High-silica nanocrystalline Beta zeolites: Efficient synthesis and catalytic application

Article abstract of DOI:10.1039/c5sc03019f

An efficient synthesis methodology to obtain homogeneous nanosized high-silica Beta zeolites (～10-20 nm) with high solid yields (above 95%) using simple alkyl-substituted flexible dicationic OSDAs is described. These dicationic OSDAs allow the synthesis o

Full text of DOI:10.1039/c5sc03019f

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High-silica nanocrystalline Beta zeolites: efficient synthesis and
catalytic application
Received 00th January 20xx,
Accepted 00th January 20xx
Raquel Martínez-Franco, Cecilia Paris, Marta E. Martínez-Armero, Cristina Martínez, Manuel
Moliner,* Avelino Corma*
DOI: 10.1039/x0xx00000x
An efficient synthesis methodology to obtain homogeneous nanosized high-silica Beta zeolites (~10-20 nm) with high solid
yields (above 95%) using simple alkyl-substituted flexible dicationic OSDAs is described. These dicationic OSDAs allow
synthesizing nanosized Beta zeolites with different Si/Al ratios (15-30) under alkaline and fluoride media, resulting in
nanocrystalline materials with different physico-chemical properties. These nanosized Beta zeolites show better catalytic
behavior for the industrially-relevant alkylation of benzene with propylene to obtain cumene than other commercially
available nanosized Beta zeolites.
www.rsc.org/
ratios (from 6 to 50), but with a low solid yield (~50%) for
samples synthesized with Si/Al ratios above 10.8 Similar results
have been described by other authors using TEAOH as OSDA
1.- Introduction
The synthesis of nanosized zeolites has received significant
attention in the last years, since the reduction of the
crystalline particle size to the nanometer scale (below 100 nm)
not only provides improved properties for traditional catalytic
applications, but also allows expanding their use to other
emerging applications, such as nanomedicine, optoelectronics,
or chemical sensing.1
under related hydrothermal synthesis conditions.9 The
synthesis of mesoporous high-silica Beta zeolites (Si/Al ~8-30)
formed by the assembly of uniform nanocrystals (20-100 nm)
with high solid yields (~80-90%) has also been described using
TEAOH as OSDA following steam-assisted conversion (SAC)
procedures.10 However, SAC methodologies are difficult to be
scaled-up for industrial applications. Recently, high-silica
Beta is an industrially relevant zeolite with catalytic
applications in petrochemistry,2 fine chemistry,3 biomass-
transformations,4 and environmental chemistry.5 This broad
applicability can be explained by the combination of a very
open crystalline structure, formed by three-directional
interconnected large pores,6 and the ability to be synthesized
under very broad chemical compositions.6,7
nanocrystalline
Beta
zeolites
with
intercrystalline
mesoporosity has been described with good solid yields
through hydrothermal synthesis methods,11 but they require
the use of rigid and bulky organic compounds containing
phenyl or biphenyl groups, such as 4,4’-trimethylenebis(N-
methyl,N-benzyl-piperidinium),11a
or
3,10-
diazoniabicyclo[10.2.2]hexadeca-12,14,15-triene-3,3,10,10-
tetramethyl-dichloride,11b,c and cationic polymers, such as
polydiallyldimethylammonium chloride.11d Therefore, the
efficient synthesis of high-silica nanocrystalline Beta zeolites
with high-solid yields using simple OSDAs is still a challenging
and relevant issue.
The synthesis of nanocrystals of Beta zeolite presenting large
external surface area and low diffusion path lengths is
particularly interesting to improve the accessibility of reactants
to the catalytic active sites.1 In this sense, nanocrystalline high-
silica Beta zeolites with particle sizes below 100 nm have been
described in the literature following different synthesis
procedures. The first nanocrystalline high-silica Beta with
crystal sizes in the 10 to 100 nm range was prepared by
hydrothermal synthesis using tetraethylammonium hydroxide
(TEAOH) as organic structure directing agent (OSDA) in the
absence of alkali metal cations.8 This methodology allows the
synthesis of nanocrystalline Beta zeolites with different Si/Al
Here, we present an efficient synthesis procedure that allows
obtaining nanosized high-silica Beta zeolites (~10-20 nm) with
solid yields above 95%, with simple alkyl-substituted flexible
dicationic OSDAs (see Figure 1) under hydrothermal synthesis
conditions. Then, nanosized Beta zeolites with different Si/Al
ratios (15-30) could be obtained with dicationic OSDAs under
alkaline and fluoride media, and materials with different
physico-chemical properties have been obtained. The catalytic
behavior of the different nanosized Beta zeolites has been
evaluated for an industrially-relevant chemical process such as
the alkylation of benzene with propylene to obtain cumene,
revealing significant improved catalytic activities compared to
commercially available nanocrystalline Beta zeolites.
