Annulation of phenols: Catalytic behavior of conventional and 2d zeolites

Article abstract of DOI:10.1002/cctc.201402007

Catalytic behavior of MFI zeolites differing in thickness of nanosheets and ordering was studied in annulation of phenols, and compared with 3D zeolites BEA and MFI containing large or medium pores as well as with micro/mesoporous zeolite USY. The highest

Full text of DOI:10.1002/cctc.201402007

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DOI: 10.1002/cctc.201402007
Annulation of Phenols: Catalytic Behavior of Conventional
and 2D Zeolites
Maksym V. Opanasenko,[a, b] Mariya V. Shamzhy,[a, b] Changbum Jo,[c] Ryong Ryoo,[c, d] and
[a]
ˇ
ˇ
Jirꢀ Cejka*
Catalytic behavior of MFI zeolites differing in thickness of
nanosheets and ordering was studied in annulation of phenols,
and compared with 3D zeolites BEA and MFI containing large
or medium pores as well as with micro/mesoporous zeolite
USY. The highest conversions of phenols studied were ach-
ieved over ordered hexagonally mesostructured zeolite with
1.7 nm wall size, followed by materials possessing 2.1 and
2.7 nm of nanosheets thickness. This corresponds to decreas-
ing surface area of materials studied. The preferences of mate-
rials with zeolitic layers and high surface areas over bulky zeo-
lites BEA and especially MFI in annulation of phenols is more
prominent for substrates with larger kinetic diameters [phenol
(0.66 nm)<1-naphthol (0.80 nm)<2-naphthol (0.89 nm)]. USY
zeolite exhibited higher conversions (32, 6, 25% for phenol, 1-
and 2-naphthol, respectively, after 300 min time on stream)
than BEA (23, 6, 8%) and MFI (13, 0, 0%) not overcoming hex-
agonally mesostructured MFI (45, 36, 55%).
Introduction
Porous solid acids with predictable and well developed textur-
al properties such as zeolites and metal-organic frameworks
have been under most intensive investigations in catalysis in
recent years. One of the reasons consists in their advantages
and prospects as heterogeneous catalysts having numerous
applications in petrochemistry, fine-chemical productions, and
environmental protection.[1] Among the advantages of zeolites,
we can stress their high thermal and mechanical stability, rela-
tively high adsorption capacity, and narrow pore-size distribu-
tion (leading sometimes to shape selectivity), and the possibili-
ty to control concentration, type, and strength of acid sites.[2]
However, zeolites generally suffer from intracrystalline diffusion
limitations owing to the molecular dimensions of micropores.
The size of zeolite pores (0.3–0.8 nm) also limits the accessibili-
ty of the active sites located in the channels for bulky reac-
tants,[1] which may negatively impact their catalytic per-
formance for transformation of large molecules.
To avoid this disadvantage, synthesis of zeolites with extra-
large micropores can be performed.[3] However, this way is lim-
ited by the usual hydrothermal lability of such zeolites and
complexity of their formation.
Another possibility to prepare effective catalysts for transfor-
mation of bulky molecules is increasing the external surface of
zeolites. Such procedure is applicable if shape selectivity is not
important for the reactions under consideration. Different
methods to increase the external surface of zeolites have been
studied recently. They include i) fabrication of micro–mesopo-
rous materials with developed surface owing to mesoporosi-
ty,[4] ii) decreasing the size of zeolite crystals to the nanoscale,[5]
iii) formation of thin zeolitic layers exhibiting large external sur-
face areas.[6]
Mesopores can be introduced in zeolite materials by use of
solid templating (in the presence of a solid material that is
eventually removed to generate porosity),[7] supramolecular
templating (by using an assembly of surfactants as porogen),[8]
synthesis with organosilanes[9] and postsynthetic treatments
(particularly, demetalation).[10]
ˇ
[a] Dr. M. V. Opanasenko, Dr. M. V. Shamzhy, Prof. J. Cejka
Department of synthesis and catalysis
´
J. Heyrovsky Institute of Physical Chemistry
Academy of Sciences of Czech Republic
ˇ
v.v.i Dolejskova 3, 182 23 Prague 8 (Czech Republic)
Fax: (+420)28658 2307
E-mail: jiri.cejka@jh-inst.cas.cz
Nanocrystalline zeolites with crystal sizes of less than
100 nm have improved characteristics (increased surface area
and decreased diffusion path lengths) in comparison with
bulky zeolites.[5] Incorporation of active sites onto the external
surface results in high surface reactivity leading to zeolites
with improved catalytic properties.[5] However, in fabrication of
nanocrystalline zeolites, the conditions have to be controlled
very delicately and the synthesis often should be stopped
at a very low yield. Thus, synthesis of zeolite nanoparticles
for catalytic applications seems to be not suitable at the
moment.
