NOx storage and soot combustion over well-dispersed mesoporous mixed oxides via hydrotalcite-like precursors

Abstract

A series of mixed oxides with highly dispersed redox components were prepared via hydrotalcite-like precursors in which Mg was partly substituted with copper and cobalt, which were employed for NO_x storage and soot combustion. The physico-chemical properties of the catalysts were characterized by XRD, TGA, IR, N₂ adsorption, H₂-TPR and in situ FTIR techniques. The results show the transition metal cations have isomorphously replaced Mg²⁺ in the layered structures forming a single hydrotalcite type phase. After calcination, the transition metal oxides exist in a highly dispersed form in the Mg(Al)O matrix and there is a cooperative effect between the copper and cobalt on the redox properties of the catalyst. The as-prepared oxide catalysts exhibit large surface areas, basic characters and improved redox properties, resulting in high performances in NO_x storage and soot combustion. Both the NO_x storage and desorption are catalytically accelerated due to the highly dispersed transition metal oxides. The presence of NO_x positively affects the activity of all the oxides catalysts for soot combustion, which may be related to the production of NO₂ during NO oxidation. NO₂-assisted mechanism and active oxygen mechanism may occur simultaneously in soot/NO/O₂ reaction.