Heterogeneous Reaction of SO₂ on Manganese Oxides: the Effect of Crystal Structure and Relative Humidity.

ABSTRACT: Manganese oxides from anthropogenic sources can promote the formation of sulfate through catalytic oxidation of SO₂. In this study, the kinetics of SO₂ reactions on MnO₂ with different morphologies (?, ?, ? and ?) was investigated using flow tube reactor and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). Under dry conditions, the reactivity towards SO₂ uptake was highest on ?-MnO₂ but lowest on ?-MnO₂, with a geometric uptake coefficient (?_obs) of (2.42?±?0.13) ×10^-2 and a corrected uptake coefficient (?_c) of (1.48?±?0.21) ×10^-6 for the former while ?_obs of (3.35?±?0.43) ×10^-3 and ?_c of (7.46?±?2.97) ×10^-7 for the latter. Under wet conditions, the presence of water altered the chemical form of sulfate and was in favor for the heterogeneous oxidation of SO₂. The maximum sulfate formation rate was reached at 25% RH and 45% for ?-MnO₂ and ?-MnO₂, respectively, possibly due to their different crystal structures. The results suggest that morphologies and RH are important factors influencing the heterogeneous reaction of SO₂ on mineral aerosols, and that aqueous oxidation process involving transition metals of Mn might be a potential important pathway for SO₂ oxidation in the atmosphere.

SUBMITTER: Yang W 

PROVIDER: S-EPMC5495761 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature