Highly efficient nano-sized TS-1 with micro-/mesoporosity from desilication and recrystallization for the epoxidation of biodiesel with H2O2

Article abstract of DOI:10.1039/c5gc00406c

The epoxidation of the unsaturated fatty acid methyl esters (FAME) in biodiesel with H₂O₂ was investigated at 323 K in the liquid phase over microporous nano-sized TS-1 as well as micro-/mesoporous nano-sized TS-1. Nano-sized TS-1 with stacked morphology exhibits a catalytic activity per number of Ti sites up to 30% higher than a conventional, industrial TS-1 catalyst. Mesoporosity was successfully introduced by a desilication-recrystallization approach. Desilication by alkaline treatment in the presence of the structure-directing agent tetrapropylammonium cation (TPA⁺) or NaOH leads to the generation of undefined mesopores (10-40 nm), probably accompanied by an increase of the surface hydrophilicity. Consequently, the alkaline-treated materials show a two times lower catalytic activity in the epoxidation of biodiesel than the purely microporous parent material. The surfactant-assisted recrystallization of the alkaline-treated materials results in more uniform and smaller mesopores (3-10 nm). In the epoxidation, the recrystallized materials are remarkably more active with respect to both the purely microporous parent and alkaline-treated materials reaching a FAME conversion of 65% with an epoxide selectivity of 82%.

Full text of DOI:10.1039/c5gc00406c

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ARTICLE
Highly Efficient Nanoꢀsized TSꢀ1 with Microꢀ/Mesoꢀ
porosity from Desilication and Recrystallization
for the Epoxidation of Biodiesel with H2O2
Cite this: DOI: 10.1039/x0xx00000x
N. Wilde, M. Pelz, S.G. Gebhardt, and R. Gläser*
The epoxidation of the unsaturated fatty acid methyl esters (FAME) in biodiesel with H2O2
was investigated at 323 K in the liquid phase over microporous nanoꢀsized TSꢀ1 as well as
microꢀ/mesoporous nanoꢀsized TSꢀ1. Nanoꢀsized TSꢀ1 with stacked morphology exhibits a
catalytic activity per number of Ti sites up to 30% higher than a conventional, industrial TSꢀ1
catalyst. Mesoporosity was successfully introduced by
a desilicationꢀrecrystallization
approach. Desilication by alkaline treatment in the presence of the structureꢀdirecting agent,
tetrapropylammonium cation (TPA+) or NaOH leads to the generation of undefined mesopores
(10ꢀ40 nm), probably accompanied by an increase of the surface hydrophilicity. Consequently,
the alkalineꢀtreated materials show a two times lower catalytic activity in the epoxidation of
biodiesel than the purely microporous parent material. The surfactantꢀassisted recrystallization
of the alkalineꢀtreated materials results in more uniform and smaller mesopores (3ꢀ10 nm). In
the epoxidation, the recrystallized materials are remarkably more active with respect to both
the purely microporous parent and alkalineꢀtreated materials reaching a FAME conversion of
65% with an epoxide selectivity of 82%.
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
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formed organic percarbonic acids 8. This route suffers from
several drawbacks: (i) the selectivity for epoxides is relatively
1 Introduction
Renewable feedstocks have recently gained considerable
interest as raw materials for the production of chemicals. By far
the largest share of utilized renewables in the chemical industry
is held by fats and oils, since they offer widespread possibilities
for different applications1. Vegetable oils represent one of the
cheapest and most abundant biomassꢀbased feedstock available
in large quantities, and its use as starting material offers
numerous advantages such as low toxicity and inherent
biodegradability 2. Among the applications of fats and oils,
their conversion to fatty acid methyl esters (FAME) for
biodiesel production is one of most prominent. FAME can be
further converted to epoxidized fatty acid esters, which play an
important role for a broad range of largeꢀscale industrial
syntheses of chemicals and intermediates such as plasticizers
and stabilizers in PVC, intermediates in the production of
low due to oxirane ring opening in the acidic reaction media,
(ii) the handling of percarbonic acids and highly concentrated
hydrogen peroxide solutions is strongly hazardous, and (iii) the
aqueous solutions of C1–C3 carboxylic acids formed as byꢀ
products are strongly corrosive. Homogeneously and
heterogeneously catalyzed epoxidations are the preferred
alternatives to conventional stoichiometric routes. FAME
epoxidation is mostly reported using organic hydroperoxides,
such as tertꢀbutylꢀ or cumene hydroperoxide, as epoxidizing
9ꢀ11
agents
. However, hydrogen peroxide would be an
economically and environmentally largely preferred oxidant.
The results from our previous work show that the epoxidation
of unsaturated esters derived from the renewable raw material
rapseed oil methyl ester (RME), i.e., biodiesel, can be
accomplished over conventional titanium silicaliteꢀ1 (TSꢀ1)
with aqueous H2O2 as the sole oxidizing agent. Thus, biodiesel
can be converted without additional purification and almost
complete biodiesel conversion can be achieved after 24 h with
polyurethane polyols or components for lubricants, cosmetics
or pharmaceuticals
epoxidation of unsaturated fatty acid compounds is mainly
carried out by the Prileshajew reaction with either preꢀ or in situ
1, 3ꢀ7
. Currently, the industrialꢀscale
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an epoxide selectivity up to 80%. However, the conversion of desilication step on the one hand and from the recrystallization
fatty acid methyl esters over TSꢀ1 is limited by massꢀtransfer step on the other hand were compared.
within the catalyst particles, largely due to the size of its
micropores with respect to the bulky FAME molecules 12
.
