Oxidation of phenol with H2O2 catalysed by Cr(III), Fe(III) or Bi(III) N,N′-bis(salicylidene)diethylenetriamine (H 2saldien) complexes encapsulated in zeolite-Y

Article abstract of DOI:10.1016/S1381-1169(02)00451-X

Cr(III), Fe(III) and Bi(III) complexes of N,N′-bis(salicylidene)diethylenetriamine (H₂saldien) encapsulated in zeolite-Y have been isolated and characterised by spectroscopic (IR and UV-Vis) studies and thermal as well as X-ray diffraction (XRD) patterns. Catalytic activities of these complexes for the decomposition of H ₂O₂ and for the oxidation of phenol to a mixture of catechol and hydroquinone using H₂O₂ as an oxidant have been studied. A best-suited condition has been optimised by considering the concentration of substrate, reaction time, amount of catalyst, oxidant and solvent for maximum transformation of phenol. Thus, for a fixed amount of phenol (4.7 g), 0.025 g of catalyst, 5.67 g of aqueous 30% H₂O ₂ and 2 ml of CH₃CN are required to carry out the reaction at 80°C in order to have maximum phenol transformation. However, selectivity towards the formation of catechol and hydroquinone vary from catalyst to catalyst. Respective neat metal complexes have also been prepared and studied for their catalytic activities for comparing these results.

Full text of DOI:10.1016/S1381-1169(02)00451-X

Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
Oxidation of phenol with H2O2 catalysed by Cr(III), Fe(III) or
Bi(III) N,Nꢀ-bis(salicylidene)diethylenetriamine (H2saldien)
complexes encapsulated in zeolite-Y
Mannar R. Mauryaa,∗, Salam J.J. Titinchia, Shri Chandb
a
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
b
Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India
Received 11 March 2002; accepted 24 July 2002
Abstract
Cr(III), Fe(III) and Bi(III) complexes of N,Nꢀ-bis(salicylidene)diethylenetriamine (H2saldien) encapsulated in zeolite-Y
have been isolated and characterised by spectroscopic (IR and UV-Vis) studies and thermal as well as X-ray diffraction (XRD)
patterns. Catalytic activities of these complexes for the decomposition of H2O2 and for the oxidation of phenol to a mixture
of catechol and hydroquinone using H2O2 as an oxidant have been studied. A best-suited condition has been optimised by
considering the concentration of substrate, reaction time, amount of catalyst, oxidant and solvent for maximum transformation
of phenol. Thus, for a fixed amount of phenol (4.7 g), 0.025 g of catalyst, 5.67 g of aqueous 30% H2O2 and 2 ml of CH3CN
are required to carry out the reaction at 80 ◦C in order to have maximum phenol transformation. However, selectivity towards
the formation of catechol and hydroquinone vary from catalyst to catalyst. Respective neat metal complexes have also been
prepared and studied for their catalytic activities for comparing these results.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Oxidation of phenol; Decomposition of H2O2; Zeolite-Y; Encapsulation; Catechol and hydroquinone formation
1. Introduction
selective, ecologically pure and consume minimum
energy. At least creating organised molecular sys-
tems, which are designed to have an optimum space
arrangement, energy and orbital correspondence of
the catalytic system components and substrates, can
solve some of these problems.
Zeolites are one of the most important catalysts
being used in chemical industries on large scale due
to their inherent capabilities of product selectivity.
Encapsulation of metal complexes in the super cages
of zeolite matrix possess the advantages of solid het-
erogeneous catalysts like easy separation, ruggedness,
etc., as well as share many advantageous features of
homogeneous catalysts. Various transition metal com-
plexes of H2salen (H2salen: N,Nꢀ-bis(salicylidene)
Catalysis is known to play a key role in mod-
ern chemical technologies. Nowadays it is generally
agreed that the key role in catalytic reactions is
played by intermediate chemical interaction of reac-
tive molecules with definite functional groups (active
sites) of homogeneous, heterogeneous or biological
(enzyme) catalysts. Modern catalytic science faces
even more complicated and challenging problems.
These are connected with the urgent necessity to cre-
ate new highly effective industrial process, which are
∗
Corresponding author. Fax: +91-1332-73560.
E-mail address: rkmanfcy@iitr.ernet.in (M.R. Maurya).
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(02)00451-X

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M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
ethane-1,2-diamine) and its other substituted deriva-
tives have been encapsulated in zeolite-Y matrix and
their catalytic activities have been studied towards
decomposition of H2O2 and tert-butyl hydroperox-
ide [1–3]; selective epoxidation/oxidation of olefins
[4–8] and styrene [9]; oxidation of cyclohexanol
and phenol [10], and selective hydrogenation [11].
Recently, oxidation of p-xylene using [Mn(salpn)]
(H2salpn: N,Nꢀ-bis(salicylidene)propane-1,3-diamine)
encapsulated in super cages of zeolite-Y [12] and
oxidation of phenol using Cr(III), Fe(III), Bi(III),
Cu(II), Ni(II) and Zn(II) complexes of H2salpn en-
capsulated in zeolite-Y matrix [13,14] have been re-
ported. The N,Nꢀ-bis(salicylidene)diethylenetriamine
(H2saldien (I)) is potential dibasic pentadentate ligand
with good flexibility and may give stable transition
metal complexes. Encapsulation of these complexes
in the cavity of zeolite-Y may, thus, provide bet-
ter catalytic activity. In the present investigation,
we have, therefore, encapsulated and characterised
Cr(III), Fe(III) and Bi(III) complexes of H2saldien
(I) in the super cages of zeolite-Y matrix. Catalytic
activities of these complexes have been studied to-
wards the decomposition of H2O2 and the oxida-
tion of phenol. Neat complexes of the above metal
ions have also been prepared and their catalytic ac-
tivities have been compared with the encapsulated
ones. Only Mn(III) complex of H2-5,5ꢀ-dinitrosaldien
(N,Nꢀ-bis(5,5ꢀ-dinitrosalicylidene)diethylenetriamine)
has been prepared and used as catalyst for the epoxi-
dation of (Z)-␤-methylstyrene [15].
further purification. All other chemicals and solvents
used were also of AR grade. Zeolite-Y (Si/Al ∼ 10)
was obtained from Indian Oil Corporation (R&D),
Faridabad, India.
2.2. Physical methods and analysis
IR spectra were recorded as KBr pellet on a
Perkin-Elmer model 1600 FT-IR spectrometer. Elec-
tronic spectra were recorded in Nujol on Shimadzu
1601 UV-Vis spectrophotometer by layering mull of
sample to inside of one of the cuvette while keeping
another one layered with Nujol as reference. Thermo-
gravimetric analyses of the pure as well as encapsu-
lated complexes were carried out using TG Stanton
Redcroft STA 780. X-ray diffractograms of solid cat-
alysts were recorded using Philips PW 1140/90 X-ray
powder diffractometer with Cu K␣ target at the Sci-
entific Instrumentation Centre of our Institute. The
metal contents were measured by using Perkin-Elmer
model 3100 atomic absorption spectrophotometer.
All catalysed reaction products were analysed using
Nucon 5700 gas chromatograph fitted with FID de-
tector, a 2 m × 2 mm (i.d.) OV-17 (s.s.) column and
ORACLE 2 computer software.
2.3. Preparations
2.3.1. Preparation of ligand (H2saldien)
H2saldien was prepared by following the litera-
ture procedure with slight modification [16]. Salicy-
laldehyde (12.2 g, 0.1 mol) was dissolved in 75 ml
of methanol, and to this was added a solution of
diethylenetriamine (5.15 g., 0.05 mol) in 25 ml of
methanol. The reaction mixture thus obtained was
refluxed on a water bath for 1 h. After reducing the
volume of the solvent to ca. 50 ml, the content was
transferred into a beaker and excess solvent was
evaporated under the current of air where viscous
yellow-red oil was obtained. This was further dried in
vacuum.
2. Experimental
2.1. Materials
2.3.2. Preparation of M-Y (metal-exchanged
zeolite-Y)
Metal nitrates (nitrates of Cr(III), Fe(III), and
Bi(III)), 30% aqueous H2O2 and phenol (Qualigens,
India) were of Analar grade. Salicylaldehyde and di-
ethylenetriamine (E. Merck, India) were used without
An amount of 5.0 g zeolite Na-Y was suspended
in 300 ml distilled water containing metal nitrate
(50 mmol) (nitrates of Fe(III), Cr(III) or Bi(III)).
The mixture was then heated while stirring at 90 ◦C

