Synthesis, Characterization and Catalytic Properties of Selected Mesoporous Solids Challapalli Subrahmanyam Department of Chemistry, Indian Institute of.

Synthesis, Characterization and Catalytic Properties of Selected Mesoporous Solids

Challapalli Subrahmanyam

Department of Chemistry, Indian Institute of Technology Madras,

Chennai-600 036. India

Outline of the seminar Introduction to mesoporous solids

Mesoporous M-MCM-48 materials syntheses and catalytic activity [M= Al,Ti,V,Cr,Mn and Fe]

Mesoporous M-AlPOs- syntheses and catalytic activity [M= V,Cr and Fe]

Coatings of M41S on stainless steel grids

Synthesis and characterization of thermally stable mesoporous titania

Summary and prospects

1

Introduction

Porous solidsPorous solids

Microporous d < 2 nmZeolites, AlPO4

Mesoporous 2 < d < 50 nm

Mobil composition of materials (M41S) Hexagonal mesoporous silica (HMS) Mesoporous structural units (MSU) Tech. Mesoporous silica (TMS)

Macroporous d > 50 nmPorous gels

2

Zeolites ---- Crystalline hydrated microporous aluminosilicates

M2x/n O [ X Al2O3 Y SiO2 ] w H2O

FAU MFI

MFIMEL 3

http://www.iza-sc.ethz.ch/IZA-SC/Atlas/data/models/MFI_mod.html

Selective oxidation reactions catalyzed by TS-1

TS-1 +30% H2O2

ONOH

NH3

OH

OH

OH

OH

+

PhOH

R2CO

R2CHOHRCH=CH2

CH2RCH

O

Isabel W.C. E. Arends et al., Angew. Chem. Int. Ed. Engl. 36 (1997) 11444

AFI (AlPO-5)

VFI ( VPI-5)

AlPOs ---- Crystalline microporous aluminophosphates [AlPO4]. yR. nH2O

5

http://www.iza-sc.ethz.ch/IZA-SC/Atlas/data/AFI.html

http://www.iza-sc.ethz.ch/IZA-SC/Atlas/data/VFI.html

Selective oxidation reactions catalyzed by microporous Cr-AlPO

Cr-AlPO-5 (11)

O2

ArCH2RO2 or TBHP

ArCOR

O2 or TBHP

R2CO

R2CHOH

R3COHTBHP

R2CHOH

O2 or TBHP

R1

O

R1 R2

O

R. A. Sheldon, J. Mol. Catal., A: Chemical 107 (1996) 75 6

Mesoporous materials– An appraisal

Pore dimensions in the range of 2 – 50 nm

Advantages of mesoporous materials

Permit free ingress of reactants and egress of product species that have cross-sections smaller than the diameter of the pores

Offer greater scope for the grafting of organometallic moieties on to the inner surface of the pores ( heterogenization of homogeneous catalyst )

Open up new strategies for the production of novel materials like porous carbons and other composite materials

Different classes of mesoporous materials

M41S (Mobil Composition of Materials) series includes hexagonal MCM-41, cubic MCM-48 and lamellar MCM-50 --ionic interactions

HMS (Hexagonal Mesoporous Silica ) --- hydrogen bonding interactions

MSU or SBA (Mesoporous Structural Units ) --- hydrogen bonding interactions

TMS ( Tech. Mesoporous Silica ) --- covalent bonding interactions

S. Biz et al., Catal. Rev.- Sci. Eng., 40 (3) (1998) 329 7

Hexagonal MCM-41 Cubic MCM-48 Lamellar MCM-50

Mesoporous M41S Materials

J.S. Beck et al., J. Am. Chem. Soc., 114 (1992) 10834 & T. Kresge et al ., Nature 359 ( 1992) 710

8

The role of quaternary directing agents

Small individual alkyl chain length quaternary directing agents generate the formation of microporous solids

Long alkyl chain length quaternary directing agents self-assemble to supramolecular Species which can generate the formation of mesoporous molecular sieves

Thomos J. Barton et al., Chem Mater., 11 (10) ( 1999) 2633 9

Summary of Possible Synthetic Strategies for M41S Materials

Notation Surfactant Inorganic precursorType of interaction Examples

Ionic(Direct pathways)

Cationic + Anionic S+-----I- M41S,M-MCM-41, 48

Anionic + Cationic S------I+ M-M41S,

Ionic(Mediated pathways )

Cationic + Cationic S+ X-I+ SBA, APM

Anionic + Anionic S- M+ I- Metal Oxides

Hydrogen bonding (Neutral )

Neutral + Amine

Neutral S0-----I0 HMS

Neutral +Polymer

Neutral S0-----I0 SBA

Covalent

Neutral + Neutral S-----I TMS

10

Possible modifications of MCM-41

1

2

3

4

5

6

J.Y. Ying et al., Angew. Chem. Int. Ed., 38 (1999) 56 & Kim et al., Chem. Commun., (1998) 259 11

What makes MCM-48 interesting candidate ?

