Host (nano cage of zeolite Y)/guest transition metal complexes of N,N-bis (salicylidene)4,5-dimethyl-1,2-phenylenediamine: Synthesis, characterization, catalytic activity for oxidation of phenol and kinetic study

Article abstract of DOI:10.1007/s13738-014-0483-x

In this work, transition metal (M = Cu(II), Mn(II), Co(II), Ni(II)) complexes of tetradentate Schiff base ligand H₂L: (C₂₂H₂₀N₂O₂) have been introduced to cavity of zeolite-Y by flexible ligand method

Full text of DOI:10.1007/s13738-014-0483-x

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0483-x
ORIGINAL PAPER
Host (nano cage of zeolite Y)/guest transition metal complexes
of N,N-bis (salicylidene)4,5-dimethyl-1,2-phenylenediamine:
synthesis, characterization, catalytic activity for oxidation
of phenol and kinetic study
•
M. Zendehdel A. Mobinikhaledi Z. Mortezaei
•
Received: 11 October 2013 / Accepted: 27 May 2014
ꢀ Iranian Chemical Society 2014
Abstract In this work, transition metal (M = Cu(II),
Mn(II), Co(II), Ni(II)) complexes of tetradentate Schiff
base ligand H2L: (C22H20N2O2) have been introduced to
cavity of zeolite-Y by flexible ligand method. These host–
guest materials were characterized by several techniques:
chemical analysis, diffuse reflectance spectroscopy, Fourier
transfer infrared, X-ray diffraction, thermo gravimetric
analysis and Burner–Emmet–Taller. The catalytic activity
of [M(L)]/NaY (M = Mn, Co, Ni, Cu) was investigated
with oxidation of phenol to catechol and hydroquinone
with hydrogen peroxide (H2O2) as oxidant in different
solvents. The reactivity of these heterogeneous catalysts
was compared with corresponding homogeneous catalysts.
The activity of phenol oxidation decreases in the series
[Cu(L)]/NaY > [Mn(L)]/NaY > [Co(L)]/NaY > [Ni(L)]/
NaY at mild conditions. We considered the effect of dif-
ferent factors on percent of products in oxidation of phenol
such as: amount of catalyst, temperature, type of oxidant
and solvent. Finally, the kinetic of phenol oxidation with
excess H2O2 over [M(L)]/NaY catalysts at several tem-
peratures of 40, 60 and 80 ꢁC was studied. These catalysts
were very stable and can be reused for more than three
times. Results show that a pseudo-first order with respect to
phenol and the catalytic reaction occurred via a radical
mechanism.
Introduction
It is now well established that some organometallic com-
plexes are eco-friendly catalysts in the oxidation of certain
organic compounds. Substitution of electron withdrawing
groups on the ligand decreases the electron density over the
metal center and thus increases the catalytic activity. While
such homogenous catalysts may have high activity and
selectivity, problems sometimes limit their industrial
application. Difficulties may occur with product separation
as can deactivation by self-aggregation of active sites. One
of the best solutions is to heterogenize the catalyst by
encapsulating it within a zeolite and several such systems
have been reported to successfully catalyze oxidation of
organic molecules [1, 2].
Zeolites are crystalline aluminosilicates whose internal
voids are formed by cavities and channels of strictly regular
dimensions and of different sizes and shapes. In particular,
the pore structure of Y zeolite consists of almost spherical
˚
12 A cavities interconnected tetrahedrally through smaller
˚
apertures of 7.4 A diameter. The metal complexes of ligands
such as phthalocyanines [3], Schiff bases [4] and polypyri-
dines [5] can be easily accommodated inside the super cages
of Y zeolite. There are two main methods which allow
complexes to be included in zeolites: the zeolite synthesis
method and the flexible ligand method [6]. With the latter,
encapsulation involves assembling metal ions and ligands
inside the zeolite, with the so-formed complex being too
large and rigid to exit [7]. Also, introduction of metal com-
plexes into zeolite leads to growing up the number of het-
erogeneous catalysts which combine the advantages of
homogeneous and heterogeneous catalytic system, reduce
the self-oxidation tendency of the complexes and promote
the catalytic activity by dispersion of the complexes inside
the zeolite pores especial for oxidation reaction [8].
