Influence of Pt location on BaCO3 or Al2O3 during NOx storage reduction

Catalysts for NOx storage–reduction (NSR) were made selectively with Pt on either the Al- or the Ba-components without altering significantly the Al2O3 or BaCO3 crystal sizes, Al/Ba weight ratio, specific surface area, porosity, and Pt dispersion using a two-nozzle flame spray pyrolysis (FSP) unit. The NOx storage performance at 300 °C was best for Pt located near Al2O3 as it facilitates the oxidation of NO to NO2 during the fuel lean period but the reduction rate during the subsequent short fuel rich period was much slower resulting in incomplete regeneration. This contributed to a gradual decrease of the NOx conversion at increasing cycling. In contrast, Pt on BaCO3 resulted in an initially lower NOx storage rate but during ten storage–reduction cycles a stable NOx conversion of about 50% was reached. When using NO2 instead of NO or higher NOx oxidation-reduction temperatures (e.g. 350 °C) the Pt location did not affect the NSR performance of the Pt/Ba/Al2O3 catalysts.