Oxidation Kinetics Of Magnesium Sulfite Catalyzed By Mesoporous Materials Supported Transition Metals

Sulfite oxidation is a key step in the wet flue gas desulfurization process.The heterogeneous catalyst prepared by mesoporous materials loaded with transition metal can effectively control the oxidation rate of sulfite.Ordered mesoporous molecular sieves with high specific surface area and high porosity,highly ordered and well-developed pore structure;pore size is centralized and easy to control,through post-modification can show different structures,composition and properties.It is expected to show excellent catalytic performance in the sulfite oxidation reaction control.In this paper,MCM-48 cobalt-based heterogeneous catalyst were prepared by hydrothermal synthesis using ethyl orthosilicate as silicon source,cobalt nitrate hexahydrate as cobalt source and cetyltrimethylammonium bromide as template.The prepared Co-MCM-48 catalyst was characterized by physicochemical properties.The specific surface area,pore volume and pore size distribution of cobalt-based MCM-48 were obtained by BET.The morphology of catalysts,the distribution of each component and the dispersion characteristics of active cobalt were investigated by SEM and MAPPING.The influence of cobalt doping on the morphology and morphology of the catalysts was investigated.TEM and EDS analysis of the internal structure of the catalyst as well as the composition and content of local elements;XRD small angle chart that when the cobalt-silicon ratio> 5:95,the structure of MCM-48 will be destroyed,and XRD wide-angle pattern analysis confirmed The high dispersibility and low crystallinity of cobalt;the existence form and content of cobalt in the catalyst are obtained by XPS spectrum.The effect of cobalt intercalation on the performance of MCM-48 catalyst was studied by kinetics of sulfite oxidation.The optimal ratio of Co:Si=5:95.On this basis,the macroscopic reaction kinetics of Co-MCM-48 catalyst for the oxidation of magnesium sulfite was studied.The effects of catalyst concentration,partial pressure of oxygen,p H and temperature on the oxidation rate and the mechanism of action were investigated.The number of fractionation of oxygen partial pressure is 0.46.The apparent activation energy was 13.1 KJ·mol-1,confirming that the total oxidation of magnesium sulfite was controlled by oxygen diffusion.Through comparison,it is found that the activity and stability of catalysts prepared by hydrothermal synthesis method are significantly higher than those of impregnation method.Combined with BET,SEM-MAPPING,TEM,XRD and XPS,the reasons are as follows:(1)Traditional impregnation method,the active component and the carrier is only a combination of physical form,that is,cobalt oxide are attached to the MCM-48 surface or pore,during the reaction due to soaking and collision,active cobalt prone to fall off.In hydrothermal synthesis method,the active cobalt and carrier organic fusion,the combination of both greatly enhanced,so as to avoid the loss of the active components of cobalt.(2)In the process of preparation by impregnation method,agglomeration of the catalytic components tends to occur.In the hydrothermal synthesis method,the active cobalt is uniformly dispersed in the MCM-48,the active sites are significantly increased,and the catalytic performance is greatly enhanced.