Influence of the post-synthesis method on the number and size of secondary mesoporous structure of NaY zeolite and its effect on catalyst loading. An efficient and eco-friendly catalyst for synthesis of xanthenes under conventional heating

Article abstract of DOI:10.1007/s13738-016-0929-4

Several identification techniques have been used to study the effect of the preparation method of dealuminated Y zeolite on catalyst loading. In this paper, NaY zeolite was dealuminated by chemical operation with ethylenediaminetetraacetic acid (H₄

Full text of DOI:10.1007/s13738-016-0929-4

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0929-4
ORIGINAL PAPER
Influence of the post‑synthesis method on the number and size
of secondary mesoporous structure of NaY zeolite and its
effect on catalyst loading. An efficient and eco‑friendly catalyst
for synthesis of xanthenes under conventional heating
Maryam Moosavifar1 · Leila Fathyunes1
Received: 24 November 2015 / Accepted: 25 June 2016
© Iranian Chemical Society 2016
Abstract Several identification techniques have been used
to study the effect of the preparation method of dealumi-
nated Y zeolite on catalyst loading. In this paper, NaY
zeolite was dealuminated by chemical operation with eth-
ylenediaminetetraacetic acid (H4EDTA) treatment. In this
method, extra-framework aluminum species removed from
the supercage of zeolite and therefore increases the Si/Al
ratio and pore volume. Consequently, the loading of the
molybdophosphoric acid (MPA) in the supercage of zeolite
is increases (0.1 g/g equal 0.049 mmol/g support) in EDTA
treatment (MPA-MDAZY) in comparison with (0.0875 g/g
equal 0.043 mmol/g support) in hydrothermal method
(MPA-DAZY). These results were also confirmed by XRF,
AAS, FTIR, SEM, BET, XRD and WDX analysis. Reduc-
ing of the reaction time and increasing of the catalytic
activity of EDTA treatment toward hydrothermal method
can be related to the high catalyst loading based on remov-
ing of extra-framework aluminum. The catalytic activity of
two catalysts has been compared in the xanthenes synthesis
reactions.
acids (HPA) are very active catalyst for both acid-catalyzed
and redox reactions [1, 2]. However, these catalytic sys-
tems have drawbacks such as low surface area, insufficient
thermal stability and difficulty in catalyst recovery based
on their high solubility in water and polar organic solvents
[3]. In order to overcome these disadvantages, consider-
able efforts including immobilizing or encapsulation of
organic material in inorganic supports have been devoted.
Silica [4, 5], alumina [6], zirconia [7], titania [8], resin [9],
zeolites [3, 10–12], MCM-41 [13], polymers [14] were the
most of investigated systems. These heterogeneous cata-
lytic systems were used in the organic reactions [15–19].
In addition, Y zeolite has been applied by several groups
of researcher as support for heteropoly acid [20, 21].
Because they have supercages with the appropriate sizes
which facilitate the formation of HPA inside the zeolite
[20]. However, the structure of Y zeolite shows basicity due
to the presence of aluminum atoms in its framework. So,
they may disrupt the formation of HPA in the supercage of
zeolite [20, 21]. Therefore, Y zeolite is required to be dea-
luminated. There are several methods for dealumination of
zeolite including hydrothermal treatment, chemical opera-
tion, chemical and hydrothermal operation [22]. However,
some of these methods require careful control to prevent
the destruction of zeolite, or sometimes, in the dealumi-
nation process, non-structure aluminum atoms cannot be
completely removed from the zeolite structure [22]. In our
previous works, we have used the hydrothermal method for
the dealumination of the zeolite, and then, catalyst loading
was investigated in these conditions [23–25]. In this paper,
to study the effect of the synthetic method on to the catalyst
loading, chemical operation includes the use of a chela-
tion agent was applied for the dealumination of zeolite
(Scheme 1). In this way, the catalyst loading was compared
with hydrothermal method by using FTIR, SEM, XRD,
Keywords Secondary mesoporous structure ·
Dealuminated zeolite · Catalyst loading
Introduction
Modification of solid acid catalysts is an interesting field
in chemistry, material and industry. Keggin-type heteropoly
* Maryam Moosavifar
m.moosavifar90@gmail.com; moosavifar@maragheh.ac.ir
1
Department of Chemistry, Faculty of Science, University
of Maragheh, P.O. Box 55181-83111, Maragheh, Iran
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J IRAN CHEM SOC
Scheme 1 Post-synthesis
method by EDTA treatment for
dealumination of NaY zeolite
Scheme 2 Synthesis of 14-substituated-14H-dibenzo [a,j] xanthenes under conventional heating in the presence of MPA-MDAZY
XRF, BET, WDX and AAS techniques. Finally, to compare
the effect of the catalyst loading on the catalytic behavior,
these catalytic systems were utilized in the xanthenes syn-
thesis reactions [26]. Iranian chemist researcher was used
several methods for preparation of xanthenes [24]. Here,
we modified our previous system and compared in the xan-
thene reactions (Scheme 2).
