novel synthesis and activation strategies leading to the formation of tuned mesostructures

Novel Synthesis and Activation Novel Synthesis and Activation strategies leading to the formation strategies leading to the formation

of tuned mesostructuresof tuned mesostructures

Optimal Sorbent and Catalyst Optimal Sorbent and Catalyst support requirementssupport requirements

A. High adsorption capacity High number of active sitesB. High selectivity: * pore volume * pore size distribution * surface area * surface compositionC. Good kinetic properties: selection of * crystal size * particle size * porosity * binder typeD. Good physical properties: * high bulk density * crush strenght * erosion resistanceE. Good lifetime performance: * high chemical, thermal and mechanical stability

Mesoporous Templated SilicasMesoporous Templated Silicas

General IntroductionGeneral Introduction

Mesoporous Templated Silicas (MTS)

MCM- 41MCM- 48

SBA-15SBA-16

PORE DIAMETER

2 - 6 nm 6 - 20 nm

Typical Laboratory Synthesis ConditionsTypical Laboratory Synthesis Conditions

MCM-41

MCM-48

SBA-15

SBA-16

CTMABrGem 16-8-16

Gem 16-12-16

Pluronic P123EO20PO70EO20

Pluronic P127EO106PO70EO106

13

13

<1

<1

TEOS/Fumed silica

TEOS/Fumed silica

TEOS

TEOS

1/ 0.251/0.06

1/ 0.061/ 0.1

1/ 0.02

1/ 0.008

Template pH Silica source

Si/Templ. SynthesisCharacteristics

24 h at RT° + 2 days at 130°C in AC + 3 days HT 5 days at 130°C in AC + 3 days HTstirring 8 h at 45°C + ageing 16 h at 80°C

stirring 8 h at RT° + ageing 16 h at 80°C


CTMABr: Cetyltrimethylammonium bromideGemini: [CmH2m+1(CH3)2N-CsH2s-N(CH3)2CnH2n+1]2Br

Structural CharacteristicsStructural Characteristics

Symmetry

Surface Area(m²/g)

Pore Volume(ml/g)

Wall Thickness(nm)

P6m(Hexagonal

)

1000

1.2

1

Ia3d(Cubic)

1200

1.2 – 1.5

1

P6mm(2D Hexagonal)

700-1000

0.7 – 1.3

4 – 6

Im3m(Cubic)

700-900

0.4 – 0.8

5 – 8

MCM-41 MCM-48 SBA-15 SBA-16


Pore Size Engineering Pore Size Engineering of MCM materialsof MCM materials

The effect of the synthesis conditions

Influence of the chain length of the surfactant

Addition of co-templates

Tuning pore size distrubution

Pore Size Engineering MCMPore Size Engineering MCM

Synthesis ConditionsSynthesis Conditions

0.5 1 1.5 2 2.5Pore Radius (nm)

dV(r

)

Tuning of the pore size of the MCM material by selecting the synthesis conditions

A

B

C

D

A = 1 day base +1 day HT *r p = 1.0 nm

B = 5 days base + 3 days HTr p = 1.2 nm

C = 10 days base + 1 days HTr p = 1.3 nm

D = 10 days base + 3 days HTr p = 1.5 nm

* HT = Hydrothermal treatment


Influence of the chain length Influence of the chain length

N+ N+

0.5 1 1.5 2Pore Radius (nm)

dV(r

)

Gem 16-12-16

Gem 18-12-18

Physical Properties:

Gem 16-12-16S BET = 1300 m2/gV P = 1.0 ml/gr P = 1.2 nm

Gem 18-12-18S BET = 1600 m2/gV P = 1.4 ml/gr P = 1.3 nm

Synthesis Conditions:5 days at 130°C followed by hydro-thermal treatment of 3 days at 130°C

Difference in surfactant side chain length


Addition of Co –TemplatesAddition of Co –Templates

0

2

4

6

8

10

12

1 1.5 2 2.5 3 3.5 4

Pore Radius (nm)

Dv(

r)

0

0.3 0.6

11.2

1.8

Gemini surfactants

Dimethylalkyl amines

Enlargement of the pore size of MCM-48 due to the addition of dimethyl-hexadecyl amine as a swelling agent with different ratio of amine/surfactant. Other additives can be used like ethanol, decane and different dimethylalkyl amines.

Mechanism:

Micelle

Ratio ofsurfactant

co–template

Morphologies of MCM

Different morphologies: - fibers- layers- gyroids- rods-spheres- ….

