Studies of styrene oxidation by catalyst based on zeolite-Y nanohybrid materials

Article abstract of DOI:10.1016/j.molcata.2016.08.031

Metal complexes of VO(IV), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and HNIMMPP (4-(((2-hydroxy-5-nitrophenyl)imino)methyl)-3-methyl-1-phenyl-1H-pyrazol-5-ol) schiff base ligand have been synthesized within zeolite-Y along with neat one. Synthesized compounds were characterized by physico-chemical techniques such as elemental analysis of catalysts, BET, XRD, SEM, FT-IR, UV–vis, ICP-OES and TGA. Synthesized zeolite-Y based nanohybrid materials and their uncovered complexes were used in styrene oxidation with TBHP as an oxidizing agent. Oxidation reaction of styrene furnished benzaldehyde as the major product and styrene glycol, chalcone and 2-phenyloxirane as minor products. Amongst all catalysts, [VO(HNIMMPP)(H₂O)]-Y produced the highest conversion at 93.35% and selectivity of benzaldehyde (45.70%) was the greatest. These nanohybrid materials can be easily reprocessed and recovered within these reaction parameters. The reaction mechanism for catalytically oxidized styrene is discussed in the present paper.

Full text of DOI:10.1016/j.molcata.2016.08.031

Accepted Manuscript
Title: Studies of styrene oxidation by catalyst based on
Zeolite-Y nanohybrid materials
Author: Nisheeth C. Desai Jiten A. Chudasama Tushar J.
Karkar Bonny Y. Patel Krunalsinh A. Jadeja Dinesh R.
Godhani Jignasu P. Mehta
PII:
S1381-1169(16)30366-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.08.031
MOLCAA 10018
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
21-7-2016
19-8-2016
29-8-2016
Pleasecitethisarticleas:NisheethC.Desai, JitenA.Chudasama, TusharJ.Karkar, Bonny
Y.Patel, Krunalsinh A.Jadeja, Dinesh R.Godhani, Jignasu P.Mehta, Studies of styrene
oxidation by catalyst based on Zeolite-Y nanohybrid materials, Journal of Molecular
Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2016.08.031
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Graphical abstract
Studies of styrene oxidation by catalyst based on Zeolite-Y
nanohybrid materials
Nisheeth C. Desai*, Jiten A. Chudasama, Tushar J. Karkar, Bonny Y. Patel, Krunalsinh A.
Jadeja, Dinesh R. Godhani and Jignasu P. Mehta
Department of Chemistry (UGC NON-SAP & DST-FIST Sponsored), Mahatma Gandhi
Campus, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364 002, India
E-mail: dnisheeth@rediffmail.com

Studies of styrene oxidation by catalyst based on Zeolite-Y
nanohybrid materials
Nisheeth C. Desai*, Jiten A. Chudasama, Tushar J. Karkar, Bonny Y. Patel, Krunalsinh A.
Jadeja, Dinesh R. Godhani and Jignasu P. Mehta
Department of Chemistry (UGC NON-SAP & DST-FIST Sponsored), Mahatma Gandhi
Campus, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364 002, India
E-mail: dnisheeth@rediffmail.com

Highlights





We have combined VO(IV) based neat and their entrapped complexes into the
nanopores of zeolite-Y.
The comparative studies of spectroscopic, thermal, morphological and crystalline
properties of complexes were achieved.
The catalytic activities were tried over oxidation of styrene reaction using TBHP as an
oxidizing agent.
The reaction parameters were optimized for higher oxidation with higher selectivity
towards allylic products.
Among all catalysts, [VO(HNIMMPP)(H2O)]-Y catalyst showed higher catalytic (TOF,
114.75 h-1) activity with 45% selectivity of benzaldehyde.

