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

A series of Ag/Al2O3 catalysts with different alumina precursors and different Ag loadings were tested for H2 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 (1h with 10ppm SO2 at 250°C followed by 10min regeneration at 670°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 deNOx feed, highly dispersed Ag ions cannot.