NOx adsorption and diesel soot combustion over La(2)O(3) supported catalysts containing K, Rh and Pt

• Published in: Applied catalysis. A, General General, 2009-09, Vol.366 (1), p.166-175
• Main Authors: Sanchez, B S, Querini, C A, Miro, E E
• Format: Article
• Language: English
• ISSN: 0926-860X
• DOI: 10.1016/j.apcata.2009.07.009

In this work we report results of NOx adsorption and diesel soot combustion on a noble metal promoted K/La(2)O(3) catalyst. The fresh-unpromoted solid is a complex mixture of hydroxide and carbonate compounds, but the addition of Rh favors the preferential formation of lanthanum oxycarbonate during the calcination step. K/La(2)O(3) adsorbs NOx through the formation of la and K nitrate species when the solid is treated in NO + O(2) between 70 and 490 'C. Nitrates are stable in the same temperature range under helium flow. However, they become unstable at ca. 360 'C when either Rh and/or Pt are present, the effect of Rh being more pronounced. Nitrates decompose under different atmospheres: NO + O(2), He and H(2). The effect of Rh might be to form a thermally unstable complex (Rh-NO(+)) which takes part both in the formation of the nitrates when the catalyst is exposed to NOx and in the nitrates decomposition at higher temperatures. Regarding soot combustion, nitrates react with soot with a temperature of maximun reaction rate of ca. 370 'C, under tight contact conditions. This temperature is not affected by the presence of Rh, which indicates that the stability of nitrates has little effect on their reaction with soot.