Ordered Mesoporous Polymers for Biomass Conversions and Cross-Coupling Reactions

Article abstract of DOI:10.1002/cssc.201600822

Amino group-functionalized, ordered mesoporous polymers (OMP-NH₂) were prepared using a solvent-free synthesis by grinding mixtures of solid raw precursors (aminophenol, terephthaldehyde), using block copolymer templates, and curing at 140–180 °C. OMP-NH₂ was functionalized with acidic sites and incorporated with palladium, giving multifunctional solid catalysts with large Brunauer–Emmett–Teller (BET) surface areas, abundant and ordered mesopores, good thermal stabilities, controllable concentrations, and good dispersion of active centers. The resultant solid catalysts showed excellent catalytic activities and good reusability in biomass conversions and cross-coupling reactions—much superior to those of various reported solid catalysts such as Amberlyst 15, SBA-15-SO₃H, and Pd/C and comparable to those of homogeneous catalysts such as heteropoly acid, HCl, and palladium acetate. A facile green approach was developed for the synthesis of ordered mesoporous polymeric solid catalysts with excellent activities for conversion of low-cost feedstocks into useful chemicals and clean biofuels.

Full text of DOI:10.1002/cssc.201600822

DOI: 10.1002/cssc.201600822
Full Papers
Ordered Mesoporous Polymers for Biomass Conversions
and Cross-Coupling Reactions
Fujian Liu,*[a, b] Qin Wu,[a] Chen Liu,[a] Chenze Qi,*[a] Kuan Huang,[b] Anmin Zheng,[d] and
Sheng Dai*[b, c]
Amino group-functionalized, ordered mesoporous polymers
(OMP-NH2) were prepared using a solvent-free synthesis by
grinding mixtures of solid raw precursors (aminophenol, ter-
ephthaldehyde), using block copolymer templates, and curing
at 140–1808C. OMP-NH2 was functionalized with acidic sites
and incorporated with palladium, giving multifunctional solid
catalysts with large Brunauer–Emmett–Teller (BET) surface
areas, abundant and ordered mesopores, good thermal stabili-
ties, controllable concentrations, and good dispersion of active
centers. The resultant solid catalysts showed excellent catalytic
activities and good reusability in biomass conversions and
cross-coupling reactions—much superior to those of various
reported solid catalysts such as Amberlyst 15, SBA-15-SO3H,
and Pd/C and comparable to those of homogeneous catalysts
such as heteropoly acid, HCl, and palladium acetate. A facile
green approach was developed for the synthesis of ordered
mesoporous polymeric solid catalysts with excellent activities
for conversion of low-cost feedstocks into useful chemicals
and clean biofuels.
Introduction
Ordered mesoporous polymers (OMPs) have been the subject
of much attention and have received extensive interest in the
research community. They have been widely used for selective
adsorption, separation, thermal insulation, water treatment,
and heterogeneous catalysis.[1–12] Compared to various report-
ed porous organic polymers—crystalline covalent organic
frameworks, porous aromatic frameworks with amorphous net-
works, conjugated microporous polymers, and mesoporous
polydivinylbenzene—OMPs possess unique characteristics such
as tunable periodic structures, ordered and uniform meso-
pores, and adjustable mesopore sizes (2–30 nm).[13–21] These
characteristics make the active sites anchored on the OMP net-
work more readily accessible to various substrates, which is fa-
vorable for enhancing their activities to catalyze the transfor-
mation of various low-cost substrates such as biomass into
fine chemicals and biofuels.[5,22,23] In addition, OMPs can be
used as a facile cost-effective approach for the synthesis of
highly ordered mesoporous carbons (OMCs) through a direct
carbonization processes,[1–3,11,24] which act as a bridge connect-
ing OMPs and OMCs.
Previously, typical OMPs were formed from ordered mesopo-
rous phenol–formaldehyde resins synthesized through the self-
assembly of phenol–formaldehyde resol with block copolymer
templates (such as P123 and F127). They were based on strong
hydrogen bond interactions and required curing at various
temperatures (75–2608C).[1–4,11,24] The synthesis of OMPs nor-
mally requires aqueous or organic solvents in the presence of
acid or base catalysts to ensure the polymerization of phenol–
formaldehyde precursors, and various research results indicate
that high-temperature hydrothermal synthesis is favorable for
the enhancement of their thermal and mechanical stability.[4]
However, safety concerns associated with high-temperature
hydrothermal synthesis, abundant pollutant emissions result-
ing from the high use of solvents, and the use of acid and
base catalysts have significantly limited the practical applica-
tion of functional OMPs in industry.