Three dimensional interwoven structure

More resistant to pore blockages

High surface area, pore volume and thermal

stability

Higher catalytic activity than one dimensional

counterpart, MCM-41.

Structures of MCM-41 and MCM-48

A. Monnier et al., Science 261 (1993) 1299 & M. Kruk et al., Chem. Mater., 11 (9) (1999) 2568 12

TMAOH/ NaOHTMAOH/ NaOH

Transition metal precursor

Transition metal precursor

Homogeneous gelSiO2:MxOy: CTAB: Na2O: EtOH: H2O

2.0: 0.015:0.24: 0.5: 1-2: 195.01

Homogeneous gelSiO2:MxOy: CTAB: Na2O: EtOH: H2O

2.0: 0.015:0.24: 0.5: 1-2: 195.01

pH ~ 10.5,Vigorous stirring

Stirred at RT – 3hAutoclaved at 428 K –12 hFiltered, oven dried

M-MCM-48 +Surfactant


Calcination at 823 K in N2 – 2h air ---10h

Synthesis and modification of MCM-48Synthesis and modification of MCM-48

Transition metal precursors

Al- Aluminium sulphate Fe- Ferric nitrate Ti- Tetrabutyl orthotitanate V-Vanadyl acetylacetonate Cr- Chromium nitrate Mn- Manganese acetate

Transition metal precursors

Al- Aluminium sulphate Fe- Ferric nitrate Ti- Tetrabutyl orthotitanate V-Vanadyl acetylacetonate Cr- Chromium nitrate Mn- Manganese acetate

TEOSTEOS

M-MCM-48M-MCM-48

Cetyltrimethyl ammonium bromideCetyltrimethyl ammonium bromide

13

XRD

Catalyst

d211

(uncalc.)

Å

d211

(calc.)

Å

a=

d (h2+k2+l2) Å

Si-MCM-48 33.7 32.9 80.5

Al-MCM-48 33.69 32.75 80.22

Fe-MCM-48 34.75 33.1 81.07

Ti-MCM-48 34.5 32.9 80.50

V-MCM-48 35.3 33.45 81.95

Cr-MCM-48 35.9 33.65 82.42

Mn-MCM-48 36.4 34.1 83.52

XRD patterns of Si-MCM-48(a) uncalc.(b) calc.

14

N2 adsorption-desorption data

Catalyst

BET surface

area (m2/g)

Pore size (Å)

Pore volume

(cc/g)

Si-MCM-48 1,020 28 1.01

Al-MCM-48 975 28.5 0.95

Fe-MCM-48 840 28 0.91

Ti-MCM-48 953 28 0.85

V-MCM-48 745 29 0.77

Cr-MCM-48 640 29 0.70

Mn-MCM-48 850 28 0.87

N2 adsorption-desorption isotherms of Si-MCM-48

15

Catalyst Observed bands (nm)

Assignment of the bands

Ti-MCM-48 uncalc.

Ti-MCM-4 8calc.

V-MCM-48uncalc.

V-MCM-48 calc.

Cr-MCM-48 uncalc.

Cr-MCM-48 calc.

Fe-MCM-48 uncalc.

Fe-MCM-48 calc.

210-230

210-230

250-280

350-370

250-280

350-370

420-440

610-630

360-390

230-260

230-260

LMCT (O Ti +4)

LMCT ( O Ti +4)

LMCT (O V+5 )

LMCT (O V+4)

LMCT ( O V+5 )

LMCT ( O V+4)

d d (Cr+3, Oh )

d d (Cr+3, Oh )

LMCT (O Cr+ 6)

LMCT (O Fe+3)

LMCT (O Fe+3)

UV-VIS (nujol ) data of M-MCM-48

16

Catalyst g A (Gauss) Assignment of the signals

V-MCM-48uncalc.

V-MCM-48 calc.

Cr-MCM-48 uncalc.

Cr-MCM-48 calc.

Mn-MCM-48 uncalc.

Mn-MCM-48 calc.

Fe-MCM-48 uncalc.