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filtered to separate the inorganic salt. Finally, after elimination
of solvent and purification, 1-butylazepane was obtained as
transparent oil with 77.4 % yield.
N
N
OSDA-C4
OSDA-C6
Synthesis of 1,1'-(pentane-1,5-diyl)bis(1-butylazepan-1-ium)
bromide (OSDA-C6). The 1-butylazepane (22.36 g, 0.144 moles)
obtained in the previous step was introduced in a two-neck
round flask equipped with a glass condenser. 400 ml of
anhydrous DMF was added to the flask under an argon flow.
Then, 1.5-dibromopentane (16.56 g, 0.072 moles) was
gradually added under vigorous stirring. After the addition was
finished, the mixture was allowed to react overnight at 70ºC. A
white precipitate was formed, when the reaction mixture was
cool down to room temperature. The solid was isolated from
the crude by filtration at reduced pressure, washed twice with
ethyl acetate to eliminate DMF and, then, dried. Finally,
OSDA-C6 was obtained as a white solid after recrystallization
with of 2-propanol/ethyl acetate solution.
N
N
Fig. 1 Organic structure directing agents used for the synthesis of nanosized Beta
zeolites.
2.- Experimental section
2.1.- OSDA syntheses
Synthesis of the 1,1'-(pentane-1,5-diyl)bis(1-butylpyrrolidin-1-
ium) [OSDA-C4]
For its use in the synthesis of zeolites, the final product was ion
exchanged to the hydroxide form using a commercially
available hydroxide ion exchange resin (Dowex SBR).
In a two-neck round flask previously dried at 110ºC and
equipped with a glass condenser, 1-butylpyrrolidine (38.17 g,
0.30 moles) was introduced and dissolved with 200 ml of
anhydrous N,N-dimethylformamide (DMF). Then, 1,5-
dibromopentane (22.99 g, 0.10 moles) was gradually added
under vigorous stirring and at argon atmosphere. The reaction
mixture was allowed to react at 90ºC overnight. Once the
reaction was finished the crude, the product formed was
decanted and separated from the reaction crude by filtration
at reduced pressure. The product was washed twice with ethyl
acetate and once with diethyl ether to eliminate rests of DMF.
Finally, the OSDA-C4 was obtained as a white solid after
recrystallization with a mixture of 2-propanol/ethyl acetate
with an 82.1% yield.
2.2.- Zeolite syntheses
In a typical synthesis, aluminum hydroxide [Al(OH)3, Sigma-
Aldrich] was dissolved in an aqueous solution of the OSDA in
its hydroxide form. Colloidal silica (Ludox AS-40, Aldrich) was
then added, and the mixture maintained under stirring for 20
minutes. If required, a 10%wt solution of NH4F (Sigma-Aldrich)
was added, and the resultant mixture gel was allowed to reach
the desired silica to water ratio by evaporation under stirring.
The final gel compositions were:
SiO2 : 0.0167-0.033 Al2O3 : 0.2-0.4 OSDA(OH)2 : 0-0.4 NH4F :
3-30 H2O
For its use in the synthesis of zeolites, the final product was ion
exchanged to the hydroxide form using a commercially
available hydroxide ion exchange resin (Dowex SBR).
where OSDA can be one of the dicationic molecules described
above.
Finally, the gels were transferred to Teflon lined stainless
autoclaves and heated at 150ºC for 10 days. The solids were
recovered by filtration, extensively washed with distilled
water, and dried at 90ºC overnight. The samples have calcined
in air at 550ºC for 4 hours. The resultant solid yields have been
calculated based on silica+alumina conversion.
Synthesis of the 1,1'-(pentane-1,5-diyl)bis(1-butylazepan-1-
ium) [OSDA-C6]
Synthesis of 1-butylazepan-1-ium bromide. In a two-neck
round flask connected with a glass condenser, 22 g of
hexamethyleneimine (0.222 moles) was dissolved with 100 ml
of anhydrous acetonitrile. Under vigorous magnetic stirring
and argon atmosphere, 30.40 g of 1-bromobutane (0.222
moles) was added dropwise over one hour-time. After the
addition finished, the mixture was heated at 70 ºC and left for
reaction during 8 hours. The molten salt was separated from
the solution by filtration under reduced pressure and washed
with ethyl acetate. The 1-butylazepan-1-ium bromide was
obtained as a crystalline white solid with an 85.3% yield.
