Sol-Gel Entrapped Metal-Acetylacetonate Complexes And Their Catalytic Performance For Epoxidation Of Alkene

Epoxidation play an important role in the organic synthesis since epoxides are an important organic intermediates and raw materials.In the last years,the researches on epoxidation have made big progress.A lot of new methods were developed.With environmental protection being taken into consideration increasingly,chemists are more and more interested in green chemical technololgy.Therefore, epoxidation of alkenes with molecular oxygen catalyzed by heterogenized transition metal complexes has been the subject of intersive research over the past years.However, some critical problem,such as catalyst leakage and difficult to recycle, are still not complete solved. Fortunately,sol-gel method can overcome the above difficulties. Generally,sol-gel technololy is much better than the traditional methods employed in heterogenizing the homogeneous catalyst because the sol-gel matrixes are stable to heat,inert and protectable to the entrapped molecules.They also have the porous character and high surface areas.In the thesis,several metal-acetylacetonate complexes were encapsulated in inorganic oxide matrixes.By using sol-gel method,their catalysis on expoxidation of alkenes was investigated and the entrapping conditions which influence the conversion of alkenes were obtained.First, The xerogel catalysts in SiO2 matrixes were characterized by FT-IR spectroscopy^ TG-DTA> XPS. It was found that metal complexes entrapped in the matrixes and the thermostability of the complexes is enhanced.lt was also found that the other properities of the complexes are not changed.Second, Ni(acac)2-2H2O-SiO2 was found to be the catalyst with high activity among all the metal-acetylacetonate complexes we studied. L32(46} orthogonal layout was arranged to optimize the experiments by using Ni(acac)2-2H2O-SiO2 as the catalyst.The optimal operating conditions were obtained.Here is the optimal conditions: pH=3,R(H2O/TEOS)=6,drying temperature is 80癈.The volumes of isobutyraldehyde and solvent(CH2Cl2) were 10ml and120ml, respectively.Reaction time is 8h, under the optimal conditions,the yield of 1,2-epoxycyclohexane (ECH) was 98.01%.The encapsulated homogenous catalyst can run 3 times without the lose of activity .Compared with the corresponding homogenous catalyst, it has advantages of recylcling usage and having no corrosion to facilities. Furthermore,the catalysis on arerobic epoxidation of cyclohexene of different encapsulated metal complexes was compared with that of Ni(acac)2-2H2O-SiO2. The yield of 1,2-epoxycyclohexane are 41.15%> 70.57% with Fe(acac)3-SiC>2 and Co(acac)2'2H2O-SiO2 as catalysts,respectively.Third, Ni(acac)2'2H2O were encapsulated in A^Oa and TiC>2 matrixes too. It was found not only the pH value but the molar ratio of H2O to Al(OPr)3 has effect on the surface areas. When Al(OPr)3 was used as the precusor.For Ti(OC4Hg)4,because it is prone to hydrolysis, the sol-gel process was influences by the quantity of water ^ ethanol and acetic acid .The gelation time increase of water, ethanol and acetic acid. Both the surface areas and pore diameters of the xerogel catalysts are too small. When use SiC^ TiO2 and A^Os as matrixes to encapsulate Ni(acac)2-2H2O, Ni(acac)2-2H2O-SiO2 is the best and with high catalytic activity. But the catalytic activities of Ni(acac)2'2H2O-Ti02 and Ni(acac)2-2H2O- A12O3 are very bad.Finally, the catalysis of the encapsulated catalysts was studied with styrene and octylene as substrates.The catalytic activity order is same as that with cyclohexene.lt was also found that cyclohexene is the easiest and octylene is the poorest to be epoxidized among the three substrates.