Liquid Phase Preparation Of CeO₂&Its Composites And Their Catalytic Applications

CeO₂and cerium-based catalysts,such as Au/CeO₂,MnO₂/CeO₂,Pt/CeO₂can be used in many catalytic reactions（CO oxidation,NO reduction,Methylene blue solution degradation,Imine catalysis,VOC oxidation,etc）.CeO₂materials synthesized by microwave-assisted have high quality and different morphologies bearing more defects and more active centers.Thus,microwave-synthesized nanomaterials have broad application prospects in catalysis due to their special properties.In this paper,a series of studies about cerium dioxide and cerium-based composites are synthesized.The main results are as follows:（1）A series of CeO₂samples with nanoflake structure are synthesized with or without application of pressure（P）by the aid of a combination of microwave（MW）,ultraviolet（UV）and ultrasonic（US）.These CeO₂structure are systematically characterized by XRD,SEM,HRTEM,N₂adsorption,XPS,Raman and H₂-TPR.Characterization of microwave assisting facilitates the formation of more surface Ce³⁺/(Ce³⁺+Ce⁴⁺)ratios and surface oxygen vacancies.CO oxidation and imine conversion results indicate that MW+P is the best condition for producing high quality CeO₂nanosheet catalysts with large defects on the surface,and its catalytic activity is much better than that of CeO₂prepared by solvothermal method.（2）Different morphologies of CeO₂are synthesized by different microwave assisted methods by using acetic acid as mineralizer.Microwave（M）,microwave combine with ultraviolet（MV）produce CeO₂with particle morphologies,while microwave combine with pressure（MP）yielded CeO₂of nano-fusiform.CeO₂nanospheres were prepared by microwave plus ultrasonic（MS）.Microwave plus ultrasonic（MS）samples have the lowest imine reaction rate(1.54 mmol?g^-1?h^-1).The MP sample has the highest Ce³⁺ratio（26.4%）,the lowest OH*/CO₃^2-ratio and the highest surface area,resulting in an optimum imine reaction rate of 14.13 mmol?g^-1?h^-1.Based on this,different sizes of fusiform CeO₂are synthesized by microwave ultrasonic（MS）modification by changing the amount of deionized water.The sample with 1 m L H₂O has the highest Ce³⁺ratio（28.1%）,and the imine reaction rate is 5.48 mmol?g^-1?h^-1.The sample with 5 m L H₂O,which imine reaction rate is 1.71 mmol?g^-1?h^-1.In conclusion,the properties of CeO₂can be adjusted by adding acetic acid as mineralizer and changing water amount.（3）CeO₂composites are synthesized basing on the preparation of pure CeO₂.Different molar ratios（1:2,1:1,2:1）of Bi₂O₃-CeO₂composites are prepared by microwave-aided solvothermal method.The overall catalytic activity of the composite is not high,but there is a large difference in adsorption.The imine reaction rate of Bi:Ce=1:2 is 0.26 mmol?g^-1?h^-1.Meanwhile,Fe₃O₄-CeO₂with different molar ratios（1:1,1:2,1:4）are also prepared.The Fe₃O₄:CeO₂=1:4 sample has the best adsorption performance to methylene blue among the composites at 3.5 h.Fe₃O₄-CeO₂composite catalysts are far superior to Bi₂O₃-CeO₂composite catalysts（Degredation of MB）.The imine reaction rate of Fe₃O₄:CeO₂=1:4 is 0.25 mmol?g^-1?h^-1.