The geometric, electronic and chemical properties of Au nanoparticles supported by TiO2 have been the subject of much work since the discovery by Haruta that Au is a low temperature oxidation catalyst. Despite this earlier work there is no definitive evidence for the binding site or the direction of charge transfer associated with gold atoms and nanoparticles on the model substrate TiO2(110). In this work we have used STM to examine the nucleation properties of Au nanoparticles dispersed over a reduced rutile TiO2 (110) surface. From comparisons of the surface before and after Au deposition, and using atomic manipulation, the nucleation site of single Au atoms was directly observed to be at oxygen vacancies on the substrate (Ob-vacs). Statistical analysis of the atomic manipulation method applied provides some insight into the nature of the bonding between Au and Ob-vac sites. In an attempt to gauge the degree of Au/TiO2 charge transfer, synchrotron based X-ray photoelectron emission microscopy (XPEEM) was used in conjunction with STM and low energy electron microscopy (LEEM) to probe the electronic character of Au nanoparticles as a function of particle size and coverage. Core-level binding energy measurements reveal a two stage shift in Au 4f binding energy as the nanoparticle size increased in line with electron transfer from Ob vacs to Au for small nanoparticles (&lt;4 nm) on TiO2 (110). To reduce experimental error, a method was developed to precisely pattern the substrate with discrete regions of varying Au coverage on the nanometer scale. High resolution electron energy loss spectroscopy (HREELS) was used to measure the vibrational spectrum of an Au/TiO2 sample before and after ethanol exposure. After exposure, loss features appear that correspond to acetate, however, this is not observed for Au coverages less than 0.1-0.3 MLE. From this, it is suggested that Au nanoparticle size affects the reactivity of TiO2 towards ethanol oxidation, which is likely related to the degree of charge transfer.

Au nanoparticle interactions with TiO2(110) and their modification of the reactivity

254th National Meeting (2017)

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