Electric Field-composite Metal Catalysts Synergistically Promote Magnesium Desulfurization Products Oxidation

With the rapid development of society,more and more fossil fuel is used to provide electricity.The large-scale use of fossil fuel has caused serious sulfur dioxide（SO₂）pollution.Therefore,the treatment of SO₂ cannot be delayed.At present,the most common desulfurization technology is wet flue gas desulfurization technology.Among them,magnesium flue gas desulfurization technology gradually popularized due to its unique benefits.Due to the low utilization rate of magnesium flue gas desulfurization products,it is necessary to research the oxidation and reuse of the desulfurization product magnesium sulfite（MgSO₃）.At present,the oxidation research of MgSO₃ mainly used supported cobalt-based catalysts to accelerate the oxidation of MgSO₃ to obtain high-purity magnesium sulfate（MgSO₄）products.Although the use of catalyst can increase the oxidation rate of MgSO₃to a certain extent,the improvement degree of the oxidation rate by catalyst alone is still very limited.This subject aimed at the improvement in MgSO₃ catalytic oxidation rate.Electric field was introduced into the reaction system to study the reaction kinetics and mechanism of MgSO₃catalytic oxidation under the action of the electric field.The physicochemical properties of catalysts were analyzed through a series of characterizations,and the reaction mechanism was deduced.A series of magnetic Co _XFe_3-XO₄ catalysts supported on MCM-41 carrier(Co _XFe_3-XO₄/MCM-41)were prepared by co-precipitation method.Electric field was introduced into the reaction system through a budget graphite electrode.The best catalyst Co Fe₂O₄/MCM-41 can increase the oxidation rate of MgSO₃ to 0.0660 mmol·L^-1·s^-1,which was 5 times than under pure aeration conditions.After the introduction of electric field,the oxidation rate of MgSO₃can reach to 0.1205 mmol·L^-1·s^-1 when the current density was66.7m A·cm^-2.In addition,the best p H was 8.0 by testing the oxidation rate of MgSO₃ at different p H.The reaction kinetics was studied by adjusting different conditions.The reaction order respect to the amount of catalyst and the amount of MgSO₃ was 0.46 and 0,respectively.The apparent activation energy of the reaction was 16.73 k J/mol.Combined with the kinetic model,it was determined that the control step was the external diffusion of oxygen.The reaction mechanism was deduced by free radical quenching experiment and XRD,SEM,TEM,HRTEM,XPS,EPR and CV characterization methods.Co²⁺was proved to be the main active substance in Co Fe₂O₄/MCM-41.And the major free radicals in reaction solution were·O₂^-and·SO₅^-.During the reaction,dissolved oxygen was activated by Co²⁺to generate·O₂^-,which further generate·SO₅^-and then accelerated the oxidation of MgSO₃.Electric field played a role in promoting the regeneration of Co²⁺,which not only improved the catalytic activity,but also enhanced the cycle stability of the catalyst.The conductive catalyst M/N-C and M₁-M₂/N-C were prepared by pyrolysis and used as particle electrodes to construct a three-dimensional electrode system.Co/N-C SAC was proved to be the best single-atom catalyst,the catalytic activity of which is 0.1120 mmol·L^-1·s^-1.In addition,it was found that Co was the active substance in the catalyst.The activity of catalyst gradually increased with the increase of Pd,and Co₂Pd₁/N-C SAC was the best catalyst with a catalytic activity of 0.1742 mmol·L^-1·s^-1.It was proved that metals in Co₂Pd₁/N-C SAC had a single atom distribution.With the addition of Pd,the single-atom state is broken,resulting in a decrease in catalytic activity.It was shown that N doping was of great significance to the improvement of catalyst activity.A certain interaction between N and metal was proved by XPS,which was conducive to the formation of single-atom sites and the stability of catalyst performance.The low metal loading and the metal-support interaction in Co₂Pd₁/N-C SAC ensured its excellent cycle stability.After ten cycles,the catalytic performance of Co₂Pd₁/N-C SAC only dropped by 6.74%.Based on the free radical quenching experiments,the species of free radicals in Co/N-C SAC and Co₂Pd₁/NC system were compared respectively.The results showed that the major free radical in Co/N-C SAC system was·SO₅^-.But·SO₅^-,·OH^-and·O₂^-all existed in Co₂Pd₁/NC system.The oxidation rate of MgSO₃reached a higher level under the combined action of these free radicals in Co₂Pd₁/NC system.