2 Experimental Section
To overcome massꢀtransfer limitations in TSꢀ1, intensive
research has been carried out, focused on increasing the
accessibility of active sites by decreasing the crystal size or
2.1 Catalyst Synthesis
13
Nanoꢀsized titanium silicaliteꢀ1 with stacked morphology
(TSꢀ1_ns) was prepared according to by microwaveꢀassisted
13
by incorporation of intraꢀcrystalline mesoporosity. The first
12
approach was shown to be feasible in our earlier work using
synthesis using tetraethyl orthosilicate (TEOS, >99%, Merck),
tetrapropylammonium hydroxide (TPAOH, 10 wt.% aqueous
solution, Sigma Aldrich), titanium(IV) isopropoxide (TIP, 97%,
Sigma Aldrich). isopropanol (99%, BDH Prolabo) and
deionized water. Typically, TEOS (36.5 g), TPAOH solution
(35.7 g) and deionized water (39.2 g) were mixed under stirring
for 1 h. TIP (0.71 g) and isopropanol (8.15 g) were mixed under
stirring in a separate beaker for 45 minutes. Subsequently, the
solutions were combined and stirred, first for 2 h at room
temperature and, then, at 353 K for 1 h to remove the
isopropanol. The resulting mixture was separated into two parts
of 42 cm3 each, added to a 100 cm3 PTFE autoclave and
transferred to a microwave oven (MLS, Start 1500) for
crystallization. For that purpose, the synthesis mixture was
heated for 5 min with an irradiation power of 600 W to 438 K
and held at this temperature under autogeneous pressure for
10 minutes (TSꢀ1_ns10), 20 minutes (TSꢀ1_ns20), 60 minutes
(TSꢀ1_ns60) and 70 minutes (TSꢀ1_ns70), respectively. After
cooling to room temperature, the obtained solids were
recovered by centrifugation, washed five times with 25 cm3
deionized water, dried at 393 K for 6 h and calcined in an air
atmosphere at 823 K for 6 h.
Microꢀ/mesoporous TSꢀ1 catalysts were obtained in two steps
including a partial desilication of TSꢀ1_ns in alkaline solution
followed by a hydrothermal treatment for recrystallization in
the presence of the structureꢀdirecting agent CTMA+ (OHꢀ/Brꢀ).
Desilication was carried out by alkaline treatment of the parent
TSꢀ1_ns70 with aqueous solutions of NaOH (≥98%, pellets,
Sigma Aldrich) or NH3 (25 wt.% aqueous solution, AnalaR
NORMAPUR, BDH Prolabo) partly in the presence of
tetrapropylammonium cation TPA+ (TPAOH, 10 wt.% aqueous
solution, Sigma Aldrich) as an additional structureꢀdirecting
agent. In a typical preparation, 3 g of the parent TSꢀ1_ns and
50 cm3 of the alkaline solution, i.e., 0.1 M NaOH,
0.1 M NaOH/1.0 M TPAOH or 13 M NH3/1.0 M TPAOH)
were transferred into a roundꢀbottom flask (V = 100 cm3)
followed by heating under reflux to 338 K for 70 min. After
cooling to room temperature, the solids were separated by
centrifugation, washed with deionized water until neutral
reaction of the washing water, dried at 358 K and calcined in
air at 813 K for 5 h. The resulting materials are referred to as
TSꢀ1 with stacked morphology and crystals in the subꢀ
micrometer scale. A goal of the present work was, thus, to
further explore the potential of this approach by preparing
nanoꢀsized TSꢀ1 catalysts, but different crystal sizes using
different irradiation times during microwaveꢀassisted synthesis.
The latter approach, i.e., the incorporation of intraꢀcrystalline
mesoporosity into zeolite crystals, represents an elegant
strategy, since in the corresponding catalysts the major
advantages of microꢀ and mesoporous materials are combined.
Several routes were reported to incorporate mesoporosity into
TSꢀ1, e.g., by using amphiphilic organosilica zeolite
16ꢀ19
precursors 14, 15, by utilizing hard templates
or by the topꢀ
down technique that involves the removal of silica via
desilication by treatment in alkaline solutions 20ꢀ23. However,
mesopore introduction by desilication is poorly controllable
with respect to, e.g., size, shape, connectivity and location of
the mesopores, and it often leads to a random and disordered
mesopore system.
In contrast, several studies have demonstrated that a variety of
different hierarchical zeolites with highly controlled
mesoporosity can be obtained by a procedure involving zeolite
desilication and recrystallization in the presence of a mesopore
surfactant24. In these procedures, the degree of desilication is
the most important parameter for tuning the structural and
textural properties of recrystallized zeolites.
Despite the large number of reports on the synthesis,
characterization and application of recrystallized MFIꢀtype
zeolites 25, studies on the preparation of microꢀ/mesoporous
TSꢀ1 using the recrystallisation approach are rather scarce 26, 27
.
Another goal of the present work was, thus, devoted to the
preparation of nanoꢀsized TSꢀ1 with stacked morphology and
additional mesoporosity introduced by a twoꢀ stepꢀapproach
including zeolite desilication by alkaline treatment and
subsequent pseudomorphic transformation via recrystallization
in the presence of the surfactant cetyltrimethylammonium
cation (CTMA+). One question was, thus, whether additional
mesoporosity can be introduced into nanoꢀsized TSꢀ1 particles
by desilication in alkaline media and in the presence of an
aqueous basic solutions of the structureꢀdirecting agent,
tetrapropylammonium cation (TPA+). Furthermore, the
influence of the desilication step on the properties of the
recrystallized materials was systematically studied. In addition,
the potential of the obtained materials for the heterogeneously
catalyzed liquidꢀphase epoxidation of rapseed methyl ester, i.e.
biodiesel, with aqueous H2O2 was investigated. In particular,
the catalytic properties of the materials resulting from the
D_NaOH,
D_NaOH/TPAOH,
and
D_NH3/TPAOH,
respectively.
For recrystallization, 1 g of the desilicated materials was mixed
under stirring with an aqueous solution 21 cm3 CTMAOH
(0.08 M) and 21 cm3 CTMABr (0.08 M). The CTMAOH
solution was prepared by ion exchange of 1 g CTMABr (99%,
2 | Green Chem., 2015, 00, 1-3
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Acros) dissolved in 42 cm3 deionized water with 10 g (V = 25 cm3) with a septum for sampling and a reflux
Ampersep (900 OH, Fluka) at room temperature for 15 h. The condenser with magnetic stirring (400 rpm) as described
resulting suspension was transferred to a polypropylene flask earlier 12. Biodiesel (FAME, methyl oleate: 72 wt.%, methyl
(Nalgene, V = 50 cm3) and held at 383 K for 24 h. Then, the linoleate + methyl linolenate: 19 wt.%, rest: not determined;
resulting solid was removed by filtration, washed five times JCN NeckermannꢀBiodiesel GmbH Halle) was used as
with 25 cm3 deionized water and once with 20 cm3 anhydrous substrate, hydrogen peroxide (35 wt.% aqueous solution,
ethanol (99%, BDH Prolabo), and dried in air at 363 K for 15 h. SolvayꢀWolfen) as oxidant, acetonitrile (99.9%, BDH Prolabo)
The obtained materials were calcined in air at 473 K for 2 h, at as a solvent and chlorobenzene (STD, 99.8%, Aldrich) as
673 K for 2 h and at 813 K for 15 h with a heating rate of internal standard. In a typical experiment, 10 cm3 solvent,
10 K minꢀ1 between each of the steps. Depending on the 90 mg (0.30 mmol) FAME, 70 mg (1.44 mmol) hydrogen
preceeding alkaline treatment, the recrystallized materials are peroxide and 67 mg (0.6 mmol) chlorobenzene were mixed.
labelled
as
R_DNaOH,
R_DNaOH/TPAOH,
and The reaction was started by addition of the catalyst (150 mg)
preꢀtreated in air at 373 K for 8 h. Samples taken periodically
R_DNH3/TPAOH, respectively.
