"Nafion"-functionalized mesoporous MCM-41 silica shows high activity and selectivity for carboxylic acid esterification and Friedel-Crafts acylation reactions

Article abstract of DOI:10.1016/j.jcat.2005.01.007

Hybrid organic-inorganic MCM-41 silicas functionalized with perfluoroalkylsulfonic acid groups analogous to that of Nafion were prepared in a simple single step by a condensation reaction between surface silanol groups of the mesoporous silicas and 1,2,2-trifluoro-2-hydroxy-1-trifluoromethyl-ethane sulfonic acid Beta-sultone. The catalysts showed very high activity for the esterification of long-chain fatty acids with ethanol and high-molecular-weight alcohols with essentially complete selectivity at high conversion (>95%). Acylation of anisole was also possible, with high selectivity for 4-methoxyacetophenone. The catalysts showed more activity conversion than commercial Nafion-silica composite catalysts.

Full text of DOI:10.1016/j.jcat.2005.01.007

Journal of Catalysis 231 (2005) 48–55
www.elsevier.com/locate/jcat
“Nafion”-functionalized mesoporous MCM-41 silica shows high activity
and selectivity for carboxylic acid esterification
and Friedel–Crafts acylation reactions
Mercedes Alvaro, Avelino Corma ∗, Debasish Das, Vicente Fornés, Hermenegildo García ∗
Instituto de Tecnología Química CSIC-UPV and Departamento de Química, Universidad Politécnica de Valencia,
Avda. de los Naranjos s/n, 46022 Valencia, Spain
Received 10 November 2004; revised 23 December 2004; accepted 10 January 2005
Abstract
Hybrid organic–inorganic MCM-41 silicas functionalized with perfluoroalkylsulfonic acid groups analogous to that of Nafion were
prepared in a simple single step by a condensation reaction between surface silanol groups of the mesoporous silicas and 1,2,2-trifluoro-
2-hydroxy-1-trifluoromethyl-ethane sulfonic acid Beta-sultone. The catalysts showed very high activity for the esterification of long-chain
fatty acids with ethanol and high-molecular-weight alcohols with essentially complete selectivity at high conversion (> 95%). Acylation of
anisole was also possible, with high selectivity for 4-methoxyacetophenone. The catalysts showed more activity conversion than commercial
Nafion–silica composite catalysts.
2005 Elsevier Inc. All rights reserved.
Keywords: Perfluorosulfonic acid; Nafion; MCM-41; Esterification; Fatty acids; Acylation; Anisole
1. Introduction
needed. In addition to this, troublesome work-up steps are
also necessary for treating the liberated hazardous and toxic
waste products. To avoid major environmental hazards and
to satisfy growing stringent global environmental regula-
tions, it is imperative to develop a truly catalytic process
with minimal waste production.
Consequently much attention has now been paid to sim-
plifying the existing Friedel–Crafts process through the de-
sign of strong heterogeneous acid catalysts that can replace
the conventional hazardous liquid- or traditional waste-
generating Lewis-acid catalysts [5]. For many organic reac-
tions involving nonbulky substrates and products, acidic zeo-
lites are quite efficient. Although the acidity of zeolites is not
as strong as that of anhydrous AlCl3 or liquid mineral acids,
they were found to be quite promising catalysts for acylation
reactions of activated aromatic compounds such as toluene,
xylenes, anisole, veratrole, or methoxynaphthalene [6–12].
On the other hand, sulfonic acid groups immobilized on
solid supports like silica were found to catalyze many or-
ganic reactions [13,14]. In recent years this idea was further
Acid-catalyzed carboxylic acid esterification and Friedel–
Crafts acylation reactions are important synthetic reactions
for the preparation of key organic value-added intermedi-
ates [1]. Preparation of alkyl esters and acylated aromatic
ketones is of particular importance in the manufacture of
intermediates for the fragrance and pharmaceuticals indus-
tries [2–4]. In normal practice, strong mineral acids, such
as H2SO4, HF, or supported Lewis-acid catalysts like anhy-
drous AlCl3/SiO2 and BF3/SiO2, are used for such reactions.
However, the use of corrosive mineral acids or Lewis-acid
catalysts is associated with a number of environmental prob-
lems [3,4]. A major drawback of such catalytic systems
is that they cannot be regenerated, and for Friedel–Crafts
acylation more than stoichiometric amounts of catalyst are
*
Corresponding authors.