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
167
for 24 h. The solid was filtered, washed with hot
distilled water till the filtrate was free from any
non-encapsulated metal ion content and dried for 12 h
at 150 ◦C in air.
reaction mixture and the reaction was considered to
begin. The reaction products were analysed using a gas
chromatograph after specific interval of time by with-
drawing small aliquot out. The effect of various pa-
rameters such as amount of oxidant, amount of catalyst
and volume of solvent have been taken into considera-
tion in order to study their effect on the reaction. How-
ever, basic procedure is same as outlined previously.
2.3.3. Preparation of [M(saldien)·H2O]Cl-Y
The encapsulated complexes were prepared by gen-
eral flexible ligand method [1,4]. An amount of 1.0 g
M-Y and 2.5 g H2saldien were mixed in a round bot-
tom flask. The reaction mixture was heated at 100 ◦C
overnight (∼14 h) in an oil bath with constant stirring.
The ligand acted as solvent as well as reactant. The
resulting material was taken out and extracted with
methanol using Soxhlet extractor till the complex was
free from unreacted H2saldien. The non-complexed
metal ions present in the zeolite were removed by
exchanging with aqueous 0.01 M NaCl solution. The
resulting solid was finally washed with hot distilled
water till no precipitation of AgCl was observed on
reacting filtrate with AgNO3 solution. This was then
dried at 150 ◦C for several hours till constant weight
was achieved.
2.4.3. Oxidation of 2,4-dichlorophenol and
1-naphthol
An amount of 2,4-dichlorophenol (8.15 g, 0.05 mol)
or 1-naphthol (7.2 g, 0.05 mol) and H2O2 (5.67 g,
0.05 mol) was taken in 2 ml of CH3CN and heated
at 80 ◦C. After addition of [Cr(saldien)·H2O]Cl-Y
(0.025 g), the reaction was carried out for 4 h and at
the end, the products were analysed as mentioned
previously.
3. Results and discussion
3.1. Syntheses and characterisation of catalysts
2.4. Catalytic activity studies
Synthesis of metal encapsulated complexes in the
super cages of zeolite-Y was carried out by flexible
ligand method which consisted of mainly two steps:
(i) the preparation of M-Y (M: Cr(III), Fe(III) and
Bi(III)), which is straight forward; and (ii) the heat-
ing of metal-exchanged zeolite in excess of ligand at
100 ◦C for ca. 14 h. Second step allowed the insertion
of the ligand in the cavity of the zeolite followed by
its complexation with metal ions. Complexation of
H2saldien with Cr(III) and Fe(III) ions were accompa-
nied by the colour change, while Bi(III) gave colour-
less compound. The crude mass was finally purified
by Soxhlet extraction method using methanol. The
remaining non-complexed metal ions in zeolite were
removed by exchanging with aqueous 0.01 M NaCl
solution. The percentage of metal contents estimated
before and after encapsulation by atomic absorption
spectroscopy (AAS) is presented in Table 1. The
metal ion contents thus estimated after encapsulation
are only due to the presence of metal complexes in
zeolite framework. The physico-chemical properties
of the metal complexes encapsulated in the zeolite-Y
were confirmed by recording their IR and UV-Vis
spectra, thermal analysis and X-ray powder diffraction
2.4.1. Decomposition of H2O2
An amount of 0.025 g of encapsulated catalyst was
added to an aqueous solution of 30% H2O2 (5.5 g,
0.049 mol) at room temperature (25 ◦C) and the re-
action mixture was stirred for the stipulated time (1
or 2 h). At the end of the reaction, the catalyst was
filtered and the filtrate was diluted to 250 ml with
distilled water. Ten millilitres of this solution was
withdrawn and after addition of 20 ml of 2 M H2SO4
and 20 ml of distilled water, it was titrated against
standard KMnO4 solution. Similar experiment was
also performed with neat complexes by using 0.004 g
of catalyst, while keeping other conditions same as
mentioned previously.
2.4.2. Oxidation of phenol
The catalytic activity measurements were carried
out in a 50 ml glass reaction flask fitted with a water
condenser. Phenol (4.7 g, 0.05 mol) and 30% aqueous
H2O2 (5.67 g, 0.05 mol) were mixed in 2 ml of CH3CN
and the reaction mixture was heated with continuous
stirring in an oil bath maintained at 80 ◦C. The cat-
alyst for the activity test (0.025 g) was added to the

