Research On Cobalt-based MOF Catalyst For Catalytic Oxidation Of Magnesium Sulfite

Wet magnesium flue gas desulfurization is a technology that has developed rapidly in recent years.In addition,it also has the characteristics of high desulfurization efficiency,small footprint,low operating cost,high benefit of by-product recovery and wide application range,which makes it a more economical and practical desulfurization method.However,the low oxidation rate of magnesium sulfite,a by-product of desulfurization,leads to high energy consumption in the subsequent process of oxidation,evaporation and crystallization.Therefore,efficient oxidation of magnesium sulfite is a key problem that needs to be solved at present.The oxidation of magnesium sulfite to produce magnesium sulfate has significant economic benefits and can realize the utilization of waste resources.Some carbon-based,silica-based and molecular sieve-based catalysts have been studied to improve the catalytic effect of sulfite,but the effect is not high enough.Based on the unique structure and excellent physical and chemical properties of metal-organic frameworks（MOFs）materials,two cobalt（Co）-based MOF composite catalysts with high catalytic efficiency for magnesium sulfite and certain reusability were synthesized.In this article,a binary composite catalyst Co-MOF-74@MWCNT was synthesized by a solvothermal method using the active role of transition metal Co and cobalt nitrate hexahydrate as the active component,and the oxidation rate of magnesium sulfite could reach 0.1162 mmol·L^-1·s^-1,which is about 11-12 times higher than that of sulfite under non-catalytic conditions.ZIF-67 was synthesized with 2-methylimidazole and cobalt nitrate hexahydrate,and then prepared by high-temperature pyrolytic carbonization to obtain the nitrogen-doped porous carbon material Co@NC,which was used to catalyze the oxidation of magnesium sulfite at a rate of 0.1332 mmol·L^-1·s^-1,which was about 13-14 times higher than that of magnesium sulfite under non-catalytic conditions.The pyrolysis temperature was regulated to screen the optimal pyrolysis temperature for the preparation of the material.The catalytic oxidation kinetics of magnesium sulfite was explored,and the influence of key factors such as magnesium sulfite concentration,reaction temperature,oxygen partial pressure,p H and gas flow rate on the oxidation rate of magnesium sulfite was investigated.The optimal reaction conditions were determined as C（Mg SO₃）=50g·L^-1,T=308 K,p（O₂）=0.21 atm,p H=8,and Q=1 L·min^-1.Kinetic parameters such as apparent activation energy,magnesium sulfite grade number,oxygen grade number and reaction rate constant under the action of each catalyst were obtained.The physicochemical properties,microscopic morphology,the morphology of active components and the composition of active substances of the two catalytic materials were analyzed by combining XRD,SEM,TEM,BET,FTIR,XPS and other characterization methods.The research results provide an important reference for the catalytic oxidation of magnesium sulfite,a by-product of wet magnesium desulfurization.