Photocatalytic removal of low concentration SO2 by titanium dioxide

• TiO2 immobilized on glass beads were used for the removal of low concentration SO2.
• Different operational factors that influence the photocatalytic process of SO2 were studied.
• Long-term performance of the TiO2 catalyst on the removal of SO2 was recorded.
• Deactivation of the catalyst was observed and discussed.
• Possible mechanism of the photo-oxidation of SO2 was proposed.

Titanium dioxide (TiO2) immobilized on glass beads synthesized by a simple physical method was used as a photocatalyst for the removal of low concentration sulfur dioxide (SO2) in flue gas. The performance of the composite was tested in a fixed bed reactor under UV irradiation. The effects of some important operating parameters, including SO2 concentration, oxygen, gas humidity, temperature, and space time, on SO2 removal efficiency were studied. With flue gas consisted of 5% O2, 2.9% H2O, and 40 ppm SO2, the efficiency dramatically increased to 100% right after the UV lights were applied. And the removal efficiency maintained stable for approximately 100 min. However, after the catalyst breakthrough, the efficiency dropped to 47%, mainly due to the deactivation of the catalyst. According to the X-ray photoelectric spectroscopy (XPS) analysis and experimental results, the deactivation was caused by the photo-oxidation products of SO2 and water vapor which blocked the further reaction on the TiO2 surface. The possible reaction mechanism of the photocatalytic removal process was also proposed in this report.