Slightly higher surface Ti concentration of Ru/12%Ti-SiO2 and Ru/16%Ti-SiO2 corroborates the finding that TiO2 crystals form on the catalyst surface. Fig. presents the spectra of Ru 3d and C 1s of freshly calcined Ru/x%Ti-SiO2 catalysts. The spectra can be deconvoluted into three components, including metallic Ru, oxidized Ru 4+ and C 1s components, as tabulated in Fig. . A doublet with an asymmetric shape at 279.9 eV belongs to metallic Ru, whereas a main doublet at 280.7 eV along with a satellite doublet at 282.6 eV represents oxidized Ru 4+ state . These signals are fitted using two symmetric Gaussian-Lorentzian functions with separated binding energy (B.E.) of 4.17 eV and area ratio of 3:2. The satellite and the main doublet are separated by about 1.9 eV with close to 50% ratio. It is noted that C 1s components overlap with Ru 3d3/2 components; thus, the signals are fitted using Gaussian-Lorentzian functions, in which full width at half-maximum (fwhm) and binding-energy constraints are kept consistent across all spectra . The surface Ru/(Si+Ti) atomic ratio obtained from XPS analysis and Ru content measured from ICP-AES are shown in Table . Ru/SiO2 has a surface Ru/(Si+Ti) ratio of 0.03, while other Ti-containing catalysts, especially Ru/12%Ti-SiO2, exhibit lower surface Ru/(Si+Ti) ratio. This finding indicates that Ru species are highly dispersed in the pores rather than being aggregated on the surface of Ti-containing catalyst microspheres.