| With the acceleration of industrialization and urbanization,atmospheric environmental issues have become increasingly serious,especially the increasing emission of volatile organic compounds（VOCs）.Catalytic oxidation technology has a good application prospect in environmental remediation due to its advantages of no secondary pollution,low energy consumption,and high efficiency.Manganese-based materials are environmentally friendly,inexpensive,and have excellent redox properties.However,traditional manganese-based materials have some disadvantages,such as low reactivity,insufficient thermal stability,and poisoning susceptibility.Therefore,exploring the preparation of a novel manganese-based catalyst for the catalytic oxidation of VOCs with high activity,high stability,and anti-poisoning ability has a good theoretical significance and practical value.The specific research contents are as follows:（1）With MnCO3 microspheres as homologous templates,KMnO4 was used to conduct redox reactions with the MnCO3 microspheres to form porous flower-like MnO2.Then,the internal template was removed by etching with HCl to obtain a flower-like MnO2 hollow microsphere catalyst with a micro/nano hierarchical porous structure.The catalyst was characterized by scanning electron microscope（SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,H2 temperature-programmed reduction（H2-TPR）,O2temperature-programmed desorption（O2-TPD）,CO2 temperature-programmed desorption（CO2-TPD）,and pyridine-infrared（Pyridine-IR）.The catalytic performance for toluene oxidation was investigated.The structure-activity relationship and catalytic mechanism were explored.The results show that the flower-like MnO2 hollow microsphere has a large specific surface area(214 m2·g-1)and a unique cavity structure.When the space velocity is 15 000m L·g-1·h-1 and the concentration of toluene is 1000 ppm,the T90 is 237°C.After 120 h of continuous operation,its catalytic activity did not decrease significantly.High specific surface area,a large number of acid sites,and abundant oxygen vacancies are crucial to the high catalytic activity of porous flower-like MnO2 hollow microspheres.The porous flower-like MnO2 hollow microspheres have micro/nano hierarchical structure,which can not only maintain the activity advantages of the primary nano-assemblies but also overcome the defects of easy sintering,easy agglomerating,and deactivation of nano-particles,therefore,show higher activity and stability,which making them promising for the catalytic oxidation of VOCs.（2）The micro/nano porous hollow normal-reverse coexisted spinel CoxMn3-xO4 catalysts with different morphologies were prepared by adjusting the Co/Mn molar ratios to achieve the ordered self-assembled mixed carbonates as the precursors followed by non-equilibrium heat-treatment.The catalysts were characterized by XRD,SEM,XPS,H2-TPR,O2-TPD,and so on.The catalytic performance for toluene oxidation was investigated.The structure-activity relationship and catalytic mechanism were explored.The results show that CoxMn3-xO4catalysts with different morphologies exhibit different physical and chemical properties,which results in the catalysts with different oxidation-reduction capabilities,and thus exhibit different catalytic activities for toluene oxidation.Among them,Co Mn2O4 with a micro-cubic porous hollow structure shows the best catalytic performance for toluene oxidation.When the space velocity is 15 000 m L·g-1·h-1 and the concentration of toluene is 1000 ppm,the T90 is250°C.More favorable is that Co Mn2O4 exhibits excellent water vapor resistance.There is a non-significant decrease of the catalytic activity during the 100 h of operational stability experiment containing 5 vol.%water vapor.The micro-cubic porous hollow structured Co Mn2O4 with abundant oxygen vacancies as well as an optimal ratio of Co3+/Mn2+–Co2+/Mn3+coupled redox ion pairs exhibit high adsorption and activation capabilities for gaseous oxygen molecules,which makes it exhibit good low-temperature catalytic oxidation ability for toluene removal.The self-supporting porous hollow micro/nano hierarchical structure of Co Mn2O4 can not only effectively take advantage of the high activity of primary nano-particle components but also effectively avoid sintering deactivation.The porous hollow structure is also conducive to efficient mass transfer,showing long-lasting stability and excellent water vapor resistance.（3）With oleic acid as a reducing agent and morphology directing agent,nano-sheet self-assembled flower sphericalα-MnO2-F were facilely prepared by one-step reaction with KMnO4 under mild conditions at room temperature.Subsequently,a series of Ce/α-MnO2-F bimetallic oxide catalysts were prepared by doping Ce.The catalysts were characterized by XRD,SEM,XPS,H2-TPR,O2-TPD,and so on.The catalytic performance for toluene oxidation was investigated.The structure-activity relationship and catalytic mechanism were explored.The results show that Ce doping inα-MnO2-F can effectively regulate the specific surface area,asymmetric oxygen vacancy content,and oxygen storage capacity of the sample.Among them,5%Ce/α-MnO2-F shows the best catalytic activity for toluene oxidation.When the space velocity is 15 000 m L·g-1·h-1and the concentration of toluene is 1000 ppm,the T90 is203°C.The abundant asymmetric oxygen vacancies and the redox reaction betweenCe and Mn ions can effectively promote the activation of gaseous oxygen molecules and the migration of active oxygen species,which are key factors to improve the catalytic activity.5%Ce/α-MnO2-F has excellent stability.After continuous operation for 60 h,the removal efficiency of toluene is only slightly reduced by 3%.The single-layer dispersed Ce/α-MnO2-F catalyst can maximize the exposure of Ce species to the toluene reactant,thereby exhibiting the best catalytic activity,coupled with the stable nano-sheet self-assembled flower spherical structure,therefore,has both high catalytic activity and excellent stability,and has a good industrial application prospect. |
