Synthesis And Catalytic Performance Of (salen)Sn Compounds And Sn-NaY Catalysts Prepared By Isomorphous Substitution For Baeyer-Villiger Oxidation Of Cyclohexanone

ε-Caprolactone is an very important organic intermediate in synthesizing many chemical products,which has an extremely wide range of applications.At present,Baeyer-Villiger oxidation of cyclohexanone is the most effective and economic method for the production of ε-caprolactone.Industrial oxidants,i.e.peroxide organic acids entail by-products,have a poor atomic economy,and are potentially explosive.The advantages of hydrogen peroxide as an oxidant are its ease of use,commercially available,the large amount of active oxygen and being environmentally friendly,producing water only as by-product.From the atomic economy and environmentally friendly point of view,the replacement of the peroxy acids by H₂O₂ is necessary.However,H₂O₂ is the weakest oxidation compared to a wide range of peroxides and peroxy acids,not enough to activate carbonyl groups in ketones Therefore,development of efficient catalysts becomes the key technology of preparing ε-carprolactone through the Baeyer-Villiger oxidation of cyclohexanone.At the first part of this thesis,（salen）SnCl₂ and（salen）Sn（Ⅱ）compounds are synthesized by the direct reaction between the salenH₂ ligend with tin sources SnCl₄ and SnCl₂·2H₂O,separately.The detailed characterizations of the compounds are determined with FT-IR,UV-vis and ICP-AES.The relationship between the addition of trimethylamine during the systhesis process and catalytic performances and the stability of the compounds are discussed.The results show that the addition of trimethylamine is necessary to remove the HCl generated fom the coordination process,which would react with cyclohexanone,produing 2-cholocyclohexanone as by-product.Lewis acidity of the（salen）Sn compounds is quite useful in the Baeyer-Villiger oxidation of cyclohexanone.The conversion of cyclohexanone is 25% and the selectivity of ε-caprolactone is 50% with the（salen）Sn（Ⅱ）compound as the catalyst.The Cl atoms leached from（salen）SnCl₂ would react with cyclohexanone,leading the a lower selectivity.These compounds are sensitive in solution and tend to decompose on the presence of H₂ O and H₂O₂.As a result,the catalytic performances of the recycled compounds are distinctly worse than those of the fresh catalysts.This thesis mainly studies the post-synthesis of Sn-containing NaY zeolite catalysts by isomorphous substitution.The preparation of the catalysts could be divided into two steps: hydrothermal dealumination of NaY zeolite precursor and post-incorporation of Sn⁴⁺ species.Post-synthesis methods are employed by introducing the Sn ions into the defects in the pretreated zeolite framework by impregnation or CVD methods,which are generated by the removal of framework heteroatoms,such as Al atoms.Firstly,the molecular sieve catalysts of Sn-NaY are prepared by impregnation method using dealuminated NaY as support and SnCl₄·5H₂O as tin source.The influence of dealumination pretreatment and calcination on the structure and active sites amount of Sn-NaY（DeAl）are discussed and the samples are characterized by FT-IR,UV-vis,XRD,N₂ physical adsorption,ICP-AES,NH3-TPD,pyridine adsorption IR and laser Raman.The results show that the dealumination pretreatment contributes to the well-maintained zeolite structure of NaY molecular sieve during the preparation process.Calcination is beneficial for incorporation of tin into the zeolite framework as tetrahedrally coordinated active Sn through bonding with silanols in the framework.Calcination in air atmosphere is responsible for the formation of SnO₂.The catalytic performances of Sn-NaY in Baeyer-Villiger oxidation of cyclohexanone are investigated.Catalytic activity results show that the catalyst through isomorphous substitution of dealuminated zeolites calcinated in N₂ atmosphere shows the best catalytic performance,the conversion of cyclohexanone and the selectivity of ε-caprolactone reach 44% and 62%,respectively.At last,the molecular sieve catalyst of Sn/NaY（DeAl）is prepared by CVD method using anhydrous SnCl₄ as tin source.In consideration of the possible formation of extraframework SnO₂ species owing to the high temperature in the synthesis process,the product is treated with 0.1mol/L HCl with the purpose to remove the SnO₂ by acid treatment after the preparation.The detailed characterizations of the Sn/NaY（De Al）before and after acid pickling are determined with FT-IR,UV-vis,XRD,N₂ physical adsorption,SEM,ICP-AES,XPS,NH3-TPD,Py-FT-IR and 29 Si MAS NMR.The results show that the bulk SnO₂ species in Sn/NaY（DeAl）can’t be removed by acid treatment,which also lead to the removal of part of tetrahedrally coordinated Sn,while the small extra-framework SnO₂ species can be washed out from the zeolites.The leached Sn atoms as Br?nsted acid and SnO₂ are responsible for the decomposition of H₂O₂ and the hydrolysis of ε-caprolactone,which have adverse effects on the reactions.In addition,Sn/NaY（DeAl）displays a better catalytic performance on the Baeyer-Villiger oxidation of cyclohexanone even though the Sn content is lower（1.71wt%）,the conversion of cyclohexanone and the selectivity of ε-caprolactone reach 48% and 65%,respectively.