[a] Prof. F. Liu, Q. Wu, C. Liu, C. Qi
College of Chemistry and Chemical Engineering
Shaoxing University
Shaoxing, 312000 (China)
E-mail: fjliu@usx.edu.cn
qichenze@usx.edu.cn
[b] Prof. F. Liu, Dr. K. Huang, Prof. Dr. S. Dai
Department of Chemistry
University of Tennessee
Knoxville TN 37996 (USA)
E-mail: dais@ornl.gov
[c] Prof. Dr. S. Dai
Chemical Sciences Division
Oak Ridge National Laboratory
Oak Ridge TN 37831 (USA)
E-mail: dais@ornl.gov
OMP networks are usually constructed by the condensation
of phenolic precursors such as phenol, resorcinol, and phloro-
glucinol with aldehydes, which usually results in samples with
catalytically inert networks. Various catalytically active heteroa-
toms, such as nitrogen and sulfur, can be introduced into their
networks by introducing heteroatom-containing precursors or
by post-treatment during the synthetic processes. This partially
[d] Prof. Dr. A. Zheng
Wuhan Center for Magnetic Resonance
State Key Laboratory of Magnetic Resonance and Atomic and Molecular
Physics
Wuhan Institute of Physics and Mathematics
Wuhan 430071 (China)
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cssc.201600822.
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sacrifices the ordering of mesopores in the OMPs, resulting in
limited concentrations and poor dispersion of catalytically
active sites.[22–26]
To the best of our knowledge, it remains a challenge to de-
velop a green approach to synthesize catalytically active OMPs
employing pure heteroatom-containing precursors, which
would be favorable for enhancing the concentration and dis-
persion of active centers. Herein, we report the solid-phase,
fast synthesis of amino-group-functionalized, ordered, thermal-
ly stable mesoporous polymers (OMP-NH2) by employing m-
aminophenol as a precursor. The precursor was ground well
with block copolymer templates and terephthaldehyde and
cured at 1808C without the use of acid or base catalysts. The
solvent- and catalyst-free synthesis overcomes the safety con-
cerns and pollutant emissions related to traditional synthetic
technologies for the synthesis of OMPs. OMP-NH2 was used as
an efficient solid base, incorporated with palladium (Pd) nano-
crystals, and functionalized with acidic sites, which were homo-
geneously dispersed into the samples. The resulting multifunc-
tional OMP materials could serve as highly efficient, reusable
catalysts in various reactions including biomass conversion,
Knoevenagel condensation, and cross-coupling reactions. The
catalytic activities of the OMPs proved to be superior to those
of various reported catalysts such as commercial Amberlyst 15,
SBA-15-SO3H, and Pd/C. The activity of OMP solid acids for the
depolymerization of crystalline cellulose into various fine
chemicals was comparable to those of homogeneous HCl. In
this work, we developed a novel green approach for the syn-
thesis of OMPs functionalized with various active centers,
which offers great opportunities for the wider application of
OMPs for catalyzing the transformation of low-cost feedstocks
into clean biofuels and fine chemicals.
Figure 1. Small-angle XRD patterns of various calcinated OMP-based solid
catalysts.
1,4-butanesultone) can be attributed to different amounts of
shrinkage in the networks of OMP-NH2.[1,2] In addition to F127,
OMP-NH2 was also synthesized using P123 and F108 as tem-
plates (Figure S1, Supporting Information).
Figure 2 shows N2 isotherms and pore size distributions of
various OMP samples. All these samples show typical type IV
isotherms with sharp capillary condensation steps at relative
pressures (P/P0) ranging from 0.50 to 0.80, which confirm that
many mesopores were formed in the samples.[1,2,27] The Bruna-
uer–Emmett–Teller (BET) surface areas ranged from SBET =84 to
581 m2 gÀ1 (Table 1), and the mesopore sizes in these samples
with very sharp distributions were centered in a range from
5.5 to 11.1 nm, indicating that fairly uniform mesopores
formed in the samples (Figure 2). Compared with calcinated
OMP-SO3H (179 m2 gÀ1, 5.5 nm), the extracted OMP-SO3H
showed a smaller SBET (84 m2 gÀ1) and enlarged mesopores
(11.1 nm). The different structural characteristics of the two
samples can be attributed to the different number of micro-
pores and the degree of shrinkage of the OMP networks, in
good agreement with the XRD results.
