U1
Rodrigo Benedetti
Kamal Banjara
Bob DeBorde
John DeLeonardis
What is a Catalyst?
 Changes the rate of a
reaction
 ↑ rate: catalyst
 ↓ rate: inhibitor
 Does not affect
equilibrium
composition
 Neither a product nor
reactant
www.pnl.gov/.../highlights/highlight.asp?id=383
 Often specific to one
reaction
 Can promote one product
if there are competing
reactions
 the catalyst can be
recovered unchanged at
the end of the reaction it
has been used to speed up,
or catalyze.
www.cnms.ornl.gov/nanosci/lp10.sht
m
How do they work?
 Changes activation energy
 Offers an alternative reaction pathway
 New pathway requires less kinetic energy in molecular
collisions
Types of Catalyst
• Catalysts can be either heterogeneous
or homogeneous, depending on
whether a catalyst exists in the same
phase as the substrate
•Other classifications:
Electrocatalyst
Organocatalyst
http://www.bnl.gov/bnlweb/pubaf/pr/photos/2009%5C05%
5CPlatinumCatalyst-300.jpg
Common Examples
 Enzymes
 DNA Polymerase
 Industrial catalysts
 Alumina
 Platinum
www.bionutrisyon.co
m/e-nutrients.html
 Catalytic converter
 Platinum or rhodium
www.allproducts.co
m/.../product4.html
http://maremare1225.wordpress.com/2008/03/31/slee
p-with-one-eye-closed-one-eye-on-catalyticconverter/
2 CO + 2 NO → 2 CO2 +
N2
Intro to Nanocatalysts
http://www.news.cornell.edu/stories/Nov08/nanocatalysts.ws.htm
l
 Definition:
A Nanocatalyst is a substance or material with catalytic properties
that has at least one Nanoscale dimension, either externally or in
terms of internal structures1
 Generally, catalysts that are able to function at atomic scale are
Nanocatalysts
https://www.jyu.fi/fysiikka/en/research/material/compns/research/index_html/supported.j
pg
1http://www.the-infoshop.com/report/bc21463_nanocatalysts.html
Growing interest
 The chart below represents the number of the
publish reports on nanostructured metal catalyst
http://www.bepress.com/cgi/viewcontent.cgi?article=2132&context=ijcre
Specific metal catalyst
Interest in specific elements in the preparation of Nanoparticles in the period 20002007
http://www.bepress.com/cgi/viewcontent.cgi?article=2132&context=ij
cre
Physical properties
 Sizes may varies but can be controlled at
less then 10 nm depending upon the
application
 Particle position can be controlled
increasing the reaction stability and
mechanism
 Controllable exposed atomic structure
 Uniform dispersion
http://news.princeton.edu/uploads/243/image/nanocatalyst_diagram.j
pg
http://www.htigrp.com/data/upfiles/pdf/Nanocatalysts0304.p
df
Chemical Properties
 Catalytic activity
 Stability
http://www.tacc.utexas.edu/research/users/features/stefano.php
Catalytic Activity
 Very important factor in choosing a nanocatalyst
 Porous nanostructure provides high surface to volume ratio hence
increase the catalytic activity1
 Example : in a Direct Formic Acid Fuel Cells, CO poisoning
significantly limits the catalytic activities of Pt/Ru and Pt/Pd alloys
for formic acid oxidation
 Solution to the Poisoning ; Decoding the nano particles with carbon
support2
1Nanocatalyst
http://tinyurl.com/yzqps4
d
fabrication and the production of hydrogen by using photon energy; ming –Tsang Lee, David J. Hwang, Ralph Greif
and Costas P Gigoropoulous
2References:
Performance characterization of Pd/C nanocatalyst for direct formic acid fuel cells; S.HA, R. Larsen and R.I. Masel
Stability
 Most notable property
 Stability helps in achieving
desire size nanopartilces with
uniform dispersion on the
substrate like carbon
 Nanocalatyst like Pt can be
stabilize by stabilizing agents
like surfactants, ligands or
polymers
http://www.natureasia.com/asia-materials/article_images/425.jpg
Effect of temperature and pressure
on the Nanocatalysts
 Melting point may lower from the original
metal species
- For example: platinum has melting point is
around 2000K but the nano catalyst made up
of Pt has melting point around 1000K
 Change in melting point have both pros
-
-
and cons
Pros
Possibility of using these Nanocatalysts in
liquid phase
In case of fuel cells it may penetrate through
the layers to increase the surface area of
reaction
Cons
May not be useful in some reactions
Durability may change as it might reduce the
adherence capability to substrate
References: Dr. Balbuena; Chemical Engineering professor at
TAMU
http://www.ufz.de/index.php?en=5979
Advantages of Nanocatalyst
 These advantages are
related to the inherent
properties of the
material.
