蒸汽辅助结晶法合成多级孔整体型ZSM-5分子筛（英文）
发布时间：2018-07-24 18:44
【摘要】：多级孔分子筛由于其高的比表面积、良好的传质性能和可调控的孔径等特性,引起了广大科研工作者的研究兴趣.近年来,通过选择性脱除骨架硅或铝,成功合成了多级孔沸石分子筛材料.但是由于骨架原子的脱除使分子筛的结晶度降低,进而使其催化效率降低.通过硬模板法(如炭黑、介孔硅球、气凝胶等),也用于合成多级孔沸石分子筛.然而,这种方法制备过程较为复杂,且成本较高.因此,亟需发展新的多级孔分子筛的制备方法.此外,在工业应用中,沸石分子筛催化剂通常需要做成整体柱状或片形以消除固定床反应器的床层压降.合成整体型沸石分子筛的传统方法是在沸石分子筛成型过程中添加SiO_2和Al_2O_3等无机粘结剂.虽然该方法简单易行,但沸石分子筛的孔道结构容易被破坏,而且无机粘结剂的存在使分子筛活性中心的密度减少.为了解决这些问题,合成整体型多级孔沸石分子筛,不仅具有较强的机械稳定性,适应于工业,而且其多级孔道有利于分子的扩散,从而具有较高的催化活性.针对上述问题,我们以海绵作为模板,通过蒸汽辅助结晶(steam-assisted crystallization,SAC)方法,制备具有多级孔道的整体型ZSM-5分子筛.通过X射线衍射(XRD)、氮吸附脱附、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、固态核磁共振和氨气的程序升温脱附(NH3-TPD)等手段对分子筛进行了结构与性质表征.XRD和固态核磁共振的结果表明,成功合成了不同Si/Al的ZSM-5分子筛.SEM和TEM结果进一步确定了合成的整体型多级孔ZSM-5分子筛(记作M-ZSM-n,n代表Si/Al的摩尔比),由于分子筛颗粒的堆积形成的介孔,海绵模板提供的固体骨架形成的大孔,分子筛本身的微孔,共同构成了微孔-介孔-大孔的整体型ZSM-5分子筛.透射电子显微镜上配备的X射线能谱仪(EDS)结果表明,分子筛中的Si和Al元素能够均匀的分布.氮吸附脱附证明所得整体型分子筛具有明显的介孔结构.NH3-TPD结果表明,不同Si/Al的整体型多级孔ZSM-5分子筛具有不同强度的酸性,其酸性强度:ZSM-5(60)M-ZSM-90M-ZSM-40M-ZSM-60.苯甲醇和己酸的液相反应进一步验证了这一结论,而且合成的整体型多级孔ZSM-5分子筛比传统的ZSM-5分子筛(记作ZSM-5(60))表现出更优异的催化活性.
[Abstract]:Because of its high specific surface area, good mass transfer performance and controllable pore size, multilevel porous molecular sieve has attracted many researchers' interest. In recent years, multilevel porous zeolite materials have been successfully synthesized by selective removal of skeleton silicon or aluminum. However, due to the removal of skeleton atoms, the crystallinity of molecular sieve decreased and the catalytic efficiency decreased. It is also used in the synthesis of multilevel porous zeolite by hard template (such as carbon black, mesoporous silica ball, aerogel, etc.). However, the preparation process of this method is more complex and costly. Therefore, there is an urgent need to develop a new method for the preparation of multiporous molecular sieves. In addition, in industrial applications, zeolite catalysts usually need to be monolithic or lamellar to eliminate the pressure drop in the bed of the fixed-bed reactor. The traditional method of synthesis of monolithic zeolite is to add inorganic binders such as SiO_2 and Al_2O_3 in the molding process of zeolite molecular sieve. Although the method is simple and feasible, the pore structure of zeolites is easily destroyed, and the density of active centers of zeolites decreases due to the existence of inorganic binders. In order to solve these problems, the synthesis of monolithic multi-porous zeolite not only has strong mechanical stability and is suitable for industry, but also has higher catalytic activity because of its advantages of molecular diffusion. In order to solve the above problems, we used sponge as template and synthesized monolithic ZSM-5 molecular sieve with multilevel pores by steam assisted crystallization (steam-assisted) method. Adsorption and desorption of nitrogen by X-ray diffraction (XRD),). The structure and properties of molecular sieve were characterized by (SEM), transmission electron microscope (SEM), (TEM), solid-state NMR and ammonia temperature programmed desorption (NH3-TPD). The synthesis of ZSM-5 molecular sieves with different Si/Al and TEM results further confirmed the synthesis of monolithic multiporous ZSM-5 molecular sieves (denoted as M-ZSM-nn representing the molar ratio of Si/Al), and the mesoporous structure formed by the accumulation of molecular sieve particles. The spongy template provides macropores formed by solid skeleton and micropores of molecular sieve itself, which together form the monolithic ZSM-5 molecular sieve with micropore mesoporous and macroporous. The (EDS) results of transmission electron microscopy (TEM) show that the Si and Al elements in the molecular sieve can be uniformly distributed. The results of nitrogen adsorption and desorption show that the monolithic molecular sieve has obvious mesoporous structure. NH3-TPD results show that the monolithic multiporous ZSM-5 molecular sieve with different Si/Al has different acidity and its acidic strength is: ZSM-5 (60) M-ZSM-90M-ZSM-40M-ZSM-60. The liquid phase reaction of benzyl alcohol with hexanoic acid further verifies this conclusion, and the synthesized monolithic multiporous ZSM-5 molecular sieve exhibits better catalytic activity than the traditional ZSM-5 molecular sieve (described as ZSM-5 _ (60).
