Zeolite-Y encapsulated nanohybrid materials: Synthesis, spectroscopic characterization, and catalytic significance

Article abstract of DOI:10.1080/00958972.2012.656616

The goal of this study is to synthesize zeolite-Y encapsulated nanohybrid materials (ZENMs) of the general formulae [M(VTCH)₂]-Y or [M(VFCH)₂]-Y (where M=Mn(II), Co(II), Ni(II), and Cu(II); VTCH=vanillin thiophene-2-carboxylic hydraz

Full text of DOI:10.1080/00958972.2012.656616

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Zeolite-Y encapsulated nanohybrid materials:
synthesis, spectroscopic characterization, and
catalytic significance
C.K. Modi & Parthiv M. Trivedi
To cite this article: C.K. Modi & Parthiv M. Trivedi (2012) Zeolite-Y encapsulated nanohybrid
materials: synthesis, spectroscopic characterization, and catalytic significance, Journal of
Coordination Chemistry, 65:3, 525-538, DOI: 10.1080/00958972.2012.656616
To link to this article: http://dx.doi.org/10.1080/00958972.2012.656616
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Date: 09 December 2015, At: 16:16

Journal of Coordination Chemistry
Vol. 65, No. 3, 10 February 2012, 525–538
Zeolite-Y encapsulated nanohybrid materials: synthesis,
spectroscopic characterization, and catalytic significance
C.K. MODI* and PARTHIV M. TRIVEDI
Department of Chemistry, Bhavnagar University, Bhavnagar – 364 002, Gujarat, India
(Received 19 September 2011; in final form 12 December 2011)
The goal of this study is to synthesize zeolite-Y encapsulated nanohybrid materials (ZENMs) of
the general formulae [M(VTCH)2]-Y or [M(VFCH)2]-Y (where M ¼ Mn(II), Co(II), Ni(II), and
Cu(II); VTCH ¼ vanillin thiophene-2-carboxylic hydrazone; VFCH ¼ vanillin furoic-2-car-
boxylic hydrazone) and describe their selective catalytic activities. ZENMs are characterized by
various physico-chemical techniques, namely ICP-OES, elemental analysis, (FT-IR and
electronic) spectral studies, SEMs, X-ray diffraction patterns as well as surface area
measurements. The catalytic activities of ZENMs were found to be highly advantageous in
yielding significant amounts of cyclohexanone and cyclohexanol in the liquid-phase oxidation
of cyclohexane.
Keywords: Zeolite-Y; Encapsulated nanohybrid materials; Oxidation of cyclohexane
1. Introduction
Oxidation of cyclohexane is an industrial process of great importance but to date of
little efficiency [1–4]. The classic homogeneous process of cyclohexane oxidation to give
cyclohexanone and cyclohexanol is carried out with air using cobalt catalysts at
443–503 K and high pressures (10–15 bar) [5]. In this homogeneous process, cyclohex-
ane conversion is lower than 10% (usually around 4%) and very low yields of
cyclohexanol and cyclohexanone are obtained [6]. As a consequence, oxidation of
cyclohexane continues to be a challenge [7] and attention has been devoted to
heterogenizing homogeneous catalysts onto solid supports to increase catalyst stability
and allow for catalyst recycling and product separation [8–13]. Generally, homogeneous
catalysts are heterogenized either through covalent attachment or encapsulation into
porous supports, like MCM-41 [14], SBA-15 [15], and zeolite-Y [16–18].
Zeolite crystals are porous on a molecular scale, with internal pores containing
regular arrays of channels and cavities with regular dimensions, but of different sizes
and shapes. In particular, the structure of zeolite-Y consists of almost spherical 1.3 nm
˚
˚
(13 A) cavities interconnected tetrahedrally through smaller apertures of 0.74 nm (7.4 A)
diameters [19, 20]. The exchangeable properties of extra-framework cations and the
suitable cavity size of the zeolites allow their modification by inclusion of homogeneous
*Corresponding author. Email: chetank.modi1@gmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.656616