[b] Dr. M. V. Opanasenko, Dr. M. V. Shamzhy
Department of porous materials
L.V. Pisarzhevskiy Institute of Physical Chemistry
National Academy of Sciences of Ukraine
pr. Nauky 31, 03028 Kiev (Ukraine)
[c] Dr. C. Jo, Prof. R. Ryoo
Center for Nanomaterials and Chemical Reactions
Institute for Basic Science
Daejeon 305-701 (Korea)
[d] Prof. R. Ryoo
Department of Chemistry
KAIST, Daejeon 305-701 (Korea)
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Results and Discussion
To significantly increase the accessibility of acid sites for sub-
strate molecules, delamination methods for fabrication of thin
zeolitic layers were essayed particularly for MCM-22 precur-
Structure, textural, and acidic properties of the catalysts
sor[11] and respective derivatives.[12] Recently, Cejka and co-
ˇ
workers reported the use of UTL zeolite for the synthesis of
a 2D precursor with its further manipulation including swel-
ling, delamination, pillaring, or even formation of new
zeolites.[13]
Hiererchical zeolites prepared in this work are depicted as Nn-
xd, for which Nn corresponds to the type of structure-directing
agent used: C18H37–N+(Me)2–{C6H12–N+(Me)2}nÀ2–C6H12–N+
(Me)2–C18H37][BrÀ]n (n=3, 4, and 5); and x is the duration of the
synthesis (x=1, 5, 9 d).
Ryoo and co-workers discovered and developed fundamen-
tally different approaches for the synthesis of 2D zeolites.[14]
The method employs designed multiammonium surfactants
combining both zeolite structure-directing agents (SDAs) and
long alkyl chains as mesoporogens. Such surfactant molecules
(gemini-type organic surfactants) can form micelles functioning
as SDA in mesostructure (tails) and zeolitic level (multiammoni-
um head groups). Mesophase materials with different zeolite
framework topologies (MFI, MTW, BEA, MRE) were prepared by
using this surfactant-directed synthesis route.[15] However, most
of such mesophase materials do not contain individual layers
of zeolites, their walls are constructed from very thin crystalline
component with zeolitic structure. Thus, the mentioned mate-
rials may be considered as 2D zeolitic materials with mesoscale
arrangement of the crystalline domains. Such 2D zeolites can
exhibit not only excellent textural characteristics, but also
promising catalytic properties in acid-catalyzed and oxidative
reactions,[16] sometimes superior to those of conventional
zeolites.
XRD patterns and TEM images of synthesized material (Fig-
ure 1a,b) reveal that N3-1d sample exhibits MCM-41-like hexag-
In this contribution, we aimed to compare the catalytic be-
havior of conventional 3D zeolites (MFI, BEA), micro-mesopo-
rous ultrastable zeoliteY (USY), and novel 2D zeolites obtained
by using multiammonium surfactants in annulation reaction
between 2-methyl-3-buten-2-ol (MBO) and phenols (Scheme 1).
Figure 1. a) XRD patterns and TEM images of b,c) N3-1d; d,e) N3-5d; and
f,g) N3-9d.
onal structure (with low-angle diffraction lines at 1.9,
3.2, and 3.88 2q) containing noncrystalline mesopore
walls. In the case of the N3-5d sample, well resolved
diffraction lines in the low-angle region of the XRD
pattern are also present (Figure 1a). These lines cor-
respond to a hexagonal mesostructure similar to that
of the N3-1d material but with slightly expanded lat-
tice in comparison with the sample obtained after
1 d. The structure of N3-5d sample was previously re-
ported as hexagonally ordered mesoporous MFI zeo-
lite.[6] XRD patterns and TEM images of the sample
N3-5d (Figure 1a,d,e) evidenced the transformation of
original mesopore walls (Figure 1b) to a crystalline
microporous zeolitic structure with the prolongation of hydro-
thermal treatment up to 5 d.
