into MOFs can be challenging because, in many
cases, the use of thermally labile ligands can be limited by
solubility and coordination issues.[ In the case of phosphonic
acid modified MOFs, the direct synthesis approach leads to
densely packed or even amorphous materials.[ Here, the PSM
method was used to overcome such issues. Briefly, parent UiO-
T.Chen, Dr. S. Caratzoulas, Prof. D.G. Vlachos
Department of Chemical & Biomolecular Engineering
University of Delaware
221 Academy Street, Newark, DE ,19716 (USA)
Prof. M. Tsapatsis
Department of Chemical and Biomolecular Engineering
Johns Hopkins University
21]
3400 N. Charles Street, Baltimore, MD, 21218 (USA)
22]
Prof. M. Tsapatsis
Applied Physics Laboratory, Johns Hopkins University
11100 Johns Hopkins Road, Laurel, MD, 20723 (USA)
Supporting information for this article is given via a link at the end of
the document.
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Angewandte Chemie
10.1002/ange.202001332
RESEARCH ARTICLE
6
6 was submitted to solvent-assisted ligand exchange for five
presence of larger pores, most likely created by the introduction
of defects during the ligand exchange process.[24]
days (Scheme 1) in a KOH/THF solution in the presence of the
phosphorus ligand. The exchanged materials were washed with
water and methanol and then heated (180 oC for 20 h under
TGA profiles of the materials are presented in Figure 1C. P-
UiO66-PSM and P-UiO66-PSM-AW exhibit the onset of
decomposition at 510 C compared to 540 oC for UiO-66. The
treatment with acidified water does not affect the MOF
decomposition temperature, which can be attributed to the high
stability of UiO-66 under acidic conditions.[25] Finally, Figures 1D-
vacuum) for solvent removal. Finally, P-UiO66-PSM was further
treated with acidified water (AW: 1M HCl) to install POH moieties
in the ligands by removing protecting isopropyl groups and
potassium; the obtained material is called P-UiO66-PSM-AW.
o
1
F show SEM images of the parent and modified MOFs, where
no apparent changes in morphology are visible. The particles
retain their size of about 260 nm after PSM and acid water
treatment. Particle size distributions can be found in Figure S2.
Having established that the P-exchanged materials retain
the topology of the parent UiO-66, their chemical composition was
investigated. Ligand exchange was confirmed by digesting the
materials and analyzing the liquid solution by 1H NMR (Section
S6.1). The 1H NMR spectrum shows a singlet at 7.8 ppm
attributed to the magnetically equivalent protons in unmodified
Scheme 1. Post-synthesis modification (PSM) of UiO-66 using 2-diisopropyl
phosphonate-terephthalic acid.
2
- [26]
BDC . The aromatic region also includes three multiplets at 8.1,
2 3
7.7, and 7.2 ppm, that match the chemical shifts of H PO
-BDC2
-
The PXRD patterns in Figure 1A show no changes for P-
exchanged UiO-66 relative to the parent material; relative peak
intensities remain the same after PSM. Figure 1B shows the Ar-
sorption isotherms of these materials. The pristine, defect-free
[
27]
in solution (see ligand characterization in the SI, section S5).
1
The H NMR spectra of digested MOFs reveal that about 23 % of
the original BDC ligands in UiO-66 were exchanged with
phosphonate-TPA (Table 1).
UiO-66, shows inflection points in Ar uptake at P/P
0
values of 10-
and 10 . They are attributed to the filling of 4 and 6 Å micropores,
respectively.[23] In general, P-exchanged UiO-66 exhibits lower Ar
4
-2
-4
uptake in the low P/P
o
(10 , microporous) range and higher Ar
-2
uptake in the high P/P
0
(>10 ) range. The latter indicates the
Figure 1. Structural characterization of PSM UiO66 materials: (A) PXRD patterns, (B) Ar sorption isotherms (closed symbols refer to adsorption and open symbols
to desorption), (C)TGA profiles, and SEM images of (D) UiO66, (E) P-UiO66-PSM, and (F) P-UiO66-PSM-AW.