【作者单位】： 中国科学院化学研究所 分子纳米结构与纳米技术院重点实验室;中国科学院大学;
【基金】：supported by the National Natural Science Foundation of China(21333009) the Youth Innovation Promotion Association of CAS(2017049)~~
【分类号】：O643.36
，
本文编号：2142299
[Abstract]:Because of its high specific surface area, good mass transfer performance and controllable pore size, multilevel porous molecular sieve has attracted many researchers' interest. In recent years, multilevel porous zeolite materials have been successfully synthesized by selective removal of skeleton silicon or aluminum. However, due to the removal of skeleton atoms, the crystallinity of molecular sieve decreased and the catalytic efficiency decreased. It is also used in the synthesis of multilevel porous zeolite by hard template (such as carbon black, mesoporous silica ball, aerogel, etc.). However, the preparation process of this method is more complex and costly. Therefore, there is an urgent need to develop a new method for the preparation of multiporous molecular sieves. In addition, in industrial applications, zeolite catalysts usually need to be monolithic or lamellar to eliminate the pressure drop in the bed of the fixed-bed reactor. The traditional method of synthesis of monolithic zeolite is to add inorganic binders such as SiO_2 and Al_2O_3 in the molding process of zeolite molecular sieve. Although the method is simple and feasible, the pore structure of zeolites is easily destroyed, and the density of active centers of zeolites decreases due to the existence of inorganic binders. In order to solve these problems, the synthesis of monolithic multi-porous zeolite not only has strong mechanical stability and is suitable for industry, but also has higher catalytic activity because of its advantages of molecular diffusion. In order to solve the above problems, we used sponge as template and synthesized monolithic ZSM-5 molecular sieve with multilevel pores by steam assisted crystallization (steam-assisted) method. Adsorption and desorption of nitrogen by X-ray diffraction (XRD),). The structure and properties of molecular sieve were characterized by (SEM), transmission electron microscope (SEM), (TEM), solid-state NMR and ammonia temperature programmed desorption (NH3-TPD). The synthesis of ZSM-5 molecular sieves with different Si/Al and TEM results further confirmed the synthesis of monolithic multiporous ZSM-5 molecular sieves (denoted as M-ZSM-nn representing the molar ratio of Si/Al), and the mesoporous structure formed by the accumulation of molecular sieve particles. The spongy template provides macropores formed by solid skeleton and micropores of molecular sieve itself, which together form the monolithic ZSM-5 molecular sieve with micropore mesoporous and macroporous. The (EDS) results of transmission electron microscopy (TEM) show that the Si and Al elements in the molecular sieve can be uniformly distributed. The results of nitrogen adsorption and desorption show that the monolithic molecular sieve has obvious mesoporous structure. NH3-TPD results show that the monolithic multiporous ZSM-5 molecular sieve with different Si/Al has different acidity and its acidic strength is: ZSM-5 (60) M-ZSM-90M-ZSM-40M-ZSM-60. The liquid phase reaction of benzyl alcohol with hexanoic acid further verifies this conclusion, and the synthesized monolithic multiporous ZSM-5 molecular sieve exhibits better catalytic activity than the traditional ZSM-5 molecular sieve (described as ZSM-5 _ (60).
【作者单位】： 中国科学院化学研究所 分子纳米结构与纳米技术院重点实验室;中国科学院大学;
【基金】：supported by the National Natural Science Foundation of China(21333009) the Youth Innovation Promotion Association of CAS(2017049)~~
【分类号】：O643.36
，
本文编号：2142299
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