Effect of Ag, Cu, and Au Incorporation on the Diesel Soot Oxidation Behavior of SiO2: Role of Metallic Ag

The catalytic behaviors of Ag, Cu, and Au loaded fumed SiO2 have been investigated for diesel soot oxidation. The diesel soot generated by burning pure Mexican diesel in laboratory was oxidized under air flow in presence of catalyst inside a tubular quartz reactor in between 25 and 600 °C. UV–Vis optical spectroscopy was utilized to study the electronic states of Ag, Cu, and Au(M) in M/SiO2 catalysts. The soot oxidation was seen to be strongly enhanced by the presence of metallic silver on 3 % Ag/SiO2 surface, probably due to the formation of atomic oxygen species during the soot oxidation process. The catalyst is very stable due to the stability of Ag0 species on the catalyst surface and high thermal stability of SiO2. Obtained results reveal that though the freshly prepared 3 % Cu/SiO2 is active for soot oxidation, it gets deactivated at high temperatures in oxidizing conditions. On the other hand, 3 % Au/SiO2 catalyst does not present activity for diesel soot oxidation in the conventional soot oxidation temperature range. The catalytic behaviors of the supported catalyst samples have been explained considering the electron donating ability of the metals to generate atomic oxygen species at their surface.