Potassium effect on the thermal stability and reactivity of NOx species adsorbed on Pt,Rh/La2O3 catalysts

In this paper we analyzed the effect of potassium on the thermal stability of NOx species adsorbed on lanthanum supported catalysts. Catalysts containing only noble metals (Pt and/or Rh) or noble metals and potassium were prepared. The soot combustion process in the presence of NOx species previously adsorbed on the catalysts has also been studied in order to evaluate the possibility of using these materials for the simultaneous abatement of soot and nitrogen oxides. It was shown that lanthanum supported catalysts containing Pt and/or Rh exhibited great capacity to decompose previously adsorbed nitrate species in an inert atmosphere. When potassium was added to the formulation this capacity was modified, which proves the existence of a strong interaction between the potassium and noble metals. Such interaction was much stronger in the case of platinum and, therefore, the Pt-K catalyst was able to decompose only a small fraction of the adsorbed compounds in helium stream. However, when decomposition took place in reducing atmosphere (H-2), the NOx species were reduced at a lower temperature in the presence of platinum. For all the lanthanum supported catalysts under study, the activity for soot combustion increased in the presence of previously adsorbed nitrate species, even though some of the samples were not very effective for NOx decomposition. This indicates that NOx species are capable of reacting with soot in oxidant atmosphere without the need for their previous decomposition, as previously observed in an inert stream. (C) 2010 Elsevier B.V. All rights reserved.