ABSTRACT
Metal complexes of VO(IV), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and HNIMMPP
(4-(((2-Hydroxy-5-nitrophenyl)imino)methyl)-3-methyl-1-phenyl-1H-pyrazol-5-ol)
schiff base ligand have been synthesized within zeolite-Y along with neat one.
Synthesized compounds were characterized by physico-chemical techniques such as
elemental analysis of catalysts, BET, XRD, SEM, FT-IR, UV-Vis, ICP-OES and
TGA. Synthesized zeolite-Y based nanohybrid materials and their uncovered
complexes were used in styrene oxidation with TBHP as an oxidizing agent.
Oxidation reaction of styrene furnished benzaldehyde as the major product and
styrene glycol, chalcone and 2-phenyloxirane as minor products. Amongst all
catalysts, [VO(HNIMMPP)(H2O)]-Y produced the highest conversion at 93.35% and
selectivity of benzaldehyde (45.70%) was the greatest. These nanohybrid materials
can be easily reprocessed and recovered within these reaction parameters. The
reaction mechanism for catalytically oxidized styrene is discussed in the present
paper.
Keywords: Zeolite-Y; Nanohybrid materials; Styrene oxidation

1. Introduction
Oxy-functionalized derivatives of olefins are vital raw constituents for fine
chemicals, pharmaceuticals, agrochemicals, and fragrance industry because they
usually demonstrate interesting organoleptic properties [1-4]. Oxidation of olefins
produces significant products like acids, aldehydes, epoxides, alcohols and ketones
etc. These products are key ingredients in many chemical industries [5, 6]. Catalytic
oxidation of olefins can be easily completed by metal complexes in homogeneous
reaction media [7, 8]. Heterogeneous catalysis is a dynamic field of research for
oxidation in many industrial reactions as compared to homogeneous catalyst [9, 10].
For the growth of novel chemical technologies, zeolite imprisoned metal complexes
hold a significant place amongst heterogeneous catalysts [11, 12].
Several transition metal complexes (TMC) as homogeneous catalyst are
crucial for various organic reactions. However these catalysts faced the problems of
corrosion, contamination of products, reusability and difficulties in separation at the
time of reaction accomplishment. To overcome these technical issues, the recent
advancements in catalysis are mainly concentrated on entrapment of metal
complexes either on inert or on porous solid materials [13-22]. These heterogeneous
catalysts afford the following advantages to liquid phase reaction such as
minimization of waste, recyclability and reprocessing from the reaction mixture [23-
25]. Zeolite-Y imprisoned TMCs are more appropriate since they do not easily come
out for the duration of the catalytic reaction after the complexation [26, 27].
Homogeneous as well as heterogeneous catalysts were used for the
epoxidation of styrene [28-33]. Styrene oxidation furnished important products such
as diols, carbonyl compounds, epoxides, and oxidative cleavage of C-C bond. With
the advancement in homogeneous catalysis along with a heterogeneous catalyst as
zeolite-Y imprisoned TMCs played a significant role to enhance the styrene
oxidation [34-36].
In the present work our focus was based on nanohybrid catalytic studies
related to zeolite-Y of VO(IV), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) transition metal
complexes and HNIMMPP Schiff base ligands. These heterogenic catalysts were
used for oxidation of styrene with TBHP as oxidant and characterised by GCMS. For