Keywords Zeolite-Y ꢀ Schiff base ligand ꢀ Pseudo-first
order ꢀ Kinetic study
M. Zendehdel (&) ꢀ A. Mobinikhaledi ꢀ Z. Mortezaei
Department of Chemistry, Faculty of Science,
Arak University, 38156-8-8349 Ara¯k, Iran
e-mail: m-Zendehdel@araku.ac.ir;
mojganzendehdel@yahoo.com
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J IRAN CHEM SOC
H3C
CH 3
The petrochemical, chemical and pharmaceutical
industries produce waste waters containing organics, such
as phenols, which are extremely toxic to aquatic life. The
phenol derivatives are generally toxic even at very low
concentrations. In general, these pollutions exist in con-
centration range of 500–10,000 ppm, mostly too toxic for
conventional biotreatment methods, and too low to treat by
combustion. Thus, chemical oxidation emerges as a
promising route for phenol removal at intermediate con-
centrations. Investigation about oxidation of phenol that
catalyzed by peroxides is significantly important due to
providing useful information for the elucidation of the
reaction mechanism and also its application in analytical
clinical chemistry, in the synthesis of phenolic polymers
and in the protection of the environment [9].
H
H
N
N
OH
HO
Scheme 1 4,5-Dimethyl-1,2-phenylenediamine
Catalysts preparation
Synthesis of M(II)-Y (M = Mn, Co, Ni, Cu)
In this work, we report the synthesis and characteriza-
tion of M = Mn(II), Co(II), Ni(II) and Cu(II) complexes of
N,N-bis (salicylidene) 4,5-dimethyl-1,2-phenylenediamine
that incorporated onto nanodimensional pores of NaY
zeolite. The catalytic activity of [M(L)]/NaY for oxidation
of phenol to catechol and hydroquinone under mild con-
dition with hydrogen peroxide (H2O2) as an oxidant in
different solvents was considered. The effect of different
factors on percent of products in oxidation of phenol was
considered and found the higher activity and selectivity of
[M(L)]/NaY for phenol hydroxylation using H2O2 towards
the corresponding other catalyst [5, 6, 10]. Hence, the
kinetic of phenol oxidation with excess H2O2 over [M(L)]/
NaY catalysts at several temperatures of 40, 60 and 80 ꢁC
was studied.
Metal ions incorporated onto the zeolite using ion
exchange in aqueous solution as reported previously [11].
Typically, 1 mmol of metal chloride was dissolved in
100 ml deionized water. The 1 g of NaY zeolite was added
to it and stirred for 24 h at room temperature. Solid product
was filtered and washed with deionized water until the
product was free from metal ion on the surface of the
zeolite and atomic absorption spectroscopy confirmed the
used water is free from metal ions, and dried at 100 ꢁC.
Synthesis of ligand H2L (C22H20N2O2)
1.835 mmol of 4,5-dimethyl-1,2-phenylenediamine was
dissolved in 20 ml of ethanol, then 3.671 mmol salicylal-
dehyde and 0.0024 g of Cu(NO3)2 was added to it. Then
mixture was stirred for 0.5 h at room temperature. After
adding water to it crystals formed. The solid was filtered
and washed with cold ethanol to remove the untreated
materials and ligand (Scheme 1) dried at room temperature
[12].
