Titanium Silicalite(TS-1):Low Cost Preparations,Modifications And Applications In Green Catalytic Oxidation Reactions

Since the first report of its synthesis in 1983 by Taramasso,titanium silicalite-1(TS-1)zeolite,with a MFI structure,has been paid significantly large attentions.This is due that TS-1,behaving as a kind of green catalyst,is capable of catalyzing the selective oxidation of many organic molecules under warm conditions(at low temperature and with diluted hydrogen peroxide as oxidant).Up till now,some oxidation processes catalytzed by TS-1,being more effective and green than conventional processes,such as,the selective oxidation of phenol to catechol and the ammoximation of cyclohexanone to cyclohexanone oxime,have achieved,to some extent,an industrial-scaled production.However,it is still far away from the industrial applications of TS-1 in much more large scale and wide field.The complexion is mainly caused by the reasons as follows.Firstly,the cost of TS-1 synthesized via conventional method is verh high;Secondly,although the cost of TS-1 synthesized via many modified methods reported in the literature could be slightly reduced,the quality of TS-1 is stll quite low,as manifested by the large crystal size,low content of framework Ti and high level of non-framework Ti,thus resulting in the low catalytic performances.In addition,the application of TS-1 is also limited by its intrinsic properties,such as,the simplex active sites(tetra-coordianation Ti species),the relatively small diameter of 10-member ring pore,and the hard separation of small crystal-sized TS-1 from reaction system.Therefore,the exploration of low-cost sysnthsis of TS-1 with specific textural and structural properties is of considerablely large therotical and practical interstes.In this dissertation,the synthsis of TS-1 with tetrapropylammonium hydroxide(TPAOH)as template by several methods was studied.By the methods of reducing the amount of template,adjustment conditions of synthesis and optimization synthesis technology,reducing the cost of TS-1;By adjusting the surface properties and framework of TS-1,modificating the pore structure of TS-1,leading magnetic function into TS-1,the structure and texture properties of TS-1 were adjusted and multifunctional catalyst was gotten;The samples were characterizated by XRD,UV-vis,FT-IR,SEM,TEM,N2 adsorption-desorption,BET and NH3-TPD,and was used in the reaction of ammoximation of cyclehexanone to cyclohexanone-oxime,oxidation of benzene to phenol,oxidation of phenol to dihydroxyhenzene,the oxidation of ethyl lactate to ethyl pyruvate and oxidation of cyclohexene.The dissertation focuses on the following five parts:(1)Modifications commonly synthesis method of TS-1 zeoliteInfluencing factors,such as,the solvent kinds of Ti sources,the preparation temperature of Ti-Si gel,the molar ratio of H2O/SiO2 and TPAOH/SiO2 in the co-gel,and temperature-programmed crystallization of the co-gel,were investigated systematically.The catalytic performances of TS-1 samples are tested in the ammoximation reaction of cyclohexanone.As the results:It was found that the preparation way of sol with one-time feeding system operation is most simple of all and the molar ratio H2O/SiO2 of col-gel had to larger than 15;Compared to the Ti-Si co-gel prepared by room temperature,the TS-1 synthesized by the Ti-Si cogel prepared in ice water bath,had better performance.Compared to constant-temperature crystallization,the high-performanced TS-1 can be effectively generated from a batch with lower molar ratio of H2O/SiO2 and TPAOH/SiO2 by temperature-programmed crystallization,and reducing the template dosage and raising the solid yield of autoclave.It was also concluded that the TS-1 with a large content of framework Ti but without anatase,exhibiting high catalytic performance,could be synthesized by ethanol instead of isopropanol assistant.This method simplified procedures of preparation of co-gel and cut down the time of preparation of co-gel.(2)Synthesis of TS-1 with TS-1 precursor sol and temperature-programmed hydrothermal crystallizationA novel method for the synthesis of low cost TS-1 involving a combinational employment of temperature-programmed hydrothermal crystallization procedure and TS-1 precursor sol was developed in this work.This novel sythesis method of TS-1 was compared to commonly synthesis method of TS-1,synthesis method of TS-1 with TS-1 precursor,synthesis method of TS-1 with temperature-programmed hydrothermal crystallization method and synthesis method of TS-1 at low usage of TPAOH.The influencing factors,such as,the preparation conditions and usage of TS-1 precursor sol,crystallization procedure,crystallization time,crystallization