MFI-type zeolite nanosheets for gas-phase aromatics chlorination: A strategy to overcome mass transfer limitations

Article abstract of DOI:10.1039/c4ra02747g

The continuous gas-solid (environmentally-friendly) chlorination of deactivated arenes using trichloroisocyanuric acid (TCCA, C₃N ₃O₃Cl₃) as a chlorination agent was chosen to compare the catalytic performances of various MFI-type catalysts in a reaction demanding a strong acidity. Mass transfer limitations were also evaluated by reacting either chloro- or nitrobenzene through a ZSM-5 zeolite porous network having different crystal sizes and morphologies. Whereas, the reaction rate was completely controlled by internal diffusion in 10-15 μm-sized big ZSM-5 zeolite crystals (Weisz modulus, _{big crystals} ～ 10), the impact of internal diffusion could be ruled out for ZSM-5 nanocrystals (200-400 nm) and in stacked ZSM-5 nanosheets (thickness 2 nm). Based on reactivity differences in arene halogenation between the two nano-sized ZSM-5 zeolites, we were able to estimate the quantity of mild acidic silanol groups in ZSM-5 nanosheets to roughly 1/3 of the total amount of Brnsted acid sites.

Full text of DOI:10.1039/c4ra02747g

RSC Advances
View Article Online
View Journal | View Issue
PAPER
MFI-type zeolite nanosheets for gas-phase
aromatics chlorination: a strategy to overcome
mass transfer limitations
Cite this: RSC Adv., 2014, 4, 27242
a
a
a
b
b
Marilyne Boltz, Pit Losch, Benoit Louis,* Guillaume Rioland, Lydie Tzanis
and T. Jean Daou*b
The continuous gas–solid (environmentally-friendly) chlorination of deactivated arenes using
trichloroisocyanuric acid (TCCA, C Cl ) as a chlorination agent was chosen to compare the catalytic
3 3
N O
3
3
performances of various MFI-type catalysts in a reaction demanding a strong acidity. Mass transfer
limitations were also evaluated by reacting either chloro- or nitrobenzene through a ZSM-5 zeolite
porous network having different crystal sizes and morphologies. Whereas, the reaction rate was
completely controlled by internal diffusion in 10–15 mm-sized big ZSM-5 zeolite crystals (Weisz modulus,
Received 28th March 2014
Accepted 10th June 2014
f
big crystals ꢀ 10), the impact of internal diffusion could be ruled out for ZSM-5 nanocrystals (200–
4
00 nm) and in stacked ZSM-5 nanosheets (thickness 2 nm). Based on reactivity differences in arene
DOI: 10.1039/c4ra02747g
halogenation between the two nano-sized ZSM-5 zeolites, we were able to estimate the quantity of mild
acidic silanol groups in ZSM-5 nanosheets to roughly 1/3 of the total amount of BrØnsted acid sites.
www.rsc.org/advances
9
catalytic properties. Recently, several groups tempted to
enhance the mass transfer in zeolite-catalyzed reactions, either
1
. Introduction
Zeolites are crystalline materials possessing a well-dened via inhibiting the zeolite growth beyond the nanometer-scale to
1
0–14
porosity. These tectosilicates are obtained by the polymeric shorten diffusion paths,
combination of TO
4
tetrahedra, where T can be either silicon or size.
or by raising the zeolite pore
Another approach consists of introducing a hierar-
aluminum. The difference of valence between aluminum and chical porosity, i.e.; micro- and mesoporosities (even macro-
15–17
18–23
silicon atoms induces the incorporation of a charge compen- porosity) within the zeolite crystals.
Despite a signicant
sation cation within zeolite frameworks. If this cation is a raise in the catalysts performance, these methods remain rather
proton, an intrinsic BrØnsted acidity is present which, coupled costly and sometimes hampered by stability issues, thus
with a high thermal stability, is responsible for zeolites inter- restricting their use at an industrial scale.
1
esting adsorption, diffusion and catalytic properties.
In 2009, Ryoo and co-workers christened the dawn of new
More than two hundred zeolite structures have been zeolitic materials, by using specically designed bifunctional
discovered during the past decades. However, only few of them compounds including at least two quaternary ammonium
2
–6
have found an industrial application.
Zeolites are very important in petrochemical industry. alkyl spacer and a hydrophobic alkyl chain inhibiting a further
functions directing the formation of MFI zeolite, linked by an
24,25
Indeed, the acid sites present within the zeolite framework growth of the material.