10 % ammonium chloride solution. Molybdophosphoric
acid encapsulated into the supercage of modified dealumi-
nated Y zeolite (MPA-MDAZY) was synthesized according
to the reported procedure [15]. In a typical procedure, 2.0 g
of modified dealuminated zeolite (MDAZY) (treated with
H4EDTA) and 7.2 g of molybdenum (VI) oxide were mixed
in 70 ml deionized water and then stirred for 24 h at room
temperature. Next, 0.48 g of phosphoric acid (99 % purity)
was added, and the mixture was stirred for 3 h at 363 K.
Finally, the synthesized samples (MDAZY-MPA) was fil-
tered off and dried at 383 K. The samples were individually
immersed into hot water to removing of Al extra-framework.
Then, they were agitated for 1 h and then filtered and dried at
363 K. In order to remove the unreacted species of metal cat-
ions in the lattice, the samples were exchanged with aqueous
1 M solution of NaCl for 4 h under vigorous stirring. Finally,
the catalyst was filtered, washed with distilled water and
dried at 363 K. To confirm the location of MPA into super-
cage of zeolite, the samples were studied with spectroscopic
technique such as FTIR, XRD, XRF, SEM, WDX and BET
technique. The catalyst loading was also determined using
atomic absorption spectroscopy (AAS).
Experimental
All material and reagent were of commercial grade and
attained from Merck or Fluka. FTIR spectra were obtained
in the range of 400–4000 cm−1 with a Nicolet Impact 400D
spectrometer. XRD powder diffraction was carried out on
Advanced Bruker D8 powder diffraction using Cu Kα radia-
tion (=1.54 A). Nitrogen adsorption measurements were
conducted at liquid nitrogen temperature (77 K) using an
NOVA 2200 micrometrics. The BET surface area was calcu-
lated using the adsorption data in the relative pressure range
of 0.05–1 for samples. Porous volumes were estimated from
the amounts of nitrogen adsorbed at a relative pressure. The
morphology of samples before and after putting off the cata-
lyst inside nanocage of zeolite was examined using a scan-
ning electron microscopy. SEM photographs and WDX
analysis were obtained on a XL30 from Philips Company.
NaY zeolite was purchased from Sigma-Aldrich Chemi-
cal Company. This zeolite was treated using ethylenediami-
netetraacetic acid (H4EDTA) to obtain modified dealumi-
nated Y zeolite (MDAZY) by chemical operation according
to the reported procedure. In this manner, controlling the
rate of H4EDTA addition, amount of H4EDTA and reaction
temperature is essential to minimize amorphization of zeo-
lite [27]. The dealuminated samples are washed with hot
distilled water, dried and followed with ion exchange with
The catalytic activity of the prepared catalyst investi-
gated in the xanthenes synthesis reactions similar to that of
the reported method in our previous work [25]. The results
of two methods were compared upon the product yield and
reaction time.
