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under constant stirring to a solution of tetraethyl ammo-

niumhydroxide (TEAOH) and NaOH at ambient tem-

perature. After 4 h colloidal silica was added dropwise

over a period of 1 h, followed by vigorous stirring for

4 h. The Si/Al ratio of the gel was 40. Crystallization

took place over 24 h at 105 C. The resulting white solid

was washed with water and dried at 120 C. The tem-plate was removed by heating the material to 500 C

for about 12 h. The Si/Al ratio of the Al-MCM-1 was

15.

2.2. Synthesis of meso-tetraphenyl porphyrin, tetrapyridyl

porphyrin and other meso-substituted porphyrins

As in general, the synthesis of porphyrins from pyr-

role and benzaldehyde need acidic catalysts, we synthe-

sized these tetrapyrrolic macrocycles over acidic zeolite

molecular sieves under microwave irradiation in dry

media. The reaction was carried out in a pyrex bottle,in which equimolar ratio of pyrrole and aldehyde were

mixed with 0.5 g zeolite molecular sieves in appropriate

solvent which was then evaporated. The bottle was

closed with cotton plug. The mixture was then subjected

to microwave irradiation for 12 min with intervals, in

BPL domestic microwave oven, with microwave fre-

quency of 2450 MHz and 1.2 kW. After the reaction,

+ve catalyst was separated by filtration and washed

thoroughly with 100 mL (5 20 mL) chloroform. Then,

the solvent was removed under vacuum to have a vis-

cous residue. Products were separated by column chro-

matography using silica (100200 mesh size) with

n-hexane as eluent. Thus, obtained porphyrin was char-

acterized by UVvis spectrometer, NMR and mass spec-

trometry. Quantification was done by CAMAG HPTLC

system and compared with isolated yields.

Commercially available meso-tetraphenyl porphyrin

(TPP), meso-tetraphenyl porphyrin iron(III) complex

(TPP-Fe), meso-tetrapyridyl porphyrin (TpyP), meso-

tetrakis(pentafluorophenyl) porphyrin iron(III) complex

(TPFP-Fe) were obtained from Aldrich, USA.

2.3. Immobilization of Feporphyrin complexes

The basic approaches as well as the recently devel-

oped methods of entrapping and stabilizing the com-

plexes inside the zeolites were used to prepare various

catalysts, in order to screen the best possible catalytic

system. Among the various methods employed to incor-

porate metal complexes inside the pores or cavities of

zeolite are

1. Impregnation method.

2. Flexible ligand method.

3. Template synthesis method.

4. Zeolite synthesis method.

5. Anchoring or grafting of complexes in the mesopor-

ous zeolites.

(1) Impregnation method. First, an ion exchange of

commercially available HY and synthesized Al-MCM-

41 was done in aqueous solution of ferric nitrate, to have

1 wt% FeY and FeMCM-41. The mixture was stirredover for 4 h. Then, it was filtered and washed with dis-

tilled water until no color was found in the mother li-

quor. The reddish-brown solid (Fe) was first dried at

room temperature and then in an oven at 100 C, for

12 h.

(2) Flexible ligand method. Using the principle of the

diffusion of ligands into an already metal exchanged

zeolite pores, meso-tetraphenyl porphyrin (TPP) and

5,10,15,20-tetra-(4-pyridyl) porphyrin (TPyP) ligands

which are sufficiently volatile and stable during the

adsorption were employed as ligands and incorporated

in FeY and FeMCM-41 molecular sieves.

For this, the above-mentioned 1 wt% Fe exchanged

molecular sieves were stirred with both the ligands in

N2 atmosphere for 24 h under reflux conditions. The sol-

vent employed was dichloromethane. The round bottom

flask was covered with Al foil to exclude light. The resul-

tant supernatant liquid was filtered and thoroughly

washed with dichloromethane. The excess ligand and

metal complexes present on the external surface was re-

moved by soxhlet extraction with various solvents so as

to avoid the possibility of diffusional constrains to the

reactant molecules.

