【摘要】：多級孔分子篩由于其高的比表面積、良好的傳質(zhì)性能和可調(diào)控的孔徑等特性,引起了廣大科研工作者的研究興趣.近年來,通過選擇性脫除骨架硅或鋁,成功合成了多級孔沸石分子篩材料.但是由于骨架原子的脫除使分子篩的結(jié)晶度降低,進而使其催化效率降低.通過硬模板法(如炭黑、介孔硅球、氣凝膠等),也用于合成多級孔沸石分子篩.然而,這種方法制備過程較為復雜,且成本較高.因此,亟需發(fā)展新的多級孔分子篩的制備方法.此外,在工業(yè)應用中,沸石分子篩催化劑通常需要做成整體柱狀或片形以消除固定床反應器的床層壓降.合成整體型沸石分子篩的傳統(tǒng)方法是在沸石分子篩成型過程中添加SiO_2和Al_2O_3等無機粘結(jié)劑.雖然該方法簡單易行,但沸石分子篩的孔道結(jié)構(gòu)容易被破壞,而且無機粘結(jié)劑的存在使分子篩活性中心的密度減少.為了解決這些問題,合成整體型多級孔沸石分子篩,不僅具有較強的機械穩(wěn)定性,適應于工業(yè),而且其多級孔道有利于分子的擴散,從而具有較高的催化活性.針對上述問題,我們以海綿作為模板,通過蒸汽輔助結(jié)晶(steam-assisted crystallization,SAC)方法,制備具有多級孔道的整體型ZSM-5分子篩.通過X射線衍射(XRD)、氮吸附脫附、掃描電子顯微鏡(SEM)、透射電子顯微鏡(TEM)、固態(tài)核磁共振和氨氣的程序升溫脫附(NH3-TPD)等手段對分子篩進行了結(jié)構(gòu)與性質(zhì)表征.XRD和固態(tài)核磁共振的結(jié)果表明,成功合成了不同Si/Al的ZSM-5分子篩.SEM和TEM結(jié)果進一步確定了合成的整體型多級孔ZSM-5分子篩(記作M-ZSM-n,n代表Si/Al的摩爾比),由于分子篩顆粒的堆積形成的介孔,海綿模板提供的固體骨架形成的大孔,分子篩本身的微孔,共同構(gòu)成了微孔-介孔-大孔的整體型ZSM-5分子篩.透射電子顯微鏡上配備的X射線能譜儀(EDS)結(jié)果表明,分子篩中的Si和Al元素能夠均勻的分布.氮吸附脫附證明所得整體型分子篩具有明顯的介孔結(jié)構(gòu).NH3-TPD結(jié)果表明,不同Si/Al的整體型多級孔ZSM-5分子篩具有不同強度的酸性,其酸性強度:ZSM-5(60)M-ZSM-90M-ZSM-40M-ZSM-60.苯甲醇和己酸的液相反應進一步驗證了這一結(jié)論,而且合成的整體型多級孔ZSM-5分子篩比傳統(tǒng)的ZSM-5分子篩(記作ZSM-5(60))表現(xiàn)出更優(yōu)異的催化活性.
[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).
【作者單位】： 中國科學院化學研究所 分子納米結(jié)構(gòu)與納米技術(shù)院重點實驗室;中國科學院大學;
【基金】：supported by the National Natural Science Foundation of China(21333009) the Youth Innovation Promotion Association of CAS(2017049)~~
【分類號】：O643.36
，

本文編號：2142299