E-mail addresses: acorma@itq.upv.es (A. Corma),
hgarcia@qim.upv.es (H. García).
0021-9517/$ – see front matter
doi:10.1016/j.jcat.2005.01.007
2005 Elsevier Inc. All rights reserved.

M. Alvaro et al. / Journal of Catalysis 231 (2005) 48–55
49
developed for the design of hybrid organic–inorganic meso-
porous silicas functionalized with alkylsulfonic acid groups
[11,15–23]. These hybrid materials combine extremely high
surface areas and larger and more tunable pore diameters
than conventional zeolites. They exhibited very high activ-
ity for many liquid-phase acid-catalyzed reactions like car-
boxylic acid esterification [16,17], aromatic alkylation [23],
and condensation reactions [16,21]. Covalent anchoring of
the sulfonic acid functional groups to the silica surface by
alkyl chain tethers could be achieved either by a direct syn-
thesis route [15,17,19,20] or via an indirect postsynthetic
anchoring technique [15,21] followed by an oxidation step
to generate the sulfonic acid groups [15,21]. Recently we re-
ported anchoring of Nafion-like perfluorinated sulfonic acid
groups to mesoporous silica surfaces by a simple one-step
method [24]. Nafion is one of the most versatile acid cata-
lysts that contains terminal sulfonic acid groups attached to
a perfluoroalkyl polymeric backbone [25,26]. The presence
of electron-withdrawing fluorine atoms in the structure sig-
nificantly increases the acid strength of the terminal sulfonic
acid groups, which is quite comparable to that of pure sul-
furic acid. However, as Nafion has a very low surface area
and exhibits low catalytic activity, we show in this report
that perfluoroalkylsulfonic acid chains anchored to MCM-
41 give rise to catalysts that are very active for esterifica-
tion of long-chain fatty acid with alcohols and for acyla-
tion of anisole with acetic anhydride. The activity of this
hybrid organic–inorganic catalyst gives better performance
than commercial Nafion silica catalysts or sulfonic groups
anchored on mesoporous molecular sieves.
solid was filtered and washed thoroughly with toluene to re-
move any unreacted 1 or by-products. Finally the solid was
dried at 100 ◦C overnight. We adjusted the amount of the
organic loadings by varying the amounts of 1 in the treat-
ment solution. For purposes of comparison, we also prepared
one alkylsulfonic acid anchored on MCM-41 (MPS) accord-
ing to the general method described in the literature [21]
by first anchoring mercaptopropyl groups to MCM-41 silica
and then oxidizing the thiol groups to sulfonic acid groups,
with the use of a mild oxidation step. Commercial Nafion sil-
ica composite catalyst (SAC-13) was obtained from Aldrich.
2.2. Characterization
X-ray diffraction patterns of the ordered mesoporous sil-
icas with the anchored perfluorinated sulfonic group were
recorded with a Philips X’pert diffractometer operating at
40 kV and 35 mA, with the use of nickel filtered Cu-Kα ra-
diation (λ = 1.54178 Å). Infrared spectra of the solids at var-
ious temperatures under vacuum were recorded in a Nicolet
710 spectrophotometer with the use of thin self-supporting
wafers and mounted in a special high-temperature IR cell.
The organic content of the solids was determined by com-
bustion analysis in a Fisons EA 1108 elemental analyzer.
Thermogravimetric analysis of the solids was performed in
a Mettler 851 at a heating rate of 10 ◦C/min in an air stream.
TG-MS analyses were carried out in a Perkin–Elmer TGA
thermobalance coupled to a Fisons mass spectrometer. We
measured specific surface area and pore size distribution of
the solids by recording the nitrogen adsorption/desorption
isotherms at liquid N2 temperature (77 K), with the use
of a Micromeritics ASAP 2000 system. Before measure-
ments, the samples were outgassed at 150 ◦C under vacuum
(10−3 Torr) for 6 h to remove any adsorbed species. Pore size
distribution was determined from the desorption branch of
the isotherm by the BJH (Barrett–Joyner–Halenda) method
with the use of the Halsey equation. Solid-state 19F MAS
NMR spectra were recorded with a Bruker 400 spectrome-
ter with samples packed in zirconia rotors spinning at 30 and
5.5 kHz, respectively.