Fe-MCM-48 calc.

g | | = 1.93

g = 2.0

g | | = 1.93

g = 2.0

g = 2.0

----

g= 2.0

-----

g= 4.3

g= 2.0

g= 4.3

g= 2.0

A | | = 180

A= 70

A | | = 180

A= 70

A= 80

V+4 in a distorted Oh environment

Decrease in intensity of the signal

Confirms oxidation of V+4 to V+5

Cr+3 in a distorted Oh environment

Oxidation of Cr+3 to Cr+6

Mn +2 in a distorted Oh environmentOxidation of Mn+2 to Mn+3

Fe+3 in a Td environment

Fe+3 in a distorted Oh environment



ESR data of M-MCM-48

17

Catalyst Temp. (K)

Conv. (%)

Product selectivity (%)

-isopropyl

naphthalene

-n-propyl

naphthalene

di-substituted naphthalene

H-Y

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

HY

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

HY

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

HY

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

598

598

598

598

623

623

623

623

648

648

648

648

673

673

673

673

28.6

33.2

34.1

32.8

17.3

30.5

30.5

29.4

12.5

30.5

34.5

28.5

7.4

18.7

19.4

14.6

78.0

82.0

84.1

71.9

88.0

83.5

85.0

72.5

>99

83.5

87.0

84.7

>99

96.0

92.0

>99

--

13.0

9.5

22.1

-

13.0

10.0

27.5

--

13.0

6.6

15.1

--

--

--

traces

22.0

5.0

6.4

--

12.0

3.5

5.0

--

--

3.5

6.4

traces

--

4.0

8.0

--

Reaction conditions: Weight of the catalyst=500 mg, Flow rate =10ml/h Naphthalene: Alcohol= 1:100 (mole)

Propylation of naphthalene over acid catalysts

18

Catalyst Temp. (K)

Conv. (%)


-isopropyl

naphthalene

-n-propyl

naphthalene


H-Y

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-Y

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-Y

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-Y

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

598

598

598

598

623

623

623

623

648

648

648

648

648

673

673

673

34.6

35.8

37.5

34.0

20.2

31.3

32.7

29.9

15.0

27.4

27.4

25.6

9.2

24.0

24.7

22.9

80.0

84.5

83.5

87.1

90.0

88.5

87.0

90.1

95.0

90.0

87.5

91.1

98.0

89.1

90.2

87.1

--

15.1

12.8

12.9

11.4

10.5

9.9

--

9.8

11.5

8.9

--

10.2

9.5

12.9

--

traces

3.7

--

10.0

traces

2.5

--

4.7

traces

1.0

--

traces

traces

traces

-- Reaction conditions: Weight of the catalyst=500 mg, Flow rate =12.5 ml/h Naphthalene: Alcohol= 1:100 (mole)

19

Mechanism of propylation

H-MCM-48CH3-CH2-CH2--OH

CH2--CH2-CH3

CH3--CH-CH3

II

+

I II

+

I

CH3-CH2-CH2

CH

CH3

CH3

CH

CH3

CH3

CHCH3

CH3

+

20

H-MCM-48

CH3CH2CH2OH +

CH2--CH2-CH3

+

CH

CH3

CH3

CH

CH3

CH3

CHCH3

CH3

+

Catalyst

Temp. (K) Conv. (%)


-isobutyl

naphthalene


H-Y

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

598

598

598

598

623

623

623

648

648

648

673

673

673

0.0

5.4

5.4

4.9

5.5

5.7

5.2

5.5

6.4

5.1

5.0

5.8

4.3

--

>99

95

>99

>99

91.2

>99

>99

92.0

>99

>99

92.8

>99

--

traces

5.0

--

--

8.8

--

--

8.0

-

-

7 .2

---

Reaction conditions: Weight of the catalyst=500 mg, Flow rate =10ml/h Naphthalene: Alcohol= 1:100 (mole)

Butylation of naphthalene over acid catalysts

21

Catalyst

Temp. (K) Conv. (%)


-isobutyl

naphthalene


H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

H-MCM-41

H-Al-MCM-48

H-Fe-MCM-48

598

598

598

623

623

623

648

648

648

673

673

673

5.0

5.4

4.5

5.6

6.0

5.2

5.0

5.0

4.8

4.8

5.0

4.5

> 99

95

>99

> 99

97

> 99

> 99

99

> 99

> 99

> 99

> 99

-

5.0

--

--

3.0

--

--

traces

--

--

--

-- Reaction conditions: Weight of the catalyst=500 mg, Flow rate =12.5 ml/hNaphthalene: Alcohol= 1:100 (mole)

22

Mechanism of butylation

CH3-CH2-CH2-CH2-OH

H-MCM-48

CH3-CH2-CH2-CH2+

CH3-CH2-CH-CH3

+

I II

+ II

CH2-CH3CH

CH3

CH2-CH3

CH3-CH2

CH

CH3

CH

CH3

+

23

CH2-CH3CH2-CH3

CH3-CH2

CH

CH3

CH

CH3

CH

CH3+

+H-MCM-48

CH3-CH2-CH2-CH2-OH

-isobutylnaphthalene 2,6-di-isobutylnaphthalene

Hydroxylation of phenol over M-MCM-48 [M= Ti, V, Cr and Mn]