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Angewandte Chemie
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RESEARCH ARTICLE
-
+
We also analyzed the materials by XPS (Table 1). The near-
surface P/Zr atomic is 0.22 for both P-UiO66-PSM and P-UiO66-
PSM-AW, which agrees with the values observed by solution-
that of the PO K sites. In the case of P-UiO-66-PSM-AW, ICP
indicates that acid washing removes a significant amount of
potassium (K/P of 0.04, Table 1). Therefore the shoulder at 6 ppm
1
state H NMR after digestion. More details on XPS analysis can
in this material is likely from hydrogen-bonded POH groups, as
suggested by Davidowski et al. [30] and Bibent et al.[31]. Finally, the
be found in Figure S3. Furthermore, ICP analysis shows a P/Zr
atomic ratio between 0.17 - 0.19. In three independently
performed syntheses using identical procedures, the P/Zr
determined by XPS is 0.22 ± 0.03, while the ligand exchange by
digestion NMR is 21 ± 4 %, indicating good reproducibility and
agreement between these characterization methods (Table S2).
ATR-IR of the exchanged MOFs (Figure S4) shows a band at
peak at -2 ppm is assigned to phosphonates that are bonded to
zirconium. The resulting POZr bonds with the cluster can account
for the more significant decrease in chemical shifts due to the low
electronegativity of Zr.[30] The assignments invoke the expected
decrease in the chemical shift of the “free” phosphonic acid signal
at 9 ppm upon the interaction between the phosphonic acid and
the Zr cluster. The magnitude of the decrease depends on the
-1
[28]
1
100 cm , attributed to the presence of P=O stretching, further
supporting the presence of the phosphonate ligand.
strength of this interaction, ranging from hydrogen bonding to
bonding directly with the cluster by a POZr bond.[30] In the case of
Table 1. Near-surface (from XPS) and bulk (ICP) composition of P-UiO66
materials.
the 6 ppm peak, this shift decrease is relatively small (Δδ=-3 ppm),
in accordance with hydrogen bonding involving either
a
Material
Ligand
exchange (%)
P/Zrb
(at/at)
P/Zrc
(at/at)
K/Pc
(at/at)
P=O…HOZr, or a POH…POH interaction between nearby
phosphonates.[31] Solid-state NMR data suggests that P-UiO66-
PSM-AW has the majority of P-sites (~about 80 %) as
deprotected P-OH, with small or no interactions with the cluster.
However, a small portion of the ligands binds strongly to Zr during
the PSM process.
a
P-UiO66-PSM
20 ± 4
21 ± 4
0.22 ± 0.03
0.22 ± 0.03
0.17
0.19
0.44
0.04
P-UiO66-PSM-AW
a From NMR; b From XPS; c From ICP.
To further probe the chemical environment of phosphorus,
we acquired solid-state 31P NMR spectra (Figure 2). There are
four distinct signals. Three are present in the 31P MAS-NMR
spectrum of heated P-UiO66-PSM, which shows a main peak at
6
1
ppm representing 60 % of the total intensity, with a shoulder at
1 ppm (25 %), and a tail at -2 ppm (15 %). The other signal
appears in the spectra of P-UiO66-PSM-AW, which shows a main
peak at 9 ppm representing 49 % of the total intensity, with a
shoulder at 6 ppm (31 %) and a tail at -2 ppm (20%). Spectral
deconvolution is also shown in Figure 2, and a summary of the
chemical shifts from it can be found in Table S3. The peaks are
assigned as follows: according to solution 31P NMR (see Section
S5.1), the fully protected PO(OPr)
and the fully deprotected H PO -TPA ligand at 9 ppm. The peak
at 11 ppm in the P-UiO66-PSM is then assigned to PO(OPr) -TPA
2
-TPA ligand appears at 12 ppm,
2
3
2
but slightly shifted because of its interaction with the MOF
framework or from partially protected sites like P(O)(OR)(OH)-
TPA. The peak at 9 ppm in the P-UiO66-PSM-AW is assigned to
2 3
deprotected H PO -TPA. The peak at 6 ppm is assigned to
different structures for the two materials. In the case of P-UiO66-
-
+
PSM, it is assigned to PO K groups, as suggested by Harris et al.
for several pairs of phosphonic acid/salt derivatives[29] and
supported by ICP results, which show a K/P atomic ratio of 0.44.
