Synthesis, Characterization and Catalytic Properties of Selected Mesoporous Solids

1
Synthesis, Characterization and Catalytic
Properties of Selected Mesoporous
Solids   Challapalli Subrahmanyam Department
of Chemistry, Indian Institute of Technology
Madras, Chennai-600 036. India
2
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
3
Introduction
Porous solids
Mesoporous 2 lt d lt 50 nm
Mobil composition of materials (M41S)
Hexagonal mesoporous silica (HMS) Mesoporous
structural units (MSU) Tech. Mesoporous
silica (TMS)
Microporous d lt 2 nm Zeolites, AlPO4
Macroporous d gt 50 nm Porous gels
2
4
Zeolites ---- Crystalline hydrated microporous
aluminosilicates M2x/n O X
Al2O3 Y SiO2 w H2O
MFI
FAU
3
MFI
MEL
5
Selective oxidation reactions catalyzed by TS-1
Isabel W.C. E. Arends et al., Angew. Chem. Int.
Ed. Engl. 36 (1997) 1144
4
6
AlPOs ---- Crystalline microporous
aluminophosphates AlPO4. yR. nH2O

AFI (AlPO-5)
VFI ( VPI-5)
5
7
Selective oxidation reactions catalyzed by
microporous Cr-AlPO
6
R. A. Sheldon, J. Mol. Catal., A Chemical 107
(1996) 75
8
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

7
S. Biz et al., Catal. Rev.- Sci. Eng., 40 (3)
(1998) 329
9
Mesoporous M41S Materials
Lamellar MCM-50
Hexagonal MCM-41
Cubic MCM-48
J.S. Beck et al., J. Am. Chem. Soc., 114 (1992)
10834 T. Kresge et al ., Nature 359 ( 1992) 710
8
10
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
9
Thomos J. Barton et al., Chem Mater., 11 (10) (
1999) 2633
11
Summary of Possible Synthetic Strategies for M41S
Materials
Notation
Surfactant
Inorganic precursor
Type of interaction
Examples
Cationic
Anionic
S-----I-
M41S, M-MCM-41, 48
Ionic (Direct pathways)
Anionic
Cationic
S------I
M-M41S,
Cationic
Cationic
S X-I
SBA, APM
Ionic (Mediated pathways )
Metal Oxides
S- M I-
Anionic
Anionic
HMS
Neutral Amine
Neutral
Hydrogen bonding (Neutral )
S0-----I0
SBA
Neutral Polymer
Neutral
S0-----I0
Covalent
TMS
Neutral
Neutral
S-----I
10
12
3
4
2
5
1
6
Possible modifications of MCM-41
11
J.Y. Ying et al., Angew. Chem. Int. Ed., 38
(1999) 56 Kim et al., Chem. Commun., (1998)
259
13
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
14
Synthesis and modification of MCM-48
TMAOH/ NaOH
Cetyltrimethyl ammonium bromide
Transition metal precursor
TEOS
pH 10.5, Vigorous stirring