They obtained well-dened nano-
convert long saturated hydrocarbon molecules into smaller sheets with a controllable thickness along crystallographic b-
7
26
alkanes and alkenes, leading to fuel production. However, the axis. Recently, our group showed that MFI-type zeolites with a
narrow pores of a zeolite may hinder the diffusion of big lamellar morphology can be synthesized by using mono-
8
molecules. The decrease in the catalytic performance and the nitrogen surfactants specically designed by molecular
27
generation of coke are two consequences of this diffusion issue. modelling.
To solve that problem, both industry and academic researchers
To date, only few investigations about the catalytic properties
28–33
have struggled to develop new porous materials with enhanced of MFI-type zeolite nanosheets have been carried out.
Kim
et al. have shown that the product selectivity toward branched
isomers could be continuously raised by diminishing the MFI
Laboratoire de Synth `e se R ´e activit ´e Organiques et Catalyse (LASYROC), UMR 7177, zeolite crystal thickness to 2 nm. They have also shown that
a
28
Institut de Chimie, Universit ´e de Strasbourg, 1 rue Blaise Pascal, 67000 Strasbourg
Cedex, France. E-mail: blouis@unistra.fr
MFI-type zeolite nanosheets exhibit longer catalytic lifetime and
high selectivity for the production of 3-caprolactam via gas-
b
´
Universit ´e de Haute Alsace (UHA), CNRS, Equipe Mat ´e riaux a` Porosit ´e Contr ˆo l ´e e
29
phase Beckmann rearrangement of cyclohexanone oxime.
A
(
MPC), Institut de Science des Mat ´e riaux de Mulhouse (IS2M) UMR 7361, ENSCMu,
linear correlation between the number of external strongest
Mulhouse Cedex 68093, France. E-mail: jean.daou@uha.fr
27242 | RSC Adv., 2014, 4, 27242–27249
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
+
acid sites and the catalytic activity in decalin cracking could also
be established.
All the samples were NH
4
-ion-exchanged with a 1 M
33
ꢁ
NH NO aqueous solution at 65 C. The ion exchange process
In the present study, we report the inuence of crystal was repeated twice. Aer ltration and drying, NH -ion-
morphology, i.e.; nanosheets, nanocrystals, external surface- exchanged samples were calcined in air at 550 C to obtain the
4
3
+
4
ꢁ
+
passivated nanocrystals and conventional coffin-shaped micro- zeolite H -form.
crystals on the catalytic properties of MFI-type zeolites in a non-
conventional gas–solid reaction that requires a strong acidity.
The external surface acid sites of commercial nanosized
zeolite (CBV 5020) were then passivated to obtain our fourth
34
Our previous studies dealing with the chlorination of deacti- sample denoted as H-ZSM-5 nanocrystals-P. In a typical proce-
vated aromatics have shown the dependence between the dure, 1 g of H-ZSM-5 nanocrystals were suspended in a 4 wt.%
37
catalytic activity and the acidity and pore topology of different TEOS solution (in 25 mL n-hexane). The suspension was
35,36
zeolites.
Herein, we report the evaluation of the catalytic heated for 1 h under reux. This procedure was repeated three-
behaviour, in the continuous nitrobenzene and chlorobenzene times to ascertain the complete passivation of external surface
chlorinations with trichloroisocyanuric acid (TCCA), of four MFI- sites. Aerwards, the zeolite was ltered over a nylon membrane
type zeolite samples exhibiting distinct crystal morphologies and the passivated H-form was obtained through calcination in
ꢁ
(
nanocrystals, nanosheets, big crystals) or distinct surfaces (by an oven at 550 C during 8 h in air.
external surface passivation).
2.3 Characterization of the zeolites
2
. Experimental
X-ray diffraction patterns of the different materials were recor-
ded using a PANalytical MPD X'Pert Pro diffractometer oper-
ating with Cu Ka radiation (l ¼ 0.15418 nm) equipped with an
2.1 Structure directing agent synthesis
The di-quaternary ammonium-type surfactant, used for the
X'Celerator real-time multiple strip detector (active length ¼
+
MFI-type nanosheet synthesis, ([C22
H
45–N (CH
3
)
2
–C
6
H
12
–
ꢁ
2
.122 2q).
+
N (CH ) –C H13]Br ) was obtained in two steps following the
3 2 6 2
The size and the morphology of the crystals were determined
24
procedures reported by Choi et al. The surfactant was
composed of a long-chain alkyl group (C22) and two quaternary
ammonium groups spaced by a C alkyl linkage.
