Performance of Ce substituted hydrotalcite-derived mixed oxide catalysts Co2.5Mg0.5Al1 − x%Cex%O used for soot combustion and simultaneous NOx-soot removal

Abstract

The Co2.5Mg0.5Al1−x%Cex%O hydrotalcite-derived catalysts (CMACex) with different Ce/Al atomic ratios were synthesized by co-precipitation, which simultaneously possess multiple properties for soot combustion, lean-burn NOx storage and simultaneous NOx-soot removal. The techniques including XRD, EXAFS, BET, H2-TPR, O2-TPD and in-situ DRIFTS were used for catalyst characterization. It is found that Ce-substituted catalysts are much more active than Ce-free one for soot combustion, NOx storage and simultaneous NOx‐soot removal. Among the catalysts containing Ce, CMACe8 exhibits the highest performance, showing the lowest temperature of 384°C for the maximal soot oxidation rate (Tm), the largest NOx storage capacity (336μmolg−1), and the largest NOx reduction percentage of 15.4%. Compared with Ce-free sample, Ce-substitution increases the specific surface area, the redox properties and the amount of surface lattice oxygen species of the catalyst. The optimal Ce-substitution amount in Co2.5Mg0.5Al1−x%Cex%O is x=8. In-situ DRIFTS results reveal that NO is readily oxidized to NO2 and stored as nitrates over Ce-substituted catalysts, which are very reactive intermediates for simultaneous NOx-soot removal.