2. Experimental
2.1. Catalyst preparation
Purely siliceous MCM-41 was synthesized according to
a method described in the literature [27]. MCM-41 sili-
cas were functionalized with a 1,2,2-trifluoro-2-hydroxy-1-
trifluoromethylethane sulfonic acid beta-sultone (1) (from
ABCR chemicals) to obtain sulfonic acid groups anchored
to the silanol groups with perfluoroalkyl tethers (Scheme 1).
Calcined MCM-41 (2.0 g) was evacuated at 120 ◦C for 8 h
and cooled to room temperature, and then a solution of 1
(1.0 g) in 50 ml dry toluene was added. The mixture was
refluxed for 4–6 h under an inert atmosphere, and then the
2.3. Catalytic reactions
Catalytic reactions were carried out in the open air in a
three-necked glass flask fitted with a cooling condenser and
a heating bath. For esterification reactions, 2.0 mmol of the
Scheme 1.

50
M. Alvaro et al. / Journal of Catalysis 231 (2005) 48–55
Table 1
Physical properties of the hybrid catalysts
a
Sample
Amount of 1
(mmol) used
per g of solid
S content
of final solid
(mmol/g)
S
V
C/S
p
BET
2
3
(m /g)
(cm /g)
MCM-41
MFS-1
MFS-2
MFS-3
SAC-13
MPS
–
–
1030
912
745
680
> 200
855
0.95
0.90
0.87
0.74
–
–
0.5
1.0
1.5
–
0.16
0.22
0.45
10–20%
0.52
2.9
3.0
2.9
–
b
b
–
0.83
4.5
a
From chemical analysis.
From manufacturers data.
b
acid and an excess of alcohol (5 ml), if not otherwise men-
tioned, were used. The mixture was heated to the desired
reaction temperatures, and then 50 mg of the dry catalyst
was added and stirred continuously. Reaction products were
collected at different time intervals, separated from solid cat-
alyst particles by means of a syringe filter, and analyzed by
gas chromatography (HP5890 with HP-5 column). For acy-
lation reactions, 2.0 mmol of anisole and 2.0 mmol of acetic
anhydride were introduced into the reactor and heated to the
desired reaction temperature. Then 50 mg of the dry catalyst
was introduced. We monitored the progress of the reaction
by taking a small aliquot of the mixture and analysing it by
gas chromatography as indicated above.
Fig. 1. XRD of MCM-41 and different MFS samples.
ordering of the mesoporous silica material was not affected
by the anchoring of perfluoro-alkylsulfonic acid groups.
However, attempts to load larger amounts (> 2 wt%) of per-
fluoroalkylsulfonic acid groups caused significant damage
of the mesoporous structure, producing rather amorphous
like material. This may be related to the presence of a high
population of strong Brønsted acid sites formed during the
covalent anchoring.
3. Results and discussion
The cyclic precursor 1,2,2-trifluoro-2-hydroxy-1-trifluo-
romethylethane sulfonic acid beta sultone (1) reacts with
the silanol groups of the silica surface by opening up the
sultone ring and forming a covalent bond between the sil-
ica framework and the perfluoroalkyl chain (see Scheme 1).
Thus the silica surface becomes grafted to the perfluoroalkyl
chains with a terminal sulfonic acid functional group. In con-
trast to the methods reported earlier for the preparation of
anchored sulfonic acid silica catalysts, this new method is
much simpler in the sense that in a single step, anchoring
and formation of the sulfonic group are accomplished. Con-
ventional methods require a subsequent thiol oxidation step
after anchoring of the thiol-containing precursor molecules.
Then a nonoptimized oxidation step generally leads to the
formation of catalytically inactive disulfide species [15,16,
21], and although optimized oxidation should lead to sul-
fonic acid, this has proved to be rather difficult in covalently
attached mercapto groups. In our case, during the anchoring
step the ratio of sultone 1 to mesoporous silica can be var-
ied over a wide range (Table 1) to obtain different loadings
of the perfluoroalkylsulfonic groups. Typically a 0.5–2 wt%
sulfur loading can be obtained by adjustment of the amounts
of 1 in the treatment solution.
The amount of organic material loaded in the MCM-41
was determined by elemental analysis. For all samples the
atomic ratio of carbon to sulfur was found to be very close to
the theoretical value of 3. Thermogravimetric analysis of the
hybrid materials showed an initial loss of weight (ca. 8%)
up to 150 ◦C, which can be attributed to adsorbed water.