An industrial sample of conventional titanium silicaliteꢀ1 from the reaction mixture were diluted in acetonitrile and
(TSꢀ1(ind.), powder) was supplied by Evonik Industries AG. analyzed by capillary gas chromatography (Shimadzu GC 2010
Finally, all catalysts were pressed, crushed and sieved to obtain equipped with a flame ionization detector).
the grain size fraction between 50 and 150 µm for use in the
catalytic experiments (cf. section 2.3).
The conversion in the epoxidation of biodiesel (FAME) was
calculated as the ratio of the mass of converted unsaturated
substrates, i.e., methyl oleate, methyl linolate and methyl
linolenate, and their initial mass in the reactant mixture. The
epoxide selectivity in FAME conversions is given as the
cumulative mass of all epoxides (monoꢀ, diꢀ and triꢀepoxides)
formed relative to the converted mass of the substrates. As a
measure for the catalyst efficiency, the FAME conversion was
divided by the molar amount of titanium atoms present in the
catalysts. The H2O2 conversion was calculated from the
concentration of H2O2 in the initial reactant solution and in the
product samples as determined by iodometric titration.
2.2 Characterization
The catalysts were characterized by powder Xꢀray diffraction
(XRD,
Siemens D 5000)
using
CuKαꢀradiation
(k = 0.15418 nm) in the 2θꢀrange of 1° and 80° with an angular
step size of 0.05°.
Nitrogen sorption isotherms were recorded at 77 K using an
ASAP 2000 (micromeritics) instrument. Samples were
degassed in vacuum at 573 K for 10 h prior to measurement.
The BrunauerꢀEmmettꢀTeller (BET) method was applied to
determine the total specific surface area (AS,BET) from the
adsorption branch of the isotherm in the relative pressure range
of p/p0 = 0.01ꢀ0.10. The total specific pore volume was
determined from the amount of nitrogen adsorbed at
p/p0 = 0.99. The specific micropore volume (Vmicro) and
mesopore volume (Vmeso) as well as the specific macroꢀ and
mesopore surface area summarized as external specific surface
area (Sext) were determined with the tꢀplot method according to
Lippens and de Boer 28. The mesopore width distribution was
calculated both from the adsorption and the desorption branch
of the nitrogen sorption isotherm using the Barret–Joyner–
Hallenda (BJH) model.
Diffuse reflectance UV–Vis (DRꢀUV–Vis) spectra were
recorded at room temperature on a Perkin Elmer Lambda 650 S
equipped with a 150 mm integrating sphere using spectralon®
(PTFE, reflective value 99%) as a reference.
The titanium content of the samples was determined by
elemental analysis via optical emission spectrometry with
inductively coupled plasma (ICPꢀOES) after dissolving the
solids in a mixture of HNO3, HF and H3BO3 by chemical
extraction under pressure.
The experimental accuracy was within ± 2% for the conversion of
FAME, ± 6% for the conversion of H2O2 and to ± 5% for the epoxide
selectivity, respectively.
3 Results and Discussion
3.1 Catalysts
3.1.1 Nanoꢀsized TSꢀ1 with stacked morphology
As shown in Fig. 1, the powder XRD patterns of all nanoꢀsized
TSꢀ1 materials exhibit reflections characteristic of the MFI
framework topology. The single reflection at 2Θ = 24.35°
indicates the change from monoclinic (silicalite) to the
orthorhombic unit cell symmetry (TSꢀ1). No significant
intensity is observed for the reflection at 2Θ = 25.40, which is
characteristic for crystalline titanium dioxide (TiO2) in the
anatase modification. Consequently, the presence of extra
29
framework TiO2 in the materials can be excluded
.
Interestingly, the Tiꢀcontent of the materials can be adjusted by
the irradiation time during microwaveꢀassisted synthesis and
increases with increasing irridiation time. Thus, TSꢀ1_ns10
possesses 0.45 wt.% Ti, TSꢀ1_ns20 0.52 wt.%, TSꢀ1_ns60
0.65 wt.% and TSꢀ1_ns70 0.90 wt.% Ti, respectively (cf.
Tab. 1). This implies that the Ti content is higher in the outer
shell of the TSꢀ1 crystallites with respect to the inner core.
SEM images of the nanoꢀsized TSꢀ1 catalysts (TSꢀ1_ns) from
microwaveꢀassisted synthesis for different irradiation times are
Scanning electron microscopy (SEM) images were taken at
15 kV on a FEI Company Nova NanoLab 200 microscope with
the samples sputtered with gold prior to measurement.
2.3 Catalytic Experiments
Catalytic experiments were carried out batchwise in the liquid
phase at 323 K in a twoꢀnecked roundꢀbottom glass flask
shown in Fig
.
2. All samples exhibits puckꢀlike crystals of
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irradiation times longer than 60 minutes. To gain direct
information about the nature and coordination of the Tiꢀspecies,
the preꢀdried materials were characterized by DRꢀUV–Vis
spectroscopy. For all TSꢀ1_ns catalysts from microwaveꢀ
assisted synthesis, a band with a maximum centered at 210 nm
is observed (Fig. 3). This band is characteristic of
a
O(2p)>Ti(3d) charge transfer transition, and is generally
assigned to isolated, tetrahedrally coordinated Ti(OSi)4 species
in hydrophobic zeolite frameworks 30. Nevertheless, TSꢀ1_ns
obtained after an irradiation time of 10 minutes shows a line
width at half maximum (LWHM) of ca. 60 nm indicating the
simultaneous presence of tetrahedral tripodal Ti(OSi)3OH
and/or loosely coordinated tetrapodal Ti(OSi)4 Ti species 30. By
increasing the irradiation time during microwaveꢀassisted
synthesis up to 60 minutes, the LWHM of the DRꢀUV–Vis
bands decreases, which leads to the conclusion that TS1_ns20
and TSꢀ1_ns60 possess less tetrahedral tripodal Ti(OSi)3OH
and loosely coordinated Ti(OSi)4 species than TSꢀ1_ns10.
