AVS 65th International Symposium & Exhibition
    Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Tuesday Sessions
       Session HC+SS-TuM

Paper HC+SS-TuM6
Copper Vapor Adsorption Calorimetry on HCa2Nb3O10(001) Nanosheets: Energetics and Adsorbate Structure

Tuesday, October 23, 2018, 9:40 am, Room 201A

Session: Nanochemistry in Heterogeneous Catalysis
Presenter: Wei Zhang, University of Washington
Authors: W. Zhang, University of Washington
J.E. Eichler, University of Washington
R. Uppuluri, The Pennsylvania State University
T.E. Mallouk, The Pennsylvania State University
C.T. Campbell, University of Washington
Correspondent: Click to Email
The metal/oxide interface is essential to many current and prospective technologies, including oxide-supported metal catalysts, fuel cells, photocatalysis, and nanoscale electronic contacts, so understanding the chemical bonding strength at such interfaces is of great interest. These strengths have been measured on single-crystal oxide films of a single metal element by metal vapor adsorption calorimetry in ultrahigh vacuum (UHV), but never before on mixed oxides of two or more metal elements, yet mixed oxides are often used as supports in catalysis with considerable improvement on various aspects of catalyst performance. The preparation of atomically-smooth single-crystal mixed-oxide films in well-defined composition that would be applicable in our adsorption calorimetry is very challenging. Mallouk et. al. have reported a class of lamellar HCa2Nb3O10(001) nanosheets which can be deposited in a layer-by-layer fashion on flat substrates using Langmuir-Blodgett (LB) techniques to make thin and well-ordered mixed-oxide films. These nanosheets can extend laterally for long distances (>1 μm) indicating that they have very high surface area with homogeneous surface sites and a huge ratio of terrace sites to sheet-edge sites. Furthermore, when used as supports for transition metal oxide (or hydroxide) nanoparticles, they display unusual stability against sintering. Here, we apply the surface chemistry techniques derived for single-crystal oxide films to the much more complex perovskite mixed-oxide films by investigating the adsorption of Cu atoms on the HCa2Nb3O10(001) nanosheets (~6.3 nm thick) at both 300 K and low temperature (<150 K). Cu atoms show an initial heat of 186 kJ/mol at 300 K, which is close to the DFT value for Cu monomers. The heat of adsorption then increases quickly to the heat of sublimation of bulk Cu(s) (337 kJ/mol). Low-energy He+ ion scattering spectroscopy (LEIS) allows us to investigate the morphology and the number density of Cu particles. The possible chemical reactions between the Cu atoms and the HCa2Nb3O10(001) nanosheets during adsorption are elucidated using X-ray photoelectron spectroscopy (XPS).