The lower experimental K/P value compared to 0.6 obtained by
spectral deconvolution suggests the presence of some hydrogen-
bonded phosphonic acid sites whose chemical shift overlap with
Figure 2. Solid-state 31P NMR spectra of P-UiO66 in (A) P-UiO66-PSM and (B)
P-UiO66-PSM-AW, all recorded at 18.8 T with 20 kHz MAS frequency.
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Angewandte Chemie
10.1002/ange.202001332
RESEARCH ARTICLE
Figure 3. Optimized clusters modeling Brønsted sites in phosphonate-modified UiO-66: (A) structure 1: free -PO(OH)
2
; (B) structure 2: -P=O hydrogen-bonded with
-
ZrOH; (C) structure 3: phosphonate group acts as a bidentate ligand to Zr
second -PO(OH) located on an adjacent ligand. Acidic protons are indicated by green circles. Note that, for structure 4, a circle also indicates the proton in -COOH,
which could be acidic (DPE values in Table S3). Blue dashed lines indicate hydrogen bonds. Atoms shown: H (white), O (red), C (gray), P (orange), Zr (blue).
6 4 4 2
O (OH) ; (D) structure 4: -PO(OH) on one terephthalate ligand hydrogen-bonded to a
2
To identify the sites most likely to participate in acid
catalysis, we estimated deprotonation energy (DPE) using
quantum chemical calculations. Four sites were modeled
according to the major possibilities from solid-state NMR. The
detailed structures can be found in Figure 3, and the results are
presented in Table S4. Across all the P-structures probed, the
not acidic enough for catalysis given their high DPEs, even when
compared to the bridging OH in the Zr-cluster of UiO-66 (Table
S4), which does not show any catalytic activity for the reactions
tested (see below).
We studied the catalytic performance of the P-modified
material in several Brønsted acid-catalyzed reactions (Scheme 2).
First, the number of Brønsted acid sites (BAS) was determined by
the Hoffman elimination of two different alkylamines using the
Reactive Gas Chromatography (RGC) technique details of which
are reported elsewhere.[33] Dehydration of two alcohols (ethanol
and isopropyl alcohol) and the dehydra-decyclization of 2-
methyltetrahydrofuran (2-MTHF) were performed to benchmark
the catalytic performance of the material against those of a
traditional, strong solid acid (the aluminosilicate H-ZSM-5) and a
structurally analogous weak acid (the P-containing all-silica zeosil
P-SPP).[14,15]
-1
DPE values varied by up to 80 kJ mol . Phosphonate without
interactions with the cluster (‘free’ P-O(OH) ) (Figure 3A) exhibits
2
-1
the lowest DPE (1306 kJ mol ). Phosphonates in which the P=O
sites engage in a hydrogen-bond with a ZrOH (Figure 3B) have a
-1
slightly higher DPE (1315 kJ mol ) followed by mutually H-
-1
bonded neighboring phosphonates (1341 kJ mol , Figure 3D),
-1
and phosphonates bonded to Zr cluster (1386 kJ mol , Figure 3C).
These results suggest that the ‘free’ P-OH sites and sites in which
the P=O engages in hydrogen-bonding with ZrOH sites are
expected to be the most active in Brønsted acid catalysis. Most
notably, the DPE values obtained in all cases are >100 kJ mol-1
higher than those previously calculated for aluminosilicate
BAS densities measured by the Hoffman elimination of both
tert-butylamine and tert-amylamine are listed in Table 2. The
-1 [32]
zeolites (1200 ± 11 kJ mol ), consistent with a much weaker
acidity in P-UiO66-PSM-AW relative to bridging hydroxyls in
aluminosilicates.
-1
corresponding values for P-SPP (Si/P=27, 136 μmol g ) and
-1
ZSM-5 (Si/Al=140, 94 μmol g ) are included for reference. The
BAS counts for both UiO66 and P-UiO66-PSM are low but non-
Combining the solid-state 31P NMR signals and the DFT
calculations, we conservatively assume that 80 % of the P-sites
are active sites in P-UiO66-PSM-AW, including both ‘free’ P-OH
and H-bonded P-OH to Zr-OH. The remaining 20 % of P-sites are
bonded to the Zr-cluster, and the associated protons are probably
3
zero. There are likely μ -bridging OH sites on the clusters or
defect sites (i.e., terminal OH groups from missing ligand-defects)
present in the materials that are capable of protonating these
investigated amines. In contrast, the production of isobutene from
the Hoffman elimination of tert-butylamine is significantly higher
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Angewandte Chemie
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RESEARCH ARTICLE
-1
for P-UiO66-PSM-AW, giving a BAS count of 66 μmol g .