the characterization of the synthesized compounds standard analytical techniques
were used.
2. Experimental
2.1. Materials and reagents
AR grad chemicals were utilized without further refinement. POCl3 (99%),
DMF (99.5%) (Spectrochem, India), 1-phenyl-3-methyl-2-pyrazoline-5-one (99%)
(Sigma-Aldrich, Germany) and 2-amino-4-nitro phenol (Sigma-Aldrich, Germany).
MnSO4∙H2O, FeSO4∙7H2O, CoSO4, NiSO4∙6H2O, CuSO4∙5H2O and VOSO4∙5H2O
were procured from Merck. Sodium form of zeolite-Y (Na-Y, By-600, mole ratio of
SiO2/Al2O3 5:2, nominal cation hydrogen, surface area = 660 m2/g) was procured
from Reliance, India. The catalytic activities of the prepared samples were
monitored by substrates like (commercially obtained 70%) TBHP (Spectrochem,
India) and styrene-99% (Sigma-Aldrich, Germany). Solvents such as acetone (99%),
methanol (99%), ethanol (99.9%) and THF (99.5%) have been used. Compounds are
characterized by standard analytical techniques and details were given in
supplementary data.
2.2. Preparation of Schiff base
The Schiff base was prepared in two steps:
Step 1. Preparation of 1-Phenyl-3-methyl-4-formyl-1H-pyrazol-5-ol
1-Phenyl-3-methyl-4-formyl-1H-pyrazol-5-ol (PMFP) was prepared by the
condensation
reaction
of
1-phenyl-3-methyl-1H-pyrazol-5-ol
(PMP)
in
dimethylformamide and POCl3 [24]. 1-Phenyl-3-methyl-1H-pyrazol-5-ol (8.7 g,
0.050 mol) in dimethylformamide (10.0 cm3, 0.050 mol) was chilled to 0 °C in ice
bath. Drop wise addition of phosphoryl chloride (5.50 cm3, 0.060 mol) was
performed to control the temperature between 10 to 20 °C. After completion of
addition, the reaction mixture was heated on steam bath for 1.5 h and at that point
transferred into ice water. Then it was allowed to stand overnight and product was
filtrated, washed with water and dried. It was further crystallized using ethanol
(99.9%). Yellow crystals of PMFP were obtained in 83% yield and m.p. 176 °C [37]
(Fig. 1).

Step 2. Preparation of 4-(((2-Hydroxy-5-nitrophenyl)imino)methyl)-3-methyl-1-
phenyl-1H-pyrazol-5-ol (HNIMMPP)
4-(((2-Hydroxy-5-nitrophenyl)imino)methyl)-3-methyl-1-phenyl-1H-pyrazol-
5-ol (HNIMMPP) was prepared by condensation reaction of 1-phenyl-3-methyl-4-
formyl-1H-pyrazol-5-ol (PMFP) and 2-amino-4-nitrophenol. They were mixed in a
RBF containing 40 mL of THF and refluxed under water bath for 4-6 h. Filtered,
dried and collected crude product was recrystallized in 1,4-dioxane (Fig. 2).
2.3. Preparation of transition metal complexes
TMCs were prepared by a condensation reaction between ligand (HNIMMPP)
and respective metal salt. Prepare 1 mole of HNIMMPP solution in ethanol (95%)
and 1 mole of metal salt (MnSO4∙H2O, FeSO4∙7H2O, CoSO4, NiSO4∙6H2O,
CuSO4∙5H2O, and VOSO4∙5H2O) solution in distilled water, mix both of these
solutions in RBF and refluxed for 4-6 h. The progress of reaction was monitored by
TLC. The mixture was allowed to settle overnight then filtered and dried. The
separated product was recrystallized by THF (Fig. 3).
2.4. Preparation of zeolite-Y imprisoned transition metal complexes
Flexible ligand method (FLM) was used to synthesize zeolite-Y imprisoned
transition metal complexes. The stepwise method to imprison TMCs in inner side to
the nanocavity of zeolite-Y is as shown below:
2.4.1. Synthesis of metal-exchanged zeolite-Y [M(II/IV)-Y]:
In this step of ion-exchange, alkali metal ion such sodium would be replaced
by transition metal ion from the matrix of zeolite-Y. A quantity of 5 g of zeolite-Y
(Na-Y) was taken in 300 mL of deionized water containing 12 mmol metal salts [For
Mn(II), Fe(II), Co(II), Ni(II) Cu(II), and VO(IV): 2.49 g, 3.33 g, 2.98 g, 2.98 g, 2.39
g, and 3.13 g, respectively] through continuous stirring at 90 °C for 22 to 30 h. The
solid M (II/IV)-Y was filtered, washed with hot deionized water till the filtrate was
free from metal ion content and then dried for 15 h at 120 °C. The schematic
diagram is shown in Fig. 4.

