The selective catalytic reduction of NO by hydrocarbons over Pt- and Ir-based catalysts

Platinum- and iridium-based catalysts are the most active ones among noble metals for the selective catalytic reduction of NO by hydrocarbons (HC-SCR). Yet, the level of our understanding of the behavior of these two metals varies greatly. From the early stages of the research efforts in the HC-SCR field Pt-based catalysts were identified as "promising" and have been studied extensively for this application. Subsequently, there is a substantial body of literature focusing on the catalytic performance of such systems, as well as on the fundamental chemistry taking place on their surface under HC-SCR conditions. A fairly good understanding of the behavior of such catalysts has been developed and different reaction mechanisms have been proposed and debated extensively. In contrast, limited information is available regarding the properties and HC-SCR behavior of Ir-based catalysts. Recent reports have demonstrated advantages in the HC-SCR performance of such catalysts and have documented substantial iridium particle size, support and promoter effects.