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首页> 外文期刊>Chemistry: A European journal >Exploring meso-/microporous composite molecular sieves with core-shell structures
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Exploring meso-/microporous composite molecular sieves with core-shell structures

机译：探索具有核-壳结构的中孔/微孔复合分子筛

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A series of core-shell-structured composite molecular sieves comprising zeolite single crystals (i.e., ZSM-5) as a core and ordered mesoporous silica as a shell were synthesized by means of a surfactant-directed sol-gel process in basic medium by using cetyltrimethylammonium bromide (CTAB) as a template and tetraethylorthosilicate (TEOS) as silica precursor. Through this coating method, uniform mesoporous silica shells closely grow around the anisotropic zeolite single crystals, the shell thickness of which can easily be tuned in the range of 15-100 nm by changing the ratio of TEOS/zeolite. The obtained composite molecular sieves have compact meso-/micropore junctions that form a hierarchical pore structure from ordered mesopore channels (2.4-3.0 nm in diameter) to zeolite micropores (≈0.51 nm). The short-time kinetic diffusion efficiency of benzene molecules within pristine ZSM-5 (≈7.88×10 ~(-19) m ~2s ~(-1)) is almost retainable after covering with 75 nm-thick mesoporous silica shells (≈7.25×10 ~(-19) m ~2s ~(-1)), which reflects the greatly opened junctions between closely connected mesopores (shell) and micropores (core). The core-shell composite shows greatly enhanced adsorption capacity (≈1.35 mmolg ~(-1)) for large molecules such as 1,3,5-triisopropylbenzene relative to that of pristine ZSM-5 (≈0.4 mmolg ~(-1)) owing to the mesoporous silica shells. When Al species are introduced during the coating process, the core-shell composite molecular sieves demonstrate a graded acidity distribution from weak acidity of mesopores (predominant Lewis acid sites) to accessible strong acidity of zeolite cores (Lewis and Br??nsted acid sites). The probe catalytic cracking reaction of n-dodecane shows the superiority of the unique core-shell structure over pristine ZSM-5. Insight into the core-shell composite structure with hierarchical pore and graded acidity distribution show great potential for petroleum catalytic processes. Esprit de core: Meso-/microporous core-shell composite molecular sieves with hierarchical pore structures (see figure), from opened mesopore channels (2.4-3.0 nm) to accessible micropores (≈0.51 nm), and graded acidity distributions, from weakly acidic mesopores to accessible strongly acidic ZSM-5 cores, have been synthesized.
机译：通过表面活性剂定向溶胶-凝胶法在碱性介质中合成了以沸石单晶（ZSM-5）为核，有序中孔二氧化硅为核的一系列核-壳结构复合分子筛。十六烷基三甲基溴化铵（CTAB）作为模板，原硅酸四乙酯（TEOS）作为二氧化硅前体。通过这种涂覆方法，均匀的介孔二氧化硅壳在各向异性沸石单晶周围紧密生长，通过改变TEOS /沸石的比例，可以容易地将其壳厚度调节在15-100nm的范围内。所获得的复合分子筛具有紧密的介孔/微孔连接，其形成从有序介孔通道（直径为2.4-3.0 nm）到沸石微孔（≈0.51nm）的分层孔结构。原始分子ZSM-5（≈7.88×10〜（-19）m〜2s〜（-1））中苯分子的短时动力学扩散效率在覆盖75 nm厚的介孔二氧化硅壳（≈7.25）后几乎可以保留×10〜（-19）m〜2s〜（-1）），反映了紧密连接的中孔（壳）和微孔（核心）之间的极大开放的连接。相对于原始的ZSM-5（≈0.4mmolg〜（-1）），核-壳复合材料对1,3,5-三异丙基苯等大分子的吸附容量（≈1.35mmolg〜（-1））大大提高。由于介孔二氧化硅壳。当在涂层过程中引入铝物质时，核-壳复合分子筛的酸度分布从中孔的弱酸度（主要的路易斯酸位）到沸石核可达到的强酸度（刘易斯和布朗斯台德酸位）呈梯度分布。正十二烷的探针催化裂化反应显示出独特的核壳结构优于原始的ZSM-5。对具有分层孔隙和分级酸度分布的核-壳复合结构的深入了解显示出了石油催化过程的巨大潜力。 Esprit de core：具有中空结构的介孔/微孔核-壳复合分子筛（见图），从开放的中孔通道（2.4-3.0 nm）到可及的微孔（≈0.51nm），以及从弱酸性到分级的酸度分布已经合成了可接近的强酸性ZSM-5核的介孔。

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