Alumina-supported catalysts for NO reduction in an oxidizing atmosphere

Catalytic selective reduction of NO_x to N₂ using a hydrocarbon in an oxidizing atmosphere is challenging because of the competitive reaction of hydrocarbon combustion. Alumina is a rather effective catalyst for this reaction, but it requires high operating temperatures. The activity can be enhanced by adding other catalytic components, such as Pt, Ag, CoO_x, or SnO₂. Many of these catalyst systems are bifunctional. A substantial portion of the reaction pathway for propene reduction of NO_x has been elucidated for SnO₂/Al₂O₃. The function of SnO₂ is to oxidize the propene to acrolein, which is then transferred to alumina where it reacts to form acetaldehyde. Reduction of NO_x by acetaldehyde on alumina leads to N₂. The bifuncational aspect of the catalyst systems offers the potential to improve the catalytic performance by optimizing the individual components.