Experimental
Materials
Preparation of M2L2 complexes (homogeneous catalysts)
All solvents and the materials such as: NaCl, Cu(NO3)2,
(tert-butyl hydrogen peroxide) TBHP, H2O2, Phenol, sal-
icylaldehyde and Manganese (II), cobalt (II), nickel (II),
copper (II) chloride were purchased from Merck. Zeolite
NaY was purchased from SPAGE company at Tehran,
Iran. 4,5-dimethyl-1,2-phenylenediamine was purchased
from Aldrich. All newly prepared zeolites were charac-
terized using Fourier transfer infrared (FT-IR) (Galaxy
series FT-IR 5000 spectrometer), Burner–Emmet–Taller
(BET) (SIBATA, App, 1100-SA with adsorption of
nitrogen at 77 K), X-Ray diffract meter (Philips 1840)
with radiation Cu–Ka at room temperature, TGA-DSC
(Diamond PYRis TM, TG/DT 6300), 1HNMR spectra
were obtained using a Bruker Avance 300 MHz spec-
trometer, Diffuse reflectance spectra recorded by JASCO
V-570 spectrophotometer.
These complexes were synthesized by the method reported
in [13]. A hot solution of M = Mn, Co, Ni, Cu(OAc)2
(0.5 mmol in 5 ml EtOH) was added to a solution of H2L
(0.5 mmol) in hot EtOH/DMF (20–30 ml, 3:1). The reac-
tion mixture was refluxed for 8 h. Next, the solution was
cooled to precipitate the complex. The complexes were
filtered and washed with ethanol and dried at room
temperature.
Synthesis of [M complex]-NaY by flexible ligand method
0.1 g ligand H2L (C22H20N2O2) was dissolved in 20 ml of
ethanol and was added to 0.5 g of M(II)-NaY (M = Mn,
Co, Ni, Cu) and the mixture was refluxed for 18 h. The
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J IRAN CHEM SOC
analyzer and peak areas were measured. Fs was calculated
resulting slurry was filtered and the solid was further
refluxed with 1 M of NaCl (50 ml) solution for 16 h to
replace the uncomplexed M(II) ions adhering to the outer
surface of zeolite by Na?. Also, Soxhlet extracted for 48 h
with ethanol to remove excess ligand that remained in the
cavities of the zeolite or located on the surface of the
zeolite. The solid consisting of M (Schiff base)–NaY was
collected by filtration and washed with hot water to remove
the adsorbed chloride ions (silver nitrate test). The product
was dried at 383 K for 6 h. The resulting solid was char-
acterized and used for oxidation [14, 15].
from:
ꢀ ꢁ
As
Ws
ꢀ
ꢁ
Fs ¼
Abenzene
Wbenzene
Finally, the conversion percent of phenol was calculated
from:% Conversion = 100 - % phenol.
Result and discussion
Oxidation of phenol
X-ray diffraction
In a typical reaction, an aqueous solution of 30 % H2O2
(5.67 g) and phenol (4.7 g) was mixed in 2 ml of MeCN
and added catalyst (0.025 g) to reaction mixture, then
heated (80 ꢁC) and stirred for 6 h. After filtration, the solid
was washed with solvent [16, 17]. The product subjected to
GC analyzing using a GC gas chromatograph Perkin-Elmer
1800 that equipped with a packed column OV-17 (1.5 m in
length) and a flame ionization detector (FID).
Figure 1 shows X-ray diffraction (XRD) patterns of zeolite
complexes almost same as the parent NaY zeolite [11]
where no change in crystalline pattern was seen for the
encapsulated complex which might be due to fine distri-
bution in the lattice. It appears that the metal exchange and
encapsulation condition have little effect on the crystalline
of zeolite host [18–23].
Chemical analysis results
Calculation of substrates weight percent
Analytical data for NaY, M(II)Y and M (Schiff base)/NaY
are indicated in Table 1. Result shows that percent of C, N,
H, Si and Al is almost similar to alone ligand and NaY
zeolite. The parent NaY zeolite has Si/Al the molar ratio of
2.30, which corresponds to a unit cell formula Na
56[(AlO2)56(SiO2)136]. The analytical data for C, H, N and
M(II) show that the complexes have mononuclear struc-
ture. The results show that ion exchanged metals in NaY
zeolite have a little change at Si/Al ratio. But in all samples
ratio of Si/Al has remained unchanged after created
Weight percent of each composition can be calculated from
following equation:
ꢀ ꢁ
As
Fs
ꢂ
ꢃ
%S ¼ P ꢁ 100
A
F
where, As is the peak area of each composition (cm2) in GC
chromatogram and Fs is the correction factor. For calcu-
lation of correction factor, constant amounts (Ws lg) of
phenol, catechol and hydroquinone were subjected to GC
Fig. 1 XRD for Mn(L)/NaY.
