The lean NOx aftertreatment is one of the major barriers to the widespread adoption of advanced combustion powertrains for the reduction of both greenhouse gases and toxic exhausts. Urea/SCR, selective catalytic reduction of NOx by NH3 generated through urea decomposition, is commonly regarded as the best way to reduce NOx in low temperature lean exhaust. However, the urea/SCR system has inherent drawbacks, i.e., periodic refill of the aqueous urea solution and a complicated hardware system. Here, we demonstrated a state-of-the-art catalyst that is extremely selective and efficient for reducing NOx, primarily with the most abundant reductant, CO, particularly in the presence of O2 (>5%) at low temperature. Under temperatures lower than 250 °C, IrRu/Al2O3 catalysts achieved higher NOx conversion by CO only than a commercial Cu-based urea/SCR catalyst employing NH3 as a primary reductant. Furthermore, the IrRu catalyst revealed high thermal stability and SO2 tolerance, which are very important factors for real world applications.