| In this work,three modified TS-1 catalysts were prepared.The catalytic performance of 1-hexene epoxidation and butanone ammoximation and catalytic reaction mechanism of these three modified TS-1 catalysts were studied.Firstly,the preparation methods of modified TS-1 catalysts which contained Si-OH,-NH2 and alkyl groups were introduced.Through FT-IR,TG/DTG,UV-Vis,BET and EA,the load conditions and load amounts of modified TS-1 catalysts were characterized and analyzed.Secondly,the change of the amounts of Ti-OOH,Si-OH and surface acidity after adding H2O2 to modified TS-1 was analyzed by UV-Vis,NH3-TPD and Py-IR characterization.The influence of TS-1 modification on 1-hexene epoxidation and butanone ammoximation was investigated.Finally,combined the results of characterization and analysis with literature,the catalytic mechanisms of modified TS-1 were discussed.Experiments results showed that adopted ammonia solution to pretreat TS-1 catalysts could improve the Si-OH amounts on TS-1 surface,thus promote the efficiency of TS-1 silanization and not change the skeleton structure and total Ti content of TS-1.FT-IR and TG/DTG results showed that modified TS-1 catalysts which contained Si-OH,-NH2 and alkyl groups could be successfully prepared through the silanization of pretreated TS-1.UV-Vis results showed that the Ti element distribution of TS-1 was unchanged before and after modification.BET results showed that the BET specific surface area,micropore specific surface area and micropore volume after modification were all decreased,indicating the grafting of silylating reagents on TS-1 surface or internal micropores.Element analysis indicated that the grafting rate of hydrolyzation of APTES/TS-1,hydrolyzation of MTES/TS-1 and hydrolyzation of DMDES/TS-1 were respect:ively 0.664,0.833 and 0.663 mmol/g catalyst.UV-Vis results indicated that compared with unmodified TS-1/H2O2 system,the stability and amounts of Ti-OOH active centers were improved after adding H2O2 to the three modified TS-1 catalysts.NH3-TPD results showed that compared with unmodified TS-1/H2O2 system,after adding H2O2 to hydrolyzation of MTES/TS-1 and hydrolyzation of DMDES/TS-1,the amounts of Ti-OOH increased and the amounts of Si-OH decreased obviously.Py-IR results showed that TS-1 modificartion could change the surface acidity of TS-1.The reaction results of 1-hexene epoxidation and butanone ammoximation indicated that the conversion and selectivity of these two reactions were obviously promoted catalyzed by the three modified TS-1 catalysts.The conversion and selectivity of unmodified TS-1 in 1-hexene epoxidation were 59.2%and 64.1%,while the conversion of APTES,MTES and DMDES modified TS-1 were 69.0%,69.0%and 64.7%,the selectivity of them were 68.9%,95.4%and 96.7%.The conversion and selectivity of unmodified TS-1 in butanone ammoximation were 68.0%and 84.3%,while the conversion of APTES,MTES and DMDES modified TS-1 were 71.3%,73.6%and 78.0%,the selectivity of them were 86.5%,97.5%and 99.3%.Combined the results of characterization and analysis with literature,the catalytic oxidation mechanisms of modified TS-1 were discussed.In the system of hydrolyzation of APTES/TS-1,the N atom in-NH2 group can form hydrogen bond with the terminal H atom in Ti-OOH,the Si-OH group can form hydrogen bond with the terminal O atom in Ti-OOH.These two hydrogen bond structures stabilized Ti-OOH active center,improved the quantity of Ti-OOH.And the hydrogen bond of Si-OH and Ti-OOH was more likely to exist.In the systems of hydrolyzation of MTES/TS-1 and hydrolyzation of DMDES/TS-1,the terminal H atom in Si-OH can form hydrogen bond with the terminal O atom in Ti-OOH.This hydrogen-bond interaction improved the stability and quantity of Ti-OOH and made the amounts of Si-OH decrease.Meanwhile,organic groups in silylating reagents also changed the hydrophobicity of catalysts surface.These facters worked together contributing to apparently improvements of conversion and selectivity of 1-hexene epoxidation and butanone ammoximation reactions. |
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