[Co(L)]/NaY, [Ni(L)]/NaY and
[Cu(L)]/NaY
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Table 1 Analytical data for
NaY, M(II) Y and M (Schiff
base)/NaY
catalyst
color
%M
%C
%N
%H
C/N
%Si
%Al
%Na
Si/Al
NaY
White
–
–
–
–
–
20.83
20.78
20.64
20.80
20.61
20.83
20.41
20.73
20.45
8.82
9.03
8.97
9.04
8.96
9.07
8.87
9.01
8.89
7.22
3.62
5.16
3.33
4.87
3.29
4.78
3.73
5.29
2.36
2.30
2.30
2.30
2.30
2.27
2.30
2.30
2.30
Mn-NaY
Mn(L)/NaY
Co-NaY
Bright pink
White
2.96
2.86
3.28
3.21
3.33
3.25
2.53
2.46
–
–
–
–
11.49
–
1.28
–
2.18
–
8.97
–
Pink
Co(L)/NaY
Ni-NaY
Brown
11.76
–
1.32
–
2.22
–
8.85
–
Bright green
Red
Ni(L)/NaY
Cu-NaY
12.29
–
1.36
–
2.63
–
9.03
–
Bright blue
Green
Cu(L)/NaY
12.36
1.35
2.34
9.15
complex. This indicates no change in the zeolite frame-
work due to the absence of dealumination in the metal ion
exchange, which has been already reported by other works
[2, 17]. The unit cell formulae of metal-exchanged zeolites
shows a metal dispersion of around 9–12 mol per unit
cell, Na33.5Mn11.2[(AlO2)56(SiO2)136]ꢀ41H2O; Na31.1Co12.4
[(AlO2)56(SiO2)136]ꢀ40H2O; Na30.8 Ni12.6[(AlO2)56(SiO2)136]ꢀ
41H2O; Na 37.4Cu9.7[(AlO2)56(SiO2)136]ꢀ53H2O. The ana-
lytical data of each complex indicate M:C:H molar ratios
almost close to those calculated for the mononuclear
structure. However, the presence of minute traces of free
metal ions in the lattice could be assumed as the metal
content is slightly higher than the stoichiometric require-
ment. Only a portion of metal ions in metal-exchanged
zeolite has undergone complexation and the rest is expec-
ted to be removed on re-exchange with sodium chloride
solution. The results show that there are free metal ions in
the lattice. These free metal ions, which could not be re-
exchanged due to the barrier by the molecules, are not
expected to cause any serious interference in the behavior
of encapsulated complexes.
Table 2 Surface area and pore volume data of complexes encapsu-
lated in nanoporous of zeolite Y
Sample
Surface area (m2/g)
Pore volume (ml/g)
NaY
620
545
422
542
417
540
415
543
420
0.36
0.31
0.27
0.31
0.26
0.31
0.24
0.31
0.25
Mn(II)-NaY
Mn(L)/NaY
Co(II)-NaY
Co(L)/NaY
Ni(II)-NaY
Ni(L)/NaY
Cu(II)-NaY
Cu(L)/NaY
1,022 cm-1 attributable to the asymmetric stretching of
Al–O–Si chain of zeolite. The symmetric stretching and
bending frequency bands of Al–O–Si framework of zeolite
appear at ca. 791 and 463 cm-1, respectively [24]. Tran-
sition metal/complexes encapsulated in the zeolite nano
cage did not show any significant shift in functional groups
stretching bond of zeolite. Hence, in the free ligands, the
band at 1,618 cm-1 arise from m (C=N) [25] see Fig. 2.
These latter stretching vibrations are shifted to lower fre-
quencies upon coordination [26–28] through azomethine
nitrogen.