526
C.K. Modi and P.M. Trivedi
catalysts (i.e. metal complexes with regular Oh, Td, square planar, square pyramidal, or
distorted geometries). The use of transition metal complexes encapsulated into zeolitic
framework as heterogeneous catalysts has become very important for eco-friendly
industrial processes [21]. The encapsulation strategy is convenient and advantageous
because the metal complex once formed inside the pore cavity does not easily diffuse out
into the liquid phase during catalytic reaction.
Zeolite-Y encapsulated nanohybrid materials (ZENMs) are crystalline materials
assembled by bonding of metal ions with Schiff-base ligands. ZENMs with nano-sized
channels offer great potential for direct incorporation of catalytic sites. It could be
expected that ZENMs containing uniformly sized and shaped pores could open
possibilities for size- and shape-selectivity effects. Their attributes include high porosity,
spatial and chemical tailoring, and synthetic scalability [22, 23]. They have attracted
great attention due to their various potential applications in catalysis, adsorption,
separation, etc. [24–40].
In continuous search for new processes for oxidation of cyclohexane [41, 42], herein
we report synthesis, spectroscopic, and catalytic significance of ZENMs. The potential
benefits of this study are threefold: (1) to produce novel ZENMs by encapsulation of
transition metal complexes of Schiff bases (figure 1) vanillin thiophene-2-carboxylic
hydrazone (VTCH) and vanillin furoic-2-carboxylic hydrazone (VFCH) in the
nanovoids of zeolite-Y by flexible ligand method (FLM), (2) to characterize ZENMs
by various physico-chemical techniques, and (3) to screen ZENMs for their catalytic
activity over liquid-phase oxidation of cyclohexane.
2. Experimental
2.1. Materials and physical measurements
All chemicals and solvents were of AR grade and used without purification. Thiophene-
2-carboxylic acid, furoic-2-carboxylic acid, and vanillin were obtained from
Spectrochem (India) and 30% H2O2 was purchased from Rankem (India). Sodium
form of zeolite-Y (Si/Al ¼ 2.60) was procured from Hi-media, India. Carbon, hydrogen,
and nitrogen were analyzed with a Perkin Elmer, USA 2400-II CHN analyzer. Si, Al,
Figure 1. Schiff-base ligands (VTCH and VFCH) under study.

Zeolite-Y encapsulated nanohybrids
527
Na, and transition metal ions in the encapsulated nanohybrid materials were
determined by ICP-OES (Model: Perkin Elmer optima 2000 DV). Infrared (IR) spectra
of encapsulated hybrid materials were recorded on a Thermo Nicolet IR 200 FT-IR
spectrometer. The crystallinity was ensured by X-ray diffraction (XRD) using a Bruker
AXS D8 Advance X-ray powder diffractometer with a Cu-Ka target. The surface area
of encapsulated nanohybrid materials was measured by multipoint BET method using a
Micromeritics, ASAP 2010 surface area analyzer. The gas chromatography–mass
spectrometry (GC-MS) of Schiff-base ligands were recorded on a Shimadzu, QP-2010
equipped with a RTX-5 column. The scanning electron micrographs (SEMs) of
encapsulated nanohybrid materials were recorded using an SEM instrument (Model:
1
LEO 1430 VP). H- and 13C-NMR spectra of Schiff-base ligands were recorded on a
Avance 400 Bruker FT-NMR instrument with DMSO-d6 as solvent.
2.2. Synthesis of VTCH
An ethanolic solution (25 mL) of thiophene-2-carboxylic hydrazide (10 mmol, 1.42 g)
and an ethanolic solution (25 mL) of vanillin (10 mmol, 1.52 g) in 1 : 1 molar ratio were
mixed with constant stirring and refluxed for 4 h. The solution was cooled overnight at
room temperature. Light yellow crystals of VTCH were collected and dried in air.
Yield, 72%; m.p. 206ꢀC. Found (%): C, 56.16; H, 4.15; N, 9.58; O, 17.06; S, 11.34.
1
C13H12N2O3S requires (%): C, 56.51; H, 4.38; N, 10.14; O, 17.37; S, 11.60. H-NMR
(400 MHz, DMSO-d6): ꢀ 3.83 (3H, s, –CH3), 7.05–7.28 (3H, m, Ar–H), 7.30–8.28 (3H,
m, thiophene ring-H), 8.3 (1H, s, –CH¼N), 9.6 (1H, s, –NH), 11.7 (1H, s, –OH). m/z:
277.17, 193.08, 166, 149.92, 127, 111.10, 94. 13C-NMR (400 MHz, DMSO-d6):
ꢀ (ppm) ¼ 56.0 (C19), 114.7 (C4), 116.2 (C1), 119.1 (C6), 124.0 (C14), 128.7 (C15), 129.8
(C13), 131.3 (C5), 137.1 (C11), 145.8 (C7), 149.1 (C3), 149.9 (C2), 168.6 (C10).
2.3. Synthesis of VFCH
The Schiff base (VFCH) was prepared the same way as VTCH. Yield, 68%; m.p. 210ꢀC.
Found (%): C, 59.37; H, 4.32; N, 9.69; O, 24.26. C13H12N2O4 requires (%): C, 60.00;
1
H, 4.65; N, 10.76; O, 24.59. H-NMR (400 MHz, DMSO-d6): ꢀ 3.83 (3H, s, –CH3),
7.07–7.28 (3H, m, Ar–H), 6.84–7.29 (3H, m, furoic ring-H), 8.4 (1H, s, –CH¼N), 9.5
(1H, s, –NH), 11.6 (1H, s, –OH). m/z: 260, 150, 134, 111, 95, 77, 67. 13C-NMR
(400 MHz, DMSO-d6): ꢀ (ppm) ¼ 56.0 (C19), 109.4 (C4), 112.4 (C14), 115.0 (C13), 115.9
(C1), 122.7 (C6), 126.1 (C5), 146.1 (C15), 147.3 (C7), 148.5 (C11), 149.0 (C3), 149.5 (C2),
154.5 (C10).
2.4. Synthesis of MII-Y (metal-exchanged zeolite-Y)
Na-Y zeolite (5.0 g) was suspended in 300 mL of deionized water containing 12 mmol
metal salts [Mn(CH3COO)2 ꢁ 4H2O, Co(CH3COO)2 ꢁ 4H2O, Ni(CH3COO)2 ꢁ 4H2O, and
Cu(CH3COO)2 ꢁ H2O] with constant stirring. The reaction mixture was then heated at
90ꢀC for 24 h. The solid was filtered, washed with hot deionized water until the filtrate
was free from any metal ion content, and dried for 15 h at 150ꢀC in air.

