## 4 Discussion  
The reason for the enhancement of the catalytic activity in the PEG-stabilized materials results from a combination of factors. First, the increase in the pore volume and pore size would appear to be the dominant effect (Table 1) [30]. Second, the stoichiometric and non-stoichiometric ruthenium oxides (and hence variable ruthenium oxidation states) states might be expected to contribute to the catalyst activity as is seen, for example, for MnO\({}_{\mathrm{x}}\) (where \(x\leq 2\)) [48]. Arguments in the literature suggest that metallic Ru, as observed in the RAWS material (and as found by XPS), forms bonds with adsorbed ad-layers of oxygen (as a transient surface oxide) _in situ_ during CO oxidation and is catalytically more active below 500 K [49; 50; 51; 52]. Third, metallic catalysts such as Pd and Rh on oxide supports show structure-sensitive (size) catalytic activity [46] and favor towards high CO adsorption. [PERSON] _et al._, have reported that an increase in the CO oxidation capability of Pt nanowires over zero dimensional Pt nanoparticles is due to the large crystal facets and a small density of defect sites [53]. This means that the synergistic effect rendered by rod-structured RuO\({}_{\mathrm{x}}\) (as a manifestation of shape dependent catalytic activity) also partly explain such improvements [54]. It is reported that the difference in the geometry of nanomaterials occurs due to the changes in the surface atomic arrangement, thus exhibiting different electronic structures [55]. The binding strength between the catalyst surface and the adsorbed species (interaction) depends on such atomic arrangements (defect structures), which in turn influences the catalytic activity and selectivity [28; 56; 57]. The open coordination sites rendered by the edge and corner atoms [58] usually found in tetrahedral nanomaterials (in case of this work, Ru exhibits rutile-type structure with Ru atoms located in the corner) might significantly affect adsorption energy (activation energy) and bond enthalpy [59]. In addition, the flat sides of RuO\({}_{\mathrm{x}}\) containing large number of surface atoms would result in an increase in the contact area with the catalyst support, which can provide additional sites for the adsorption of reactant molecules [60]. Finally, the catalyst dispersion engendered in the PEG-stabilized catalysts contributes significantly to catalyst activity. Figure 8 shows the TPR profiles of the RAWOS and RAWS catalysts. The H\({}_{2}\) consumption profiles exhibit a number of maxima at different temperatures, implying the existence of  
Figure 7: Effect of (**a**) 2.5 vol.% and (**b**) 5 vol.% water content on the CO oxidation performance using RAWS and RAWOS catalyst. The inlet oxygen concentration was fixed at 1.5 vol.%. various Ru species on \(\gamma\)-Al\({}_{2}\)O\({}_{3}\). The H\({}_{2}\)-TPR for RAWOS shows reduction peaks between 100-300 \({}^{\circ}\)C. The narrow peaks at \(ca\). 168 \({}^{\circ}\)C and 225 \({}^{\circ}\)C (and 266 \({}^{\circ}\)C) correspond to the reduction of RuO\({}_{3}\) and RuO\({}_{2}\)[61, 62]. Low temperature peak at 110 \({}^{\circ}\)C refers to the formation of ruthenium from tiny RuO\({}_{2}\) particles (Figure 8a). By comparison, the RAWS catalyst exhibited a smooth and well defined ruthenium reduction peak with large peak area at a lower temperature (95.5 \({}^{\circ}\)C). The high temperature peak at 522 \({}^{\circ}\)C is the result of the reduction of the mesoporous \(\gamma\)-Al\({}_{2}\)O\({}_{3}\) support [63, 64] and the peak observed as a shoulder at 331 \({}^{\circ}\)C should be due to the reduction of large RuO\({}_{2}\) nanorod structures. Comparing the peak areas, the amount of H\({}_{2}\) gas consumed by the RAWS catalyst is higher than the un-stabilized catalyst and the reduction events are shifted consistently to lower temperature (by between 35-170 \({}^{\circ}\)C).