In situ synthesis of metal clusters encapsulated within small-pore zeolites via a dry gel conversion method†
We report here a facile strategy for encapsulating Pt clusters into MFI crystals via a dry gel conversion (DGC) method, by introducing Pt-immobilized Schiff-SiO2 as the silicon resource. This protocol involves a solid phase transformation process for crystallization which occurs without significant deconstruction of the structure of the Pt-containing precursor. High-angle annular dark-field scanning transmission electron microscopy images indicate that most of the Pt clusters are less than 1 nm in size and located in defective channels or voids of MFI. Thanks to the encapsulation role, these Pt clusters are stable against sintering even after calcination at 500 °C and only grow up to ∼2.8 nm after calcination at 800 °C. The uniform pore structure of a zeolite endows the Pt@zeolite catalyst with shape-selectivity for hydrogenation and oxidation reactions over size differentiated analog substrates. This synthesis method is attainable for the embedment of stable metal clusters inside the small-pore MFI zeolite.