Why nano sized Pt

1
Why nano sized Pt?

• Why certain cluster sizes of platinum are more
  active ?
• Is it due to d- orbital like conventional
  catalysis?
• What other factor?

How to study?
2
Molecular modeling

• Understanding the fundamental
• Density Functional Theory (DFT)
• (DMol3 software)
• Stabilization energy, orbital nature and
  contribution
• Metal cluster (Pt) size (1-14)

3
Results
Stabilization energy Total energy of
cluster-Total energy of Pt atom No. of atoms /
No. of atoms
4
(a). Stabilization energy of various Pt clusters,
(b). The energy of HOMO-LUMO frontier orbital of
various Pt clusters.
5
Percentage contribution of orbital at HOMO
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(No Transcript)
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How to validate the concept?
(c)
(a)
(b)

• SWNT-arm chair type (5, 5)- diameter of 6.78 Å
  and length 9.8 Å
• Nitrogen - substituted in the terminal carbon
  of CNT (NCNT)
• DFT- to optimize, reacted with single Pt atom
  then formic acid

8
Results

• The binding energy of Pt to NCNT (-3.26 eV) is
  greater than that of pure CNT (-13.94 eV).
• Interaction energy of formic acid is 0.25 eV
  higher for Pt-NCNT then Pt-CNT composite

9
Proposed work

• Put the various clusters of pt on the CNT and
  NCNT to study the binding energy of the cluster
  as the size changes.
• Identify the cluster which is having higher
  binding energy with the CNT and evaluate
  interaction energy of the formic acid with the
  cluster.
• A possible reaction pathway with all transition
  state theory calculation to predict the
  intermediate in formic acid oxidation will be
  proposed with a simple cluster model.

10
Experimental results

• Formic acid electrooxidation on 3 different
  carbon supports
• Vulcan XC-72 (commercial standard)
• MWNTs functionalized using oxidative route
  (F-MWNTs)
• (refluxing MWNT with 13 ratio of H2SO4HNO3)
• Nitrogen containing carbon nanotubes (NCNT)
• (template method using alumina membranes)
• Pt was deposited electrochemically
• sweeping the potential between -0.25 to 1 V vs
  Ag/AgCl for 20 cycles in chloroplatinc acid
  solution

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CO stripping voltammograms over pt loaded catalyst
CO stripping experiment were carried out n 0.5 M
H2SO4
12
cyclic voltammograms of formic acid oxidation
over pt loaded catalyst
Formic acid oxidation was performed in a 0.5 M
H2SO4 0.5 M HCOOH solution by cycling between
-2 to 0.95 V vs Ag/AgCl.
13
Variation of current density with time
0.5 M H2SO4 / 0.5 M HCOOH at 0.6 V vs Ag/ AgCl
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Proposed work

• Optimization of platinum loading to correlate
  activity of the platinum cluster size
• Deposition of platinum by other methods
• To find mechanistic pathway for formic acid
  oxidation