Kinetics and mechanism of magnesium sulphite oxidation promoted by a novel cobalt-based molecular sieve catalyst

• A novel supported catalyst was prepared and characterized for magnesium sulphite oxidation.
• The heterogeneous catalytic oxidation kinetics of magnesium sulphite was investigated.
• The overall oxidation rate relies on the internal diffusion rate of oxygen.

The oxidation of magnesium sulphite is crucial in recycling the byproduct of magnesium desulphurisation. In this study, a novel cobalt-based catalyst was prepared using a wet impregnation method by loading cobalt species on a molecular sieve carrier. The catalyst was characterised using scanning electron microscopy, X-ray fluorescence, Brunauer–Emmett–Teller analysis, X-ray diffraction, and energy dispersive X-ray spectroscopy. The catalyst was confirmed to be a mesoporous material. The macroscopic kinetics of magnesium sulphite oxidation catalysed by this cobalt-based catalyst was investigated in a stirred tank reactor. The results showed that reaction orders with respect to catalyst, magnesium sulphite, and oxygen concentrations were 0.39, 0, and 0.41, respectively. The apparent activation energy was 35.2 kJ mol−1. In addition, a comparison of the rates of external diffusion, internal diffusion, and intrinsic reaction revealed that the internal diffusion of oxygen might be the rate-controlling step of magnesium sulphite oxidation. The results provide a new approach for recycling the magnesium desulphurisation byproduct.

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