Hydroxylation of phenol over various catalysts in water

Reaction conditions Temperature = 333 K, Duration = 4 h, Mole ratio of the reactants = phenol: 30 % H2O2: Solvent = 1: 1: 10

CatalystConv. of phenol (%)


Catechol HydroquinonePara benzoquinone

Ti-MCM-48

V-MCM-48

Cr-MCM-48

Mn-MCM-48

12 . 65

10.50

10.60

10.65

51.4

50.5

50.7

51.5

43.3

41.7

40.7

40.4

5.3

7.8

8.6

8.1

PhenolCatechol Hydroquinone Parabenzoquinone

O H

+ H2O2

M-MCM-48 O HO H

O H

O H

O

O

++

24

Hydroxylation of phenol over various catalysts in acetone

Reaction conditions Temperature = 333 K, Duration = 4h, Mole ratio of the reactants = phenol: 30 % H2O2: Solvent = 1: 1: 10




Ti-MCM-48

V-MCM-48

Cr-MCM-48

Mn-MCM-48

10.25

4.46

4.96

7.86

52.6

50.7

59.1

51.5

31.3

22.7

20.0

18.7

16.1

26.6

20.9

29.8

25

Hydroxylation of phenol over various catalysts in acteonitrile

Reaction conditions : Temperature = 333 K, Duration = 4 h, Mole ratio of the reactants = phenol: 30 %H2O2: Solvent = 1: 1: 10




Ti-MCM-48

V-MCM-48

Cr-MCM-48

Mn-MCM-48

10.70

3.57

7.53

8.12

58.9

50.1

51.8

61.1

24.6

17.9

20.5

23.5

16.5

32.0

27.7

15.4

26

Synthesis, Characterization and Catalytic Properties of V, Cr and Fe Substituted Mesoporous

Aluminophosphates

27

Synthesis Information Reference

Microporous AlPO4 (1982)

AlPO-5 (1986)

Synthesis of M41 S (1992) Hexagonal mesoporous AlPO (1997)

Synthesis of AlPO (1997 )

Synthesis of SAPO (1997). Hexagonal ,cubic and lamellar aluminoborates (1997) Synthesis of hexagonal AlPO ( 1997)

Structure of AlPO4

Structure of Transition element incorporated AlPO4

Structure of mesoporous silica

Synthesis and structural characterization Synthesis of AlPO through fluoride route Structural characterization

Synthesis and characterization

Synthesis and characterization

Wilson et al J.Am.Chem.Soc.104, 1176

Flanigen et al. Proceedings of 7th international zeolite conference, tokyo, p 103 Mobil researchers Nature 359, 710 Kimura et alChem. Lett., 983 Feng et al. J. Chem.Soc.Chem.Commun. 949 Chakrborty et al. J. Chem.Soc.Chem.Commun. 911 Ayyappan et alJ. Chem.Soc.Chem.Commun. 575 Kevan et al. J. Chem.Soc.Chem.Commun. 1009

Advances in aluminophosphates

Continued…… 28

Synthesis Information Reference

Synthesis of Mn-AlPO ( 1997 ) Synthesis of Ti-AlPO ( 2000) Synthesis of Cr-AlPO (2002) Synthesis of V-AlPO (2002) Synthesis of Fe-AlPO (2002)

Structure and characterization Characterization and catalytic activity Characterization and catalytic Activity Characterization and catalytic activity Characterization and catalytic activity

Kevan et alJ.Phys.Chem. 102, 1250 Kapoor et alAppl.Catal.A: General 203, 311 Subrahmanyam et al . Catal.Commun.,3 ,45 Subrahmanyam et al. Eurasian ChemTech Journal, 4, 169

