Green route for the chlorination of nitrobenzene

Article abstract of DOI:10.1016/j.apcata.2012.09.021

A new green chlorination process of deactivated aromatics has been developed, being environmental-friendly and allowing the continuous chlorination of 1.7 kg nitrobenzene/kg catalyst per day. The triple novelty consists of using a non-conventional chlorination agent, the trichloroisocyanuric acid (TCCA, C₃N₃O₃Cl₃), along with solid acid catalysts (mainly zeolites) in a continuous flow reactor system. Different zeolites and solid acids have been tested in the chlorination of nitrobenzene, chosen as a model deactivated aromatic substrate. HUSY zeolite was found as the more promising catalyst for performing the chlorination of nitrobenzene, with good conversions (39-64%) at high selectivity toward monochlorinated products (90-99%). Finally, it is worthy to note that HUSY zeolite could be reused for at least five successive runs.

Full text of DOI:10.1016/j.apcata.2012.09.021

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Applied Catalysis A: General xxx (2012) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Green route for the chlorination of nitrobenzene
Marilyne Boltza, Márcio C.S. de Mattosb, Pierre M. Estevesb,∗
,
Patrick Palea, Benoit Louisa,∗∗
a Laboratoire de Synthèse Réactivité Organique et Catalyse (LASYROC), UMR 7177, Institut de Chimie, Université de Strasbourg, 1 rue Blaise Pascal, 67000
Strasbourg Cedex, France
b Universidade Federal do Rio de Janeiro, Instituto de Química, Av. Athos da Silveira Ramos 149, CT Bloco A, Cidade Universitária, 21941-909 Rio de Janeiro,
Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2012
Received in revised form 21 August 2012
Accepted 17 September 2012
Available online xxx
A new green chlorination process of deactivated aromatics has been developed, being environmental-
friendly and allowing the continuous chlorination of 1.7 kg nitrobenzene/kg catalyst per day.
The triple novelty consists of using a non-conventional chlorination agent, the trichloroisocyanuric acid
(TCCA, C3N3O3Cl3), along with solid acid catalysts (mainly zeolites) in a continuous flow reactor system.
Different zeolites and solid acids have been tested in the chlorination of nitrobenzene, chosen as a model
deactivated aromatic substrate.
HUSY zeolite was found as the more promising catalyst for performing the chlorination of nitrobenzene,
with good conversions (39–64%) at high selectivity toward monochlorinated products (90–99%). Finally,
it is worthy to note that HUSY zeolite could be reused for at least five successive runs.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Chlorination
Nitrobenzene
Trichloroisocyanuric acid (TCCA)
Zeolite
Green chemistry
1. Introduction
TCCA is a stable and inexpensive solid, easily available in pool
supplies, being thus frequently used as swimming-pool disinfect-
Chloroarenes are valuable starting molecules in fine chemistry,
for the synthesis of dyes, bio-active compounds such as pesti-
cides or pharmaceuticals [1,2]. Unfortunately, the conventional
industrial methods used for the chlorination of aromatics usually
produce mixtures of regioisomers, difficult to separate, thus raising
the cost for the industry [3]. Indeed, the utilization of Cl2, a toxic
gas, as chlorine source produces a large quantity of non-recyclable
wastes. Another disadvantage is the use of toxic acid catalysts such
as Lewis acids (aluminum chloride or boron trifluoride), which are
consumed and need to be neutralized after the reaction. In parallel,
strong Brønsted acid catalysts such as H2SO4 remain very corrosive
and generate a lot of salts as co-products.
During the past decades, researchers focused on the develop-
ment of more efficient and selective processes for the chlorination
of arenes [4–7]. For instance, Esteves et al. [7a] developed a
methodology for the chlorination of deactivated arenes using
trichloroisocyanuric acid (TCCA, C3N3O3Cl3) in a superelectrophilic
medium.
ant and bleaching agent. It is an efficient chlorine source due to its
high chlorine content, which can be up to 45.5% in weight, allow-
ing a priori a higher atomic efficiency than its N-chloro analogs
[7b]. TCCA was successfully used for chlorination of electron-rich
arenes [7b], alkenes [8] and carbonyl compounds [9], preparation
of N-chloro substrates [10,11] and in diverse oxidation reactions
[12].