Hollow core spheres

Hard spheres

Morphologies of MCM

Cubic core

Hexagonal channels

Morphologies of MCM

Catalytic ActivationCatalytic Activation

OverviewOverview

Methods for catalytic activation

in situ activation (during the synthesis)

post-synthesis modification (after the synthesis)

framework incorporation +

surface modifiction

surface modification

various metal oxides(V, W, Ti, Cr, Mo, Al,…)


Surface ModificationSurface Modification

The Molecular Designed Dispersion

Support-OH+

VO(acac)2

Ligand Exchange

Hydrogen Bonding

Support

O

HH3C

H3C

CH3

CH3

CHHC

O

V

O

OO

O

O

O

V

O

HC

H3C

H3CO

Support

+ Hacac

Support-O-VOx

ADSORPTION CALCINATION

VO(acac)2 : Vanadylacetylacetonate


Spectroscopic CharacterizationSpectroscopic Characterization

FTIR Spectroscopy

2800300032003400360038004000Wavenumber (cm-1)

Pho

to A

cous

tic S

igna

l (A

.U.)

Si-OH

H-bonding

V-OH

80010001200140016001800Wavenumber (cm-1)

Pho

to A

cous

tic S

igna

l (A

.U.)

acac

Si-O-V

Blank MCM

VO(acac)2 + MCM

VOx/MCM



FT-Raman

Raman frequency ~ V-O bond length~ VOx coordination

1042 cm-1 : (V=O) tetrahedral997 cm-1 : (V=O) octahedral

940980102010601100Raman Shift (cm-1)

Inte

nsit

y (A

.U.)

0.2 mmol/g

1.3 mmol/g

0.7 mmol/g

0.4 mmol/g

1042 cm-1 997 cm-1

v2o5

S

V

O

O OO

S S

• VOx/MCM catalysts < 1 mmol/g V :tetrahedrally coordinated VOx

• Raman spectroscopy is very sensitive towards micro-crystalline V2O5

0

2

4

6

8

10

12

14

16

18

200 300 400 500Wavelength (nm)

Kub

elka

Mun

k U

nits



VOx coordination Band position (nm)

tetrahedral isolated 250, 300tetrahedral 1D chains 350

square pyramidal 410octahedral 470

(a) 0.4 mmol/g V

(b) 0.7 mmol/g V

(c) 1.3 mmol/g V

OV charge transfer bands ~ VOx coordination

Progression of polymerisation as a function of the surface loading :

UV-VIS-DRS

(a) Isolated tetrahedral(b) isolated + 1D chains(c) isolated + chains + V2O5 crystals


Catalytic PerformanceCatalytic Performance

Oxidation of methanol (at T = 400°C)

0

10

20

30

40

50

60

70

80

90

100

0.00 0.25 0.50 0.75 1.00 1.25 1.50

V (mmol/g)

Con

vers

ion

and

yiel

d (%

)

Conversion COx

Formaldehyde + dimethylether

Tetrahedral VOx :

activity increases with V loading high formaldehyde yield

Formation of V2O5 clusters :

activity decreases selectivity decreases drastically


Catalytic PerformanceCatalytic Performance

Oxidation of methanol (at T = 400°C)On pure, grafted and incorporated VOx-MCM materials for different

vanadium loadings

ConvFA

DMECO

Blank

I ncorp (1 wt% V)

Graf ted (1 wt% V)

I ncorp (2.6 wt% V)

Graf ted (3 wt % V)

0

10

20

30

40

50

60

70

80

90

100Yi

eld

(%

)Acidic sites

Dimethylether (DME)

Basic sites

Carbonoxides (CO)

Redox sites

Formaldehyde (FA)


Supported Mixed Oxide CatalystsSupported Mixed Oxide Catalysts

Synthesis of a new mixed oxide phase using the Molecular Designed Dispersion method :

Vanadium oxide + Tantalum oxide

Combining different oxide phases Synergy or complementary properties Improved catalytic performance

Structural characterization

FTIR, FT-Raman, UV-VIS-DRS

Surface properties

Adsorption of pyridineCatalytic performance



FT-RamanFTIR

S

V

O

O OO

S S

S

V

O

O OO

S SS

Ta

O

OO

SO

S

Ta

O

OO

SO

SS

S

V

O

O OO

S S

60070080090010001100

Wavenumber (cm-1)

Pho

to A

cous

tic S

igna

l (A

.U.)

1003005007009001100

Raman Shift (cm-1)

Inte

nsity

(A

.U.)