S.K. Mahapatra et al Chem. Commun., 1466

29

H3PO4+ H2OH3PO4+ H2O

CTABCTAB

pH ~ 9.5 with TMAOHVigorous stirring

Stirred at RT – 3-12 hAutoclaved at 428 K –24 hFiltered, oven dried

V-AlPO +SurfactantV-AlPO +Surfactant

Calcination at 773 K in N2 – 2h Air ---10h

Al(OH)3 + Transition metal source

Al(OH)3 + Transition metal source

V-AlPOV-AlPO

Synthesis of (V, Cr and Fe)- AlPOSynthesis of (V, Cr and Fe)- AlPO

Use of NaOH resulted amorphous materials

pH 9.5 is optimum as higher pH resulted amorphous materials

Thermal stability of the material is up to 1073 K

Homogeneous gel(1-X)Al2O3: P2O5: X Mx Oy: Y CTAB: TMAOH :

wH2O, where X= 0.01-0.2,Y= 0.4-0.5

and w= 300

Homogeneous gel(1-X)Al2O3: P2O5: X Mx Oy: Y CTAB: TMAOH :

wH2O, where X= 0.01-0.2,Y= 0.4-0.5

and w= 300

30

XRD patterns of V-AlPO (a) as-synthesized (b) calcined

33.0

34.5

31

N2 adsorption-desorption isotherms of (a) V-MCM-48 and (b) V-AlPO

BET surface area of V-AlPO is 650 m2/g with a pore size distribution of 28 Å

BET surface area of V-MCM-48 is 745 m2/g with a pore size distribution of 28 Å

32

UV-VIS spectra of (a) V-AlPO calc. (b) V-MCM-48 cacl. and (c) bulk V2O5

360 nm275 nm

535nm

M. Hartmann et al., Chem. Rev., 99 (3) (1999) 635 33

ESR spectra of V-AlPO (a) uncalcined (b) calcined

gII

g

gII =1.93 and AII = 180 gauss

g =1.98 and A = 70 gauss

b

a

M. Hartmann et al., Chem. Rev., 99 (3) (1999) 635 34

XPS spectrum of V-AlPO (V2p )

Peak at 516 eV corresponding to V+4 where as 517.4 eV corresponds to V+5

35

Catalystd

[uncalc]Å

d

[calc]

Å

a= Å

BET surface area m2/g

Pore size Å

Pore volume

cc/g

AlPOV-AlPOCr-AlPOFe-AlPO MCM-48

V-MCM-48Cr-MCM-48Fe-MCM-48

33.234.535.035.833.7

35.3035.934.7

32.133.033.4

34.7432.9

33.4533.633.1

37.4738.101

38.561

40.5680.502

81.952

82.402

81.07

695650485820

1,020745640840

2828292829282928

0.650.650.510.610.990.770.700.91

Physico-chemical properties of studied catalysts

36

Catalyst Observed bands (nm)

Assignment of the bands

V-AlPO uncalc.

V- AlPO calc.

Cr- AlPO uncalc.

Cr- AlPO calc.

Fe- AlPO uncalc.

Fe- AlPO calc.

250-280

350-370

250-280

350-370

420-440

610-630

360-390

230-260

230-260

LMCT (O V+5 )

LMCT (O V+4)

LMCT ( O V+5 )

LMCT ( O V+4)

d d (Cr+3, Oh )

d d (Cr+3, Oh )

LMCT (O Cr+ 6)

LMCT (O Fe+3)

LMCT (O Fe+3)

UV-VIS data of M-AlPO

37

Catalyst g A (Gauss) Assignment of the signals

V-AlPO uncalc.

V-AlPO calc.

Cr-AlPO uncalc.

Cr-AlPO calc.

Fe-AlPO uncalc.

Fe-AlPO calc.

g | | = 1.93

g = 2.0

g | | = 1.93

g = 2.0

g = 2.0

g= 1.98

g= 4.3

g= 2.0

g= 4.3

g= 2.0

A | | = 180

A= 70

A | | = 180

A= 70

V+4 in a distorted Oh environment

Decrease in intensity of the signal

Confirms oxidation of V+4 to V+5

Cr+3 in a distorted Oh environment

Oxidation of Cr+3 to Cr+5





ESR data of M- AlPO

38

Oxidation of Toluene over Mesoporous V-AlPO & V-MCM-48

39

Solvent Conversion (%)


Benzaldehyde Benzoic acid

Benzyl alcohol

Others

NoneAcetone

AcetonitrileMethanol

Acetone(1st

recycled )

8.527.421.514.322.5

78.576.573.339.076.1

16.520.422.826.119.5

2.03.13.96.34.4

3.0-----

28.6a

--




Benzyl alcohol

Others

NoneAcetone

AcetonitrileMethanol

Acetone (1st recycled)

5.523.219.411.220.1

71.474.470.934.475.0

20.021.123.924.021.3

5.14.52.5

10.53.7

3.5--

3.031.1a

--

a is methyl benzoate

(Reaction conditions: Catalyst = 100mg, Substrate: TBHP: Solvent = 1 :2 :5 (mole ratio) T= 333 K, t= 6h)

V-MCM-48

V-AlPO

Oxidation of toluene with 70% TBHP

40

Catalyst

Conversion (%)