(3) Template synthesis method (ship-in-bottle). When

the ligand molecular dimensions are more than that ofthe pore sizes of the zeolites like HY, they cannot diffuse

into the pores of zeolite. In such cases, template synthe-

sis method is used in which the ligand itself is con-

structed inside the zeolite matrix. The molecules that

constitute the ligand species (pyrrole and benzaldehyde)

are then adsorbed into the FeY and FeMCM-41 zeolite

matrix in inert atmosphere. The molecules form the li-

gands of interest, which then complexes with the metal

ions present in the zeolite. The excess ligand precursors,

the ligand present on the external surfaces and the com-

Table 1

Synthesis of meso-tetraphenyl porphyrin (TPP) (1) over various

molecular sieves under microwave irradiation

S. no. Catalyst % Yield of

m-TPP

Soret

band (nm)

Q bands

1 Al-MCM-41 23.5 417 515, 548, 597, 645

2 HY 4.99 418 592

3 SAPO-5 0.5 418 512, 592, 642

4 HZSM-5(30) 28.0 416 512, 545, 592, 640

5 SiO2/Al2O2 1.54 417 512, 593

Catalyst weight, 0.5 g; microwave power, H1; time, 12 min; molar ratio

of pyrrole: aldehyde, 1:1. Yield and selectivity are based on pyrrole.

The catalyst was prepared by the template synthesis method.

532 V. Radha Rani et al. / Catalysis Communications 6 (2005) 531538


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plex present on the external surface were removed by the

soxhlet extraction.

(4) Zeolite synthesis method. The excess ligand and

uncomplexed metal ions are the major disadvantage of

the first three methods. In order to avoid this, the metal

complexes as meso-tetraphenylporphyrin iron(III) chlo-

ride and 5,10,15,20-tetrakis(pentafluorophenyl) porphy-

rin iron(III) chloride complexes were encapsulated during

Table 2

Synthesis of porphyrins over Al-MCM-41 molecular sieves: reactant variation

S. no. Reactants pyrrole+ % Conversion of pyrrole % Yield of the product Soret band Q bands

1 Benzaldehyde 97.9 23.5 (1) 417 515, 548, 597, 645

2 Anisaldehyde 68.5 12.6 (2) 419 519, 598, 642

3 Tolaldehyde 66.4 33.4 (3) 419 535, 592

4 3,4,5-Trimethoxy benzaldehyde 55.4 11.6 (4) 423 602

5 m-Nitro benzaldehyde 92.8 6.4 (5) 420 6016 4-Pyridine carboxaldehyde 23.2 11.7 (6) 416 512, 590

Catalyst, Al-MCM-41 (0.5 g); microwave power, H1; time, 12 min; molar ratio of pyrrole: aldehyde, 1:1. Yield is based on pyrrole. H-Al-MCM-41

was prepared by the template synthesis method.

NH

NHN

N

R

R

R

R

1: R = H2: R = p-OCH33: R = p-CH3

4: R = 3,4,5 (OCH3)5: R = m-NO2

NH

NHN

N

N N

NN

6

Fig. 1. (A) XRD patterns: (a) NaY, (b) 1 wt% FeY, (c) FePorphyrin Y. (B) XRD patterns: (a) Al-MCM-41, (b) 1 wt% FeMCM-41, (c) Fe

Porphyrin MCM-41, (d) FePorphyrin (anchored) MCM-41.

V. Radha Rani et al. / Catalysis Communications 6 (2005) 531538 533


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the synthesis of zeolite crystallization. The thermal

analysis of these catalysts is given in Figs. 2(A) and

(B).

(5) Anchoring. In case of anchoring method, there is

no need to construct metal complex in the cages like in

flexible ligand or template synthesis method as mesopor-

ous materials having pore size more than 20 A

, directencapsulation of metal complexes inside the mesoporous

materials can be achieved.

2.4. Characterization

X-ray diffraction patterns of powdered samples were

obtained using diffractometer equipped with a rotating

anode and Cu Ka radiation.

Chemical analysis was performed with inductively

coupled plasma atomic emission spectroscopy (ICP-

AES).

The thermogravimetric analysis was carried out in in-

ert atmosphere with the heating rate was 10 C min1,

and a-Al2O3 was used as reference material. FTIR and

DRS UVvis spectrum was recorded using KBr pellets.A typical oxidation reaction involved the following

procedure: to 25 ml of solvent 250 mg of catalyst was

added followed by the addition of the cyclohexene.

Then, the oxidant was added dropwise to the reaction

mixture. The reaction mixture was stirred under N2 at

room temperature and the catalytic products were ana-

lysed using a gas chromatograph equipped with SE-30

column NMR and mass spectra.

Fig. 2. (A) TGA-DTA: (a) Al-MCM-41, (b) Porphyrin complex, (c) FePorphyrinMCM-41 (flexible method), (d) 1 wt% FeMCM-41, (e) Fe

PorphyrinMCM-41 (template method), (f) FePorphyrin (during synthesis) MCM-41, (g) FePorphyrinMCM-41 (by anchoring method).

