Enhanced activity of Ca-doped Cu/ZrO2 for nitrogen oxides reduction with propylene in the presence of excess oxygen

In this work, the effect of adding alkaline-earth metals (Mg, Ca, Sr, and Ba) to the ZrO2 support on the activity of Cu/ZrO2 catalyst for selective catalytic reduction (SCR) of NOx with C3H6 was investigated. The catalytic activity of Cu/ZrO2 was greatly enhanced by the addition of 5% all of the four alkaline-earth metals to the ZrO2 support. The highest promotional effect was observed over the Ca-modified Cu/ZrO2 catalyst. BET, H2-TPR and DRIFTS results revealed that the Cu/CaZrO2 catalyst had a better metal dispersion and metal–support interaction than Cu/ZrO2 catalyst. This feature inhibited the direct oxidation of C3H6 and improved the C3H6 selectivity for the reduction of NO. On the other hand, NOx-TPD and DRIFTS results showed that Cu/CaZrO2 catalyst could adsorb much more nitrate species than Cu/ZrO2 catalyst under both static room temperature adsorption and the real reaction conditions, while nitrate species was an important intermediate in the C3H6-SCR.