Results and discussion
Preparation and characterization of MPA‑MDAZY
MDAZY was prepared by chemical operation with
H4EDTA treatment and MPA-MDAZY was synthesized
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J IRAN CHEM SOC
Table 1 Si/Al ratio, specific surface area, pore volume, unit cell dimension and unit cell formula of the samples
Sample
SiO2 (%) Al2O3 (%) Na2O (%) Si/Al ratio Unit cell formula
Specific surface area (m2/g) Pore volume (cm2/g)
NaY
24.78
49.16
9.74
17.24
4.13
8.53
3.40
2.34
3.36
2.65
4.32
4.85
7.63
4.55
6.45
Na56[(AlO2)57(SiO2)137
]
599.5
504
0.302
0.252
0.072
0.236
0.241
MDAZY
Na11.5[(AlO2)49(SiO2)136
]
MPA-MDAZY 16.02
128.9
475.5
459.4
DAZY
32.03
23.48
11.98
6.19
Na14.7[(AlO2)52.7(SiO2)136]
MPA-DAZY
Si/Al ratio, specific surface area, pore volume, unit cell dimension and unit cell formula of the samples
according with our previous work [23]. In this compound,
MPA was distributed as a fine particle inside nanocage of
zeolite. Prepared zeolite and synthetic catalyst were charac-
terized by infrared spectroscopy (FTIR), X-ray diffraction
(XRD), X-ray fluorescence (XRF), SEM, WDX, BET and
atomic absorption spectroscopy techniques (Table 1).
The content of MPA in the supercage of the modified
dealuminated Y zeolite (MPA-MDAZY) based on the Mo
content was determined to be 0.1 g [(0.049 mmol)/g of
the supported catalyst]. This value is comparable with the
amount of existing catalyst in the dealuminated zeolite by
the hydrothermal method (MPA-DAZY), i.e., [0.0875 g
(0.043 mmol/g support)]. According to the dealumina-
tion of zeolite by EDTA treatment, dealumination was
occurred, in addition, the extra-framework aluminum
species removed from the zeolite structure and therefore
mesoporous structure to be form with a larger diameter
size (≥1.5 nm) [28]. Consequently, the amount of catalyst
loading in the supercage of zeolite is increased [3]. In addi-
tion, in the process of dealumination of zeolite with EDTA
treatment, the resistance to degradation was increased in
the acidic medium [29], so the zeolite structure was not
completely destroyed using aqueous HF. To destroy the
zeolite structure in order to investigate the Mo content
using atomic absorption spectroscopy (AAS), a concen-
trated solution of H2SO4 and HCl at high temperatures is
required.
Table 1 shows the Si/Al ratio, the unit cell formula,
pore volume, surface area of MDAZY, MPA-MDAZY,
DAZY and MPA-DAZY for comparison. In the MDAZY
compound, surface area and pore volume were more than
DAZY which indicates the removal of more aluminum
atoms from the structure. Consequently, both diameter and
the number of secondary mesoporous structure increased
[3]. In addition, in the case of MPA-MDAZY, the surface
area and pores volume were lesser than that of MDAZY
which proves the filling of secondary mesoporous cavities
with MPA [3]. In addition, more reducing of surface area
and pore volume of MPA-MDAZY compared to MPA-
DAZY confirmed that the catalyst loading is higher than
later due to the high number of secondary mesoporous
structure which in turn, related to the synthesis method.
In MPA-DAZY, secondary mesoporous structure has been
formed, but the extra-framework Al species has been still
retained in the secondary pores; therefore, the catalyst
loading was decreased in comparison with EDTA treat-
ment which extra-framework aluminum atoms have been
removed [20]. Comparing of Si/Al ratio of MPA-MDAZY
with MPA-DAZY and DAZY with MDAZY is reason-
able proof for this claim. The Si/Al ratio of MDAZY and
MPA-MDAZY in comparison with NaY, MPA-DAZY and
DAZY is increased which shows that the chemical opera-
tion facilitates dealumination process and leaving of Al
extra-framework atoms from structure [27]. Also, in the
case of MPA-MDAZY, this ratio is higher than that of other
samples, which showed considerable rejection of the pro-
duced extra-framework aluminums from zeolite structure
[3]. It is noted that the framework Si/Al ratio of samples
was determined by X-ray fluorescence spectroscopy.
