Construction Of Efficient Catalytic Materials Based On Hydrotalcite-like Compounds And Their Catalytic Performance In The Oxidation Of Aromatic Side Chains

The selective oxidation of aromatic side chains has been a focus and a challenge in chemical industry,playing a very important role in organic synthesis,fine chemicals and pharmaceutical intermediates.Traditionally,the oxidation of aromatic side chains has been achieved using strong oxidants such as potassium permanganate,but with poor product selectivity,environmental pollution and high cost.With the development of catalytic oxidation technology,the efficient catalytic oxidation of aromatic side chains using green methods has become a popular research topic.This thesis reviews the research progress of catalysts for aromatic side chain oxidation,combining the possible mechanisms of different aromatic side chain oxidation and the structure,physical and chemical properties of hydrotalcite-like compounds,and designs and synthesizes a series of novel hydrotalcite-like catalytic materials to study their performance in catalytic aromatic side chain oxidation reactions.（1）The oxidation of C-H bonds of aryl alkanes is a crucial reaction in organic synthesis because the products of this reaction,aromatic ketones,are important organic chemical raw materials.By tuning the structure and properties of catalytic materials by reduction methods,Mg Fe-LDH（R）with enhanced redox activity and oxygen activation ability were synthesized.These materials were then characterized by XRD,XPS,HRTEM and N₂ adsorption/desorption methods to analyze their crystal structure,metal ion valence states,and surface properties.The performance of Mg Fe-LDH（R）in the oxidation of aryl alkanes was then investigated,which showed that it has excellent catalytic activity in the oxidation of diarylmethane with O₂,as well as good stability and reusability.In addition,the substrate suitability of the catalyst for other aryl alkane compounds was investigated under optimal reaction conditions.Subsequently,a systematic kinetic study was performed,which revealed that the number of oxygen vacancies in the structure of Mg Fe-LDH（R）was significantly higher than that of unreduced Mg Fe-LDH,thereby improving its adsorption and activation capacity for oxygen.Furthermore,the main reactive oxygen species of the system were identified as superoxide radicals and singlet oxygen.Finally,based on the kinetic study and comparative experimental results,reaction pathways for Mg Fe-LDH（R）-catalyzed oxidation of arylalkane compounds with O₂ were postulated.（2）Acetophenone is an essential chemical raw material,and the selective oxidation of ethylbenzene to acetophenone is of great practical importance.For this purpose,a series of Cu-based hydrotalcite catalysts were designed and prepared based on the characteristics of the O₂/NHPI（N-hydroxyphthalimide）oxidation process of ethylbenzene.By XRD,FT-IR,ICP and N₂ adsorption/desorption,the crystal structure,elemental composition and surface properties of Cu Mg Al-LDH were analyzed;and its catalytic performance in the O₂/NHPI oxidation of ethylbenzene system was also investigated.The results showed that Cu Mg Al-LDH exhibited good catalytic activity,stability and reusability in the reaction,as well as good substrate suitability.Comparative experiments revealed that the surface basicity of hydrotalcites was advantageous for improving the catalytic oxidation activity of the catalyst,resulting in high selectivity of acetophenone.In addition,the oxidation of 1-phenylethanol was found to be crucial for the high selectivity of acetophenone.Consequently,Cu Mg Al-LDH could improve both the catalytic activity and the oxidation of the intermediate 1-phenylethanol to acetophenone,thereby increasing the selectivity of acetophenone.（3）The epoxidation of styrene is typically carried out using peroxyacetic acid.The disadvantages of this method include poor operability and low selectivity in the formation of reaction products.So it is highly desirable to develop heterogeneous catalytic styrene epoxidation using oxygen as the oxidant.To this end,a series of hydrotalcite-like materials were designed and prepared to investigate their catalytic performance in the oxidation of olefins（O₂/IPA system）.It was found that the Co-based hydrotalcite had high catalytic activity and good substrate suitability.The effects of its crystal structure and surface properties on the catalytic activity of styrene epoxidation were also investigated based on the results of XRD,FT-IR,SEM and Hammett experiments.The mechanism study showed that the basicity of the hydrotalcite could inhibit the formation of the by-product,benzaldehyde,thereby improving the selectivity of ethylene oxide.In this catalytic system,two pathways may exist for the generation of epoxide,involving two intermediates,peroxy acid and peroxy radical,respectively.（4）The oxidative decomposition of aromatic 1,2-diols is an essential reaction in organic synthesis and the oxidative depolymerization of lignocelluloses.Homogeneous catalytic systems based on metal complexes present the problem of difficult catalyst recovery and product separation,requiring additional alkali promoters in heterogenous systems.Ni Mg Mn hydrotalcite containing Mn³⁺and Mg have been synthesized and endowed with high oxidative properties and surface basicity,facilitating the efficient oxidative decomposition of 1,2-diols.The catalysts were characterized by XRD,BET,SEM,FT-IR,TG and XPS and their performance in the model reaction was investigated.Ni₂Mg₂Mn-LDO（350）,calcined at 350℃,was found to be the best catalyst,which is mainly related to the Mn³⁺species,as well as its strong surface basicity,which facilitates the electron and proton transfer processes in the hydroxyl structure.Ni₂Mg₂Mn-LDO（350）has superior structural stability and catalytic performance,along with good substrate suitability in the oxidative decomposition of 1,2-diols.Through a series of control and kinetic experiments,combined with characterization analysis,it was proposed that the Ni₂Mg₂Mn-LDO（350）-catalyzed oxidative decomposition of 1,2-diols undergo a double electron transfer mechanism.