2.4.2. Synthesis of zeolite-Y imprisoned transition metal complexes:
1.0 g of M(II/IV)-Y was uniformly mixed with an excessive amount of Schiff
base ligands (nligand/nmetal = 3) in THF. The mixture was heated (~24 h) in an oil-bath
through continuous stirring. After crude material of novel catalyst was precipitated
out, Soxhlet extraction method was utilized to remove the undesired part of raw
materials and complex stuck on the outer surface of zeolite-Y with help of suitable
solvents THF, acetone, ethanol and finally by acetonitrile (6-8 h). 0.01 M NaCl
solution was used for ion-exchange of the extracted part for 22-24 h to eliminate
uncoordinated metal ions and washed by deionized water till no chloride ions could
be detected with AgNO3 solution. The final material was collected and dried at 120
°C. The schematic diagram is shown in Fig. 4.
3. Results and discussion
3.1. Characterization of Zeolite-Y based nanohybrid materials
The elemental data of Schiff base ligand, neat complexes, zeolite-Y and its
imprisoned TMCs are specified in Table 1. The elemental study of the imprisoned
compounds revealed the existence of organic matter and central metal ions with C-N
ratio equivalent to that of neat complexes. Furthermore, the Si and Al contents in
M(II/IV)-Y and their imprisoned complexes were almost in the same ratio as in the
parent zeolite. This indicated tiny changes in the zeolite structure due to lack of
dealumination during metal ion exchange.
The textural properties of catalysts were quantified by means of BET
technique (Table 2). The parent Na-Y possessed the biggest surface area and the
biggest entire pore size. Contrarily on imprisoning the TMCs, surface vicinity and
pore size significantly decreased in comparison to the parent Na-Y. This occurred
due to the method of synthesis used for imprison of metal and ligand [38]. The
decreased pore size of materials revealed that the encapsulation was occurring inside
the cavity of zeolite-Y and not on the outside.
Scanning electron micrograph (SEM) technique was performed to check the
crystallinity and purity of the zeolite. We took catalyst Co(HNIMMPP)(H2O)]-Y and
recorded micrographs beforehand and afterward Soxhlet extraction as presented in
Fig. 5. This showed strongly defined rock crystal of zeolite imprisoned complexes

after Soxhlet extraction free from any shadow of the metal complex present on the
exterior of zeolite [39].
The crystallites of the vacant zeolite possessed well defined orbicular grain
like crystals. Given sample of encumbered zeolite also showed the orbicular rock
crystals indicating that the zeolite crystallites were not affected by the imprisonment
[40].
The X-ray powder diffraction shapes of [Fig. 6(a), (b)] were observed at 2θ
(degree) values for studying crystallinity of Na-Y and their imprisoned transition
metal complexes. XRD patterns of the zeolite-Y imprisoned complexes showed the
diffraction lines of the neat zeolite that displayed no appreciable change in peak
positions. This indicated that the crystallinity of the zeolitic framework stayed
undamaged upon imprisonment of complex moiety [41]. Conversely, the
comparative strengths of some of the diffraction lines underwent slight change
because of imprisonment.
The data obtained by vibrational spectroscopy provided evidence on the
reliability of the ligand (HNIMMPP), zeolite-Y imprisoned TMCs and the
crystallinity of the host framework. The intensity of the bands of the imprisoned
complex was feeble because of their low concentration in the matrix. The FT-IR
spectroscopic statistics of the ligand (HNIMMPP) and their imprisoned TMCs were
formulated and are presented in Table 3 and Fig. 7 respectively. The IR bands of
imprisoned complexes were similar to those of the neat metal complexes. However,
a significant change in some bands of the free ligand was observed. At ~1070 cm-1a
shrill band was obtained in all imprisoned complexes which were not observed in the
equivalent neat complexes and in ligand Fig. 7. The zeolitic framework [TO4
tetrahedral (T = Si or Al)] band dominated the spectra under 1200 cm-1 [42]. The
bands detected at ~580, ~700, and ~1110 cm-1 were attributed to T−O (structure
sensitive band) double ring, symmetric stretching and asymmetric stretching
vibrations, respectively.
The bands of HNIMMPP and their imprisoned TMCs were evaluated for
studying the coordinating mode of ligand in entrapped complexes. The spectroscopic
studies of HNIMMPP showed sharp and strong band at 1603 cm−1 owing to the
azomethine (ν(C=N)) group. This band indicated the hypsochromic impact in the

