Synthesis Of Magnetically Nano Organic-inorganic Hybrid Materiats For Styrene Epoxidation

Olefin epoxidation has attained extensive consideration because the epoxideproduct is versatile and indispensable intermediate in the manufacture of both finechemicals and pharmaceuticals. During the past decade, considerable effort has beenpaid to develop inexpensive, recyclable, high active and selective metal-basedcatalysts to realize large-scale production. Despite homogenous transition metalcomplexes (e.g. metal-salen complexes, and chiral metalloporphyrins) exhibit highcatalytic activity and selectivity in the epoxidation reactions. Many inherentdrawbacks hamper their industrial application:(a) difficulty in the catalystregeneration and product separation,(b) deactivation of the catalysts by formation ofdimeric peroxo-and μ-oxo species and (c) increasing the negative influence onenvironment and reducing industrial interest. With the rapid development of catalystseparation and preparation technology, encapsulation various transition metal Schiffcomplexes on insoluble solid supports to realize heterogenization of homogeneouscatalysis has become a universal means to solve the above questions. Periodicallymesoporous silica materials, such as SBA-15, MCM-41, MCM-48and hexagonalmesoporous silica (HMS), have been widely used as catalyst support. Afterimmobilization of transition metal complexes by post-grafting method, the resultedorganic-inorganic hybrid materials are efficient in alkene epoxidation. Therefore,development of heterogeneous catalytic system that can operate with eco-friendlyoxidants has drawn tremendous interest. The main contributions are as follows:1、Different transition metal (Fe2+, Co2+, Ni2+, Cu2+or VO2+) Schiff complexesimmobilized onto three-dimensional mesoporous silica KIT-6for the epoxidationof styreneHighly ordered three-dimensional Ia3d mesoporous silica KIT-6wasfunctionalized with3-aminopropyltriethoxysilane (3-APTES), following bypost-grafting of various transition metal (Fe2+, Co2+, Ni2+, Cu2+or VO2+) Schiffcomplexes onto amino-functionalized KIT-6. The surface functionalized materials were analyzed by a series of characterization techniques such as XRD, XPS, N2adsorption-desorption, FT-IR，ICP, SEM and TGA. The characterization resultsdemonstrated structural intact of the mesoporous hosts throughout the graftingprocedures and successfully anchoring of transition metal Schiff complexes on themodified KIT-6. The obtained organic-inorganic hybrid materials were subsequentlyemployed as catalysts for the epoxidation of styrene under optimized reactionconditions. It was indicated that Cu-NH2-KIT-6showed very high substrateconversion (98.6%) and excellent epoxide selectivity (97.8%) when using tert-butylhydroperoxide (TBHP) as oxidant at80oC after6h. It was also observed that thecatalyst could be recycled three times without obvious loss in catalytic activity andselectivity.2、 Core-shell structured Fe3O4@SiO2supported cobalt(II) or copper(II)acetylacetonate complexes: magnetically recoverable nanocatalysts for aerobicepoxidation of styreneOrganic-inorganic hybrid heterogeneous nanocatalysts were successfullyfabricated via covalent anchoring cobalt(II) or copper(II) acetylacetonate complexes([Co(acac)2] or [Cu(acac)2]) onto core-shell structured Fe3O4@SiO2previouslyfunctionalized with3-aminopropyltriethoxysilane (3-APTES). Surface functionalizednanomaterials were analyzed by a series of characterization techniques such as SEM,TEM, XRD, FT-IR, XPS, ICP-AES and VSM. The catalytic performance of theprepared nanocatalysts was evaluated in the epoxidation of styrene using eco-friendlyair as oxygen source. Both of the nanocomposites Fe3O4@SiO2-NH2-Co andFe3O4@SiO2-NH2-Cu presented excellent styrene conversion (90.8%vs.86.7%) andgood epoxide selectivity (63.7%vs.51.4%), much higher than the correspondinghomogeneous counterparts. In addition, the magnetically recoverable nanocatalysts(MRNCs) can be conveniently separated and recovered from the reaction system byapplying an external magnetic field, and reused for four cycles with insignificant lossof catalytic activity. These results demonstrate that the heterogeneous nanocatalystspossess potential application from the point of green and sustainable development. 3、Epoxidation of styrene over Fe(Cr)-MIL-101metal organic frameworksMetal-organic frameworks (MOFs) are rapidly emerging class of porousorganic-inorganic hybrid materials synthesized by self-assembly of metal ions withorganic ligands. For catalysis, the most valuable preponderance of MOFs is the largeconcentration of uniform accessible metal centers and coordination unsaturation. Incomparison with other organic-inorganic hybrid heterogeneous catalysts, MOFs doesnot need cumbersome multi-step grafting procedure to achieve heterogenization ofhomogeneous catalysts. In this paper, we investigated the effect of different metal ionsin MIL-101metal organic framework on styrene epoxidation using various oxidantssuch as air, H2O2and TBHP. For aerobic epoxidation of styrene, Fe-MIL-101andCr-MIL-101presented good styrene conversion (87.2vs.65.5%) and epoxideselectivity (54.4%vs.37.7%) The styrene epoxidation activity for the differentoxidants over Fe-MIL-101was as follows: air> TBHP> H2O2, while it overCr-MIL-101showed a different trend: H2O2> air> TBHP. Moreover, the selectivityto styrene oxide for the different oxidants was similar for the two catalysts: TBHP>air> H2O2. The influence of various solvent can conclude that CH3CN might be theoptimum solvent for aerobic epoxidation styrene. Furthermore, the catalysts could bereused three times without significant loss in catalytic activity.