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Theoretical Calculations On The Solvent Effect And Allyl Chloride Reaction Mechanism In Ti-MWW/H2O2 Catalyst

Posted on:2017-11-02Degree:MasterType:Thesis
Country:ChinaCandidate:J ZouFull Text:PDF
GTID:2311330488972035Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Ti-MWW molecular sieve has a unique channel system.One set is the 10 MR sinusoidal channel system and another set is the 10 MR straight channel linked to the super cages of 12 MR,with diameter of about 0.7 nm.On its surface exist the 12 MR side cups.It plays an excellent catalytic role in H2O2 solution to the oxidation reaction,and exibits different solvent effect in comparation with TS-1.Meanwhile,Ti-MWW zeolite was charactered by a very high catalytic activity and selectivity in the reaction with olefins.In this work,density functional theory calculations are performed to research the solvent effect in Ti-MWW/H2O2 catalyst system and the catalytic oxidation mechanisms of allyl chloride on different center.The results are as follows:1.The different active centers that located in T1 and T3 sites in Ti-MWW/H2O2 system were studied,which respectively corrspond to the five-membered ring Ti-?1-OOH and three-membered ring Ti-?2-OOH with adsorbed CH3OH and CH3CN molecules.Meanwhile,we calculated the adsorption energy,performed BSSE correction and NBO analysis.The results indicated that the adsorption energies of three kinds of solvent adsorbing on different Ti-peroxide species decreased as the following order:Ti-?2-OOH-H2O>Ti-?2-OOH-CH3OH>Ti-?2-OOH-CH3CN.In view of different active center,absorption capacity of the Ti-?1-OOH is somewhat stronger than Ti-?2-OOH,and the adsorption strength of solvent is as T1>T3 site for different Ti center.In addition,solvent adsorption also influenced the electropositivity of the active oxygen atom.It's concluded that from the analysis of NBO,the O? has the most positive electricity in Ti-?2-OOH-CH3CN active center,implying the larger oxidation ability.2.We studied the reaction mechanisms of allyl chloride epoxidation Ti-r)-OOH and Ti-?1-OOH,as well as their adsorption complexes with solvents(H2O,CH3CN).The results indicated that the activation energy of allyl chloride epoxidation on different Ti-peroxide species increase in the order:Ti-?2-OOH<Ti-?1-OOH.In aqueous solutions,the main active centers are formed as Ti-?2,OOH-H2O,Ti-?1-OOH and Ti-?1-OOH-H2O,which have higher reaction energy barrieres for allyl chloride epoxidation.For CH3CN solvent,the stable active center is Ti-?2-OOH due the weak adsorption of CH3CN,so the active center is Ti-?2-OOH structure,which has the lowest activation energy barrier as catalyst within reaction with allyl chloride.
Keywords/Search Tags:Ti-MWW Zeolite, Structures of Active Centers, Density Functional Theory, Solvent Effect, Allyl Chloride Epoxidation
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