Catalytic Performance Of Ionic Liquids Functionalized Layered Mineral Materials For Synthesis Of Lactones

In-depth understanding with concepts of"sustainable development"and"green chemistry",safe and efficient catalysts for CO₂cycloaddition and Baeyer-Villiger oxidation are essential in the synthesis of lactones chemicals.The heterogeneous catalyst has been developed to overcome the traditional synthesis reaction among using toxic solvents,tedious preparation of catalysts,and difficulty in recycling.The clay mineral is an excellent support with plentiful storage,abundant silicon/aluminum hydroxyl group on the surface,and adjustable pore structure and specific surface area.Considering the requirements of catalytic performances and the possible binding sites between catalytic molecules and mineral materials,this thesis was devoted to obtain more active sites via thermal and acid treatment on the surface of fibrous palygorskite,tubular halloysite,and sheet ball clay,which was benefit for the selective loading of catalytic molecules.The prepared catalysts of functionalized layered mineral materials were investigated the performance and mechanism for synthesis of lactones,and the interaction between clays and molecules was revealed.The problems were solved in separating products from catalysts,catalyst loss and reusability,broadening the application scope of clay minerals,and to promote the application of clay-supported catalysts.The main research contents and results are as follows:1.The one-step immobilization of tetramethylguanidine（TMG）on palygorskite（Pal）with nanofiber structure,adjustable surface area and pore structure,TMG@P-Pal was investigated to catalyze the cycloaddition of CO₂.More hydroxyl sites and oxygen vacancies were produced in palygorskite via thermal and acid treatment,which was benefit for loading of TMG stably.In combination with zinc halides,TMG@P-Pal showed the superior catalytic performance,the conversion reached 99%,and the selectivity was>99%.The kinetic model indicated that the reaction was first-order kinetics,and the apparent activation energy(E_a=76.93 k J·mol^-1)was obtained.Density functional theory（DFT）calculation confirmed that the catalytic activity of zinc halides in the CO₂ cycloaddition was Zn Br₂>Zn Cl₂>Zn I₂,especially,TMG molecule and Pal support were using HN···HO-as the binding site,and both were observed to activate CO₂.2.To further improve the reusability and operability of catalyst,Zn Br₂/IL@P-Hal was prepared via one-step encapsulation of Lewis acid ionic liquid（Zn Br₂/IL）in roll-up tubular halloysite（Hal）for CO₂ conversion.The lumen tubes of Hal were enlarged by acid treatment,which was benefit for the loading of ionic liquid and the storage/conversion of CO₂ in the reaction.Zn Br₂/IL@P-Hal showed good CO₂adsorption capacity of 6.43 cm³·g^-1,and superior catalytic performance（conversion98%）.The composite displayed the superior recyclability with a slight decrease（7.0%）of conversion after five cycles.Binding sites of-Br···HO-or-N···HO-between Zn Br₂/IL and Hal,and the overall pathway of CO₂ cycloaddition were theoretically confirmed via DFT calculation.3.To avoid environmental hazard for metal leaching of catalyst,IL@P-BC catalyst was prepared via one-step silane grafting the metal-free ionic liquid（IL）onto ball clay（BC）with sheet structure for CO₂ cycloaddition.More oxygen vacancies and hydroxyl sites on the surface of BC were obtained via thermal and acid treatment,which was benefit for the stable loading of metal-free IL.The catalyst IL@P-BC displayed the good catalytic performance,the yield reached 94%,and the selectivity was>99%.The catalyst also showed excellent recyclability with a slight decrease（3.0%）of yield after five cycles.The mechanism of CO₂ cycloaddition catalyzed by ball clay was revealed,and the synergistic effect between carboxyl group and bromine ion of catalyst was found.4.To further enlarge the application of halloysite nanotubes in the synthesis of lactones,Mg Al-layered double hydroxide（Mg Al-LDH）was one-step immobilized on the inner and outer surfaces of nanotubes to catalyze the Baeyer-Villiger oxidation,respectively.Compared to loading on the outer surface of halloysite（Mg Al-LDH@Hal600）,Mg Al-LDH@Hal was prevented hydration by encapsulating in halloysite lumen.When Mg Al-LDH@Hal was used as the catalyst,the conversion of cyclohexanone reached 57%,and the superior reusability with a slight decrease（1.0%）of conversion after five cycles,whereas Mg Al-LDH@Hal600 displayed the worse recyclability with a slight decrease（10.0%）of conversion after five cycles.These computational and experimental results indicated that the depletion electron of Mg-sites in Mg Al-LDH@Hal,which was benefit for the activation of H₂O₂ and affording empty orbitals for Baeyer-Villiger oxidation.In conclusion,based on the different structure of layered mineral materials,this thesis was designed via thermal and acid treatment to increase the specific surface area,the number of hydroxyl（-OH）on the surface,etc.The ionic liquids with guanidino group,Lewis acid,and carboxyl group,and hydrotalcite-like materials with Br?nsted base were one-step loaded on the clay materials by hydrogen bonding,electrostatic interaction,and silanization.The excellent reaction performance and recyclability catalyzed by functionalized layered mineral materials were obtained,and the catalytic mechanisms were revealed for CO₂ cycloaddition and Baeyer-Villiger oxidation.