Unraveling the nature of sulfur poisoning on Cu/SSZ-13 as a selective reduction catalyst

In order to investigate sulfate poisoning of Cu/SSZ-13 catalysts used for NOx removal by selective catalytic reduction with ammonia (NH3-SCR), they were exposed to SO2 at different temperatures in the presence and absence of NH3. Standard physicochemical characterization and density functional theory calculations were performed to probe the nature of the sulfate species formed on the catalyst and the corresponding effects. The results showed that sulfate poisoning has little effect on the chabazite structure of the catalyst, but the sulfate species formed blocks the Cu/SSZ-13 pores. For sulfation with pure SO2, copper bisulfate forms and its content increases with sulfation temperature. However, in the presence of NH3, the major sulfate formed is ammonium bisulfate (similar to 80%). Moreover, the total sulfate contents are lower for higher sulfation temperatures because of difficulties in ammonium bisulfate formation. Regardless of the kind of sulfate species formed, the poisoning leads to lower availability of active sites, causing inferior NOx conversion. Importantly, as copper bisulfate and ammonium bisulfate on Z-Cu(OH)(+) are interconvertible, our study reveals that using NH3 to promote the transformation from copper bisulfate to ammonium bisulfate is a viable method to improve the recovery effect of sulfated Cu/SSZ-13. (c) 2021 Published by Elsevier B.V. on behalf of Taiwan Institute of Chemical Engineers.

Automated summary

The study found that sulfation negatively impacts the availability of active sites on Cu/SSZ-13 catalysts, resulting in lower NOx conversion efficiency. Copper bisulfate and ammonium bisulfate on Z-Cu(OH)(+) are interconvertible, and promoting this transformation with NH3 can improve the recovery effect of sulfated Cu/SSZ-13.