TEM images (Fig. and Fig. ) illustrate the morphology and structure of Ru-based catalysts as well as how Ru/RuO2 nanoparticles are dispersed over aerosol materials. All Ru/x%Ti-SiO2 catalysts possess a spherical morphology with microsphere sizes ranging between 0.2 and 1 m, as the spherical shape is the most stable form during the drying of liquid droplets. Hollow structure can be formed when drying happens rapidly at the droplet surface, quickly creating a solid layer . A regular porous structure with mesopores is also visible, which is consistent with the N2 physisorption results. In Fig. nanoparticles occurs for all catalysts, as indicated by a decrease in their Eg values (Fig. and Table ). The HAADF-STEM-EDS mapping images of reduced Ru/SiO2, Ru/4%Ti-SiO2, Ru/8%Ti-SiO2 and Ru/16%Ti-SiO2 catalysts are also shown in Fig. . It is evident that Ru nanoparticles in Ti-promoted catalysts are less agglomerated as compared to those in Ru/SiO2.