(B) TGA-DTA: (a) NaY, (b) Porphyrin complex, (c) PorphyrinY, (d) 1 wt% FeY, (e) FePorphyrin Y, (f) FePorphyrin (during synthesis) Y.



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3. Results and discussion

In order to get a first impression of whether a partic-

ular zeolite type can be chosen as carrier system that

would be a suitable host for encapsulating homoge-

neously active porphyrin complex, these macromole-

cules were synthesized over various types of zeolites

and as can be seen from the Table 1. Among the various

zeolites used, the porphyrin molecule could be obtained

selectively over HY and Al-MCM-41. The presences of

Soret band at 419 nm in the UVvis spectra confirmed

the formation of the macrocycle inside these two types

of molecular sieves.

Further, we have attempted to various substitute

these porphyrin ligands at both meso- and b-positions,

as a step towards stabilizing them from self-oxidation.

Table 2 shows that meso-tetrakis(4-pyridyl) porphyrin

and meso-tetrakis(4-methylphenyl) porphyrin could be

obtained in high yields and selectivity over Al-MCM-

41.

The immobilization of iron porphyrin complexes in-

side Al-MCM-41 and HY leads to strong interaction

of the complex in the mesoporous system of the carrier

material. The carrier material turned greenish, indicat-

ing the homogeneous catalyst was loaded onto the sup-

port. It is assumed that the complex is adsorbed on the

inner and outer surfaces of the Al-MCM-41 structure.

The binding energy of this adsorption varies on the dif-

ferent reactive sites like Bronsted and Lewis acid sites

and silanol groups. Upon the extraction with methanol,

which in contrast to nonpolar dichloromethane adsorbs

strongly on the zeolite surface, the complex desorbs

from silanol groups due to a competitive reaction with

the polar alcohol. The amount of complex immobilized

on the carrier was determined by elemental analysis.

Iron contents vary between 0.02 and 0.07 mmol per g

of zeolite depending on the amount of complex

encapsulated.

The X-ray diffraction pattern of the isolated materials

showed a strong characteristic peaks corresponding to

both Al-MCM-41 and Y-zeolite, indicating that the

crystallographic structure of the carrier material remains

unchanged during the immobilization procedure, Figs.

1(A) and (B).

Fig. 2 (continued)



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Quantitative loading of the complex was demon-

strated by thermal analysis. Thermogravimetric and dif-

ferential scanning calorimetric (DSC) measurements

show that the immobilized complex is stable up to

450 C when anchored in Al-MCM-41 whereas decom-

poses at around 350 C when encapsulated in HY zeolite

(Figs. 2(A) and (B)). The first decomposition occurs at100130 C and is slightly endothermic. Oxidation

decomposition of the fixed complex took place in two

steps at 350 and 450 C. The loss of weight of 4.5 wt%

caused by the burning of the complex is consistent with

the content determined by chemical analysis.

The infrared spectra shows no change of wave

number but a decrease of intensity for the signal at

3740 cm1 which is assigned to the stretching vibration

of terminal silanol groups. The vibration bands of

immobilized complex are similar to those in the solution

of dichloromethane. However, these signals resulting

from organic compounds are very weak and not charac-

teristic enough to surely identify or resolve a structure.

The diffuse reflectance spectra show that the complex

when anchored in Al-MCM-41 is most stable as no

additional peaks at higher wavelength appear. A strong

characteristic peak corresponding to Al-MCM-41 indi-

cates that the structure of the carrier material remains

unchanged during the immobilization procedure. All

other methods of immobilization in HY zeolite basically

resulted in some distortion of the complex, as seen in

Figs. 3(A) and (B).Among the catalysts presented here, it could be seen

that several forces could be involved in the bonding of

the complex on the carrier material. Electrostatic inter-

action of the cationic complexes occurs with the anionic

framework of the Al-MCM-41 structure. Direct bridg-

ing of the iron to surface oxygen of the zeolite walls

has also been observed and could occur after cleavage

of the complex during the reaction.

3.1. Catalytic tests

Several ligands have been applied and the corre-

sponding complexes have been tested for the immobili-

zation. As a test reaction for the catalytic activity the

epoxidation of cyclohexene was employed, where the

Fig. 3. (A) DRS UV-Vis: (a) NaY, (b) 1 wt% FeY, (c) FePorphyrin Y (flexible method), (d) FePorphyrin (template method) Y, (e) FePorphyrin

(during synthesis) Y. (B) DRS UV-Vis: (a) Al-MCM-41, (b) 1 wt% FeMCM-41, (c) FePorphyrinMCM-41 (flexible method), (d) FePorphyrin

MCM-41 (template method), (e) FePorphyrin (during synthesis) MCM-41, (f) FePorphyrinMCM-41 (modified with anchoring agent), (g) Fe

PorphyrinMCM-41 (by anchoring method).