Figure 1 shows XRD patterns of the NaY, MDAZY
and MPA-MDAZY. The comparison of XRD spectrum of
NaY with MDAZY indicated almost identical crystallin-
ity which improved based on the dealumination of NaY
zeolite using chemical operation with EDTA treatment,
the intensity of mean peaks slightly reduces with a slight
shift indicating that the framework of the zeolite structure
is still maintained (Fig. 1B). In addition, in MPA-MDAZY
compound, the intensity of the main peak in the region of
2θ ~ 6 considerably has been reduced because of the high
amount of catalyst within zeolite cavity [12]. This proved
by the appearance of the peak in the region of 2θ = 7.2
which confirmed MPA was entrapped into zeolite cages
(Fig. 1C) [23]. In the chemical operation with EDTA treat-
ment, more secondary mesopores structure formed, and
therefore, loading of catalyst increased in comparison with
hydrothermal method and consequently, intensity of zeo-
lite main peaks is reduced in XRD spectra. Similar results
were achieved using XRF data. Unit cell formula Na14.7
[(AlO2)52.5(SiO2)136] was calculated for DAZY [23] while
Na11.5 [(AlO2)49(SiO2)136] obtained for MDAZY. These
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J IRAN CHEM SOC
Fig. 1 XRD patterns of: a NaY
zeolite, b MDAZY and c MPA-
MDAZY
results indicate that in the latter compound, more aluminum
atoms have left the structure and subsequently, reducing the
negative charge is followed with decreasing in the number
of sodium atoms. These results are brought in Table 1.
Figure 2 shows FTIR spectra of MDAZY, MPA
and MPA-MDAZY. Strong wide bands at 1637 and
3200 ~ 3500 cm−1 are attributed to O–H stretch vibration
of hydroxyl groups and vibration at ~1950 attributed to
bending mode (Fig. 2a, b, c). The FTIR spectra of molyb-
dophosphoric acid encapsulated into zeolite confirm the
presence of MPA in the zeolite matrix (Fig. 2c). The pres-
ence of double peak in region 3200–3600 cm−1 is related to
the interaction of both zeolite structure and polyoxometal
with OH groups [23]. In the IR spectra of MPA-MDAZY,
all of characteristic peaks are observed with little shift at
1635, 1410, ~1052 (P–O), 940–967(Mo=Ot), 794 (Mo–
Oe–Mo) (Ot: terminal oxygen, Oe: edge-sharing oxygen),
575 and 520 cm−1 (Fig. 2c). This reveals that the structure
of keggin type interacts with Y zeolite mostly through cor-
ner-shared [12, 23]. These results are comparable to those
that with results which previously obtained using hydro-
thermal synthesis method [24], except that in this method
all of peaks were observed with high intensity due to the
high catalyst loading. In this compound, all of the adsorp-
tion complexes are removed from the zeolite surface using
Soxhlet extraction, and therefore, the presence of IR bands
of MPA in the MPA-MDAZY spectra proves the formation
of MPA in the supercage of zeolite.
Figure 3 shows the N2 physisorption isotherms of the
parent material and the modified samples. The nitrogen
adsorption isotherms were recorded in 77 K for the zeolite
samples. All isotherms were type IV with hysteresis loops
similar to those of type of H3/H4. The type IV isotherms
indicated that, at low relative pressure (P/P0 = 0.05−0.15),
absorption curve showed the presence of microporous [30,
31]. In other hands, the height of inflection in this area for
NaY was more than that of other samples (Fig. 3a), which
improved the presence of microporous volume [32, 33].
Greater curvature at medium relative pressure (P/
P0 = 0.15−0.85) was observed for MDAZY and DAZY
because of the formation of secondary mesoporous struc-
ture according to the post-synthesis treatment (Fig. 3b,
c) [32, 33]. This curvature for MPA-DAZY and MPA-
MDAZY is decreased which related to the reduction pore
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J IRAN CHEM SOC
Fig. 2 FT-IR spectra of a M
DAZY; b MPA; and c MPA-
MDAZY
volume and surface area due to inclusion of MPA in the
supercage of zeolite (Fig. 3d, e) [23].
the dealumination of Y zeolite which followed by the
formation of polyoxometal in the supercage of zeolite,
the amounts of Al and Na atoms are decreased, and Mo
atoms appeared in the MPA-MDAZY compound. These
results proved that the Si/Al ratio increased when the
zeolite was dealuminated, in order to balance charge;
the number of Na atoms decreases. In addition, the pres-
ence of Mo in the nanocage of zeolite proved that poly-
oxometal has been formed inside the nanocage of zeolite.
These results were verified by XRF, FTIR and SEM anal-
yses (Fig. 5).