TSꢀ1_ns70 exhibits also a broader LWHM than TSꢀ1_ns20 and
TSꢀ1_ns60, respectively. Obviously, the irradiation time during
submicrometer size and
a stacked morphology through
connection of the crystals on top of one another along their
[010] direction. As reported previously, this stacking is
sufficiently robust and a result of strong chemical bonds
between the crystals 13. In contrast to results reported by Jin et
al. 13, the stacked morphology observed here was already
obtained after an irradiation time of 10 minutes. The size of the
crystals noticeably increases with irradiation time up to 60
minutes during microwaveꢀassisted synthesis, whereas no
significant increase of the particle size is observed for
Tab. 1 Titanium content and textural properties of nanoꢀsized TSꢀ1_ns, desilicated (Dꢀseies) and recrystallized TSꢀ1 (R_Dꢀseries).
b
c
c
b
d
Vmicro
/
V3ꢀ10nm
/
V10ꢀ40nm
/
Amicro
/
AS,BET
m2gꢀ1
/
ωTi a/ wt.%
Aext b/ m2gꢀ1
cm3gꢀ1
0.17
0.18
0.17
0.20
0.13
0.11
0.12
0.13
0.18
0.14
cm3gꢀ1
n.d.
cm3gꢀ1
n.d.
m2gꢀ1
327
320
323
420
280
245
270
248
258
305
0.46
0.52
0.65
0.90
1.00
1.20
1.10
1.10
1.30
1.20
46
3
373
323
330
433
358
290
403
483
503
443
TSꢀ1_ns10
n.d.
n.d.
TSꢀ1_ns20
n.d.
n.d.
7
TSꢀ1_ns60
n.d.
n.d.
13
TSꢀ1_ns70
0.04
0.02
0.06
0.13
0.15
0.07
0.11
0.12
0.03
0.05
0.05
0.04
78
D_NH3/TPAOH
D_NaOH/TPAOH
D_NaOH
50
133
235
245
138
R_DNH3/TPAOH
R_DNaOH/TPAOH
R_DNaOH
b
afrom ICPꢀOES tꢀplotꢀ DeBoer c BJH d BET
n.d. not determined
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incorporation of Ti into the framework.
Lowꢀtemperature nitrogen sorption isotherms for the nanoꢀsized
TSꢀ1 catalysts are shown in Fig. 4. All samples exhibit a
reversible type
I
isotherm (according to the IUPAC
classification) with a steep rise at relative pressures p/p0 < 0.01,
confirming their microporous character, although having an
enhanced nitrogen uptake at higher relative pressures
p/p0 > 0.9. The uptake increases with increasing irradiation time
during microwaveꢀassisted synthesis and is most pronounced
for the material obtained after 70 minutes. The uptake
(p/p0 > 0.9) is uncommon for microcrystalline TSꢀ1 and can be
attributed to the stacked morphology (cf. SEMꢀimage, Fig. 2),
i.e., the existence of larger mesopores between the stacked
nanoꢀsized crystallites. Additionally,
a step in nitrogen
adsorption isotherm at p/p0 = 0.1ꢀ0.2 is observed. This can be
explained by the ”fluidꢀtoꢀcrystalline“ like phase transition of
the adsorbed phase inside the micropores 31. This step does not
indicate “real” porosity, but corresponds to a false peak in the
PSD with a maximum at aprox. 2 nm 31
.
3.1.2 Nanoꢀsized TSꢀ1 with microꢀ/mesoporosity from
desilication and recrystallization
In case of both the desilicated and recrystallized materials, the
XRD patterns show clear evidence of the presence of the MFI
structure (Fig. 5) However, in comparison to the parent
TSꢀ1_ns70, a significant reduction in the intensity of the
diffraction reflections is observed for all desilicated materials.
This can be explained by the attacking of SiꢀOꢀSi or SiꢀOꢀTi
bonds by the hydroxide anions of the alkaline solution causing
partial disrupture of the crystal framework and, thus, lower
longꢀrange order in the materials.
The recrystallized materials show
a relative degree of
crystallinity comparable to or even slightly higher than that of
the parent TSꢀ1_ns70 material. In agreement with the literature
25, this effect can be attributed to the recovery of zeolitic phase
due to the healing of defects within the framework during
recrystallization. Moroever, amorphous material generated
during desilication may have been dissolved25.
The smallꢀangle XRD patterns (not shown) point out the
absence of any structured mesoporous phase in the
recrystallized materials.
Elemental analysis (Tab. 1) of both the filtrate and the solids
confirm the preferential leaching of Si, leading to a slightly
increased Tiꢀcontent in the alkalineꢀtreated and recrystallized
materials. Note, however, that the Tiꢀcontents in the desilicated
and recrystallized materials are comparable.
Scanning electron microscopy of the desilicated materials show
that all materials possess an increased surface roughening due
to the introduction of additionally porosity as proven by results
from nitrogen sorption (cf. Tab. 1). The overall size of the
crystals as well as the stacked morphology are virtually not
affected by the alkaline treatment (Dꢀseries, Fig. 6). The crystal
size and morphology also remain unaffected after
recrystallization step (R_Dꢀseries, Fig. 6).
The TSꢀ1 samples obtained by alkaline treatment in the
presence of the structureꢀdirecting agent TPA+ exhibit debris
microwaveꢀassisted synthesis plays
a key role for the
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tetrapodal Ti(OSi)4 Tiꢀspecies in higher amounts than in the
30
with diameter of aprox. 50 nm on the external surface of the
crystallites (Fig. 6 B,C). TSꢀ1_ns70 treated with pure NaOH
did not show such deposition of debris (Fig. 6 D). This strongly
suggests that during the alkaline treatment silica is dissolved
from the framework, while in the presence of TPA+ a partial
restructuring of dissolved silica and deposition of debris occurs.
parent TSꢀ1_ns70
.
Moreover, the band spread is
characteristic of Tiꢀcontaining mesoporous silicas such as Tiꢀ
MCMꢀ41 and can be attributed to the simultaneously presence
of isolated Tiꢀatoms in tetra, pentaꢀ or hexahedral
coordination 32. For D_NaOH and R_DNaOH LWHM is much
broader than for the materials treated with TPAOH during
desilication. However, the absence of bands above 300 nm for
all materials suggests that nonꢀdesired extraꢀframework TiO2
phases related to the anatase structure are not present. This
observation is in good agreement with results from XRD (see
above).
A recrystallization of TSꢀ1 in the presence of TPA+ was
20
described by Wang et al.
conditions.
