| third General Session | Catalysis On Nanoparticles |
Nanoparticle Catalysts with Tailored Activities:
Catalysis on Ordered Porous Materials
M. Samy El-Shall
Department of Chemistry
Virginia Commonwealth University
Richmond, VA 23284-2006, USA
Nanoparticle catalysts are characterized by large surface area, high dispersion and strong metal-support interaction. Using the Laser Vaporization Controlled Condensation (LVCC) method1-4 and a microwave synthesis technique5, a variety of nanoparticle catalysts for CO oxidation have been prepared.5,6 The effects of the nanoparticle support on the activity of the catalyst have been investigated. The results indicate that the Pd/CeO2 and Au/CeO2 systems show great promise for the efficient low temperature oxidation of CO.
In the microwave synthesis method, a remarkable enhancement of the catalytic activity is observed and directly correlated with the change in the morphology of the supported catalyst and the efficient dispersion of the active metal on the support achieved by using capping agents during the microwave synthesis.5
Ordered mesoporous materials with well-controlled pore diameters are promising candidates as catalytic supports for active nanoparticle catalysts (Au, Pd and Cu) for the selective oxidation of CO. The large internal surface areas and narrow pore size distributions of the mesoporous supports are expected to result in high activity and stability of the nanoparticle catalyst. We will present different approaches to synthesize thermally stable mesoporous oxides such as MCM-41 and MCM-48, and mixed oxide supports containing nanoparticle catalysts. A modified sol-gel method was developed to prepare Au nanoparticles supported on mesoporous TiO2 containing variable amounts of CeO2. The characterization of these materials and comparison of their catalytic activities for CO oxidation will be presented. The results demonstrate that the surface modified porous supports can provide a viable route to tailor the activity and stability of the nanoparticle catalysts.
References
1. “Synthesis of Magnetic Intermetallic FeAl Nanoparticles from a Non-Magnetic Bulk Alloy”, Y. B. Pithawalla, M. S. El-Shall, S. C. Deevi and K. V. Rao, J. Phys. Chem.B 105, 2085-2090 (2001).
2. “Decay Dynamics and Quenching of Photoluminescence from Silicon Nanocrystals by Aromatic Nitro Compounds”, I. N. Germanenko, S. Li and M. S. El-Shall, J. Phys. Chem. 105, 59-66 (2001).
3. “Nanoparticles: Synthesis, Assembly, Properties and Applications” M. S. El-Shall, McGraw-Hill Year book of Science & Technology, 268-272 (2003).
4. “Vapor Phase Growth and Assmbly of Metallic, Intermetallic, Carbon, and Silicon Nanoparticle Filaments”, M. S. El-Shall, V. Abdelsayed, Y. B. Pithawalla, E. Alsharach and S. C. Deevi, J. Phys. Chem. B. 107, 2882-2886 (2003).
5. “Microwave Synthesis of Supported Au and Pd Nanoparticle Catalysts for CO Oxidation” G. Galspell, L. Fuoco and M. S. El-Shall, J. Phys. Chem. B. 109, 17350-17355 (2005).
6. “Vapor Phase Synthesis and Characterization of Bimetallic Alloy and Supported Nanoparticle Catalysts”, V. Abdelsayed, K. M. Saoud and M. S. El-Shall, J. Nanoparticle Research, in press (2005).
Studies of Metal Oxide Catalysis Employing Gas Phase Metal Oxide Nanoparticles
Elliot R. Bernstein
Department of Chemistry, Colorado State University
Fort Collins, CO 80523, USA
Our work deals with modeling of heterogeneous condensed phase and surface chemistry based on the behavior of small neutral clusters or nanoparticles. At present, our research is focused on small (< 20 atoms) gas phase, neutral metal oxide clusters and small molecules as accessed by photoionization, time-of-flight mass spectroscopy, optical spectroscopy, and density functional theory calculations. The metal oxide nanoparticles serve as model systems for the local site surface structure at which heterogeneous catalysis can occur. Specifically, we are studying the following cluster/reaction systems: (1) Conversion of CO and NO to CO2 and N2 by gas phase, neutral iron oxide and copper oxide clusters; (2) Conversion of SO2 to SO3 by gas phase, neutral vanadium oxide clusters; (3) Decomposition of water into H2 and O2 by gas phase, neutral titanium oxide clusters and (possibly) UV radiation; and (4) Conversion of CO/H2 (water gas) to CH3OH by gas phase, neutral copper oxide and zinc oxide clusters and mixed metal oxide clusters. The seminar will report on the first two of these systems.
