1. KAVI MONICA,V. M.TECH. (CATALYSIS TECHNOLOGY) NANOPLATINUM IN CATALYSIS

2. NANOMATERIALS Materials with particles of nanometer size (1-100 nm) Unique properties at the nanoscale are the driving force for the exploitation of Nanomaterials. Nanoparticles have a high surface to volume ratio. As the crystal domains become smaller, the ratio of the corner to edge atoms to terrace atoms increases.

3. GENERAL PROPERTIES OF PLATINUM metalPt Atomic number78 Mass number195.08 Electronic configuration [Xe]4f 14 5d 9 6s 1 StructureFCC Lattice constant(nm)0.392 Metallic radius(nm)0.1385 Density (g/cm 3 )21.41 1769 4170 First ionisation energy KJ/mol866 Standard reduction potentials, V Pt 4+ /Pt 1.0 Pt 2+ / Pt 1.18 Conductivity m ohm-cm -1 94.34

4. NANOPLATINUM Platinum nanoparticles are usually in the form of suspension or colloid. They can be made with sizes between 2-20 nm depending on reaction conditions. In the form of nanoparticles, platinum has a substantially higher effectiveness because of the increased surface area. At sizes of 10 nm, 20% of Pt atoms directly interact with surroundings of nanoparticles.

5. VARIATION IN PROPERTIES MACRO TO NANO  Particle size of a material has significant influence on their properties.  Nanoparticles vary from their bulk counterpart in the following properties.  Electrical and electronic properties  Mechanical properties  Magnetic properties  Chemical properties  Thermal properties  Optical properties

6. 1.ELECTRICAL AND ELECTRONIC PROPERTY From continuous to discrete energy levels

7. CONTINUOUS TO DISCRETE The spacing between energy states gets larger as the volume gets smaller. At the bottom, a single atom has just one energy state per sublevel. As atoms are group together to form particles, there are as many splits per sublevel as there are atoms in a particle. As the volume increases to the size of a solid, the spacing between splits gets so tight that the sublevel is best characterised as a band.

8. DISCRETE ENERGY LEVELS Consider sodium atom with one valence electron. At large separations the two electrons have the same energy. When two sodium atoms are close to each other, these outer electron orbitals start to overlap. As a result, outermost energy subshell begins to split At larger separations,the two electrons have the same energy.

9. SIZE INDUCED METAL INSULATOR TRANSITION

10. QUANTUM CONFINEMENT

11. 2.CHEMICAL PROPERTY Reactivity and catalytic property It is mainly due to electronic and geometric effect At the nanoscale, there is an increases in surface to volume ratio So significant proportion of atoms in nanoscale structures are actually surface atoms. Presence of dangling electrons and kinks (as the size is reduced)exists. Thus extent of chemical reaction that occurs on surface is amplified.

12. REACTIVITY The catalytic activity in structure sensitive processes is directly related to the existence of sites with low energy electronic fluctuations. The fluctuations are dominant in transition metal atoms of high coordination number. Different facets shows different reactivity and it increases in the following order: FCC(111)<FCC(100)<FCC(110)<FCC(hkl)

13. REACTIVITY FacetCoordination number (100)8 (110)7 (111)9

14. Guisbiers et al. Nanoscale Research Letters 2011 6:396

15. CATALYTIC ACTIVITY The catalytic activation energy is the energy quantity that must be overcome in order for a chemical reaction to occur in presence of a catalyst. The low the catalytic activation energy is, the most active the catalyst is. It is thus an important kinetic parameter linked to the chemical activity The size-dependent catalytic activation energy, E ca could be obtained by, (E ca /E ca,∞ )=(T m /T m, ∞ ) Therefore, catalytic activation energy decreases with size.

