During the selective reduction of NOx under lean-bum conditions with Pt/SiO
2 solids, a particle size dependency has previously been observed. Furtherm
ore, under the reactant mixture up to 773 K, the Pt particles sinter at the
same time as the solids are activated. In fact, the size dependency is lin
ked to the strength of the Pt-O bond and to the ease of NO dissociation.