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M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
at 150 ◦C for several hours, it is expected that even
at this temperature intra-zeolite water will remain
present in the catalyst. In fact, the presence of at least
four such water molecules have been reported for
[Cu(salen)]-Y [10,17–19]. Thermal decomposition of
remaining anhydrous moieties occurs in two steps.
The exothermic loss starts immediately after the first
step. This loss may be due to one water molecule and
chloride ion associated with the complex. As these
catalysts were treated with aqueous NaCl, the pres-
ence of Cl− counter ion is expected in all cases. A
rather small weight loss (8–10%) occurs in the next
step (which starts immediately after the second step)
having a wider temperature range of 275–800 ◦C.
This is due to the decomposition of chelating ligand.
A very small weight percentage loss indicates the
insertion of only small amount of metal complexes in
the zeolite-Y matrix.
Table 1
Chemical composition, physical and analytical data of M-Y and
encapsulated catalysts
Serial no. Compound
Colour
Metal content
(wt.%)
1
2
3
4
5
6
Cr-Y
Fe-Y
Bi-Y
Green
Brown
White
1.67
0.55
2.17
[Cr(saldien)·H2O]Cl-Y Light green 1.34
[Fe(saldien)·H2O]Cl-Y Light brown 0.36
[Bi(saldien)·H2O]Cl-Y White
1.90
(XRD) pattern and comparing their properties with
that of the simple complexes prepared by the reaction
of H2saldien with the respective metal nitrates. The
formulations of the encapsulated complexes (Table 1)
are, thus, based on the respective simple complex.
The Si/Al ratio of 9.67 corresponds to a unit cell
of formula Na18(AlO2)18(SiO2)174. If we consider
about 250 water molecules associated with this, then,
from the metal content estimated in encapsulated
complexes, the calculated metal complex per unit cell
corresponds to ∼1.1 for Fe-based, ∼4.2 for Cr-based
and ∼1.5 for Bi-based catalysts.
3.3. X-ray powder diffraction studies
The X-ray powder diffraction pattern of Na-Y, its
metal-exchanged zeolite M-Y (M: Cr(III), Fe(III)
and Bi(III)) and encapsulated metal complexes
[M(saldien)·H2O]Cl-Y were recorded at 2θ values
between 5 and 70◦. Typical XRD patterns of Cr-Y
and [Cr(saldien).H2O]Cl-Y are shown in Fig. 1.
All metal-exchanged and encapsulated species ex-
hibit essentially similar pattern to that observed for
Na-Y. However, slight change in the intensities of the
peaks could be observed. The appearance of peaks
in metal-exchanged zeolite and encapsulated ones
suggest that the super cages of the zeolite are able to
accommodate these complexes and the crystallinity
3.2. TGA studies
The thermogravimetric analysis (TGA) data of
the encapsulated catalysts along with the percent-
age weight loss at different steps and their probable
assignments are presented in Table 2. All catalysts
record an endothermic loss of 14–16% in the tem-
perature range 150–280 ◦C due to the presence of
intra-zeolite water. Though all catalysts were dried
Table 2
Thermogravimetric analysis data of catalysts
Catalyst
Temperature range (◦C)
Loss (wt.%)
Group losta
Type of loss
[Cr(saldien)·H2O]Cl-Y
150–230
230–275
275–650
16.0
2.0
8.0
nH2O
H2O + Cl
L
Endothermic
Exothermic
Exothermic
[Fe(saldien)·H2O]Cl-Y
[Bi(saldien)·H2O]Cl-Y
150–240
240–295
295–800
15.0
4.0
10.0
nH2O
H2O + Cl
L
Endothermic
Exothermic
Exothermic
150–280
280–360
360–560
14.0
4.0
10.0
nH2O
H2O + Cl
L
Endothermic
Exothermic
Exothermic
a L stands for saldien2−
.

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
169
Fig. 1. XRD patterns of (a) Cr-Y, and (b) [Cr(saldien)·H2O]Cl-Y.
of the zeolite-Y is maintained during encapsulation.
Two new peaks with d values of 3.392 nm (at 2θ =
29.2) and 2.181 nm (at 2θ = 46.0) were observed in
Cr-Y as well as in [Cr(saldien)·H2O]Cl-Y. In Bi-Y as
well as [Bi(saldien)·H2O]Cl-Y, two new peaks with
d values of 3.415 nm (at 2θ = 29.0) and 2.741 nm
(at 2θ = 36.3) were also observed. As encapsulated
complexes were carefully extracted with methanol
and then re-exchanged with NaCl to remove surface
species and non-complexed metal ions, respectively,
the existence of new peaks in the metal-exchanged
and encapsulated zeolites could be attributed to
atomic level integration resulting in non-vanishing
structure factor for certain peaks which were extinct
in Na-Y structure. Location of any new peaks in
[Fe(saldien)·H2O]Cl-Y was not possible due to poor
resolution of these peaks in the XRD pattern.
presented in Table 3 and the spectra of the encapsu-
lated complexes are reproduced in Fig. 2. The spec-
trum of H2saldien exhibits four bands at 402, 316,
255 and 220 nm. As molar absorptivity of the first
two bands are comparatively low, these bands seem
∗
to be splitter band of n–␲ transition. Other bands
∗
∗
are due to ␲–␲ and ␾–␾ transitions, respectively.
A weak shoulder band also appears at 280 nm, which
is assigned as intramolecular hydrogen bonding. The
shoulder band is completely absent in the spectra of
all complexes, thereby indicating the destruction of
hydrogen bonding and coordination of phenolic oxy-
gen to metal ion. In complexes, the first two bands
merge and appear at 306–385 nm, while 255 nm
band shifts to higher wave length (255–282 nm) and
220 nm band has no definite trend. The absorption
spectra of encapsulated complexes are essentially
similar to the corresponding neat complexes. The
spectral bands appearing at 553 (weak and broad)
and 385 nm (which is merging with the ligand band)
in [Cr(saldien)·H2O]Cl-Y or at 560 and 415 nm in
[Cr(saldien)·H2O]Cl compare well with the reported
3.4. UV-Vis and IR spectral studies
Electronic absorption spectra of ligands and cat-
alysts (encapsulated as well as neat complexes) are