Scheme 1. Annulation of phenol with MBO.
The selected reaction provides chromanes (dihydrobenzopyr-
anes), which represent (with their unsaturated derivatives-chro-
menes) a widely distributed and biologically active class of nat-
ural products.[17]
The N3-5d sample possessed relatively high surface area and
pore volume (Table 1) in contrast to the sample obtained after
1 d. N3-5d exhibited a type-IV adsorption isotherm with pore-
size distribution having maxima related to pore diameters
2D zeolites may overcome limitations of conventional bulky
zeolites having smaller pores. Therefore, materials consisting of
thin zeolitic layers appear as promising solid catalysts for
liquid-phase reactions. Comparison of the performance of 2D
and 3D zeolites in annulation reaction is of high interest
aiming to show the potential of layered materials in acid-cata-
lyzed processes.
D
micro =0.55 nm and Dmeso =3.3 nm.[18] The pore diameter of
0.55 nm corresponds to the 10-ring channels in the zeolite
framework. Thus, the architecture of N3-5d can be described as
mesoporous structure with the walls composed of the micro-
porous zeolitic framework, probably similar to that of MFI.
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Table 1. Textural properties of the materials under investigation.
Sample
Description
Si/Al[a]
Dmicro
[nm]
Dmeso
[nm]
SBET
[m2 gÀ1
Sext
[m2 gÀ1
Vtotal
[cm3 gÀ1
dwall
[nm]
[c]
]
]
]
N3-1d
N3-5d
N3-9d
N4-5d
N5-5d
MFI
hexagonally mesostructured amorphous MCM-41-like framework
ordered hexagonally mesostructure, 10-ring zeolite
1.5 nm thick MFI nanosheet
disordered mesostructure, 10-ring zeolite of 2.1 nm thickness
disordered mesostructure, 10-ring zeolite of 2.7 nm thickness
3D pore system of intersecting sinusoidal and straight 10-ring channels
3D pore system of intersecting 12-ring channels
3D pore system of interconnected supercages and mesopores with
wide range diameters
20.2
30.2
38.4
28.2
27.3
11.5
12.5
15
n.d.[b]
0.55
0.55
0.55
0.55
0.54
0.66
0.74
2.4
3.3
3.0
3.4
5.1
–
221
1090
693
970
810
305
670
770
220
990
555
805
0.16
1.40
1.01
1.52
1.53
0.16
0.2
1.5[d]
1.7[d]
1.5[e]
2.1
2.7
–
622
n.d.[b]
n.d.[b]
335
BEA
USY
–
–
n.d.[b]
[a] Evaluated from the FTIR measurements. [b] Not defined. [c] Evaluated from the t-plot method. [d] Wall thickness was determined from Dmeso and hexag-
onal lattice parameter (XRD). [e] Wall thickness was measured from the TEM image.
In contrast to the mentioned samples, N3-9d exhibited no
low-angle reflections in XRD pattern (Figure 1a). At the same
time, the high-angle diffraction peaks were better resolved
than those of N3-5d and they can be attributed to the (h0L) re-
flections corresponding to the MFI zeolite structure. The ab-
sence of the reflections with k-indices distinct from zero (along
the b-axis) indicates that the zeolite morphology could be ex-
tremely thin in this direction not providing interlayer
connections.
percages of 1.22 nm in diameter interconnected tetrahedrally
through windows of 0.74 nm in diameter. Zeolite USY also con-
tains mesopores with broad pore size distribution.
TEM images (Figure 1 f,g) confirmed that N3-9d possess zeo-
litic 2D nanosheet morphology. Each nanosheet is composed
of a single “layer” of micropores corresponding to 1.5 nm
thickness and 3/4 of the b lattice parameter of the MFI unit
cell. Thus, N3-9d can be described as 2D nanomorphic MFI zeo-
lite with disordered assembly of the zeolitic nanosheets. De-
spite the absence of ordering, the nanosheets maintain rela-
tively high interparticle porosity (Table 1).