 Also to their:
 Size
 Charge
http://www.inano.au.dk/research/research-areas/nanoenergy-materials/nanocatalysis/
 Surface area
Size and surface area
 Nanocatalyst can fit where
many of the traditional
catalyst will not.
 By nanocatalyst being very
chemistry.brown.edu/research/sun/research.html
http://www.bnl.gov/bnlweb/pubaf/pr/photos/2002/nanoparticlesw.jpg
small in size, this property
creates a very high surface to
volume ratio. This increase
the performance of the
catalyst since there is more
surface to react with the
reactants
Charge
 Some Nanocatalyst can develop partials and
net charges that help in the process of making
and braking bonds at a more efficient scale.
Nano-catalysts are part of
tomorrow’s cutting edge
technology.
 One example is the use of Hydrogen as a
domestic fuel.
As you may know, Hydrogen is as abundant
as it is environmentally friendly. Companies
would love to develop an efficient Hydrogen
Fuel cell that is financially feasible.
A typical Hydrogen fuel
cell1.
 One major problem however, is the method
of reversible storage of Hydrogen. One
company, HRL Laboratories, is currently
working on a multi-million dollar project
that will increase the efficiency of current
Hydrogen storage methods by utilizing the
properties of Nano-catalysts.
Imagine filling up your tank
with a gas instead of liquid2.
The next slide shows the project overview
HRL Laboratories are working hard
to meet and exceed Department of
Energy standards for hydrogen
storage.
http://www.hydrogen.energy.gov/pdfs/review06/st_16_olson.p
df
Hydride Destabilization Cycle
•The system cycles between Hydrogencontaining alloy and a stabilized-alloy
state.
•There is a lower ∆H for the stabilized alloy
(where Hydrogen is destabilized).
•The alloy allows for Hydrogen to become
released at a lower temperature and energy
level.
•Nano-catalysts decrease the diffusion
distance resulting in fast exchange rates
making the whole process more efficient.
•Nano-catalysts also can act as a scaffold
for the metal hydride, allowing structuredirected agents as well as deterring particle
conglomeration.
http://www.hydrogen.energy.gov/pdfs/review06/st_16_olson.p
df
8.
3.
4.
7.
With Nano-catalysts, many
companies are on the verge of
breaking through the Hydrocarbon
age and transforming how we
imagine energy and fuel for domestic
as well as industrial purposes.
5.
6.
Close to home…
 Dr. Balbuena’s research is
Perla Balbuena
http://www.che.tamu.edu/people/faculty/info?fid=16
focused on molecular
simulations to help predict
the chemical and physical
behavior of new materials.
 Her main contributions are
improved power sources
such as lithium-ion batteries
and the development of new
catalysts.
Information about her Research
9
 Balbuena’s Research group is funded
heavily by the DOE, Department of
Energy and also by the NSF.
 As part of her research she works closely
with companies that are looking for
better materials for catalysts or energy
storage.
 If she discovers an exciting new
material then she collaborates with the
companies to try and figure out if it is
something that can be manufactured
for use.
13
12
10
11
Sergio R. Calvo, Perla B. Balbuena
Department of Chemical Engineering, Texas A&M University, 3122
TAMU, College Station, TX77843, USA
Received 26 June 2006; accepted for publication 11 September 2006
Background on Nano-clusters
 This term is used to categorize
some powerful, tiny mineral
clusters that energize virtually
all nutrients with which they
come into contact. These
molecules have an enormous
surface area of about 240,000
square feet per once.
