MnO2-Functionalized Hydrophobic Ceramic Membrane for Sulfite Oxidation

Catalytic oxidation of sulfite is critical for the fixation of sulfite in the flue gas desulfurization process and is also an essential step related to the treatment of air and water pollution. This work designed and prepared a nano-MnO2-functionalized hydrophobic ceramic membrane with a hydrophobic surface by a hydrothermal method. The chemical composition and the nanostructure of the prepared MnO2 composite membranes were characterized using several identification techniques (X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy). The results show that the prepared nano-MnO2 was sea urchin-like, the crystal form was β-MnO2, and it grows uniformly on the surface of the ceramic membrane. The molar ratios of Mn4+/Mn3+ and Olatt/Ototal were associated with high catalytic activity and enhanced with increasing preparation concentration. The catalytic ability of nano-MnO2 composite membranes to Na2SO3 was studied by the membrane dispersion-catalysis process. The catalytic efficiency with a loaded amount of 1.6–4.5 mg was 5.4–8.3 times higher than that without the catalyst. The free radical quenching experiment showed that SO5•– was identified as the key free radical in the chain reaction. The oxidation kinetics of sulfite were investigated using a membrane dispersion reactor. The results showed that the catalyst, sulfite, and oxygen partial pressure reaction orders were 0.411, 0.243, and 0.640, respectively, and showed an apparent activation energy of 1.89 kJ·mol–1. Based on the three-phase reaction model analysis, sulfite oxidation was considered to be controlled by the mass transfer process of oxygen from the gas phase to the liquid phase.