Results and Discussion
Figure 1 shows small angle X-ray diffraction (XRD) patterns of
various OMPs functionalized with amino groups, sulfonic
groups, and Pd nanocrystals. All of these samples show three
well resolved diffraction peaks indexed as (110), (200), and
(211), indicating that highly ordered mesopores with body-cen-
tered cubic (bcc) structures (Im3m, Figure 1a–e) were formed
in these samples.[1,2,4] An amino-group-grafted ordered meso-
porous resin (OMP-NH2) gives d (110) values at approximately
11.04 nm. This material was used as an effective material for in-
corporating with Pd active species because of its unique inter-
actions. The resultant OMP-NH2-Pd shows a similar d (110)
value (11.30 nm) to OMP-NH2. OMP-NH2 was also grafted with
an acidic ionic liquid to give OMP-[C4NH2][SO3CF3], which also
showed three diffraction peaks associated with highly ordered
mesopores (Im3m), and a decreased d (110) value (10.25 nm)
compared with OMP-NH2 because the OMP networks partially
shrank during the acidification process. An OMP functionalized
by an acidic ionic liquid (OMP-[C4NH2][SO3H]) was synthesized
by the acidification of calcinated or solvent-extracted OMP-
NH2. It also showed an ordered mesostructure, giving different
d (110) values at approximately 11.24 nm and 9.76 nm. The dif-
ferent d (110) values of OMP-NH2 and OMP-[C4NH2][SO3H] (C4 is
Notably, the block copolymer templates in the OMPs could
be removed by thermal decomposition or solvent extraction,
which provided OMP materials with opened mesopores. Ther-
mal treatment usually results in the formation of an abundance
of micropores and shrinkage of the networks in the OMPs,
whereas the solvent extraction method provides samples with
a very small amount of micropores and nearly no shrinkage of
the OMP networks.[1,2,4]
Figure 3 shows scanning electron microscopy (SEM) images
of OMP-NH2, which exhibits a monolithic morphology with dis-
ordered shapes. The highly resolved SEM images indicate that
OMP-NH2 has rough surface characteristics and abundant mes-
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Figure 2. N2 adsorption–desorption isotherms and BJH mesopore size distributions of (a) solvent-extracted OMP-SO3H, (b) calcinated OMP-SO3H, (c) OMP-Pd,
(d) OMP-NH2, (e) OMP-NH2-Pd, (f) OMP-F108-NH2, and (g) OMP-P123-NH2.
Table 1. The textural parameters of OMP-based solid catalysts.
[b]
[c]
[d]
Samples
X[a]
[mmolgÀ1
SBET
Vp
Dp
]
[m2 gÀ1
]
[cm3 gÀ1
]
[nm]
OMP-F108-NH2
OMP-NH2
OMP-NH2-Pd
OMP-HMTA-Pd
OMP-Pd
2.02[e]
1.98[e]
0.094[f]
0.098[f]
0.095[f]
1.94[h]
1.89[h]
1.42[h]
2.11[e]
280
538
427
581
515
179
84
0.26
0.46
0.35
0.45
0.43
0.15
0.20
0.30
0.24
5.6
6.6
6.4
4.2
4.9
5.5
11.1
5.2
7.4
OMP-SO3H
OMP-SO3H[g]
OMP-[C4NH2][SO3CF3]
OMP-P123-NH2
333
339
[a] Heteroatoms content. [b] Measured by N2 adsorption isotherms.
[c] Vp =pore volumes estimated at relative pressure of 0.975. [d] Pore size
distributions estimated using the BJH model. [e] The contents of nitrogen
were tested by elemental analysis. [f] The content of Pd in the OMPs was
analyzed using inductively coupled plasma spectroscopy. [g] The tem-
plate was removed from the extraction using a mixture of ethanol and
HCl. [h] The contents of sulfur were tested by elemental analysis.
Figure 3. (a–d) Scanning electron microscopy images of OMP-NH2; the scale
bars of a and b are 1 mm; the scale bars of c and d are 200 and 100 nm.
opores. In addition, electro dispersive X-ray spectroscopy and
elemental maps show the signals of C, N, and O and C, S, and
O in OMP-NH2 and OMP-SO3H, respectively, which are homoge-
neously dispersed into these samples. The signals indicate the
successful introduction of sulfonic and amino groups into the
networks of OMP-NH2 and OMP-SO3H (Figure 4).
a template and solvent, possess enough mobility during the
synthesis of the OMPs owing to the high temperature (140–
1808C), which ensures that the self-assembly of the surfactant–
polymer composites can be achieved. The controllable and
property interaction between the template and the polymer
precursor results in the formation of ordered mesopores in the
phenolic polymers. Furthermore, OMP-NH2 could be efficiently
loaded with Pd because of the unique interactions between
Pd and the amino groups, and the synthesis was a one-step
solvent-free process. The resultant OMP-NH2-Pd showed
a highly ordered mesostructure, and Pd nanocrystals were ho-
mogeneously dispersed in the samples.
Figure 5 shows transmission electron microscopy (TEM)
images of OMP-NH2, OMP-SO3H, and OMP-NH2-Pd. TEM was
used to confirm the regularity of the mesopores in these sam-
ples. The images of OMP-NH2 were viewed along the [111],
[110], and [100] directions. They indicate a highly ordered, bcc
mesostructure (Im3m) in the sample.[1,2,4] The cell parameters
of OMP-NH2 estimated from the TEM images was approximate-
ly 10 nm, in agreement with the XRD results. In addition, OMP-
SO3H showed extensive porosity with large areas of ordered
cubic mesostructures, in good agreement with the XRD results.