Nowadays, organic chemistry is increasingly moving toward
green chemistry, where both homogeneous and heterogeneous
catalysis are at the core of this concept. In heterogeneously cat-
alyzed reactions, zeolites represent the key solid acid materials in
petrochemistry [13,14]. In addition, thanks to their internal poros-
ity, zeolites provide a highly organized channel structure and strong
acidity. The combination of these properties led them to exhibit
high conversions and excellent selectivities in targeted reactions
[15,16].
The chlorination of nitrobenzene is a very important process for
the production of series of useful compounds in dye chemistry [17].
It is worthy to study the chlorination of nitrobenzene in order to
produce valuable intermediates for the synthesis of azo dyes.
The aim of the present study is therefore to develop
a
new chlorination process of deactivated aromatics, being more
environmental-friendly by the use of solid acids instead of liquid
acids. In order to achieve this goal, we set up both a catalytic and a
∗
Corresponding author. Tel.: +55 2125627444.
Corresponding author. Tel.: +33 368851344.
E-mail addresses: pesteves@iq.ufrj.br (P.M. Esteves), blouis@unistra.fr (B. Louis).
∗∗
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.09.021
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Scheme 1. Chloration reaction of deactivated arenes over solid acid catalysts.
continuous process to chlorinate nitrobenzene (chosen as a model
deactivated arene) while using TCCA as a chlorination agent and
different solid acids as catalysts (Scheme 1).
2. Experimental
2.1. Reagents and catalysts
Trichloroisocyanuric acid (98%, Aldrich) and nitrobenzene (99%,
Merck) were used as received. Several commercial zeolites were
employed: H-Y (Aldrich), H-BETA (Zeolyst), H-MOR (Zeolyst), H-
EMT (IS2M, Mulhouse), H-USY (Zeolyst), H-FER (Petrobras). Prior to
use, these zeolites were activated by calcination at 550 ◦C overnight
under air.
Fig. 2. Experimental setup to perform chlorination in a continuous flow system.
In addition, H-USY zeolite has been chemically modified to
investigate the influence of its Lewis acidity. H-USY zeolite (200 mg)
was suspended in a 0.1 M solution of Na2H2-EDTA (17.4 mL,
2 equiv.). The mixture was heated at 62 ◦C and stirred for 24 h.
Afterwards, the solution was cooled down to room temperature,
filtered over a nylon membrane and thoroughly washed with dis-
tilled water (60 mL). The solid was reintroduced in the flask and
a 1 M solution of NH4Cl (20 mL) was added. The solution was then
heated at 80 ◦C and stirred for 24 h. Finally, the solution was filtered,
washed with distilled water (60 mL) and dried at 105 ◦C in an oven.
According to van Bokhoven et al. [18], extra-framework aluminum
(EFAl) was completely removed from pristine FAU material.
titration method. The catalyst (300 mg) was first activated under
dry nitrogen flow (40 mL/min) at 450 ◦C for 1 h to desorb water.
The deuteration of the catalyst was carried out at 200 ◦C by flow-
ing, through the catalyst, nitrogen (40 mL/min), previously bubbled
at room temperature through a U-shaped tube containing D2O
(about 0.05 g), during 1 h. Dry nitrogen was then sweeping through
the sample during 60 min to remove the excess of D2O. After this
purge, the titration of O-D sites was performed by back-exchanging
the deuterium present on the solid surface with distilled water
(3% of H2O in N2 stream) at 200 ◦C for 1 h. During this step the
partially exchanged water named HxODy, composed by H2O, D2O
and HDO, was collected in a cold U-tube trap at −117 ◦C. Collected
HxODy was then weighted and allowed to react with trifluoroacetic
anhydride, used in a two-fold excess. The acid solution obtained
was then transferred to a NMR tube for analysis. Spectra were
recorded on a Bruker AM400 spectrometer, after addition of a
CDCl3 (10 wt%)/CHCl3 mixture used as reference. Finally, an accu-
rate quantification of the H/D content in the different samples was
achieved by the integration of CF3COOH(D) and CH(D)Cl3 on both
1H and 2H spectra.
2.2. Brønsted acid sites titration
Our home-developed H/D exchange isotope technique was used
to quantify the number of Brønsted acid sites present in solid acids
[19,20]. Fig. 1 presents the experimental set-up used to perform this
2.3. Continuous chlorination process
All the reactions were performed in a glass flow system with a
cylindrical reactor. The gas flow was regulated by means of Brooks
5850E mass flow controllers and the dry nitrogen flow was set to
100 mL/min for each experiments. Fig. 2 shows the experimental
set-up to perform these catalytic tests in a continuous manner.
