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
Interesting Facts About Carbon Nanotubes Strength to weight ratio 500x for Al, steel, Ti A few nm across Up to 100 m in length Can with- stand repeated buckling and twisting Transports heat better than any known material Can conduct electricity higher than Cu, or act as a semiconductor like Si Can be functionalized Maximum strain ~10% much higher than any material
Arc discharge Laser Furnace Chemical Vapor Deposition (CVD) Synthesis of Carbon Nanotube What are the different methods to synthesis CNTs ? • Mullti-wall and single-wall Nanotube synthesis technique
Productivity of commercial techniques: 40 g/day and more Price drop from $2500/g to $500/g, expecting to be $6/g Quality: High selectivity–narrow distribution of tube diameters (80%) Development of CVD techniques reduces the cost of the process Purification efficiency: from 1% toward ~ 30% and more development Development of CNT vs Economy Reference: http://nanomaterials.drexel.edu
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 metal-free catalysis ?
TPRS-MeOH:O2=3, HSV=11700 hr-1 168 hr wet graphite 72 hr dry 168 hr dry graphite 168hr dry Catalysis is Controlled by Defects Defects change the ratio of prismatic to basal face area and thus affect the steady state between activation and decarboxylation kinetics: proof of principle • The selective oxidation of methanol is used as test reaction.
Two quinoid groups Concept: Tune the C-O bond 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)
+ H2 Oxidative dehydrogenation + 1/2 O2 + H2O DH = -116 KJ/mol Dehydrogenation of Ethylbenzene to Styrene Dehydrogenation (non oxidative) Industrial Process: Treaction = 600 - 650°C Excess of overheated steam H2O/EB = 10-15/1 Conversion 50-60 % Selectivity 90-95 % DH = +124,9 KJ/mol
Designing material as a CNT Catalyst • Cheap • Reproducible • Accessible • Chemically and mechanically stabile
Support Impregnated Catalyst CNT Supported CNT Material candidates: Activated carbon Clay
Thermal-CVD Reactor Maximum loading: 20 gram
Images CNT/AC • Multiwalled defective CNT Activated Carbon CNT/AC
CNT/AC for ODH catalyst CNT after reaction
Images CNT/Clay clay CNT/clay
Commercial catalyst Commercial: baytubes Loose fluffy powder Used as a comparison to the ODH catalytic ability of the nanotube samples
Reduced clay CNT/clay Commercial CNT 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)
Mechanical stability test for CNT/Clay After CNTs are still attached to the clay support!! Mechanically stabile.
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.
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
understanding synthesis application technical catalyst model catalyst new catalyst nanostructured carbons graphite nanodiamonds activated carbons The catalliance rational design approach concept in-situ analysis kinetics 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 Schematic drawing of the catalytic oxidative dehydrogenation over carbon nanofilaments: 5- Desorption of water 4- Adsorption of oxygen and reaction with OH groups 1- Adsorption of ethylbenzene 3- Desorption of styrene 2- Dehydrogenation at basic centres Angew. Chem. Intl. Ed. (2001) 40 No.11
CO2 Styrene yield - 34 % carbon black CO Styrene Styrene % yield % yield Benzene Benzene Toluene Toluene Ethene Ethene CO2 CO Styrene yield - 52 % CNT Structure-Sensitivity of Carbon Oxidative Dehydrogenation of EB without any water addition at 100 K lower temperature than DH. Metal-free catalysis works well!