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M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
Table 3
IR and electronic spectral data of ligand and its neat and encapsulated complexes
Compound
IR (cm−1
)
λmax
=
=
ν(C N), (C C)
ν(M-O)/(M-N)
Solvent
Band (nm)
H2saldien
1583, 1634
1543, 1625
1540, 1622
1545, 1632
1548, 1630
1542, 1636
1542, 1620
–
MeOH
Nujol
DMF
Nujol
DMF
Nujol
Nujol
402, 316, 280, 255, 220
553, 385, 265, 215
560, 415, 306, 277
480, 325, 265, 230
470, 308, 281
[Cr(saldien)·H2O]Cl-Y
[Cr(saldien)·H2O]Cl
[Fe(saldien)·H2O]Cl-Y
[Fe(saldien)·H2O]Cl
[Bi(saldien)·H2O]Cl-Y
[Bi(saldien)·H2O]Cl
412, 427, 481, 503
436, 480, 517
466, 499
466, 486
451, 472, 506
417, 435, 463, 508
255, 210
263, 220
value for [Cr(H2O)6]3+ [20], where these bands ap-
pear at 574.7 and 405 nm, respectively. Accordingly,
complexes, the intensity of the peaks is weak due to
low concentration of the complexes in zeolite matrix.
Comparison of the band positions of ligands with
metal complexes reveal the following facts: (i) the
band appearing in the 2550–2700 cm−1 region due to
intramolecular hydrogen bonding between phenolic
–OH and azomethine nitrogen is absent. This observa-
tion indicates the coordination of phenolic oxygen to
the metal after destruction of hydrogen bond; and (ii)
4
4
these bands are assigned due to A2g(F) → T2g(F)
4
4
(ν1) and to A2g(F) → T1g(F) (ν2) transitions,
respectively, in an octahedral fields. The band due
4
4
to A2g(F) → T2g(P) transition, which appears
at 270 nm in [Cr(H2O)6]3+ could not be located in
present Cr(III) complexes due to strong absorption of
ligand band in this region. Iron complexes exhibit one
d–d band at ∼480 nm as a weak band [21] while Bi(III)
complexes exhibit, as expected, ligand bands only.
A partial list of IR spectral data of H2saldien and en-
capsulated as well as neat complexes is also presented
in Table 3. Though, IR spectra of all encapsulated
complexes are essentially similar to that of neat
=
the free ligand exhibits ν(C N) (azomethine) stretch
at 1583 cm−1. This band shifts to lower frequency
in complexes and appears at 1540–1548 cm−1, in-
dicating the involvement of azomethine nitrogen in
coordination. The coordination of –NH group could
not be ascertained due to the appearance of broad
Fig. 2. Electronic spectra of: (– – –) [Cr(saldien)·H2O]Cl-Y, (—) [Fe(saldien)·H2O]Cl-Y, (— · —) [Bi(saldien)·H2O]Cl-Y.