The reactions were carried out by diluting the catalytic bed
(TCCA and catalyst) in an amorphous silica (Grace, USA) matrix to
insure the same height for all catalyst beds. To investigate the influ-
ence of the solid acid structure on its catalytic performance, we
have decided to work at iso-site conditions. Indeed, all the catalytic
tests were performed by keeping a constant number of Brønsted
acid sites for the catalysts, which was set to 0.44 mmol H+. Table 1
Fig. 1. Experimental setup to perform the H/D isotope exchange technique.
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Table 1
ortho- and para-chloronitrobenzene, as a priori expected for the
nitro electron attracting group.
Brønsted acidity of the solid acids used in the chlorination process.
Solid acids
Si/Al
mmol H+/g
It seems that the zeolite pore size acts as a limiting factor for this
˚
reaction. Whilst no reaction occurred over H-FER zeolite (∼4 A pore
H-MOR
H-FER
H-EMT
H-BETA
H-ZSM-5 (zeolyst)
H-Y (Aldrich)
H-Y (UOP)
H-USY
Silica–alumina
H3PW12O40
Cs2PW12O40
SAC-13
5
10.5
6.5
13.6
15
2.2
5.0
2.8
3.6
–
1.90
2.26
2.38
1.07
1.04
5.34
2.20
3.90
3.68
0.91
0.32
1.00
1.87
aperture), nitrobenzene reacted with TCCA over medium pore H-
˚
ZSM-5 zeolite, which possesses a rather narrow pore size of 5.5 A,
affording 21% conversion. In contrast, 39% of nitrobenzene was con-
˚
verted over H-USY (pore size of 7.4 A). This tends to support an
effect of higher accessibility of those large organic molecules to the
catalytic sites in H-USY zeolite [21].
On the other hand, the chlorination reaction appears to be
positively influenced by the channel architecture of a zeolite
framework. Indeed, the SAC-13 catalyst (Nafion-H supported over
MCM-41), being a polymer-grafted on mesoporous silica, only led
to a 5% nitrobenzene conversion (Fig. 4). Likewise, gallium-doped
mesoporous silica (Ga-SBA-15) [22] also led to poor catalytic per-
formance (conversion of 7%) with respect to zeolites.
Following the same trend, the selectivity toward monochlo-
rination is also governed by the zeolite porosity. In parallel, the
beneficial effect of microporosity has been further evidenced
–
–
–
Ga-SBA-15
presents the number of Brønsted acid sites titrated by H/D exchange
for all solid acids used for the chlorination reaction.
The solid acid catalyst (0.44 mmol H+), trichloroisocyanuric acid
(0.15 mmol) and silica matrix (17 mmol, 1 g) were blended closely
by grinding. The mixture was then transferred into the cylindri-
cal reactor and the reactor was fixed to the set-up. The catalytic
bed was first dried under dry N2 flow at 150 ◦C for 30 min to des-
orb the water present in the void volume of the zeolite. Then,
nitrobenzene was supplied in its gaseous state by sweeping a dry
N2 flow through a stripping U-shaped reactor containing liquid
nitrobenzene (Fig. 2). Hence, this dry nitrogen flow saturated with
nitrobenzene’s vapor pressure was allowed to pass through the cat-
alytic bed during 5 h. The products were trapped at −196 ◦C and
recovered downstream to the reactor with toluene (4 mL). They
were analyzed by gas chromatography (HP 5890 Series II) equipped
with a capillary column (PONA, 50 m). Retention times were com-
pared with standards and used to characterizethe different reaction
products. The degree of conversion and the selectivity toward
the different products were calculated by taking into account the
response factor of the substrate (nitrobenzene) and those from the
products (mono-, di- and tri-chlorinated aromatics) through the
use of an external standard (styrene).
with the use of strongly acidic polyoxometalate H3PW12O40
.
Whereas, this non porous solid acid led to an appreciable degree
of nitrobenzene conversion (14%), in contrast the selectivity dras-
tically diminished with respect to zeolites in favor of dichlorination
products. However, Cs2HPW12O40 that exhibits a higher SSA value
(123 m2/g) and porosity with respect to its protonic counterpart
(5 m2/g) led to 2.6 fold increase in activity. The same behavior was
observed with amorphous silica–alumina, which converted only
5% of nitrobenzene probably due to the absence of zeolite’s highly
organized pore architecture.