, although under different
For the desilicated materials, a broader band is observed in the
DRꢀUVꢀVis spectra between 200 and 300 nm with a maximum
centered at ca. 220 nm (Fig. 7). Compared to the parent
TSꢀ1_ns70, which possesses a line width at half maximum
(LWHM) of approximately 40 nm, the band width increases
and the maximum shifts to higher wavelengths. After
recrystallization, the position of the band maximum (around
220 nm) remains practically unchanged, while the LWHM
slightly increases with respect to the desilicated materials. The
red shift of the maximum to 220 nm in both the desilicated and
the recrystallized materials suggests the simultaneous presence
of tetrahedral tripodal Ti(OSi)3OH and loosely coordinated
Alkaline treatment of TSꢀ1_ns70 leads to nitrogen sorption
isotherms representing combined type I and type II behavior. A
remarkably enhanced uptake of nitrogen occurs at higher
relative pressures of p/p0 = 0.85, which is more pronounced for
the materials treated in the presence of TPAOH (Fig. 8, B/C).
While the material treated with pure NaOH shows only a
slightly pronounced hysteresis, the presence of TPAOH during
desilication results in the development of a distinct H2 type
hysteresis loop. The forced closure of the hysteresis loop for
both D_NH3/TPAOH and D_NaOH/TPAOH is due to a sudden
drop in the volume adsorbed along the desorption branch in the
range of p/p0 = 0.41ꢀ0.50. This phenomenon is often referred to
as the “Tensile Strength Effect” (TSE) 31. Furthermore, the
shape of the nitrogen adsorptionꢀisotherm with the steep closing
of the hysteresis loop is typical for mesoporous systems with
pore openings considerably smaller than diameter of the inner
pores, e.g., for inkꢀbottle shaped pores or partially constricted
interconnected porous systems. For such a pore geometry, the
cavitation mechanism of emptying the mesopores leads to
sudden release of the adsorbate when its partial pressure is
below a certain critical value 31, 33
.
In case of the occurrence of TSE phenomena, the application of
the BJH model to the desorption branch of the isotherm leads to
a completely different result compared to that obtained from the
adsorption branch, which is hardly affected by TSE (cf. ESI,
Fig. S1). The pore size distribution (PSD) obtained from
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state, the corresponding poreꢀdiameter distributions are also not
quite reliable 33
.
Upon recrystallization of the desilicated TSꢀ1 materials
(Dꢀseries) in the presence of the surfactant cation CTA+, the
shape of the nitrogen adsorption isotherms in the recrystallized
materials (R_Dꢀseries) is unchanged and also displays a
combined type I and type II behavior (Fig. 8). In contrast to
desilicated materials, however, the enhanced nitrogen uptake in
the relative pressures range of p/p0 = 0.3ꢀ0.8 is more
pronounced and indicates the presence of smaller mesopores
(3ꢀ10 nm) after recrystallization. This finding is in good
agreement with the substantially enhanced contribution of the
mesopore volume in the range of 3ꢀ10 nm (Tab. 1). Moreover,
the hysteresis loops of the recrystallized TSꢀ1 materials are less
pronounced than that of the desilicated materials and can be
assigned to a combined H2 and H4 type.
Values of the specific BET surface area as well as the microꢀ
and mesopore volume determined with the tꢀplotꢀDeBoer
method 28, 34 are summarized in Tab. 1. It must be kept in mind
that the specific surface area calculated by the BETꢀmodel is
not valid for materials, which contain a substantial amount of
microporosity, and hence can only be regarded as a BETꢀ
equivalent surface area for comparative purposes 35, 36
.
The parent TSꢀ1_ns70 possesses a specific BET surface area of
433 m2 gꢀ1 which is in excellent agreement with values
previously reported for nanoꢀsized TSꢀ1 with stacked
13
morphology (AS,BET = 398 m2 gꢀ1)
.
Furthermore, 13 m2 gꢀ1 is
contributed by the external surface area from tꢀplot analysis,
i.e., surface area from the true external crystal surfaces and
from internal voids larger than micropores due to the stacked
morphology.
Upon alkaline treatment of the parent TSꢀ1_ns70 in the
presence of TPA+, a significantly increased amount of
mesoporosity with diameters of 10ꢀ40 nm is developed, i.e.,
V10ꢀ40nm = 0.11 cm3 gꢀ1
for
D_NH3/TPAOH
and
V10ꢀ40nm = 0.12 cm3 gꢀ1 for D_NaOH/TPAOH, respectively. The
mesopore formation by selective silicon removal is
accompanied by a reduction of the micropore volume of aprox.
45% with respect to the parent TSꢀ1_ns70 (Tab. 1).
Surprisingly, while no substantial mesopore formation is
observed for the material from treatment with aqueous NaOH
solution
only
(D_NaOH,
V3ꢀ10nm = 0.06 cm3 gꢀ1,
V10ꢀ40nm = 0.03 cm3 gꢀ1), the external surface area on this
material is highest (Aext = 133 m2 gꢀ1) among all deslicated
samples. The absence of a pronounced hysteresis loop in the
nitrogen sorption isotherm of this material supports that the
relatively high value of Aext is due to contributions of
intercrystalline rather than to intracrystalline mesoporosity. In
contrast, the specific BET surface area is strongly decreases for
nitrogen desorption isotherms are dominated by narrow peaks
with maxima at about 3.9 nm, respectively, while this peak is
absent in the PSD calculated from the adsorption branches.
Therefore, the analysis of nitrogen adsorption isotherms is
recommended 31. Taking into account the BJHꢀPSD from
adsorption branches of nitrogen isotherms of desilicated TSꢀ1
catalysts, the presence of undefined mesopores and a broad
poreꢀdiameter distribution in the range of 10ꢀ40 nm is
D_NH3/TPAOH
(358 m2 gꢀ1)
and
D_NaOH/TPAOH
(295 m2 gꢀ1) with respect to the parent TSꢀ1_ns70, which can be
directly attributed to the high contribution of mesopore volume
in the range of 10ꢀ40 nm.
confirmed. It should be noted, however
adsorption isotherms correspond to the metastable adsorption
, that, since the
The recrystallized materials exhibit specific BET surface areas
of 483 m2 gꢀ1 for R_DNH3/TPAOH and 503 m2 gꢀ1 for
R_DNaOH/TPAOH, i.e., 130 and 200 m2 gꢀ1 higher than that of
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specific mesopore volume in the diameter range of 3ꢀ10 nm
(V3ꢀ10nm = 0.13/0.15 cm3 gꢀ1 vs 0.04/0.02 cm3 gꢀ1, Tab. 1) and
provide proof of the surfactantꢀassisted recrystallization as
.
