Urealess NOx Reduction by Carbon Monoxide in Simulated Lean-Burn Exhausts

Abstract

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.