Integration of Noble Metal Nanocrystals in a Hollow Metal–Organic Framework Shell

Metal–organic frameworks (MOFs) encapsulating noble metal nanocrystals (NCs) have aroused great attention in catalysis, especially for selective catalysis owing to the existence of strong interfacial interactions and synergistic functions. In noble metal NCs@MOF, the crystalline framework shell provides the molecular sieving effect, unsaturated metal sites, and functional channels. However, in many cases, it impedes the mass transfer and diffusion of precursors toward noble metal NCs, thus resulting in suboptimal catalytic performance and inefficient use of the noble metal catalysts. Integration of noble metal NCs in a hollow MOF shell could address this concern. Herein, by using ZIF-67 as a self-sacrificial template, we reported a simple strategy for synthesizing Pd@Hollow ZIF-67. Pre-formed Pd NCs are uniformly confined within a hollow ZIF-67 shell through the dissolution of the interior of a ZIF-67 sacrificial template and re-growth of a new ZIF-67 shell due to the competitive coordination of chloride ligands to cobalt ions in ethanol. This method can be easily extended to fabricate other hollow hybrid materials including Au@Hollow ZIF-67, Pt@Hollow ZIF-67, and sandwich Pd@Hollow ZIF-67. The synthesis of these hollow hybrid nanostructures is expected to provide possibilities for the development of a new category of organic–inorganic hybrid materials for catalytic applications.