The surfactants and block copolymers, which may act as both
Figure 6 shows the XPS spectra of OMP-NH2-Pd, which show
peaks associated with C1s, N1s, and Pd3d. The C1s spectra
were fitted and de-convoluted into two peaks at approximate-
ly 284.2 and 285.7 eV, which were assigned to the CÀC bond in
the benzene ring and the CÀN bond.[18] The peaks of N1s at
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Figure 4. SEM image and elemental maps of (a–d) OMP-SO3H and (e–h) OMP-NH2.
and the peaks at approximately 337.2 and 342.3 eV were as-
signed to Pd2+(ꢀ39.8%).[27] These results indicate that Pd spe-
cies with different valences were successfully incorporated into
OMP-NH2, which strongly stabilized the Pd species owing to
the presence of coordination interactions between Pd and
amine groups in the sample. Figure S3 shows XPS spectra of
OMP-SO3H, which exhibit the peaks associated with C1s and
S2p. The C1s spectra could be fitted and de-convoluted into
two peaks centered at approximately 284.7 and 286.5 eV,
which were assigned to the CÀC and CÀS bonds, respectively
(Figure S2A). The S2p spectra showed two broad signals cen-
tered at approximately 169 and 171.2 eV (Figure S2B), which
can be attributed to the sulfonic groups connected with the
benzene ring and phenolic hydroxyl group that produce the
acidic sites of ÀSO3H and ÀOÀSO3H. These results further con-
firm that different active heteroatoms were successfully intro-
duced into OMPs.
Figure 7 shows FTIR spectra of OMP-SO3H and OMP-NH2. For
OMP-SO3H, a peak at approximately 1042 and 1180 cmÀ1 asso-
ciated with the CÀS and S=O bonds can be clearly observed,
indicating successful grafting of a sulfonic group in the
sample.[18] For OMP-NH2, the peaks at approximately 1298 cmÀ1
were associated with the CÀN stretch, and the peak at
1630 cmÀ1 was attributed to the deformation vibrations of the
NÀH bond.[28] The broad peak at approximately 3400 cmÀ1 in
both samples was attributed to absorbed water. These results
confirmed that both sulfonic and amino groups were success-
fully introduced into the OMPs, in agreement with the XPS re-
sults.
Figure 5. TEM images of (a–c) OMP-NH2, (d) OMP-SO3H, and (e,f) OMP-NH2-
Pd; the scale bars of c, d, e, and f are 20, 100, 100, and 50 nm, respectively.
approximately 399 and 405.5 eV were assigned to nitrogen in
the amino groups and nitrogen coordinated with the Pd spe-
cies, respectively. In addition, the peaks of Pd3d at approxi-
mately 335.2 and 340.4 eV were assigned to Pd0 (ꢀ60.2%),
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Figure 6. XPS spectra of (a) C1s, (b) N1s and (c) P3d of OMP-NH2-Pd.
Figure 8. TG curves of various OMP-based solid catalysts.
Figure 7. FTIR spectra of amine- and sulfonate-functionalized OMPs.
Figure 8 shows thermogravimetric (TG) curves of as-synthe-
sized OMP-NH2, OMP-NH2, OMP-NH2-Pd, and acidic-site-func-
tionalized OMPs. The weight loss below 2008C in these sam-
ples was attributed to desorption of water. As-synthesized
OMP-NH2 showed a very strong weight loss step in the tem-
perature range from 300 to 4508C because of the decomposi-
tion of the copolymer templates in the samples, whereas the
weight loss step in the temperature range from 450 to 8008C
was attributed to the decomposition of the amino group and
carbonization of the polymer network. For OMP-NH2, almost
no weight loss step could be observed in the temperature
range from 300 to 4508C because the copolymer template in
OMP-NH2 had been removed, giving the sample with opened
mesopores. However, it showed a similar amount of weight
loss associated with decomposition of the amino groups and
carbonization of the polymer network in the temperature
range from 450 to 8008C (Figure 1a and b). After loading with
Pd nanocrystals, the resulting OMP-NH2-Pd showed thermal
stability similar to that of OMP-NH2 (Figure 1c). OMP-SO3H and
OMP-[C4NH2][SO3CF3] showed weight losses associated with
the decomposition of acidic groups and the polymer network
in a range from 450 to 8008C (Figure 1d and e). These results
confirm the superior thermal stabilities of both active sites and
networks in OMP-based solid catalysts.
based solid acids showed catalytic activities superior to those
of commercial Amberlyst 15 and SBA-15-SO3H. After the OMP-
SO3H was reused five times, the yield of methyl palmitate cata-
lyzed by the recycled OMP-SO3H (95.7%) was almost as high as
the yield using fresh OMP-SO3H (98.5%, Table 1).
