Unveiling the significant promoting effect of SO2 on Ir/SiO2 catalyst for the CO-SCR of NOx in the presence of O2

Selective catalytic reduction of NOx by CO (CO-SCR) in the presence of O2 is challenging because in this process CO is prone to being oxidized by O2, thus inhibiting NOx reduction by CO. Furthermore, SO2 typically leads to the deactivation of the CO-SCR catalyst. Herein, a significant promoting effect of SO2 on Ir/SiO2 catalyst for the CO-SCR of NOx in the presence of O2 is reported. In-situ X-ray Absorption Fine Structure (XAFS) and X-ray photoelectron spectroscopy (XPS) analysis showed that SO2 does not affect the chemical nature of Ir0 under reaction conditions. However, SO2 can be oxidized to sulfate and deposit on the catalyst surface. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that the presence of SO2 can inhibit the CO + O2 reaction, thus leaving more CO available to reduce NOx over the active Ir0 sites. As a result, the reduction of NOx is remarkably promoted even in the presence of O2 and SO2.