24
described by GarciaꢀMartinez et al.
for zeolite Y. These
authors suppose that the surfactant cations form micelles within
the zeolite crystals and cause a structural rearrangement to
generate uniform mesopores around the micelles. Accordingly,
a scheme for the introduction of controlled mesoporosity into
crystalline microporous materials through a surfactantꢀassisted
crystal rearrangement mechanism for TSꢀ1 is proposed in
Fig. 9.
3.2 Epoxidation of Biodiesel with H2O2
In order to minimize acidꢀcatalyzed secondary products,
acetonitrile was chosen as the solvent for the conversion of
biodiesel (FAME) with H2O2 over the TSꢀ1ꢀbased catalysts.
Because of its slightly basic nature, it was shown before that it
supports the formation of epoxides and hinders the formation of
undesired sideꢀproducts 12. In Fig. 10, the reaction scheme for
the epoxidation of methyloleate, i.e., the major compound in
biodiesel, with H2O2 in acetonitrile over TSꢀ1 is shown.
Besides the major product methyl 9,10ꢀepoxy stearate (typically
with a selectivity of S > 80%), several sideꢀproducts are
formed, predominantly in consecutive reactions (Fig. 10). The
product from acidꢀcatalyzed hydrolysis, methyl 9,10ꢀdihydroxy
stearate, and the products from oxidative cleavage of the
epoxide are present in about equal amounts. Ketones derived
from rearrangement are formed in negligible amounts only
the starting material from desilication. More remarkably,
235 m2 gꢀ1
(R_DNH3/TPAOH)
and
245 m2 gꢀ1
(R_DNaOH/TPAOH) are from the external surface for the
recrystallized materials, respectively. These values are about
three and five times higher than that of the respective TSꢀ1
from desilication. They can be directly related to the increased
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(S < 1%). The amount of detected cleavage products increases microwaveꢀirradiation time 13. More FAME molecules are
with reaction time. However, the exact amount of the sideꢀ adsorbed on the more hydrophobic surface, so that the
products was not further quantified.
concentration of adsorbed reactants in close proximity of the
Recently, it was reported for the epoxidation of methyloleate active Ti sites is higher leading to a higher catalytic activity per
with H2O2 in acetonitrile at 358 K that the epoxide formation Ti site. This explanation is supported by the observations from
37
can occur through an uncatalyzed Payneꢀtype oxidation
.
DRꢀUV–Vis spectroscopy from which we conclude that
higher density of
absence of a catalyst (Vacetonitrile = 10 cm3, cFAME = 0.03 mol lꢀ1, Ti(SiO3)OHꢀspecies on the surface (cf. Fig. 7) . Note also that
nH O T = 323 K), significant the Ti content on the outer shell of the nanoꢀsized TSꢀ1
2 nFAME) = 5 mol molꢀ1,
contribution of uncatalyzed oxidation pathways can be catalysts increases with increasing particle size (cf. section 3.1,
Since, however, no FAME conversion was observed in the TSꢀ1_ns10 and TSꢀ1_ns70 have
a
(
/
a
2
excluded under the conditions applied in the present study.
Tab. 1) leading to a higher density of accessible active Ti sites.
The epoxide selectivity (SeFAME) follows a similar trend. It
increases from 42% (TSꢀ1_ns10) to 68% (TSꢀ1_ns20), 77%
(TSꢀ1_ns60).
3.2.1 Conversion over nanoꢀsized TSꢀ1 with stacked
morphology
Fig. 11 shows the results of the epoxidation of FAME with
H2O2 over nanoꢀsized TSꢀ1 with different crystallite sizes. By
increasing the irradiation time during microwaveꢀassisted
synthesis, the activity of the nanoꢀsized TSꢀ1 catalysts for the
epoxidation increases (see Fig. 2). While over the catalyst
obtained after 10 minutes irradiation time (TSꢀ1_ns10) a
catalyst efficiency, i.e., FAME conversion relative to the
number of Ti atoms present in the catalyst, of 0.8 % µmolꢀ1 is
achieved, the catalyst efficiency increases with particles size
and amounts to 1.18 % µmolꢀ1 and 1.20 % µmolꢀ1 for
TSꢀ1_ns20 and TSꢀ1_ns60, respectively. Interestingly,
TSꢀ1_ns70 is less active and the catalyst efficiency is close to
that of TSꢀ1_ns10. Previously, it was reported that the
formation of the stacked morphology through condensation of
hydroxyl groups on the crystal surface is accompanied by an
increase of the surface hydrophobicity with increasing
While the eFAME selectivity increases for the catalyst from the
longest microwaveꢀirradiation (TSꢀ1_ns70), its catalytic
efficiency is lower than the other catalysts with stacked
morphology. This might be due to either a too high density of
active Ti sites on the surface which cannot be fully utilized by
the adsorbed large FAME molecules or a hindrance of access to
the active Ti sites as a result of closer stacking of the TSꢀ1
crystallites. Interestingly, both catalyst efficiency and eFAME
selectivity of TSꢀ1_ns70 are comparable to those for the
conventional industrial catalyst TSꢀ1 (ind.). Thus, TSꢀ1_ns70
was chosen as parent material for the postꢀsynthetic
modification for the introduction of mesoporosity.
3.2.2 Conversion over nanoꢀsized TSꢀ1 with microꢀ
/mesoporosity
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As shown above, the selective desilication of framework Si shaped or the partially constricted interconnected pores as
leads to the introduction of mesopores (cf. Section 2.1). It has present in D_NaOH/TPAOH and D_NH3/TPAOH are
previously been reported that mesopores are highly beneficial responsible for the lower catalytic activity rather than a slightly
for improving the efficiency for phenol hydroxylation over higher hydrophilicity. These textural properties of the catalysts
alkaline treated TSꢀ1 catalysts23. However, over the desilicated desilicated in the presence of TPAOH may hinder access to the
TSꢀ1 catalysts prepared in the present study, the catalyst active Ti sites when compared to the catalysts from desilication
efficiency for biodiesel conversion was less than 0.40 % µmolꢀ1 with NaOH only.
and, thus, significantly lower compared to the parent Recrystallization of the desilicated materials results in a
microporous TSꢀ1_ns70 (0.87 % µmolꢀ1) (Fig. 13). Likewise, significantly higher catalytic activity with respect to desilicated
the epoxide selectivity is up to 20 % lower than that for and the parent TSꢀ1_ns70 materials (Fig. 13). Over the
TSꢀ1_ns70. This lower epoxide selectivity is mainly due to the recrystallized catalysts, the values for the catalyst efficiency of
formation of diols resulting from acidꢀcatalyzed hydrolysis of 1.29 % µmolꢀ1
(R_DNH3/TPAOH),
1.05 % µmolꢀ1
the epoxide (cf. Fig. 10). The generation of larger mesopores by (R_DNaOH/TPAOH) and 1.58 % µmolꢀ1 (R_DNaOH) are three
desilication is accompanied by a considerable development of to four times higher than those of the parent analogues before
external surface area and a partial damage of the framework of recrystallization. Also the epoxide selectivity is as high as for
the crystals. This generates hydroxyl groups (Fig. 12) and the initial catalyst (TSꢀ1_ns70) before any modification. In
increases the hydrophilicity of the catalyst surface. A similar
14
observation was reported by Cheneviere et al. and Sanz et al.