spectroscopic data of imprisoned complexes, leading to harmonization of nitrogen in
the azomethine [43]. The side chain appeared at ~3190 and ~1690 cm-1 due to the
occurrence of ν(N-H) and ν(C=O) groups of ligands (HNIMMPP) [44, 45] (Fig. 8). This
showed that the ligands existence as keto-imine tautomer shown in Scheme 1.
Additionally, we observed disappearance of phenolic -OH vibration of ligand (3380
cm−1) from the entrapped complexes. The ligand responded in enol arrangement with
prototrophy combined into proton transfer through oxygen atoms of the ligand,
forming two bonds with the metal ion. All zeolite-Y imprisoned complexes
displayed bands at 1135, 1020, 790, and 720 cm−1 owing to the host zeolite structure
[46, 47]. No shift was observed upon introduction of metal ions and the inclusion of
metal complexes. Introduction of metal ions and metal lead to no additional shift
because the zeolite-Y framework remained an unaltered complex.
The ultra-violet spectroscopic data of ligand (HNIMMPP) and their VO(IV),
Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) based imprisoned complexes along with
their respective neat complexes are tabularized in Table 4. The HNIMMPP ligand
exhibited three bands at 223, 255, and 347 nm caused by intra-ligand charge transfer
transitions π→π*. The bands of discrete neat complexes of VO(IV), Mn(II), Fe(II),
Co(II), Ni(II) and Cu(II) were seen at 212 and 245 nm as similar to 223 and 255
bands in HNIMMPP ligand. However, n→π* transition underwent hypsochromic
shifts 368 nm in VO(IV), 386 nm in Mn(II), 396 nm in Fe(II), 390 nm in Co(II), 403
in Ni(II) and 409 nm in Cu(II) neat complexes ensuing from the chelation of the
ligand with the transition metal as displayed in Fig. 9. These values were equivalent
to the values for the imprisoned VO(IV), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)
complexes observed at ~405 nm Fig. 10. Restriction of complexes within the
nanopores of zeolite-Y was observed [48].
The d-d absorption spectroscopic data of VO(IV) complexes with square
pyramidal geometry (C4v symmetry) present three bands corresponding to the
transitions b2→e, b2→b1 and b2→a1 [49]. The distortion of the square pyramidal
geometry was specified by splitting of the absorption bands [50]. The spectroscopic
data of VO(IV) imprisoned complex showed two additional absorption bands at 570
and 699 nm due to b2→b1 and b2→e transitions, respectively [51]. In the electronic
spectrum of entrapped complex Mn(II)-Y, the characteristic bands appeared at 316
6
4
and 242 nm due to A1g→4A1g, Eg (ν3) and metal to ligand charge transfer (MLCT)

transitions, respectively. This was due to distorting octahedral geometry covered to
the metal ion. The electronic spectrum of Fe(II)-Y exhibited a band at 306 nm owing
to MLCT transition. The non-appearance of d-d transitions in the spectroscopic data
of imprisoned Fe(II) complex was caused by the lower concentration on the inner
side the pores of zeolite-Y. Co(II)-Y showed bands at 421, 386, and 241 nm due to
4
4T1g(F)→4A2g(F), T1g(F)→4T1g(P), and MLCT transitions of an octahedral geometry
around the metal ions. The absorption spectrum of Ni (II)-Y exhibited two bands at
3
3
406 and 237 nm due to A2g→3T1g(P) (ν3) and A2g→3T1g(F) (ν2) transitions
respectively [52]. The electronic spectroscopic data of Cu(II)-Y consisting a band at
221 nm and a shoulder at 366 nm assigned to the dxz,yz→dxy and MLCT transitions for
tetrahedrally distorted (D2h) mononuclear copper(II) complexes respectively [53].
TGA curves are displayed in Fig. 11 and Fig. 12. For the analysis of all
imprisoned complexes, the decomposition designs were discovered to be of similar
type. At the initial stage, water molecule was removed followed by the
decomposition of complex present into the zeolite cavities. Zeolite matrix was robust
to decomposition from extreme temperature at 580-700 °C in the investigation. Only
20 to 30% mass loss was recorded till ~550 °C indicating the extraordinary thermal
constancy of zeolite matrix and low loading of metal complex in the cavities.
3.2. Catalytic liquid-phase oxidative reaction of styrene
Catalytic liquid-phase oxidative reaction of styrene was performed by
synthesized heterogeneous catalysts like zeolite-Y imprisoned TMCs using oxidant
(TBHP). The outcome of these catalytic activities yielded benzaldehyde with the
highest selectivity while styrene glycol, styrene oxide, and chalcone with less
selectivity.
3.3. Optimism of catalysis
[VO(HNIMMPP)(H2O)]-Y was used as a representative catalyst to optimize
reaction conditions. The conditions included the impact of various solvents, the
amount of catalyst, temperature, reaction time, oxidant and the mole ratio of
reactant. The legible explanation for the oxidation of styrene was:

3.3.1. Impact of various solvents
The impact of a variety of solvents on the oxidative reaction of styrene was
studied by keeping other reaction parameters fixed. Five different solvents viz.,
acetone, chloroform, acetonitrile, ethanol and carbon tetrachloride gave 81.10,
83.69, 93.35, 80.29 and 31.73% conversion to product respectively. As demonstrated
in Fig. 13, the behaviour of styrene oxidation in various solvents was strikingly
different. Acetonitrile provided the finest conversion results, followed by
chloroform. These observations revealed the reduction in conversion (%) of styrene
in acetone, chloroform, ethanol, and CCl4 was due to the lower solubility of TBHP
in the solvent as a result of which the reaction could not proceed fast. THBP and
styrene were highly soluble in acetonitrile owing to its polar surface and high
dielectric constant catalytic activity. It improved adsorptivity on the catalyst surface
and augmented the effectiveness of the conversion. Polar solvents similar to
acetonitrile simplified the establishment of active oxygen species and thus enhanced
the catalytic activity [54].
3.3.2. Impact of quantity of catalyst
The quantity of catalytic agent had a noteworthy impact on the oxidative
reaction of styrene. Dissimilar quantities of [VO(HNIMMPP)(H2O)]-Y catalyst viz.,
0.03, 0.05, 0.07 and 0.10 g were used by keeping other parameters static. The data
shown in Fig. 14 indicated 52.18, 77.64, 93.35 and 93.13% conversion
corresponding to 0.03, 0.05, 0.07 and 0.10 g catalyst respectively. Greater
conversion percentage was observed with 0.07 g catalyst. When 0.10 g of catalytic
agent was used, no further progress in the conversion was noticed. Therefore, 0.07 g
quantity of catalytic agent was considered to be optimal.
3.3.3. Impact of temperature
The oxidative reaction of styrene was examined over the temperature range of
50 to 90 ˚C as presented in Fig. 15. The (%) of conversion styrene was increased
from 60.41 to 93.35% for 10 h when the temperature was increased from 50 to 80 ˚C.
Conversion of styrene decreased on heating at 90 ˚C. This was due to rapid
decomposition of TBHP. By this we concluded that the optimum temperature was 80
˚C for the oxidative reaction of styrene.