528
C.K. Modi and P.M. Trivedi
2.5. Synthesis of [M(VTCH)2]-Y and [M(VFCH)2]-Y
ZENMs were prepared using the FLM. First, 1.0 g of MII-Y was thoroughly mixed with
an excess of VTCH (nligand/nmetal ¼ 3) in ethanol and sealed into a round bottom flask.
The reaction mixture was refluxed (ꢂ24 h) in an oil bath with stirring under inert
atmosphere. The resulting material was taken out, followed by Soxhlet extraction with
ethanol, acetone and finally with acetonitrile (6 h) to remove uncomplexed ligand and
the complex adsorbed on the exterior surface of zeolite-Y. The extracted sample was
ion-exchanged with 0.01 mol Lꢃ1 NaCl aqueous solution for 24 h to remove
uncoordinated MII ions, followed by washing with deionized water until no Clꢃ
could be detected with AgNO3 solution. The product was collected and dried at 120ꢀC.
The same procedure was applied for the preparation of [M(VFCH)2]-Y.
2.6. Catalytic experiments
Catalytic activity of ZENMs was evaluated for liquid-phase oxidation of cyclohexane
with 30% H2O2 as an oxidizing agent. Reaction conditions for the liquid-phase
oxidation of cyclohexane were optimized as follows: cyclohexane (10 mmol), 30% H2O2
(10 mmol), catalyst (60 mg), acetonitrile (2 mL) at 80ꢀC for 2 h. ZENMs catalyzed
oxidation of cyclohexane gives cyclohexanol (CyOL) and cyclohexanone (CyONE). The
progress of the reaction was monitored as a function of time by withdrawing portions of
the sample at 30 min. time intervals and analyzing them by GC.
3. Results and discussion
3.1. Morphological and textural properties of materials
Chemical analyses of the neat zeolite-Y and ZENMs reveal the presence of organic
matter with a C/N ratio as given in table 1. Moreover, the Si/Al ratio is 2.60 for the neat
zeolite-Y, indicating no dealumination during the encapsulation by FLM. The surface
area and pore volume values estimated by nitrogen adsorption isotherms are given in
table 2. The results exhibit a decrease in surface area and pore volume of zeolite-Y on
encapsulation of metal complexes, which show the presence of complexes inside the
nanovoids of zeolite-Y [43, 44].
Figure 2 presents SEMs of [Ni(VTCH)2]-Y recorded before and after Soxhlet
extraction. It is clear from the well-defined crystals after Soxhlet extraction that
ZENMs have no surface complexes and the particle boundaries on the external surface
of zeolite-Y are clearly distinguishable. These micrographs reveal the efficiency of the
purification procedure to effect removal of extraneous complexes, leading to the
presence of well-defined encapsulation in the cavity.
The powder XRD patterns of Na-Y and ZENMs are presented in figure 3. Similar
diffraction patterns were observed for ZENMs, except small change in relative peak
intensities. This indicates that the crystallinity of the zeolitic matrix remained intact
with no major structural modifications upon encapsulation of the metal complex. This
is further supported by SEMs analysis that all ZENMs retain the crystallinity of the
zeolite-Y.