38
who successfully prepared hierarchically structured TSꢀ1 in
the presence of amphiphilic organosilanes. In both studies, it
was found that the hierarchical TSꢀ1 exhibits a lower activity
than purely microporous TSꢀ1 in the epoxidation of olefins
when H2O2 is used as the oxidant. This was explained by the
hydrophilic nature of the hierarchically structured materials as a
result of a high surface hydroxyl groups density associated to
the secondary porosity. The beneficial effect of surface
hydrophobicity on the activity, selectivity and lifetime of TSꢀ1ꢀ
based catalysts for the epoxidation of alkenes with aqueous
39
H2O2 solution was proven in several studies (see
review).
for a
Comparing the desilicated TSꢀ1 materials and taking into
account that the catalyst desilicated by only NaOH (D_NaOH)
is more hydrophilic than those obtained by alkaline treatment in
the presence of TPA cation, one can conclude that the inkꢀbottle
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particular, the catalysts from recrystallization after desilication significantly contribute to further improve the catalytic activity,
with NaOH (R_DNaOH) show the highest catalyst efficiency selectivity and stability of TSꢀ1ꢀbased catalysts for alkene
with an approx. two times higher conversion per number of Tiꢀ epoxidation.
sites than the parent TSꢀ1_ns70. Note also that the activity of
the other two catalysts obtained after recrystallization relative
to R_DNaOH is the same as after desilication, i.e., the catalytic
efficiency of R_DNH3/TPAOH is higher than that of
R_DNaOH/TPAOH.
5 Acknowledgements
The authors are grateful to Prof. Dr. W.ꢀD. Einicke, Institute of
Chemical Technology, Universität Leipzig, for his assistance
with measuring the nitrogen sorption isotherms. Thanks are
also due to Dipl.ꢀPhys. Jörg Lenzner, Institute of Experimental
Physics II, Universität Leipzig, for conducting the SEM
investigations.
Evidently, the active Ti sites in the recrystallized TSꢀ1 catalysts
(R_Dꢀseries) are more readily accessible for the reactant
molecules with respect to the alkalineꢀtreated ones. This can be
attributed to a more uniform distribution of mesopores observed
in the recrystallized materials. Such mesopores would also
facilitate removal of epoxide molecules from the catalyst
surface before undergoing consecutive reactions to undesired
sideꢀproducts. This is in accordance with the higher epoxide
selectivity observed for the recrystallized compared to the
desilicated materials. In addition, the recrystallization probably
leads to a healing of defects, e.g., a condensation of silanol
groups on the catalyst surface generated during the alkaline
treatment. This, then, results in an increased hydrophobic
character of the catalyst surface (Fig. 12). Support for this
conclusion is supplied by XRD results which confirms that
recrystallized materials possess a higher degree of crystallinity
than the desilicated ones and the parent TSꢀ1_ns70.
6 Notes and references
Institute of Chemical Technology, Universität Leipzig, Linnéstr. 03,
04103 Leipzig, Germany. Eꢀmail: roger.glaeser@uniꢀleipzig.de;
Tel.:+49 341 9736300
Electronic Supplementary Information (ESI) available: Figures for the
BJHꢀPSD (Fig. S1) and conversion of biodiesel, epoxide selectivity and
conversion of hydrogen peroxide as a function of reaction time (Fig.S2ꢀ
S4). See DOI: 10.1039/b000000x/
1. U. Biermann, U. Bornscheuer, M. A. R. Meier, J. O. Metzger and H.
J. Schafer, Angew. Chem., Int. Ed., 2011, 50, 3854ꢀ3871.
2. U. Biermann, W. Friedt, S. Lang, W. Luhs, G. Machmuller, J. O.
Metzger, M. R. Klaas, H. J. Schafer and M. P. Schneider, Angew.
Chem., Int. Ed., 2000, 39, 2206ꢀ2224.
4 Conclusions
3. F. D. Gunstone and F. B. Padley, in Epoxidiesed oils ed. F. D.
Gunstone, Marcel Dekker, New York, 1997, p. 759.
In order to improve the accessibility of Ti sites in TSꢀ1
catalysts, nanoꢀsized TSꢀ1 catalysts with stacked morphology
and different particle sizes were prepared by microwaveꢀ
assisted synthesis. By increasing the microwave irradiation time
of the synthesis gel up to 60 minutes, the activity of the TSꢀ1
catalysts for the epoxidation of biodiesel with H2O2 was
enhanced. Furthermore, nanoꢀsized TSꢀ1 exhibits a catalytic
activity per Ti site up to 30% higher than a conventional
TSꢀ1(ind.) catalyst. By applying a twoꢀstep desilicationꢀ
recrystallization treatment, mesoprosity was successfully
incorporated into the nanoꢀsized TSꢀ1 catalysts.
4. A. Campanella, E. Rustoy, A. Baldessari and M. A. Baltanas, Biores.
Technol., 2010, 101, 245ꢀ254.
5. R. D. Kulkarni, P. S. Deshpande, S. U. Mahajan and P. P. Mahulikar,
Ind. Crops Prod., 2013, 49, 586ꢀ592.
6. Z. S. Petrovic, L. T. Yang, A. Zlatanic, W. Zhang and I. Javni, J.
Appl. Polym. Sci., 2007, 105, 2717ꢀ2727.
7. E. Del Rio, M. Galia, V. Cadiz, G. Lligadas and J. C. Ronda, J.
Polym. Sci., A, 2010, 48, 4995ꢀ5008.
8. M. Guidotti, N. Ravasio, R. Psaro, E. Gianotti, L. Marchese and S.
Coluccia, Green Chem., 2003, 5, 421ꢀ424.