Surface area (BET)
Table 2 shows BET of the catalysts are investigated. In com-
parison to the host material, a decrease in the BET surface area
and the porous volumes can be detected with all catalysts. Such
changes may be due to encapsulation occurring in them or
accessible cages at the periphery of the crystallites and not
uniformly through out the bulk of the crystallites. As the su-
percages are interconnected, a blockage at the fringe can reduce
the accessibility of many more cages in the interior [18, 19].
The diffuse reflectance of complexes when incorporated
on to zeolite is almost similar to alone complex indicating
that maintain their geometry even after encapsulation
without significant distortion. The electronic spectrum of
ligand showed two p ? p* transition at 268,336 nm
region assignable to the phenyl rings [29] and azomethine
group respectively. The electronic spectrum of the Co
(Schiff base) incorporated onto zeolite Y ([Co(L)]/NaY)
exhibits two bands at 556,652 nm which are assigned to
d ? d transitions. In addition, higher energy absorption at
425 nm has been observed such high energy bands which
have recently been shown to be characteristic of square-
planar cobalt (II) chelates [30–36]. In the electronic spec-
trum of [Ni(L)]/NaY, we have seen one peak at 436 nm
FT-IR and DRS
Table 3 shows the results of FT-IR and diffuse reflectance
spectroscopy (DRS) for M (Schiff base)/zeolite. Although,
the FT-IR bands for M (Schiff base) complex are weak due
to their low concentration in the zeolite, IR spectra of
all the hybrid materials show an intense band at ca.
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J IRAN CHEM SOC
tC=N (cm-1
)
d ? d
Table 3 The DRS and FT-IR
data of the free H2L ligand,
NaY and M(L)/NaY
Sample
Internal vibrations
External vibrations
T-O bend T-O tsym T-O tasym T-O tsym D-R Pore
opening
H2L
–
–
–
–
–
–
1,618
–
–
NaY
463
723
725
725
736
727
1,030
1,022
1,024
1,024
1,026
791
793
791
793
792
577 384
579 384
577 384
579 384
581 386
–
Mn(L)/NaY 461
Co(L)/NaY 459
1,603
1,605
1,607
1,613
–
556,652
436
Ni(L)/NaY
457
Cu(L)/NaY 459
440,549
are assigned to desorption of physical and chemical water in
NaY. The TGA curves of Mn(L)/NaY show four stage from
25 to 750 ꢁC, two stages with 7.33 % weight loss related to
desorption of water accompanied with endothermic peaks at
DTA and third step with 8.45 % weight loss is accompanied
by exothermic effect in the DTA curve indicating the
decomposition of the encapsulated complex onto zeolite. In
the case of Co(L)/NaY, the TG curve showed four stages of
decomposition in the temperature range from 25 to 750 ꢁC.
The first two stages with 7.24 % weight loss refer to the
removal of the adsorbed water from the zeolite while the third
stage from 190 to 485 ꢁC with 8.82 % weight loss is
accompanied by exothermic effect in the DTA curve indi-
cating the decomposition of the encapsulated complex and
the last stage related to phase change of zeolite. Also TG
curves for Ni(L)/NaY and Cu(L)/NaY have been shown in
four steps corresponding to a substantial loss of weight from
25 to 750 ꢁC. Two stages until 200 ꢁC with 7.35 and 9.67 %
weight loss for Ni(L)/NaY and Cu(L)/NaY, respectively,
accompanied with endothermic peaks are associated to
dehydration of physically and chemically bonded water in
samples. The third step of TGA in the temperature range from
190 to 490 ꢁC (8.25 % weight loss) and 200 to 400 ꢁC
(7.38 %) for Ni(L)/NaY and Cu(L)/NaY, respectively, due
the decomposition of the encapsulated complex that is
accompaniedbyexothermiceffectintheDTAcurve. Atleast,
the last steps with 7.30 and 6.98 % weight loss until 750 ꢁC
for Ni(L)/NaY and Cu(L)/NaY, respectively, related to phase
change of zeolite.
