The Studies On The Synthesis?Characterization And Theoretical Calculations Of EU-1 Zeolites

The EU-1 molecular sieve consist of 10-membered ring(10-MR)channels with deep side-pockets circumscribed by 12-MRs and Br(?)nsted acidity and shape-selectivity.This material has been proved to have potentials in many industrial applications such as dimethyl benzene isomerization reactions.Incorporation of heteroatoms into the framework can change the pore structure and acidity of zeolites and then alter catalytic activity,selectivity and stability.Its catalytic activity originates from the bridged hydroxyl groups,which are produced by the Si or A1 in the framework that is replaced by other heteroatoms acting as strong Br(?)nsted acid sites.Generally acid sites in different positions of a zeolite framework have different acid strengths,and therefore information about the location of Al,heteroatoms and the bridged hydroxyl groups has great importance in better understanding of catalytic processes.In the synthesis of EU-1 zeolite,alkali metal cations not only balance the framework negative charges generated by the incorporation of Al but also play a structure-directing role in the crystallization of EU-1.In this paper,the siting of Al,Fe,Ga,B,La and the bridging hydroxyl group in EU-1 zeolite framework were studied by using density functional theory(DFT)methods.The influence of the presence of Fe,Ga,B,La in the framework on the Br(?)nsted acidity of EU-1 zeolite was investigated.The calculations of 26T cluster model performed with BLYP hydride functional and DNP basis.It was shown that energetically,when heteroatoms replacing Si in EU-1 zeolite framework,Al,Fe,Ga,or B prefered to the same T-sites,T1,T2,T3,T6,T7 and T8,but La prefered to the T-sites,T1,T2 and T8.When Al replace Si in EU-1 zeolite framework,the preferable Br(?)nsted acid sites locate at All-012H-Si2,All-013H-Si6,A13-015H-Si2,A13-018H-Si5 and A13-019H-Si7;When Fe replace Si in EU-1 zeolite framework,the preferable Br(?)nsted acid sites locate at Fe1-013H-Si6,Fe2-014H-Si2 and Fe8-O29H-Si10;When Ga replace Si in EU-1 zeolite framework,the preferable Br(?)nsted acid sites locate at Ga3-O15H-Si2,Ga3-018H-Si5 and Ga3-019H-Si7;When B replace Si in EU-1 zeolite framework,the preferable Br(?)nsted acid sites locate at B6-024H-Si7,B7-019H-Si3 and B8-O29H-Si10;When La replace Si in EU-1 zeolite framework,the preferable Br(?)nsted acid sites locate at Lal-012H-Si2,Lal-013H-Si6 and La2-012H-Sil.The proton affinity caculations showed that the acidity of isomorphously substituted EU-1 zeolite decreases in the order:Al-EU-1?La-EU-1>Ga-EU-1>Fe-EU-1>B-EU-1.EU-1 zeolites were synthesized by traditional method,the products were characterized by NH3-TPD.It turned out that the tempreture of the desorption isotherm and the acidity were declined when the Fe,Ga,B or La was presented in the framework.And the the area of the desorption isotherm and the amount of the acid were rised when the Fe,Ga,B or La was presented in the framework.The results were consistent with the theory caculations.The P-EU-1 zeolite was synthesized by the traditional method.The products were characterized by X-ray powder diffraction(XRD),FT-IR,scanning electron microscopy(SEM),TG-DTG,XPS analysis et al,and compared with the EU-1 zeolite.The affection of the difference of phoshorus source,the amount of phoshorus,n(OH-)/n(Al2O3),n(SiO2)/n(Al2O3),and crystallization time toward the crystallinity and purity of product was analyzed.The siting of P and Bronsted acidity in P-EU-1 zeolite framework were studied by using density functional theory(DFT)methods.It was shown that energetically,when P replaces Si in EU-1 zeolite framework,it prefers to the T-sites,T1,T2,T3,T6,T7 and T8.The proton affinity caculations showed that the acidity of P-EU-1 zeolite stronger than EU-1,and the amount of acid P-EU-1 zeolite more than EU-1.Different alkali metal cations(Li+,Na+,K+,Ba2+)should be added into the composite of EU-1 zeolite which was synthesized by the traditional hydrothermal method and solid-solid mass transformation method.In this process,it turned out that Li+ and K+ showed much weaker structure-directing ability than Na+,although Li+ was superior to K+.