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

Homogeneous gel SiO2MxOy CTAB Na2O EtOH
H2O 2.0 0.0150.24 0.5 1-2 195.01
Stirred at RT 3h Autoclaved at 428 K 12
h Filtered, oven dried
M-MCM-48 Surfactant
Calcination at 823 K in N2 2h air ---10h
M-MCM-48
13
15
XRD
Catalyst d211 (uncalc.) Å d211 (calc.) Å a d ?(h2k2l2) 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
16
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
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UV-VIS (nujol ) data of M-MCM-48
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 V5 ) LMCT (O V4) LMCT ( O V5 ) LMCT ( O V4) d d (Cr3, Oh ) d d (Cr3, Oh ) LMCT (O Cr 6) LMCT (O Fe3) LMCT (O Fe3)
16
18
ESR data of M-MCM-48
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 V4 in a distorted Oh environment Decrease in intensity of the signal Confirms oxidation of V4 to V5 Cr3 in a distorted Oh environment Oxidation of Cr3 to Cr6 Mn 2 in a distorted Oh environment Oxidation of Mn2 to Mn3 Fe3 in a Td environment Fe3 in a distorted Oh environment Fe3 in a Td environment Fe3 in a distorted Oh environment
17
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Propylation of naphthalene over acid catalysts
Catalyst Temp. (K) Conv. () Product selectivity () Product selectivity () Product selectivity ()
Catalyst Temp. (K) Conv. () ?-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 gt99 83.5 87.0 84.7 gt99 96.0 92.0 gt99 -- 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 catalyst500
mg, Flow rate 10ml/h Naphthalene Alcohol
1100 (mole)
18
20
Catalyst Temp. (K) Conv. () Product selectivity () Product selectivity () Product selectivity ()
Catalyst Temp. (K) Conv. () ?-isopropyl naphthalene ?-n-propyl naphthalene di-substituted 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 catalyst500
mg, Flow rate 12.5 ml/h Naphthalene Alcohol
1100 (mole)
19
21
Mechanism of propylation
H-MCM-48
20
22
Butylation of naphthalene over acid catalysts
Catalyst   Temp. (K) Conv. () Product selectivity () Product selectivity ()
Catalyst   Temp. (K) Conv. () ?-isobutyl naphthalene di-substituted 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 -- gt99 95 gt99 gt99 91.2 gt99 gt99 92.0 gt99 gt99 92.8 gt99 -- traces 5.0 -- -- 8.8 -- -- 8.0 - - 7 .2 ---
Reaction conditions Weight of the catalyst500
mg, Flow rate 10ml/h Naphthalene Alcohol
1100 (mole)
21
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Catalyst   Temp. (K) Conv. () Product selectivity () Product selectivity ()
Catalyst   Temp. (K) Conv. () ?-isobutyl naphthalene di-substituted 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 gt 99 95 gt99 gt 99 97 gt 99 gt 99 99 gt 99 gt 99 gt 99 gt 99 - 5.0 -- -- 3.0 -- -- traces -- -- -- --
  Reaction conditions Weight of the catalyst500
mg, Flow rate 12.5 ml/h Naphthalene Alcohol
1100 (mole)
22
24
Mechanism of butylation
?-isobutylnaphthalene
2,6-di-isobutylnaphthalene
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Hydroxylation of phenol over M-MCM-48 M Ti,
V, Cr and Mn
  Hydroxylation of phenol over various
catalysts in water
O
H
O
O
H
O
H
M
-
M
C
M
-
4
8
O
H





H
O
2
2
Phenol
O
O
H
Catechol
Hydroquinone
Parabenzoquinone
Catalyst Conv. of phenol () Product selectivity () Product selectivity () Product selectivity ()
Catalyst Conv. of phenol () Catechol Hydroquinone Para 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
 Reaction conditions Temperature 333 K,
Duration 4 h, Mole ratio of the reactants
phenol 30 H2O2 Solvent 1 1 10
24
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Hydroxylation of phenol over various catalysts
in acetone  
Catalyst Conv. of phenol () Product selectivity () Product selectivity () Product selectivity ()
Catalyst Conv. of phenol () Catechol Hydroquinone Para benzoquinone
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
Reaction conditions Temperature
333 K, Duration 4h, Mole ratio
of the reactants phenol 30 H2O2 Solvent
1 1 10
25
27
Hydroxylation of phenol over various catalysts in
acteonitrile  
Catalyst Conv. of phenol () Product selectivity () Product selectivity () Product selectivity ()
Catalyst Conv. of phenol () Catechol Hydroquinone Para benzoquinone
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
Reaction conditions Temperature 333 K,
Duration 4 h, Mole ratio of the
reactants phenol 30 H2O2 Solvent 1 1 10
26
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Synthesis, Characterization and Catalytic
Properties of V, Cr and Fe Substituted
Mesoporous Aluminophosphates
27
29
Advances in aluminophosphates
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 al Chem. Lett., 983   Feng et al. J. Chem.Soc.Chem.Commun. 949   Chakrborty et al. J. Chem.Soc.Chem.Commun. 911   Ayyappan et al J. Chem.Soc.Chem.Commun. 575   Kevan et al. J. Chem.Soc.Chem.Commun. 1009
28
Continued
30
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 al J.Phys.Chem. 102, 1250   Kapoor et al Appl.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
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Synthesis of (V, Cr and Fe)- AlPO
H3PO4 H2O
CTAB
Al(OH)3 Transition metal source
pH 9.5 with TMAOH Vigorous stirring