In addition to esterification of fatty acids, the OMP solid
acids were very active in the transesterification of tripalmitin
with methanol, which is an important model reaction for the
production of biodiesel from raw feedstocks such as plant and
animal oils.[29] The yields of methyl palmitate catalyzed by
OMP-SO3H and OMP-[C4NH2][SO3CF3] were as high as 90.2 and
95.3%—much higher than the yields from H3W12O40 (66.7%),
Table 2. Catalytic data from the esterification of palmitic acid with meth-
anol over various samples.[a]
Catalyst
Yield of methyl palmitate[b] [%]
OMP-[C4NH2][SO3CF3]
OMP-SO3H
>99.5
98.5
Amberlyst 15
SBA-15-SO3H
OMP-SO3H[c]
55.9
61.8
95.7
[a] Reaction conditions: 1.28 g palmitic acid, 2.5 mL methanol, 0.05 g cat-
alyst. The reaction was performed at 658C for 2 h. [b] The yields of the
methyl ester catalyzed by various catalysts were characterized using gas
chromatography based on an internal standard method. The selectivity
for methyl palmitate was higher than 99.5%. [c] The catalyst used had
been recycled 5times.
Table 2 presents the activities of various solid acids in the
esterification of palmitic acid with methanol. The product,
methyl palmitate, is a typical component of biodiesel. OMP-
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Amberlyst-15 (40.6%), and SBA-15-SO3H (47.6%) and slightly
lower than the yield from homogeneous H2SO4 (Figure 9). Bio-
diesel production catalyzed by OMP solid acids was also evalu-
ated through the direct transformation of sunflower oil under
similar reaction conditions (Figure 10). The results showed that
Table 3. Yield of sugars and dehydration products in the depolymeriza-
tion of Avicel catalyzed by various acids.
Catalysts
Yield [%]
Glucose[a]
Cellobiose[a]
HMF[a]
TRS[b]
Amberlyst 15
HCl
OMP-SO3H
OMP-[C4NH2][SO3CF3]
OMP-SO3H[c]
OMP-[C4NH2][SO3H]
22.4
59.8
54.8
63.7
52.9
60.7
10.8
12.5
11.2
9.6
10.6
10.3
3.1
9.1
8.6
10.1
7.8
9.7
48.6
87.1
81.3
93.6
77.8
91.2
[a] Measured by HPLC; the reaction time was 5 h. [b] Total reduced sugar
(TRS) was estimated by the DNS method. [c] The catalyst used had been
recycled 5 times.
(87.1%), and superior to that of Amberlyst 15 (48.6%). Corre-
spondingly, the yields of the main products of glucose (52.9–
63.7%), cellobiose (9.6–11.2%), and HMF (7.8–10.1%) catalyzed
by OMP-based solid acids were as high as the yields from HCl
(59.8, 12.5, and 9.1%, respectively). In contrast, Amberlyst 15
produced low glucose, cellobiose, and HMF yields of 22.4, 10.8,
and 3.1%, respectively.
Figure 9. Catalytic activities for transesterification of tripalmitin with MeOH
over (a) OMP-SO3H, (b) OMP-[C4NH2][SO3CF3], (c) SBA-15-SO3H, (d) H3O40PW12,
(e) Amberlyst 15, and (f) H2SO4.
OMPs were also used as efficient catalysts and catalyst sup-
ports in other types of reactions. Table 4 presents the catalytic
activities of OMP based solid catalysts in Suzuki–Miyaura and
Heck cross-coupling reactions and in Knoevenagel condensa-
tion. For instance, OMP-NH2-Pd showed excellent catalytic ac-
tivity in the Suzuki–Miyaura and Heck reactions, and various
bromo and iodo aromatic substrates were effectively trans-
formed into useful compounds by using OMP-NH2-Pd as the
catalyst (Table 4). The activity of OMP-NH2-Pd surpassed that of
a Pd/C catalyst and was comparable to that of a homogeneous
Pd acetate catalyst. In addition, OMP-NH2 was used as a highly
efficient solid base in Knoevenagel condensation, and benzal-
dehyde was completely transformed into 2-benzylidene-malo-
nonitrile under mild conditions catalyzed by OMP-NH2
(Table 4). The excellent catalytic activity of OMP solid catalysts
is attributed to their large SBET, highly ordered and uniform
mesopores, and homogeneous dispersion of active centers,
which make the active sites anchored to the OMP network
more easily accessible to various reactants, resulting in
a higher degree of exposure to active sites.
Figure 10. The yields of methyl esters in the transesterification reaction of
sunflower oil with MeOH catalyzed by OMP-SO3H.