Benzaldehyde

Benzoic acid

Benzyl alcohol

O-Cresol P-Cresol Others

V-AlPOV-MCM-48V-MCM-41V-Al-Beta

VS-1V-AlPO( 1st

recycled)

28.422.720.814.011.724.6

64.467.262.056.052.265.0

4.16.0------

5.6

4.01.52.04.07.74.0

12.015.520.021.019.711.8

9.8

10.514.017.017.110.1

1.04.02.02.03.73.5

Oxidation of toluene with 30 % H2O2

(Reaction conditions: Catalyst = 100mg, Toluene: 30 % H2O2 : Acetonitrile =

3:1:10; T= 353 K, t= 24h )

41

Performance of various catalysts for oxidation of toluene with 70 % TBHP( Literature comparison )

Catalyst Temp (K)

Conv. Of Toluene (%)


(o + p) cresol

Benzaldehyde Benzylalcohol

Others

VAPO-31V-AlPOa

V-MCM-48a

Cr-S-1 VAPO-5

VS-1Cr/ S-1

303333333353343353353

44.021.519.418.413.08.33.3

---------0.7---8.05.6

65.096.194.528.589.058.057.4

6.03.92.5

25.75.0

24.837.0

29.0

--3.0

45.16.0------

Reaction conditions: weight of the catalyst = 100 mg,solvent ---acetonitrile, reaction duration (t) = 24 h, a reaction duration ---6 h,

42

CatalystTemp (K)

Conv. Of

Toluene


(o + p) cresol

BenzaldehydeBenzylalcohol

Others

V-AlPOa

V-MCM-48a

V-MCM-41a

V-Al-Betaa

VS-2a

Vanado peroxo complex

H4PVMo11O40

H5PV2Mo10O40

H6PV3Mo9O40

H5PV2Mo10O40

333333333333333303

303303303331

28.422.720.814.011.752.0

21.425.648.435.4

21.825.534.038.036.896.2

89.291.591.691.4

73.268.562.056.052.2 3.8

10.1 7.7 8.4 8.6

4.01.52.04.07.7--

< 1<1----

1.04.02.02.03.7--- --------

Reaction conditions : Solvent –acetonitrile, reaction duration (t) = 3 h a –weight of the catalyst = 100 mg; duration of the reaction ( t) = 18 h

Performance of various catalysts for oxidation of toluene with 30 % H2O2

( Literature comparison )

43

Catalytic activity of Mesoporous Cr-AlPO & Cr-MCM-48

Vapour phase oxidation of toluene with molecular oxygen

44

Temperature

( K)

Conversion of Toluene

(%)


Benzaldehyde Benzene Others

523548573598623648

0.750.901.402.234.859.19

91.083.560.450.642.425.3

2.42.63.06.18.2

12.4

6.613.936.643.349.462.3

Cr-AlPO

( Reaction conditions : 40 % oxygen + 2 % toluene diluted in argon )

45

Temperature (K) Conv. of Toluene (%)


Benzaldehyde Others

523548573598623648

0.901.242.203.406.88

11.33

75.3961.5744.7633.9020.6216.0

24.6138.4355.2466.1079.3884.0

Toluene oxidation over Cr-MCM-48

46

TPDA profile of Cr-AlPO

47

d es o

r be d

am

mo n

i a (

a .u )

Possible reaction scheme of toluene oxidation on Cr-AlPO

1. Oxidation of toluene on redox sites (Cr+5/+6 )

2. Dealkylation on acid sites (Al+3) 3. Combustion on acid sties

CH3

COx + H2O

O2O2

O2

O2

CHO

1

2

3

48

Liquid phase oxidation of Ethylbenzene with TBHP over Cr-AlPO and Cr-MCM-48



Acetophenone Others

None

Acetonitrile

Acetone

9.8

23.2

28.5

94.6

97.0

97.7

3.0

2.3

5.4



Acetophenone Others

None

Acetonitrile

Acetone

7.6

18.9

20.4

93.7

97.6

98.2

6.3

2.4

1.8

Cr-AlPO

Cr-MCM-48

Reaction conditions : Ethylbenzene : TBHP: Solvent = 1: 1: 5Weight of the catalysts = 100 mg; T= 333 K ; t= 6 h

49

Liquid phase oxidation of Benzyl alcohol with TBHP over Cr-AlPO and Cr-MCM-48

Cr-AlPO

Cr-MCM-48

Reaction conditions : Benzyl alcohol : TBHP: Solvent = 1: 1: 5Weight of the catalysts = 100 mg; T= 333 K ; t= 6 h