• 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
Stirred at RT 3-12 h Autoclaved at 428 K 24
h Filtered, oven dried
V-AlPO Surfactant
Calcination at 773 K in N2 2h Air ---10h
V-AlPO
30
32
33.0
34.5
XRD patterns of V-AlPO (a) as-synthesized (b)
calcined
31
33

• 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

N2 adsorption-desorption isotherms of (a)
V-MCM-48 and (b) V-AlPO
32
34
360 nm
275 nm
535nm
UV-VIS spectra of (a) V-AlPO calc. (b) V-MCM-48
cacl. and (c) bulk V2O5
M. Hartmann et al., Chem. Rev., 99 (3) (1999) 635
33
35
gII
a
gII 1.93 and AII 180 gauss g? 1.98 and A?
70 gauss
b
g?
ESR spectra of V-AlPO (a) uncalcined (b) calcined
M. Hartmann et al., Chem. Rev., 99 (3) (1999) 635
34
36
XPS spectrum of V-AlPO (V2p )

• Peak at 516 eV corresponding to V4 where as
  517.4 eV corresponds to V5

35
37
Physico-chemical properties of studied catalysts
36
38
UV-VIS data of M-AlPO
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 V5 ) LMCT (O V4) LMCT ( O V5 ) LMCT ( O V4) d d (Cr3, Oh ) d d (Cr3, Oh ) LMCT (O Cr 6) LMCT (O Fe3) LMCT (O Fe3)
37
39
ESR data of M- AlPO
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 V4 in a distorted Oh environment Decrease in intensity of the signal Confirms oxidation of V4 to V5 Cr3 in a distorted Oh environment Oxidation of Cr3 to Cr5 Fe3 in a Td environment Fe3 in a distorted Oh environment Fe3 in a Td environment Fe3 in a distorted Oh environment
38
40
Oxidation of Toluene over Mesoporous V-AlPO
V-MCM-48
39
41
Oxidation of toluene with 70 TBHP
Solvent Conversion () Product selectivity () Product selectivity () Product selectivity () Product selectivity ()
Solvent Conversion () Benzaldehyde Benzoic acid Benzyl alcohol Others
None Acetone Acetonitrile Methanol Acetone(1st recycled ) 8.5 27.4 21.5 14.3 22.5 78.5 76.5 73.3 39.0 76.1 16.5 20.4 22.8 26.1 19.5 2.0 3.1 3.9 6.3 4.4 3.0 --- -- 28.6a --
V-AlPO
Solvent Conversion () Product selectivity () Product selectivity () Product selectivity () Product selectivity ()
Solvent Conversion () Benzaldehyde Benzoic acid Benzyl alcohol Others
None Acetone Acetonitrile Methanol Acetone (1st recycled) 5.5 23.2 19.4 11.2 20.1 71.4 74.4 70.9 34.4 75.0 20.0 21.1 23.9 24.0 21.3 5.1 4.5 2.5 10.5 3.7 3.5 -- 3.0 31.1a --
V-MCM-48
a is methyl benzoate
 (Reaction conditions Catalyst 100mg,
Substrate TBHP Solvent 1 2 5 (mole ratio)
T 333 K, t 6h)
40
42
Oxidation of toluene with 30 H2O2

