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 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 (1 h with 10 ppm SO2 at 250 °C followed by 10 min 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.

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► Sulphur tolerance of different Ag/Al2O3 catalysts for SCR of NOx was tested.
► High SBET and high Ag load are important for high sulphur tolerance.
► SBET affects the NH3 adsorption capacity, i.e. availability of NH3 for SCR.
► A higher Ag load means more Ag clusters and particles that can be regenerated.