Metal Nanoparticle/Carbon Nanotube Catalysts

1
Metal Nanoparticle/Carbon Nanotube Catalysts

• Brian Morrow
• School of Chemical, Biological and Materials
  Engineering
• University of Oklahoma

2
Introduction
Armchair
Zigzag
Chiral

Carbon nanotubes have many properties which make
them ideal supports for catalytic metal
nanoparticles. However, the surfaces of
nanotubes are relatively inert, and they tend to
form bundles which reduces their surface
areas. Metal nanoparticle/carbon nanotube
materials are being investigated for use in
catalytic and electrocatalytic applications such
as fuel cells.
Baughman et al., Science 297 (2002) 787
3
Example
Anode (methanol oxidation) CH3OH H2O ? CO2
6H 6e- Cathode (oxygen reduction) (3/2)O2
6H 6e- ? 3H2O Overall CH3OH (3/2)O2 ? CO2
2H2O
K. Kleiner, Nature 441 (2006) 1046-1047
Possibility for powering devices such as cell
phones and computers - Potentially 3-10 times as
much power as a battery - Methanol cheaper and
easier to store than hydrogen Problems -
Methanol crossover - Requires catalysts, usually
platinum expensive!
4
Example
Methanol oxidation - anode of direct methanol
fuel cells
Oxygen reduction - cathode of direct methanol
fuel cells
Langmuir 22 (2006) 2392-2396
5
Other Examples
Selective hydrogenation Oxidation of formic acid
and formaldehyde Hydrogen peroxide
oxidation Environmental catalysis Synthesis of
1,2-diphenylethane
6
Synthesis
Metal particles can be grown directly on the
carbon nanotubes
- Precursor metal salts (H2PtCl6, H2PdCl6, etc.)
heated and reduced - Particle size can be
controlled by temperature and reducing
conditions - Particles can be anchored by
oxidizing nanotubes (via acid treatment or
microwave irradiation), but this can also damage
the nanotubes
Georgakilas et al., J. Mater. Chem. 17 (2007)
2679-2694
Other techniques include chemical vapor
deposition, electrodeposition, laser ablation,
thermal decomposition, substrate enhanced
electroless deposition
7
Synthesis
Already-grown metal particles can be connect to
the carbon nanotubes
Hydrophobic interactions and hydrogen bonds
Covalent Linkage
Han et al. Langmuir 20 (2004) 6019
p-stacking
Coleman et al., J. Am. Chem. Soc. 125 (2003) 8722
Ou and Huang, J. Phys. Chem. B 110 (2006) 2031
8
Characterization
TEM/SEM
Bittencourt et al., Surf. Sci. 601 (2007)
2800-2804
AFM
Hrapovic et al., Analytical Chemistry 78 (2006)
1177-1183
9
Characterization
Raman spectroscopy
Lee et al., Chem. Phys. Lett. 440 (2007) 249-252
10
Future Directions

• Minimizing use of expensive metals
• Synthesis techniques that yield nearly
  monodisperse nanoparticle size distributions
• Synthesis techniques that can control final
  structure of nanoparticles
• Better understanding of metal-carbon nanotube
  interactions

11
Questions?
12
(No Transcript)
13
Characterization
X-ray photoelectron spectroscopy was employed to
investigate the binding energy of
d-band electrons of Pt. As shown in Figure 6, a
shift of 0.4 eV to a higher binding energy was
found in both 4d and 4f electrons of Pt deposited
on PW-SWCNT, proving the role of SWCNTs
in modifying the electronic properties of Pt.
A. Kongkanand et al., J. Phys. Chem. B 110 (2006)
16185-16188