 Nano-clusters can act as
transporters of other molecules
and can increase the efficiency
of a reaction up to completion.
http://accelrys.com/solutions/industry/aerospace-defense/
Bimetallic Nanoclusters
 These clusters are composed, as
their name says, by two metals
which have different properties
that make the cluster unique
for certain applications.
 The most used nano-clusters
http://www.ms.buct.edu.cn/research.aspx
used in synthesis process are
made out of Pd, Pt, Au, Cu, Rh.
PtxPdy Bimetallic Nano-cluster
 The ideal Ptx-Pdy nano-cluster
catalyst used in this research are
about 500 atoms and about 2nm
in diameter.
 A combination of Pt and Pd
atoms (with x + y = 10 and
various x:y ratios) were tested
obtain the best arrangement and
to characterize their reactivity.
Motivation
 Oxygen reduction reaction is a key reaction
in Hydrogen Fuel cells.
 Certain metals, Pt for instance, can catalyze
this reaction as shown in previous slides.
 The Reaction can be categorized into two
parts:
1- The binding of 02 to a metal
atom and the addition of a
proton.
2- The dissociation of –OOH,
addition of 3 protons, and the
formation of water.
14
 We will now refer to these as:
 Reaction 1
 Reaction 2
http://www.fotosearch.com/bthumb/CSP/CSP105/k1051206.jpg
 The motivation behind this experiment is to try and combine different
metals to optimize the catalysis of these two reactions.
 For instance, Platinum will catalyze Reaction 1 very well, but Palladium is a
much better catalyst for Reaction 2.
Pure Pt catalyst
Pure Pd catalyst
PtPd alloy
G
G
G
∆G1
∆G2
∆G1
∆G1
Reaction
∆G2
∆G2
Reaction
Reaction
 Obviously, if one can combine the properties of both metals into a single
species then one can fully utilize both catalysts for a faster overall reaction.
The Experiment
15
 Balbuena’s group uses Texas A&M
University’s super-computers to
perform high level computations
for molecular modeling.
 In this experiment they are
16
researching Platinum-Palladium
alloys to see their catalytic
properties and to speculate on the
activity of such catalysts.
Experiment (cont)
 For their computations, they chose 6 different
configurations/computations.
 Shown here is the side view (first row) and the top view.
Experiment (cont)
 The “control” molecule is
this experiment is a pure
platinum nano-cluster.
 This is the industry
standard for oxygen
reduction catalysis.
 Balbuena’s group compares
their experimental materials
to this Pt species to try and
find something more
reactive
Pure Pt species.
Atomic Ratio: Pt10Pd0
Geometry: Uniform
Experiment (cont)
 Other nano-clusters they analyzed were PtPd alloys:
Atomic Ratio:
Pt7Pd3
Geometry: Mixed
Atomic Ratio:
Pt3Pd7
Geometry: Mixed
Atomic Ratio:
Atomic Ratio:
Pt7Pd3
Pt3Pd7
Geometry: Ordered Geometry: Ordered
Conclusions
 The research group focused their energy into calculating the activity for
each species and specifically ignored the stability and effect of the
substrate is not considered.
 They analyzed different properties such as ground state energy, charge
distribution between atoms, bond energy, bond length, and most
importantly– reactivity.
This is a chart showing the ∆G for both reactions and for each species.
Conclusions (cont)
Here is a Graph displaying the ∆G for both reactions combined with respect to
the “control” species– pure Pt.
As you can see, species E
and C are the most reactive
of the compounds studied.
C and E correspond to the
Pt3Pd7 composition in
mixed and ordered
geometry, respectively.
Conclusions (cont)
 These results indicate that we could catalyze the O2 reduction reaction
much faster with a PtPd alloy compared to pure Platinum.
 As exciting as the results are however, this is only the first step towards
creating a new compound that is safe, cost-effective, and can be easily
manufactured for everyday use.
17
18
Typical Molecular Modeling
A Finished Product
Further research
 By talking in person to Dr. Balbuena, we discussed the current problems
with the PtPd alloy catalyst.
