Poisoning effect of sulphate on the selective catalytic reduction of NOx by C3H6 over Ag-Pd/Al2O3

The Ag-Pd/Al2O3 catalyst showed a higher NOx conversion than Ag/Al2O3 in the selective catalytic reduction (SCR) of NOx by C3H6 especially at temperatures ranging from 573 to 773 K. However, the presence of SO2 in the feed gas decreased the activity of NOx reduction over Ag-Pd/Al2O3 more greatly than that over Ag/Al2O3. The sulphate species formed on the poisoned Ag-Pd/Al2O3 and Ag/Al2O3 were characterized by BET, inductively couple plasma optical emission spectrometer (ICP-OES), XRD, temperature programmed desorption (TPD) and in situ diffuse reflectance infra-red fourier transform spectroscopy (DRIFTS) methods. Two kinds of sulphate species were found on the SO2 poisoned Ag-Pd/Al2O3 catalyst, and the formation of nitrate was blocked by the surface sulphate species. The addition of Pd into Ag/Al2O3 promoted the formation of sulphate on the Ag sites in the presence of SO2, which was considered to be the possible reason for the weak sulphur resistance of Ag-Pd/Al2O3.

Pd-promoted Ag/Al2O3 (Ag-Pd/Al2O3) showed a better performance than Ag/Al2O3 in the selective catalytic reduction (SCR) of NOx by C3H6. However, the situation is just the contrary in the presence of SO2. This phenomenon is due to the formation of sulphate on Ag sites promoted by Pd. The accumulation of surface sulphate on Ag-Pd/Al2O3 inhibited the formation of nitrate and –NCO species, subsequently inhibiting the SCR of NOx. Figure optionsDownload as PowerPoint slide