Zeolite-Y encapsulated nanohybrids
Table 1. Analytical and physical data of compounds.
529
Elements % found
Sr. no.
Compounds
%C
%H
%N
C/N
%Si
%Al
%Na
%M
Si/Al
1
2
3
4
5
6
7
8
9
10
11
12
13
Na-Y
MnII-Y
[Mn(VTCH)2]-Y
[Mn(VFCH)2]-Y
CoII-Y
[Co(VTCH)2]-Y
[Co(VFCH)2]-Y
NiII-Y
[Ni(VTCH)2]-Y
[Ni(VFCH)2]-Y
CuII-Y
–
–
–
–
–
–
–
–
17.16
17.08
16.61
16.73
16.80
16.55
16.49
16.98
16.40
16.45
16.90
16.70
16.65
6.60
6.56
6.39
6.43
6.46
6.36
6.34
6.53
6.30
6.32
6.50
6.42
6.40
9.86
5.68
7.30
6.81
4.87
5.88
6.05
3.92
5.42
5.52
7.01
6.20
6.33
–
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.60
2.40
2.19
2.20
3.53
2.22
2.24
3.62
2.28
2.27
4.71
2.25
2.21
4.72
4.76
–
4.85
4.88
–
4.80
4.78
–
4.69
4.65
1.41
1.45
–
1.48
1.52
–
1.47
1.50
–
1.42
1.39
0.95
0.96
–
1.03
1.06
–
1.06
1.04
–
0.98
0.97
4.97
4.95
–
4.61
4.60
–
4.52
4.56
–
4.78
4.75
[Cu(VTCH)2]-Y
[Cu(VFCH)2]-Y
Table 2. Surface area and pore volume data of compounds.
Compounds
Surface area (m2 gꢃ1
)
Pore volume (cc gꢃ1 a
)
Na-Y
MnII-Y
[Mn(VTCH)2]-Y
[Mn(VFCH)2]-Y
CoII-Y
[Co(VTCH)2]-Y
[Co(VFCH)2]-Y
NiII-Y
[Ni(VTCH)2]-Y
[Ni(VFCH)2]-Y
CuII-Y
548
538
265
280
530
272
276
527
269
275
534
261
263
0.32
0.29
0.15
0.19
0.30
0.17
0.18
0.30
0.16
0.17
0.31
0.13
0.14
[Cu(VTCH)2]-Y
[Cu(VFCH)2]-Y
aCalculated by the BJH-method.
3.2. Spectroscopic characterization
Table 3 shows a list of FT-IR spectral data of Schiff bases, [M(VTCH)2]-Y and
[M(VFCH)2]-Y. The intensity of peaks in ZENMs is weak due to their low
concentration in the zeolite matrix. Comparison of the spectra of Schiff bases namely
VTCH or VFCH with ZENMs provides evidence for coordinating mode of ligand in
ZENMs. The ꢁ(N–H) and ꢁ(C¼O) of the lateral chain in the uncoordinated Schiff bases
are at 3180–3189 and 1690–1695 cmꢃ1, respectively, indicating that the ligands exist in
keto form in the solid state [45]. However, these bands are absent in spectra of ZENMs
with a new band at 1344–1353 cmꢃ1 due to ꢁ(C–O) [46, 47]. From these observations,
the ligand reacts in enol form via proton transfer through oxygen forming a bond with
the metal ion. The sharp and strong band at 1635–1639 cmꢃ1 is due to ꢁ(C¼N) of
azomethine of the lateral chain. The low-energy shift of this band in spectra of ZENMs,

530
C.K. Modi and P.M. Trivedi
Figure 2. SEM images of [Ni(VFCH)2]-Y (A) before and (B) after Soxhlet extraction.
at ꢂ1620 cmꢃ1, suggests the coordination of azomethine nitrogen [48]. The framework
vibration bands of zeolite-Y are below 1200 cmꢃ1 for all samples. Bands at 556–583,
720–786, and 1012–1134 cmꢃ1 are attributed to double ring, symmetric stretching, and
asymmetric stretching vibrations, respectively [49]. No shift is observed upon
introduction of metal ions and inclusion of metal complexes, further substantiating
that the zeolite-Y framework remains unchanged.
Electronic spectral bands of VTCH and/or VFCH and ZENMs are discussed and
tabulated in table 4. From 200 to 800 nm, the electronic spectra of Schiff bases showed
an intense band at ꢂ329 nm due to intra-ligand charge transfer transitions (ꢂ ! ꢂ*);
this band undergoes bathochromic shifts in Mn(II) and hypsochromic shifts in Co(II)

Zeolite-Y encapsulated nanohybrids
531
Figure 3. XRD patterns of Na-Y and its modified zeolites.
Table 3. FT-IR assignments of Schiff bases and ZENMs.
Internal vibrations External vibrations
asymT–O symT–O D–R symT–O ꢁasymT–O ꢁ(C¼N) ꢁ(C¼O) ꢁ(N–H) ꢁ(O–H) ꢁ(C–O)
Compounds
ꢁ
ꢁ
ꢁ
VTCH
VFCH
–
–
–
–
–
–
–
–
–
–
1635
1639
1616
1615
1624
1623
1618
1615
1620
1622
1690 3180 3422 1286
1695 3189 3432 1291
[Mn(VTCH)2]-Y
[Mn(VFCH)2]-Y
[Co(VTCH)2]-Y
[Co(VFCH)2]-Y
[Ni(VTCH)2]-Y
[Ni(VFCH)2]-Y
[Cu(VTCH)2]-Y
[Cu(VFCH)2]-Y
1017
1019
1027
1025
1012
1014
1021
1025
721
726
729
728
725
720
730
727
574
569
571
566
560
556
576
583
786
781
769
776
770
775
783
780
1120
1128
1134
1124
1120
1130
1125
1122
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3442 1348
3448 1344
3442 1350
3444 1347
3433 1352
3438 1345
3448 1353
3440 1351