 She informed me that the biggest problem right now is that the electrolyte
substrate that the catalyst is observed in is acidic.
 More specifically, the Chlorine ions in solution are stripping away the
Platinum out of the nano-clusters, basically dissolving the catalyst.
 As you can imagine, this poses a severe problem to the viability of such
catalysts.
19
Further research (cont)
20
 We did find out that Dr. Balbuena has
very recently analyzed a compound
that meets the catalytic requirements
we have discussed as well as being a
stable suitable for production.
 Currently she is collaborating with a
catalyst company to try and devise
ways to manufacture this product. She
didn’t give too many details about this
new catalyst or its specific properties
but she seemed very hopeful that it
would come to fruition.
21
 Hopefully in a short time all of her
hard work will be realized and better
catalysts will be produced, which will
help alleviate our energy crisis.
Perhaps Balbuena’s catalyst will be used to power the next
generation of Fuel Cell cars.
Follow up work on Pt-Pd catalyst
for fuel cells
 Pd-Pt Bimetallic Nanodendrites
with High Activity for Oxygen
Reduction: synthesis of an array of Pt
branches in a Pd core, this arrangement
showed to have a larger surface area and a
overall higher efficiency in catalyzing the
oxygen reduction reaction (ORR), the rate
determining step in a proton-exchange
membrane fuel cell.
 This is a more recent publication (2009)
by another group at Washington
Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction
Byungkwon Lim,1 Majiong Jiang,2 Pedro H. C. Camargo,1 Eun Chul Cho,1
Jing Tao,3 Xianmao Lu,1 Yimei Zhu,3 Younan Xia1*
University researching the same catalyst.
Pd-Pt Bimetallic Nanodendrites with High Activity for
Oxygen Reduction (continuation)
 This research goes one step further
in the manipulation of Pd-Pt arrays
and proved that to achieve better
results and efficiency on catalyzing
ORR. They not only variatedthe PdPt mass ratio, but also changed the
size and distribution of the
molecules in the array . In this shape
the molecule would give new
advantages and characteristics to
Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction
Byungkwon Lim,1 Majiong Jiang,2 Pedro H. C. Camargo,1 Eun Chul Cho,1
the catalyst.
Sergio R. Calvo, Perla B. Balbuena
Department of Chemical Engineering, Texas A&M University, 3122
TAMU, College Station, TX77843, USA
Received 26 May 2003; accepted for publication 16 August 2003
Potential Application of
nanoclustes
Heterogeneous
catalyst
Optoelectronics
Microelectronics
Nanoelectronics
Properties that we have to considered
before we can start using the nanoclusters
 Thermal properties
 Structural properties
 Dynamical properties
http://images.iop.org/objects/ntw/news/7/3/19/080319.j
Properties (cont)
 In addition
 Nanoclusters when deposited on
the surface, their physical and
chemical properties not only
depend on their particle size but
also on the structure of the
metal/substrate interface
 Chemical, thermal, and
mechanical treatments may
significantly affect the structure
of the exposed faces, and
therefore the catalytic activity
http://www.informaworld.com/ampp/image?path=/713172968/713
557621/F0001.png
Overview of the paper
 Temperature dependence of Nanoclusters
 Research based on Cu and Ni metals
Melting point
 Solid-liquid transition in nanoclusters differ from that
of bulk materials
 Melting point change variation with the nanocluster
size
 At low temperature; nanoclusters exist in solid like
and with temperature increases the structure acquires
liquid features, passing through the intermediate state
called Dynamic Equilibrium
Cu and Ni density profile ρ(z) in the direction
perpendicular to the substrate plane during the
heating process
Copper
Nickel
From the figure (a) and (b), it is clear that there is enhancement in the peak
closest to the substrate, due to the wetting effect of the metal on graphite
surface.
Cu structures becomes liquid-like at temperatures close to 870 K whereas for
Ni structure, at 870 K liquid features start to be evident.