Synthesis of 1-butylazepane. Equimolar quantities of 1-
butylazepan-1-ium bromide and sodium carbonate (0.187
moles), were introduced in a one-neck round flask and
dissolved with distilled water. The resulting mixture was left
for reaction during one hour at room temperature under
magnetic stirring. A pale oily product was formed at the
bottom of the flask. The organic phase was decanted and
separated from the aqueous solution. The organic phase was
dried with anhydrous magnesium sulphate salt, and then,
2.3.- Characterization
Powder X-ray diffraction (PXRD) measurements were
performed with a multisample Philips X’Pert diffractometer
equipped with a graphite monochromator, operating at 45 kV
and 40 mA, and using Cu Kα radiation (λ = 0,1542 nm).
The chemical analyses were carried out in a Varian 715-ES ICP-
Optical Emission spectrometer, after solid dissolution in
HNO3/HCl/HF aqueous solution.
The morphology of the samples was studied by field emission
scanning electron microscopy (FESEM) using a ZEISS Ultra-55
microscope and by field emission transmission electron
microscopy (TEM) using a JEM 2100F microscope.
Textural properties were obtained from the N2 adsorption-
desorption isotherms measured at 77 K with a Micromeritics
ASAP 2020 apparatus.
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Solid NMR spectra were recorded at room temperature with a Table 1 Chemical analyses of the as-prepared nanosized Beta zeolites.
Bruker AV 400 MAS spectrometer. 27Al MAS NMR spectra were
recorded at 104.2 MHz with a spinning rate of 10 kHz and 9o
pulse length of 0.5 μs with a 1 s repetition time. 27Al chemical
shift was referred to Al3+(H2O)6.
Sample
Beta-15-OH
Beta-30-OH
Beta-15-F
Beta-30-F
CP811
Si/Al
15.3
30.6
16.0
29.8
13.0
Infrared spectra were measured with a Nicolet 710 FT IR
spectrometer. Pyridine adsorption-desorption experiments
were made on self-supported wafers (10 mg.cm-1) of original
samples previously activated at 673K and 10-2 Pa for 2 hours.
After wafer activation, the base spectrum was recorded and
pyridine vapor (6.5 102 Pa) was admitted in the vacuum IR cell
and adsorbed onto the zeolite. Desorption of pyridine was
performed in vacuum over three consecutive one-hour periods
of heating at 423, 523 and 623K, each of them followed by the
IR measurement at room temperature. The spectra were
scaled according to the sample weight.
As seen in Figure 2a, the OSDA-C4 allows the preferential
crystallization of ZSM-5 materials under most of the studied
conditions, especially for high Si/Al ratios (~30), and diluted
gels (H2O/Si ~ 30). Similar ZSM-5 materials have been recently
reported by Burton under analogous synthesis conditions.13
Interestingly, Beta zeolite material was crystallized at Si/Al,
OSDA/Si and H2O/Si molar ratios of 15, 0.4 and 10,
respectively, in the gel (see Beta-15-OH in Figure 2a). The as-
prepared Beta-15-OH zeolite shows a Si/Al ratio of 15.3 (see
Table 1) and, 27Al MAS NMR spectroscopy reveals that all the
aluminum species are tetrahedrally coordinated within the
zeolitic framework (see Figure 4a). Moreover, the solid yield
obtained is above 95%, according to the initial oxide sources
used in the synthesis.
2.4.- Catalytic test
Liquid phase alkylation of benzene with propylene was carried
out with the acid zeolites, pelletized, crushed, and sieved at
0.25–0.42 mm diameter. The reaction was performed in an
automated high pressure stainless steel reactor, at 3.5 MPa,
398 K, WHSV = 25 h-1 referred to the olefin, and benzene to
propylene (B/P) molar ratio of 3.5. Composition of outlet
(b)
(a)
CP811
Beta-30-F
Beta-15-F
Beta-30-F_Calc
stream was analyzed on-line on
chromatograph equipped with
a
Varian-450 gas
5%phenyl-
Beta-15-F_Calc
a
30
m
Beta-30-OH
Beta-15-OH
15
Beta-30-OH_Calc
95%dimethylpolysiloxante capillary column connected to a
flame ionization detector. More details can be found in a
previous study.12
Beta-15-OH_Calc
5
10
20
25
30
35
5
10
15
20
25
30
35
Angle (2θ)
Angle (2θ)
Fig. 3 PXRD patterns of the as-prepared (a) and calcined (b) nanosized Beta zeolites
3.- Results and discussion
The low-intense and broad diffraction peaks observed in the
PXRD pattern of this Beta zeolite suggest that this material
should be in the form of small crystallites (see Beta-15-OH in
Figure 3a). FE-SEM microscopy confirms the formation of very
small homogeneous crystals (see Beta-15-OH in Figure 5), and
TEM microscopy reveals that the average particle size is ~ 10
nm (see Beta-15-OH in Figure 6).
