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What is a Catalyst?Changes the rate of a
reaction↑ rate: catalyst↓ rate: inhibitorDoes 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.shtm
How do they work?Changes activation energy
Offers an alternative reaction pathwayNew 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 ExamplesEnzymes
DNA Polymerase Industrial catalysts
AluminaPlatinum
Catalytic converterPlatinum or rhodium2 CO + 2 NO → 2 CO2
+ N2
www.bionutrisyon.com/e-nutrients.html
www.allproducts.com/.../product4.html
http://maremare1225.wordpress.com/2008/03/31/sleep-with-one-eye-closed-one-eye-on-catalytic-converter/
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
1http://www.the-infoshop.com/report/bc21463_nanocatalysts.html
https://www.jyu.fi/fysiikka/en/research/material/compns/research/index_html/supported.jpg
Growing interestThe 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 2000-2007
http://www.bepress.com/cgi/viewcontent.cgi?article=2132&context=ijcre
Physical propertiesSizes 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://www.htigrp.com/data/upfiles/pdf/Nanocatalysts0304.pdf
http://news.princeton.edu/uploads/243/image/nanocatalyst_diagram.jpg
Chemical Properties
Catalytic activity Stability
http://www.tacc.utexas.edu/research/users/features/stefano.php
Catalytic ActivityVery important factor in choosing a nanocatalystPorous 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
2References: Performance characterization of Pd/C nanocatalyst for direct formic acid fuel cells; S.HA, R. Larsen and R.I. Masel
1Nanocatalyst fabrication and the production of hydrogen by using photon energy; ming –Tsang Lee, David J. Hwang, Ralph Greif and Costas P Gigoropoulous
http://tinyurl.com/yzqps4d
StabilityMost notable propertyStability 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 NanocatalystThese advantages
are related to the inherent properties of the material.
Also to their:Size Charge Surface areahttp://www.inano.au.dk/research/research-areas/
nano-energy-materials/nanocatalysis/
Size and surface areaNanocatalyst can fit where
many of the traditional catalyst will not.
By nanocatalyst being very 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
chemistry.brown.edu/research/sun/research.html
http://www.bnl.gov/bnlweb/pubaf/pr/photos/2002/nanoparticles-w.jpg
ChargeSome 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.
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.
The next slide shows the project overview
A typical Hydrogen fuel cell1.
Imagine filling up your tank with a gas instead of
liquid2.
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.pdf
Hydride Destabilization Cycle •The system cycles between
Hydrogen-containing 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 structure-directed agents as well as deterring particle conglomeration.
http://www.hydrogen.energy.gov/pdfs/review06/st_16_olson.pdf
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.
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Pictures cited1.http://www.ngdir.org/SiteLinks/Kids/html/energy_mfahem_
%20%20HYDROGEN.html.htm2. http://www.fastfocus.tv/Media.aspx?id=183. http://www.casfcc.org/2/StationaryFuelCells/WhyFuelCells.aspx4. http://www.netl.doe.gov/technologies/coalpower/fuelcells/seca.html5. http://www.hydrogenics.com6. http://www.hydrogendiscoveries.com/index.html7. http://energiatechnologies.com/contact.asp8. http://www.h2fc.com/Newsletter/Companies/PRs/axane_041504.html
SourcesWikipedia.orghttp://www.htigrp.com/data/upfiles/pdf/Nanocatal
ysts0304.pdfhttp://www.the-infoshop.com/report/bc21463_nan
ocatalysts.htmlFaculty member: Dr. Perla B. Balbuena