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
171
Table 4
Percentage decomposition of H2O2 after 1 and 2 h of contact time
Catalyst
Percentage
decomposition
after 1 h
TOF
Percentage
decomposition
after 2 h
TOF
[Fe(saldien)·H2O]Cl-Y
[Cr(saldien)·H2O]Cl-Y
[Bi(saldien)·H2O]Cl-Y
[Fe(saldien)·H2O]Cl
[Cr(saldien)·H2O]Cl
[Bi(saldien)·H2O]Cl
4.9
11.0
13.3
3.5
1.8
4.7
44.9
95.7
174.5
164.5
74.8
6.2
12.6
15.9
5.9
7.0
11.8
24.4
39.9
74.2
137.5
148.3
389.4
313.0
Turn over frequency (TOF): moles of substrate converted per mole of metal (in solid catalyst) per hour.
band of water ∼3400 cm−1. However, appearance
of two to four bands in the low frequency region
(400–550 cm−1) should indicate the coordination of
phenolic oxygen, azomethine nitrogen and nitrogen
of –NH group. Thus, IR data further supports the
encapsulation of the complex in the zeolite matrix.
higher than the encapsulated one where only 0.025 g
of catalysts are used.
3.6. Oxidation of phenol
The catalytic oxidation of phenol usually gives
two products catechol and hydroquinone as shown by
Eq. (1). These products are the only expected ones,
as –OH group of phenol is ortho and para directing.
Similar oxidation using H2O2 as an oxidant were
also conducted with three different catalysts, viz.
[Cr(saldien)·H2O]Cl-Y, [Fe(saldien)·H2O]Cl-Y and
[Bi(saldien)·H2O]Cl-Y in CH3CN. Only two prod-
ucts, i.e. catechol and hydroquinone were obtained
with a mass balance of about 96% for all catalysts.
Minor product (e.g. polymeric materials), if any, is not
detectable in GC under the condition used herein. For
comparison, their respective neat metal complexes,
viz. [Cr(saldien)·H2O]Cl, [Fe(saldien)·H2O]Cl and
[Bi(saldien)·H2O]Cl have also been examined for
their catalytic activities. In order to find suitable reac-
tion conditions to get maximum oxidised products for
a fixed amount of phenol, effect of various parame-
ters, such as, amount of catalyst, H2O2 concentration
(moles of H2O2 per mole of phenol) and volume of
solvent have been taken into consideration.
3.5. Decomposition of H2O2
The catalytic activity of all encapsulated complexes
for the decomposition of H2O2 at different reaction
times was tested and the relevant data are presented
in Table 4. The decomposition of H2O2 catalysed
by Fe-based catalyst after 1 h reaction time is rather
slow (4.9%), while Cr- and Bi-based catalysts showed
decomposition of 11.0 and 13.3%, respectively. In-
creasing contact time to 2 h has improved partially the
decomposition and were found in the order: Bi(III)
(15.9%) > Cr(III) (12.6%) > Fe(III) (6.2%). The turn
over frequency (TOF) calculated for the decompo-
sition of H2O2 after 1 and 2 h of contact time is
presented in Table 4. The TOF for 1 h of contact fol-
lows the same order as for percentage decomposition.
Due to marginal increase in percentage decomposi-
tion of H2O2 in the next 1 h, there is considerable
decrease in TOF during that period. However, the
order with respect to the catalysts is same as noted
previously.
The catalytic activity of neat complexes in the de-
composition of H2O2 at two different reaction times
(e.g. 1 and 2 h) has also been determined and the data
are is presented in Table 4. It is clear from the TOF
values that neat complexes show better catalytic activ-
ity than the encapsulated ones. It is expected as num-
ber of metal centres in 0.004 g of neat catalysts are
(1)
Using three different concentrations of aqueous
30% H2O2, viz. 0.015 mol (1.7 g), 0.03 mol (3.4 g)

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M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
and 0.05 mol (5.67 g) for a fixed amount of phenol
(4.7 g) and catalyst [Cr(saldien)·H2O]Cl-Y (0.025 g),
the percentage of phenol conversions are 15.3, 31.2
and 45.0%, respectively. For these concentrations
of H2O2, the percent selectivity for the conversion
of H2O2 follows the order: 50.3% (0.015 mol) <
53.0% (0.03 mol) < 45.0% (0.05 mol). These results
suggest that oxidation of phenol is highest with 1:1
phenol/H2O2 molar ratio, though selectivity of H2O2
conversion is relatively low at this ratio. Further in-
crement in H2O2 concentration hardly improved the
conversion. This clearly suggests that large concen-
tration of oxidant is not an essential condition to max-
imise phenol transformation. Similarly, out of three
different weights of 0.01, 0.025 and 0.03 g of cata-
lyst, an amount of 0.025 g for all three catalysts was
found to be sufficient enough for the effective phenol
conversion. Variation in the volume of the solvent
was also studied by taking 1, 2 and 4 ml of CH3CN.
It was observed that for 4.7 g of phenol, 0.025 g of
catalyst and 5.67 g of 30% H2O2, 2 ml of CH3CN
was sufficient enough to carry out the reaction to get
good transformation of phenol. Thus, all conditions
as concluded previously were considered essential
and applied for the maximum transformation of phe-
nol into a mixture of catechol and hydroquinone. In
order to compare the efficiency of the catalysts under
best-required conditions, the percentage of phenol
conversion and the percentage of the formation of
catechol and hydroquinone were plotted as a function
of time and are presented in Figs. 3–5.
Fig. 3. Phenol oxidation: (ᮀ) [Cr(saldien)·H2O]Cl-Y, (᭹)
[Fe(saldien)·H2O]Cl-Y, (᭝) [Bi(saldien)·H2O]Cl-Y.
Fig. 4. Percentage catechol formation: (ᮀ) [Cr(saldien)·H2O]Cl-Y,
(᭹) [Fe(saldien)·H2O]Cl-Y, (᭝) [Bi(saldien)·H2O]Cl-Y.
Fig. 5. Percentage hydroquinone formation: (ᮀ) [Cr(saldien)·H2O]Cl-Y, (᭹) [Fe(saldien)·H2O]Cl-Y, (᭝) [Bi(saldien)·H2O]Cl-Y.

