In recent years, many studies have been devoted to understand the atomic and electronic structure of TiO2 because it has wide applications, for example, (1) as an alternative to indium tin oxide in the field of transparent conductors, (2) in dye-sensitized solar cells, (3) photocatalysis, (4) water splitter, (5) in paints and (6) support in heterogeneous catalysis in automobile industry for pollution control (Czekaj et al. 2009; Diebold 2003; Feng et al. 2008; Henrich and Cox 1994; Kaden et al. 2009, 2010; Menzies et al. 2004; Sellidj and Koel 1993; Zeng et al. 2008). In the latter application, noble or near noble metal nanoclusters supported on a TiO2 surface are used to oxidize (reduce) hazardous CO (NO) gas that is present in the exhaust of an automobile. In this process the role of metal clusters as well as support are crucial. The combined system, first, oxidizes CO gas where an additional oxygen atom is generally obtained from either the process of NO reduction or the environment. Second, the system is capable of releasing the oxidized CO gas into the environment from the active sites of catalyst to provide further oxidation of CO to continue the heterogeneous catalyst. If the CO2 is not released in such a catalyst, poisoning can occur (Wang et al. 2011). Much attention has been focused on nanoclusters of platinum, palladium and gold and their alloys as suitable candidates for supported clusters for such reactions. In an actual catalyst there is a distribution of cluster sizes, but it is believed that among these different-sized clusters, small clusters may be catalytically more active. Therefore, understanding the interaction of small clusters of such elements and their alloys as well as their interaction with CO molecules has attracted much interest.