532
C.K. Modi and P.M. Trivedi
Table 4. Electronic spectral data of VTCH, VFCH, and ZENMs.
ILCT (ꢂ ! ꢂ*)
MLCT
transition in nm
d–d transition
in nm
Compounds
transition in nm
VTCH
VFCH
329
324
335
333
323
322
302
308
–
–
–
–
–
–
–
778
792
647
630
401
405
[Mn(VTCH)2]-Y
[Mn(VFCH)2]-Y
[Co(VTCH)2]-Y
[Co(VFCH)2]-Y
[Ni(VTCH)2]-Y
[Ni(VFCH)2]-Y
[Cu(VTCH)2]-Y
[Cu(VFCH)2]-Y
220
233
244
243
–
–
–
–
–
and Ni(II) encapsulated hybrid materials resulting from chelation of the ligand with the
transition metal. As expected for Mn(II) encapsulated hybrid materials, d–d transition
bands are not observed in dilute solution because of their being doubly forbidden. The
spectra of Co(II) encapsulated hybrid materials show two additional absorption bands
at ꢂ244 and 792–778 nm attributed to metal-to-ligand charge transfer (MLCT) and
2
2B2g ! Eg transitions, concordant with square-planar structure [50]. The same bands
are present in the UV-Vis spectrum of neat Co(VTCH)2 complex, which means the
configuration of cobalt complex had no change when encapsulated inside the nanopores
of zeolite-Y (figure 4). Square-planar d8 metal complexes are characterized by three
spin allowed d–d bands, dxy(b1g) ! d
(b1g), d2(a1g) ! d
(b1g), and dxz, yz(eg) !
x2ꢃy2
x2ꢃy2
z
1
1
1
1
1
1
dx2ꢃy2 (eg) corresponding to A1g ! A2g (ꢁ1), A1g ! B1g (ꢁ2), and A1g ! Eg (ꢁ3)
transitions [51]. Of the three expected low energy ligand field (d–d) bands,
corresponding to transitions from the three lower d-levels to the empty dx2ꢃy2 orbitals,
only one is observed in the visible spectra of [Ni(VTCH)2]-Y and [Ni(VFCH)2]-Y near
1
1
647 nm. This may be assigned to A1g ! A2g (ꢁ1) transition of Ni(II) in square-planar
structure. The weak band observed near 405 nm for Cu(II) encapsulated hybrid
2
2
materials is assigned to B1g ! Eg transition of square-planar geometry [52].
3.3. Catalytic activity studies
3.3.1. Oxidation of cyclohexane. Catalytic oxidation of cyclohexane was undertaken
in a two-necked 50 mL round bottomed flask. In a typical reaction, 10 mmol of the
substrate was taken in 2 mL of acetonitrile, 60 mg of the catalyst added to it and
equilibrated at 80ꢀC in an oil bath. 10 mmol of 30% H2O2 solution was added to this with
continuous stirring for 2 h and the results are given in table 5. Blank experiments
performed without catalyst or with Na-Y zeolite show a lesser amount of conversion. The
products were collected at different time intervals and identified and quantified by GC.
The absence of metal ions in filtrate indicates that no leaching of complexes occurred
during reaction, as they are intact in the nanopores [53].
Blank reactions performed over zeolite-Y and MII-Y under identical conditions
show only negligible conversion, indicating that zeolite host is inactive for oxidation.
The VTCH and VFCH ligands alone in the absence of metal were not

Zeolite-Y encapsulated nanohybrids
533
Figure 4. The electronic spectra of (a) VTCH Schiff base, (b) Neat Co(VTCH)2, and (c) [Co(VTCH)2]-Y.
Table 5. Oxidation of cyclohexane to cyclohexanol and cyclohexanone with 30% H2O2 catalyzed by
ZENMs.
Selectivity (%)
Sr. no.
Compounds
Conversion (%)
CyOL
CyONE
1
2
3
4
5
6
7
8
9
10
[Mn(VTCH)2]-Y
[Mn(VFCH)2]-Y
[Co(VTCH)2]-Y
[Co(VFCH)2]-Y
[Ni(VTCH)2]-Y
[Ni(VFCH)2]-Y
[Cu(VTCH)2]-Y
[Cu(VFCH)2]-Y
[Cu(VTCH)2]-Ya
[Cu(VTCH)2]-Yb
12.4
10.9
23.6
21.8
16.9
15.4
36.7
35.1
34.8
32.6
29.3
25.6
27.1
34.7
45.2
40.6
18.1
24.2
20.3
21.7
70.7
74.4
72.9
65.3
54.8
59.4
81.9
75.8
79.7
78.3
CyOL is cyclohexane-1-ol product; CyONE is cyclohexane-1-one product.
aFirst reused catalyst.
bSecond reused catalyst.
catalytically active. Figure 5 summarizes the percentage conversion of cyclohexane
along with cyclohexanol and cyclohexanone formations. Selectivity of cyclohexanone
formation varied (54.8–81.9%) from catalyst to catalyst; all these catalysts are selective
toward the cyclohexanone formation.
The coordinatively unsaturated M(II) (where M ¼ Mn(II), Co(II), Ni(II), and Cu(II))
species within nanocages of zeolite-Y play a crucial role in enhancing catalytic
performance. Scheme 1 demonstrates a possible mechanism for catalytic oxidation of
cyclohexane. The first step involves formation of metal-peroxo species, which have
powerful oxidation ability [54, 55]. In the next step, formation of intermediate species

