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17.8.2015

The design and synthesis of silica-based

catalytic microreactors

Raed Abu-Reziq

Institute of Chemistry, Casali Center of Applied Chemistry and

The Center for Nanoscience and Nanotechnology

The Hebrew University of Jerusalem, Israel

Ceramics-2015, Chicago, USA

Catalysis

Health

Food

Basic

and fine

chemicals

Environment

Energy

New

Materials

Catalysis shapes our world

Importance of catalysis: more than 90% of the industrial processes

are catalyzed (chemicals, pharmaceutics, materials, polymers, energy, etc.)

Catalysis Homogeneous Heterogeneous

• Organometallic complexes

•Enzymes

•Organocatalysts

• Supported metals

• Supported organometallic complexes

• Metal oxides, sulfides (PtO2, RuO2 etc.)

Homogeneous catalysis Heterogeneous catalysis

K. D. Wiese et al, Top Organomet. Chem., 2006, 18, 1.

H. W. Bohnen et al, Adv. Catal. 2002, 47, 1.

• High activity and selectivity

• Not easily recovered

• Expensive

• Decrease of activity and selectivity

• Easily recovered

• Economic

How to bridge homogeneous and heterogeneous catalysis?!!

Catalysis

Nanocatalysis??

Nanocatalysis; Quasi-homogeneous catalysis; Semi-

heterogeneous catalysis

W. J. Stark et al, Chem. Eur. J., 2010, 16, 8950.

Metal nanoparticles as active catalyst Metal nanoparticles as support

Preparation of heterogeneous catalysts in the nanometer length scale

Nanocatalysis

Size Effects

K. An and G. A. Somorjai, ChemCatChem, 2012, 14, 1512.

Nanocatalysis

Shape Effects

S.U. Son et al, Angew. Chem. Int. Ed. 2007, 46, 1152

Nanocatalysis: Magnetically separable systems

a) V. Polshettiwar et al, Chem. Rev., 2011, 111, 3036. b) S. Shyles et al, Angew. Chem. Int. Ed., 2010, 49, 3428. c) Y. Zhu et

al, ChemCatChem, 2010, 2, 365. d) V. Polshettiwar et al, Green Chem., 2010,12, 743.

Our current research activity

Magnetically separable systems

Supports with well-defined

nanostructures

Nano- and Microreactors

Bridging

homogeneous

and

heterogeneous

catalysis

Nano & Microreactors

Yolk-shell nanoreactors

Y. Yang et al, Angew. Chem. Int. Ed. 2012, 51, 9164. E. V. Shevchenko et al, Adv. Mater. 2008, 20, 4323.

Carbon nanotubes as nanoreactors

S. A. Miners et al, Chem. Commun., 2013, 49, 5586.

m.p. (°C) for NaCl= 803

m.p. (°C) for BMIm[PF6]= -78

Ionic liquid based microreactors

P. Wasserscheid, T. Welton in “ Ionic Liquids in Synthesis” 2002.

• Salts that are liquid at ambient temperatures.

• Have stable liquid range of over 300 °C.

• Very low vapour pressure at room temperature.

Ionic Liquids

Applications of ionic liquids:

• Solvent and catalysts (synthesis, catalysis, microwave chemistry, nanochemistry,

multiphasic reactions and extractions)

• Biological uses (biomass processing, drug delivery, biocides, personal care, embalming)

• Engineering (coatings, lubricants, plasticisers, dispersing agents, compatibilisers)

• Physical chemistry ( refractive index, thermodynamics, binary and ternary systems)

• Electrochemistry (metal plating, solar panels, fuel cells, electro-optics, ion propulsion)

N. V. Plechkova, K. R. Seddon, Chem. Soc. Rev. 2008, 37, 123

The high viscosity of ionic liquids limits its applications in industrial processes

Ionic liquid based microreactors

BMIm-PF6@SiO2 microcapsules

Size distribution

TEM image SEM image

E. Weiss et al, Chem. Mater., 2014, 26, 4781.

Particulated ionic liquids: Converting ionic liquids into solid form

BMIm-PF6@SiO2 microcapsules

TGA analysis indicates that the microcapsules are composed of 68% ionic liquid

Parameters affecting the microcapsules synthesis: 1. Type of surfactant

2. Surfactant concentration

3. Ionic liquid: TEOS ratio

BMIm-PF6@SiO2 microcapsules

Brij 78

Tween 80

Triton X-100

Reax 88A Reax 88B

5% Bu-PVP

SDS PS- sulfonated Pluronic 123

BMIm-PF6@SiO2 microcapsules

Characterizations

BMIm-PF6@SiO2 microcapsules

Immobilization of palladium nanoparticles

BMIm-PF6@SiO2 microcapsules

Catalytic applications

Entry Catalyst Solvent Conversion (%) Products (%)

1 Pd/BMIm-PF6@SiO2 water 100 cis-4-octene (88), trans-4-octene (10), n-octane (2)

2 Pd/BMIm-PF6@SiO2 hexane 10 cis-4-octene (10)

3 Pd/BMIm-PF6@SiO2 xylene 100 cis-4-octene (84), trans-4-octene (5), n-octane (11)

4 Pd/BMIm-PF6@SiO2 diethyl ether 100 cis-4-octene (85), trans-4-octene (6), n-octane (9)

5 Pd/C diethyl ether 100 n-octane (100)

6 Pd(OAc)2 BMIm-PF6 100 cis-4-octene (8), n-octane (92)

E. Weiss et al, Chem. Mater., 2014, 26, 4781.

Pd/BMIm-PF6@SiO2 microcapsules

Stability and Recyclability

TEM image SEM image

SEM and TEM images of Pd/BMIm-PF6@SiO2after catalytic applications

Recyclability

BMIm-PF6@SiO2 microcapsules

PEG@SiO2 microcapsules

Surfactants:

Oil phase:

Toluene

Heptane

Cyclohexane

Unpublished results

1 µm

10 µm 1 µm

PEG@SiO2 microcapsules

PEG@SiO2 in toluene PEG@SiO2 in heptane

SEM images SEM image

TEM image TEM image

PEG@SiO2 microcapsules Characterizations

PEG@SiO2 microcapsules [Pt]/PEG@SiO2: Selective hydrosilylation catalyst

Entry Solvent Conversion (%) Selectivity (ratio β:α)

1a Toluene 0 ---

2a Heptane 33 73:27

3a Cyclohexane 57 40:60

4b Cyclohexane >99 92:8

a the catalyst was prepared in the presence of Agrimer AL22 b the catalyst was prepared in the presence of Span 80

Heterogeneous hydrosilylation:

M. Chauhan et al, J. Organomet. Chem. 2002, 645,1.

PEG@SiO2 microcapsules [Pt]/PEG@SiO2: Selective hydrosilylation catalyst

Unpublished results

Chiral ruthenium catalyst@ magnetically separable

silica microreactors

SEM image TEM image

A. Zoabi et al, Eur. J. Inorg. Chem., 2015, 2015

200 nm_ 500 nm_

a b

200 nm_ 500 nm_

a b

Chiral ruthenium catalyst@ magnetically separable

silica microreactors

29Si CP-MAS NMR

XRD pattern STEM/EDS analysis

Characterizations

Chiral ruthenium catalyst@ magnetically separable

silica microreactors Characterizations 13C NMR and 13C CP-MAS NMR

Entry Surfactant

Conversion (%) Enantioselectivity (ee %)

1 Non 0 -

2 CTAB 100 95

3 CTAC 100 95

4 SDS 57 91

5 Bu-PVP 88 92

6 Brij 78 89 93

Chiral ruthenium catalyst@ magnetically separable silica

microreactors

Chiral ruthenium catalyst@ magnetically separable silica

microreactors

Postulated mechanism for the transportation of the reactants to the core of

catalytic microreactors

Surfactant Zeta potential (mv)

Non -26.4

CTAC +44.4

Bu-PVP -3.2

SDS -41.2

Chiral ruthenium catalyst@ magnetically separable silica

microreactors

Entry Catalyst Yield Enantiomeric

excess (%)

1 Microreactors 90 86

2 Empty capsule anchored catalyst 8 N/A

3 Sol-gel anchored catalyst 41 76

Chiral ruthenium catalyst@ magnetically separable silica

microreactors

Tethering the catalyst in the homogeneous zone of the microreactors is

required for obtaining high reactivity and selectivity

Comparison of catalytic activity of the microreactors versus sol-gel entrapped and

anchored catalyst in the asymmetric transfer hydrogenation of 4-bromoacetophenone

Our current research activity

Magnetically separable systems

Supports with well-defined

nanostructures

Nano- and Microreactors

Bridging

homogeneous

and

heterogeneous

catalysis

Palladium nanoparticles supported on magnetically

recoverable hybrid organic-silica nanoparticles

Preparation of Pd(nano)/MNP@IL-SiO2 catalytic hybrid nanoparticles :

Magnetically separable systems

S. Omar et al, J. Phys. Chem. C, 2014, 118, 30045

Characterizations

200 nm

100 nm

100 nm

20 nm

SEM of MNP@IL-SiO2

TEM of MNP@IL-SiO2

TEM of Pd(nano)/MNP@IL-SiO2

STEM of Pd(nano)/MNP@IL-SiO2

Pd(nano)/MNP@IL-SiO2

Si O

Fe Pd

Pd(nano)/MNP@IL-SiO2

Characterizations TGA

XRD

δ (ppm)

δ (ppm)

29Si CP-MAS NMR

13C CP-MAS NMR

Pd(nano)/MNP@IL-SiO2

Catalytic applications

Pd(nano)/MNP@IL-SiO2

Catalytic applications

S. Omar et al, J. Phys. Chem. C, 2014, 118, 30045

0

20

40

60

80

100

1 2 3 4 5

Co

nv

ersi

on

%

Number of cycles

500 nm

Suzuki reaction between bromonenzene and phenyl boronic acid

Heck reaction between iodobenzene and ethyl acrylate

SEM images of recycled catalyst

after 4 cycles

Pd(nano)/MNP@IL-SiO2

Recycling of the catalysts

Conclusions:

•Two methods for preparing new materials based on ionic liquids or PEG encapsulated

in silica shells were developed

•The methods enable particulating ionic liquids or PEGs and converting them in

powder form.

•The methods give opportunities to design ionic liquids or PEGs with new properties.

•The methods enable controlling selectivity and reactivity of catalysts

•Magnetically separable nanocatalysts were designed and applied successfully in

different organic transformations.

Group members:

1. Suheir Omar

2. Esti Weiss

3. Suzana Natour

4. Amani Zoabi

5. Charlie Batarseh

6. Ahmad Zarour

7. Sumaya Abu-Ghannam

8. Diana Gertopski

9. Dr. Maneesh Gupta

Thank You!

Funding support

1. Dr. Gilat Nizri

2. Dr. Saleh Abu-Lafi

3. Dr. Bishnu Dutta

4. Dr. Khalil Hamza

5. Rony Schwarz

6. Yafit Schnell

Former group members:

Casali Foundation Ministry of Science and Culture of Lower Saxony