Heterogeneous reactions of SO2 on ZnO particle surfaces

Abstract

Heterogeneous reactions of SO2 on ZnO particle surfaces were studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The influences of relative humidity (RH) and UV radiation (λ ≈ 365 nm) were investigated. In the absence of UV radiation, sulfite was the prominent product on the particle surfaces, and a negative relationship between RH and sulfite production was observed. In the presence of UV radiation, infrared (IR) absorption of sulfite and sulfate was evident in the spectra. With increasing RH or UV intensity, sulfite was gradually transformed into sulfate. UV intensity and RH exhibited a synergistic effect on the heterogeneous oxidation of SO2 on ZnO. On dry particles and with no UV radiation, the reaction order of SO2 on ZnO particles was 1.6. The initial uptake coefficient for the formation of sulfite, using the Brunauer-Emmett-Teller (BET) area as the reactive surface area of SO2, was 4.87 × 10−6. At 40% RH and with UV radiation, the reaction order was 0.91, and the initial uptake coefficient was 2.29 × 10−5.