6
by scanning electron microscopy (SEM) using a Philips XL 30
FEG microscope or a JEOL FEG 6700F microscope working at 9
kV accelerating voltage. Nitrogen adsorption/desorption
isotherms were measured using a Micromeritics ASAP 2420
apparatus. The specic surface area (SBET) and microporous
volume (Vmicro) were calculated using BET and t-plot methods,
2.2 Zeolite syntheses
The MFI-type nanosheets were synthesized using the following respectively.
procedures: 0.24 g of sodium hydroxide (Riedel de Ha ¨e n, 99%)
The Si/Al molar ratio of the zeolite was determined using the
was dissolved in 7.17 g of distilled water in a 45 mL Teon-lined X-ray Fluorescence (Philips, Magic X). H/D isotope exchange
+
stainless steel autoclave. 0.73 g of C22
H
45–N (CH
3
)
2
–C
6
H
12
–
technique was used to determine the number of Brønsted acid
+
38–41
3 2 6 2
N (CH ) –C H13Br and 0.07 g of aluminum sulfate (Rectapur) sites present in the different solid acids.
were then added, under stirring. Aer homogenization, 2.13 g
of tetraethoxysilane (TEOS, Aldrich, 98%) were added, drop-
wise. Finally, 0.18 g of sulfuric acid (Aldrich) were added in
2.4 Catalytic tests
order to set the molar composition of the gel to: All the catalytic tests were performed in an all-glass ow system
+
1
00SiO
2
: 1Al
–C
2
O
3
: 30Na
2
O : 18H
SO
2 4
: 10C22
H
45–N (CH
3
)
2
–C
6 12
H –
2
with a cylindrical reactor. The gas ow (N ) was regulated by
+
N (CH
3
)
2
6
H13Br
2
: 4000H
2
O. The gel was stirred at 1000 rpm means of Brooks 5850E mass ow controllers. The reactions
ꢁ
during 30 min and placed in a tumbling oven at 150 C for 4 were carried out by diluting the catalytic bed (TCCA and zeolite
days. The autoclaves were tumbled at 30 rpm. Aer synthesis, catalyst) in an amorphous matrix to maintain the same height
the product was ltered, washed with distilled water and dried for all catalytic beds. To investigate the inuence of the MFI-
overnight at 100 C. The surfactants were nally removed by type zeolite morphologies and crystal sizes on their catalytic
calcination in a muffle furnace at 550 C for 8 h in air. The as- performances, we have decided to work at iso-mass conditions.
ꢁ
ꢁ
synthesized zeolite sample is denoted as ZSM-5 nanosheets.
However, the catalyst weight was different for the two
For comparison, MFI-type zeolite nanocrystals were aromatics, being 62 mg and 250 mg for chlorobenzene and
purchased from Zeolyst (CBV 5020) (denoted as ZSM-5 nano- nitrobenzene, respectively.
crystals) and typical MFI zeolite large crystals with a coffin-
Table 1 summarizes the reaction conditions used for either
shape morphology (denoted as big crystals) were synthesized in chlorobenzene or nitrobenzene chlorination reactions. The
the same condition described above for MFI nanosheets. The solid acid catalyst, the TCCA and the matrix were blended
only difference relied on 2.03 g of a tetrapropylammonium closely by grinding. The intimate solid mixture was then
hydroxide (TPAOH) aqueous solution (20% in weight, Fluka) transferred to a cylindrical reactor and xed to the set-up. The
ꢁ
use instead of the appropriate amount of diquaternary ammo- catalytic bed was rst dried under nitrogen ow at 150 C for 30
nium-type surfactant. The composition of the gel was therefore min. Then, the aromatic vapor pressure was allowed to pass
27
100SiO
2
: 1Al
2
O
3
: 30Na
2
O : 18H
2
SO
4
: 20TPAOH : 4000H
2
O.
through the catalyst bed for a dened reaction time.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 27242–27249 | 27243

View Article Online
RSC Advances
Paper
Table 1 Experimental conditions for aromatics chlorination reaction
TCCA equivalent Aromatic equivalent Acid site equivalent Diluting
T
( C)
reaction
ꢁ
T
( C)
aromatic trap Flow rate
Reaction
duration (h)
ꢁ
ꢂ1
Aromatic
(mol)
(mol)
(mol)
agent
(mL min
)
ꢂ4
ꢂ4
ꢂ4
ꢂ4
ꢂ4
ꢂ4
Nitrobenzene
Chlorobenzene 5.0 ꢃ 10
2.5 ꢃ 10
2.5 ꢃ 10
5.0 ꢃ 10
2.5 ꢃ 10
1.0 ꢃ 10
Silica
Glass rings 150
150
r.t.
