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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, - PowerPoint PPT Presentation
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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!