The structural and textural properties of N4-5d and N5-5d
samples are considerably similar to those of N3-5d material as
deduced from XRD and sorption data (Figure 2a, Table 1). Both
N4-5d and N5-5d exhibit a reflection in the low-angle region
(the less distinct peak for N5-5d may be attributed to the thick-
er walls of mesopores and their lower structural coherence)
and three broad diffraction lines in the wide-angle region in
the XRD pattern. Based on the results of Ar adsorption, the
presence of 10-ring channels similar to those in N3-5d can be
assumed for N4-5d and N5-5d samples.[18]
The TEM images of these materials (Figure 2b–e) evidenced
the disordered interconnection of zeolitic layers. It was found
that the thicknesses of the zeolite layers (forming mesopore
walls) increased with the increasing number of quaternary N
atoms in used SDA (number of ammonium groups). In this
way, the thicknesses of the mesopore walls in N3-5d, N4-5d,
and N5-5d samples were equal to 1.7, 2.1, and 2.7 nm, respec-
tively (Table 1).
Zeolite MFI is characterized by a sinusoidal pore system of
intersecting 10-ring channels with sizes of 0.51ꢂ0.55 and
0.53ꢂ0.56 nm (Figure 3a). Zeolite BEA (Figure 3b) possesses
a 3D pore system of intersecting 12-ring channels (0.64ꢂ0.76
and 0.56ꢂ0.56 nm), whereas ultrastable zeolite Y (Figure 3c)
belongs to the large-pore zeolites that have quasispherical su-
Figure 2. a) XRD patterns and TEM images of b,c) N4-5d and d,e) N5-5d.
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spectroscopy of adsorbed 2,6-di-tert-butylpyridine (2,6-DTBP)
from the integral intensity of the band at 1531 cmÀ1 (Table 2).
The kinetic diameter of the 2,6-DTBP molecule is approximate-
ly 0.79 nm,[21] which is larger than the size of pores in 10-ring
zeolites under investigation, which makes accessible only acid
centers on the outer surface of Nn-xd and MFI samples. At the
same time, in the case of 3D 12-ring systems, such as BEA and
FAU (USY) zeolites, an easy penetration of 2,6-DTBP into their
pore network was demonstrated in Ref. [21]. In agreement
with Ref. [21], the most Brønsted acid centers in BEA and USY
zeolites are accessible for interaction with 2,6-DTBP molecules
(Table 2), however, it does not guarantee the accessibility of in-
ternal sites for bulky substrates (such as naphthols) during re-
action. In contrast, only 10% of Brønsted acid centers in 3D
MFI zeolite interact with bulky 2,6-DTBP molecules. The frac-
tion of surface acid sites in prepared 2D 10-ring zeolites (e.g.,
39% for N3-9d) significantly exceeds the value for conventional
3D MFI zeolite. However, the contribution of surface silanol
groups with increased acidity, as a result of the interaction
with the nearest Al Lewis acid sites,[22] to the intensity of ab-
sorption band at 1531 cmÀ1 cannot be excluded for Nn-xd (x=
5), which is characterized by highly developed surface Lewis
acidity.
Figure 3. Frameworks of a) MFI, b) BEA, c) FAU, and d) XRD patterns of the
corresponding zeolites.
The X-ray diffraction patterns of all 3D zeolites under study
(Figure 3d) match well with those reported in the literature.[19]
Zeolites BEA and MFI show a type I isotherm, typical for micro-
porous solids, and the adsorption isotherm for USY zeolite is
a combination of types I and IV with hysteresis loop created by
capillary condensation in the mesopores within the pore sys-
tems of FAU. The textural properties of all 3D zeolites are sum-
marized in Table 1.
Thus, the increased 1) specific pore volume (Vtotal), 2) external
surface area, 3) fraction of Lewis acid centers, and 4) surface
Brønsted acid sites are found to be the features distinguishing
2D zeolites from 3D MFI analogue.
To evaluate the total concentrations of acid sites in the cata-
lysts under investigation FTIR spectroscopy of adsorbed pyri-
dine was used. The concentrations of Brønsted and Lewis acid
sites calculated from the integral intensities of the bands at
1546 and 1454 cmÀ1 by using extinction coefficients[20] are
given in Table 2.