Diffusion and structural changes
with temperature
 At around 700 to 800 K both the cluster is still solid
 At this temperature, Cu occupies the cluster outer layers
Diffusion and structural changes with
temperature
 When the temperature reaches to 1000K, some Cu atoms
move to the inner space previously occupied by the Ni
atomic core, whereas Ni atoms move outside layers
 Diffusion process reaches to equilibrium at 1300K with the
structures appears uniform
Cluster mobility on graphite
surface
 The bimetallic clusters
diffuses as an entity an the
substrate
 In solid phase (at 800 K)
the cluster motion is to a 1
A^2
 At this temperature,
atomic vibration resembles
typical atomic motion in
bulk solid and the
vibration increases with
temperature
Temperature effect on clusters diffusion
constant for Cu-Ni 343 atom cluster
Conclusion
 Bimetallic nanoclusters supported
on graphite substrate melt at a
much lower temperature than the
bulk metal
 Although their melting
temperature is slightly higher than
that of isolated nanoclusters of
identical size and composition in
vacuum
 Specific melting temperature
depends on size and composition
of cluster as well as the thermal
treatment at which the cluster has
been exposed
http://www.physics.purdue.edu/nanophys/images/goldunlink.jpg
Sergio R. Calvo, Perla B. Balbuena
Department of Chemical Engineering, Texas A&M University, 3122
TAMU, College Station, TX77843, USA
Received 18October 2004; accepted for publication 28 February
2005
Goals of Research
 Use Molecular
Dynamics (MD)
Simulations to model
various nanoclusters
 Use simulations to
identify the
contributions of inner
and surface atoms to
the characteristic
phonon modes.
math.duke.edu
Motivation
 We want to be able to measure a sample and determine
its metallic composition
 Phonons are a function of composition!!!
 Measure Phonons  use model  find composition
people.na.infn.it
Procedure: Simulation Details
 Nanoclusters characteristics
 Face centered cubic (FCC) crystal
structure
 Molecules Randomly distributed
and allowed to reach minimum
energy level for given morphology
 All particles are point masses
governed by classical mechanics
 1000 atom in each nanocluster
 Elements studied: Pt, Ag, Au
seas.upenn.edu
Procedure: Simulation Details
 Nanoclusters supported by
graphite slab
73.8X73.8X6.7 Å
 Equations of motion
calculated using Verlet
Leapfrog method with a
time step of 0.001 ps
schools-wikipedia.org
Procedure: Force Fields
 Metal-Carbon interactions are simulated with
Leannard-Jones Potential
 Metal-Metal interactions are simulated with SuttonChen potential
U Total
n
1

a
  SC        c   i 
 2 i  j j  rij 

i


Procedure: Force Fields
 ρi is metallic bonding energy defined as
a
 i    
j  i  rij 
m
 rij = distance between atoms i and j
 c = dimensionless parameter
 εSC = energy parameter
 a = FCC Lattice constant
Procedure: Force Fields
Procedure: Phonon DOS
 Vibrational Density of States
(DOS) gives information on
microstructures and
dynamics of a material
 Phonon DOS
astro.phys.au.dk
 Vibrational spectrum of
system
 Found via spectroscopy
 Molecules: bond vibrations
 Bulk systems: seen as broad
bands
oxford-instruments.com
Procedure: Phonon DOS
 Intermediate systems
(nanoclusters)
 Mixture of bulk and molecular
systems
 Depends on number of atoms
in cluster
 DOS can indicate atomic
mtchm.bris.ac.uk
distribution
 Need 500 atoms to produce 2
peaks
Procedure: Phonon DOS
10 Pt atom cluster
Procedure: Phonon DOS
20 (green), 40 (red), 80 (black)Pt atom clusters
Procedure: Phonon DOS
