The Development Of MnO_x-CeO₂ Catalysts Towards Soot Combustion And The Study Of Oxygen Species Evolution And Electron Transfer

Particulate matter,including carbon black,is a vital pollutant that is harmful to the ecological environment and human health.It is a multisource pollutant with high emission and a difficult task of governance.However,the technical support for carbon black treatment is still under development.Catalytic combustion is an advanced technology for carbon black elimination,which depends on the performance of the catalysts.Therefore,the enhancement of catalytic technology is crucial to efficiency improvement and cost reduction.This article selected the hydrothermal method as the synthesis method of Mn O_x-Ce O₂.The selection was based on the principles of environment-friendly,excellent activity,and application prospects.Then we used 3D geometric models and several characteristic methods to investigate the effects of morphology on the utilization of active oxygen species,and the stimulation effect of active oxygen species on the catalytic process.These findings could be foundations of the quantitative observation on the evolution of active oxygen species,and the further improvement of catalytic performance in the future.Firstly,we selected the synthesis method of catalyst.We synthesized seven types of catalysts by seven different methods and in the same Mn-Ce atomic ratio.The sample synthesized by the hydrothermal method was the best in catalytic activity.Then,we analyzed the structure-function relationship in five aspects,including specific surface area,crystalline structure,morphology,chemical properties?oxygen parameters and element valance state?.We found that the carbon black catalytic combustion mainly affected by two factors:the improvement of contact efficiency caused by the change of morphology,and the enhancement of oxygen parameters and activation ability of oxygen species caused by the change of synthesis method and the concentration increase of low valance Mn ions.Secondly,we conducted research on the effect of morphology on the catalysis process.We synthesized Mn O_x-Ce O₂ catalysts in two different morphologies?nanoparticle and nanorod?with different hydrothermal temperatures and the same Mn content.The nanoparticle one was better in catalytic activity(T₁₀:314°C,T₅₀:346°C,T₉₀:383°C).Then,we introduced 3D geometric models to analyze the contact probabilities of two catalysts and realized that the nanoparticle catalyst was better in contact probability?9.549>7.539?.Furthermore,we conducted In-situ UV-Raman experiments to prove that the nanoparticle catalyst performed better in the utilization of active oxygen species in the catalysis process.These findings revealed that morphology and the utilization of active oxygen species were the important factors affecting the catalytic activity.Thirdly,we studied the effect of the active oxygen species on the catalysis process.We synthesized a series of catalysts with several Mn-Ce atomic ratios and the same morphology and found the one whose ratio was 7:3 performed best in catalytic activity.The advance on the activity should be attributed to the better formation of solid solution and more generation of low valance Mn and Ce species because they were beneficial to the improvement of the concentration of surface oxygen vacancies and active oxygen species.More than that,we conducted a Pearson correlation analysis between the two concentrations,which were significantly positively correlated.These findings were able to be the research basis for further research on the quantitative observation of active oxygen species.