Ta=

OV

=O

Si-

O-V

Ta=

O

Si-

O-T

a

Blank

VOx

TaOx

VOx-TaOx

Well-mixed and well-dispersed

VOx-TaOx catalysts



Catalyst with active redox and active acid sites

Oxidation of methanol (at T = 250°C)

Redox siteVOx

Acid siteTaOx

+

VOx-TaOx

Redox site : formaldehyde, methylformateAcid site : dimethylether

Sel

ecti

vity

(%

)

(0.4 mmol/g)(0.2 mmol/g)

(0.4 mmol/g V + 0.2 mmol/g Ta)

VOxTaOx

VOx-TaOx

Formaldehyde

Methylformate

Dimethylether

0

10

20

30

40

50

60

70

80

90

100

SBA-15 and SBA-16SBA-15 and SBA-16

Promising MaterialsPromising Materials

Qualities of SBA materials

Relatively large mesopores

Large amount of micropores

Thick pore walls

Incorporation of hetero-elements in thicker walls

Higher hydrothermal and mechanical stability

Use of non-toxic, biodegradable, non-ionic triblock copolymers as template

0

200

400

600

800

1000

1200

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

P/P0

Vo

lum

e (

cc

/g)

SBA-15 and SBA-16SBA-15 and SBA-16

A comparison with MCM-48A comparison with MCM-48

SBA-15SBA-16

MCM-48

5.03.01.4

1.30.61.0

9008001200

SBET

(m³/g)Vp

(ml/g)rp

(nm)

Tuning pore size distribution Tuning pore size distribution

Pore size engineeringChanging synthesis conditions

size of surfactant

use of swellers

Synthesis temperature

Size of surfactant

Length of EO blocks (ethyleneoxide) Characteristic for mesophase (structure)

Wall thickness

Triblock copolymers (pluronics) (EO)x(PO)y(EO)x

EO 4 units

17 - 37 units

132 units

lamellar

hexagonal

cubic

Length of PO blocks (propyleneoxide) influences porediameter

PO 30 units

70 units

3 nm ø

8 nm ø

Pore size engineering Pore size engineering

Addition of swellers

(TMB, 1,3,5- trimethylbenzene)

0200400600800

10001200140016001800

0 0.2 0.4 0.6 0.8 1

P/P0

volu

me

ST

P (

ml/g

)

MCF SBA-15

0 50 100 150 200 250poreradius (Å)

Dv(

r)

Pore enlargement

mesocellular foam

MCF


In situ control of mesopore radius by changing the synthesis conditions using the same surfactant (EO70PO20EO70)

The SBA-15 materials were aged for 16 h at different temperatures:

Sample A = 75°C Sample B = 90°C Sample C = 105°C

A part of non calcined sample A had a hydrothermal treatment for 3 days at 100°C (Sample D)

A

BD

C


0,00

0,02

0,04

0,06

0,08

0,10

0,12

0 20 40 60 80 100Pore Radius (Å)

Dv(

r)

In situ control of micro/mesopore volume ratio by changing the synthesis conditions using the same surfactant (EO70PO20EO70)

Variable micro/mesopore volumeVariable micro/mesopore volume


0

0,2

0,4

0,6

0,8

1

1,2

A D

pore

volu

me

(ml/g

)

microporevolume

mesoporevolume

Sample A: aged for 16h at 75°C Sample D: part of non calcined sample A after a hydrothermal treatment at 100°C for 3 days

Morphologies of SBAMorphologies of SBA

1 micron

1 micronFibers of SBA


Spherical SBA

low µm range high µm range cm range


Growth mechanism of spherical SBA

Catalytic activity of VOx and TiOx / SBA-15 in SCR of NO with ammonia.

DeNOx: 4 NO + 4 NH3 + O2 4 N2 + 6 H2O

0

20

40

60

80

100

100 200 300 400 500

Temperature (°C)

Co

nve

rsio

n / S

elec

tivi

ty (

%)

TiOx / SBA-15 VOx / SBA-15

0

20

40

60

80

100

100 200 300 400 500

Temperature (°C)

Co

nve

rsio

n / S

elec

tivi

ty (

%)

Not active below 350°C Not higher than 55% of conversion

Activation of SBA materials by MDD and Activation of SBA materials by MDD and Catalytic performanceCatalytic performance

Post-synthesis modificationPost-synthesis modification

SBASBACatalytic performance Catalytic performance

Mixed oxide TiOx - VOx / SBA-15 catalyst

0

20

40

60

80

100

100 150 200 250 300 350 400

Temperature (°C)

Co

nve

rsio

n /

Sel

ecti

vity

(%

)

VOx - TiOx / SBA-15

• Very active in a low temperature range

•~100% NO conversion (above 250°C)•~100% N2 selectivity (all temp. range)