0
100
25
5
3
ꢁ
The products were then trapped at ꢂ196 C and recovered
The SEM micrographs given in Fig. 2 reveal the shape of the
downstream to the reactor with dichloromethane. The analysis zeolite particles. ZSM-5 big crystals synthesized in the presence
was performed by gas chromatography (HP 6590) equipped with of TPAOH exhibit the characteristic prismatic shape of 10–15 mm
a capillary column (HP-5MS, 30 m). Retention times were in length. In contrast, MFI-type zeolite synthesized in the pres-
compared with standards and used to characterize the different ence of diquaternary ammonium surfactant exhibits a nano-
products. The degree of conversion and the selectivity toward sheet morphology. A multi-lamellar stacking of MFI nanosheets
the different products were calculated by taking into account was three-dimensionally intergrown. The overall thickness of the
the response factor of the substrate (aromatic) and those from lamellar stacking was normally 20–40 nm. The zeolite layer was
the products (mono-, di- and trichlorinated aromatics) through composed of three pentasil sheets, which corresponds to a single
2
4
the use of an external standard (styrene).
unit cell dimension along the b-axis (1.974 nm). The
commercial MFI nanoparticles (ZSM-5 nanocrystals) exhibit
spherical shape with an average size between 200 and 400 nm. As
expected for microporous solids, typical type I nitrogen adsorp-
tion isotherms were observed for ZSM-5 nanocrystals and big
crystals (Fig. 3), with a slight hysteresis for ZSM-5 nanocrystals
due to nanocrystals agglomeration. In the presence of the
diquaternary ammonium-type surfactant, the isotherms are of
type I and IV. The presence of mesopores generated by the
planar stacking of ZSM-5 nanosheets (intercrystalline porosity)
is responsible for the higher adsorbed volume (mesoporous
volume). The associated Brunauer–Emmett–Teller (BET) surface
area, microporous volume and external surface of the three MFI-
type zeolites are reported in Table 2.
3. Results and discussion
3.1 Characterization
The crystallinity and purity of the three zeolite samples were
checked by XRD. According to these patterns, the sole crystal-
line MFI phase was obtained for all zeolites (Fig. 1). As ‘a priori’
expected, XRD reections of ZSM-5 nanoparticles and ZSM-5
nanosheets are broader than those of micron-sized ZSM-5 big
crystals synthesized in the presence of conventional structure
directing agent (TPAOH). This can be explained by the smaller
crystal size of ZSM-5 nanosheets and nanocrystals with respect
to ZSM-5 crystals synthesized in the presence of TPAOH (Fig. 2).
In addition, for the ZSM-5 nanosheets, the major part of the
diffraction lines belong to the (h0l) crystallographic plane,
providing the sign that a one-dimensional growth-inhibition is
undertaken along the b-axis, thus conrming the formation of
3
.2 Mass transfer evaluation and catalytic activity in the
chlorination reactions
25
In this contribution, we have tested three different MFI zeolites
in the continuous gas–solid phase chlorination of nitrobenzene
and chlorobenzene to investigate the inuence of crystal
morphology (Table 3). In parallel, ZSM-5 nanocrystals modied
by silylation (named H-ZSM-5 nanocrystals P), adapted from
nanosheets.
37
Lercher et al. procedure, were also tested. Fig. 4 and 5 present
the nitrobenzene conversion and the selectivities toward mon-
ochlorination products and meta-chloronitrobenzene, and the
chlorobenzene conversion, the selectivity to monochlorination
products and the ortho/para ratio, respectively.
It is noteworthy that the selectivity in monochlorination
products remains nearly the same for both nano-sized zeolites,
being 60% toward meta-chloronitrobenzene produced as shown
in Fig. 4. Likewise, the selectivities toward o,p-dichlorobenzenes
remained nearly equal for both zeolite nanocrystals and nano-
sheets (Fig. 5).
Besides, one can observe that micron-sized ZSM-5 big crys-
tals exhibit almost no activity (<1%) in both aromatics haloge-
nation reactions. These results can be explained by a hindered
diffusion in those large crystals with respect to the two nano-
sized ZSM-5 zeolites.
Fig. 1 XRD patterns of ZSM-5 zeolites, big crystals (a), nanocrystals (b)
and nanosheets (c).
27244 | RSC Adv., 2014, 4, 27242–27249
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Fig. 2 SEM micrographs of ZSM-5 zeolites, big crystals (a), nanosheets (b) and nanocrystals (c).