Nevertheless, its BAS counts are only ~10-14% of the theoretical
value assuming one BAS per P-site, indicating that the
alkylamines either are not protonated at most P sites, or they
could desorb without undergoing Hoffman elimination. Unlike in
aluminosilicates, the BAS count was found to be dependent on
the identity of probe alkylamine.[33] Thus, the BAS count is ~ 1.5x
isopropyl groups or occupied by potassium sites. The observed
low activity probably comes from a small number of POH sites
available. P-UiO66-PSM-AW, on the other hand, shows
considerably higher activity compared to UiO66 and P-UiO66-
PSM (i.e., before hydrolysis). Relative to P-SPP, the propylene
formation rate of P-UiO66-PSM-AW is similar (STYs within a
factor of ~2, Figure 4A), although the latter shows higher
propylene selectivity (~98% per C basis) than P-SPP (~80%)
under identical reaction conditions at strictly differential
conversions (<1%). Both P-materials exhibit lower activity
compared to aluminosilicates.[33]
-1
higher using tert-amylamine (proton affinity 938 kJ mol ) (Table
-1
2
) than using tert-butylamine (proton affinity 934 kJ mol ). Both
observations are consistent with results obtained in P-SPP, and
confirm the weakly acidic nature of POH sites in such materials,
as previously noted.[14,34] The BAS counts obtained from Hoffman
elimination of amines reflect the probe-dependent nature of the
active sites in these materials. However, using these counts to
normalize rates would overestimate them. Instead, the site-time
yields (STYs) reported in the probe reactions below were
normalized by the active phosphorus content (assuming 80% of
total phosphorus, see Figure 2B). We further compared the acidity
of these materials by ammonia TPD (Figure S5 and Table S5).
The data agree well with the expectation of weak acidity observed
by titration with the alkylamines.
Table 2. Brønsted-acid site (BAS) densities of P-UiO-66 and other materials.
Material
BAS (TBA)
BAS (TAA)
(μmol g )
BAS theor.
(μmol g )
-
1
-1
-1
(μmol g )
UiO66
20
32
-
-
-
P-UiO66-PSM
P-UiO66-PSM-AW
P-SPP
-
66
92
169
95
673
680
119
136
100
ZSM-5[33]
We then probed the activity of P-UiO66-PSM-AW for
dehydra-decyclization of 2-MTHF (Figure 4B). This reaction is
studied for the production of bio-renewable linear pentadienes. [
As in the case of IPA dehydration, UiO66 showed nearly no
dehydra-decyclization reactivity, while P-UiO66-PSM exhibited a
low but non-zero activity for pentadiene production. The dehydra-
decyclization activity and selectivity to linear pentadienes for P-
UiO66-PSM-AW are similar to the corresponding values reported
for P-SPP.[15] The performance of P-UiO66 and its weak Brønsted
acidity shows very high selectivity at the expense of activity of one
order-of-magnitude lower than other aluminosilicate zeolites.[37]
Kumbhalkar et al. tested zeolites of different pore sizes, as the 10
MR ZSM-5 and the 12 MR BEA. They did not observe a significant
change in the activity or selectivity (about 65 % at 35 % 2-MTHF
conversion), providing no direct evidence for confinement effects.
37]
Scheme 2. Brønsted-acid reactions catalyzed by P-UiO66-PSM-AW: (1)
Hoffman elimination of tert-butylamine (analogous for tert-amylamine); (2)
ethanol dehydration; (3) isopropyl alcohol dehydration; (4) 2-
methyltetrahydrofuran dehydra-decyclization.
2 3
Other catalysts, such as the Lewis acid Al O or Al-Sn-BEA, also
performed poorly.[38] On a recent report, Kumar et al. reported
activity data on MCM-22 and its pillared derivative MCM-36. It was
observed that mesopores were detrimental to dienes production.