(Reaction conditions Catalyst 100mg, Toluene
30 H2O2 Acetonitrile 3110 T 353 K, t
24h )
41
43
Performance of various catalysts for oxidation of
toluene with 70 TBHP ( Literature comparison )
Reaction conditions weight of the catalyst
100 mg,solvent ---acetonitrile, reaction
duration (t) 24 h, a reaction duration ---6
h,
 
42
44
Performance of various catalysts for oxidation of
toluene with 30 H2O2 ( Literature comparison )
Reaction conditions Solvent acetonitrile,
reaction duration (t) 3 h a weight of the
catalyst 100 mg duration of the reaction ( t)
18 h
43
45
Catalytic activity of Mesoporous Cr-AlPO
Cr-MCM-48 Vapour phase
oxidation of toluene with molecular oxygen
44
46
Cr-AlPO
( Reaction conditions 40 oxygen 2
toluene diluted in argon )
45
47
Toluene oxidation over Cr-MCM-48
Temperature (K) Conv. of Toluene () Product selectivity () Product selectivity ()
Temperature (K) Conv. of Toluene () Benzaldehyde Others
523 548 573 598 623 648 0.90 1.24 2.20 3.40 6.88 11.33 75.39 61.57 44.76 33.90 20.62 16.0 24.61 38.43 55.24 66.10 79.38 84.0
46
48
desorbed ammonia (a.u)
TPDA profile of Cr-AlPO
47
49

1. Oxidation of toluene on redox sites (Cr5/6 )
2. Dealkylation on acid sites (Al3)
3. Combustion on acid sties

Possible reaction scheme of toluene oxidation on
Cr-AlPO
48
50
Liquid phase oxidation of Ethylbenzene with TBHP
over Cr-AlPO and Cr-MCM-48
Solvent Conversion () Product selectivity () Product selectivity ()
Solvent Conversion () Acetophenone Others
None Acetonitrile Acetone 9.8 23.2 28.5 94.6 97.0 97.7 3.0 2.3 5.4
Cr-AlPO
Solvent Conversion () Product selectivity () Product selectivity ()
Solvent Conversion () Acetophenone Others
None Acetonitrile Acetone 7.6 18.9 20.4 93.7 97.6 98.2 6.3 2.4 1.8
Cr-MCM-48
Reaction conditions
Ethylbenzene TBHP Solvent 1 1 5 Weight of
the catalysts 100 mg T 333 K t 6 h
49
51
Liquid phase oxidation of Benzyl alcohol with
TBHP over Cr-AlPO and Cr-MCM-48
Solvent Conversion () Product selectivity () Product selectivity () Product selectivity ()
Solvent Conversion () Benzaldehyde Benzoic acid 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
Cr-AlPO
Solvent Conversion () Product selectivity () Product selectivity () Product selectivity ()
Solvent Conversion () Benzaldehyde Benzoic acid 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
Cr-MCM-48
Reaction conditions Benzyl
alcohol TBHP Solvent 1 1 5 Weight of the
catalysts 100 mg T 333 K t 6 h
50
52
Catalytic activity of mesoporous Fe-AlPO
Fe-MCM-48 Aerial oxidation of cyclohexane
51
53
Aerial oxidation of cyclohexane over Fe-AlPO
Catalyst Conversion () Product selectivity () Product selectivity () Product selectivity ()
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
Reaction conditions Pressure 20 bar, T 403
K, t 24 h, 30 bar
52
54
Can we replace existing catalysts with M41S in
industrial processes ?
Coatings of M41S on stainless steel grids
53
55

• 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
56
Photograph of the grid used to prepare M41S
Composition of the stainless steel grids Fe(65-70
) Mo (2-2.5), Ni (11-14) and Cr ( 16.5-18.5
),
55
57
In-situ Synthesis of M-MCM-41/ Stainless steel
grids
CTAB NaOH
TEOS
pH 10.5, Vigorous stirring
Homogeneous gel
Pretreatment of the grid Washed in boiling
acetone 30 min Washed 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
Stirred at RT 3h Autoclaved at 428 K 12
h Filtered, oven dried
M-MCM-41 Surfactant
Calcination at 823 K in N2 2h Air ---10h
MCM-41 / Stainless steel grid
56
58

