The Studies On The Synthesis And Theoretical Calculations Of EU-1Zeolite

EU-1zeolite have been proved to have potentials in xylene isomerizationreactions because of its peculiar pore architecture and adjustable Br nstedacidity and shape selectivity. Xylene isomerization reaction occurred in thecenter of Br nsted acid (B acid). In this thesis, the relationship betweenBr nsted acidity and the sitting and the content of Al were investigated by usingdensity functional theory (DFT). Firstly,35T cluster model of EU-1wereselected to study the possible siting of Al, Fe and the priority sitting of Br nstedacid were obtained. According to the calculated energy, the stable sites of Alwere located at T1, T2, T3, T6, T7and T8while Si was replaced by Al; thestable acid sites of EU-1zeolite were located at Al3-O15H-Si2, Al8-O27H-Si8,Al3-O18H-Si5, Al1-O12H-Si2, Al3-O19H-Si7. The stable sites of Fe werelocated at T1, T2, T3and T8while Si was replaced by Fe; the stable acid sitesof EU-1zeolite were located at Fe8-O27H-Si8, Fe2-O16H-Si4, Fe2-O12H-Si1,Fe3-O17H-Si3, Fe3-O15H-Si2, Fe2-O14H-Si2. The calculation of proton affinity indicated that the Br nsted acid strength of Al-EU-1were stronger thanthe Fe-EU-1.According to L wenstein’s rule, when framework Al pairs were found inEU-1zeolite, the closest position of Al pairs in zeolite had to be on theNext-Nearest-Neighbour position (NNN) or on the next-next-nearest-neighborposition(NNNN). The substitution of framework Al pairs at T1, T2, T3, T6, T7and T8sites in EU-1zeolite was calculated based on the44T cluster model ofEU-1zeolite, and the stability and Br nsted acidity of the neighboring acid siteswere theoretically studied. According to the calculated results, the stable acidsites of EU-1zeolite were located at Al7(Si6-Si7)Al8, Al1(Si2-Si2)Al1,Al2(Si1-Si2)Al2, Al1(Si2-Si2)Al3, Al1(Si2)Al3. The localization of acidicproton was explored by calculating the substitution energy of (Al/Si,H), and thestable proton sites of EU-1zeolite were at (O12-H)Al1-(O12-H)Al1,(O12-H)Al1-Al1(O13-H),(O12-H)Al1-Al1(O12-H),(O14-H)Al2-(O14-H)Al2,Al2(O12-H)-(O14-H)Al2, Al1(O12-H)-(O15-H)Al3,(O26-H)Al7-Al8(O28-H).The calculation of proton affinity indicated that the Br nsted acid strength ofNNNN sites were stronger than the NNN sites. The synthesized products withdifferent SiO2/Al2O3molar ratio were characterized by MAS NMR, NH3-TPD,the results showed that, the area of Br nsted acid were increased with thedecreasing of the SiO2/Al2O3molar ratio of EU-1zeolite, whereas the acidstrength were decreased.Xylene isomerization was controlled by diffusion. Microporous EU-1 zeolite with molecular-size pores, not conducive to the molecule diffusion.Micro-mesoporous zeolites will be significant for the improvement of catalystefficiency. The micro-mesoporous EU-1zeolite was synthesized by theconcentrated system method with a moderate amount of citric acid added in theinitial gel. The effects of the technological conditions were examined. Thephysical properties and structure of EU-1zeolite were studied by the XRD,SEM-EDX, TEM, FT-IR, N2adsorption desorption, electrophoresis, TG-DTGand so on. The results revealed that the appearance of EU-1zeolite showed anagglomeration of nanoparticles. The total specific area, mesoporous volume ofthe EU-1zeolite obviously increased by the increasing amount of citric acid.Thus it would be benefit to the diffusion of molecule.