Lattice oxygen activity in ceria-praseodymia mixed oxides for soot oxidation in catalysed Gasoline Particle Filters

摘要

Two series of ceria-praseodymia catalysts with varying composition have been systematically investigated in the oxidation of soot under inert atmosphere in order to find out its potential utilization in Gasoline Particulate Filters for GDI engines. The samples have been widely characterized by XRD, Raman spectroscopy, TEM, FESEM, XPS, N2 adsorption at -196 degrees C and O-2-TPD. The praseodymium incorporation onto the ceria enhances the oxygen mobility in the subsurface/bulk of the sample favoring higher O-2 released amounts under inert atmosphere. The intermediate compositions can promote more accentuated O-2 emissions at moderate temperatures (up to 500 degrees C). The efficiency of the own active oxygen species released from the catalyst to oxidize soot under inert atmosphere, even under loose contact mode, has been well demonstrated. The pathways of the mechanism taking place seem to be dependent on the temperature and mainly on the type of contact among soot and catalyst. Under loose contact conditions and low-medium temperatures, the O-2 freshly emitted from the catalyst can oxidize soot more efficiently than a diluted O-2-gas stream. Conversely, under more severe conditions (higher temperature or tight contact conditions), the soot acts as a "driving force" and the own lattice oxygen species can be transferred directly towards soot surface in an efficient way.