In the same paper, the authors show that introducing boron into
the framework of the all-silica zeolites MWW, BEA and MFI yield
selective materials for 2-MTHF dehydra-decyclization as a
consequence of the weak acidity of the boron sites.[39] The
phosphoric acid impregnated zeosils were not extensively
investigated for dehydra-decyclization of 2-MTHF, but the related
reaction of 3-MTHF to pentadienes and isoprene. The Al-free
phosphorus-containing zeolites were all active and relatively
selective to isoprene (30 % < S< 70 %), especially compared with
Next, the catalytic performance of P-UiO66-PSM-AW was
probed in the acid-catalyzed dehydration of two alcohols (namely,
ethanol, and isopropyl alcohol). Alcohols can undergo
unimolecular dehydration to the corresponding olefin, or
bimolecular dehydration to the di-alkyl ether.[35,36] P-UiO66-PSM-
AW gives unimolecular dehydration products, namely, ethylene
o
and propylene, at reaction temperatures of 130-150 C. STYs for
ethylene and propylene production can be found in Figure S6, and
are analyzed in more detail in the SI.
We compared the activity and selectivity for propylene
formation from IPA by P-UiO66-PSM-AW with the parent UiO66,
as well as P-UiO66-PSM, and P-SPP. The results are shown in
Figure 4A. UiO-66 is inactive for IPA dehydration. P-UiO66-PSM
regular aluminosilicates like ZSM-5 and FAU (5 – 40 %
selective).[40]
-1
shows weak activity (STY 0.03 h ) with high selectivity to
propylene (98%). As suggested by solid-state NMR and ICP data,
most of the sites in P-UiO66-PSM are either protected by
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Angewandte Chemie
10.1002/ange.202001332
RESEARCH ARTICLE
Consistent with its weak acidity, it is moderately active for the
dehydration of both ethanol and isopropyl alcohol. For the
dehydra-decyclization of 2-methyl-tetrahydrofuran, P-UiO-66-
PSM-Hy exhibits site-time yields and selectivity similar to that of
highly selective phosphoric acid supported on zeolites (P-SPP),
holding promise for this and other reactions for the biomass
conversion to chemicals. The tunability of MOFs combined with
the PSM method and synthesis of phosphonic acids can provide
a more uniform distribution of acid sites throughout the framework
compared to the wide distribution observed in supported
phosphoric acid catalysts.
Experimental Section
Experimental procedures, other characterization, and reaction
data are given in Supporting Information.
Acknowledgments
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. M.D.dM.’s
doctoral fellowship was partially supported by the Brazillian
National Council for Scientific and Technological Development
Figure 4. STYs (green bars) and selectivities (blue bars), for two reactions
catalysed by various P-containing materials: (A) Isopropyl alcohol dehydration
to propylene (0.050 g cat, 30 Torr IPA, 130 oC, WHSV 3.8 h , conversions
-1
maintained below 1 %); and (B) dehydra-decyclization of 2-MTHF (0.050 g cat,
-1
4
.9 Torr 2-MTHF, 280 oC, WHSV 0.31 h , determined at 25 % conversion).
STYs were calculated for P-UiO-66-PSM-AW using the estimated of accessible
P sites (80% of total P determined by 31P solid-state NMR, see Figure 2B) and
for P-UiO66-PSM and P-SPP based on total P content. UiO66 did not show any
activity (STYs are shown as zero just for comparison purposes). All carbon
balances close to ±10 %.
(
CNPq) under grant 202982/2014-9.
Keywords: MOFs • phosphonates • solid Brønsted acids •
biomass conversion
The catalytic activities and selectivities to products for
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and moderate (~23%) 2-MTHF conversion. Some catalyst
deactivation was observed, but it is less severe for P-UiO66-PSM-
AW than for P-SPP (Figure S7). Furthermore, regeneration
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Entry for the Table of Contents
RESEARCH ARTICLE
Matheus Dorneles de Mello, Gaurav
Kumar, Tarnuma Tabassum, Sheetal K.
Jain, Tso-Hsuan Chen, Stavros
Caratzoulas, Dionisios G. Vlachos,
Songi-I Han, Susannah L. Scott, Paul
Dauenhauer, and Michael Tsapatsis*
Text for Table of Contents
Page No. – Page No.
Phosphonate-modified zirconium
metal-organic frameworks with
intrinsic Brønsted acidity and its use
in dehydra-decyclization of 2-
methyltetrahydrofuran to pentadienes
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