Irregularly shaped mesopores in the range of 10ꢀ40 nm with
reduced accessibility incorporated by desilication have a
negative impact on the catalytic activity. Thus, over the
desilicated catalysts, the catalytic activity per active Ti site and
epoxide selectivity were strongly reduced compared to the
purely microporous TSꢀ1. More uniform mesopores as present
in the recrystallized TSꢀ1 materials are most beneficial for the
catalytic activity. Thus, the catalytic activity per active Ti site is
up to two times higher with respect to the initial untreated TSꢀ1
and the epoxide selectivity reaches 82%.
9. M. A. Camblor, A. Corma, P. Esteve, A. Martinez and S. Valencia,
Chem. Commun., 1997, 795ꢀ796.
10. M. Guidotti, R. Psaro, N. Ravasio, M. Sgobba, E. Gianotti and S.
Grinberg, Catal. Lett., 2008, 122, 53ꢀ56.
11. M. Guidotti, N. Ravasio, R. Psaro, E. Gianotti, S. Coluccia and L.
Marchese, J. Mol. Catal. A: Chem., 2006, 250, 218ꢀ225.
12. N. Wilde, C. Worch, W. Suprun and R. Glaser, Microporous
Mesoporous Mater., 2012, 164, 182ꢀ189.
13. H. L. Jin, N. Z. Jiang, S. M. Oh and S. E. Park, Top. Catal., 2009, 52
,
169ꢀ177.
In addition to a balanced degree of microꢀ and mesoporosity as
well as a uniform shape and accessibility of larger pores, the
hydrophobic/hydrophilic surface properties of the catalysts
have to be considered. The quantitative assessment of the
surface hydrophobicity and its relationship to hierarchical
porosity and catalytic performance are attractive goals for
future research. The clarification of these relations may
14. Y. Cheneviere, F. Chieux, V. Caps and A. Tuel, J. Catal., 2010, 269
,
161ꢀ168.
15. D. Serrano, R. Sanz, P. Pizarro and I. Moreno, Chem. Commun.
,
2009, 1407ꢀ1409.
16. Y. C. Zou, S. G. Wei and X. J. Qu, Chem. J. Chin. Uni.-Chin., 2008,
29, 1926ꢀ1929.
This journal is © The Royal Society of Chemistry 2015
Green Chem., 2015, 00, 1-3 | 11

Green Chemistry
Page 12 of 12
View Article Online
ARTICLE
Green Chemistry
DOI: 10.1039/C5GC00406C
17. Q. Zhao, P. Li, D. Q. Li, X. G. Zhou, W. K. Yuan and X. J. Hu,
Microporous Mesoporous Mater., 2008, 108, 311ꢀ317.
18. P. Birke, P. Kraak, R. Pester, R. Schodel and F. Vogt, Zeolites
Microporous Crystals, 1994, 83, 425ꢀ432.
19. Y. M. Fang and H. Q. Hu, Catal. Commun., 2007, 8, 817ꢀ820.
20. Y. R. Wang, M. Lin and A. Tuel, Microporous Mesoporous Mater.
2007, 102, 80ꢀ85.
,
21. S. T. Tsai, P. Y. Chao, T. C. Tsai, I. K. Wang, X. X. Liu and X. W.
Guo, Catal. Today, 2009, 148, 174ꢀ178.
22. A. SilvestreꢀAlbero, A. GrauꢀAtienza, E. Serrano, J. GarciaꢀMartinez
and J. SilvestreꢀAlbero, Catal. Commun., 2014, 44, 35ꢀ39.
23. P. Y. Chao, S. T. Tsai, T. C. Tsai, J. B. Mao and X. W. Guo, Top.
Catal., 2009, 52, 185ꢀ192.
24. J. GarciaꢀMartinez, M. Johnson, J. Valla, K. H. Li and J. Y. Ying,
Catal. Sci.Technol., 2012, 2, 987ꢀ994.
25. I. I. Ivanova and E. E. Knyazeva, Chem. Soc. Rev., 2013.
26. Y. Zhu, Z. L. Hua, X. X. Zhou, Y. D. Song, Y. Gong, J. Zhou, J. J.
Zhao and J. L. Shi, RSC Adv., 2013, 3, 4193ꢀ4198.
27. Y. Zuo, W. C. Song, C. Y. Dai, Y. P. He, M. L. Wang, X. S. Wang
and X. W. Guo, Appl. Catal., A, 2013, 453, 272ꢀ279.
28. J. H. Deboer, B. C. Lippens, B. G. Linsen, Broekhof.Jc, Vandenhe.A
and T. J. Osinga, J. Colloid Interface Sci., 1966, 21, 405ꢀ&.
29. Y. G. Li, Y. M. Lee and J. F. Porter, J. Mater. Sci., 2002, 37, 1959ꢀ
1965.
30. P. Ratnasamy, D. Srinivas and H. Knozinger, Adv. Catal., 2004, 48
,
1ꢀ169.
31. J. C. Groen, L. A. A. Peffer and J. PerezꢀRamirez, Microporous
Mesoporous Mater., 2003, 60, 1ꢀ17.
32. S. Gontier and A. Tuel, Zeolites, 1995, 15, 601ꢀ610.
33. M. Thommes, Chem. Ing. Tech., 2010, 82, 1059ꢀ1073.
34. P. Voogd, J. J. F. Scholten and H. Vanbekkum, Colloids Surf., 1991,
55, 163ꢀ171.
35. M. Thommes, B. Smarsly, M. Groenewolt, P. I. Ravikovitch and A.
V. Neimark, Langmuir, 2006, 22, 756ꢀ764.
36. K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A.
Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl. Chem.
,
1985, 57, 603ꢀ619.
37. M. Guidotti, E. Gavrilova, A. Galarneau, B. Coq, R. Psaroa and N.
Ravasio, Green Chem., 2011, 13, 1806ꢀ1811.
38. R. Sanz, D. P. Serrano, P. Pizarro and I. Moreno, Chem. Eng. J.
,
2011, 171, 1428ꢀ1438.
39. R. Gläser and J. Weitkamp, in Handbook of Porous Solids, eds. F.
Schüth, K. S. W. Sing and J. Weitkamp, WileyꢀVCH, Weinheim
2002, pp. 395ꢀ431.
40. H. van Koningsveld, J. C. Jansen and H. van Bekkum, Zeolites, 1990,
10, 235ꢀ242.
12 | Green Chem., 2015, 00, 1-3
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