temperature,were investigated.The activity and stability of TS-1 samples were characteristic of ammoximation of cyclohexanone reaction.As the result:the TS-1 with small crystal size(ca.0.3 ?m)and high content of framework Ti(2.33 mol%)can be effectively generated from a batch with a molar ratio SiO2:0.033 TiO2:0.05TPAOH:0.6 n-BA:35 H2O by the temperature-programmed hydrothermal crystallization procedure at 393 K for 2 d and at 443 K for 1 d.The molar ratio of TPAOH/SiO2 of batch was 5 times smaller than that is commonly used in the literature.Using this TS-1 as the catalyst for the ammoximation of cyclohexanone,a best conversion(98.5%)of cyclohexone at 99.4%selectivity to cyclohexanone-oxime had been achieved.(3)Synthesis of TS-1 with TS-1 precursor sol by the steam-assisted DGC crystallization techniqueA novel synthesis method of TS-1 based on the inorganic materials as Si and Ti sources,TS-1 precursor sol and steam-assisted by dry-gel conversion method,was developed in this work.This novel method was characteristic of the low usage of TPAOH and the low waste liquor,being 1/6 times of those in commonly method.The TS-1 samples prepared are firstly used as catalyst in the oxidation reaction of ethyl lactate to ethyl pyruvate,and the Influencing factors,such as,solvents and temperature,were studied.As the results:the optimal solvent of this reaction is a mix liquid consisted of an equal volume of tert.-butyl alcohol and acetone;the optimal temperature of this reaction is 80.Using this TS-1 as the catalyst for the oxidation reaction of ethyl lactate to ethyl pyruvate,a 83.2%conversion of ethyl lactate at 92.1%selectivity to ethyl pyruvate had been achieved,which are close to those(87.7%and 93.4%)catalysed by commly TS-1.(4)Synthesis of magnetical titanium silicalite-1,MTS-1,by the steam-assisted DGC crystallization techniqueA novel synthesis method of MTS-1 based on the inorganic materials as Si and Ti sources,TS-1 precursor sol and steam-assisted by dry-gel conversion,was developed in this work.The impact of embedding magnetically in TS-1 to crystal pattern and sizes,the content of framkwork Ti and extra-framkwork Ti,were investigated.As the results:after embedding magnetical particle into TS-1,the crystal of MTS-1 has been changed significantly(turn in to around and bigger);The content of framkwork Ti of MTS-1 is lower than that of TS-1 and the content of extra-framkwork Ti of MTS-1 is more than TS-1.Comparing MTS-1 with TS-1 as the catalyst for the oxidation of benzene to phenol,the conversion of benzene reduce from 10.0%to 7.7%,but the selectivity to phenol enlarge from 80.6%to 98.5%.And the MTS-1 catalyst can be separated from reaction mixture by the external magnetic field.5)Modifications of TS-1 zeoliteModified the acid active center in the surface of TS-1,synthesis of transition metal ion TS-1 and modification of pore structure were study.A-TS-1 was prepared by post-treating of TS-1 with sulfuric acid and M-TS-1(M=Ni,Co,Cr,Pb,Mn,Al,Zn)was synthesized by a batch of transition metal oxide gel and Ti-Si cogel.The active of A-TS-1 and MTS-1 was characterizated by oxidation of cyclohexene.As the results:compared to original TS-1,the conversion of cyclohexene and selectiviy of products of the reaction catalyzed by A-TS-1 increased;The conversion of cyclohexene of the reaction catalyzed by M-TS-1 turned down,but the selectiviy of products of the reaction increased.The catalysis evaluation results show that A-TS-1 and Ni-TS-1 catalyst significantly enhances the catalytic activity,the yield of oxidation of cyclohexne enlarge from 68.0%to 78.8%and 81.4%.The hydrothermal post-treatment of TS-1 with different basic TPAOH solution is demonstrated.The impact of hydrothermal post-treatment of TS-1 to its crystal phase,the content of framkwork Ti and extra-framkwork Ti,distribution of Ti,area,pore size,pore volume,pore structure were investigated.The catalytic performances of TS-1 samples are tested in the phenol hydroxylation reaction.As the results:after hydrothermal post-treated TS-1 with TPAOH solution,The samples had porous structure but keeped the same phase with those of the original crystals;the content of framkwork Ti of samples was lower than that of original TS-1 and the content of extra-framkwork Ti of samples was more than original TS-1;The post-treatment process enriches the surface of the porous crystals with Ti.The catalytic performance of porous TS-1 show that post-treatment with 12.5<pH<13 TPAOH solution on TS-1 would be got the best catalyst of phenol hydroxylation.Comparing with TS-1,the TS-1 sample post-treated with that solution used as the catalyst for the phenol hydroxylation reaction,the yield of dihydroxyhenzene increases from 9.13%to 17.7%.