16. 3.THERMAL PROPERTY

17. SOLID SURFACE ENERGY OF PLATINUM Guisbiers et al. Nanoscale Research Letters 2011 6:396

18. MATERIAL PROPERTIES OF PLATINUM Guisbiers et al. Nanoscale Research Letters 2011 6:396

19. MELTING POINT Property is a consequence of average coordination number of participating atoms. Surface energy corresponds to the number of broken bonds of surface atoms relative to bulk situation. Large surface is related to large surface energy. The work necessary to increase the surface by adding atoms is proportional to the increment of the area dA, the proportionality factor is the surface free energy Dw=γdA

20. SIZE-DEPENDENT MELTING TEMPERATURE OF PLATINUM VERSUS THE SIZE FOR DIFFERENT SHAPES. GUISBIERS ET AL. NANOSCALE RESEARCH LETTERS 2011 6 :396

21. At the nanoscale, the shape which exhibits the highest melting temperature is the one which minimizes the most the Gibbs' free energy (G = H - TS) and is then the favored one. The four most-stable shapes among the ones considered are 1.dodecahedron 2.truncated octahedron 3. icosahedron and 4. cuboctahedron.

22. 4.MAGNETIC PROPERTY Platinum is actually paramagnetic Superparamagnetism arises from structural changes associated with size effects When it is sufficiently small,it acts like single magnetic spin that is subject to brownian motion. Its response to a magnetic field is qualitatively similar to response of a paramagnet but larger.

24. 5.OPTICAL PROPERTY Absorption and scattering of light Change in colour and transparency Mainly due to two reasons  Increased level spacing as the system becomes more confined  Surface plasmon resonance

25. APPLICATIONS Automotive catalytic converters Petroleum reforming catalysts Electrocatalysts Magnetic nanopowders Polymer membranes Cancer therapy Coatings,plastics, nanofibers and textiles And in various chemical reactions

27. REACTIONS Pt is catalytically active for both oxidation and reduction reactions. 2NO x → xO 2 + N 2 2CO + O 2 → 2CO 2 C x H 2x+2 + [(3x+1)/2]O 2 → xCO 2 + (x+1)H 2 O.

30. PEM FUEL CELLS The catalyst is a special material that facilitates the reaction of oxygen and hydrogen. It is usually made of platinum nanoparticles very thinly coated onto carbon paper or cloth. The catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the PEM.

31. PEMFC Hydrogen is oxidized at the anode into protons and oxygen is reduced at the cathode to produce water. Both reactions can be catalyzed by platinum. While hydrogen oxidation over platinum is intrinsically very fast, oxygen reduction over platinum is very slow. Carbon-supported platinum (Pt/C) catalysts have higher active surface areas and are the materials of choice in today’s fuel cells.

32. PEMFC

33. CATALYTIC REFORMING Pt is used along with rhenium on alumina or silica support in petroleum reforming process (Platforming). Catalytic reforming process involves dehydrogenation, dehydrocyclization and isomerisation. Hydrocracking and coking are the undesirable reactions in the catalytic reforming process.

34. PT AS CATALYST Pt is catalytically active for oxidation reduction reactions. Hydrogenation of cyclohexene to cyclohexane and styrene to ethyl benzene. Dehydrogenation of isobutane to isobutene. Hydrogenation of benzoic acid to cyclohexane carboxylic acid Hydrogenation of dimethyl teraphthalate to 1,4- cyclohexane dimethanol.

35. REFERENCES Greogory Guisbiers,Size dependent catalytic and melting properties of Pt-Pd nanoparticles,Nanoscale research letters. Nanotechnology: Principles and Practices by Sulabha K.Kulkarni,3 rd edition. Nanoscience and Technology,Nanocatalysis,edited by U.Heiz and U.Landman. Nanotechnology -understanding small systems by Ben Rogers,Sumita Pennathur Jesse Adams,2 nd edition. Nanomaterials by B.Viswanathan. Principles of Nanoscience and Technology by M.A.Shah Tokeer Ahmad. Rao Huang a, Yu-Hua Wen, Zi-Zhong Zhu and Shi-Gang Sun, Structure and stability of platinum nanocrystals: from low-index to high-index facets,J.Mater.chem., 2011, 21. Zhi-You Zhou, Na Tian, Jun-Tao Li, Ian Broadwell and Shi-Gang Sun Nanomaterials of high surface energy with exceptional properties in catalysis and energy storage Chem. Soc. Rev., 2011, 40