Defect-engineered cobalt-based solid catalyst for high efficiency oxidation of sulfite

We report a defect-engineered Co-based solid catalyst, namely the Co₃O₄ nanocubes (NCs)/graphitic C₃N₄ (g-C₃N₄) hybrid, for enhancing the oxidation of magnesium sulfite (MgSO₃) in the desulfurization of wet magnesia. Abundant oxygen vacancies were induced successfully on the Co₃O₄ NCs/g-C₃N₄ hybrid. The creation of oxygen vacancies promoted MgSO₃ oxidation by enhancing the adsorption of reactant MgSO₃ and accelerating the striping of product MgSO₄ to refresh the Co active sites. The oxygen vacancies also promoted the transfer of oxygen molecules and subsequent activation of oxygen molecules to active oxygen species. The size effect of Co₃O₄ NCs, which may be a crucial factor for improving the catalytic activity, considerably enhanced the efficiency of Co species. Moreover, because the g-C₃N₄ support had a large surface area and large number of unpaired electrons, the coupling of Co₃O₄ NCs and g-C₃N₄ improved the dispersion of Co₃O₄ NCs, which substantially decreased the usage of Co species. During the MgSO₃ oxidation reaction, the hybrid catalyst exhibited an unprecedented MgSO₄ yield per Co site of 1678.9 mmol/mmol Co at 30 min and a rapid MgSO₃ oxidation rate of 0.068 mmol·L⁻¹·s⁻¹.