Catalytic investigations
The annulation reaction includes two acid-catalyzed reaction
steps (Scheme 1): 1) isoprenylation of phenols with MBO result-
ing in formation of isoprenylphenol followed by 2) its intramo-
lecular cyclization with the formation of target derivatives of
3,4-dihydro-2H-1-benzopyran (chroman).[23] Phenols differing in
size (i.e., phenol, 1-naphthol, 2-naphthol) were used as sub-
strates to establish the influence of structure, textural, and
acidic properties of catalysts on their efficiency in annulation
reaction. The kinetic diameters of phenol, 1-naphthol, and 2-
naphthol total 0.66, 0.80, and 0.89 nm, respectively (values
were obtained by using HyperChem Molecular Modeling
System, release 8.0.8).
Notably, all 3D zeolites under investigation possess signifi-
cantly higher amounts of Brønsted acid centers (0.200–
0.619 mmolgÀ1) than prepared Nn-xd materials (0.03–
0.072 mmolgÀ1). At the same time, the fraction of Lewis acid
centers in Nn-xd samples (71–89%) notably exceeds that char-
acteristic for 3D zeolites (25–63%). It is an expected result, re-
garding the missing connectivities in the third dimension of
Nn-xd materials resulted in an increased concentration of de-
fects. The surface acidity of Nn-xd samples was studied by FTIR
In all cases (phenol, 1-naphthol, 2-naphthol), we
observed in the reaction mixture the formation of in-
termediate prenylphenols (PP, Figure 4a), targeting
Table 2. Concentrations of acid sites in Nn-xd samples and conventional zeolites mea-
sured by pyridine and 2,6-DTBP adsorption.
2,2-dimethylbenzopyranes (DMBP, Figure 4b), and
the products of their thermal rearrangement,[24] 2,2,3-
trimethylbenzofuranes (TMBF, Figure 4c). Moreover,
the side product of MBO oxidative dimerization was
detected (Figure 4d).
Sample
Pyridine
c(Lewis)/c(Lewis+Brønsted)
2,6-DTBP
c(Brønsted)
[mmolgÀ1
]
c(Lewis)
[mmolgÀ1
c(Brønsted)
[mmolgÀ1
]
]
[%]
N3-1d
N3-5d
N3-9d
N4-5d
N5-5d
MFI
0.007
0.252
0.179
0.261
0.269
0.201
0.280
0.340
0
100
89
71
84
84
25
47
63
0.008
0.068
0.028
0.067
0.066
0.005
0.281
0.202
The conversion of phenol was found to increase in
the following order: MFI<N3-1d<N3-9d<BEA<
USY<N5-5d<N4-5d<N3-5d (Figure 5a). It should be
pointed out, that the highest conversions (38–46%
after 300 min time on stream, TOS) were achieved
over N3–5-5d samples characterized by the largest ex-
ternal surface area, the highest pore volume
0.030
0.072
0.048
0.050
0.619
0.311
0.200
BEA
USY
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tants in pore system of 3D zeolites in comparison with the dif-
fusion in Nn-xd materials. N3-1d sample, possessing the lowest
concentration of acid sites at reasonable porosity, provided
slightly higher conversion than MFI zeolite (19% versus 13% at
300 min TOS).
Relatively low conversion over N3-9d sample having consid-
erable porosity may be caused by low concentration of surface
acid sites (Table 2). The overall selectivities to substituted
DMBP/TMBF over all catalysts under investigation were in the
range of 60–85%, but the regioselectivities differed significant-
ly (Figure 5b). Notably, the catalysts giving the lowest conver-
sion (MFI, N3-1d, N3-9d) exhibited higher selectivity to TMBF
(59–66% in DMBP/TMBF fraction) than more active catalysts
(6–39%). This can be explained by thermally induced rear-
rangement of the DMBP derivative to the corresponding TMBF,
which is assumed to play a significant role in the case of low-
active catalysts as a result of the relatively low rate of annula-
tion to DMBP relative to that of thermally induced rearrange-
ment consuming this product.
