L. Emdadi et al. / Applied Catalysis A: General 530 (2017) 56–65
57
topologies, crystalline characteristics, and acid properties into
single particles, result in multiple levels of microporosity and
compensated acidity to enable excellent catalytic performances
99.99+% purity), benzyl alcohol (99 +%), and 2,6-di-tert-
butylpyridine (DTBP, 97+% purity) were purchased from Alfa Aesar.
Ludox colloidal silica (30 wt%), sodium hydroxide (NaOH, ≥97.0%
purity), and ammonium nitrate (NH NO , ≥99.0%) were bought
[
15,18,19]. The integration of hierarchical meso-/microporosity
4
3
into zeolite composites is expected to further advance their
performance in combined adsorption, separation, and catalysis
applications.
Zeolite composites have been synthesized mainly via epitaxial
growth [15,20–23] or overgrown [4,7,24–27] methods. In epitaxial
growth, the pre-synthesized zeolite particles are added into the
precursor yielding another type of zeolite crystals. This synthe-
sis method has been used for formation of core-shell [15,20] or
bi-phase [28–30] structured zeolite composites that have similar
framework structures.
from Sigma-Aldrich. Mesitylene was supplied by Acros Organ-
ics. Deionized (DI) water was used throughout the experiment.
+
Diquaternary ammonium surfactant ([C22H45-N (CH ) -C H12-
3 2
6
+
N (CH ) -C H ]Br , (C22-6-6)) was synthesized based on the
3 2 6 13 2
method reported by Ryoo et al. [37] and the C22-6-6 synthesis
method has also been described in our previous publications
[34,38,39].
2.2. Zeolite composite synthesis
The overgrown method is generally used to create core-shell
zeolite composites that have different framework structures. In
this synthesis, the incompatibility between chemical compositions
and crystallization conditions of the core and shell zeolite crys-
tals is circumvented by the preliminary seeding of core crystals
with shell nanoparticles to induce the growth of the shell. Table
S1 in Supplementary information of this paper summarizes the
zeolite framework types and structural properties of zeolite com-
posites synthesized via these methods. It should be noted that both
epitaxial growth and overgrown methods require multiple syn-
thesis steps to obtain the zeolite composites. Additionally, they
have limited capability of creating the multi-level porosities in
the zeolite composites. One-step synthesis of zeolite composites
has been practiced in a fluoride growth media [31,32]. The zeolite
shell thickness typically exceeds 1 m and with limitation of gen-
erating mesoporosity in the composites [33]. Our previous work
reported the successful synthesis of meso-/microporous lamellar
MFI on microporous MFI zeolite via a one-step dual template syn-
thesis approach [34,35]. To the best of our knowledge, synthesis of
hierarchical meso-/microporous zeolite composites with dissimi-
lar framework types in one-step, however, has not been previously
reported.
The
the
recipe
BBLM
used
zeolite
for
composite
/36TEAOH/1692H O,
dual
template
was as
synthesis
follows:
where
of
100SiO /1.4Na O/1Al O /xC
2
2
2
3
22-6-6
2
x = 0, 1, 3, and 9, respectively. Typically, the synthesis was per-
formed by dissolving 0.0667 g NaOH into 8.7353 g TEAOH (35 wt%).
Then, 11.5487 g Ludox silica (30 wt%) and 0.236 g Al[OCH(CH ) ]
were added to the mixture and the mixture was sonicated
at room temperature for 0.5 h until complete dissolution of
Al[OCH(CH ) ] . Finally, this solution was mixed with a C
solution that was prepared by dissolving the desired amount of
C22-6-6 in 3.8462 g DI water at 333 K. After continuous mixing for
2 h at room temperature, the resultant gel was transferred into a
Teflon-lined stainless-steel autoclave, followed by hydrothermal
synthesis for 14 days by tumbling the autoclave vertically at 30 rpm
in an oven heated at 423 K. After synthesis, the zeolite product was
filtered, washed with DI water, and dried at 343 K overnight. The
as-obtained sample was named BBLM-x/36 based on the molar
ratio of C22-6-6 and TEAOH templates used in the synthesis recipe.
