The generation of sulfate species on Ir-based catalysts for boosting NO reduction with CO under the coexistence of O and SO atmosphere.

Generally, sulfur poisoning is considered to be one of the main factors contributing to the deactivation of selective catalytic reduction of NO by CO (CO-SCR) catalysts, while the promotional effect of SO on NO reduction over Ir/SiO is observed which is an interesting scientific phenomenon. After the introduction of 20 ppm SO, NO conversion increased from ∼ 40 % to ∼ 90 % at 275 °C, and N selectivity increased from ∼ 80 % to 100 % at 200 ∼ 300 °C. Furthermore, the promoting effect could remain unchanged after 24 h of continuous reaction. However, the temperature point for achieving complete conversion of CO increased from 225 °C to 275 °C after the introduction of SO. Experimental characterization and theoretical calculation jointly proved that the inhibition of CO oxidation by the generation of sulfate was the main reason for promoting NO reduction. Under the coexistence of O and SO, SO was firstly oxidized to SO on the iridium surface and generated sulfate species on surface hydroxyl groups of SiO. Some active sites for O adsorption were covered by the generated surface sulfate, and adsorbed CO was hard to react with adsorbed O, resulting in Langmuir-Hinshelwood (L-H) reaction pathways for CO oxidation being inhibited. Therefore, unoxidized CO reacted with NO adsorbed species and generated NO to generate N and CO, improving NO reduction. This new insight has implications for understanding the promotional effect of SO on NO reduction with CO in the presence of O.