Optimisation of Ag loading and alumina characteristics to give sulphur-tolerant Ag/Al2O3 catalyst for H2-assisted NH3-SCR of NOx

A series of Ag/Al2O3 catalysts with different alumina precursors and different Ag loadings were tested for H-2 assisted NH3-SCR of NO. The catalysts were characterised (BET, XRD, NH3-TPD, ICP-OES, TEM and UV-vis spectroscopy) and tested as fresh catalyst, during long-term cycling tests with SO2 present and after the sulphur testing. The aim was to find an optimal configuration of the Ag/Al2O3 catalyst for automotive applications. Catalysts with a high sulphur tolerance during long-term SO2 cycling (1 h with 10 ppm SO2 at 250 degrees C followed by 10 min regeneration at 670 degrees C, repeated until no difference between cycles was seen) were demonstrated. The high sulphur tolerance and activity was attributed to high surface areas of the catalyst supports, together with a high Ag loading. The high surface area allows a larger NH3 storage on the surface which is previously reported necessary for the SCR reaction. A higher Ag loading will affect the state of Ag by increasing the ratio of Ag-clusters and particles to highly dispersed Ag ions. SO2-poisoned Ag-clusters and particles can be regenerated by the high temperature treatment in the deNO(x) feed, highly dispersed Ag ions cannot. (C) 2012 Elsevier B.V. All rights reserved.