Investigation of the ammonia adsorption on monolithic SCR catalysts by transient response analysis

The adsorption of ammonia on three different monolithic SCR catalysts was investigated experimentally. Two of the examined monoliths were coated cordierite honeycombs, containing either V2O5–WO3/TiO2 or V2O5/TiO2 as active components. The third sample was a commercially available extruded monolithic honeycomb consisting of V2O5–WO3/TiO2, and was tested for comparison. Different transient response methods and a modified temperature programmed desorption (TPD) method were used to investigate the ammonia adsorption in the presence of water (5%) and oxygen (10%). Under typical SCR conditions (stoichiometric ratio NH3:NO<1), the ammonia coverage of the WO3-free catalyst sample was significantly lower. Ammonia is more strongly adsorbed on the WO3-containing catalyst. The extruded catalyst adsorbed substantially larger amounts of ammonia especially at low temperatures, leading to a slow response under transient conditions.