(754a) Nanoscaling Effects On the Electronic Structure of TiO2 Supported Gold Nanoparticles and Their Impact On Electrocatalytic CO Oxidation

It is known that atomically flat, Au 111 surfaces are inactive for gas phase CO oxidation.  Several decades ago, it was found that when gold is nanoscaled to less than 5 nm in diameter on certain metal oxide supports, it becomes one of the most active CO oxidation catalysts.  Gold has also been shown to be electrocatalytically active for CO oxidation.  The physical origins are widely debated.  Possible explanations include: 1. Size dependent coordination number effects; 2. Support directed coordination number effects; 3.  Gold lattice strain; 4. Support electronic promotion; 5. Gold surface oxidation; 6. Support activation of oxygen.  It is our objective to establish a nanoscaling factor hierarchy from this list by measuring the physical, electronic, and electrocatalytic factors for the highly active Au on TiO2 system. 

Our approach entails the design of a well defined, flat TiO2 support and the deposition of Au nanoparticles using a contamination free, size controlled e-beam technique. This design approach is well suited for determination of size, shape and lattice strain that we measure by Scanning Electron Microscopy and Transmission Electron Microscopy.  Additionally, we measure the electronic structure using the 5d subshell sensitive hard x-ray valence band photoelectron spectroscopy to help disentangle the previous nanoscaling effects.  There is a trend in the valence band electronic structure that we attribute to a surface coordination number effect.  Finally, we measure the CO electrocatalytic oxidation activity versus Au nanoparticle size on TiO₂ in both base (0.1 M KOH) and acid (0.1 M H2SO4).  It is our goal to obtain information about the mechanism of the CO electro-oxidation reaction on Au nanoparticles.