Others

None

Acetonitrile

Acetone

29.1

38.9

43.1

74.5

58.8

69.2

21.3

37.5

29.5

4.2

3.7

1.4




Others

None

Acetonitrile

Acetone

26.3

38.0

39.8

67.1

60.0

56.5

29.0

36.1

40.6

3.9

3.9

2.9

50

Catalytic activity of mesoporous Fe-AlPO & Fe-MCM-48

Aerial oxidation of cyclohexane

51

Catalyst Conversion

(%)


cyclohexanol cyclohexanone Others

Fe-AlPO

Fe-AlPO + 3 wt% TBHP

Fe-AlPO + 3 wt % HQ

Fe-MCM-48

Fe-AlPO*

7.5

14.2

1.4

1.3

7.7

86.6

92.0

68.0

99

87.2

7.0

3.7

29.6

--

6.1

6.4

4.3

--

--

6.7

Aerial oxidation of cyclohexane over Fe-AlPO

Reaction conditions : Pressure = 20 bar, T = 403 K, t= 24 h, *= 30 bar

+ AirO

OH

52

Coatings of M41S on stainless steel grids

Can we replace existing catalysts with M41S in industrial processes ?

53

General limitations of M41S materials

Poor crystallinity ----- Limited heat and mass transfer

Fine particle size ----- High pressure drop

Alternative methods to be used to over come these limitations

To coat M41S on inert support ( stainless steel, glass fiber etc.)

Coating of M41S on glass fiber ----- not stable in alkaline medium

Support used for the present study : Stainless steel

54

Composition of the stainless steel grids Fe(65-70 % ) Mo (2-2.5%), Ni (11-14%) and Cr ( 16.5-18.5 %),

Photograph of the grid used to prepare M41S

55

CTAB +NaOH

CTAB +NaOH

Homogeneous gelHomogeneous gel






In-situ Synthesis of M-MCM-41/ Stainless steel gridsIn-situ Synthesis of M-MCM-41/ Stainless steel grids

Pretreatment of the grid

Washed in boiling acetone – 30 minWashed in toluene – 30 min.

1 NH4OH: 1 H2O2: 5 H2O – 30 min.1 HCl: 1 H2O2: 6 H2O – 30 min.

Ultrasonification – 15 min.

0.1 M CTAB – 1 h, oven dried –2 h






TEOSTEOS

MCM-41 / Stainless steel grid

MCM-41 / Stainless steel grid

56

Formation of MCM-41 has been confirmed

d100 spacing ~ 37.5 Å

Type IV isotherm with a hysteresis loop

BET Surface area ~ 550 m2/g

Pore size distribution around 28 Å

XRD pattern of MCM-41/ grid

N2 adsorption-desorption isotherms of MCM-41/ grid 57

Complete coverage on the grid

Spherical morphology has been observed

Material remains intact on the grid even after calcination

SEM images of MCM-41/ stainless steel grids

58

Regular pores around ~3 nm consistent with N2 adsorption- desorption dataTEM image of MCM-41/ Stainless steel grid

59

CTAB +NaOH

CTAB +NaOH

Homogeneous gel2 SiO2: 0.24 CTAB: 0.5 NaOH:

1-3 EtOH: 195 H2O

Homogeneous gel2 SiO2: 0.24 CTAB: 0.5 NaOH:

1-3 EtOH: 195 H2O



Si-MCM-48 +Surfactant

Si-MCM-48 +Surfactant


In-situ Synthesis of MCM-48/ Stainless steel gridsIn-situ Synthesis of MCM-48/ Stainless steel grids











TEOSTEOS

Si-MCM-48 / Stainless steel grid

Si-MCM-48 / Stainless steel grid

60

Formation of MCM-48has been confirmed

d211 spacing --32.5 Å

Type IV isotherm with a hysteresis loop

BET Surface area ~ 740 m2/g

Pore size distribution around 28 Å

XRD pattern of MCM-48/ grid

N2 adsorption-desorption isotherms of MCM-48/ grid

0

500

1000

1500

2000

2500

3000

0 2 4 6 8Two theta

61

SEM images of MCM-48/ stainless steel grids

Complete coverage on the grid

Spherical morphology has been observed

Material remains intact on the grid even after calcination

62

TEM image of MCM-48/ Stainless steel grid

Regular pores around ~3 nm consistent with N2 adsorption- desorption data

63

Synthesis and Characterization of Thermally Stable Mesoporous Titania

Can we extend this approach to prepare other transition metal oxides ?