OMP solid acids such as OMP-SO3H exhibit extraordinary activi-
ty in the reaction. The main components of the biodiesel were
palmitate (C16:0), methyl stearate (C18:1), methyl oleate (C18:2),
methyl linoleate (C18:3), methyl arachidate (C20:0), 11-eicosenoic
methyl (C20:1), methyldocosanoate (C22:0), and methyltetracosa-
noate (C24:0) with yields of 89.1, 90.3, 85.2, 87.3, 82.5, 88.1, 80.7,
79.8%, respectively. These yields confirm that OMP solid acids
are highly efficient solid acids for catalyzing biodiesel produc-
tion.
Conclusions
Functionalized OMPs containing various active groups, such as
ÀNH2, ÀSO3H, acid ionic liquids, and Pd nanocrystals, were syn-
thesized using a solvent-free methodology. The synthesis was
achieved by facile grinding of solid mixtures containing block
copolymer templates, aminophenol, and catalytically active
precursors, and curing at 140–1808C using no acid or base cat-
alysts. The synthesized OMP-based solid catalysts showed
highly ordered and uniform mesopores, large Brunauer–
Emmett–Teller (BET) surface areas, and controllable and homo-
geneous dispersion of the active centers. These properties re-
sulted in much improved catalytic activity compared with
other catalysts, and good reusability in biomass conversion
To further expand the applications of OMP-based solid acids
in biomass conversion, we investigated their catalytic perform-
ances in the depolymerization of microcrystalline cellulose. The
main products of this reaction were glucose, cellobiose, and
hydroxymethylfurfural (HMF). The total reduced sugars cata-
lyzed by OMP solid acids ranged from 77.8 to 93.6% (Table 3),
a performance equal to that of homogeneous HCl catalyst
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dehyde, malononitrile, hexamethylenetetramine (HMTA),
1,4-butane sultone, HCl, HSO3CF3, H2SO4, dimethyl sulf-
oxide (DMSO), acetone, sunflower oil, and dodecane
were obtained from Sinopharm Chemical Reagents Co.
Ltd.
Table 4. Catalytic data of OMP-NH2-Pd in Heck and Suzuki–Miyaura cross-coupling re-
actions and OMP-NH2 in Knoevenagel condensation.
Synthesis of the samples
OMPs were synthesized by grinding of mixtures contain-
ing phenolic precursors, terephthaldehyde, and block
copolymer templates of F127, P123, or F108, and curing
at 140–1808C. As a typical run for the synthesis of OMP-
NH2, 2.5 g of F127 powder, 0.45 g of m-aminophenol,
and 0.56 g of terephthaldehyde were mixed well and
ground for 10 min at room temperature. The solid mix-
ture was transferred into an autoclave and cured at
1508C for 24 h to give as-synthesized OMP-NH2. As a typ-
ical run for the synthesis of OMP-HMTA, 2.5 g of F127
powder, 0.45 g of resorcinol, 0.56 g of terephthaldehyde,
and 0.05 g of HMTA were mixed well and ground for
10 min at room temperature. The solid mixture was
transferred into an autoclave and cured at 1508C for
24 h to give as-synthesized OMP-HMTA. The templates
in the samples could be removed by calcination at
3608C under an inert gas, or extracted with boiling etha-
nol for 48 h. In this work, during the whole processes of
preparation of ordered mesoporous polymers, no sol-
vent was used even during the autoclave step. There-
fore, the autoclave just acts as container for the curing
of the network of ordered mesoporous polymers, and
no changes of the pressure during the thermal curing
processes, which is basically the same as ambient pres-
sure. Glass bottles can also be used as the reaction con-
tainer instead of autoclaves for the preparation of or-
dered mesoporous polymers.
Run
Substrate 1
Substrate 2
Yield [%]
OMP-NH2-Pd
OMP-NH2-Pd
OMP-NH2-Pd
OMP-NH2-Pd
OMP-NH2-Pd
OMP-NH2-Pd[a]
palladium acetate[b]
OMP-NH2-Pd
OMP-NH2-Pd
Pd/C[b]
>99.5
>99.5
96.4
97.5
>99.5
99.1
>99.5
99.1
>99.5
95.1
[c]
OMP-NH2
>99.5
To synthesize OMP-NH2-Pd, a quantitative amount of
palladium acetate was introduced into the mixture
during the grinding process, followed by curing at
1408C and calcination at 3608C under an inert gas.
