Use of Multifunctional Materials to Combust C s and Trap NOx

Nanoparticulate Pt is used to oxidise NO to NO in NSR systems to facilitate NOx trapping, and it is also used to carry out the same reaction in the presence of C(s) to facilitate PM combustion. We were interested to see whether the two roles could be combined and therefore the NSR system could be a precursor to a diesel or lean-burn 4-way catalysis system [87-90]. 

Various Sets of experiments were carried out to look at the effects of NOx trapping materials on the activity of supported nanoparticulate Pt with N0(g)/02(g) on the C(s) combustion reaction, and also to look at how the presence of C(s) affected the Pt/BaO system designed for lean NOx trapping. 

The first series of experiments show that the operation of an active NOx trapping and reduction cycle did indeed promote C(s) combustion. Further work showed that his improvement was due to periodic localised increased in [NO J during the trap regeneration step. 

Each NO molecule released can be cycled (through NO/NO couples) where NO is oxidised on the catalyst and NO reduced on C(s). This cycle can happen numerous times before the NO is removed from the catalyst bed. In this way, the sudden localised increase of [NO J has an effect (orders of magnitude larger than the [NO j increase) on the combustion of C(s). we have confirmed this effect is not related to localised exotherms related to the fuel-rich pulse through a series of experiments using the injection of additional labelled CH OH to the reactant stream to generate such exotherms (via CHjOH combustion) and not noticed similar improvements in C(s) combustion. 

This was an encouraging first series of experiments which confirmed the beneficial effect of the operation of a NOx trap (rather than the presence of a NOx storage material per se) promoted PM combustion. 

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