Table 3 Chemical composition (Si/Al molar ratio) and Brønsted acidity
of four MFI-type zeolites
Brønsted acid
ꢂ1
Zeolite
Si/Al
sites [mmol g
]
H-ZSM-5 nanosheets
H-ZSM-5 big crystals
H-ZSM-5 nanocrystals
H-ZSM-5 nanocrystals P
48
28
25
49
1.17
0.59
0.90
0.37
The estimation of Thiele–Weisz modulus has therefore
2
been undertaken according to the following formula: f ¼ RL /
42b
eff
(D Caromatic), in which L represents the characteristic diffu-
sion length, R the reaction rate, Caromatic the substrate concen-
tration and Deff the effective diffusivity of a mono-substituted
Fig. 3
2
N adsorption–desorption isotherms of ZSM-5 zeolites, big
ꢂ2
aromatic within the zeolite pores. A reaction rate of 5.2 ꢃ 10
crystals (solid circles), nanosheets (empty circles), nanocrystals (empty
square).
ꢂ3 ꢂ1
mol m
s
was calculated for the more active sample and used
for all estimations. Likewise, the same concentration of
aromatic molecule as well as identical effective diffusion was
In heterogeneous-catalyzed reactions by zeolites, especially
involving bulky molecules, internal mass transfer limitations
have to be taken into account.
ꢂ3
used to determine Thiele–Weisz criteria, being 65.1 mol m
ꢂ14
2
ꢂ1
and 10
m s , respectively. The characteristic diffusion
22,23,42
42b
length was dened by the crystal size, thus the values were the
2
Table 2 Textural properties of the zeolites measured by N sorption
2
ꢂ1
3
ꢂ1
3
ꢂ1
Zeolite
S
BET (m g
)
V
micro (cm g
)
V
meso (cm g )
H-ZSM-5 nanosheets
H-ZSM-5 big crystals
H-ZSM-5 nanocrystals
H-ZSM-5 nanocrystals P
503
351
402
321
0.18
0.18
0.18
0.18
0.48
0
0.08
0.07
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 27242–27249 | 27245

View Article Online
RSC Advances
Paper
Fig. 4 Nitrobenzene chlorination reaction over the four MFI-type zeolite samples.
Fig. 5 Chlorobenzene chlorination reaction over the four MFI-type zeolite samples.
42,43
followings: 30 nm (nanosheets), 300 nm (nanocrystals) and reaction rate.
In contrast, mass transfer issues completely
15 mm (big crystals). A Thiele–Weisz modulus for micron-sized hinder the reaction in micron-sized ZSM-5 big crystals
ZSM-5 big crystals fbig crystals ꢀ 18 was estimated, whereas (fbig crystals ꢀ 18). The superior catalytic performance of zeolite
ꢂ4
f
ꢀ 0.01 and f
ꢀ 10 were obtained for ZSM- nanocrystals and nanosheets can therefore be rationalized by
nanocrystals
nanosheets
5
nanocrystals and nanosheets, respectively. In terms of intra- enhanced diffusion properties.
To further highlight the importance of diffusion
admitted when f < 0.1) conrms a full utilization of zeolite phenomena, a comparison was drawn before and aer the
catalyst particle, thus the reaction rate equals the intrinsic external surface passivation of ZSM-5 nanocrystals. It appeared
particle transport, the latter two values for Weisz modulus
(
27246 | RSC Adv., 2014, 4, 27242–27249
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
that the silylated catalyst exhibited a lower activity for both nanosheets exhibit a 30% higher number of BrØnsted acid sites
+
ꢂ1
aromatics, i.e.; 2% versus 19% for nitrobenzene (Fig. 4), 7% (1.17 versus 0.90 mmol H g for the ZSM-5 nanocrystals).
versus 20% for chlorobenzene (Fig. 5), respectively. The drastic In the case of nitrobenzene chlorination (Fig. 4), the two
loss in activity observed in aromatics chlorination reactions ZSM-5 catalysts led to nearly the same nitrobenzene conversion,
might be explained by both reduced microporous volume i.e.; 19% for the ZSM-5 nanocrystals and 18% for the nanosheets.
2
ꢂ1
accessibility and decrease in BET surface area (i.e.; 321 m g
It is noteworthy that ZSM-5 nano-sized crystals/nanosheets
2
ꢂ1
versus 402 m
g ), which may impact nitrobenzene/chloro- improved signicantly the catalytic performance of MFI-type
benzene adsorption on the acid sites within ZSM-5 channels. catalysts when compared with conventional coffin-shaped big
Hence, an inuence of the acid site density was also evidenced crystals. Unfortunately, the three-dimensional architecture of
while testing a nanocrystalline ZSM-5 (Zeolyst CBV 8020) having ZSM-5 nanosheets did not further raise the nitrobenzene reac-
nearly 40% lower amount of BrØnsted acid sites (Table 3). tivity in nano-sized ZSM-5 zeolites. Surprisingly, a 38% higher
Indeed, the rates of chlorobenzene converted referred to the TOF was achieved over ZSM-5 nanocrystal catalyst, i.e.; 1.1 ꢃ
ꢂ4
ꢂ4
ꢂ4
2
ꢂ1
amount of Al were 2.8 ꢃ 10 and 2.2 ꢃ 10 molaromatic con- 10 molnitrobenzene converted per acid site per m g in one
ꢂ1
verted per molAl
s
for H-ZSM-5 nanocrystals (Si/Al ¼ 25) and hour. The TOF values were corrected by the specic surface area
Zeolyst CBV 8020 catalyst (Si/Al ¼ 40), respectively. A roughly values to avoid its inuence.