64

Mechanism Surfactant Inorganic precursor

pH, method

Removal of surfactant

Reference

Ionic

S+ --- I-

S- --- I+

S- --- I+

HydrogenBonding

So --- Io

NeutralNo --- Io

CTAB

Dodecylphosphate

Dodecylphosphate

Dodecylamine

ABA tri-block copolymer

Ti-alkoxide +Triethanolamine

Ti-alkoxide+Acetylacetone Ti-alkoxide

Ti-alkoxide+acetylacetone Ti-alkoxide

10.5150 oC

1-3,RT 1-3,RT 5.0,RT RT

Calcination at 500 oC

Extraction with EtOH Extraction

Extraction

Calcination/extraction

Solid State science 2(2000) 513

Micro.Meso.Mat 30 (1999) 315

Chem.Mater 9(1997) 2690

Angew.Chem.Int.Ed.Engl 4 (1995) 2014 Nature 396(1998) 152

Advances in the synthesis of mesoporous titania

65

TMAOHTMAOH

(1) Ti-orthotitanate + Polyethylene glycol (1) Ti-orthotitanate + Polyethylene glycol

Homogeneous gel

Homogeneous gel


Stirred at RT – 1 h

Autoclaved at 428 K –12 hFiltered, oven dried

TiO2 +

Surfactant

TiO2 +

Surfactant

Calcination at 823 K in N2 –5 h

air ---10hTiO2TiO2

Cetyltrimethylammonium bromideCetyltrimethylammonium bromide

Points to be considered

Control of the rate of hydrolysis of

titanium precursor

Choice of the base

Specific temperature for the synthesis

Removal of the surfactant.

Synthesis of mesoporous titania

66

Thermogram of mesoporous TiO2

250 oC 430 oC

CTABPEG

67

0.00E+00

1.00E+03

2.00E+03

3.00E+03

4.00E+03

5.00E+03

6.00E+03

7.00E+03

8.00E+03

0 2 4 6 8 10 12

0.00E+00

5.00E+02

1.00E+03

1.50E+03

2.00E+03

2.50E+03

3.00E+03

3.50E+03

4.00E+03

0 2 4 6 8 10 12

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12

0

2000

4000

6000

8000

10000

12000

0 1 2 3 4 5 6

XRD patterns of mesoporous TiO2 a) as-synthesized (b) calcined at 823 K (c ) calcined at 923 K and (d) calcined at 1023 K

(a) (b)

(c) (d)

45.9 Å 41.1Å

41.5 Å

Two thetaTwo theta

Two thetaTwo theta

68

P/p0N2 adsorption-desorption isotherms of mesoporous TiO2

BET surface area of mesoporous titania is 675 m2/g with a pore size distribution of 30 Å

69

Cubic MCM-48 has been synthesized at lower

concentration of the surfactant Cubic MCM-48 is a better catalytic system compared

to hexagonal counterpart MCM-41Ti-MCM-48 exhibits higher activity for phenol

hydroxylation and water is a better solvent Mesoporous V-AlPO shows higher conversion and

selectivity for oxidation of toluene Side chain oxidation is predominant over mesoporous

V-AlPO with both 70 %TBHP and 30 % H2O2

Summary and Prospects

Continued …………. 70

Mesoporous Cr-AlPO shows both acidic and redox

properties where as Cr-MCM-48 is purely a redox

catalystMolecular oxygen/air has been employed as

oxidant over mesoporous AlPOs Mesoporous Fe-AlPO promotes aerial oxidation of

cyclohexane Coatings of M41S/ Stainless steel grids open new

directions for potential applications of mesoporous

materials Synthesis of thermally stable mesoporous titania opens

new strategies for the preparation of other oxide

materials in mesoporous form 71

Acknowledgements Acknowledgements

Prof. T.K. Varadarajan & Prof. B. Viswanathan

Prof. A. Renken & Dr. L. K. Minsker Prof. A. Renken & Dr. L. K. Minsker

Profs. UVV, KV, MSS and DVS Murthy Profs. UVV, KV, MSS and DVS Murthy

Prof. KKB and Head RSICProf. KKB and Head RSIC

Benoit Louis and Fabio RainoneBenoit Louis and Fabio Rainone

Mr. A. Narayanan and Mr. SivaramakrishnanMr. A. Narayanan and Mr. Sivaramakrishnan

Dr. MRK Prasad, Dr. K.V. S. Subba Rao (IICT, Hyd), Dr. C. Patra (NCL, Pune) Dr. MRK Prasad, Dr. K.V. S. Subba Rao (IICT, Hyd), Dr. C. Patra (NCL, Pune) and Dr. Suja (CUSAT, Cochin) and Dr. Suja (CUSAT, Cochin)

Friends and colleagues Friends and colleagues

72

Synthesis, Characterization and Catalytic Properties of Selected Mesoporous Solids Challapalli Subrahmanyam Department of Chemistry, Indian Institute of.

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