Synthesis of Carbon Nanostructure For Catalysis

A. Rinaldi, N. Abdullah, I. S. Mohamad, Sharifah Bee. Abd. Hamid, D.S. Su, R.

Schloegl

Nanotechnology and Catalysis Research Centre,Institute Of Postgraduate Studies

University Malaya, Kuala Lumpur, Malaysia

FHI, The Max-Planck Society, Berlin, Germany

Presentation Outline

History of Carbon Nanotubes

Properties and Applications of Carbon Nanotubes

Synthesis of Carbon Nanotubes

Concept

Application as Catalysis

The Industrial Revolution That Changed The World

Interesting Facts About Carbon Nanotubes

Strength to weight ratio 500x for Al,

steel, Ti

A few nmacross

Up to 100m in length

Can with-stand repeatedbuckling and

twisting

Can conduct electricity

higher than Cu, or act as a semiconductor

like Si

Transports heat better than any known material

Maximum strain ~10% much higher than any material

Can be functionalized

Synthesis of Carbon Nanotube

• Mullti-wall and single-wall Nanotube synthesis technique

Arc discharge Laser Furnace Chemical Vapor Deposition (CVD)

What are the different methods to synthesis CNTs ?

Development of CNT vs Economy

Productivity of commercial techniques: 40 g/day and more

Quality: High selectivity–narrow distribution of tube diameters (80%)

Purification efficiency: from 1% toward ~ 30% and more development

Price drop from $2500/g to $500/g, expecting to be $6/g

Development of CVD techniques reduces the cost of the process

Reference: http://nanomaterials.drexel.edu

Application in Catalysis

The anisotropy of sp2 carbon

If we can control the kinetic steady state between oxygen functional group formation

and the decarboxylation reaction of the substrate

then we can mimic an oxide reactivity (redox and acid-base)

at a metal-like surface without using a real metal

0 100 200 300 400 500 600 700 800

0.0

5.0x10-6

1.0x10-5

1.5x10-5

2.0x10-5

Rea

ctiv

ity [µ

mol

C/m

2 .sec

]

Temperature [°C]

graphite

168hr dry

Catalysis is Controlled by Defects

200 400

0

2

Vol

CH

2O(m

l)

Temperature [°C]

graphite

72 hr dry

168 hr dry

168 hr wet

TPRS-MeOH:O2=3, HSV=11700 hr-1

Defects change the ratio of prismaticto basal face area

and thus affect the steady statebetween activation and

decarboxylation kinetics:proof of principle

Defects change the ratio of prismaticto basal face area

and thus affect the steady statebetween activation and

decarboxylation kinetics:proof of principle

• The selective oxidation of methanol is used as test reaction.

Concept: Tune the C-O bond properties

Two quinoid groups

By changing the bending of the graphene unit

through nanostructuring a continuous modification

of the polarity of the C-O bonds will be possible: control redox vs. basic properties.

By changing the bending of the graphene unit

through nanostructuring a continuous modification

of the polarity of the C-O bonds will be possible: control redox vs. basic properties.

Catalytic activity for Oxydehydrogenation reaction (ODH)

(ethylbenzyne to styrene)

An Example: The Styrene Synthesis

Production:

20.000.000 t

per year

(2000)

Dehydrogenation of Ethylbenzene to Styrene

DH = +124,9 KJ/mol

+ H2

Dehydrogenation (non oxidative)

+ 1/2 O2 + H2O

DH = -116 KJ/mol

Oxidative dehydrogenation

Industrial Process:Treaction = 600 - 650°C

Excess of overheated steam H2O/EB = 10-15/1Conversion 50-60 % Selectivity 90-95 %

Designing material as a CNT Catalyst

• Cheap• Reproducible• Accessible• Chemically and mechanically stabile

Schematic Concept

Ni particles

Ni/AC catalystCarbon from nature source

Impregnationreduction

Activation

Activated carbon

CVD methodC2H4 ? C + H2

CNFs/AC composite

Palm kernel shell

Hierarchically structured carbon

One chemical elementStrong interaction

Super adsorption properties

Support Impregnated Catalyst

Supported CNT

CNT

Thermal-CVD Reactor

Maximum loading: 20 gram

Images CNT/AC

Activated Carbon CNT/AC

• Multiwalled defective CNT

CNT/AC for ODH catalyst

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Time (days)

