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.