Transformation\nof Stober Silica Spheres to\nHollow Hierarchical Single-Crystal ZSM‑5 Zeolites with Encapsulated\nMetal Nanocatalysts for Selective Catalysis

The activity of zeolite-supported\nnanocatalysts is dependent on\nboth the dispersion, size, and location of metal nanoparticles around\nthe zeolite and the size and pore structure of the zeolite. In this\nstudy, a synthetic approach was developed to encapsulate metal catalysts\nwithin hollow interiors of single-crystal ZSM-5. Briefly, Stöber\nsilica spheres were synthesized and then transformed to single-crystal\nnano-ZSM-5 (Si/Al = 60), followed by growth of embedded metal nanoparticles\nand subsequently creation of a nanosized (30–50 nm shell thickness)\nhollow hierarchical zeolite structure. Metal nanoparticles such as\nCo, Cu, Cu–Zn, Fe, and Ni can be supported on the inner wall\nof the hollow zeolite and the surrounding satellite mesopores, without\nany particles present on the external zeolite surface. When evaluated\nas a catalyst for the Fischer–Trøpsch reaction, the Fe@h-ZSM5\ncatalyst shows high activity, sintering and coking resistance (50%\nlonger stability than Fe@ZSM5), and secondary cracking reactions in\nthe acid sites in the ZSM-5 shell, which reduce C₅₊ hydrocarbon\nselectivity and increase smaller-chain hydrocarbon selectivity. In\naddition, when Pt was further deposited inside the hollow structure,\nshape-selective alkene hydrogenation was demonstrated. These configured\nnanoscale zeolite catalysts have potential applications for reactions\nthat involve supported metal nanoparticle catalysis, shape selectivity,\nor secondary cracking reactions.