 Velocity autocorrelation function (VAF)
 Obtained from MD simulations
 Used to calculate DOS
Results: Pt-Ag Nanoclusters
Phonon DOS for Pt
Results: Pt-Ag Nanoclusters
Phonon DOS for Ag
Results: Pt-Ag Nanoclusters
 The previous graphs are phonon DOS of Ptx-Ag1-x
 0≤x≤1
 Cluster size = 1000 atoms
 2 Peaks
 Low frequency peak: caused by surface atoms
 High frequency peak: caused by inner atoms
diamondsnews.com
museice.blogspot.com
Results: Pt-Ag Nanoclusters
 As Ag ↑
 Pt low-frequency peaks are unaltered
 Pt high-frequency peaks are shifted and intensities
decrease
 Let’s see why…
Results: Pt-Ag Nanoclusters
Layer-by-layer atomic distribution of Pt (80% in purple)
and Ag (20% in Red)
Results: Pt-Ag Nanoclusters
Layer-by-layer atomic distribution of Pt (20% in purple)
and Ag (80% in Red)
Results: Pt-Au Nanoclusters
 Same procedure and measurements
as were used for the Ptx-Ag1-x
nanoclusters
 Use only Pt and Au atoms
 Use 1000 total atoms
 0≤x≤1
 Again, both metals produced a high
and low frequency peak
cbed.mse.uiuc.edu
Results: Pt-Au Nanoclusters
Phonon DOS for Pt
Results: Pt-Au Nanoclusters
Phonon DOS for Au
Results: Pt-Au Nanoclusters
Layer-by-layer atomic distribution of Pt (80% in purple)
and Au (20% in Green)
Results: Pt-Au Nanoclusters
Layer-by-layer atomic distribution of Pt (20% in purple)
and Au (80% in Green)
Implications of Work
 Spectroscopy can be used to
determine atomic compositions
and distributions within
moderately sized groupings
 The ability to distinguish between
outer and inner atomic positions
 Ultimate goal: creation of a
method for determining atomic
distribution to analyze potential
catalysts
thefutureofthings.com
Future Research
 More research must be done with metals used
commonly as catalysts
 Research the interactions of three or more metals
 Research different geometries (planes, spheres)
 Could lead to more powerful catalysts
ndsu.edu
bti.cornell.edu
Pictures cited
1.http://www.ngdir.org/SiteLinks/Kids/html/energy_mfahem_%20%20HYDROGEN.html.htm
2. http://www.fastfocus.tv/Media.aspx?id=18
3. http://www.casfcc.org/2/StationaryFuelCells/WhyFuelCells.aspx
4. http://www.netl.doe.gov/technologies/coalpower/fuelcells/seca.html
5. http://www.hydrogenics.com
6. http://www.hydrogendiscoveries.com/index.html
7. http://energiatechnologies.com/contact.asp
8. http://www.h2fc.com/Newsletter/Companies/PRs/axane_041504.html
9. http://www.all-creatures.org/hope/gw/US_DOE_logo_400.jpg
10. http://www.cs.missouri.edu/~reu/REU08/iptvGroup/NSF-logo.jpg
11. http://www.icis.com/assets/getAsset.aspx?ItemID=21148
12. http://www.bnl.gov/world/
13. http://www.casfcc.org/2/images/logos/UTC_web_logo.jpg
14. http://www.odec.ca/projects/2007/truo7j2/fuel_cell_small.JPG
15. http://upload.wikimedia.org/wikipedia/commons/c/c7/Roadrunner_supercomputer_HiRes.jpg
16. http://s3.amazonaws.com/memebox/uploads/3716/090313_platinum-hirez_Argonne_Lab_Propone.jpg
17. http://icnanotox.org/files/2009/01/screenshot_img2.jpg
18. http://www.falmouthproducts.com/images/300-CATALYST.jpg
19. http://www.green-planet-solar-energy.com/images/chloride-ion.gif
20. http://steynian.files.wordpress.com/20096/01/new-top-secret.jpg
21 . http://image.motortrend.com/f/9480535+w750/112_0803_06z+2008_chevrolet_equinox_fuel_cell+car_engine_view.jpg
Sources
 Wikipedia.org
 http://www.htigrp.com/data/upfiles/pdf/Nanocatalysts030
4.pdf
 http://www.theinfoshop.com/report/bc21463_nanocatalysts.html
 Faculty member: Dr. Perla B. Balbuena
 Anything not cited was received from the papers supplied
by Dr. Balbuena.