Co

nv

ers

ion

-Se

lec

tiv

ity

(%

)

EB Conversion

ST Selectivity320 ºC

350 ºC

375 ºC

CNT after reaction

Images CNT/Clay

clay CNT/clay

Commercial catalyst

Commercial: baytubesLoose fluffy powderUsed as a comparison to the ODH catalytic ability of the nanotube samples

CNT/clay for ODH catalyst

• CNT/clay shows superior activity in comparison to the commercial CNTs possibly due to :

-open structure of the bentonite support materials and -the amount of defects present in the CNTs on clay (defects=active

sites)

0%

20%

40%

60%

80%

100%

0 200 400 600 800 1000

Time on stream (min)

Co

nve

rsio

n /

Sel

ectiv

ity /

Yie

ld

Ethylbenzene conversion

Styrene selectivity

Styrene yield

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200

Time on stream (min)

Sty

ren

e ra

te (m

mo

l g–1

h–1

)

Reduced bentonite CNTs/bentonite Commercial CNTs

Reduced clayCNT/clayCommercial CNT

Mechanical stability test for CNT/Clay

CNTs are still attached to the clay support!!

Mechanically stabile.

After

Summary

• CNT is an important material in nanotechnology• CNT with “tunable” electronic property hold catalytic

activity sites as metal-like based catalysis.• Some geometrical design of the final material are needed

to properly utilize CNT as catalyst.• Activated carbon and clay material are potential material

to immobilize CNTs for ODH reaction• Future modifications are needed to optimize the

application.

Thank You

Synthesis of Carbon Nanotube

Arc discharge

The most investigated technique Produces good quality samples Ratio NT/Nanoparticles is around 2:1 in the best cases Yields are low and very sensitive to He pressure

Voltage: 20 V (DC)•Current: 50-100 A•Helium atmosphere (500 Torr)

Synthesis of Carbon Nanotube

Laser Furnace

High yield of nanotubes and nanoparticles Highly graphitic and structural perfect

• Oven temperature: 1200oC• Laser to vaporize graphite• Gas carrier: Ar, He•

Synthesis of Carbon Nanotube

Chemical Vapor Deposition (CVD)

Mostly developed and applicable produces pure, well alignment CNT large area deposition capability controlled growth of CNT diameter and density right combination of carbon, precursor, matched catalysts, support material and carrier gases

Activation of di-oxygen

The selectivity problem in oxidation catalysis arises from different options for the intermediate binding of activated oxygen to the catalyst:

• electrophilic (oxidising)• nucleophilic (basic)

carbon offers the unique chance to achieve oxygen activation metal-free

The catalliance rational design approach

understanding synthesis application

model catalyst technical catalyst new catalyst

graphitenanodiamonds

activated carbonsnanostructured

carbons

in-situ analysis kinetics

concept

strategy

realization

The model system

graphite

oxidation behavior

Theoretical Underpinning

defectation leads to double bond localization (band gap opening) and drastically changes the energetics of adsorption (H as model)

M. Scheffler, J. Carlson

Schematic concept of ODH

1- Adsorption of ethylbenzene

2- Dehydrogenation at basic centres

3- Desorption of styrene

4- Adsorption of oxygen and reaction with OH groups

5- Desorption of water

Schematic drawing of the catalytic oxidative dehydrogenation over carbon nanofilaments:

Angew. Chem. Intl. Ed. (2001) 40 No.11

Structure-Sensitivity of Carbon

0

5

10

15

20

25

30

35

1 2 3 4 5 6S

tyre

ne

CO CO

2

Ben

zen

e

Tol

uen

e

Eth

ene

% y

ield

Styrene yield - 34 %carbon black

0

10

20

30

40

50

60

1 2 3 4 5 6

Eth

ene

CO

2

COSty

ren

e

Tol

uen

e

Ben

zen

e

% y

ield Styrene yield - 52 %

CNT0

20

40

60

80

100

0 200 400 600 800 1000Time on stream, min

Eth

ylb

enze

ne

con

vers

ion

s, % KFe2O3 MWNTs arc d.Oxidative Dehydrogenation of EB

without any water additionat 100 K lower temperature than DH.

Metal-free catalysis works well!