Reducing the poisoning effect of adsorbed alkaline earth metal on Nb active sites with sulfates for NH3-SCR
Reducing the poisoning effect of alkaline earth metals over catalysts in industrial fields presents a great challenge to selective catalytic reduction (SCR) of NO x with ammonia. Herein, we successfully introduce sulfates to the surface of supported manganese-based oxides (Nb/MnO 2 -S) for trapping calcium species, and Nb/MnO 2 -S catalyst with superior low-temperature performance and calcium-resistant property still exhibits excellent de-NO x activity in a wide operating temperature window (175–350 °C, over 80 % NO x conversion with a gas hourly space velocity of 60,000 h −1 ) after calcium poisoning. In this case, the addition of sulfates increased the quantity of chemisorbed oxygen on Nb/MnO 2 -S, thus accelerating the redox cycle in NH 3 -SCR reaction. Significantly, compared with calcium-poisoned Nb/MnO 2 , relevant spectroscopy analysis and theoretical calculations further reveal that sulfates species prefer to interact with calcium and release the Nb active sites, which maintains the efficient NH 3 adsorption and preserves a large amount of Brønsted acid sites over calcium-poisoned Nb/MnO 2 -S, thus promoting calcium-resistant performance. This work will provide a general strategy to develop calcium-resistant SCR catalysts with low-temperature activity for industrial applications.
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