NOx storage and reduction over copper-based catalysts. part 3: Simultaneous NOx and soot removal

5% copper catalysts with Ce_0.8M_0.2O_δ supports (M = Zr, La, Ce, Pr or Nd) were studied for the simultaneous combustion of soot and removal of NOx by the NSR method. The simultaneous chemisorption of NOx and combustion of soot could be carried out above 375 °C, and nitrates were formed upon NOx chemisorption above this temperature. The nature of the M dopant played an important role in the chemisorption of NOx and in the catalysed soot-NOx reaction. As a general trend, the presence of soot had a negative impact on NOx removal by catalysts with very basic supports but had no effect or a positive influence if the support is not very basic. The combustion of soot has a very negative impact for NOx chemisorption on the catalyst with the most basic dopant (CuO/Ce_0.8La_0.2O_δ), because the CO₂ formed in the reaction of soot combustion competes with NOx for adsorption sites. On the other hand, soot combustion does not affect NOx chemisorption on the catalyst with the most acidic dopant (CuO/Ce_0.8Zr_0.2O_δ), and the removal of NOx increases in this case because the reduction of NOx by soot contributes to NOx removal. The simultaneous reduction of NOx to N₂ and soot combustion can be carried out under NSR conditions at 400 °C over the 5%Cu/Ce_0.8Pr_0.2O_δ catalyst and with H₂ micropulses, and the NSR process has a positive impact on the catalytic combustion of soot.