In situ surface and reaction probe studies with model nanoparticle catalysts

This review paper discusses the in situ surface characterization and catalytic measurements of colloidally synthesized model metal nanoparticle (NP) catalysts studied in the Somorjai lab. Sum Frequency Generation (SFG) vibrational spectroscopy technique revealed the vibrational signatures of binding geometry and surface orientation of adsorbate molecules by probing the immediate surface structure during the catalytic reactions. Metal surfaces were studied by Synchrotron-based spectroscopic techniques at the Advanced Light Source in the Lawrence Berkeley National Laboratory. Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) was employed to measure chemical and elemental structure of bimetallic NP catalysts under the catalytically relevant pressures in the Torr range. Surface chemical structure (i.e., oxidation states) of metals was obtained by X-ray Absorption Fine Structure Spectroscopy by constructing a gas flow cell that operates under atmospheric pressures as the reaction occurs. Environmental Transmission Electron Microscopy (E-TEM) supplemented the bimetallic structure that was obtained by X-ray spectroscopies. The morphology and chemistry induced by gas reactants on the stepped single crystal surfaces as determined by high-pressure in situ Scanning Tunneling Microscopy (HPSTM) and APXPS were also described.