Low-Cost CuX Catalyst from Blast Furnace Slag Waste for Low-Temperature NH3-SCR: Nature of Cu Active Sites and Influence of SO2/H2O

A series of Cu-exchanged zeolite NaX (derived from blast furnace slag) catalysts were synthesized by an ion-exchanged method. The low-temperature catalytic activity and SO2 or/and H2O resistance of the catalysts were studied as well. The results found that the Cu(N)X catalyst exhibited excellent low-temperature selective catalytic reduction (SCR) activity, whose NO conversion was nearly 100% at ca. 175 degrees C and remained stable, while the Cu(C)X catalyst showed the poorest catalytic performance. When SO2 and H2O was introduced, the NO conversion of the Cu(N)X catalyst declined from 100% to 60%, and it could recover to ca. 63% after cutting off SO2 and H2O. More isolated Cu2+ species and surface chemisorbed oxygen species on the Cu(N)X catalyst could provide more active sites for SCR reaction, and more surface oxygen vacancies accelerated the oxidation of absorbed NH3 species and NO species. Besides, the higher surface acidity and redox ability on the Cu(N)X catalyst promoted the SCR reaction performance. In addition, after the poisoning of SO2/H2O, the surface acidity decreased, redox ability became poor, and the Cu active species was less than that of the Cu(N)X catalyst, indicating that the Cu active sites were consumed during the reaction. Furthermore, it could also be found that the generated sulfate species occupied the main active sites and reduced the varieties of nitrate species and intermediates, thereby reducing the SCR activity of the catalyst.

Automated summary

Cu-exchanged zeolite NaX catalysts showed excellent low-temperature selective catalytic reduction (SCR) activity, with nearly 100% NO conversion at about 175 degrees C. The presence of surface oxygen vacancies and isolated Cu2+ ions played crucial roles in the catalytic performance, while SO2 and H2O could decrease the catalyst's SCR activity.