Fig. 2 FT-IR for H2L (a), [Ni(L)] (b), [Ni(L)]/NaY (c), NaY (d)
which is assigned to d ? d transitions of Ni?2
1
(1A1g ? Eg transitions) [15]. That it seems, correspond-
ing to square-planar geometry. The electronic spectrum of
[Cu(L)]/NaY shows one band at 549 nm, attributed to
d ? d transitions for Cu?2, indicating square-planar con-
figuration [37, 38]. The electronic spectrum of the [Mn(L)]/
NaY indicated a tetrahedral geometry, which is similar to
geometry of known tetrahedral complexes containing
oxygen–nitrogen donor atoms [39].
Catalytic activity
Thermal analysis
The effect of transition metal complexes encapsulated in
zeolite on the hydroxylation of phenol to catechol and
hydroquinone with H2O2 in CH3CN (Scheme 2) was
studied and the results are shown in Table 4.
Thermal behavior of catalysts was investigated by thermo
gravimetric analysis (TGA) and DTA (Fig. 3). The TGA
curve of NaY zeolite shows two steps from 25 to 200 (4 %)
and 220 to 550 (12.5 %) that these weight-loss steps corre-
spond to adsorption of physically and chemical water mole-
cules and assigned to some sort of phase change zeolite,
respectively, which is a typical behavior for this compound
[11]. The endothermic peaks at 110 and 150 ꢁC in DTA curve
Table 4 shows the oxidation of phenol is negligible in
the absence of transition metal catalyst under condition of
the experiments. The alone ligand was not catalytically
active. Also other products present as minor constituents
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J IRAN CHEM SOC
Fig. 3 TGA and DTA for Na Y, Mn(L)/NaY, [Co(L)]/NaY, [Ni(L)]/NaY and[Cu(L)]/NaY
could not be detected by the gas chromatography under the
conditions used herein and were neglected. The absence of
complexes in solution was confirmed by testing it for metal
ions using atomic absorption spectrophotometer and we did
not have any changes in FT-IR spectra of [ML]-NaY
zeolite. The activity of phenol oxidation decreases in
the series[Cu(L)]/NaY [ [Mn(L)]/NaY [ [Co(L)]/NaY [
[Ni(L)]/NaY. The oxidation reaction was also studied by
Niasari and co-workers [15, 35] with different complex-
based heterogeneous catalysts with radical initiator in
variety of solvents. The authors found that the conversion
of changed according to the following metal order:
Mn [ Co [ Cu [ Ni. This series is in agreement with our
study, the low catalytic activity of the nickel (II) complex
can be explained by the DFT calculations (density func-
tional theory) [40]. Accordingly, nickel (II) formed six-
coordinated pseudo-octahedral complex in the zeolite
cavity with the aromatic rings from the ligand moiety
occupying the zeolite channels. This makes the diffusion of
reactants to the active site more difficult than when the
complexes have a planar structure and they are localized
mainly in the zeolite cavity. In order to achieve suitable
reaction conditions for the maximum hydroxylation of
phenol the catalyst [Cu(L)]/NaY showed higher activity
with CH3CN solvent compared to other solvents (chloro-
form, dichloromethane and methanol in the Table 5). It
seems, CH3CN is polar solvent and there are good inter-
action between it and phenol, H2O2, catechol and hydro-
quinone, but the solvent with the donor atoms same as
methanol have the low activity because set around the
metal center. Result show the yield of catechol is further
because the intra molecular hydrogen bond at catechol
caused the interaction between it and catalyst weaker than
hydroquinone that hydroquinone keeping near the catalyst
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Table 6 The influence of the volume of CH3CN on the reaction
reflux for 6 h with 0.025 g catalyst [Cu(L)]/NaY
Amount of solvent
(ml)
Conversion
(%)
Selectivity (%)
Catechol
(%)
Hydroquinone
(%)
2
81.95
61.26
56.53
44.12
54.74
51.01
44.18
43.47
45.26
48.99
55.18
56.53
4
Scheme 2 Hydroxylation of phenol to catechol and hydroquinone
7.5
15
Table 4 Oxidation of phenol with H2O2 catalyzed by nanodimen-
sional pores of zeolite-Y-encapsulated metal complexes in CH3CN
and reflux for 6 h with 0.025 g catalyst
Fig. 4 show that the 80 ꢁC give the maximum hydroxyl-
ation yield of phenol (ca. 81.95 %). This observation seems
to imply that the reaction rate obeys the Arrhenius law.