This was followed by a second weight loss (ca. 3 wt%) step
that extended to 350 ◦C. The observed weight loss between
150 and 350 ◦C is relatively minor in comparison with that
observed for MCM-41 silica functionalized with n-propyl-
tethered sulfonic acid groups. In the latter case, loss of the
organics was almost complete in this temperature range [28],
whereas in the case of the MFS materials prepared here,
most of the weight loss (depending on the perfluoroalkyl-
sulfonic group loading) occurs at temperatures higher than
350 ◦C. This thermogravimetric analysis shows the higher
thermal stability of our perfluoroalkylsulfonic MCM-41. To
further confirm the thermal stability of the perfluoroalkyl-
sulfonic groups, thermal analysis coupled with mass spec-
troscopy was performed. Mass spectrometric data revealed
that up to 350 ◦C mostly water molecules were desorbed
from the solids. A small amount of SO2 was also detectable,
but only above 350 ◦C [24].
XRD patterns for the solids (Fig. 1) were found to be very
similar to those for the parent MCM-41 silica material, thus
indicating that under the reaction conditions the long-range

M. Alvaro et al. / Journal of Catalysis 231 (2005) 48–55
51
The nitrogen adsorption–desorption isotherms of the sol-
ids show Type IV curves according to the IUPAC nomencla-
ture, indicating the mesoporous nature of the solids. A typ-
ical isotherm is shown in Fig. 2. The BET surface area and
pore volume of the samples are given in Table 1. It can be
seen that the specific surface area and pore volume decreased
continuously with higher loading of the organics. Also it was
noted that the pore size distribution measurements showed a
slight decrease and broadening of the average pore diameter
with the anchoring of the organics.
tic of νS=O stretching vibrations of undissociated –SO3H
groups as reported previously for Nafion films and triflic
acid [29,30]. Strong binding of the perfluoroalkylsulfonic
acid groups to the surface of the mesoporous silicas and
thus the increased thermal stability were also reflected by
the preservation of the strong intensity of this band even
at elevated outgassing temperatures. Other bands observed
at 1650 and 1760 cm−1 were assigned to the vibrations of
adsorbed and protonated water molecules respectively, as re-
ported by other workers in IR studies on Nafion [29,30]. As
a matter of fact, upon degassing at increasing temperatures,
these bands undergo some shift to higher wavenumbers and
a decrease in intensity until they become very weak. This
decrease in intensity of the bands attributable to protonated
water varies independently of the band corresponding to the
–SO3H group.
The presence of sulfonic acid groups can be observed
from the FT-IR spectra of the self-supporting wafers of
the solids. The band at 1420 cm−1 (Fig. 3) is characteris-
Covalent attachment of the perfluoroalkylsulfonic acid
chains to the silica surface was also confirmed by 19F MAS
NMR experiments. Fig. 4 shows a MAS 19F NMR spectrum
for a typical solid. Three separate peaks were observed in ac-
cordance with the presence of three different environments
of the F atoms. Peaks around −164 and −157 ppm can be
assigned to F atoms from C–F and C–CF2 moieties. In con-
trast, the signal for CF3 group appeared markedly downfield
at −74 ppm. Integration of the signal peaks showed the ratio
of the peaks to be close to 1:3:2, which is in full agreement
with the theoretical value. We notice that the peak attribut-
able to CF2 appears as a very broad signal as compared with
the other two peaks. This broadness could be due to a distrib-
ution of groups with different environments or to anisotropy
or some other inhomogeneity arising from the immobiliza-
tion on the solid surface. While in solution the chemical shift
of the CF3 corresponding to the Beta-sultone appearing at
−76 ppm is similar to the value measured for the solid; the
chemical shifts corresponding to the CF and CF2 of Beta
Fig. 2. Adsorption–desorption isotherm and pore size distribution (inset) of
MFS-2 sample.
◦
Fig. 3. FT-IR spectra of MFS-2 sample at different temperatures (a) 30, (b) 100, (c) 200, and (d) 300 C.

52
M. Alvaro et al. / Journal of Catalysis 231 (2005) 48–55
Table 2
a
Esterification of alcohols with fatty acids
Substrate
Acid
Solvent
T
Conversion
(%)
◦
( C)
Ethanol
Ethanol
Ethanol
Dodecanol
Dodecanol
Dodecanol
Dodecanol
Octanoic acid
Ethanol excess
Ethanol excess
Ethanol excess
Toluene
Toluene
Toluene
60
60
80
60
80
60
80
99
61
81
58
98
60
90
Dodecanoic acid
Dodecanoic acid
Octanoic acid
Octanoic acid
Dodecanoic acid
Dodecanoic acid
Toluene
a
Catalyst MFS-3, reaction time 24 h.
solid catalyst, the reaction was comparatively considerably
slower.
