1. Tuning Reactivity by Tailoring Nanostructures Group:Sheng Dai Abhaya Datye Bruce Gates Mike Henderson Jan Hrbek Tobin Marks Chuck Mims Hans Nemanstsverdriet Scott Perry Annabella Selloni Michael Tsapatsis Bill Tumis Ruqien Wu

2. Tuning Reactivity by Tailoring Nanostructures Overview Science of Nanostructured Materials - New Synthetic Strategies for Nanostructured Materials - Molecular Patterning of Nanostructured Materials - Innovative Characterization Methods - Stabilization of Nanostructures - Role of Supports and Defects - Nanostructures as Links between Homogeneous and Heterogeneous Catalysis - Prediction of Structure and Catalytic Properties Summary Statement/Recommendations

3. Tuning reactivity by tailoring nanostructures Overview Unique changes occur in the electronic structure and chemical properties of solids when their dimensions are reduced to the nanoscale [A. Henglein., Chem. Rev., 89 (1989) 1861; M. B. Mohamed, C. Burda, and M. A. El-Sayed, Nanolett., 1 (2001) 589; J. H. Fendler, Chem. Mater., 8 (1996) 1616] including development of discrete electronic structure, quantum confinement, structural strain and distortion, and altered interfacial/surface reactivity. These changes translate into new physical and chemical behaviors not observed in the ‘bulk’ form of the material. Given that processes at the gas/solid and liquid/solid interfaces are largely controlled by local phenomena (e.g., the availability, reactivity and density of surface sites), changes in the local electronic and physical structures of a solid brought about by ‘nanostructuring’ should have a tremendous impact on heterogeneous chemistry (catalysis). Examples:  Au for selective oxidation (Haruta)  Arene and alkene hydrogenation by Ir, Rh (Gates)  Photocatalytic activity of TiO 2 (Zhang)  Unique reactivity of oxide nanoparticles (Klabunde)

4. Science of Nanostructured Catalysts - New Synthetic Strategies for Nanostructured Materials (a)Evaporation of metals, employing nucleation and growth phenomena to manipulate particle sizes [C. R. Henry, Surf. Sci. Rep. 31, 231 (1998)] (b)Soft-landed mass-selected nanoclusters deposition [U. Heiz and W-D. Schneider, J. Phys. D: Appl. Phys. 33, R85 (2000)] (c)Self-assembly on templates or strain-relieved substrates [S. Helveg, et al., Phys. Rev. Lett. 84, 951 (2000)] (d)Electron beam lithography [A. S. Eppler, et al., J. Phys. Chem. B 101, 9973 (1997)] (e) Synthesis based on molecular precursors of nanoparticles [A. M. Argo, et al., Nature 415, 623 (2002); G. Schmid, et al., Chem. Soc. Rev. 28, 179 (1999); B. C. Gates, Chem. Rev., 95, 511 (1995); B. C. Gates, Top. Catal., 14, 173 (2001)] (f)Exchange or anchoring of molecular precursors in solution and deposition of oxidic precursors by wet chemical impregnation possible [P. L. J. Gunter, J. W. Niemantsverdriet, F. H. Ribeiro and G. A. Somorjai, Catal. Rev.--Sci. Eng. 39, 77 (1997)] (g)Incorporation and confinement of nanoparticles into mesoporous solids[A. Fukuoka et al., Catal. Today 66, 23 (2000)], and spontaneous deposition on electrode surfaces [S. R. Brankovic, et al., J. Electroanal. Chem. 503, 99 (2001)] (h)Nanomachining of metal clusters [J. Bosbach, D. Martin, T. Wenzel, and F. Traeger, Appl. Phys. Lett., 74, 2605 (1999); S. Link, C. Burda, B. Nikoobakht, and M. A. El-Sayed, J. Phys. Chem. B, 104, 6152 (2000)

5. Science of Nanostructured Catalysts - New Synthetic Strategies for Nanostructured Materials Other opportunities: Wet impreganation of planar realistic oxide supports. Films of a single layer of zeolite nanoparticles on a planar oxide surface, e.g. silica, for reaction mechanistic studies without diffusion limitations. Patterning polymerization catalysts on substrates for the growth of nanostructures of polymers. Mechanistic and kinetic studies of layered systems made by lithography, evaporation, CVD, ALE, or impregnation in small batch reactors.

6. Science of Nanostructured Catalysts - Molecular Patterning of Nanostructured Materials Imprinting - incorporation of the template into rigid solid networks through in-situ copolymerization; removal of the template, leaving cavities with a predetermined number and arrangement of ligands that later “recognize” or selectively rebind the template or target molecule. (e.g., Wulff, Morihara) Templating - include the use of inorganic and small organic cations to direct the structure of microporous frameworks and of supermolecular templates like block copolymers and micellar structures to direct ordered mesoporous materials. (e.g., Davis) Lithography - “hard” techniques such as electron beam, holographic, focused ion beam, scanning probe, and x-ray lithography, and “soft” techniques include nanoimprint lithography, microcontact printing, and dip pen lithography. (e.g. Somorjai, Kosemo)

7. Science of Nanostructured Catalysts - Innovative Characterization Methods High resolution (in-situ) TEM In-situ STM, AFM High pressure XPS Synchrotron based in-situ EXAFS, XANES, time-resolved XRD, grazing X-ray Spatially resolved spectroscopies (PEEM, LEEM) In-situ vibrational techniques (PM-IRAS, SFG) Neutrons

8. Science of Nanostructured Catalysts - Stabilization of Nanostructures Role of sintering in catalyst deactivation Strategies for immobilizing nanostructures on supports Kinetics and energetics of nanostructure sintering - Role of Supports and Defects Investigate structural and electronic defects in nanostructures and their role in modifying reactivity Example: Inclusion of surface defects in MgO has profound effect on the nanoscale structure of Fe 3 O 4 overlayers [Chambers, Surf. Sci. Rep. 39, 105 (2000)]

9. Science of Nanostructured Catalysts - Nanostructures as Links between Homogeneous and Heterogeneous Catalysis Ligand effects analogous to surface modifiers and promoters Site isolation in homogeneous catalysts vs. metal site dilution in ordered mesoporous heterogeneous catalysts Homogeneous anchoring, i.e. “ship in a bottle” Soluble models for metal oxides, i.e. silsequioxanes (Feher) Hybride organometallic complexes bound to metal oxides through M-O linkages (Basset)

10. Science of Nanostructured Catalysts - Prediction of Structure and Catalytic Properties Simulation via first principles molecular dynamics of simple reactions, then parameters used for larger micro-kinetics simulations; useful for describing more complex reactions Stability of nanostructure size and shape on various substrates as a function of the coverage of impurites, defects, metal deposition rate, etc. Adsorbate properties calculated and compared with experiment, i.e., XPS, UPS, EELS, IRAS, SFG, etc. Nanostructure property-function relationships Properties of mixed-metal nanostructures