The primary goal of our work is to obtain an atomic level (quantum mechanical) understanding of heterogeneous reaction rate enhancement. In particular, we focus on elucidating the reaction mechanisms, energetics, electronic state, and structural dependencies of the metal oxide enhancement of the above reactions. We wish to answer the following questions concerning these reactions: 1) How do the reactions occur?; 2) What are the active site (geometric and electronic) structures at which these reactions occur?; and 3) What are the detailed mechanisms for the conversions of interest?
References
1. M. Foltin, G. J. Stueber, and E. R. Bernstein, "Investigation of the Structure, Stability, and Ionization Dynamics of Zirconium Oxide Clusters” J. Chem. Phys. 114, 8971 (2001).
2. D. N. Shin, Y. Matsuda, and E. R. Bernstein, "On the Iron Oxide Neutral Cluster Distribution in the Gas Phase: I. Detection Through 193 nm Multiphoton Ionization" J. Chem. Phys. 120, 4150 (2004).
3. D. N. Shin, Y. Matsuda, and E. R. Bernstein, "On the Iron Oxide Neutral Cluster Distribution in the Gas Phase: II. Detection Through 118 nm Single Photon Ionization" J. Chem. Phys 120, 4157 (2004).
4. Y. Matsuda, D. N. Shin, and E. R. Bernstein, "On the Neutral Copper Oxide Cluster Distribution in the Gas Phase: Detection Through 355 nm and 193 nm Multiphoton, and 118 nm Single Photon Ionization" J. Chem. Phys. 120, 4165 (2004).
5. Y. Matsuda, D. N. Shin, and E. R. Bernstein, "On the Zirconium Oxide Neutral Cluster Distribution in the Gas Phase: Detection Through 118 nm Single Photon, and 193 and 355 nm Multiphoton Ionization” J. Chem. Phys. 120, 4142 (2004).
6. Y. Matsuda and E. R. Bernstein, "On the Titanium Oxide Neutral Cluster Distribution in the Gas Phase: Detection Through 118 nm Single Photon, and 193 Multiphoton, Ionization" J. Phys. Chem. A, 109, 314 (2005).
7. Y. Matsuda, and E. R. Bernstein, "Identification, Structure, and Spectroscopy of Neutral Vanadium Oxide Clusters" J.. Phys Chem., accepted (2005).
8. E. R. Bernstein, "Role of Excited Electronic States in the Decomposition of Energetic Materials" in Overviews of Recent Research on Energetic Materials, D. Thompson, T. Brill, R. Shaw, Eds. (World Scientific, New Jersey, 2004), in press.
9. E. R. Bernstein and Y. Matsuda, "Toward a Molecular Understanding of Environmental Catalysis: Studies of Metal Oxide Clusters and Their Reactions," Vicki Grassian, Ed. (Dekker, New York City, 2004), in press.
Electrodeposited Platinum at Conducting Polymer Electrodes.
II. Application in the oxidation of methanol
Ahmed Galal*, Soher A. Darwish, Nada F. Atta, Shimaa M. Ali
Department of Chemistry, College of Science, University of Cairo
PO Box 12613, Giza - EGYPT
Conducting polymers are electrochemically polymerized at inert surfaces of glassy carbon, platinum or graphite. The thickness, porosity and surface morphology of the resulting films are controlled by the charge passing during electro-polymerization step and preparation conditions. The films are undoped by subjecting the polymer to negative potentials. The extent of doping/undoping is monitored by the amount of current passing through the electrochemical cell. The conducting polymer films are modified by electrochemically depositing platinum particles. The technique of deposition depends on applying a programmed potential pulse at the polymer film from a solution containing platinum complex. The size of the platinum particles was controlled by the time interval of the pulse signal.
The effect of changing the size of platinum particles and polymer film thickness on the voltammetric behavior of the resulting hybrid material showed noticeable change in the electro-catalytic current in sulfuric acid medium. On the other hand, the electrochemical impedance experiments at the same films proved that the diffusion and charge transfer differed significantly when comparing the polymer films with those containing platinum particles. The increase in diffusion and charge transfer rate increased in the order: unmodified polymer films, platinum-containing polymer films, thin polymer films containing average size platinum particles, and relatively thick polymer films containing average size platinum particles.
The morphology of polymer films, size and distribution of platinum particles in the film were studied by scanning electron microscopy. The presence of platinum and its distribution over the film surface was confirmed from the X-ray dispersive analysis and surface mapping. The hybrid materials are good candidates for the application in energy conversion devices namely fuel cells. We are presenting the results and discussion of the efficiency of chemical conversion as a function of the method of particle deposition and conducting polymer film characteristics.