3.3.4. Impact of reaction period
As shown in Fig. 16, by cumulative reaction spell starting from 2-12 h,
styrene conversion increased from 21.58 to 93.35%. Additional rise in reaction time
didn’t show any change in the conversion of styrene. Therefore, 10 h reaction time
was considered as optimum.
3.3.5. Impact of mole ratio of reactant to oxidant
We used mole ratio of styrene to oxidant TBHP on oxidative reaction of
styrene with four different mole ratios (1:1, 1:1.5, 1:2 and 1:2.5). Rest of the
reaction parameters were taken at constant value (10 mL acetonitrile, 0.07 g
VO(HNIMMPP)(H2O)]-Y, 80 ˚C, 10 h). As displayed in Fig. 17, percentage
conversion of styrene increases from 79.24 to 93.35% by increasing the mole ratio of
styrene and TBHP from 1:1 to 1:2. This amount of oxidant was taken to be optimal
as increase in the mole ratio to 1:2.5 lead to reduction in the styrene conversion to
90.19%. Concentration of TBHP was determined by iodometric method [56].
After optimization of reaction conditions, the oxidative reaction of styrene
was performed by using Na-Y zeolite, metal exchanged zeolite-Y, neat complex and
zeolite-Y imprisoned complexes as catalyst. In a usual reaction, TBHP as oxidants
gives major products viz. benzaldehyde, styrene glycol, styrene oxide, and chalcone.
Reaction conditions for the liquid-phase oxidative reaction of styrene were
optimized as follows: styrene (30 mmol), 60 mmol of TBHP, catalyst (0.07 g),
acetonitrile (10 mL) at the temperature point 80 ˚C for 10 h (Table 6) (Fig. 18).
As revealed in Table 6, negligible conversion occurs in the occurrence of
Na-Y zeolite and metal exchanged zeolite-Y, suggesting that complexes were
responsible of oxidative reaction of styrene. Therefore, zeolite-Y imprisoned
complexes of all three series were tested over styrene oxidation under similar
reaction conditions. The proportion transformation of styrene to benzaldehyde,
styrene oxide, styrene glycol and chalcone are presented in Table 5 (Fig. 19). This
clearly indicated that the styrene conversion varied from the catalyst to catalyst. The
transformation of styrene by zeolite-Y imprisoned complexes increased in the order:
[Mn(HNIMMPP)(H2O)3]-Y<[Fe(HNIMMPP)(H2O)3]-Y<[Co(HNIMMPP)(H2O)]-
Y<[Cu(HNIMMPP)(H2O)]-Y<[Ni(HNIMMPP)(H2O)]-Y<[VO(HNIMMPP)(H2O)]-Y.

Amongst them, zeolite-Y imprisoned oxovanadium complexes exhibited exceptional
performance by providing high catalytic transformation of styrene oxidation.
[VO(HNIMMPP)(H2O)]-Y was run repeatedly three times to check the
reusability of catalyst and the results are illustrated in Table 6 (Fig. 18). The used
catalytic agent was recuperated and washed through an abundant quantity of
condensed water and then by acetone after each catalytic run. Before reuse the
washed [VO(HNIMMPP)(H2O)]-Y was dried at 100-120 ˚C for 22-24 h. After the
primary cycle of the catalytic activity, it showed fall in the conversion with
compared to fresh one. This fall in the activity was continuous with decline in the
extent of vanadium content. This shortfall in the activity was due to low quantity of
vanadium and excess quantity of ligand in the catalyst [VO(HNIMMPP)(H2O)]-Y
framework. The imprisoned complex reacted with reactant on the surface of catalyst
with this ratio of vanadium and ligand in the reaction solution. Through the result of
AAS analysis, this assumption of vanadium content in the reaction mixture
confirmed. The content of vanadium in the catalyst remained unchanged with no
significant catalytic activity drop after second cycle. The sensitive centers were
afforded by the complex which was shielded through porous support of catalyst. This
prevented decomposition and dimerization under reaction conditions and made it
recoverable. This result showed that the catalytic agent was stable and ecological in
the behavior with negligible change in the reactivity.
3.3.6. Catalytic reaction scheme
The catalytic reaction scheme [55] for the oxidative reaction of styrene by
zeolite-Y imprisoned VO(IV) complexes is demonstrated in Scheme 2.
Theoretically, this catalytic oxidation reaction of styrene may undergo through two
possible paths. The catalytic agent reacted with TBHP to produce metal-oxo species
(II). During the process, an active metal-oxo species (II) attacked double bond. The
>C=C< double bond of styrene molecule furnished an intermediary species (III) by
oxidative addition of metal-oxo species •OOV5+L/NaY. This intermediary species
furnished cyclic styrene oxide (IV) and regenerated OV4+L/NaY. On reaction with
H+/H2O styrene oxide (IV) furnished styrene glycol (V).