2
0% loss in the reaction rate was observed over MFI-type zeolite In contrast, the two nano-sized MFI zeolites exhibited
possessing roughly a 40% lower density of BrØnsted acid sites. different activities in the chlorobenzene chlorination (Fig. 5).
Besides the inuence of ZSM-5 zeolite textural properties, it is ZSM-5 nanosheets zeolite led to a twice higher chlorobenzene
worthy to mention here that the acid site density also inu- conversion, with respect to the ZSM-5 nanocrystals, i.e.; 44%
ꢂ3
ences, even moderately, the reactivity in the chlorination versus 20%. By taking into account TOF values, 1.9 ꢃ 10 and
ꢂ3
ꢂ2 ꢂ1 ꢂ1
reaction.
2.8 ꢃ 10 molchlorobenzene conv. per mol
H
+
m
g
h
over ZSM-
Based on Weisz modulus estimations, internal mass transfer 5 nanocrystals and nanosheets were reached, respectively. A
limitations could be excluded for all these nano-sized MFI nearly 33% higher TOF could therefore be achieved on ZSM-5
zeolites. In spite of those Weisz moduli low values, one cannot nanosheets, thus suggesting that the layer morphology in ZSM-
neglect surface permeability barriers which are readily to occur in 5 nanosheets catalyst plays an important role in chlorobenzene
44–46
nanocrystals.
Krishna has highlighted discrepancies in the chlorination. Ryoo and co-workers outlined the point that MFI
modelling of diffusion kinetics at high surface coverage by the nanosheets, thanks to their larger number of external acid sites,
4
4
reactants/products along with strong connement effects.
exhibited a higher catalytic activity for large organic
24,25
Likewise, Karger et al. conrmed that these surface barriers may molecules.
differ up to a factor 2, thus indicating a higher resistance for bulky
molecules to enter inside the pores in smaller nanocrystals.
Nevertheless, the reverse tendency was observed for the
nitrobenzene chlorination reaction which requires a stronger
45
The difference between these two zeolites is related to their acidity due to the presence of deactivating nitro- group (TOF
three-dimensional arrangement and to their textural properties. diminished by approx. 35%). Since the TOF values for the two
2
The ZSM-5 nanocrystals exhibit a specic surface area of 402 m
nano-sized zeolites deviate from approx. ꢄ 32–38% ranging
ꢂ1
3
ꢂ1
g
and a mesoporous volume of 0.08 cm g , whereas ZSM-5 from chlorobenzene to nitrobenzene, one can roughly estimate
nanosheets possess a specic surface area above 500 m g and the density of external silanol groups present at the nanosheets'
2
ꢂ1
3
ꢂ1
a mesoporous volume of 0.48 cm
g
. In addition, ZSM-5 outer surface, representing thus nearly one third of the total
amount of BrØnsted acid sites.
Fig. 6 Schematic representation of aromatics reaction over ZSM-5 nanosheets: either within the pore network or at the external surface. The
zeolite model has been taken from ref. 48.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 27242–27249 | 27247

View Article Online
RSC Advances
Paper
To summarize, ZSM-5 zeolite organization into nanosheet
layers led to a 32% raise in the TOF for chlorobenzene haloge-
nation, suggesting that all O–H groups from the catalyst are
accessible and probably involved in the catalytic reaction
5 Z. Liu, Y. Wang and Z. Xie, Chin. J. Catal., 2012, 33, 22.
6 T. F. Degnan, Jr, Top. Catal., 2000, 13, 349.
7 W. Vermeiren and J. P. Gilson, Top. Catal., 2008, 52, 1131.
8 D. M. Ruthven and M. F. M. Post, in, Introduction to Zeolite
Science and Practice, ed. H. van Bekkum, E. M. Flanigen, P.
