After the methanation reaction, spent Ru/x%Ti-SiO2 catalysts were subjected to TEM, XRD and XPS analyses. TEM images of spent catalysts in Fig. illustrate that the sphere-like morphology with mesoporous structure is maintained. Visibly, extensive aggregation of Ru nanoparticles can be found on the surface of Ru/SiO2 catalyst (Fig. and Ti 2p region for spent catalysts are also presented in Fig. and Fig. . As expected, the proportion of surface metallic Ru increases after the reduction and methanation comparing with the freshly calcined samples (Fig. ). The surface Ru/(Si+Ti) ratio on all spent catalysts remains similar to the values obtained before the reaction (Table ). Likewise, the Ti concentrations on the surface of spent catalysts closely match those of freshly calcined catalysts.