Insight into structural role of 2D/3D mesoporous silicon in catalysis of magnesium sulfite oxidation

Sulfite oxidation is a key step in wet flue gas desulfurization. Cobalt was used as the active species, and the catalysts supported using three silicon mesoporous molecular sieves (SMMSs) in two (Co-MCM-41, Co-SBA-15) and three (Co-KIT-6) dimensions were fabricated through ethanol impregnation. Compared with the non catalytic oxidation rate (0.009 mmol L-1 s(-1)), the catalytic oxidation rate reached 0.078, 0.063, and 0.048 mmol L-1 s(-1) in the presence of Co-SBA-15, Co-KIT-6, and Co-MCM-41, respectively. Their physic-chemical properties were characterized to reveal the role of structure in this catalytic process through N-2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, inductively coupled plasma optical emission spectrometry, H-2-pulse adsorption, temperature programmed reduction, transmission electron microscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy mapping. The structural effect on the catalytic activity of cobalt nanoparticles was reflected by varying the dispersion and morphology of active cobalt, the facility of diffusion of reactants, and the binding force between the active cobalt and supports. The kinetics of MgSO3 catalytic oxidation by SMMS catalysts were investigated, indicating that the reaction was controlled by the internal diffusion of oxygen. The results suggest the feasibility of reclaiming the byproduct and downsizing the oxidation pool for magnesia desulfurization.