Kinetic and mechanism of the reduction of NO by n-octane over Pt/Al2O3 under lean burn conditions

The effect of temperature, contact time, and reactant concentration on the reduction of NO by n-C8H18 over Pt/Al2O3 under oxidising conditions was investigated. The oxidation of n-C8H18 appears to be delicately balanced between two kinetic regimes. At low [C8H18]/[O2] the coverage of oxygen on the Pt surface is high, while that of carbonaceous species is negligible, resulting in hydrocarbon oxidation being inhibited by oxygen and in the oxidation of NO to NO2. At higher [C8H18]/[O2] the surface is saturated with carbonaceous species, while the coverage of oxygen is negligible, resulting in hydrocarbon oxidation being zero order in hydrocarbon concentration and in no NO2 formation being observed. The state of the Pt surface affects the mechanism of NOx reduction. Thus, NOx reduction via dissociation of NO on the Pt surface is favoured by a high coverage of carbonaceous species, while a high coverage of oxygen favours NOx reduction by reaction between n-C8H18-derived species and spilt-over NO2 on the Al2O3 support and/or metal-support interface. Separate kinetic models capable of fitting the data in these two regions have been developed.