3.1.- Synthesis and characterization of the nanosized Betas
In a preliminary experimental design under alkaline conditions
using the OSDA-C4 molecule (see Figure 1) as OSDA, the
influence of different synthesis variables, such as Si/Al (15, 30),
OSDA/Si (0.2, 0.4) and H2O/Si (15, 30) molar ratios, have been
explored at 150ºC and 10 days synthesis time.
OH media, T=150ºC, t=10d
(a)
Si/Al
15
30
OSDA/Si
OSDA/Si
OSDA-C4
0.2
0.4
Beta-15-OH
0.2
0.4
10
30
H2O/Si
Si/Al
15
OSDA/Si
30
OSDA/Si
OSDA-C6
0.2
0.4
0.2
0.4
Beta-30-OH
Amorphous
ZSM-5
10
30
H2O/Si
Beta+ZSM-5
Beta
(b)
F media, T=150ºC, t=10d
OSDA/Si=0.4
H2O/Si=15
OSDA/Si=0.4
OSDA-C4
OSDA-C6
F/Si
Si/Al=30
F/Si=0.4
Beta-30-F
0.25
0.4
15
30
Beta-15-F
3
Si/Al
H2O/Si
15
Fig. 4 27Al MAS NMR spectra of the as-prepared (a) and calcined (b) nanosized Betas
Fig. 2 Phase diagrams obtained using OSDA-C4 and OSDA-C6 as OSDAs.
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image for CP811 in Figure 8) and lower BET and external
surface areas (580 and 203 m2/g, respectively, see Table 2).
Thus, the nanosized high-silica Beta zeolite with a Si/Al ratio of
15 prepared using OSDA-C4 (see Figure 1) shows improved
physico-chemical properties compared to the commercially
available nanocrystalline Beta zeolite.
Fig. 5 FE-SEM images of the as-prepared nanosized Beta zeolites.
The N2 adsorption-desorption isotherms of Beta-15-OH (see
Figure 7) after calcining the sample at 550ºC in presence of air
shows a steep rise uptake at low P/Po pressure, which is
typical for microporous materials, and an inflection and
hysteresis loop at P/Po between 0.6-0.9, which can be
explained by a large interparticle capillary condensation due to
the presence of small crystal sizes. The measured BET surface
area is 757 m2/g, with an external surface area and a
micropore volume of 440 m2/g and 0.15 cm3/g, respectively
(see Table 2).
Fig. 7 N2 adsorption isotherms of the nanosized Beta zeolites in their calcined form.
Table 2 Textural properties of the nanosized Beta zeolites in their calcined form
measured by N2 adsorption/desorption.
Area BET
(m2/g)
757.4
Ext. surface
area (m2/g)
439.9
Micr. area
(m2/g)
317.5
Micr. Vol.
(cm3/g)
0.15
Sample
Beta-15-OH
Beta-30-OH
Beta-15-F
Beta-30-F
CP811
738.2
428.7
309.5
0.14
719.8
396.2
323.6
0.15
568.5
241.1
327.4
0.16
580.0
203.1
378.4
0.18
However, the attempts to synthesize nanosized Beta zeolites
with higher Si/Al ratios using OSDA-C4 as OSDA resulted in the
crystallization of ZSM-5 materials (see Figure 2a).
To favor the nucleation and crystallization of the nanosized
large pore Beta instead of the medium pore ZSM-5 zeolite at
higher Si/Al ratios, we thought to use a dicationic OSDA
molecule similar to OSDA-C4 but presenting larger heterocyclic
end-groups (see OSDA-C6 in Figure 1). We based this
hypothesis on the fact that larger heterocyclic end-groups
would hardly allow the nucleation of the medium pore ZSM-5
zeolite by host-guest size constraints, favoring the
crystallization of the large pore Beta zeolite. Thus, the OSDA-
C6 molecule was tested as OSDA under the same synthesis
conditions used before for the OSDA-C4. As can be seen in
Figure 2a, the OSDA-C6 allows the preferential formation of
Beta zeolite in a wider range of conditions (see Figure 2a),
Fig. 6 TEM images of the synthesized nanosized Beta zeolites.