534
C.K. Modi and P.M. Trivedi
Conversion (%)
CyOL
CyONE
1. [Mn(VTCH) ]-Y 4. [Co(VFCH) ]-Y 7. [Cu(VTCH) ]-Y
2
2
2
2. [Mn(VFCH) ]-Y 5. [Ni(VTCH) ]-Y 8. [Cu(VFCH) ]-Y
2
2
2
a
3. [Co(VTCH) ]-Y 6. [Ni(VFCH) ]-Y 9. [Cu(VTCH) ]-Y
2
2
2
80
60
40
20
0
1
2
3
4
5
6
7
8
9
Figure 5. Conversion % of oxidation of cyclohexane.
aFirst reused catalyst.
transfers the coordinated oxygen to the substrate to obtain product. In the case of
[M(VTCH)2]-Y or [M(VFCH)2]-Y (where M ¼ Ni, Co, or Mn) slow formation of
peroxo species with H2O2 or sluggishness to transfer of peroxo oxygen to the substrate
limits the reaction. In contrast, the performance of [Cu(VTCH)2]-Y is much better,
giving highest percentage conversion of CyONE (table 5). To achieve suitable reaction
conditions for maximum oxidation, parameters such as effect of amount of catalyst and
effect of temperature were studied using [Cu(VTCH)2]-Y as a representative catalyst.
The results of these effects along with their possible explanations are summarized
below.
3.3.2. Effect of amount of catalysts. The amount of catalyst has a significant effect on
the oxidation of cyclohexane. Four different amounts of [Cu(VTCH)2]-Y catalyst
namely 40, 50, 60, and 65 mg were used, keeping all other reaction parameters
unchanged (temperature (80ꢀC), cyclohexane (10 mmol), 30% H2O2 (10 mmol) in
acetonitrile (2 mL), and reaction time (2 h)). The results are shown in figure 6, indicating
28.5%, 35.7%, 36.7%, and 36.7% conversion corresponding to 40, 50, 60, and 65 mg
catalyst, respectively. Lower conversion of cyclohexane with 40 and 50 mg catalyst may
be due to fewer catalytic sites. The greater conversion percentage was observed with
60 mg catalyst but there was no difference in the progress of reaction when more than
65 mg of catalyst was employed. Therefore, 60 mg amount of catalyst was taken to be
optimal.
3.3.3. Effect of temperature. For four different temperatures namely 60ꢀC, 70ꢀC,
75ꢀC, and 80ꢀC, the oxidation of cyclohexane (figure 7) was examined under the

Zeolite-Y encapsulated nanohybrids
535
Zeolite-Y nanocage
N
O
O
N
N
O
O
N
30% H2O2
H
Cyclohexane
M
O
O
M
H
ZENMs
where M = Mn(II), Co(II), Ni(II) and Cu(II)
N
O
O
N
+
H H
H
M
O
-
O
H
H2O
O
N
O
+
+
M
OH
O
N
Cyclohexanone
Cyclohexanol
Scheme 1. The proposed mechanism illustrating the formation of cyclohexanol and cyclohexanone in
catalytic oxidation of cyclohexane.
40 mg
50 mg
60 mg
65 mg
60
40
20
0
0
30
60
90
120
150
180
Reaction/min
Figure 6. Effect of amount of catalyst on the oxidation of cyclohexane.
above reaction conditions, cyclohexane (10 mmol), 30% H2O2 (10 mmol), catalyst
(60 mg) in acetonitrile (2 mL) for 2 h. On increasing the temperature from 60ꢀC to
80ꢀC, improvements were observed with no change in percentage conversion for
oxidation of cyclohexane, consequently at 80ꢀC for 2 h time is considered to be the
optimum.

