Promotional effect of sulfur trioxide (SO3) on elemental mercury removal over Cu/ZSM-5 catalyst

The Cu/ZSM-5 was used to study the effects of SO3 on mercury removal. The addition of SO2 decreased the Hg-0 removal efficiency but the efficiency increased from 82% to 95% after 21 ppm SO3 was introduced at 200 degrees C. The inhibition effect of SO2 on mercury removal was weakened at 400 degrees C and the promotion effect of SO3 on mercury removal was enhanced significantly. HgSO4 was the main mercury species formed on the catalyst in the presence of SO3. The in-situ FTIR results showed a large number of S-related peaks were generated on the surface of the catalyst with SOx (SO2 and SO3). The peak of adsorbed SO2 weakened when SO2 and SO3 coexisted in the reaction atmosphere. This is due to the SO3 inhibiting the adsorption of SO2. The peak of adsorbed SO3 was the most obvious and was then gradually consumed after Hg-0 introduced. Meanwhile, the peak of sulphate appeared on the surface of the catalyst. This indicated SO3 preferentially adsorbed on the catalyst to form active sites for oxidizing Hg-0 to HgSO4. The adsorption of SO(3 )on the catalyst was promoted at 400 degrees C, compared with 200 degrees C, which directly contributed to the enhancement of Hg-0 removal.