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
173
Table 5
The plot presented in Fig. 3 shows that phenol
conversion increases considerably in the first 75 min
for Cr-based catalyst and reaches to a steady state
thereafter. The activities of Fe- and Bi-based catalyst
were fast enough till first 60 and 90 min, respectively,
and slowly go down in the next 30 min in both cases.
Among these three catalysts, [Cr(saldien)·H2O]Cl-Y
performed best and gave a highest conversion of
about 45%, whereas, [Bi(saldien)·H2O]Cl-Y and
[Fe(saldien)·H2O]Cl-Y recorded conversions of about
33 and 28%, respectively.
Selectivity of catechol and hydroquinone formation after 6 h of
reaction time
Catalyst
Catechol (%)
Hydroquinone (%)
[Cr(saldien)·H2O]Cl-Y
[Fe(saldien)·H2O]Cl-Y
[Bi(saldien)·H2O]Cl-Y
[Cr(saldien)·H2O]Cl
[Fe(saldien)·H2O]Cl
[Bi(saldien)·H2O]Cl
68.8
83.9
84.8
63.9
63.8
70.5
31.2
16.1
15.2
36.1
36.2
29.5
tive (∼16%) for the hydroquinone formation (Table 5).
The [Cr(saldien)·H2O]Cl-Y has shown only ∼69%
selectivity for the formation of catechol and ∼31%
for the formation of hydroquinone.
Fig. 4 presents percentage catechol formation as
a function of reaction time. A maximum of 31%
of catechol formation was recorded with Cr-based
catalyst. On the other hand, using Bi-based catalyst,
catechol formation was only about 28%, which was
followed by Fe-based catalyst (24%). In compar-
ison to catechol formation, the hydroquinone for-
mation (Fig. 5) is much lower in all the cases and
follow the order: [Cr(saldien)·H2O]Cl-Y (13%) >
[Fe(saldien)·H2O]Cl-Y (5%) > [Bi(saldien)·H2O]Cl-Y
(4%). Increasing the reaction time from 6 to 24 h does
not show appreciable change in either phenol trans-
formation or catechol and hydroquinone formation.
Fig. 6 summarises all these results together as bar di-
agram after 6 h of reaction time. On comparing plots
it is clear that [Cr(saldien)·H2O]Cl-Y is much bet-
ter catalyst in comparison to [Bi(saldien)·H2O]Cl-Y,
which in turn is better than [Fe(saldien)·H2O]Cl-Y in
terms of phenol transformation as well as formation
of catechol and hydroquinone. However, in terms of
selectivity, the later two catalysts are more selective
(∼84%) for the catechol formation, while less selec-
Catalytic oxidation of phenol using the corre-
sponding neat complexes, viz. [Cr(saldien)·H2O]Cl,
[Fe(saldien)·H2O]Cl and [Bi(saldien)·H2O]Cl as cat-
alyst and H2O2 as oxidant have also been studied
in CH3CN. A similar trend, i.e. higher conversion
of phenol with 0.05 moles of H2O2, as noted pre-
viously was also observed among the three concen-
trations of oxidant, viz. 0.015, 0.03 and 0.05 moles
for a fixed amount of phenol (4.7 g) and catalyst
(0.004 g). However, conversion was considerably
lower in comparison to that of encapsulated ones
and followed the order: [Cr(saldien)·H2O]Cl (31%)
> [Fe(saldien)·H2O]Cl (22%) > [Bi(saldien)·H2O]Cl
(21%) after 6 h of reaction time. The Fig. 7 plotted
for the phenol conversion as a function of time indi-
cates that conversion also increases in the first 60 min
considerably and reaches the steady state in next
few min. The percentage catechol and hydroquinone
Fig. 6. Bar diagram showing phenol conversion and catechol and
hydroquinone formation for various catalysts (encapsulated). Inset
shows notation for respective catalyst.
Fig. 7. Phenol oxidation: (ᮀ) [Cr(saldien)·H2O]Cl, (᭹)
[Fe(saldien)·H2O]Cl, (᭝) [Bi(saldien)·H2O]Cl.