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catalytic run was performed with cyclohexene in dichlo-

romethane with 1:4 molar ratio of TBHP at room tem-

perature for 8 h. No reaction took place in the blank test

when the carrier Y and Al-MCM-41 itself was used as

catalyst. The catalytic results of the immobilized iron

complexes are depicted in Table 3. The complex when

anchored on Al-MCM-41 (Entry 12 and 13) shows the

best results with high selectivity of cyclohexenone, at

around 99% conversion of cyclohexene.

These catalysts can easily be recovered and reused

without further treatment. The supported catalyst was

recycled four times. After these consecutive runs a de-

crease in catalytic performance was observed. This phe-nomenon goes along with the formation of lumps of the

catalyst.

In order to prove that the reaction is catalyzed heter-

ogeneously and to exclude the possibility of leaching

and homogeneous catalysis, the reaction mixture was

separated from the catalyst before complete conversion

occurs. Oxidation of the reaction solution following fil-

tration after 3 h does not give any further reaction. After

8 h the conversion of the filtered sample remains at

around 26% whereas the original batch with anchored

catalyst goes to complete conversion of cyclohexene.

This test proves that no homogeneous catalysis tookplace. ICP-AES analysis of the filtered reaction solution

showed traces of iron, silicon and aluminium. The rela-

tive amounts of this analysis correspond to the compo-

sition of the heterogeneous catalyst used. This

indicates that this loss occurs by attrition of the Al-

MCM-41 and not leaching of the complex.

4. Conclusion

Homogeneous iron porphyrin catalyst was heteroge-

nized best in Al-MCM-41. The bonding forces could

be due to the ionic interaction of the cationic complex

with the anionic host framework. A reduction of the

weak acidic sites of Al-MCM-41 has also been observed.

After heterogenation also the iron porphyrin complex

were suitable for the oxidation of olefins. The complexes

remain stable within the mesopores of the carrier under

the reaction conditions. The catalyst can be recycled by

filtration and no leaching of the homogeneous complex

was observed.

Acknowledgment

One of the authors, M.R.K. is thankful to CSIR,

New Delhi for Senior Research Fellowship.

References

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Table 3

Encapsulation of porphyrin complex in Y and Al-MCM-41: catalytic activity towards oxidation of cyclohexene

S. no. Catalyst % Conversion of cyclohexene Liquid product distribution (%)

Epoxide Cyclohexanol Cyclohexenone Cyclohexenol Diol Dione Others

1 FeY 4.7 0.15 0.49 1.53 0.6 0.21 1.71 0.01

FeMCM-41 3.7 0.22 1.59 0.04 0.25 1.56 0.04

2 FeY-A 11 0.015 0.49 2.46 0.07 7.9 0.07FeMCM-41-A 6.9 0.04 3.27 0.08 0.12 3.35 0.04

3 FeY-B 24.3 0.15 5.6 0.3 0.24 10.6 7.41

FeMCM-41-B 42.5 0.8 10.6 0.04 3.7 26.6 0.76

4 FeY-C 6.7 0.062 0.02 2.14 0.08 0.54 3.78 0.08

FeMCM-41-C 10.7 0.16 0.05 2.44 0.06 7.87 0.12

5 MCM-41-D 21.09 0.20 0.025 10.2 0.08 0.76 9.63 0.195

6 Y-E 2.5 0.18 0.76 0.03 0.29 1.23 0.01

MCM-41-E 32.9 0.22 0.02 18.0 0.01 0.49 13.8 0.36

7 MCM-41-F 43.2 0.35 10.0 1.3 20.38 11.17

8 MCM-41-G 98.8 59.4 6.1 0.16 24.4 8.74

A, meso-tetraphenyl porphyrin; B, 5,10,15,20-tetrapyridylporphyrin; C, pyrrole + benzaldehyde; D, meso-tetraphenylporphyrin iron(III) chloride; E,

5,10,15,20-tetrakis(pentafluorophenyl); F, 3-aminopropyl trimethoxysilane (APTMS) + meso-tetraphenylporphyrin iron(III) chloride; G, 3-amino-

propyl trimethoxysilane (APTMS) + 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin iron(III) chloride.



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