Temperature programmed desorption/surface-reaction study of an anodic alumina supported Ag catalyst for selective catalytic reduction of nitric oxide with propene

On an anodic alumina supported silver catalyst with a low Ag loading (1.68 wt.%), No, (NO/He, NO/O-2/He, NO2/He) adsorption measurements and NOx-temperature programmed decomposition (TPD)/temperature programmed surface-reaction (TPSR) measurements in different gas streams (He, C3H6/He, C3H6/O-2/He) were conducted to investigate the formation, consumption and reactivity of surface adsorbed NO, species. During NO adsorption, no noticeable uptake of NO was detected. Introducing oxygen greatly improved the formation of ads-NO, species. A greater quantity of surface nitrate species was found after NO2 adsorption, accompanied with gaseous NO release. The result of TPSR demonstrates the surface nitrate species can be effectively and preferentially reduced by propene. When introducing oxygen into the propene gas stream of TPSR test, the significantly increased amount of reacted nitrate undoubtedly shows the importance of oxygen in activating propene. The pathway for the selective reduction of NO, in the presence of excess oxygen is proposed to pass through the selective reduction of the adsorbed nitrate species with the activated propene. The enhanced NOx conversion when replacing NO with NO2 was attributed to the stronger NOx adsorption capacity and oxidation ability of NO2, than those for NO. With increasing oxygen concentration, the difference between NO and NO2 would gradually decrease, and finally disappear in a high excess of oxygen. (c) 2007 Elsevier B.V. All rights reserved.