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  1. Nanocatalyst U1 Rodrigo Benedetti KamalBanjara Bob DeBorde John DeLeonardis

  2. What is a Catalyst? • Changes the rate of a reaction • ↑ rate: catalyst • ↓ rate: inhibitor • Does not affect equilibrium composition • Neither a product nor reactant

  3. 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.

  4. How do they work? • Changes activation energy • Offers an alternative reaction pathway • New pathway requires less kinetic energy in molecular collisions

  5. 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

  6. Common Examples • Enzymes • DNA Polymerase • Industrial catalysts • Alumina • Platinum • Catalytic converter • Platinum or rhodium 2 CO + 2 NO → 2 CO2 + N2

  7. Intro to Nanocatalysts

  8. Definition: ANanocatalyst 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 1

  9. Growing interest • The chart below represents the number of the publish reports on nanostructured metal catalyst

  10. Specific metal catalyst Interest in specific elements in the preparation of Nanoparticlesin the period 2000-2007

  11. 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

  12. Chemical Properties • Catalytic activity • Stability

  13. 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 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

  14. 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

  15. 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

  16. Advantages of Nanocatalyst • These advantages are related to the inherent properties of the material. • Also to their: • Size • Charge • Surface area

  17. Size and surface area • Nanocatalyst 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

  18. Charge • Some Nanocatalyst can develop partials and net charges that help in the process of making and braking bonds at a more efficient scale.

  19. 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. A typical Hydrogen fuel cell1. Imagine filling up your tank with a gas instead of liquid2. The next slide shows the project overview

  20. HRL Laboratories are working hard to meet and exceed Department of Energy standards for hydrogen storage.

  21. 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.

  22. 8. 3. 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. 4. 6. 5.

  23. The Future of Catalysts BimetallicNanoclusters

  24. Close to home… • Dr. Balbuena’s research is 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. Perla Balbuena

  25. 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. 10 11 12 13

  26. Part 1:Density functional theory analysis of reactivity of PtxPdy alloy clusters 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

  27. 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.

  28. 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 used in synthesis process are made out of Pd, Pt, Au, Cu, Rh.

  29. PtxPdyBimetallic Nano-cluster • The ideal Ptx-Pdynano-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.

  30. 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

  31. We will now refer to these as: • Reaction 1 • Reaction 2

  32. 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. • 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. Pure Pt catalyst PtPd alloy Pure Pd catalyst G G G ∆G1 ∆G2 ∆G1 ∆G2 ∆G1 ∆G2 Reaction Reaction Reaction

  33. 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 researching Platinum-Palladium alloys to see their catalytic properties and to speculate on the activity of such catalysts. 16

  34. Experiment (cont) • For their computations, they chose 6 different configurations/computations. • Shown here is the side view (first row) and the top view.

  35. 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

  36. Experiment (cont) • Other nano-clusters they analyzed were PtPd alloys: Atomic Ratio: Pt7Pd3 Geometry: Mixed Atomic Ratio: Pt3Pd7 Geometry: Mixed Atomic Ratio: Pt7Pd3 Geometry: Ordered Atomic Ratio: Pt3Pd7 Geometry: Ordered

  37. 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.

  38. 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.

  39. 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

  40. 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

  41. 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. • 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. 21 Perhaps Balbuena’s catalyst will be used to power the next generation of Fuel Cell cars.

  42. 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 University researching the same catalyst. Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction Byungkwon Lim,1 Majiong Jiang,2 Pedro H. C. Camargo,1 EunChul Cho,1 Jing Tao,3 Xianmao Lu,1 Yimei Zhu,3 Younan Xia1*

  43. 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 Pd-Pt 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 the catalyst. Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction Byungkwon Lim,1 Majiong Jiang,2 Pedro H. C. Camargo,1 EunChul Cho,1

  44. Part 2:Structure and dynamics of graphite-supported bimetallic nanoclusters 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

  45. Potential Application of nanoclustes

  46. Properties that we have to considered before we can start using the nanoclusters • Thermal properties • Structural properties • Dynamical properties

  47. 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

  48. Overview of the paper • Temperature dependence of Nanoclusters • Research based on Cu and Ni metals

  49. 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

  50. Cu and Ni density profile ρ(z) inthe 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.