Self-Templated Formation of Pt@ZIF-8/SiO2 Composite with 3D-Ordered Macropores and Size-Selective Catalytic Properties

Metal-organic frameworks (MOFs) and related derivatives have attracted significant research attention due to their potential applications in a variety of fields. However, it remains challenging to fabricate MOF-based composites into multidimensional structures, especially to endow them with ordered structures. Here, a facile strategy is developed for the preparation of Pt@ zeolitic imidazolate frameworks (ZIF)-8/SiO2 composite with 3D-ordered macroporous (3DOM) structure (denoted as 3DOM-Pt@ZIF-8/SiO2) by the in situ self-templated transformation of Pt/ZnO/SiO2 composite with 3DOM structure (denoted as 3DOM-Pt/ZnO/SiO2), which is prepared by a nanocasting method with face-centered cubic (fcc) polystyrene spheres as the template. The sampling analysis at various crystallization times confirms the detailed dissolution-precipitation process from 3DOM-Pt/ZnO/SiO2 to 3DOM-Pt@ZIF-8/SiO2, in which Pt nanoparticles (NPs) are fully encapsulated into the 3DOM framework of ZIF-8/SiO2 by a continuous ZIF-8 shell in the surface. Besides, it is found that choosing suitable volume ratio of N,N-dimethylformamide (DMF):H2O and SiO2 content is crucial to induce the in situ nucleation and growth of continuous ZIF-8 shell on the 3DOM structure and also to prevent the 3DOM structure from collapsing. Crucially, the obtained 3DOM-Pt@ZIF-8/SiO2 shows high size-selective catalytic properties for the hydrogenation of n-hexene and cis-cyclooctene due to the molecular sieve effect of ZIF-8 shell on the framework.