Near-Zero NOx Control for Diesel Aftertreatment

A two-chamber catalyst system for the aftertreatment of No. 2 Diesel exhaust is demonstrated. NOx conversion efficiencies greater than 95% were obtained over a broad range of operating temperatures and NOx levels. The system incorporates a NOx catalyst (SCONOx™) for the removal of CO, hydrocarbons, and NOx from the exhaust stream and a SO₂ catalyst (SCOSOx™) for the protection of the NOx catalyst from sulfur poisoning. Both catalysts are of sorbate or “trap” type. Hydrogen is used as the reductant and can be supplied by on-board fuel reformers. Tests of the catalysts were performed with various loads, temperatures, and NOx levels. A light-duty diesel engine with no particulate control was used for the tests. All tests were conducted using No. 2 Diesel fuel.