We have studied the oxidation chemistry of mass-selected metal oxide clusters deposited on TiO2 (110) surfaces as a function of size and composition. We have deposited mass-selected VxOy clusters deposited on TiO2 (110) and FeOx on Pt (111) via ion soft-landing. The cluster-decorated samples were characterized by scanning tunneling microscopy (STM) and the chemistry was probed using temperature-programmed reaction (TPR). Density functional theory (DFT) was used to calculate the structure of the clusters on the surface and compared with experimental results. We have shown that both V2O6 and V3O9 clusters are highly active in the oxidative dehydrogenation of methanol. The V2O6 clusters catalyze the production of formaldehyde and methyl formate. The production of methyl formate represents a previously undiscovered reaction path in the reaction of methanol and oxygen on vanadia-supported catalysts. Structural models from DFT and STM images have allowed us some insight into the mechanism of this reaction. The models indicate that on a stoichiometric surface the V2O6 cluster contains a peroxo group, which is active for the production of species required for methyl formate production such as CH2O and CH3O. However, STM and theory also agree that in the presence of oxygen vacancies the peroxo group dissociates to heal the vacancy. TPR has revealed that the production of methyl formate is highly dependent on the oxidation state of the surface, in a manner consistent with the peroxo group being responsible for this conversion. STM results also show a variation in the cluster structure as a function of the oxidation state of the TiO2. In addition, we show that oxidative dehydrogenation of methanol on V3O9-decorated TiO2 surfaces results in methyl formate production at a lower temperature, a two-fold increase in signal relative to that of V2O6/TiO2, and formaldehyde production with a ten-fold increase in signal. Finally, size selected iron oxide (Fe1Ox x=1-4) clusters have been deposited on a Pt (111) surface for investigation of catalytic activity towards CO oxidation. TPD has shown that catalytic activity depends strongly on cluster stoichiometry. STM has been used to examine the location and frequency of oxygen disassociation near these clusters on the surface. The disassociation of oxygen is considered to be the limiting step for this reaction; we have found that the catalytic activity of a cluster is correlated with an increase in oxygen disassociation.

Size-selected vanadium oxide clusters on TiO2(110) and iron oxide clusters on Pt(111): Discovering mechanisms of oxidative reactions at interfaces: Every atom counts

251st National Meeting (2016)

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