The effect of catalyst amount is shown in Fig. 5, and the
best amount was 0.025 g with the highest percent of con-
version. Literature review shows that when the catalyst
loading increased, the activity decreased oxidation reac-
tions that proceeded from free radicals. The negative effect
of catalyst amount could be confirm termination steps
occur on the surface of catalyst. We know there are active
sites complex in the cavity and pores of zeolite [41].
The effect of phenol:H2O2 molar ratios (1:1, 2:1, 3:1 and
4:1) was studied. It is evident that the 1:1 molar ratio is the
best ratio for hydroxylation reaction.
Catalyst
Conversion (%) Selectivity (%)
Catechol (%) Hydroquinone(%)
NaY
H2L
17.82
–
67.70
–
32.30
–
[Mn(L)]/NaY 79.01
Mn/NaY 65.09
[Co(L)]/NaY 63.55
56.64
51.85
56.17
51.79
51.22
54.91
54.74
52.47
43.36
48.15
43.83
48.21
48.78
45.09
45.26
47.53
Co/NaY
57.19
45.58
79.31
[Ni(L)]/NaY
Ni/NaY
[Cu(L)]/NaY 81.95
Cu/NaY 70.50
In order to investigate of the catalytic activity of [ML]-
NaY, the catalyst was separated from the reaction system
by filtering and drying, followed by transfer to the next
reaction recycle. In recycling study, the catalyst was sep-
arated from the reaction mixture after each experiment by
filtration, washed with the solvent and dried carefully
before using it in the subsequent run. As Table 7 shows, a
rather stable conversion could be achieved after four
reactions runs.
Table 5 The effect of different solvent in oxidation reaction, reflux
for 6 h with 0.025 g catalyst [Cu(L)]/NaY
Different
solvents
Conversion
(%)
Selectivity (%)
Catechol
(%)
Hydroquinone
(%)
Acetonitrile
Chloroform
81.95
73.71
54.74
53.20
42.58
54.63
45.26
46.8
The results show that the condition of this catalyst is
mild related to other catalysts with fine yield to oxidation
reaction [42].
Dichloromethane 67.83
Methanol 59.7
57.42
45.37
Concerning the reaction mechanism, introduction of a
hydroxyl group into an aromatic ring has been considered
as a hallmark of the generation of hydroxyl radical. Thus, it
is proposed that electron transfer between framework M2?
and H2O2 will generate M3? and HO•. This high valence
for transition ions is certainly uncommon. The cycle is
closed when M3? is reduced to M2? by the cyclohexa-
dienyl radical derived from phenol [11, 27]. Scheme 3
illustrates the proposed reaction mechanism.
and H2O2 by hydrogen bond [9]. The influence of the vol-
ume of solvent (CH3CN) on the reaction is illustrated in
Table 6. The performance with 2 ml of solvent was found
to be the best under reaction conditions with 81.95 %
phenol conversion. Literature reviews show that solvent
plays an important role in catalytic behavior because it can
make different phases uniform, thus promoting mass
transportation which could also change the reaction mech-
anism by affecting the intermediate species, the surface
properties of catalysts and reaction pathways [2, 35]. In
order to study, the effect of temperature was studied with
keeping other parameters fixed. The results presented in
Kinetics of reaction
Oxidation of phenol was studied exclusively for kinetic
measurements and results of the study are as follows. In
this kinetic study, the depletion of phenol concentration in
123

J IRAN CHEM SOC
Table 7 Catalytic activity after
4 runs with 0.025 g catalyst
[Cu(L)]/NaY
T= 80 ºC
T= 60 ºC
T= 40 ºC
Catalyst
Run Conversion
(%)
90
80
70
60
50
40
30
20
10
0
[Cu(L)]/
NaY
1
2
3
4
81.95
80.53
79.28
77.85
[Cu(L)]/
NaY
[Cu(L)]/
NaY
[Cu(L)]/
NaY
0
2
4
6
8
Time (h)
Fig. 4 Effect of temperature on phenol conversion (%) for [Cu(L)]/
NaY catalyst
Conversion
Catechol
Hydroquinone
90
80
70
60
50
40
30
20
10
0
0.013
0.025
0.037
Concentrations
Fig. 5 The influence of amount of catalyst on the percentage phenol
hydroxylation
Scheme 3 The mechanism conversion of phenol to catechol and
hydroquinone
the presence of excess H2O2 was monitored and plotted
with respect to time (Fig. 6).