Conventional microporous BEA zeolite was synthesized using
the same recipe mentioned above without adding any C22-6-6
(x = 0) as the template for comparison, and it was designated as
BEA. Synthesis of lamellar MFI was listed in section S2 of the
Supplementary information of this paper.
All the as-synthesized zeolite samples were calcined in flowing
air (100 mL min , ultrapure, Airgas) by increasing the temperature
from ambient temperature to 873 K at 1.45 K min and holding
the sample at 873 K for 6 h. The calcined samples were then ion-
exchanged three times using 1 M aqueous NH NO3 (weight ratio
of zeolite to NH NO3 solution = 1:10) at 353 K for 12 h, and sub-
sequently, collected by centrifugation, washed with DI water three
times, and dried at 343 K overnight. The second calcination in dry air
(100 mL min , ultrapure, Airgas) was conducted by increasing the
temperature from ambient temperature to 823 K at 1.45 K min
and holding the sample at this condition for 4 h to thermally decom-
3
2 3
3
2 3
22-6-6
Here, we report a facile one-step dual template synthesis
strategy to construct hierarchical zeolite composites containing
dissimilar framework structures and dual meso-/microporsity via
synergistic integration of 2D layered ultra-thin MFI and 3D bulk
BEA nanosponge zeolites. In contrast to previous epitaxial growth
or overgrowth methods, both BEA and MFI zeolite phases in the bulk
BEA nanosponge-lamellar MFI (BBLM) composites were formed
sequentially in one step synthesis under the assistance of tetraethyl
ammonium hydroxide (TEAOH) and diquaternary ammonium sur-
−
1
−
1
4
4
+
+
−1
factant ([C22H45-N (CH ) -C H -N (CH ) -C H ]Br , (C22-6-6))
3 2
6
12
3 2
6
13
2
−
1
templates, respectively. TEAOH is the traditional molecular tem-
plate to assist BEA zeolite synthesis [36]; while C22-6-6 leads to
the coherent assembly of the zeolite layer and the surfactant to
produce 2D lamellar MFI zeolite nanosheet structures [37]. The co-
existence of C22-6-6 and TPAOH template in the synthesis led to the
formation of 2D MFI nanosheet covering on the surface of or pen-
etrating into the 3D BEA particles. A fractioning of bulk BEA into
a nanosponge-like morphology that was comprised of randomly
aggregated nanoparticles was simultaneously observed. The cat-
alytic reactions of benzyl alcohol in mesitylene showed that the
BBLM zeolite has an excellent activity and stability compared to
single zeolites or their physical mixture.
+
+
pose NH4 to NH3 and H . Eventually, the zeolite samples in the
H -form were used for acidity characterization and catalytic reac-
tion tests discussed below.
+
2.3. Materials characterization
Powder X-Ray diffraction (XRD) patterns were collected by a
Bruker D8 Advance Lynx Powder Diffractometer (LynxEye PSD
detector, sealed tube, Cu K˛ radiation with Ni ˇ-filter). Scanning
electron microscopy (SEM) and transmission electron microscopy
(TEM) observations of the samples were performed using a Hitachi
SU-70 and a JEM 2100 LaB6 electron microscope, respectively.
The argon (Ar) adsorption-desorption isotherms were measured
using an Autosorb-iQ analyzer (Quantachrome Instruments) at
87 K. Prior to the measurement, samples were evacuated overnight
at 623 K and 1 mm Hg. Si and Al contents of zeolite samples were
determined by inductively coupled plasma optical emission spec-
troscopy (ICP-OES, iCAP 6500 dual view). The magic angle spinning
2
. Experimental
2.1. Materials
Tetraethylammonium hydroxide (TEAOH, 35 wt%) aqueous
solution, aluminum isopropoxide (metal basis) (Al[OCH(CH ) ] ,
3
2 3