In addition, a non-conventional acid catalyst, sulfated tin dioxide,
2−
was also tested. This SnO2/SO4 catalyst, which possesses exclu-
sively Lewis acid sites and almost no porosity, was not a good
candidate at all, since no activity could be observed.
Besides, a rather surprising difference in reactivity between H-Y
and H-USY zeolites was observed (Fig. 3). H-USY zeolite is usu-
ally obtained by dealumination via a high temperature steaming
of pristine H-Y zeolite [23]. The dealumination process consists of
removing aluminum atoms from the zeolite framework and thus
to create new extra-framework aluminum species (EFAl) present
either as amorphous species (pseudo Al2O3) [24] or aluminum
species exhibiting exalted Lewis acidity (AlOOH, AlO+ species, etc.)
[25]. This phenomenon is beneficial for the chlorination process
since the conversion of nitrobenzene was drastically improved to
39% with H-USY compared to HY zeolite (16%).
To summarize these preliminary tests, one can observe that the
optimal catalyst for performing the chlorination of nitrobenzene
remains the H-USY zeolite. Indeed, the faujasite structure allows
catalyzing the chlorination of nitrobenzene by combining a high
selectivity in monochlorinated compounds (99%) at an acceptable
degree of nitrobenzene conversion.
3. Results and discussion
3.1. Methodology
In preliminary experiments, we initially performed the reaction
between TCCA and nitrobenzene by changing only one parame-
ter between each experiment. Firstly, we performed a screening of
the different solid acid catalysts (working under iso-Brønsted site
conditions). The effects of pore topologies and sizes along with the
quantity of Brønsted acid sites were investigated among the differ-
ent solid acids. Furthermore, we also decided to refine the number
of catalysts tested to find adapted reaction conditions by analyzing
the effect of temperature on the performance of the more promis-
ing catalyst. In parallel, the influence of Lewis acidity (EFAl) has
been evaluated for chosen “optimal” catalyst.
3.3. Influence of reaction temperature
Fig. 5 shows the results of the chlorination reaction at different
reaction temperatures. As ‘a priori’ expected, a raise in the temper-
ature led to higher nitrobenzene conversion, but at the expense
of the selectivity in monochlorinated products. The decrease in
selectivity is due to the formation of di- and tri-chlorinated prod-
ucts. For instance, the selectivity toward monochlorination was
diminished to 63% at 200 ◦C. Selectivities in di-chlorinated and tri-
chlorinated products were 32% and 5%, respectively. Among the
products of di-chlorination, 1,4-dichloro,2-nitrobenzene was formed
as major isomer (71%) whilst 1,2-dichloro,4-nitrobenzene repre-
sented nearly 28% selectivity among the dichlorinated products.
It is therefore worthy to mention that the second chlorination
Finally, the chlorination process was further optimized by mod-
ifying different reaction parameters, as quantities of TCCA, the
weight hourly space velocity (WHSV) while varying the catalyst
mass. Likewise, the potential reuse of the catalyst was also tested.
3.2. Behavior of the different solid acid catalysts
Fig. 3 shows the degree of nitrobenzene conversion and the
selectivity to mono-chloronitrobenzenes among the different cat-
alysts. It is noteworthy that the meta-chloronitrobenzene was
always found as prominent isomer, i.e.; >90% with respect to the
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Fig. 3. Nitrobenzene conversion and selectivity to monochlorination products over different zeolite catalysts. Conditions: nTCCA = 0.15 mmol; nH+ = 0.44 mmol; reaction
duration = 5 h; temperature = 150 ◦C.
(involving deactivated meta-chloronitrobenzene) is favored in
ortho and para positions of the chlorine atom. The higher selec-
tivity in 1,4-dichloro,2-nitrobenzene major isomer might be explain
by lower steric hindrance than 1,2-dichloro,4-nitrobenzene iso-
mer.
Based on these results, we have arbitrary chosen the tempera-
ture of 150 ◦C as an optimal temperature, since a good compromise
between a high selectivity and a reasonable conversion of nitroben-
zene was achieved.
species (EFAl) at nearly 0 ppm (Fig. 6). Two distinct signals were
detected over pristine HUSY zeolite (before EDTA treatment): one
located at 50 ppm and one broad near 0 ppm (Fig. 6a). These signals
correspond, respectively, to framework aluminum species and to
extra-framework aluminum (EFAl) species. The later species rep-
resent about 29% of the total aluminum present within the zeolite.
