Carbon oxidation with Ag/ceria prepared by self-dispersion of Ag powder into nano-particles

This study reports a unique and novel method of preparation of Ag/CeO2 catalyst for carbon oxidation. A calcination of physical mixture of Ag metal powder and CeO2 at 500 °C results in self-dispersion of Ag into nano-particles on CeO2. From TEM images, the average diameter of Ag particles in Ag power before calcination was around 66 nm, while the particle size of Ag became smaller around 8 nm with very narrow distribution. Oxygen vacancy on CeO2 surface is suggested to play an important role in the self-dispersion of Ag. The obtained catalyst showed high activity for soot oxidation comparable to Ag/CeO2 prepared by impregnation method. The promotion effect of CeO2 was not observed in physical mixtures with Cu, Au and Pt. Mechanical mixtures of Ag and various metal oxide supports were also examined. The addition of Ag to CeO2, SnO2, ZrO2, ZnO, TiO2, and Nb2O5 significantly lowered the temperature of carbon oxidation than those of supports, while that to Co3O4, CaO, La2O3, NiO, SiO2, Al2O3 and MgO did not.