Laboratory for Surface Modification (LSM)

Seminars Archives

May 2019 | September 2019 | October 2019

Thursday, September 19, 2019
Nanomaterials in Operando Conditions
Darío Stacchiola
Brookhaven National Laboratory
12:00 Noon CHEM 260

Heterogeneous catalysts undergo changes in their structure as they mediate a chemical reaction. Multiple experimental approaches have been developed to understand these changes. Due to their structural and chemical complexity, and the difficulty of interrogating them under reaction conditions, catalysts are generally characterized before and after chemical reactions. Thus, dynamic active phases formed in catalysts under reaction conditions, which generate nanometer sized multifunctional active centers at metal/oxide/modifiers interfaces, and the associated reaction mechanisms are generally unknown. Since the structure of catalysts change as reacting molecules interact with it in route to forming products, only in-situ techniques allow following the dynamic processes involved on the surface of a catalyst. There has been considerable progress in the development and use of surface science techniques to follow catalytic reactions in-situ. Photon-in/photon-out techniques, such as IR spectroscopy, were used early on but photo-electron spectroscopic techniques, where electrons interact strongly with the reactants in the gas phase, took much longer to become widely available. Electron based structural techniques, such as scanning tunneling microscopy (STM), are still only available on a limited number of laboratories. I will present case studies showing how complementary in situ techniques including ambient pressure (AP) X-ray photoelectron spectroscopy (AP-XPS), infrared reflection absorption spectroscopy (AP-IRRAS) and AP-STM can be applied to study heterogeneous interfaces in model catalysts.

“Ultrathin TiO2 on nanowires: Optimization of conformal growth and elucidation of atomic-scale motifs”
Nano Letters doi: 10.1021/acs.nanolett.8b04888 (2019)
“Ionization‐Facilitated Formation of 2D (Alumino)Silicate–Noble Gas Clathrate Compounds”
Adv. Funct. Mater doi: 10.1002/adfm.201806583 (2019)
“Stabilization of oxidized copper nanoclusters in confined spaces”
Top. in Catal. 61, 419 (2018)
“Single Atoms in Nano-Cages: Immobilization of Ar Atoms in Two-Dimensional Zeolite Models”
Nature Communications 8, 16118 (2017)
“Highly Active Copper-Ceria and Copper-Ceria-Titania Catalysts for Methanol Synthesis from CO2”
Science 345, 546-550 (2014)
Thursday, September 26, 2019
Metastable Materials Discovery in Extreme Environments
Shriram Ramanathan
Purdue University
12:00 Noon Fiber Optic Aud

Metastable semiconductors with complex energy landscapes offer properties such as glass-like relaxations, frustration, mixed ionic-electronic conduction and order parameter inversion with subtle compositional perturbations. In this presentation, we will discuss oxide electron and ion conductors that can be formed in extreme thermodynamic environments such as ultra-low oxygen partial pressures and quenched to ambient conditions. Examples include synthesis of oxide-ion conducting apatites and electron conducting disordered vanadium oxides that can enable hydrogen fuel cells, ion-selective membranes and artificial synapses. The phase formation can be tracked real-time by high temperature electrical conductivity and correlated to synchrotron spectroscopy. We will then outline a general framework for discovery of novel nanostructured materials and transient phases that can be formed under strong chemical potential gradients and how this can be further guided by collaborations with first principles theorists. Such systems are of broad relevance to emerging frontiers spanning energy sciences to quantum technologies.

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