Figure 4. Isomeric products formed during annulation reaction of phenol:
a) PP, b) DMBP, c) TMBF, d) 1-(2-methylbut-3-en-2-yloxy)-3-methylbutane-2,3-
diol.
The differences in conversions of bulkier 1-naphthol over 3D
and 2D zeolites are more dramatic (Figure 6a). N3–5-5d samples
exhibited 30–35% conversion after 300 min of the reaction
time whereas conventional zeolites, mesostructured amor-
phous N3-1d, and N3-9d samples with relatively low external
acidity showed conversions <10%.
Notably, annulation of 1-naphthol practically did not pro-
ceed over 3D MFI zeolite, which may be connected with the
low concentration of surface active sites and unaccessibility of
internal acid centers through the pore system of the zeolite for
bulky 1-naphthol molecules. As the mesophase and lamellar
materials with MFI structure of zeolitic layers (having access to
active sites from two sides) were reasonably active in annula-
tion of 1-naphthol under the same reaction conditions, we can
assume that the studied process requires a reaction space
larger than the unilateral pore mouth of MFI.
Significantly higher conversion of phenol was achieved over
USY zeolite than over BEA, both catalysts showed almost equal
conversion of bulkier 1-naphthol. This result may be connected
with partial blocking of the inner faujasite cavities (1.2 nm di-
ameter) by bulky products (kinetic diameter of pyranyl isomer
molecule is approximately 1.03 nm), whereas 1-naphthol (mol-
ecule size is 0.64ꢂ0.75 nm) can penetrate through 0.74 nm mi-
cropore windows in USY. The conversions of 1-naphthol over
both N3-1d and N3-9d samples were similar (5–10%) but signifi-
cantly lower than over N3–5-5d materials (31–36%). We assume
fundamentally different reasons for this. In the case of MCM-
41-like solid, the amount of acid sites (of low acid strength) is
very low for transformation of relatively inert 1-naphthol, and
the diffusion limitation owing to the stacking of the layers
and/or irregularity of interlayer pore system (Figure 1e,f) might
be the reason for the low conversion of the respective
substrate.
Figure 5. a) Conversion of phenol and b) selectivities to TMBF and DMBP at
30% conversion (or at maximal conversion if 30% is unachievable) over 2D
and conventional zeolites.
In contrast to selectivities to phenol, selectivities to pyranyl/
furanyl derivatives of 1-naphthol were similar for all used cata-
lysts (Figure 6b). However, the ratio of DMBP/TMBF formed
over low-active catalysts was almost unchanged during the
course of the reaction (0–1300 min, selectivities to furanyl
(Table 1), and the amount of accessible acid centers (Table 2).
At the same time, significantly lower conversions reached over
zeolites BEA (23% after 300 min TOS) and especially MFI (13%
after 300 min TOS) may be caused by slower diffusion of reac-
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Figure 7. a) Conversion of 2-naphthol and b) ratio between corresponding
TMBF and DMBP isomers over Nn-xd and conventional materials under
investigation.
Figure 6. a) Conversion of 1-naphthol and b) selectivities to corresponding
TMBF and DMBP isomers over solids under study.
catalysts under investigation. The ratio increased with time
over 3D zeolites and MCM-41-like material whereas it de-
creased over all 2D zeolites studied (Figure 7b). The depend-
ence of DMBP/TMBF ratio on the reaction time indicates that
in the case of bulky substrate (2-naphthol) local surrounding
the acid site may govern the preferential formation of these
isomeric products. Notably, in comparison with initial reaction
periods, the absolute amount of TMBF (if it was minor compo-
nent, over conventional solids and N3-1d) has changed with
time insignificantly. This means that such isomer formed at the
beginning of the reaction and its concentration almost did not
change further.
(TMBF) isomer were in the range of 63–70%), but it slightly de-
creased with time in the case of more active N3–5-5d materials
(selectivities to TMBF changed from 65–70 to 58–59%). Ob-
served differences in selectivities for more or less active cata-
lysts can again be explained by competition between forma-
tion of pyranyl product and its rearrangement to furanyl
isomer.