Fig. 6b, corresponding to the zeolite HUSY after one EDTA treat-
ment, shows the quasi-disappearance of the EFAl signal with only
12% of the remaining aluminum present as EFAl in the zeolite chan-
nels. It appears therefore that one EDTA treatment alone did not
remove all the EFAl species in the H-USY. As a control experi-
ment, no EFAl could be detected in the H-Y spectrum (Fig. 6c),
all the aluminum cations are present in the framework as T-
atoms.
3.4. Influence of the Lewis acidity
In order to highlight the effect of Lewis acidity in H-USY zeo-
lite, we have performed a treatment to remove extra-framework
aluminum species (EFAl) by complexing them with EDTA. The
catalyst was then analyzed by 27Al MAS NMR to assess the dis-
appearance of the characteristic signal attributed to octahedral
Furthermore, this dealumination treatment had another impact
on the structural properties of H-USY zeolite. The complexation of
EFAl species led to intense leaching of those species, thus reducing
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Fig. 4. Comparison in terms of nitrobenzene conversion and selectivity toward monochlorination between HUSY zeolite and non-zeolitic solid acids. Conditions:
nTCCA = 0.15 mmol; nH+ = 0.44 mmol; reaction duration = 5 h; temperature = 150 ◦C.
pore obstruction, thus introducing also a high level of mesoporosity
inside the FAU structure. Hence the diffusion of products/reactants
can be seriously improved [26,27].
H-USY (by the removal of EFAl fragments) enhanced the catalytic
performance.
Fig. 7 presents the catalytic data obtained with the H-USY zeo-
lite treated and non-treated with EDTA. One can observe that
the presence or not of EFAl species strongly influence the cat-
alytic performance of H-USY zeolite. Indeed, the EDTA treatment
of H-USY led to a significant increase in nitrobenzene conver-
sion, up to 64% while the selectivity in monochlorinated products
remained slightly affected. This phenomenon could be due to
the higher accessibility of the reactants to the active sites within
the pores, emptied from their alumina aggregates [24]. Hence,
the molecules easily access to the active sites, thus raising the
conversion of nitrobenzene to mono- and also to di-chlorinated
products.
3.5. Optimization of the reaction conditions
To complete our study, we have further optimized the reaction
conditions by changing the quantities of TCCA and H-USY zeolite
(WHSV alteration).
Fig. 8 shows the results obtained for different quantities of H-
USY catalyst. We realized these experiments in comparison to the
reference, where the ratio between TCCA and H-USY was 1/3 (based
on the number of Brønsted acid sites). It is important to note that the
value 0.15 mmol corresponds to nTCCA/nBrønsted acid sites = 1. Hence,
this implies that 3 chlorine atoms could be potentially involved in
the reaction (nCl/nH+ = 3). Based on the results depicted in Fig. 8,
it can be concluded that the optimal amount of catalyst for reach-
ing maximal conversion corresponds to a nTCCA/nBrønsted acid sites = 1
To summarize, Lewis acidity did not play a direct role in the
chlorination reaction but the creation of mesoporosity in the
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Conversion
Selectivity in monochlorinated products
100
75
50
25
0
Fig. 7. Comparison in terms of nitrobenzene conversion and selectivity toward
monochlorination between HUSY zeolite and HUSY treated by EDTA. Conditions:
nTCCA = 0.15 mmol; nH+ = 0.44 mmol; reaction duration = 5 h; temperature = 150 ◦C.
120
140
160
180
200
Temperature, [°C]
Fig. 5. Influence of reaction temperature on the chlorination process in terms of
nitrobenzene conversion and selectivity in monochlorinated products. Conditions:
nTCCA = 0.15 mmol; nH+ = 0.44 mmol; reaction duration = 5 h.
Conversion
Selectivity in monochlorinated products
100
75
50
25
0
ratio (0.15 mmol H+). This ratio allowed the conversion of 24%
of nitrobenzene with an excellent selectivity toward monochlori-
nated compounds of 95%.
