Study On The Synthesis Of Heteroatom Framework Doped MFI Zeolite For Catalytic Oxidation Reactions

Heteroatom framework doped MFI zeolite has unique pore structure,adjustable Lewis acidity and good hydrothermal stability,which endows it with significant applications in liquid-phase selective oxidation reactions.In this dissertation,framework titanium,tungsten and vanadium doped MFI zeolite catalysts were prepared and their catalytic activities as well as stabilities were evaluated in the oxidation of three typical thiophene-type organosulfur compounds as dibenzothiophene(DBT),benzothiophene(BT)and 4,6-dimethyldibenzothiophene(4,6-DMDBT).The main work is as follows:(1)Hierarchical TS-1 stacked nanoplates were hydrothermally synthesized with the aid of P123 lamellar micelles.Their formation processes with crystallization time were investigated,and accordingly the possible process was proposed.The obtained hierarchical TS-1 stacked nanoplates possessed a large number of constrained mesopores in the range of 2 nm to 20 nm.Moreover,the prepared hierarchical TS-1stacked nanoplates could realize almost total oxidation of DBT in 40 min as well as almost total oxidation of 4,6-DMDBT in 105 min.Hierarchical TS-1 stacked nanoplates revealed obvious decrease for its catalytic oxidation ability in the recycle tests.Calcination at 823 K could effectively renew its reactivity,and on the same time retain its MFI topology structure.(2)In order to resolve fine hierarchical TS-1 zeolite separation problems,an interfacial sol-gel method was put forward for the synthesis of micron-sized TS-1/Si O₂ colloidosomes.The obtained TS-1/Si O₂ colloidosomes could be easily recovered via a filtration process from the reaction system.The effect of water-to-oil volume ratio(R_w/o)and ratio of TS-1 weight to oil volume(R_s/o)on TS-1colloidosome dimension were investigated.The prepared TS-1/Si O₂ colloidosomes could realize the oxidation of 98.4%of DBT in 150 min.In addition,the obtained TS-1/Si O₂ colloidosomes showed good stability and did not display any obvious change of microstructure and catalytic activity after four recycle runs.(3)WTS(3/3)zeolite was synthesized via the insertion of tungsten into the MFI framework of TS-1 zeolite through a one-pot hydrothermal synthesis.The obtained WTS(3/3)zeolite possessed a Lewis acidity of 318.4?mol/g,which is 1.5 fold of TS(29)zeolite.Moreover,WTS(3/3)zeolite could oxidize 99.5%of DBT in 120 min and its initial reaction rate enhanced 1.6 fold in comparison to TS(29)zeolite.The calcined WTS(3/3)zeolite did not show any decrease of tungsten species after four recycle runs,which indicated it had good stability.(4)Three framework vanadium doped MFI zeolites N-VS(3),N-VS(4)and N-VS(5)were hydrothermally synthesized with the aid of crystallization regulator ammonium carbonate.In comparison with C-VS(3),C-VS(4)and C-VS(5)zeolite,vanadium insertion amount for N-VS(3),N-VS(4)and N-VS(5)zeolite increased 4.4fold,4.8 fold and 4.2 fold respectively.Moreover,framework vanadium for N-VS(3),N-VS(4)and N-VS(5)zeolite enhanced 1.1 fold,0.6 fold and 0.9 fold respectively in comparison to C-VS(3),C-VS(4)and C-VS(5)zeolite.The obtained N-VS(4)zeolite could achieve almost total oxidation of DBT in 240 min.The calcined N-VS(4)zeolite did not display any decrease of catalytic performance after four recycle runs,which revealed its good stability.