Improved low temperature removal of NOX from lean-burn exhaust via adsorption on TiO2-modified Ag–alumina

Abstract TiO 2 -modified Ag–alumina was studied as an NO X trapping material with the aim of improving the removal of NO X from lean-burn exhaust at low temperatures. This trapping material, in which both Ag and TiO 2 were finely dispersed throughout the alumina support on a nanometre scale, effectively adsorbed NO X at temperatures as low as 150 °C. The TiO 2 -modification of Ag–alumina improved the NO X trapping performance of the material by enhancing NO adsorption in the presence of other gases, including CO, hydrocarbons, CO 2 and H 2 O. This modified material also exhibited less deterioration resulting from sulfur poisoning as compared to either conventional NO X storage and reduction (NSR) catalysts or unmodified Ag–alumina. TiO 2 was shown to be dispersed throughout the alumina in an octahedral structure, and spectroscopic analyses along with DFT calculations demonstrated that this dispersion is effective at stabilizing Ag in the material. It was also determined that Ag supported on octahedral TiO 2 formed active sites at which the redox reaction between Ag 0 and Ag + proceeded, and that NO was effectively oxidized and adsorbed as nitro and nitrite species on the active surface composed of the dispersed Ag and TiO 2 .