The Ru-based catalysts (2 wt% Ru nominal loading) were prepared by wet impregnation of aerosol supports with RuO2 nanoparticles. The RuO2 colloidal suspension was pre-synthesized as described elsewhere . First, 0.81 mmol of RuCl3 was dissolved in 40 mL of distilled water under stirring. Next, 23 mL of aqueous hydrogen peroxide (14%) was added dropwise and mixed for 5 min. The solution was then incubated in an oven at 95 C for 2 h to obtain a black RuO2 colloidal suspension. After cooling to room temperature, 4 g of aerosol-made support was added into the entire batch of RuO2 colloidal suspension and stirred while heating at 50 C for 16 h. The solution was evaporated by a rotavapor set at 50 C under vacuum, and the obtained powder was finally calcined in static air at 450 C for 16 h with a ramping rate of 5 C/min. These catalysts are denoted as Ru/x%Ti-SiO2 (x is mol% of Ti loading).