TOCAT7ABSTRACT

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TOCAT7ABSTRACT
Synthesis, characterization and catalytic activity of
hierarchical zeolite, ZH-5
Rajesh Kumar Parsapura and Parasuraman Selvam*a,b
a
NCCR and Department of Chemistry, Indian Institute of Technology-Madras, Chennai 600 036, India
Industry Creation Hatchery Centre, Tohoku University, Sendai 980 8579, Japan
b New
E-mail: [email protected]
Keywords: Hierarchical zeolites, mesoporous ZSM-5, solid acid catalysts, glycerol dehydration, bio-acrolein
2. Experimental
A dual templating strategy has been implied in which
dimethyloctadecyl[3(trimethoxysilyl)propyl]ammoni
um chloride (DOAC) is used as the mesoporogen and
TPABr is used as the micropore structure directing
agent. In a typical synthesis, a prescribed amount of
sodium aluminate was added to the NaOH solution
under stirring followed by the addition of TPABr.
Then a mixture of TEOS and DOAC are added under
vigorous stirring and the solution was further stirred
for 2 h. The obtained solution with the composition
1Al2O3: 10TPABr: 10Na2O: 38SiO2: 4ODAC was
hydrothermally treated at 150ºC for 48 h. The
resulting solid was filtered, washed and dried
followed by calcination at 550ºC in air. The calcined
and proton exchanged sample is designated as ZH-5.
3. Results and discussion
Figure 1 depicts the XRD pattern of hierarchical
ZSM-5 which shows characteristic reflections in the
low-angle (inset) typical of 2D-hexagonal structure
(MCM-41) while the high-angle pattern is distinctive
of orthorhombic (MFI) crystal symmetry.
2000
1500
1000
110
501
6000
101
8000
500
200
Intensity (cps)
100
200
10000
Intensity (cps)
503
600
4
6
2 (deg.)

2
303
241
2000
400
4000
301
1. Introduction
The tremendous success of the zeolites as the
prominent heterogeneous catalysts is due to their
unique physicochemical properties, viz., high surface
area, strong acidity, shape selectivity, ion-exchange
and high thermal stability. Among the various
zeolites, the structures with MFI (ZSM-5) topologies
are of paramount importance in catalysis.
Nevertheless, the presence of micropores in these
zeolites not only restricts the bulkier molecules to
exploit the internal surface but also retards the
molecular diffusion of the reactants and in-turn
deactivate the catalyst. Therefore, attempts have been
made to synthesize extra-large pore zeolites and
ordered mesoporous materials (OMM) by using
various templates [1]. However, the practical
applications of such materials are limited owing to
their moderate acidities and low stabilities. On the
other hand, in recent years, hierarchical zeolites (ZH)
with ordered mesopores and crystalline zeolitic walls
with mircropores are gaining considerable interest
due to their ability to overcome the difficulties
encountered by both microporous and mesoporous
materials. However, synthesis of such structures is
extremely challenging, and only few have succeeded
in synthesizing so called hierarchical zeolites [2]. In
this study, we present a successful synthesis of
hierarchical zeolite, designated as ZH-5, with MFItype micropores and MCM-type mesopores, and their
use in selective dehydration of glycerol.
0
10
20
30
2 (deg.)
40
50
Figure 1. XRD patterns of ZH-5.
The formation of the hierarchical structure is further
supported by the presence of type-I and type-IV
isotherms in N2 sorption measurements (not shown
here). The structural properties of ZH-5 are shown in
table 1. Figure 2 depicts the NH3-TPD profile of ZH5 in comparison with microporous ZSM-5. The
presence of broad peak around 670 K indicates the
presence of strong Brønsted acid sites. However, the
less acidity compared to its microporous counterpart
can be attributed to the interrupted frameworks by the
mesopores.
Figure 4 presents the TEM images of ZH-5 which
shows the presence of mesopores amidst the matrix
of zeolitic micropores. The orthorhombic crystal
symmetry of the ZH-5 is further reflected in the
SAED pattern (inset).
weak
TCD signal (a.u.)
strong
moderate
(a)
(b)
Figure 4. TEM images of ZH-5. Inset: SAED pattern.
600
700
800
Temperature (K)
Figure 2. NH3-TPD profiles of (a) ZSM-5; (b) ZH-5.
Figure 3a depicts the 27Al MAS NMR spectra of ZH5 which shows a single peak at 55 ppm corresponding
to aluminium in the tetrahedral coordination (55 ppm)
and the absence of a peak at ‘0 ppm’ indicates the
absence of extra-framework aluminium species.
Figure 3a shows the 29Si MAS NMR spectra of ZH-5
which shows a broad peak above ‘-110 ppm’
corresponding to Q4 sites of the zeolite. Whereas, the
broad satellite at -99 and -105 ppm could be attributed
to the Q3 silanol groups and 3Si(1Al) type
coordination respectively.
27
Al
29
55 ppm
30
27
(b)
-80
-95
-110
-125
 (ppm)
ZSM-5
ZH-5
a
40
40
20
0
4
8
12
16
4. Conclusion
In this study, we have demonstrated a successful
synthesis of hierarchically zeolite, ZH-5. Further, we
have also shown that the catalyst exhibit excellent
activity and enhanced lifetime for the selective
dehydration of glycerol to acrolein. Further work is
in progress.
Al (a) and 29Si (b) MAS-NMR of ZH-5.
Table 1. Textural properties of various zeolites.
Catalyst
Glycerol
Acrolein
Hydroxyacetone
Figure 5. Catalytic activity of ZH-5
 (ppm)
Figure 3.
60
Time on stream (h)
-99 ppm
0
60
-117 ppm
(a)
60
80
0
-105 ppm
90
80
0
Intensity (a.u.)
Intensity (a.u.)

100
20
-112 ppm
Si
Figure 5 shows the catalytic activity of ZH-5 in
selective dehydration of glycerol. The enhanced
diffusion by mesopores is clearly reflected in the
improved catalytic performance and enhanced
lifetime up to 15 h even at high concentrations (25
wt%) of glycerol which is hitherto not reported.
Selectivity (%)
500
Conversion (%)
400
SSAa (m2g1)
DBJHb (nm)
__________________
________
Micro
230
Meso
103
143
403
b
c
Vpc (cm3g1)
___________________
Meso
---
Micro
0.09
Meso
0.05
3.0
0.07
0.50
Specific surface area, Pore size, Pore volume.
Acknowledgments
The authors thank DST, New Delhi for funding NCCR. One of
the authors, RKP thanks CSIR for the award of SRF.
References
[1] P. Selvam, S. K. Bhatia, C. G. Sonwane, Ind. Eng. Chem.
Res., 2001, 40, 3237.
[2] M. Choi, H. S. Cho, R. Srivastava, C. Venkatesan, D. -H.
Choi, R. Ryoo, Nat. Mater., 2006, 5, 718.

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