Construction Of Cerium Based Non-Noble Metal Catalysts And Application In Oxidative Coupling Reaction

CeO₂ based catalysts have many advantages,such as rich oxygen vacancies,reversible Ce⁴⁺/Ce³⁺redox pairs,acid base amphoteric properties,and excellent light absorption properties.It is of great significance to broaden the application scope of CeO₂ based catalysts and further study their catalytic mechanism,especially to clarify the active site of CeO₂.Based on this,firstly,this article aims to solve the problem of using additives and explosive H₂O₂ in the catalytic oxidation coupling of 2-aminophenol to 2-amino-3H-phenoxazine-3-one（APXO）.A cerium doped manganese oxide catalyst was prepared,and the introduction of cerium significantly improved the oxidation ability,oxygen activation ability,and alkalinity of the catalyst,achieving green synthesis of APXO using air oxygen as the oxidant.Secondly,CdS/CeO₂heterojunction photocatalyst were prepared to deal with the disadvantages such as harsh reaction conditions,the need of additives,and the difficulty of achieving atomic economy in the non-noble metals catalyzed oxidative coupling of alcohols and amines.Ce⁴⁺/Ce³⁺redox couple was used to improve the separation efficiency of photogenerated electron-hole,and atom-economic photocatalytic synthesis of imines without additives was successfully achieved under visible light at room temperature.The main contents are as follows:1.The cerium doped manganese oxide catalyst was prepared by a simple coprecipitation method,which realized the green synthesis of APXO and showed excellent catalytic performance.This is the first non-noble metal heterogeneous catalysis system that only uses air oxygen as oxidant,and does not need any additional additives.After the introduction of cerium,the oxidation ability,oxygen activation ability and alkalinity of the catalyst were greatly improved,thus enhancing the catalytic activity of the catalyst.It is worth noting that we found that 2-amino-1,9-dimethyl-3H-phenoxazine-3-one exhibits fluorescence properties and can be used as a fluorescent molecular probe for various detection and labeling studies.The good substrate applicability and low metal leaching rate of the catalytic system further illustrate the stability of the heterogeneous catalyst.This method provides an environmentally friendly and economic strategy for industrial synthesis of APXO.2.The employ of stoichiometric alcohols and amines for imines synthesis under mild and green reaction conditions is still a challenge in the field.In this work,based on our research foundation in the thermocatalytic synthesis of imines over ceria,CdS/CeO₂ heterojunction photocatalyst was constructed and successfully realized atom-economic synthesis of imines under visible-light without additives at room temperature.Mechanistic experiments and corresponding characterizations indicated that the CdS/CeO₂ heterojunction can improve photogenerated carriers separation efficiency,which can be further enhanced by the Ce⁴⁺/Ce³⁺redox pair through rapidly combining photogenerated e^-.The in-situ reduced Ce³⁺can better activate O₂ to form Ce-O-O·,together with h⁺efficiently accelerate alcohol oxidation,which is the rate-determined step for the synthesis of imines via oxidative coupling reaction of alcohols and amines.In addition,our photocatalyst exhibited fairly decent reusability and substrate universality.This work solves problems of using base additives and non-stoichiometric alcohols and amines in the reported photocatalytic systems,providing innovative insight for designing CeO₂ based oxidative coupling photocatalysts.