Invited Paper SS+NS-WeM3
Size-dependent Correlations between Supported Cluster Electronic Properties and Catalytic/Electrocatalytic Activity

Wednesday, October 30, 2013, 8:40 am, Room 201 A

We prepare model catalysts or catalyst-decorated electrodes by depositing size-selected Pd_n and Pt_n clusters on planar supports, including TiO₂(110), alumina/Ta(110), alumina/Rh(0001) as well as glassy carbon and ITO/glass electrodes. The samples are prepared in UHV and characterized in situ by a combination of X-ray and UV photoelectron spectroscopy (XPS, UPS), and low energy He⁺ ion scattering (ISS). The activity of the model catalysts for gas-surface reactions such as CO oxidation is studied using mass spectrometric methods, such as temperature-programmed reaction/desorption (TPR, TPD). Electrochemistry is done in an attached UHV antechamber fitted with a three electrode cell that can be sealed against the sample surface, allowing electrochemistry to done both without, and with prior exposure to laboratory air. Electrocatalytic activity is drastically altered by air exposure. Results will be presented for CO oxidation over various M_n/oxide catalysts, and for electrochemical reactions observed under conditions appropriate for oxygen reduction or ethanol oxidation. One interesting result seen in many of these systems is a size-dependent anti-correlation between activity as oxidation catalysts, and shifts in the catalytic metal core level binding energies. Potential reasons for this correlation, and related studied of valence level shifts with UPS, will be discussed.