Magnetic Nano-Size Solid Acid Materials: Synthesis, Characterization And Their Catalytic Performance

Nowadays in industry, homogenous acid catalysts including corrosive protic acids, Lewis acids are widely applied in the large-scale synthesis of industrial bulk chemicals as well as the production of fine chemicals. However, it is urgent to replacing highly corrosive, hazardous and polluting acid catalysts with eco-friendly and renewable solid acid catalysts for meeting green chemistry demands, which may be a challenge of green chemistry and green engineering. Recently, the facile recovery and reuse of homogeneous catalysts by covalent tethering to heterogeneous support are extensively investigated, which become an important field of catalytic research.Magnetic nano-solid acid catalyst as magnetic response characteristics of solid acid catalyst, not only has excellent properties of nanomaterials and different excellent catalytic activity than conventional acid catalyst, but also has the magnetic separation characteristics, which can strengthen the chemistry and separation process, also can simplify the whole process in chemical production process, therefore, magnetic nano-solid acid catalyst will be wide application prospects in the chemical acid catalysis. However, since the development of magnetic nano solid acid catalyst is still in the stage of experimental study and their applied field is relatively limited, therefore, some problems still needs further study and magnetic solid acid catalyst were few reported at home and abroad.1. The facile preparation procedure of a magnetic nano-solid acid catalyst is described, which includes grafting an ionic liquid onto Fe3O4 nanoparticles, followed by the sulfonation of phenyl groups in the ionic liquid. And the catalytic performance of this material is studied systematically for the reaction of acetalization and ketalization:the influence of the reaction conditions is studied systematically including the quality of catalyst, reactant ratio, the amount of an agent entraining water, and based on above study, the reaction conditions are optimized. Under the optimized reaction conditions, for the the reaction of acetalization and ketalization using glycol and carbonyl compounds, the yield of the corresponding products obtained are around 95%. After the catalyst reaction, the catalysts is readily separated by use of additional magnetic field and it is reusable without any significant decrease in catalytic activity, therefore, it is a simple and feasible approach provided for the catalyst separation and the reuse of catalyst for meeting the basic requirements of green chemistry.2. A new magnetic nano-solid acid was prepared by a facile process of sulfonic acid functionalized carbon-coated magnetic Fe3O4/FeO nanoparticles. And the catalytic performance of this material is studied systematically for the reaction of acetalization and ketalization:the influence of the reaction conditions is studied systematically including the quality of catalyst, reactant ratio, the amount of an agent entraining water, and based on above study, the reaction conditions are optimized. Under the optimized experimental conditions, it was found that the new magnetic nano-solid acid is an efficient, magnetically separable and recyclable catalyst for the acetalization of carbonyl compounds with a higher yield, compared with other heterogeneous catalysts.3. Synthesis of a novel magnetic heteropolyacids/cross-linked chitosan/Fe3O4 nano sized solid acids (HSiW-CS-Fe3O4) was carried out by immobilization of Keggin-type 12-silicotungstic acid (HSiW) in the three-dimensional network coating of cross-linked chitosan (CS) coated on magnetic FesO4 nanoparticles for the acetalization. This hybrid type nano sized solid acid catalyst exhibited high activity with a yield of 99% for the synthesis of acetal via ethylene glycol with benzaldehyde under the optimized reaction conditions. Furthermore, the physicochemical features of the recovered catalyst after reaction were not dramatically changed, and it was found that the catalyst is reused five times without any significantly decrease in catalytic activity. Therefore, the results manifested that the loss of HSiW can be greatly overcome to some extent and the processes are suitable for large-scale industrial preparation of acetals and ketals.