Simultaneous removal of soot and nitrogen oxides from diesel engine exhausts

PISARELLO, MA.LAURA; MILT, VIVIANA; PERALTA, MA.ARIELA; QUERINI, CARLOS; MIRÓ, EDUARDO

CATALYSIS TODAY

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Lugar: Amsterdam; Año: 2002 vol. 75 p. 465 - 470

0920-5861

In this paper, our findings previously reported and new results presented here are discussed whith the main objetive of establishing the reaction mechanism for soot oxidation on different supports and catalysts formulations. Catalysts containing Co, K and/or Ba supported on MgO, La2O3 and CeO2 have been studied for diesel soot catalytic combustion. Among them, K/La2O3 and K/CeO2 showed the best activity and stability for the combustion of soot with oxygen. A reaction mechanism involving redox sites and surface-carbonate species takes place on these catalysts. On the other hand, Co,K/La2O3 and Co,K/CeO2 catalysts display activity for the simultaneous removal of soot and nitric oxide. The soot-catalyst contacting phenomenon was also addressed.  A synergic La-K effect was observed by which mechanical mixtures of soot with K-La2O3 showed higher combustion rates than those observed when K and La were directly deposited on the soot surface. The effect of the addition of Ba was explored, with the aim of promoting the interaction of the solid with NO2 thus combining the NOx catalytic trap concept with the soot combustion for filter regeneration. Ba/CeO2 and Ba,K/CeO2 were effective in NOx absorption as shown in microbalance experiments. However, the formation of stable nitrate species inhibits the soot combustion reaction.