Effect of ZrO2 addition method on the activity of Al2O3-supported CuO for NO reduction with CO: Impregnation vs. coprecipitation

Supported copper oxide catalysts (CuO/Al2O3, CuO/ZrO2/Al2O3, CuO/ZrO2–Al2O3) were prepared from different procedures and tested in the catalytic reduction of NO with CO to investigate the effect of ZrO2 addition method. The catalysts were characterized by means of ICP, BET, XRD, Raman, H2-TPR, XPS, FTIR of NO or/and CO adsorption. Activity results demonstrated that the addition of ZrO2 could improve catalytic performance, which is dependent on the addition method. The sequence of activity is CuO/ZrO2–Al2O3 > CuO/ZrO2/Al2O3 > CuO/Al2O3. Based on the results of composition and texture, CuO/ZrO2–Al2O3 sample shows more surface zirconia species and larger surface area than CuO/ZrO2/Al2O3. XRD and Raman results suggest amorphous ZrO2 and highly dispersed copper oxide species are mainly present in the ZrO2-added catalysts except for a few CuO crystallites in CuO/ZrO2/Al2O3. Highly dispersed copper oxide species strongly interacting with amorphous zirconia (Cu⋯O⋯Zr species) was observed in H2-TPR and XPS, which was considered as the origin of the enhanced activity. In addition, the adsorption type and configuration of NO was similar over these catalysts. However, CuO/ZrO2–Al2O3 sample shows the greater capacity to activate the adsorbed NO species than CuO/ZrO2/Al2O3.

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► Cu–Zr–Al catalysts were prepared from two different procedures.
► The addition of ZrO2 improves the catalytic activity, depending on the addition method.
► The enhanced activity is attributed to highly dispersed copper species interacting with ZrO2.