The activity per gram of hybrid mesoporous silica cata-
lysts is almost double that of the commercial Nafion silica
composite SAC-13 [24]. On the other hand, the turnover fre-
quency (activity per sulfonic acid group) was one order of
19
Fig. 4. F MAS NMR of MFS-2 sample.
sultone appear at −84 and −90 ppm and are notably shifted
with respect to the perfluoro chains in the solids.
magnitude higher for the hybrid catalysts (9.7 × 10−3 s−1
)
Although the initial covalent attachment of the perfluo-
roalkylsulfonic groups on the mesoporous MCM-41 struc-
ture appears to have been firmly demonstrated, a point that
deserves further study is the persistent tendency of this bond
to undergo hydrolysis under catalytic conditions.
than for commercial SAC-13 catalyst (1.1 × 10−3
s
−1).
Since commercial SAC-13 has a higher density of sulfonic
groups than do the hybrid catalysts, we have to conclude that
the accessibility of sulfonic groups is higher in our hybrid
MCM-41 catalyst and/or the interactions of sulfonic acid
groups with the surface silanol groups of the silica matrix in
SAC-13 catalysts decrease its acidity and therefore its cat-
alytic activity. It is obvious that as the reaction progresses
the formation of water as a by-product will cause the acid
strength of the Brønsted sites to level off; therefore, it ap-
pears that accessibility may be the key factor responsible for
the relative catalytic activity.
3.1. Esterification of alcohols
The catalytic performance of the hybrid MCM-41 mate-
rials was tested for the esterification of long-chain aliphatic
acids with alcohols at ambient atmosphere. The catalysts are
very active for the esterification of C8 and C12 aliphatic acids
with alcohols like ethanol and dodecanol (Table 2). In the
case of octanoic acid esterification with ethanol, the conver-
sion of acid reached 95–96% within 6 h at a relatively low
temperature of 60 ◦C. Although blank controls revealed that
the esterification reaction also proceeds in the absence of any
Fig. 5 shows the time conversion plots for three different
catalysts, namely hybrid MFS-3, MPS, and SAC-13, for the
esterification of octanoic acid with ethanol at 60 ◦C. It can be
seen there that the activity per gram of our perfluoroalkylsul-
fonic MCM-41 catalyst MFS-3 is also much higher than the
◦
Fig. 5. Time–conversion curves for esterification of octanoic acid with ethanol at 60 C with different MFS catalysts and SAC-13.

M. Alvaro et al. / Journal of Catalysis 231 (2005) 48–55
53
◦
Fig. 6. Time–conversion curves for acylation of anisole with acetic anhydride at 60 C with different MFS catalysts and SAC-13.
corresponding alkylsulfonic acid MCM-41 (MPS). This is a
reflection of the expected influence of perfluorination on the
acidity and catalytic activity of the sulfonic acid group. Af-
ter recovery of the solid and washings with ethanol, MFS-3
was reused six times under the same conditions with only a
minor decrease (15%) in activity between the first and the
second run; the self-esterification was still much lower when
it was uncatalyzed than when it was catalyzed.
It was noticed that with longer chain fatty acids and
higher alcohols the reaction proceeded more slowly and an
increase in the reaction temperature had a favorable effect
on the conversion (see Table 2). The selectivity for the cor-
responding esters was always very high, with almost no
side-product formation. Mass balances were also high and,
therefore, ester yields correspond very well with the acid
conversions indicated in Table 2. Reactions performed in the
absence of any catalyst or in the presence of only siliceous
MCM-41 support showed negligible conversion of the acids,
indicating the truly catalytic nature of the reaction. In addi-
tion, we found the catalyst to be reusable by washing with
ethanol after the reaction, with an initial slight loss in activ-
ity after the first run.
we preferred to avoid halogen-containing acid chlorides, and
instead acetic anhydride was used as an acylating agent.
Although cesium-containing heteropoly acids have been re-
ported to be able to acylate anisole with aliphatic acids [34],
our attempts to acylate anisole with aliphatic acids in the
presence of Nafion MCM-41 or SAC-13 catalysts were not
successful.