The catalytic activity of MPA-MDAZY was investigated
in the xanthenes synthesis reactions. The optimized condi-
tions were achieved with 4-chlorobenzaldehyde substrate
(Scheme 3). Catalytic activity of two systems (EDTA treat-
ment vs. hydrothermal method) in the xanthenes reactions
is compared and is brought in Table 2. The results showed
based on the usage of MPA-MDAZY catalyst, the time of
reaction is decreased and the yield of reaction is enhanced
that can be related to the high catalyst loading.
Figure 4 indicate BJH pore size distribution (PSD) of
NaY, MDAZY and MPA-MDAZY. Based on dealumination
of zeolite using EDTA treatment and in the MPA-MDAZY
case, the size of pores is increased which confirmed dea-
lumination causes the formation of secondary mesoporous
structure, and therefore, the average size of large pore is
changed from 6.5 A° in the NaY to almost 8.55 and 8.71A°
in MDAZY and MPA-MDAZY, respectively.
Scanning electron micrographs (SEM) of the molyb-
dophosphoric acid encapsulated modified dealuminated Y
zeolite (MPA-MDAZY) is similar to that of NaY zeolite
which indicated the presence of well-defined crystals that
were free from any shadow of metal ions or complexes on
their external surfaces. This confirms that the polyoxometal
is formed inside nanocage of zeolite, not on external sur-
face [34] (Fig. 5a, b).
Furthermore, WDX analysis of two species NaY and
MPA-MDAZY shows the distribution of elements. Upon
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J IRAN CHEM SOC
A
B
C
E
D
Fig. 3 Nitrogen adsorption–desorption isotherm plots for a NaY zeolite, b DAZY, c MDAZY, d MPA-DAZY and e MPA-MDAZY samples
10
Conclusions
9
In this work, we studied the preparation method effect of
dealuminated Y zeolite on the catalyst loading. Catalyst
characterization was directed using FTIR, XRD, XRF,
AAS, SEM, WDX and BET techniques. In the MPA-
MDAZY compound toward MPA-DAZY, catalyst load-
ing is increased. In addition, reductions in aluminum and
sodium atoms number, unit cell formula, surface area, pore
volume and increase in the Si/Al ratio of MPA-MDAZY
toward MPA-DAZY indicate that more dealumination
occur in the chemical operation with EDTA treatment. This
can be related to the removal of the extra-framework alu-
minum species from the zeolite cage. Therefore, the cata-
lyst loading increased to a greater extent than that of the
hydrothermal method. Consequently, in this system, the
8
7
6
5
4
3
2
1
0
MPA-MDAZY
MDAZY
NaY
0
5
10
15
Fig. 4 Pore size distributions of for NaY zeolite, MDAZY and MPA-
MDAZY samples
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J IRAN CHEM SOC
Fig. 5 SE micrographs of a NaY and b MPA-MDAZY and distribution of elements in the zeolite structure
75min
28
Catalyst concentration
45min
15
60min
20
90min
38
120min
50
Catalyst free
0.1
0.2
0.3
0.4
27
68
74
68
35
78
82
74
55
90
92
80
68
95
96
90
72
95
95
90
Scheme 3 The effect of loading of catalyst in synthesis of 14-substituated-14H-dibenzo [a,j] xanthenes under conventional heating
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J IRAN CHEM SOC
Table 2 Synthesis of
14-substituated-14H-dibenzo
Entry
Substrate
Xanthenes
[a,j] xanthenes under
MPA-DAZY (hydrothermal
treatment)
MPA-MDAZY (EDTA
treatment)
conventional heating using
MPA-DAZY and MPA-
Yieldb,c (%)
Time (min)
Yieldb,c (%)
Time (min)
a
MDAZY
1
2
3
4
5
6
7
8
4-Chlorobenzaldehyde
2-Chlorobenzaldehyde
3,4-dimethoxybenzaldehyde
4-benzyoxybenzaldehyde
benzaldehyde
75
85
95
78
82
93
87
80
80
120
90
95
90
98
90
95
95
98
85
75
75
90
45
60
70
45
75
95
85
4-Nitrobenzaldehyde
3-Nitrobenzaldehyde
Cinnamaldehyde
110
80
110
a
Reaction condition: aldehyde (1 mmol), β-naphthol (2 mmol), catalyst (0.3 g for MPA-DAZY and 0.2 g
for MPA-MDAZY)
b
Isolated yield
c
The products were identified by m.p. and IR and NMR spectroscopic data
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