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

The development of efficient catalysts for the selective catalytic reduction of NO by CO (CO-SCR) in the presence of O₂ is highly desirable for controlling the emission of toxic gases from tailpipes. Here, a bimetallic IrRu/ZSM-5 catalyst was prepared for the selective catalytic reduction of NO by CO in the presence of O₂ (5%) for the low-temperature treatment of exhaust gas. IrRu/ZSM-5 afforded 90% NO_x conversion in the range of 225-250 °C and maintained 90% NO_x conversion after 12 h of reaction. Ru addition inhibited agglomeration of the Ir particles during the reduction process and provided more active sites for NO adsorption. Isotopic C¹³O tracing and in situ diffuse reflectance infrared Fourier-transform spectroscopy experiments were used to elucidate the CO-SCR mechanism in the absence or presence of O₂. NCO could easily form on the surface of catalysts in the absence of O₂, whereas NCO formation has been inhibited owing to the quick consumption of CO in the presence of O₂. Moreover, some byproducts such as N₂O and NO₂ are generated in the presence of O₂. Finally, a possible mechanism for CO-SCR under different conditions was proposed based on in situ experiments and physicochemical analyses.