• 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
59

• 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
60
TEM image of MCM-41/ Stainless steel grid

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

59
61
In-situ Synthesis of MCM-48/ Stainless steel grids
CTAB NaOH
TEOS
pH 10.5, Vigorous stirring
Homogeneous gel 2 SiO2 0.24 CTAB 0.5 NaOH
1-3 EtOH 195 H2O
Pretreatment of the grid Washed in boiling
acetone 30 min Washed 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
Stirred at RT 3h Autoclaved at 428 K 12
h Filtered, oven dried
Si-MCM-48 Surfactant
Calcination at 823 K in N2 2h Air ---10h
Si-MCM-48 / Stainless steel grid
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• 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

Two theta
XRD pattern of MCM-48/ grid
N2 adsorption-desorption isotherms of MCM-48/
grid
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63

• Complete coverage on the grid
• Spherical morphology has
• been observed
• Material remains intact on the
• grid even after calcination

SEM images of MCM-48/ stainless steel grids
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63
TEM image of MCM-48/ Stainless steel grid

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

65
Can we extend this approach to prepare other
transition metal oxides ?
Synthesis and Characterization of Thermally
Stable Mesoporous Titania
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66
Advances in the synthesis of mesoporous titania
Mechanism Surfactant Inorganic precursor pH, method Removal of surfactant Reference
Ionic S --- I- S- --- I S- --- I Hydrogen Bonding  So --- Io Neutral No --- Io  CTAB Dodecylphosphate Dodecylphosphate      Dodecylamine   ABA tri-block copolymer Ti-alkoxide Triethanolamine Ti-alkoxide Acetylacetone   Ti-alkoxide     Ti-alkoxide acetylacetone     Ti-alkoxide 10.5 150 oC 1-3,RT     1-3,RT       5.0,RT       RT Calcination at 500 oC Extraction with EtOH   Extraction     ExtractionCalcination /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
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Synthesis of mesoporous titania
 
TMAOH

• 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.

Cetyltrimethylammonium bromide
(1) Ti-orthotitanate Polyethylene glycol
pH 10.5, Vigorous stirring
Homogeneous gel  
  Stirred at RT 1 h Autoclaved at 428 K 12
h Filtered, oven dried
TiO2 Surfactant
Calcination at 823 K in N2 5 h air ---10h
TiO2
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68
PEG
CTAB
430 oC
250 oC
Thermogram of mesoporous TiO2
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69
41.1Å
45.9 Å
(a)
(b)
Two theta
Two theta
(d)
41.5 Å
(c)
Two theta
Two theta
XRD patterns of mesoporous TiO2 a)
as-synthesized (b) calcined at 823 K (c )
calcined at 923 K and (d) calcined at 1023 K
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70
P/p0
N2 adsorption-desorption isotherms of mesoporous
TiO2

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

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71
Summary and Prospects

• 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-41
• Ti-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

Continued .
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72

• Mesoporous Cr-AlPO shows both acidic and redox
• properties where as Cr-MCM-48 is purely a
  redox
• catalyst
• Molecular 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

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Acknowledgements Prof. T.K. Varadarajan
Prof. B. Viswanathan Prof. A. Renken Dr. L. K.
Minsker Profs. UVV, KV, MSS and DVS Murthy
Prof. KKB and Head RSIC Benoit Louis and
Fabio Rainone Mr. A. Narayanan and Mr.
Sivaramakrishnan Dr. MRK Prasad, Dr. K.V. S.
Subba Rao (IICT, Hyd), Dr. C. Patra (NCL, Pune)
and Dr. Suja (CUSAT, Cochin) Friends and
colleagues
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