Insight into the Mechanism of Selective Catalytic Reduction of NO by CO over a Bimetallic IrRu/ZSM-5 Catalyst in the Absence/Presence of O₂ by Isotopic C¹³O Tracing Methods

This work explores the mechanism of selectivecatalyticreduction of NO by CO over the bimetallic IrRu/ZSM-5 catalyst in theabsence or presence of O-2. The development of efficient catalysts for the selectivecatalyticreduction of NO by CO (CO-SCR) in the presence of O-2 ishighly desirable for controlling the emission of toxic gases fromtailpipes. Here, a bimetallic IrRu/ZSM-5 catalyst was prepared forthe selective catalytic reduction of NO by CO in the presence of O-2 (5%) for the low-temperature treatment of exhaust gas. IrRu/ZSM-5afforded 90% NO x conversion in the rangeof 225-250 degrees C and maintained 90% NO x conversion after 12 h of reaction. Ru addition inhibited agglomerationof the Ir particles during the reduction process and provided moreactive sites for NO adsorption. Isotopic (CO)-O-13 tracing andin situ diffuse reflectance infrared Fourier-transform spectroscopyexperiments were used to elucidate the CO-SCR mechanism in the absenceor presence of O-2. NCO could easily form on the surfaceof catalysts in the absence of O-2, whereas NCO formationhas been inhibited owing to the quick consumption of CO in the presenceof O-2. Moreover, some byproducts such as N(2)Oand NO2 are generated in the presence of O-2.Finally, a possible mechanism for CO-SCR under different conditionswas proposed based on in situ experiments and physicochemical analyses.