For comparison purposes,
a
commercially available
nanocrystalline Beta zeolite (CP811, Zeolyst) with a similar
Si/Al ratio (~13) has also been characterized. This nanosized
Beta zeolite shows larger particle sizes (~20-25 nm, see TEM
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achieving the crystallization of a pure Beta zeolite with a Si/Al crystallites than the reported synthesis of Beta in fluoride
ratio of 30 in the synthesis medium (see Beta-30-OH in Figure media with sizes within several microns.14
2a). This as-prepared sample shows a Si/Al ratio of 30.6 in the
final solid (see Table 1) and the 27Al MAS NMR spectrum only
shows a band at ~54 ppm, associated to aluminum in
tetrahedral coordination (see Figure 4a). The solid yield
achieved is above 95%, based on the initial oxide sources.
As observed above for the BET-15-OH sample, the PXRD
pattern of Beta-30-OH also shows the presence of broad
diffraction peaks, which are typical of zeolites with very small
crystal sizes (see Figure 3a). SEM and TEM images confirm the
formation of nanosized Beta crystals, with an average size
comprised between 10-15 nm (see Beta-30-OH in Figures 5
and 6). In addition, adsorption-desorption N2 characterization
gives a BET surface area of 738 m2/g, with an external surface
area and a micropore volume of 428 m2/g and 0.14 cm3/g,
respectively (see Table 2).
Fig. 8 FE-SEM (left) and TEM (right) images of the commercial nanocrystalline Beta
zeolite (CP811)
Fig. 9 Transmission FTIR spectra in the stretching C–C region of the different nanosized
Beta zeolites after adsorbing pyridine followed by desorption at 150, 250, and 350ºC
The results obtained could be an indication that this type of
dicationic OSDAs would be in the origin of the small crystallites
3.2.- Catalytic application of the nanosized Betas
obtained. If this was so, they may generate nanocrystalline
For the application of these materials as heterogeneous acid
Beta even during the synthesis in the presence of F-, in where
catalysts in industrially-relevant chemical processes is very
large crystal sized zeolites are most generally obtained. Then,
important to evaluate their acid properties. Since Brønsted
the synthesis of high-silica nanosized Beta zeolites was
acidity is directly related to the amount of aluminum in
attempted using dicationic OSDA-C4 and OSDA-C6 molecules
framework positions, the stability of aluminum species on the
under fluoride media (see Figure 2b). As can be seen in Figure
calcined nanosized Beta samples has been studied by solid 27Al
2b, the crystallization of the Beta zeolite in presence of
MAS NMR spectroscopy. As it can be seen in Figure 4b, the 27Al
fluoride anions in the synthesis media could be accomplished
MAS NMR spectra show that close to 80% of the aluminum
with two different Si/Al ratios, 15 and 30 (see Beta-15-F and
species remain as AlIV within the calcined nanocrystalline Beta
Beta-30-F in Figure 2b). These as-prepared solids show similar
zeolites. Notice that this percentage is similar for the small
Si/Al ratios to the ones introduced in the synthesis gels (16 and
crystallite commercial CP811 material. The Brønsted acidity of
29.8 for Beta-15-F and Beta-30-F, respectively, see Table 1),
these materials has been studied by in-situ FTIR spectroscopy
being all the aluminum species in tetrahedral coordination in
combined with the adsorption/desorption of pyridine. The
the zeolitic frameworks (see 27Al MAS NMR spectra in Figure
FTIR spectra of adsorbed pyridine after desorption treatments
4a). In this sense, the solid yields were also above 95% in both
at 150, 250, and 350°C are represented in Figure 9. As it can be
cases.
seen in Figure 9, all the nanosized Beta zeolites show the
TEM images reveal crystallites with average particle sizes of 10
characteristic IR band of the pyridinium ion at 1545 cm-1,
and 30-50 nm for Beta-15-F and Beta-30-F, respectively (see
which is associated with the presence of Brønsted acid sites.
