Catalytic soot oxidation over Ce- and Cu-doped hydrotalcites-derived mesoporous mixed oxides

Abstract

Ce- and Cu-doped hydrotalcites derived mixed oxides were prepared through co-precipitation and calcination method, and their catalytic activities for soot oxidation with O₂ and O₂/NO were investigated. The solids were characterized by XRD, TG-DTG, BET, H2-TPR, in situ FTIR and TPO techniques. All the catalysts precursors showed the typical diffraction patterns of hydrotalcite-like materials having layered structure. The derived mixed oxides exhibited mesoporous properties with specific surface area of 45–160 m²/g. After both Ce and Cu incorporated, mixed crystalline phases of CuO (tenorite), CeO₂ (fluorite) and MgAl₂O₄ (spinel) were formed. As a result, the NO_x adsorption capacity of this catalyst was largely increased to 201 µmol/g, meanwhile, it was also the most effective to convert NO into NO₂ in the sorption process due to the enhanced reducibility. The in situ FTIR spectra revealed that NOx were stored mainly as chelating bidentate and monodentate nitrate. The interaction effect between Cu and Ce in the mixed oxide resulted in different NO_x adsorption behavior. Compared with the non-catalyzed soot oxidation, soot conversion curves over the mixed oxides catalysts shift to low temperature in O₂. The presence of NO in the gas phase significantly enhanced the soot oxidation activity with ignition temperature decreased to about 320°C, which is due to NO conversion to NO₂ over the catalyst followed by the reaction of NO₂ with soot. This explains the cooperative effect of Ce and Cu in the mixed oxide on soot oxidation with high activity and 100% selectivity to CO₂ formation.

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ORCID for Zheng Jiang: orcid.org/0000-0002-7972-6175

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