Further differentiation of 3D zeolites and materials contain-
ing thin crystalline layers was observed in the case of the most
bulky substrate, 2-naphthol. Similarly to previously discussed
phenols, N3–5-5d materials exhibited the highest conversion of
2-naphthol (Figure 7a). Again, this correlates with the values of
external surface area and agrees with the highest amount of
surface acid sites. 3D materials with the narrower pores (MFI,
BEA) and MCM-41-like sample with the lowest concentration of
acid sites predictably showed minor conversion.
It was found that the nature of the used solvent strongly in-
fluences the yields in annulation reaction of 2-naphthol. In par-
ticular, conversion of 2-naphthol over N3-5d catalyst dramati-
cally decreased with increasing solvent polarity in the follow-
ing sequence: p-xylene (relative polarity is 0.074)>chloroben-
zene (0.188)>1,2-dichloroethane (0.327)@dimethylsulfoxide
(DMSO, 0.444, Figure 8a). Regarding the better stabilization of
the polar intermediate complex in a more polar solvent, the
result obtained indicates the competition between reactant
and the solvent for interaction with active sites. At the same
In contrast to the cases of phenol and 1-naphthol transfor-
mation, the ratio of DMBP/TMBF in the case of 2-naphthol
transformation varied during the course of the reaction for all
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time, the selectivities significantly decreased with time for reac-
tions performed in different solvents at 808C (Figure 8b).
In contrast, the change of reaction temperature impacted
the conversion of 2-naphthol insignificantly (Figure 8a), influ-
encing mainly the selectivity to the DMBP/TMBF isomeric prod-
ucts (Figure 8b). The decreasing reaction temperature resulted
in significant increase in the ratio DMBP/TMBF, which is obvi-
ously caused by deceleration of the thermal rearrangement of
DMBP to corresponding TMBF.
To investigate the catalytic performance of the most active
N3-5d catalyst in more detail, two additional experiments were
performed: 1) adding of an extra amount of the MBO
(4.5 mmol), and 2) addition of a fresh portion of the catalyst
(50 mg) at 240 min TOS. Notably, doubling the amount of cata-
lyst (Figure 8c, red line) had less effect (+11%) on the increas-
ing substrate conversion related to the standard experiment
(Figure 8c, black line) than addition of extra MBO (+18%, Fig-
ure 8c, blue line). The additional amount of the catalyst mainly
triggered the isomerization process (indicated by decreasing
DMBP/TMBF ratio, Figure 8c), whereas the increase in the MBO
concentration led to the formation of DMBP (indicated by in-
creasing relative content in the mixture of isomers, Figure 8c).
Thus, as soon as conversion of 2-naphthol over N3-5d catalyst
reaches plateau, the DMBP-to-TMBF rearrangement becomes
dominant over the annulation reaction. The obtained results
indicate that reaching the plateau is caused by both partial de-
activation of the catalyst and adsorption/desorption competi-
tion between reactants and products.
Conclusions
Catalytic properties of mesophase and lamellar materials com-
posed of MFI nanosheets of different thickness were investigat-
ed in annulation of phenols differing in size of the molecules
(i.e., phenol, 1-, and 2-naphthol).
The conversions of phenols under study decreased in the
following sequence of materials: N3-5d>N4-5d>N5-5d>N3-9d,
following the decreasing external surface area and concentra-
tion of surface acid sites. The preferences of 2D zeolites
having improved textural characteristics (i.e., higher specific
pore volume, external surface area) over bulky zeolites BEA
and especially MFI in annulation of phenols become more
prominent with increasing the size of substrates under investi-
gation (phenol<1-naphthol<2-naphthol). The 2D material
containing one pentasil layer (N3-9d) surpasses not only
medium-pore zeolite MFI and large-pore zeolite BEA, but also
micro-/mesoporous USY zeolite, which seems to be caused by
higher void volume within N3-9d sufficient for a) the activation
of substrates and b) the formation of bulky intermediates aris-
ing from its superior textural characteristics at reasonable
acidity.
Figure 8. a) Conversion of 2-naphthol and b) ratio between corresponding
pyranyl/furanyl products over N3-5d material in annulation reaction using
different solvents (808C) and at different temperatures (60, 70, 808C; 1,2-di-
chloroethane as the solvent); c) change of conversion of 2-naphthol (solid
lines) and 6/5-ring isomers ratio (dotted lines) after adding of catalyst or
MBO after 240 min.
