†Department of Chemical and Biomolecular Engineering, University of Houston, 4800 Calhoun Road, Houston, Texas 77204, United States.
‡Department of Chemical, Biological, and Materials Engineering, University of Oklahoma, 100 East Boyd Street, Norman, Oklahoma 73019, United States.
ACS Nano. 2015 Apr 28;9(4):4006-16. doi: 10.1021/acsnano.5b01308. Epub 2015 Apr 6.
The design of materials with spatially controlled chemical composition has potential advantages for wide-reaching applications that span energy to medicine. Here, we present a method for preparing a core-shell aluminosilicate zeolite with continuous translational symmetry of nanopores and an epitaxial shell of tunable thickness that passivates Brønsted acid sites associated with framework Al on exterior surfaces. For this study, we selected the commercially relevant MFI framework type and prepared core-shell particles consisting of an aluminosilicate core (ZSM-5) and a siliceous shell (silicalite-1). Transmission electron microscopy and gas adsorption studies confirmed that silicalite-1 forms an epitaxial layer on ZSM-5 crystals without blocking pore openings. Scanning electron microscopy and dynamic light scattering were used in combination to confirm that the shell thickness can be tailored with nanometer resolution (e.g., 5-20 nm). X-ray photoelectron spectroscopy and temperature-programmed desorption measurements revealed the presence of a siliceous shell, while probe reactions using molecules that were either too large or adequately sized to access MFI pores confirmed the uniform shell coverage. The synthesis of ZSM-5@silicalite-1 offers a pathway for tailoring the physicochemical properties of MFI-type materials, notably in the area of catalysis, where surface passivation can enhance product selectivity without sacrificing catalyst activity. The method described herein may prove to be a general platform for zeolite core-shell design with potentially broader applicability to other porous materials.
具有空间控制化学成分的材料设计在从能源到医学等广泛应用中具有潜在优势。在这里，我们提出了一种制备具有纳米孔连续平移对称性和可调节厚度的外延壳的核壳铝硅酸盐沸石的方法，该方法可以钝化与外表面骨架 Al 相关的 Brønsted 酸位。在这项研究中，我们选择了商业上相关的 MFI 骨架类型，并制备了由铝硅酸盐核（ZSM-5）和硅壳（silicalite-1）组成的核壳颗粒。透射电子显微镜和气体吸附研究证实，silicalite-1 在 ZSM-5 晶体上形成外延层，而不会阻塞孔开口。扫描电子显微镜和动态光散射相结合用于确认可以以纳米分辨率（例如，5-20nm）调整壳厚度。X 射线光电子能谱和程序升温脱附测量揭示了硅壳的存在，而使用太大或尺寸合适以进入 MFI 孔的分子的探针反应证实了均匀的壳覆盖。ZSM-5@silicalite-1 的合成提供了一种定制 MFI 型材料物理化学性质的途径，特别是在催化领域，表面钝化可以提高产物选择性而不会牺牲催化剂活性。本文所述的方法可能被证明是沸石核壳设计的通用平台，对于其他多孔材料可能具有更广泛的适用性。