536
C.K. Modi and P.M. Trivedi
40
30
20
10
0
60 °C
70 °C
75 °C
80 °C
0
30
60
90
120
150
180
Reaction time/min
Figure 7. Effect of temperature on the oxidation of cyclohexane.
3.3.4. Test for recyclability. [Cu(VTCH)2]-Y was recycled for oxidation of cyclohex-
ane to establish the effect of encapsulation on stability. The initial run shows a
conversion of 35.1% and it was just marginally reduced to 34.8% and 32.6% after first
and second recycling of the catalyst, respectively. These results indicate that
[Cu(VTCH)2]-Y can be recycled for oxidation of cyclohexane without much loss in
activity. Consequently, the encapsulation of metal complexes inside the nanocavity of
zeolite-Y increases the life of catalyst by reducing dimerization due to restriction of
internal framework structure.
4. Conclusions
The results obtained in this study allow the following conclusions:
(1) Manganese(II), cobalt(II), nickel(II), and copper(II) complexes of VTCH and/or
VFCH have been encapsulated in the nanocages of zeolite-Y, leading to the
formation of ZENMs. Chemical analysis, spectroscopic studies, BET, SEMs, and
XRD patterns present clear evidence for encapsulation.
(2) Among these nanohybrid materials, [Cu(VTCH)2]-Y catalyzes the oxidation of
cyclohexane with very good yield of cyclohexanone selectively, which is followed
by [Cu(VFCH)2]-Y which in turn is better than [Mn(VFCH)2]-Y and so on.
(3) Under the best reaction conditions, the selectivity of cyclohexanone formation is
about 81.9% with [Cu(VTCH)2]-Y catalyst.
(4) The test for recyclability using [Cu(VTCH)2]-Y as a representative catalyst has
been carried out. The results reflect the reusability of the nanohybrid materials as
not much loss in their catalytic activity was noticed.

Zeolite-Y encapsulated nanohybrids
537
Acknowledgments
We express our gratitude to the Head, Department of Chemistry, Bhavnagar
University, Bhavnagar, India for providing the necessary laboratory facilities. Mr
Parthiv M. Trivedi would like to acknowledge UGC, Delhi for providing meritorious
fellowship. An analytical facility provided by the CSMCRI and Department of Physics,
Bhavnagar University, Bhavnagar, India is gratefully acknowledged.
References
[1] K.U. Ingold. Aldrichim. Acta, 22, 69 (1989).
[2] U. Schuchardt, W.A. Carvalho, E.V. Spinace. Synlett., 10, 713 (1993).
´
[3] M.C. Esmelindro, E.G. Oestreicher, H.M. Alvarez, C. Dariva, S.M. Egues, C. Fernandes,
A.J. Bortoluzzi, V. Drago, O.A.C. Antunes. J. Inorg. Biochem., 99, 2054 (2005).
[4] M.H.N. Olsen, G.C. Salomao, C. Fernandes, V. Drago, A. Horn, L.C. Filho, O.A.C. Antunes. J.
˜
Supercrit. Fluids, 34, 119 (2005).
[5] H.A. Wittcoff, B.G. Reuben. Industrial Organic Chemicals, Wiley & Sons, New York (1996).
[6] U. Schuchardt, R. Pereira, M. Rufo. J. Mol. Catal. A: Chem., 135, 257 (1998).
[7] U. Schuchardt, D. Cardoso, R. Sercheli, R. Pereira, R.S. Da Cruz, M.C. Guerreiro, D. Mandelli,
´
E.V. Spinace, E.L. Pires. Appl. Catal. A: Gen., 211, 1 (2001).
[8] A. Corma, H. Garcia. Chem. Rev., 102, 3837 (2002).
[9] T. Sato, J. Dakka, R.A. Sheldon. J. Chem. Soc., Chem. Commun., 1887 (1994).
[10] M.A. Camblor, A. Corma, A. Martinez, J.P. Parienta. J. Chem. Soc., Chem. Commun., 589 (1992).
[11] G. Tozzola, M.A. Mantegazza, G. Ranghino, G. Petrini, S. Bordiga, G. Ricchiardi, C. Lamberti,
R. Zulian, A. Zecchina. J. Catal., 179, 64 (1998).
[12] A.P. Singh, T. Selvam. J. Mol. Catal. A: Chem., 113, 489 (1996).
[13] B.F. Sels, D. De Vos, P.A. Jacobs. Tetrahedron Lett., 37, 8557 (1996).
[14] T. Joseph, D. Srinivas, C.S. Gopinath, S.B. Halligudi. Catal. Lett., 83, 209 (2002).
[15] T. Joseph, S.B. Halligudi. J. Mol. Catal. A: Chem., 229, 241 (2005).
[16] R.A. Sheldon, I.W.C.E. Arends, A. Dijksman. Catal. Today, 57, 157 (2000).
[17] C.R. Jacob, S.P. Verkey, P. Ratnasamy. Microporous Mesoporous Mater., 22, 465 (1998).
[18] G.J. Hutchings. Chem. Commun., 301 (1999).
[19] M.J. Alcon, A. Corma, M. Iglesias, F. Sanchez. J. Mol. Catal. A: Chem., 178, 253 (2002).
´ ´
[20] M.R. Maurya, A. Kumar, J.C. Pessoa. J. Coord. Chem. Rev., 255, 2315 (2011).
[21] P. Parpot, C. Teixeir, A.M. Almeid, C. Ribeiro, I.C. Neves, A.M. Fonseca. Microporous Mesoporous
Mater., 117, 297 (2009).
[22] S.R. Batten, R. Robson. Angew. Chem. Int. Ed., 37, 1460 (1998).
[23] N.W. Ockwig, O.D. Friedrichs, M. O’Keeffe, O.M. Yaghi. Acc. Chem. Res., 38, 176 (2005).
[24] S. Kitagawa, R. Kitaura, S. Noro. Angew. Chem. Int. Ed., 43, 2334 (2004).
[25] J.L.C. Rowsell, E.C. Spencer, J. Eckert, J.A.K. Howard, O.M. Yaghi. Science, 309, 1350 (2005).
[26] O.M. Yaghi, G. Li, H. Li. Nature, 378, 703 (1995).
[27] M. Fujita, Y.J. Kwon, S. Washizu, K. Ogura. J. Am. Chem. Soc., 116, 1151 (1994).
[28] J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim. Nature, 404, 982 (2000).
[29] L.-G. Qiu, A.-J. Xie, L.-D. Zhang. Adv. Mater., 17, 689 (2005).
[30] T. Sawaki, T. Dewa, Y. Aoyama. J. Am. Chem. Soc., 120, 8539 (1998).
[31] C.-D. Wu, W. Lin. Angew. Chem. Int. Ed., 46, 1075 (2007).
[32] R.Q. Zou, H. Sakurai, Q. Xu. Angew. Chem. Int. Ed., 45, 2542 (2006).
[33] D.N. Dybtsev, A.L. Nuzhdin, H. Chun, K.P. Bryliakov, E.P. Talsi, V.P. Fedin, K. Kim. Angew. Chem.
Int. Ed., 45, 916 (2006).
[34] L. Alaerts, E. Seguin, H. Poelman, F. Thibault-Starzyk, P.A. Jacobs, D.E. De Vos. Chem. Eur. J., 12,
7353 (2006).
[35] C.D. Wu, A. Hu, L. Zhang, W.B. Lin. J. Am. Chem. Soc., 127, 8940 (2005).
[36] F.X.L.I. Xamena, A. Abad, A. Corma, H. Garcia. J. Catal., 250, 294 (2007).
[37] K.L. Wong, G.L. Law, Y.-Y. Yang, W.T. Wong. Adv. Mater., 18, 1051 (2006).
[38] M. Alvaro, E. Carbonell, B. Ferrer, F.X.L.I. Xamena, H. Garcia. Chem. Eur. J., 13, 5106 (2007).
[39] F.X.L.I. Xamena, A. Corma, H. Garcia. J. Phys. Chem. C, 111, 80 (2007).
[40] G.J. Halder, C.J. Kepert, B. Moubaraki, K.S. Murray, J.D. Cashion. Science, 298, 1762 (2002).
[41] M. Heitbaum, F. Glorious, I. Escher. Angew. Chem. Int. Ed., 45, 4732 (2006).

