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
Oxides in Extreme Environments: Synthesis and Ion Conduction
Shriram Ramanathan
Purdue University
12:00 Noon CHEM 260

This presentation will be concerned with surfaces and interfaces of thin film oxides exposed to strong oxygen chemical potential gradients. First, experimental techniques to reach thermodynamic conditions spanning room temperature to 1300K and oxygen partial pressures ranging over 30 orders of magnitude will be presented. Next, we will discuss design of suspended membrane test structures to probe electrical properties of mixed ionic-electronic conductors over this broad temperature range. Under such extreme environments, one can synthesize a range of metastable phases such as apatite starting from ceria-silica multilayers; disordered metallic vanadium oxides and Brownmillerites starting from perovskites. We will then present in-situ electrochemical measurements of the phase transformation process and surface relaxation dynamics. The studies enable one to discover and synthesize new materials via electrochemical interfaces, experimentally derive the Brouwer equilibria relations that is foundational to understanding charge compensation mechanisms in ceramics, measure activation barriers for ion diffusion that can inform first principles calculations, and in future could be useful to understanding response of functional materials to electric fields encountered in flash sintering or resistive switching.

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