Post-synthesis modifications

Simultaneous formation and activation

metal oxides nanoparticles

zeolite based nanoparticles

Related SBA materialsRelated SBA materials

In situ formation of amorphous siliceous

microporous nanoparticles

0

100

200

300

400

500

600

700

0.0 0.2 0.4 0.6 0.8 1.0P/P0

volu

me

adso

rbed

gas

(m

l/g)

0

100

200

300

400

500

0.0 0.2 0.4 0.6 0.8 1.0P/P0

volu

me

adso

rbed

gas

(m

l/g)

open mesopores ink-bottle mesopores

SBA-15 and related materialsSBA-15 and related materials

PHTS PHTS

Typical N2 sorption isotherms (77K) for various SBA-15 materials

PHTS (Plugged Hexagonal Templated Silica)

PHTSPHTS

0

100

200

300

400

500

600

0.0 0.2 0.4 0.6 0.8 1.0P/P0

volu

me a

dso

rbed

gas

(m

l/g)

Vmicropores

Vnarrowed meso

Vmeso open

metal oxides nanoparticles (TiO2)


tuneable sizetuneable crystal phase (rutile, anatase)tuneable number of active sitestuneable porous characteristics (size, number)

TPAOH 20%

TEOS

VOSO4

nanoparticles zeolites (vanadiumsilicalite)

ageing 2 days

calcined SBA-15

acidification (HCl)

SBA-15 with zeolitic plugs inside the mesopores

Dry impregnation

SBA and related materialsSBA and related materials

Silicalite-1 nanoparticle depositionSilicalite-1 nanoparticle deposition

Open mesopore

narrowed mesopore

Crystalline vanadiumsilicalite-1

nanoparticle

nanoparticles can be:

zeolitenanoparticles, metaloxides

microporous, non-porous

SBA and related materialsSBA and related materials

Silicalite-1 nanoparticle depositionSilicalite-1 nanoparticle deposition

In situ synthesis strategies In situ synthesis strategies

Mesoporous materials with zeolite-like wallsMesoporous materials with zeolite-like walls

classic (vanadium) silicalite-1 synthesis mixture:

TPAOH, H2O and TEOS, (VOSO4)

clear solution containing nanoparticles

(vanadium) silicalite-1 zeolite

hydrothermal treatmentacidification: pH<1

silicalite-1-like nanoparticles with modified surfactant

hydrothermal treatmentNO TEMPLATE

mesoporous surfactant and refluxing

short range ordered mesoporous material

with tuneable porosity and hydrophobicity

long range ordered mesoporous materialswith ink-bottle pores

Mesoporous materials with silicalite-1-like wallsMesoporous materials with silicalite-1-like walls



27002800290030003100

Raman Shift (cm -1)

Intensit

y

a

b

c

d

CH3

CH2

a) tripropylamine, b) TPAOH 20% solution, c) the full-grown VS-1 zeolite before calcination, d) SBA-VS-15 with acidified nanoparticles before calcinations

EPR and Raman show the loss of a ligand from the silicalite-1 template (TPAOH)

Consequences of acidifying the solution of vanadiumsilicalite-1 nanoparticle

14N

EPR HYSCORE spectra of SBA-VS with

acidified vanadium silicalite-1 nanoparticles

EPR HYSCORE spectra of full-grown vanadium silicalite-1

interaction of 14N with V




N

N+

V

=

V

O=

OSi

OO

O

HT

No mesotemplate

HCl

loss of n-propyl ligand stops the zeolite growth

N

N+N+

N+




hydrothermal treatmentNO TEMPLATE

Temp tuneable porosityTime tuneable porosity hydrophobicity

low pH growth of mesopores by edge-sharing (resembles sol-gel mechanism)

ConclusionsConclusions

“Abracadabra” is a well-known incantation in the magic world, although the synthesis of tuned porous materials may still seem an art to many, it nonetheless can be understood to a certain level, appreciated and successfully performed.Making a white powder is by no means the end of the road in preparing porous materials; it is equally important to be able to characterize or to indentify, to engineer the porosity and to activate these materials that have been prepared for a desired application in sorption, catalysis and membranes.

AcknowledgementsAcknowledgements

* INSIDE PORES NoE

* University of Antwerpen: Prof. P. Cool Vera Meynen Wesley Stevens Liu Shiquan* I.A. Cuza University, Iasi, Romania: A. Busuioc A. Hanu

novel synthesis and activation strategies leading to the formation of tuned mesostructures

Documents

pore size of mcm

days htr p

days base

pore size distribution

crystal size

particle size

m2gv p

mlgr p