The Studies On The Preparation Of Mesoporous CeO₂ Nanospheres And Their Catalytic Performances Of Toluene Oxidation

Toluene is the typical highly toxic and carcinogenic volatile organic compounds（VOCs）,which poses the serious hazard to the atmospheric environment and human health.It has the characteristics of aromatic hydrocarbons and the structure of alkanes,which is often used as a model gas to evaluate the catalytic performance of catalysts.Among many catalysts,the cerium dioxide（CeO₂）material may be directly used as catalysts or catalyst supports due to their abundant surface oxygen vacancies and strong oxygen storage capacity.Due to the performance limitations of CeO₂ material,it is necessary to prepare CeO₂ material with specific properties to make them possess more excellent catalytic performance so that efficient conversion of toluene can be achieved.In this dissertation,the mesoporous CeO₂ nanosphere with controlled morphology and large specific surface area is explored as catalyst support.The effect of the catalysts on the catalytic oxidation performance of toluene are systematically investigated by varying the metal precursors,additives,and catalytic oxidation reaction conditions.In addition,the reaction mechanism during the toluene oxidation reaction is investigated using in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy.The main study contents and results are as follows:（1）The Pt-embedded mesoporous cerium dioxide hollow sphere composites（Pt-MS-CeO₂-H）were prepared by the one-pot hydrothermal method.It was found that the morphologic structure could significantly affect the catalytic oxidation performance of toluene.The Pt embedding was simpler than the conventional impregnation method.It could be determined that the embedding process of Pt nanoparticles played the key role in generating oxygen vacancies and activating surface adsorbed oxygen.The Pt-MS-CeO₂-H composites could effectively inhibit the aggregation of Pt nanoparticles,so more active sites would be involved in the catalytic reaction.Compared with 1Pt/MS-CeO₂ prepared by the impregnation method,the 1Pt-MS-CeO₂-H catalyst exhibited excellent catalytic oxidation performance of toluene,which could reach 50%toluene conversion at 151°C.The large specific surface area and abundance of active oxygen of the Pt-embedded mesoporous cerium dioxide hollow sphere catalyst were the keys to the excellent performance of toluene oxidation.（2）The mesoporous cerium dioxide nanosphere material（MS-CeO₂）was successfully prepared by hydrothermal method and used it as the support for toluene oxidation catalyst.The MnO₂-based catalysts were synthesized by the impregnation method and evaluated for the catalytic oxidation performance of toluene.The performance of toluene oxidation catalysts with different MnO₂ precursors and catalyst supports was systematically investigated.The experimental results showed that the 15MnO₂/MS-CeO₂-N catalyst with with Mn（NO₃）₂·4H₂O as the precursor and MS-CeO₂ as the support exhibited the best catalytic oxidation performance of toluene,which could reach 50%toluene conversion at 206°C.The abundant oxygen vacancy on the 15MnO₂/MS-CeO₂-N catalyst could adsorb and activate the gaseous oxygen on the catalyst surfaces more easily and quickly,which would improve the oxygen migration and storage capacity to affect the oxidation performance of toluene.（3）The MnO₂-based mesoporous cerium dioxide nanosphere catalysts（MnO₂TO_x/MS-CeO₂）doped with transition metal oxides prepared by co-impregnation method had the homogeneous mesoporous nanosphere structure.The effects of doped transition metal oxides and doping ratios on the performance of toluene oxidation catalysts were investigated.Compared with the monometallic oxide（MnO₂）-based catalysts,the Co₃O₄-doped MnO₂-based catalysts generated the large number of active sites for toluene oxidation.The10MnO₂5Co₃O₄/MS-CeO₂ catalyst exhibited excellent catalytic oxidation activity of toluene,which decreased the 50%toluene conversion by about 14°C compared with the 15MnO₂/MS-CeO₂ catalyst.In combination with the characterization analysis,it was found that the introduction of Co₃O₄ increased the oxygen species content on the surface of the MnO₂-based catalyst and promoted the formation of metal-support interactions,thus improving the catalytic oxidation activity of the catalyst for toluene.（4）The MnO₂-based mesoporous cerium dioxide nanosphere catalysts（MnO₂TiO₂/MS-CeO₂）doped with semiconductor TiO₂ were prepared by co-impregnation method and performed photothermocatalysis toluene oxidation reaction.The catalysts were studied for the oxidation reaction of toluene under photocatalytic,thermocatalytic and photothermocatalytic conditions,respectively.Compared with the photocatalytic and thermocatalytic conditions,the15MnO₂/MS-CeO₂ catalyst under the photothermocatalytic condition exhibited excellent catalytic activity,which could reach 50%toluene conversion at 130°C.Under the photothermocatalytic condition,the 5MnO₂10TiO₂/MS-CeO₂ catalyst could achieve complete toluene conversion at the reaction temperature of about 200 ^oC.The characterization analysis confirmed that doped TiO₂ could improve photothermocatalytic performance of toluene by affecting the specific surface area,oxygen vacancy,electroconductibility,and high valence species of the catalyst.