个人简介

B.S., 1992, Rochester Institute of Technology Ph.D., 1997, Harvard University Postdoctoral Fellow, 1997–1999, Sandia National Laboratories Union Carbide Innovation Recognition Award, 1997 Army Young Investigator Award, 2000 NSF CAREER Award, 2002 Governor's Young Researcher Award for Excellence in Science, 2008 Michael J. Mungo Undergraduate Teaching Award, 2010 Finalist for the Ada B. Thomas Outstanding Faculty Advisor Award, 2011-2013 International Precious Metals Institute Carol Tyler Award, 2012

研究领域

Physical

Reactions at surfaces, reaction mechanisms, scanning probe microscopy, characterization of surfaces, chemistry of metal nanoparticles, catalysis. Projects Research in the Chen group focuses on understanding surface chemistry on the atomic and molecular level. One of the main motivations of this work is to guide the development of new materials for heterogeneous catalysts. Heterogeneous catalysis represents a $10 trillion dollar/year industry has a significant impact on our everyday lives. For example, the catalytic converters in automobiles transform toxic NO and CO produced by the car engines into N2 and CO2 that can be safely released into the environment. Sulfur removal catalysts are also important in the petroleum refining industry because burning sulfur-containing fossil fuels as gasoline releases sulfur oxides into the atmosphere and contributes to acid rain. Furthermore, catalysts are used to produce many starting materials for industrial synthesis reactions; the silver-catalyzed production of ethylene oxide from ethylene leads to ethylene glycol for the synthesis of polyethylene terephthalate, which is a polymer used for plastic bottles. Most catalysts consist of metal particles on an oxide support, and the catalytic chemistry occurs on the surfaces of the particles. It is therefore important to have a fundamental understanding of the reaction processes occurring on surfaces in order to systematically design catalytic materials with activity and selectivity that can be tailored for specific chemical reactions. We are growing metal nanoparticles on oxide surfaces and studying the chemical activity of these nanoparticles as a function of their size, structure, interactions with the oxide support, and metal-metal interactions in bimetallic particles. In these model systems, metal particles are vapor-deposited on single-crystal oxide surfaces with controlled sizes and size distributions. As an example, Figure 1a below shows scanning tunneling microscopy (STM) images of gold particles on a rutile TiO2 surface cut along the (110) plane, Figure 1b shows nickel-gold bimetallic particles on TiO2 at room temperature, and Figure 1c shows the nickel-gold particles after heating the surface to 800 K. Quantum effects, unique surface structures for the nanoparticles, and interactions between the particles and support are all size-dependent phenomena that can give rise to enhanced or modified activity for catalysts when their particle sizes are controlled in the nanoscale range. Despite the inactivity of bulk gold surfaces, gold nanoparticles are good catalysts for the low temperature oxidation of CO to CO2 and propene to propene oxide. Recently, we have been studying oxidation reactions on bimetallic gold-based nanoparticles (gold-platinum, gold-nickel, gold-cobalt) on titania. In these systems, interactions between the two metals and between the metal and titania support are known to give rise to unusual chemistry. For example, new surface sites are created at the edges of gold particles on titania, and these sites at the perimeter of the particles are active for the oxidation of methanol to formaldehyde. Furthermore, exposing the bimetallic particles to reactant gases results in changes in the surface composition, which determines the chemical activity of the clusters. Experimental Approach Most of our experiments are carried out in ultrahigh vacuum (UHV) chambers with pressures of <1x10-10 Torr). This provides us with a well-controlled environment in which can control every atom or molecule that strikes the surface. Scanning tunneling microscopy is used to characterize sizes and shapes of deposited metal nanoparticles on the atomic scale. X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), low energy electron diffraction (LEED), temperature programmed desorption (TPD, a form of mass spectrometry) and other surface analysis techniques provide information on surface structure, atomic composition, chemical bonding, and identification of reaction products. A catalytic reactor coupled to the UHV system allows us to evaluate reaction kinetics under realistic catalytic conditions. We are also currently constructing an infrared spectroscopy system (polarization modulation infrared absorption reflection spectroscopy) capable of studying the surfaces during catalytic reactions at elevated pressures.