A. Jacobs and J. C. Jansen, Elsevier, Amsterdam, 2001, p. 525.
9 A. Corma, J. Catal., 2003, 216, 298.
35
whatever their localization and strength. In contrast, the
chlorination of nitrobenzene requires stronger BrØnsted acid
sites able to protonate TCCA molecule and thus to activate the
36
chlorine atom. One could therefore estimate the fraction of 10 F. C. Buciuman and B. Kraushaar-Czarnetzki, Catal. Today,
mild acidic external silanol groups in ZSM-5 nanosheets to 2001, 69, 337.
roughly 1/3 of the total amount of BrØnsted acid sites. Fig. 6 11 S. Mintova, N. H. Olson, V. Valtchev and T. Bein, Science,
summarizes the possible reaction of the aromatic substrate 1999, 283, 958.
either within the zeolite porous network (for nitrobenzene and 12 A. Zabala Ruiz, H. Li and G. Calzaferri, Angew. Chem., Int. Ed.,
chlorobenzene) or at the external silanol groups from zeolite
nanosheets (chlorobenzene only).
2006, 45, 5282.
13 F. Sch u¨ th and W. Schmidt, Adv. Mater., 2002, 14, 629.
Mota et al. have developed a method to assess the acid 14 L. Tosheva and V. P. Valtchev, Chem. Mater., 2005, 17, 2494.
strength of different solid acids with the use of linear free 15 D. M. Poojary, J. O. Perez and A. Cleareld, J. Phys. Chem.,
energy relationship for the H–D exchange with mono-
1992, 96, 7709.
substituted aromatics. A combination of H/D exchange tech- 16 K. G. Strohmaier and D. E. W. Vaughan, J. Am. Chem. Soc.,
nique (to determine the whole number of O–H groups present 2003, 125, 16035.
in the zeolite) with the present strategy to perform the halo- 17 A. Corma, M. J. Diaz-Cabanas, J. L. Jorda, C. Martinez and
genation reaction of various deactivated aromatics can there- M. Moliner, Nature, 2006, 443, 842.
fore be used as a tool to estimate the fraction of acid sites 18 K. Egeblad, C. H. Christensen, M. Kustova and
involved in those electrophilic aromatic substitution reactions. C. H. Christensen, Chem. Mater., 2008, 20, 946.
Hence, one may distinguish the quantity of sites possessing 19 R. Chal, C. Gerardin, M. Bulut and S. van Donk,
47
41
milder acidity by tailoring the basicity of the probe molecule
used for the reaction.
ChemCatChem, 2011, 3, 67.
20 R. Garcia, I. Diaz, C. Marquez-Alvarez and J. Perez-Pariente,
Chem. Mater., 2006, 18, 2283.
2
1 B. Louis, G. Laugel, P. Pale and M. M. Pereira,
ChemCatChem, 2011, 3, 1263.
4
. Conclusion
The gas-solid phase chlorination of deactivated arenes (chlo- 22 B. Louis, F. Ocampo, H. S. Yun, J. P. Tessonnier and
robenzene and nitrobenzene) using TCCA, was successfully M. M. Pereira, Chem. Eng. J., 2010, 161, 397.
performed over two nano-sized ZSM-5 zeolites. Whilst no 23 J. Perez-Ramirez, C. H. Christensen, K. Egeblad,
change in the selectivity toward the reaction products could be
C. H. Christensen and J. C. Groen, Chem. Soc. Rev., 2008,
37, 2530.
24 M. Choi, K. Na, J. Kim, Y. Sakamoto, O. Terasaki and R. Ryoo,
Nature, 2009, 461, 246.
evidenced, signicant variations in TOF values were observed,
ꢂ3
ꢂ3
i.e.; 1.9 ꢃ 10 and 2.8 ꢃ 10 molconv. chlorobenzene per molH
+
ꢂ2 ꢂ1 ꢂ1
m
g
h
over ZSM-5 nanocrystals and nanosheets, respec-
tively. The reverse performance was observed for nitrobenzene, 25 K. Na, M. Choi, W. Park, Y. Sakamoto, O. Terasaki and
where a 38% higher TOF was achieved over ZSM-5 nanocrystals
with respect to ZSM-5 nanosheets.
R. Ryoo, J. Am. Chem. Soc., 2010, 132, 4169.
26 W. Park, D. Yu, K. Na, K. E. Jelfs, B. Slater, Y. Sakamoto and
R. Ryoo, Chem. Mater., 2011, 23, 5131.
2
7 J. Dhainaut, T. J. Daou, Y. Bidal, N. Bats, B. Harbuzaru,
G. Lapisardi, H. Chaumeil, A. Defoin, L. Rouleau and
J. Patarin, CrystEngComm, 2013, 15, 3009.
Acknowledgements
The authors are grateful to the Agence Nationale de la Recher-
che (ANR) for supporting the ANR-10-JCJC-0703 project (Self- 28 J. Kim, W. Kim, Y. Seo, J.-C. Kim and R. Ryoo, J. Catal., 2013,
AsZeo). PL would like to thank the National Research Fund 301, 187.