OMP-SO3H was synthesized by the sulfonation of calci-
nated OMP with HSO3Cl at 08C in the presence of
CH2Cl2 solvent. Acidification of the OMPs was also ac-
complished by treating OMP-NH2 with 1,3-propanesul-
[a] The catalyst used had been recycled 5 times. [b] The same number of active sites
as OMP-NH2-Pd. [c] 1.5 mmol of benzaldehyde, 0.03 g of catalyst, 1.0 mmol of malono-
nitrile, 5 mL of ethanol solvent, 808C for 2 h.
and cross-coupling reactions. The solvent-free technology is
tone in toluene solvent at 1008C and acid exchanging with
HSO3CF3 at 08C two times.
a green, sustainable, fast approach for the synthesis of OMPs
functionalized with various catalytically active sites and offers
great potential for wider use of OMPs in industry to catalyze
the production of useful chemicals and biofuels through heter-
ogeneous catalytic processes.
Characterization
X-ray diffractions were measured using a Rigaku D/Max-2550 using
nickel-filtered CuKa radiation. Nitrogen isotherms at À1968C were
measured using a Micromeritics ASAP 2020m system. The samples
were outgassed for 6 h at 2008C with flowing N2 before the meas-
urements, and the pore-size distribution of the mesopores was cal-
culated using the Barrett–Joyner–Halenda (BJH) model. FTIR spec-
tra were recorded using a Bruker 66 V FTIR spectrometer. Thermog-
ravimetric analyses were performed on a PerkinElmer TGA7 in flow-
ing air at a heating rate of 108CminÀ1. The acid exchange capaci-
ties of the catalysts were determined by acid–base titration with
a standard NaOH solution. X-ray photoelectron spectroscopy spec-
tra were obtained on a Thermo ESCALAB 250 with AlKa radiation,
and binding energies were calibrated using the C1s peak at
284.9 eV. CHNS elemental analyses were performed on a PerkinElm-
er series II CHNS analyzer 2400. TEM images were obtained on an
Experimental Section
Chemicals and reagents
All reagents were analytical grade and were used as purchased
without further purification. Block copolymers Pluronic F127
(PEO106-PPO70-PEO106),
P123
(PEO20-PPO70-PEO20),
F108
(PEO132PPO50PEO132), 1-n-butyl-3-methylimidazolium ([C4mim]Cl),
phenylboronic acid, Pd acetate, Avicel microcrystalline cellulose,
and tripalmitin were purchased from Sigma–Aldrich Co. Resorcinol,
methanol, tetrahydrofuran (THF), 4-chlorotoluene, m-aminophenol,
iodobenzene, CH2Cl2, toluene, 4-bromotoluene, n-butyl acrylate,
palmitic acid, styrene, dichloromethane, benzaldehyde, terephthal-
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&
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FEI Tecnai G2 F20 s-twin D573 TEM working at 200 kV. SEM images
were taken on a Zeiss Auriga Crossbeam SEM at an acceleration
voltage of 5 kV.
(86.3 mmol) and 0.1 g of catalyst were mixed in a three-neck round
flask equipped with a condenser and a magnetic stirrer. The reac-
tion was performed at 658C for 18 h. The molar ratio of tripalmitin/
methanol was 1/74.4, and the mass ratio of catalyst/tripalmitin was
0.1. The main products were methyl palmitate (C16:0), methyl stea-
rate (C18:1), methyl oleate (C18:2), methyl linoleate (C18:3), methyl
arachidate (C20:0), 11-eicosenoic methyl (C20:1), methyldocosanoate
(C22:0), and methyltetracosanoate (C24:0). They were analyzed using
an Agilent GC/MS instrument (Agilent 6890N/5975I) with a pro-
grammable split/splitless injector. The injector-port temperature
was set at 2708C. The oven temperature program was initially set
at 1408C with a ramping rate of 108CminÀ1 to 2708C. The yields of
these products were analyzed using an Agilent 7890 GC based on
an internal standard method.
Catalytic reactions
Depolymerization of crystalline cellulose: 100 mg of Avicel was
dissolved in 2.0 g of [C4mim]Cl ionic liquid. After vigorous stirring
of the mixture at 1008C for 10 h to dissolve the microcrystalline
cellulose, 20 mg of OMP solid acid was added. After that, 600 mL of
water acting as a reactant was slowly introduced into the reaction
mixture, and the reaction temperature was kept at 1008C. At differ-
ent time intervals, a portion of the reaction mixture was with-
drawn, weighed, quenched immediately with cold water, and cen-
trifuged at 14,800 rpm for 5 min to separate unreacted cellulose.
For comparison, Amberlyst 15 and HCl were also used as catalysts
in this reaction, which was performed using the same procedures
as for the OMP solid acids. In this reaction, the isolated crystalline
cellulose was thoroughly washed with water and recovered by
centrifugation. The amount of isolated cellulose was determined
by weighing.