Figure 6). In fact, the smaller crystal sizes observed for the
Interestingly, the IR band of the pyridinium ion is mostly
Beta-15-F sample results in higher BET and external surface
retained after increasing the desorption temperature at 350ºC,
areas (720 and 396 m2/g, respectively, see Table 2) compared
revealing the presence of strong Brønsted acidities (see Figure
to Beta-30-F (568 and 241 m2/g, respectively, see Table 2).
9). The amount of Brønsted and Lewis acid sites per gram of
Notice that the materials obtained present much smaller
zeolite can be determined from the IR bands centered at 1545
and 1455 cm-1, respectively.15 The nanocrystalline Beta zeolites
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synthesized with a Si/Al ratio of 15, both Beta-15-OH and Beta- With respect to the samples synthesized with a Si/Al ratio of
15-F, show the highest amount of Brønsted acid sites together 30, the Beta-30-OH shows an intermediate catalytic activity
with the commercial CP811 material (see B150 in Table 3), between Beta-15-F and the commercial CP811 zeolite (see
being remarkable the large amount of pyridine retained after Figures 10 and 11). In this sense, the lowest catalytic activity of
desorption treatments at 350ºC in these materials (~90 µmol Beta-30-OH could be explained by its lower Brønsted acidity
pyr/g, see B350 in Table 3). As expected, the two nanosized compared to Beta-15-F (see Table 3), but its high external
Beta zeolites synthesized with a Si/Al ratio of 30, show lower surface allows decreasing the catalyst deactivation compared
Brønsted acidity, as corresponds to their lower Al content (see to CP811 (see Table 2 and Figure 10).
Table 3).
Table 3 Acidity of nanosized Beta zeolites as determined by FT-IR combined with
pyridine adsorption-desorption.
Acidity (µmol pyr/g)
Sample
B150 B250 B350 L150 L250 L350
Beta-15-OH
Beta-30-OH
Beta-15-F
Beta-30-F
CP811
146
110
163
71
130
98
94
47
88
23
85
68
84
64
82
52
71
144
53
87
75
71
24
21
19
220
165
211
205
193
The catalytic activity of these nanosized Beta zeolites has been
studied for the alkylation of benzene with propylene to
produce cumene, which is an important industrial
intermediate product to obtain phenol and acetone.16 This
industrial process is mainly operated in the liquid phase using
large pore zeolites as heterogeneous acid catalysts.16 However,
the design of acid large pore zeolites presenting nanosized
crystals is convenient for this catalytic process, to reduce the
restrictions for cumene diffusion and to decrease the catalyst
deactivation by olefin oligomerization and occlusion of multi-
alkylated subproducts. As it can be seen in Figure 10, the two
nanosized Beta zeolites with a Si/Al ratio of 15, Beta-15-OH
and Beta-15-F, not only show better initial catalytic activity
compared to the commercial nanocrystalline Beta zeolite
(CP811) despite the lower acidities of the former, but also a
remarkable decrease of the catalyst deactivation with time on
stream (TOS). In addition, the yield to the desired cumene is
also significantly higher for Beta-15-OH and Beta-15-F zeolites
(see Figure 11a).
Fig. 11 Selectivity to cumene (a) and di-isopropylbenzene (b) with TOS for the liquid
phase alkylation of benzene with propylene using nanosized Betas as catalysts
Conclusions
In summary, we have presented an efficient synthesis to
achieve nanosized Beta zeolites with particle sizes comprised
between 10 and 20 nm. This has being achieved with two
different non-surfactant alkyl-substituted flexible dicationic
OSDAs that allow the synthesis of nanocrystalline Beta zeolites
under broad Si/Al ratios (15-30) in alkaline and fluoride media
with excellent solid yields (above 95%). These nanosized Beta
zeolites show better catalytic behavior to obtain cumene than
a commercially available nanosized Beta zeolite for alkylation
of benzene with propylene.
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Acknowledgements
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Financial support by the Spanish Government-MINECO
through “Severo Ochoa” (SEV 2012-0267), Consolider Ingenio
2010-Multicat, MAT2012-37160 and, MAT2012-31657 is
acknowledged. The European Union is also acknowledged by
the SYNCATMATCH project (Grant Agreement nº 671093).
M.E.M-A. thanks MINECO for economical support through pre-
doctoral fellowship (BES-2013-066800).
TOS (min)
Beta-30-OH
Beta-15-OH
Beta-15-F
Beta-30-F
CP811
Fig. 10 Propylene conversion with TOS for the liquid phase alkylation of benzene with
propylene using nanosized Betas as catalysts
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