Luxembourg for his PhD grant. The technical assistance from 29 J. Kim, W. Park and R. Ryoo, ACS Catal., 2011, 1, 337.
Thierry Romero and Jean-Daniel Sauer was highly appreciated. 30 E. Verheyen, C. Jo, M. Kurttepeli, G. Vanbutsele,
E. Gobechiya, T. I. Kor ´a nyi, S. Bals, G. van Tendeloo,
R. Ryoo, C. E. A. Kirschhock and J. A. Martens, J. Catal.,
References
2013, 300, 70.
1
2
M. E. Davis, Nature, 2002, 417, 813.
C. H. Bartholomew and R. J. Farrauto, Fundamentals of
31 S. Hu, J. Shan, Q. Zhang, Y. Wang, Y. Liu, Y. Gong, Z. Wu and
T. Dou, Appl. Catal., A, 2012, 445–446, 215.
Industrial Catalytic Processes, J. Wiley & Sons, New Jersey, 32 K. Na, C. Jo, J. Kim, W.-S. Ahn and R. Ryoo, ACS Catal., 2011,
2nd edn, 2006, p. 60.
1, 901.
3
4
A. Corma, Chem. Rev., 1995, 95, 559.
33 Y. Seo, K. Cho, Y. Jung and R. Ryoo, ACS Catal., 2013, 3, 713.
ˇ
J. Cejka, G. Centi, J. Perez-Pariente and W. J. Roth, Catal. 34 T. J. Daou, M. Boltz, L. Tzanis, L. Michelin and B. Louis,
Today, 2012, 179, 2.
Catal. Commun., 2013, 39, 10.
27248 | RSC Adv., 2014, 4, 27242–27249
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
3
5 G. F. Mendonça, A. R. Bastos, M. Boltz, B. Louis, P. Pale,
P. M. Esteves and M. C. S. de Mattos, Appl. Catal., A, 2013,
3rd edn, 1999; (b) B. Louis, L. Kiwi-Minsker, P. Reuse and
A. Renken, Ind. Eng. Chem. Res., 2001, 40, 1454.
4
60–461, 46.
43 O. Levenspiel, Chemical Reaction Engineering, John Wiley &
Sons, New York, United States, 3rd edn, 1999.
3
3
3
3
6 M. Boltz, M. C. S. de Mattos, P. M. Esteves, P. Pale and
B. Louis, Appl. Catal., A, 2012, 449, 1.
7 S. Zheng, H. R. Heydenrych, H. P. R ¨o ger, A. Jentys and 45 D. Tzoulaki, L. Heinke, H. Lim, J. Li, D. Olson, J. Caro,
J. A. Lercher, Top. Catal., 2003, 22, 101.
8 B. Louis, S. Walspurger and J. Sommer, Catal. Lett., 2004, 93,
44 R. Baur and R. Krishna, Catal. Today, 2005, 105, 173.
R. Krishna, C. Chmelik and J. Karger, Angew. Chem., Int.
Ed., 2009, 48, 3525.
81.
46 L. Karwacki, M. H. F. Kox, D. A. M. de Winter, M. R. Drury,
J. D. Meeldijk, E. Stavitski, W. Schmidt, M. Mertens,
P. Cubillas, N. John, A. Chan, N. Kahn, S. R. Bare,
M. Anderson, J. Kornatowski and B. M. Weckhuysen, Nat.
Mater., 2009, 8, 959.
9 J. P. Tessonnier, B. Louis, S. Walspurger, J. Sommer,
M. J. Ledoux and C. Pham-Huu, J. Phys. Chem. B, 2006,
110, 10390.
4
4
0 S. Walspurger and B. Louis, Appl. Catal., A, 2008, 336, 109.
1 B. Louis, A. Vicente, C. Fernandez and V. Valtchev, J. Phys. 47 V. L. C. Gonçalves, R. C. Rodrigues, R. Lorençato and
Chem. C, 2011, 115, 18603. C. J. A. Mota, J. Catal., 2007, 248, 158.
2 (a) M. Baerns, H. Hofmann and A. Renken, Chemische 48 E. L. First, C. E. Gounaris, J. Wei and C. A. Floudas, Phys.
Reaktionstechnik, Georg Thieme Verlag, Stuttgart, Germany, Chem. Chem. Phys., 2011, 13, 17339.
4
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 27242–27249 | 27249