Suzuki–Miyaura reaction: In a typical run for the Suzuki–Miyaura
reaction, 0.25 mmol of 4-iodotoluene, 0.375 mmol of aryl boronic
acids, and 0.5 mmol of K2CO3 were mixed well in a flask, followed
by the addition of 10 mg of OMP-NH2-Pd (1.0 wt% of palladium
acetate) catalyst. Subsequently, 3.0 mL of EtOH and 1.0 mL of H2O
were introduced as the solvents. The reaction was performed at
808C for 30 min. Similarly, 4-bromotoluene could also be employed
as a substrate: 1.0 mmol of 4-bromotoluene, 3.0 mmol of aryl bor-
onic acids, and 2.0 mmol of K2CO3 were mixed well in a flask, fol-
lowed by the addition of 30 mg of OMP-NH2-Pd (1.0 wt% of palla-
dium acetate) catalyst. Subsequently, 3.0 mL of dimethylformamide
(DMF) and 1.0 mL of H2O were introduced as the solvents. The re-
action was performed at 1108C for 5 h. The yields of various prod-
ucts were analyzed using an Agilent 7890 GC based on an internal
standard method.
Total reducing sugar (TRS): The TRS method was thought to be
a reliable technology to evaluate the degree of depolymerization
of microcrystalline cellulose, which was tested through the 3,5-dini-
trosalicylicacid (DNS) method.[30–34] Typically, a reaction mixture
contained 0.5 mL of 3,5-dinitrosalicylicacid (DNS) reagent; 0.5 mL
of the isolated reaction mixture was heated for 5 min at 1008C.
Then the mixture was diluted with 4 mL of deionized water. The
color changes of the mixture were measured by a NanoDrop 2000
UV-spectrophotometer at a wavelength of 540 nm. The TRS con-
centrations were obtained using a standard curves method.
Heck reaction: 1 mmol of aromatic halide, 2 mmol of alkenes,
OMP-NH2-Pd catalyst (2 mmol Pd), 3 mmol of potassium acetate,
and 3 mL of DMSO were mixed well in a three-neck flask equipped
with a condenser and a magnetic stirrer. The reaction was per-
formed at 1108C for 5 h. The yields of various products were ana-
lyzed using an Agilent 7890 GC based on an internal standard
method.
In this reaction, the concentrations of glucose, cellobiose, and HMF
products were measured by a Shimadzu LC-20 A HPLC system
based on a standard curve method, which was equipped with an
SCR-101N column. Extra-pure water with
a flow rate of
0.5 mLminÀ1 was used as a mobile phase. The temperature of the
column was set at 508C. A refraction index was used for detection
of sugars in the water. The yields of 5-HMF were analyzed by an ul-
traviolet detector with a wavelength of 254 nm for detection
based on a standard curve method. It was equipped with a CAP-
CELL PAK C18 column using methanol and water (methanol/
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (21573150, 21203122), and the Natural Science
Foundation of Zhejiang Province (LY15B030002).K.H. and S.D.
were supported by the US-DOE Office of Science, Division of
Chemical Sciences, Geosciences and Biosciences.
water=80:20) during the mobile phase, at
a flow rate of
0.7 mLminÀ1. The column temperature was set at 508C.
Catalyzing the production of biodiesel: Biodiesel was produced
through the esterification of fatty acids with methanol and transes-
terification of tripalmitin or sunflower oil with methanol catalyzed
by OMP solid acids. Typically, 0.84 g (1.04 mmol) of tripalmitin was
melted at 658C in a round flask equipped with a condenser and
a magnetic stirrer, followed by the addition of 2.47 mL (61 mmol)
of methanol and 0.1 g of the catalyst under vigorous stirring. The
reaction was performed at 658C for 16 h. The molar ratio of tripal-
mitin to methanol was 1/58.7, and the mass ratio of catalyst/tripal-
mitin was 0.119. The main product was methyl palmitate with a se-
lectivity close to 100%. The product yields were analyzed by gas
chromatography (GC) with an Agilent 7890 equipped with an HP-
INNOWax capillary column (30 m). Its initial temperature was set at
1008C, with a ramping rate of 208CminÀ1 up to 2808C. The tem-
perature of the flame ionization detector was 3008C, and dodec-
ane was used as an internal standard.
Keywords: biomass conversions · heterogeneous catalysis ·
ordered mesoporous polymers · reusability · solvent free
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Published online on && &&, 0000
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F. Liu,* Q. Wu, C. Liu, C. Qi,* K. Huang,
A. Zheng, S. Dai*
&& – &&
Ordered Mesoporous Polymers for
Biomass Conversions and Cross-
Coupling Reactions
Go OMP green: A green approach is
developed for the synthesis of amino-
group-functionalized ordered mesopo-
rous polymers (OMPs) using a solvent-
free synthesis. The catalytically active
OMPs showed excellent activity for the
conversion of low-cost biomass feed-
stock into useful chemicals and clean bi-
ofuels.
&
ChemSusChem 2016, 9, 1 – 10
www.chemsuschem.org
10
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!