Oxygen-spillover mechanism

Figure 4. Schematic representation of the mechanism of oxygen spillover in a purely catalytic system. Symbols as in Eq. (7).

Considering the overall mechanism of VOC oxidation, it could be agreed that Pt addition slows down deactivation of the catalyst in by speeding up the final oxidation step, if this step is CO oxidation as proposed in this study. As also stated in literature, oxygen spillover could be an important step in the removal of the surface deposited carbon causing deactivation [9]. 

In this case reduced ceria would be the starting point for the formation of active superoxide ions. Ceria can be reduced by soot at the contact points located at the soot/ceria interface and this will initiate the active oxygen path, which would contribute to the direct oxidation of soot particles by a spillover mechanism. The redox of ceria is therefore important in the generation of reduced ceria at the interface points and lowering the reduction temperature will therefore increase the overall activity of soot oxidation. 

In the case of LNT, different proposals have been advanced to explain the mechanisms governing the NO, release. Recent papers suggested that the NO release is provoked by the heat generated upon the reducing switch (thermal release) [40], by the decrease of the gas-phase oxygen concentration that destabilizes the stored nitrates [41], by spillover and reduction of N02 onto reduced Pt sites or by the establishment of a net reducing environment, which decreases the equilibrium stability of nitrates [12,42,43],... 

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