174
M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
Fig. 8. Percentage catechol formation: (ᮀ) [Cr(saldien)·H2O]Cl, (᭹) [Fe(saldien)·H2O]Cl, (᭝) [Bi(saldien)·H2O]Cl.
formations versus time profiles are shown in Figs. 8
and 9 and reveal that the catechol formation is al-
ways higher than hydroquinone formation. However,
within the catechol formation the order: Cr (22%) >
Fe (16%) = Bi (16%) while hydroquinone is nearly
same and is about 8.0 0.5% in all cases after 6 h of
reaction time.
phenol. Following factors may be responsible for this.
(i) The neat complexes may lead to the formation of
␮-oxo dimer or possibility of the dimerisation as such
during reaction, which is responsible for the lower cat-
alytic performance. Dimerisation of [Cu(5-X-salen)]
(where X: H, CH3O) during re-crystallisation has also
been observed [22]. (ii) Neat complexes being active
in the first cycle are partially destroyed during the pro-
longed contact time while no such possibility exists in
encapsulated complexes. However, selectivity of these
catalysts towards the product formation differs with
the increment of phenol conversion. The selectivity
to percentage catechol formation versus percentage
conversion of phenol profiles for all catalysts during
6 h reaction time are shown in Fig. 10. This indicates
that selectivity of catechol formation is relatively bet-
ter with encapsulated complexes. However, with the
conversion of phenol it slowly goes down with time
and follow the order: Bi(III) (86%) > Fe(III) (84%)
> Cr(III) (72%). In neat complexes selectivity of for-
mation of catechol suddenly decreases from ∼98 to
62% at 20% conversion of phenol with Fe(III) and
Bi(III) complexes, while from 92 to 71% at about
30% conversion with Cr(III) complex. Thus, it can
be concluded that at the expense of phenol conver-
sion selectivity of the formation of catechol decreases
while selectivity of hydroquinone increases. However,
either conversion of phenol or formation of a mixture
of catechol and hydroquinone are all stabilised after
about 6 h of reaction time and no more change in
their formations are observed beyond this time.
3.7. Catalytic activities comparison of neat and
encapsulated complexes
On comparing the data for neat complexes and
complexes encapsulated in zeolite matrix, it is clear
that encapsulated complexes are always better over
non-encapsulated ones for the transformation of
Fig. 9. Percentage hydroquinone formation: (ᮀ) [Cr(saldien)
·H2O]Cl, (᭹) [Fe(saldien)·H2O]Cl, (᭝) [Bi(saldien)·H2O]Cl.

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
175
Fig. 10. Selectivity to percentage catechol formation vs. percentage phenol conversion: (᭝) [Cr(saldien)·H2O]Cl-Y, (᭿)
[Bi(saldien)·H2O]Cl-Y, (᭛) [Fe(saldien)·H2O]Cl-Y, ( ) [Cr(saldien)·H2O]Cl, (᭹) [Bi(saldien)·H2O]Cl, (᭺) [Fe(saldien)·H2O]Cl.
3.8. Oxidation of 2,4-dichlorophenol and 1-naphthol
and 0.025 g catalyst in 2 ml CH3CN at 80 ◦C). Be-
sides, the lower percentage conversion for the oxida-
tion of 2,4-dichlorophenol or 1-naphthol using H2O2
as an oxidant further supports the encapsulation of
metal complexes in the super cages of the zeolite-Y
matrix. Steric hindrance would make their entrance
difficult through channels of the zeolite to reach the
proximity of the catalyst and thus responsible for its
poor performance.
It is concluded from the catalytic data that the en-
capsulated complexes are better catalysts than neat
ones. Under best-suited reaction conditions, catechol
formation is always higher than hydroquinone forma-
tion. However, at the expense of phenol conversion
selectivity of the formation of catechol decreases,
while selectivity of hydroquinone increases in the
beginning, but their formation stabilise after ∼6 h
of reaction time. Comparable IR spectral patterns of
fresh and used encapsulated catalysts suggest that
these can be used further for catalytic study.
Using the typical reaction conditions opti-
mised for the oxidation of phenol, oxidation of
2,4-dichlorophenol and 1-naphthol was also carried
out. As we go from smaller to bulkier substrates,
their entrance through the opening of the zeolite pore
becomes more and more difficult and would result
in lower catalytic activity. As expected, only about
4% conversion of 2,4-dichlorophenol was observed
due to branching of phenol. However, oxidation of
1-naphthol was found to be about 11%. Although, we
expect better conversion for 2,4-dichlorophenol than
1-naphthol due to relatively smaller size of the former,
the two deactivating groups (i.e. chloro substituents)
are probably responsible for less conversion.
4. Summary and conclusions
The integrity of metal complexes encapsulated
in the cavities of zeolite-Y was confirmed by spec-
troscopic studies as well as chemical and thermal
analysis. This was further supported by the fact that
no leaching of metal ion was detected in the solution
when a blank reaction was carried out (5.5 g H2O2
Acknowledgements
S.J.J.T. thanks Indian Council for Cultural Relation
(ICCR) for fellowship. The authors are thankful to

176
M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 165–176
Prof. S. Ray of Metallurgical and Materials Engineer-
ing Department, IIT Roorkee, for a fruitful discussion.
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[13] M.R. Maurya, S.J.J. Titinchi, S. Chand, I.M. Mishra, J. Mol.
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