538
C.K. Modi and P.M. Trivedi
[42] K.O. Xavier, J. Chacko, K.K. Mohammed Yusuff. Appl. Catal. A: Gen., 258, 251 (2004).
[43] B. Dutta, S. Jana, R. Bera, P.K. Saha, S. Koner. Appl. Catal. A: Gen., 318, 89 (2007).
[44] P. Chen, B. Fan, M. Song, C. Jin, J. Ma, R. Li. Catal. Commun., 7, 969 (2006).
[45] C.K. Modi, D.H. Jani, H.S. Patel, H.M. Pandya. Spectrochim. Acta, Part A, 75, 1321 (2010).
[46] M. Salavati-Niasari, M. Shakouri-Arani, F. Davar. Microporous Mesoporous Mater., 116, 77 (2008).
[47] C.K. Modi, D.H. Jani. Appl. Organomet. Chem., 25, 429 (2011).
[48] C.K. Modi, D.H. Jani. J. Therm. Anal. Calorim., 102, 1001 (2010).
[49] A.H. Ahmed, A.G. Mostafa. Mater. Sci. Eng. C, 29, 877 (2009).
[50] K. Mukkanti, K.B. Pandeya, R.P. Singh. Synth. React. Inorg. Met.-Org. Chem., 16, 229 (1986).
[51] A.B.P. Lever. Inorganic Electronic Spectroscopy, 2nd Edn, p. 411, Elsevier, Amsterdam (1984).
[52] S.A. Sallam. J. Coord. Chem., 60, 951 (2007).
[53] M. Ghadiri, M. Farzaneh, M. Ghandi, M. Alizadeh. J. Mol. Catal. A: Chem., 233, 127 (2005).
[54] L. Jian, C. Chen, F. Lan, S. Deng, W. Xiao, N. Zhang. Solid State Sci., 13, 1127 (2011).
[55] B. Xiao, H.W. Hou, Y.T. Fan. J. Organomet. Chem., 692, 2014 (2007).