Increasing of the temperature and the decreasing of the rel-
ative polarity of the solvent used (in the order: DMSO>1,2-di-
chloroethane>chlorobenzene>p-xylene) resulted in the in-
crease of the yield of target products. The results of this study
clearly demonstrate that the novel materials characterized by
improved textural characteristics, compared with conventional
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pheric pressure and temperatures of 60–1008C in a multiexperi-
ment work station StarFish. Before the catalytic experiments, cata-
lyst portions of 50 mg were activated at 4508C for 90 min with
3D zeolites, can be regarded as promising acid catalysts of re-
actions involving more bulky substrates.
a
temperature heating rate of 108CminÀ1
. Typically, phenol
(3 mmol), mesitylene (0.4 g, internal standard), catalyst (50 mg),
and 1,2-dichloroethane (10 mL, solvent) were added to the three-
necked vessel, equipped with a condenser and thermometer,
stirred, and heated. Then MBO (4.5 mmol) was added into the reac-
tion vessel through a syringe as soon as the desired reaction tem-
perature was reached. Volumes of 0.2 mL of the reaction mixture
were sampled by means of a syringe with needle after 10, 30, 60,
120, 180, 300, and 1440 min. The reaction products were analyzed
by gas chromatography (GC) using an Agilent 6850 with flame ion-
ization detector equipped with a nonpolar HP1 column (diameter
0.25 mm, thickness 0.2 mm, and length 30 m). The reaction prod-
ucts were identified by using GC–MS analysis (ThermoFinnigan,
FOCUS DSQ II Single Quadrupole GC/MS).
Experimental Section
Synthesis of zeolites
Zeolite synthesis was performed by using gemini-type multiquater-
nary ammonium surfactants having formulas [C18H37-N+(Me)2-
{C6H12-N+(Me)2}nÀ2-C6H12-N+(Me)2-C18H37][BrÀ]n (n=3, 4, and 5) as
SDAs (denoted as 18-Nn-18). The synthesis of SDAs was performed
as described elsewhere.[25] The starting gel composition for zeolite
synthesis was 30SiO2:0.5Al2O3:(0.8–1.3)18-Nn-18:6.6Na2O:1070H2O.
The bromide form of 18-Nn-18 was dissolved in water solution of
NaOH and NaAlO2. Then, tetraethyl orthosilicate was added to pre-
pared solution into a polypropylene bottle under vigorous stirring.
After further mixing by using a mechanical stirrer for 6 h in an
oven at 608C, the resultant gel was transferred into a Teflon-lined
stainless-steel autoclave. The autoclave was tumbled with mixing
baffles at 60 rpm in an oven at 1408C. If 18-N3-18 was used as
SDA, the precipitated solid was sampled after 1, 5, and 9 d. In the
case of 18-N4-18 and 18-N5-18, the synthesis was stopped after 5 d.
The collected samples were filtered, washed with distilled water,
dried at 1008C, and finally calcined in air at 5808C. The calcined
samples were treated two times with 1m aqueous solution of
NH4Cl at RT followed by profound washing in distilled water. The
Acknowledgements
R.R. acknowledges support by Institute for Basic Science (IBS)
ˇ
[CA1301]. J.C. acknowledges the Czech Science Foundation
(P106/12/G015).
+
NH4 ion-exchanged samples were then calcined at 5508C to con-
vert zeolites to the H+ ionic form. Obtained samples were denoted
as Nn-xd, for which n is the number of ammonium segments in
SDA used, x is duration of hydrothermal synthesis (days). For com-
parison, commercially available H-forms of zeolites MFI, BEA, ultra-
stable FAU (USY) were used.
Keywords: acidity · annulation · arenes · nanostructures ·
zeolites
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Published online on && &&, 0000
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M. V. Opanasenko, M. V. Shamzhy, C. Jo,
Ideal for bulky substrates: Catalytic
behavior of hierarchical MFI zeolites was
investigated in annulation reaction of
phenols differing in size with methylbu-
tenol and compared with that of
medium and large-pore zeolites MFI
and BEA.
ˇ
R. Ryoo, J. Cejka*
&& – &&
Annulation of Phenols: Catalytic
Behavior of Conventional and 2D
Zeolites
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