Styrene oxide reacted with metal-oxo species (II) to produce benzaldehyde
(VII) through intermediate (VI). In another pathway, species (II) attacked styrene to
produce species (VIII) which formed acetophenone through intermediate (IX).
Hydroxylation reaction between benzaldehyde and acetophenone yielded chalcone
(XI) as the final product with the removal of water.
4. Conclusion
Our study deals with the creation of Schiff base ligand, its transition metal
complexes, metal ion exchanged zeolite-Y and zeolite-Y imprisoned TMCs of
HNIMMPP. Characterization of that neat and imprisoned zeolite-Y complexes and
catalytic oxidative reaction of styrene by the zeolite-Y imprisoned M(II/IV) TMCs
were done over the liquid-phase using TBHP as an oxidant. During these catalytic
studies of styrene, we found that all these imprisoned complexes were more efficient
catalysts then their uncaged complexes and zeolite-Y in the liquid-phase catalytic
oxidation. Styrene gave benzaldehyde, styrene oxide, styrene glycol and chalcone as
major products at a time of the reaction. A study was carried out to get optimum
situations by altering the amount of catalysts, solvent, amount of catalyst,
temperature, the mole ratio of oxidant and time. Studies of catalytic oxidation
showed more selectivity towards benzaldehyde from styrene. The result of catalytic
oxidative reaction of styrene, among series of imprisoned catalysts
[VO(HNIMMPP)(H2O)]-Y showed the highest percentage of conversion i.e. 93.35%.
The recyclability revealed that these imprisoned complexes truly performed
as heterogeneous catalysts.
Acknowledgement
The writers are grateful to the UGC, New Delhi and Department of Science and
Technology, New Delhi for economically backing under the NON-SAP and DST-
FIST programs, respectively. Mr. Krunalsinh A Jadeja is thankful to UGC, New
Delhi for UGC-MRP Project Fellowship. Mr. Bonny Y Patel is thankful to CSIR,
New Delhi for CSIR EMR-II Senior Research Fellowship.
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Figure Captions
Fig. 1 Synthesis of PMFP.
Fig. 2 Synthesis of Schiff base ligand HNIMMPP.
Fig. 3 Synthesis of Neat Transition metal complexes.
Fig. 4 Synthesis green cycle of zeolite-Y imprisoned transition metal complex.
Fig. 5 SEM pictures of [Co(HNIMMPP)H2O]-Y with (A) Before and (B) After
Soxhlet extraction.
Fig. 6 XRD shapes of (a) Na-Y and metal ion exchanged zeolite-Y (b) Na-Y and
zeolite-Y imprisoned transition metal complexes.
Fig. 7 FT-IR spectroscopic data of Na-Y and their imprisoned transition complexes.
Fig. 8 FT-IR spectroscopic data of ligand and their uncaged complexes.
Fig. 9 Electronic spectroscopic data of Schiff base ligand and transition metal
complexes.
Fig. 10 Electronic spectroscopic data of zeolite-Y imprisoned transition metal
complexes.
Fig. 11 TGA curves of HNIMMPP and their uncaged complex.
Fig. 12 TGA curves of zeolite-Y imprisoned complexes.
Fig. 13 Impact of various solvents on the oxidative reaction of styrene.
Fig. 14 Impact of quantities of catalysts on the oxidative reaction of styrene.
Fig. 15 Impact of temperature on the oxidative reaction of styrene.
Fig. 16 Impact of reaction time on the oxidative reaction of styrene.
Fig. 17 Impact of Mole ratio of styrene to TBHP on the oxidative reaction of
styrene.
Fig. 18 Oxidative reaction of styrene with TBHP as oxidant catalyzed by Na-Y, VO-
Y, [VO(HNIMMPP)(H2O)], [VO(HNIMMPP)(H2O)]-Y.
Fig. 19 Oxidative reaction of styrene with TBHP as oxidant catalyzed by
[M(HNIMMPP)(xH2O)]-Y.
Scheme 1 keto-imine tautomer of Schiff base ligand.
Scheme 2 Plausible reaction mechanism of the catalytic oxidative reaction of
styrene.

List of Figures
Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

(a)
(b)
Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 10