b
½H2O2ꢂ ¼ constant, and J ¼ ꢃd½Phenolꢂ=dt
Combining expressions (2) and (3) gives rise to
ð3Þ
ð4Þ
The reaction was carried out in the presence of 2 ml
acetonitrile, 50 mmol phenol, 50 mmol H2O2 and 0.025 g
of [Cu(L)]/NaY catalyst at 80 ꢁC in a flask and at regular
intervals and was analyzed by GC.
a
ꢃd½Phenolꢂ=dt ¼ k½phenolꢂ
If a = 1 on integrating expression (4), from the initial
concentration at initial time to the final concentration at the
final time t, then the expression (4) can be written as
The objectives of our kinetics analysis were to deter-
mine the reaction rate constant (k), its associated
Arrhenius parameters, and the reaction orders for phenol
(a), H2O2 (b) for the power-law rate expression in Eq.
(1):
ꢃlnð1 ꢃ XÞ ¼ k t
where X was the phenol conversion to products that were
obtained after a specific time period (t)
ð5Þ
a
b
Rate ¼ k0 ½Phenolꢂ ½H2O2ꢂ
ð1Þ
lnK ¼ ꢃEa=RT þ lnA : ðArrheniusÞ:
ð6Þ
In order to find a, the rate expression (1) may be
rewritten as
To determine the reaction order with respect to phenol,
we measured the phenol conversions obtained at different
temperature [43–46]. Then we carried out the integration
indicated in Eq. (6) for different integer values for the
phenol reaction order and plotted the data as –ln(1 - X) vs.
a
Rate ¼ k ½phenolꢂ
ð2Þ
If we consider the concentration of H2O2 much more
than stoichiometric ratio, then:
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J IRAN CHEM SOC
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Conclusion
R² = 0.9486
Mn(II), Co(II), Ni(II) and Cu(II) complexes with N,N-bis
(salicylidene) 4,5-dimethyl-1,2-phenylenediamine ligands
encapsulated into NaY zeolite using the flexible ligand
method. These encapsulated complexes characterized by
XRD, BET, TGA and FT-IR show well-defined inclusion
and distribution of complexes in the Y zeolite matrix. In
the second section, we consider oxidation of phenol that
was catalyzed by host–guest catalyst with hydrogen per-
oxide. Result shows that percent of product completely
depends on catalyst. Also, encapsulated complexes can be
recovered and reused without the loss of catalytic activity.
The kinetic study of phenol oxidation with excess H2O2
over [Cu(L)]/NaY catalyst at 40, 60 and 80 ꢁC was
investigated and followed a pseudo-first order with respect
to phenol and the catalytic reaction occurred via a radical
mechanism.
T= 80 ºC
T= 60 ºC
T= 40 ºC
R² = 0.9543
R² = 0.965
0
0
0.5
1
1.5
Time (h)
Fig. 6 Plot -ln(1 - X) vs. T for [Cu(L)]/NaY catalyst at 40, 60 and
80 ꢁC
1/T
0
0.0028
0.0029
0.003
0.0031
0.0032
0.0033
-0.2
-0.4
-0.6
-0.8
-1
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y = -2855.2x + 7.817
R² = 0.9981
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