In parallel, the quantity of TCCA was also varied (Fig. 9). It is
noteworthy that a raise in the TCCA amount led to an increase in the
conversion of nitrobenzene while keeping a high selectivity toward
monochlorinated products. These experiments confirmed that the
optimal ratio between TCCA and the number of Brønsted acid sites
of the zeolite was 1 (0.45 mmol TCCA, referring to nCl/nH+ = 3).
These new conditions allowed converting 53% of nitrobenzene with
a high selectivity of 94% toward monochlorination products.
Scheme 2 rationalizes the Brønsted acid-catalyzed activation
of one TCCA molecule within the zeolite pores and cavities, thus
0,0
0,1
0,2
0,3
0,4
0,5
Number of Bronsted acid sites, [mmol]
Fig. 8. Influence of the HUSY catalyst loading on the nitrobenzene conversion. It
is worthy to mention that 0.15 mmol H+ corresponds to nTCCA/nBrønsted acid sites = 1
(or nCl/nH+ = 3). Conditions: nTCCA = 0.15 mmol; reaction duration = 5 h; tempera-
ture = 150 ◦C.
Conversion
Selectivity in monochlorinated products
100
75
50
25
0
0,1
0,2
0,3
0,4
0,5
Quantity of TCCA, [mmol]
Fig. 9. Effect of TCCA quantity on the chlorination of nitrobenzene over HUSY zeolite.
The equimolar ratio between the number of Brønsted acid sites and TCCA (nCl/nH+ =
3) corresponds to 0.45 mmol. Conditions: nH+ = 0.44 mmol; reaction duration = 5 h;
temperature = 150 ◦C.
Fig. 6. 27Al MAS NMR spectra: (a) HUSY zeolite before EDTA treatment; (b) HUSY
zeolite after EDTA treatment; (c) HY zeolite.
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Scheme 2. Brønsted acid-catalyzed activation of TCCA within the zeolite framework.
raising the electrophilicity of Cl-atom. Hence, the electrophilic aro-
matic substitution remains therefore favored on the aromatic ring
of nitrobenzene.
To complete our study in a green chemistry context, we have
also evaluated the recyclability of our “optimal” H-USY catalyst by
performing five successive runs without changing the catalyst bed.
The catalyst was treated at 550 ◦C under air during one night after
reaction to remove all organics from its surface. After calcination,
new TCCA (100 mg) was added and mixed with the catalyst. Fig. 10
shows that after the first run the catalyst lost about 20–25% in terms
of relative activity but remained stable during the four consecutive
runs. Furthermore, it is worthy to mention that the catalyst held a
constant and high selectivity toward monochlorinated compounds.
Further studies are currently under progress to evaluate numer-
ous kinetic parameters as the different reaction orders relative to
the reactants, the activation energy and the detailed mechanism of
this catalytic chlorination reaction.
Conversion
Selectivity in monochlorinated products
100
75
50
25
0
4. Conclusion
The present work describes the development of a green route
to perform the chlorination of nitrobenzene (model deactivated
aromatic) in the presence of zeolites and trichloroisocyanuric acid.
We were able to setup a continuous process for the chlorination
reaction, allowing the production of 1.7 g of chlorination products
of nitrobenzene per gcatalyst per day, along with a high selectivity in
monochlorinated products. A first generation of FAU zeolite catalyst
was designed, combining the appropriate channel/cavity structure,
with some mesoporosity, and a strong Brønsted acidity. Indeed, this
H-USY zeolite exempted from its EFAl species led to achieve a 64%
conversion at a 85% selectivity toward monochlorinated products.
Finally, the potential reuse of the catalyst has been demon-
strated but with an irreversible loss in activity after the first run
(only), which remained stable after the next consecutive runs.
run 1
run 2
run 3
run 4
run 5
Fig. 10. Recyclability of HUSY catalyst during five consecutive runs. Conditions:
nTCCA = 0.15 mmol; nH+ = 0.44 mmol; reaction duration = 5 h; temperature = 150 ◦C.
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The authors are grateful to the Agence Nationale de la Recherche
(ANR) for supporting the ANR-10-JCJC-0703 project (SelfAsZeo).
The technical assistance of M. Gaëtan Lutzweiler for electronic
maintenance was highly appreciated. PME and MCSM acknowledge
CNPq for a fellowship.
3 (2011)
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Please cite this article in press as: M. Boltz, et al., Appl. Catal. A: Gen. (2012), http://dx.doi.org/10.1016/j.apcata.2012.09.021