Fig. 6 shows the time anisole conversion plot at 60 ◦C,
where MFS catalysts have different S loadings. As expected,
the activity increases directly with the sulfur content. Fur-
thermore, the turnover number is 2.5 times lower for either
nonfluorinated MPS or commercial SAC-13. The selectivity
for the desired para isomer, 4-methoxyacetophenone, was
almost 97% for the three catalysts, and only a very small
amount of 2-methoxyacetophenone was observed.
An increase in reaction temperature has a beneficial effect
on the conversion of anisole to methoxyacetophenone and on
the yield of 4-methoxyacetophenone. This is quite expected,
and similar effects were observed for Nafion silica compos-
ite catalysts [36]. Fig. 7 shows the effect of reaction tem-
perature on the anisole conversion. 4-Methoxyacetophenone
yields follow analogous behavior. It has been observed that
at lower temperatures, conversion increased rather slowly
with time and reached the final value only after 3 h. How-
ever, at elevated temperatures the maximum conversion was
reached very quickly within 1 h, and after that there was a
very slight increase in conversion with time. From the shape
of the conversion curves it is clear that MFS catalysts be-
come deactivated during the acylation reaction.
3.2. Acylation of anisole
Acylation of anisole was also carried out with acetic an-
hydride in the presence of hybrid MCM-41 catalysts. Earlier
work reported acylation of anisole with various heteroge-
neous catalysts like Ce-exchanged clays [31], FeCl3- or
ZnCl2-impregnated clays [32], and heteropoly acid cata-
lysts [33–35]. Zeolite catalysts like Beta [9], Y [6,8,10],
and ZSM-5 [12] were also reported to be quite active for
the acylation of activated aromatic compounds. Nafion sil-
ica composite catalysts were also reported to be active for
the acylation of anisole with acid chlorides [36]. However,
I has been reported that in the case of zeolite catalysts the
activity of the acylation catalyst can be recovered by regen-
eration [9,11]. It was also possible to bring about the regen-
eration of heteropoly acid catalysts through cleaning of the
spent catalysts [33]. However, strong adsorption of carboca-
tionic compounds on the active sites can deactivate the cat-

54
M. Alvaro et al. / Journal of Catalysis 231 (2005) 48–55
Fig. 7. Time–conversion curves for acylation of anisole with acetic anhydride at different reaction temperatures with MFS-2 catalysts.
Scheme 2.
alyst easily. Although activity of the perfluorosulfonic acid-
anchored MCM-41 catalysts can be regenerated after ester-
ification reaction by washing with ethanol, in the acylation
reactions the activity of the fresh fluorinated MFS cannot be
regenerated. This may be due to strong adsorption of some
species on the active sites. Indeed, the diffuse reflectance
UV–vis spectrum of the used catalysts showed a strong peak
around 415 nm, indicating the presence of adsorbed species
on the catalyst surface. Carbocationic intermediates are the
most likely poisons at this stage, in view of the precedents in
the literature [37,38]. These species are found to be gener-
ated by secondary reactions of 4-methoxyacetophenone, as
indicated in Scheme 2.
be carried out with good conversion and a very high selec-
tivity for the desired para isomer, although deactivation by
diaryl carbocations limits at present the reusability of the
system. For both reactions the new “Nafion” MCM-41 cat-
alysts exhibit significantly higher activity than any of the
previously reported hybrid inorganic–organic acid catalysts.
Further studies are needed to establish the stability of this co-
valent bond during hydrolysis under strong acid conditions
and the influence of the presence of residual silanol groups
in the acid strength of the perfluoroalkylsulfonic groups.
Acknowledgments
Financial support by the Spanish Ministry of Science and
Technology (MAT2003-1767) is gratefully acknowledged.
D.D. thanks the Generalidad Valenciana for a fellowship.
4. Conclusions
Hybrid organic–inorganic Nafion-MCM-41 silicas repre-
sent a promising type of catalyst for acid-catalyzed reac-
tions. Anchoring of perfluorinated alkylsulfonic groups to
the high-surface-area MCM-41 silica can be achieved in a
single step and produces strong solid acid catalysts that are
stable up to 350 ◦C. The esterification of long-chain fatty
acids can be performed satisfactorily at a relatively low tem-
peratures with high yields of the desired esters. The perflu-
oroalkylsulfonic MCM-41 catalyst can be reused after re-
covery and washing. Furthermore, acylation of anisole can
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