Applied Catalysis A: General, Vol.572, 15-23, 2019
Regeneration of sulfur-deactivated TiO2 photocatalysts
The regeneration of deactivated photocatalyst, TiO2, caused by sulfur poisoning was studied in this work. It is found that over 98% of the SO2 oxidation products are adsorbed on catalyst surface in the form of H2SO4/SO42- causing the rapid deactivation of catalyst. The kinetic study reveals the activity of deactivated catalyst is only about 1.7% of that of the fresh one. Different regeneration methods including water washing, sulfuric acid washing, sodium hydroxide washing, and thermal treatment were investigated for regeneration performance. For water washing, the regeneration efficiency maintained stable at about 83% after the second regeneration cycle. The used water can be recycled for regeneration if the pH is controlled to be larger than (similar to)4. Due to the abundant hydroxyl groups in NaOH solution, the efficiency of the NaOH-regenerated catalyst is 113% after the first regeneration. However, the undermining of the catalyst substrate by NaOH causes the loss of catalyst powders, which offsets the beneficial effect of alkali washing and leads to the decrease in the regeneration efficiency as the number of recycle increases. Thermal regeneration at 400 degrees C can recover the catalyst activity to 84%. Interestingly, the regeneration efficiency increases gradually to 93% after fifth regeneration cycle. It can be inferred from the sulfating tests of TiO2 that after thermal treatment the surface adsorbed products (H2SO4) can increase the oxygen vacancy on catalyst surface and enhance the visible light response of the catalyst, thus improve the catalyst activity.