EPR investigation and reactivity of diesel soot activated (or not) with cerium compounds

Parameters influencing the diesel soot reactivity versus the combustion reaction are studied on two diesel soot samples. The presence of cerium additives favours the reactivity of the doped soot and shifts the combustion reaction towards low temperatures. However, these additives do not affect the CO-CO2 selectivity. Oxygenated and non-oxygenated radicals adsorbed on the carbon particulate are evidenced whatever the composition of the soot sample. After a vacuum treatment, the adsorbed hydrocarbons content drastically decreases and the reactivity of both soot samples is attenuated. However, the cerium-doped sample reveals higher radical contents and also higher reactivity than the non-activated soot. The presence of cerium additives stabilises and strengthens radical-carbon interactions and these hydrocarbon radical species play an important role in the activation of the diesel soot combustion.