具有纳米线镶嵌结构ZSM-5/L复合分子筛的合成及表征

Synthesis and Characterization of Nanowired ZSM-5/L Composite Molecula Sieves

采用两步晶化法,以四丙基氢氧化铵预处理ZSM-5为晶种,快速合成了纳米线镶嵌结构ZSM-5/L复合分子筛.通过XRD、SEM-EDX、TEM和N_2吸附-脱附等手段对合成样品的物理化学性质进行了表征.孔道性质表明复合分子筛具有微孔和介孔的多级孔道结构,椭球的L分子筛镶嵌在纳米线的ZSM-5分子筛周围.晶种预处理影响了溶胶的电荷及分子筛的形貌,当合成样品中ZSM-5的质量分数小于2%(重量百分比)时,凝胶的负电荷较多,易形成椭球状L分子筛;当合成样品中ZSM-5的质量分数大于2%(重量百分比)时,zeta电位在-39.822～-42.352mV之间波动,ZSM-5分子筛的形貌从长条状逐渐转变为纳米线状.阳离子比影响复合分子筛中L分子筛形成,当阳离子比R=n(K_2O)/(n(K_2O)+n(Na_2O))小于0.6时,不利于L型分子筛的形成;当阳离子比大于0.6,即K^+较多Na^+较少时,有利于L型分子筛中α-钙霞石笼的形成.

In this paper, the nanowire Mosaic structure ZSM-5/L composite molecular sieve was rapidly synthesized by a two-step crystallization method that pretreated ZSM-5 with tetrapropylammonium hydroxide to a seed crystal. The physicochemical properties of the synthesized samples were characterized by XRD, SEM, TEM and N2 adsorption-desorption. The pore properties indicate that the composite molecular sieve has multi-stage pore structure composed of micropores and mesopores. The ellipsoidal L molecular sieves are embedded in the ZSM-5 molecular sieve around the nanowire. The pretreatment of the seed crystal affect the electric charge of the synthetic sol and the morphology of the molecular sieve. When the mass fraction of ZSM-5 in the synthetic sample is less than 2%, the gel has more negative charges, forming ellipsoidal L molecular sieve. When the mass fraction of ZSM-5 in the synthetic sample is greater than 2%, the zeta potential fluctuates between -39.822 mV and -42.352 mV, the morphology of ZSM-5 molecular sieve changes from strip to nanowire. The cation ratio affects the change of the L-type molecular sieve's morphology, When the cationic ratio is less than 0.6, it is not conducive to the formation of L-type molecular sieve. When the cationic ratio is greater than 0.6, in other words, K^+ gets more and Na^+ gets less, the formation of α-calcium nepheline cages in L-type molecular sieves is facilitated.