1. U1 Rodrigo Benedetti Kamal Banjara 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 www.pnl.gov/.../highlights/highlight.asp?id=383

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. www.cnms.ornl.gov/nanosci/lp10.sht m

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 http://www.bnl.gov/bnlweb/pubaf/pr/photos/2009%5C05% 5CPlatinumCatalyst-300.jpg

6. Common Examples Enzymes DNA Polymerase Industrial catalysts Alumina Platinum Catalytic converter Platinum or rhodium 2 CO + 2 NO → 2 CO 2 + N 2 www.bionutrisyon.co m/e-nutrients.html www.allproducts.co m/.../product4.html http://maremare1225.wordpress.com/2008/03/31/slee p-with-one-eye-closed-one-eye-on-catalytic- converter/

7. Intro to Nanocatalysts http://www.news.cornell.edu/stories/Nov08/nanocatalysts.ws.htm l

8. 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 structures 1 Generally, catalysts that are able to function at atomic scale are Nanocatalysts 1 http://www.the-infoshop.com/report/bc21463_nanocatalysts.html https://www.jyu.fi/fysiikka/en/research/material/compns/research/index_html/supported.j pg

9. 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

10. 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=ij cre

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 http://www.htigrp.com/data/upfiles/pdf/Nanocatalysts0304.p df http://news.princeton.edu/uploads/243/image/nanocatalyst_diagram.j pg

12. Chemical Properties Catalytic activity Stability http://www.tacc.utexas.edu/research/users/features/stefano.php

13. Catalytic Activity Very important factor in choosing a nanocatalyst Porous nanostructure provides high surface to volume ratio hence increase the catalytic activity 1 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 support 2 2 References: Performance characterization of Pd/C nanocatalyst for direct formic acid fuel cells; S.HA, R. Larsen and R.I. Masel 1 Nanocatalyst 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/yzqps4 d

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 http://www.natureasia.com/asia-materials/article_images/425.jpg

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 http://www.ufz.de/index.php?en=5979

16. Advantages of Nanocatalyst These advantages are related to the inherent properties of the material. Also to their: Size Charge Surface area http://www.inano.au.dk/research/research-areas/nano- energy-materials/nanocatalysis/

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 chemistry.brown.edu/research/sun/research.html http://www.bnl.gov/bnlweb/pubaf/pr/photos/2002/nanoparticles- w.jpg

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. The next slide shows the project overview A typical Hydrogen fuel cell 1. Imagine filling up your tank with a gas instead of liquid 2.

20. 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

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. http://www.hydrogen.energy.gov/pdfs/review06/st_16_olson.p df

22. 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. 3. 4. 5. 6. 7. 8.

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. http://www.che.tamu.edu/people/faculty/info?fid=16 Perla Balbuena

25. Information about her Research 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. 9 10 11 12 13

26. 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. http://accelrys.com/solutions/industry/aerospace-defense/

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. http://www.ms.buct.edu.cn/research.aspx

29. Pt x Pd y Bimetallic Nano-cluster The ideal Pt x -Pd y 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.

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 0 2 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 http://www.fotosearch.com/bthumb/CSP/CSP105/k1051206.jpg

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. Reaction G ∆G 1 ∆G 2 ∆G 1 ∆G 2 ∆G 1 ∆G 2 Pure Pt catalystPure Pd catalyst PtPd alloy Reaction G G

33. The Experiment 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. 15 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: Pt 10 Pd 0 Geometry: Uniform

36. Experiment (cont) Other nano-clusters they analyzed were PtPd alloys: Atomic Ratio: Pt 7 Pd 3 Geometry: Mixed Atomic Ratio: Pt 3 Pd 7 Geometry: Mixed Atomic Ratio: Pt 7 Pd 3 Geometry: Ordered Atomic Ratio: Pt 3 Pd 7 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 Pt 3 Pd 7 composition in mixed and ordered geometry, respectively.

39. 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. Conclusions (cont) Typical Molecular ModelingA Finished Product 17 18

40. 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. Further research 19

41. 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. Further research (cont) Perhaps Balbuena’s catalyst will be used to power the next generation of Fuel Cell cars. 20 21

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 Eun Chul 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 Eun Chul Cho,1

44. 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 Heterogeneous catalyst Micro- electronics Nano- electronics Opto- electronics

46. 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 pg

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 http://www.informaworld.com/ampp/image?path=/713172968/713 557621/F0001.png

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) in the direction perpendicular to the substrate plane during the heating process 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. CopperNickel Cu structures becomes liquid-like at temperatures close to 870 K whereas for Ni structure, at 870 K liquid features start to be evident.

51. 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

52. 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

53. 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

54. Temperature effect on clusters diffusion constant for Cu-Ni 343 atom cluster

55. 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

56. 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

57. 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

58. 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

59. 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

60. 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

61. Procedure: Force Fields Metal-Carbon interactions are simulated with Leannard-Jones Potential Metal-Metal interactions are simulated with Sutton- Chen potential

62. Procedure: Force Fields ρ i is metallic bonding energy defined as r ij = distance between atoms i and j c = dimensionless parameter ε SC = energy parameter a = FCC Lattice constant

63. Procedure: Force Fields

64. Procedure: Phonon DOS Vibrational Density of States (DOS) gives information on microstructures and dynamics of a material Phonon DOS Vibrational spectrum of system Found via spectroscopy Molecules: bond vibrations Bulk systems: seen as broad bands oxford-instruments.com astro.phys.au.dk

65. Procedure: Phonon DOS Intermediate systems (nanoclusters) Mixture of bulk and molecular systems Depends on number of atoms in cluster DOS can indicate atomic distribution Need 500 atoms to produce 2 peaks mtchm.bris.ac.uk

66. Procedure: Phonon DOS 10 Pt atom cluster

67. Procedure: Phonon DOS 20 (green), 40 (red), 80 (black)Pt atom clusters

68. Procedure: Phonon DOS Velocity autocorrelation function (VAF) Obtained from MD simulations Used to calculate DOS

69. Results: Pt-Ag Nanoclusters Phonon DOS for Pt

70. Results: Pt-Ag Nanoclusters Phonon DOS for Ag

71. Results: Pt-Ag Nanoclusters The previous graphs are phonon DOS of Pt x -Ag 1-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

72. 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…

73. Results: Pt-Ag Nanoclusters Layer-by-layer atomic distribution of Pt (80% in purple) and Ag (20% in Red)

74. Results: Pt-Ag Nanoclusters Layer-by-layer atomic distribution of Pt (20% in purple) and Ag (80% in Red)

75. Results: Pt-Au Nanoclusters Same procedure and measurements as were used for the Pt x -Ag 1-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

76. Results: Pt-Au Nanoclusters Phonon DOS for Pt

77. Results: Pt-Au Nanoclusters Phonon DOS for Au

78. Results: Pt-Au Nanoclusters Layer-by-layer atomic distribution of Pt (80% in purple) and Au (20% in Green)

79. Results: Pt-Au Nanoclusters Layer-by-layer atomic distribution of Pt (20% in purple) and Au (80% in Green)

80. 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

81. 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

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83. Sources Wikipedia.org http://www.htigrp.com/data/upfiles/pdf/Nanocatalysts030 4.pdf http://www.htigrp.com/data/upfiles/pdf/Nanocatalysts030 4.pdf http://www.the- infoshop.com/report/bc21463_nanocatalysts.html http://www.the- infoshop.com/report/bc21463_nanocatalysts.html Faculty member: Dr. Perla B. Balbuena Anything not cited was received from the papers supplied by Dr. Balbuena.