近期论文

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R. P. Galhenage, H. Yan, O. Ozturk, A. S. Ahsen, and D. A. Chen, ""Understanding the Growth and Chemical Activity of Co-Pt Bimetallic Clusters on TiO2(110): CO Adsorption and Methanol Reaction"" J. Phys. Chem. C 2014, in press. DOI: 10.1021/jp505003s. S. A. Tenney, S. I. Shah, H. Yan, B. A. Cagg, M. S. Levine, T. S. Rahman and D. A. Chen, ""Methanol Reaction on Pt-Au Clusters on TiO2(110): Methoxy-induced Diffusion of Pt"" J. Phys. Chem. C 2013, 117, 26998-27006. S. A. Tenney, K. Xie, J. R. Monnier, A. Rodriguez, R. P. Galhenage, A. S. Duke, D. A. Chen, ""Novel Recirculating Loop Reactor for Studies on Model Catalysts: CO Oxidation on Pt/TiO2(110)"" Rev. Sci. Instruments 2013, 84, 104101-1-8. R. P. Galhenage, H. Yan, S. A. Tenney, N. Park, G. Henkelman, P. Albrecht, D. R. Mullins, and D.A. Chen, ""Understanding the Nucleation and Growth of Metals on TiO2: Co Compared to Au, Ni and Pt,"" J. Phys. Chem. C, 2013, 117, 7191-7201. R. P. Galhenage, S. C. Ammal, H. Yan, A. S. Duke, S. A. Tenney, A. Heyden and D. A. Chen, ""Nucleation, Growth and Adsorbate-Induced Changes in Composition for Co-Au Bimetallic Clusters on TiO2,"" J. Phys. Chem. C, 2012, 116, 24616-24629. S. A. Tenney, B. A. Cagg, M. S. Levine, W. He, K. Manandhar and D. A. Chen, ""Enhanced Activity for Supported Au Clusters: Methanol Oxidation on Au/TiO2(110)"" Surf. Sci. 2012, 606, 1233-1243. Tenney, S. A, He, W., Roberts, C. C., Ratliff, J. S., Shah, S. I., Shafai, G. S., Turkowski, V., Rahman, T. S. and Chen, D. A., ""CO-induced Diffusion of Ni Atoms to the Surface of Ni-Au Clusters on TiO2(110),"" J. Phys. Chem. C, 2011, 115, 11112-11123. Tenney, S. A., Ratliff, J. S., He, W., Mullins, D. R. and Chen, D. A., ""Characterization of Au-Pt and Au-Ni Clusters on TiO2(110),"" Topics in Catalysis, 2011, 54, 42-55. Tenney, S. A, Ratliff, J. S., Heyden, A., Ammal, S.C., Mullins, D. R., Roberts, C. R. and Chen, D. A., ""Adsorbate-Induced Changes in the Surface Composition of Bimetallic Clusters: Au-Pt on TiO2(110),"" J. Phys. Chem. C, 2010, 114, 21652-21663. Chen, D. A., Ratliff, J. S., Hu, X. Gordon, W. O., Senanayake, S. D and Mullins, D. R., ""Dimethyl Methylphosphonate Chemistry on Fully Oxidized and Partially Reduced Ceria Thin Films"" Surf. Sci. 2010, 604 (5-6), 574-587. Park, J.B., Conner, S. F., and Chen, D. A., ""Bimetallic Pt-Au Clusters on TiO2(110): Growth, Surface Composition and Metal-Support Interactions"" J. Phys. Chem. C, 2008, 112, 5490-5500. Ozturk, O., Park, J. B., Ma,S., Ratliff, J., Zhou, J., Mullins, D. R., and Chen, D. A., ""Probing the Interactions of Pt, Rh and Bimetallic Pt-Rh Clusters with the TiO2(110) Support"" Surf. Sci., 2007, 601, 3099-3113. Park, J. B., Ratliff, J. S., Ma., S., and Chen, D. A., ""Understanding the Reactivity of Oxide-supported Bimetallic Clusters: Reaction of NO with CO on TiO2(110)-supported Pt-Rh Clusters"" J. Phys. Chem. C, 2007, 111 (5), 2165-2176. Park, J. B., Ratliff, J. S., Ma, S., and Chen, D. A., ""In Situ Scanning Tunneling Microscopy Studies of Bimetallic Cluster Growth: Pt-Rh on TiO2(110)"" Surf. Sci., 2006, 600, 2913-2923 Ozturk, O., Black, T. J., Perrine, K., Pizzolato, K., Williams, C. T., Parsons, F. W., Ratliff, J. S., Gao, J., Murphy, C. J., Xie, H., Ploehn, H. J., and Chen, D. A. ""Thermal Decomposition of Generation-4 Polyamidoamine Dendrimer Films: Decomposition Catalyzed by Dendrimer-Encapsulated Pt Particles."" Langmuir, 2005, 21 (9), 3998-4006. Colavita, P. E., Miney, P. G., Taylor, L., Priore, R., Pearson, D. L., Ratliff, J., Ozturk, O., Chen, D. A., and Myrick, M. L., ""Effects of Metal Coating on Self-Assembled Monolayers on Gold. 2. Copper on an Oligo(phenylene-ethynylene) Monolayer."" 2005, Langmuir 21, 12268-12277. Ma, S. Zhou, J, Y. C. Kang, Reddic, J. E. and Chen, D. A. Chen. ""Dimethyl Methylphosphonate Decomposition on Cu Surfaces: Supported Cu Nanoclusters and Films on TiO2(110)."" Langmuir, 2004, 20(2), 9686-9694. Varazo, K., Parsons, F. W., Ma S., and Chen, D. A., ""Methanol Chemistry on Cu and Oxygen-covered Cu Nanoclusters Supported on TiO2(110)."" J. Phys. Chem. B, 2004, 108(47), 8274-18283. Illingworth, A., Zhou, J., Osturk, O., and Chen, D. A., ""Design of a Heating-Cooling Stage for STM and TPD Experiments."" J. Vac. Sci. Technol. B, 2004, 22(5), 2552-2554. Zhou, J., Ma, S., Y. C. Kang, and Chen, D. A., ""Dimethyl Methylphosphonate Decomposition on Titania-Supported Ni Clusters and Films: A Comparison of Chemical Activity on Different Ni Surfaces."" J. Phys. Chem. B, 2004, 108, 11633-11644.