A New Material for Combustion Exhaust Aftertreatment at Low Temperature

Materials which catalyse the reduction of gas phase nitrogen oxides (NOx), from combustion devices such as diesel engines, are needed to meet emissions regulations and improve air quality. Here we use flow tube and diesel engine laboratory systems to investigate an iron silicate material (LowCat) which catalyses CO oxidation and NOx reduction simultaneously and is effective at low temperatures. LowCat’s potential for emissions mitigation was assessed by combining quantitative kinetics with an understanding of its mechanism of action. Annealing LowCat transforms a goethite component to hematite, increasing its catalytic activity. A surface bound O intermediate, critical to the binding of NH3 reductant, forms from and facilitates reduction of NO2 at room temperature. This intermediate can also be formed from reduction of O2 by NO above 450 K. This mechanistic understanding allowed a quantitative assessment of LowCat’s performance. The catalyst shows significant activity under conditions relevant to automotive and other diesel combustion systems and has the particular advantage of reducing NO2 to N2 at temperatures below 150 °C. LowCat represents an exciting opportunity to create Selective Catalytic Reduction (SCR) exhaust aftertreatment systems with superior low temperature performance, which is needed for low load operation of diesel-powered vehicles and low temperature combustion devices that are often important contributors to urban air quality.