Potential of Cu–saponite catalysts for soot combustion

Abstract

H– and Na–saponite supports have been prepared by several synthesis approaches. 5% Cu/saponite catalysts have been prepared and tested for soot combustion in a NO_x + O₂ + N₂ gas flow and with soot and catalyst mixed in loose contact mode. XRD, FT-IR, N₂ adsorption and TEM characterization results revealed that the use of either surfactant or microwaves during the synthesis led to delamination of the saponite support, yielding high surface area and small crystallite size materials. The degree of delamination affected further copper oxide dispersion and soot combustion capacity of the Cu/saponite catalysts. All Cu/saponite catalysts were active for soot combustion, and the NO₂-assisted mechanism seemed to prevail. The best activity was achieved with copper oxide supported on a Na–saponite prepared at pH 13 and with surfactant. This best activity was attributed to the efficient copper oxide dispersion on the high surface area delaminated saponite (603 m² g⁻¹) and to the presence of Na. Copper oxide reduction in H₂-TPR experiments occurred at lower temperature for the Na-containing catalysts than for the H-containing counterparts, and all Cu/Na–saponite catalysts were more active for soot combustion than the corresponding Cu/H–saponite catalysts.