Simultaneous removal of SO2, NO and mercury using TiO2-aluminum silicate fiber by photocatalysis

Abstract

A novel TiO2-aluminum silicate fiber (TAS) nanocomposite, synthesized by a sol–gel method, is proposed to use as a photocatalyst for the removal of multiple pollutants. The photocatalyst has been characterized by XRD, SEM, EDX, UV–Vis spectra and BET. The TAS calcined at 500°C exhibited the biggest BET surface area and highest photocatalytic activity and was used as the photocatalyst for subsequent experiments. The oxidation and removal efficiencies of SO2, NO and elemental mercury (Hg0) in simulated coal combustion flue gas by the TAS catalyst were tested under UV irradiation. Experiments were conducted in a fixed-bed reactor at temperatures ranging from 30 to 120°C. In simulated flue gas (4% O2, 12% CO2, 2% H2O, 400ppm SO2, 50ppm NO), the removal efficiencies for SO2, NO and Hg0 at 120°C and with UV intensity of 3mWcm−2 can reach 33%, 31% and 80%, respectively. NO inhibited SO2 oxidation due to its competition for active adsorption sites. SO2 also had a prohibitive effect on NO removal. In contrast, SO2 was found to have a promotional effect on Hg0 oxidation due to the formation of HgSO4. NO inhibited the photocatalytic removal of mercury. During the simultaneous removal of SO2, NO and Hg0 on TAS, the photocatalytic oxidation efficiency decreased from 30 to 120°C. O2 exhibited a promotional effect on the photocatalytic oxidation due to the formation of lattice oxygen. However, the addition of water vapor to the simulated flue gas inhibited the oxidation of SO2, NO and Hg0. The UV intensity was the most important factor in the photocatalytic oxidation. Our discussion on the possible reaction mechanism provides some useful information for developing effective photocatalysts to oxidize SO2, NO and Hg0 in simulated coal combustion flue gas.