High catalytic activity of SCS-synthesized ceria towards diesel soot combustion

Nano-sized particles of ceria with high surface area were processed by solution combustion synthesis (SCS) and their catalytic activity towards combustion of carbonaceous materials was compared with that obtained by simple thermal decomposition of cerium nitrate, exhibiting the same specific surface area. These two kinds of ceria powders were tested by DTA and temperature-programmed combustion of diesel soot and a commercial carbon. Ceria processed by SCS was found to be more active than its counter part since it could decrease significantly both the combustion activation energy (from 115 to 111 kcal/mol) and the TPC-plot peak temperature of diesel soot (from 466 to 405 8C). The mechanism of the catalytic reaction of combustion was investigated by TPD/R experiments. Likewise other combustion catalysts acting as oxygen pumps, ceria can exchange limited amounts of oxygen even below 300 8C, the SCS-synthesized one showing a superior O2 release at low temperatures (_450 8C). Moreover, the SCS-ceria exhibited a microstructure (i.e. a foam of nano-sized crystals) particularly suitable for maximizing the number of contact points between catalyst and carbon. Finally, the effect of specific aging protocols (thermal treatment at 600 °C for 96 h) in the presence of potentially deactivating species present in diesel exhaust gases (SO2 and water) was also studied showing that the here proposed material suffers from less significant ageing than Ce(NO3)3-derived ceria.