| AVS 66th International Symposium & Exhibition | |
| Surface Science Division | Thursday Sessions |
| Session SS+AS+HC+TL-ThM |
| Session: | Surface Science of Energy Conversion and Storage |
| Presenter: | Nassar Doudin, Pacific Northwest National Laboratory |
| Authors: | N. Doudin, Pacific Northwest National Laboratory Z. Dohnálek, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Oxide clusters supported on metal oxide substrates are of great interest due to their importance in heterogeneous catalysis [1]. The nature and strength of the interactions between the metal oxide clusters and the support materials not only govern their structure and stability but also control the energetics of elementary steps that are critical for the overall activity [1]. Understanding the nature of the interactions is therefore important to tailor the supported metal oxide cluster systems to achieve the desired reactivity and selectivity. Here, we present a scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) study of the monodispersed MoO3 clusters deposited by the sublimation of MoO3 powder on anatase TiO2(101) surface at 300 K. After the deposition, the STM images of the lowest concentration of MoO3 show that the clusters initially migrate over the surface and preferentially anchor at step edges before they start to aggregate on the terraces. Interestingly, the aggregates are mostly composed of three adjacent clusters, with a small concentration of monomers and dimers. Further exposures to MoO3 increase the cluster coverage until a fully saturated over-layer is created with each clusters being are centered on top of the Ti sites. The adsorbed clusters appear as bright protrusions, with an apparent cluster height of approximately 1.5 Å and diameter of about 8.5 Å. Since the cyclic (MoO3)3 trimers are known to be a dominant gas phase species resulting from the sublimation of MoO3 [1], we propose that each cluster on the surface is a trimer. Annealing to 550 K results in a better-order of the (MoO3)3 layer, but further annealing to 650 K leads to three-dimensional clusters. The XPS results indicate that the Mo(3d5/2) binding energy in as-deposited (MoO3)3 is characteristic of Mo6+, and the oxidation state of Mo remains (+6) upon heating to 600 K. As such, this system may offers great promise as an ideal platform for reactivity studies on well-defined supported model transition-metal oxide catalysts.
[1] Zdenek Dohnálek et al. Royal Society of Chemistry 43, 7664−7680 (2014).