Keen interest is taken in zeolite-encapsulated metal nanoparticles (NPs) owing to their excellent performance and ultrastability in heterogeneous catalysis. Herein, we propose a simple and efficient method to contain Fe NPs within zeolite Y microcrystals. First, a low-pressure technique was developed to successfully synthesize the zeolite Y microcrystals. The technique was then invoked, using Fe NPs fixed in nanosized C spheres as a precursor, to prepare zeolite Y-embedded Fe composite catalysts. The C spheres served as a template that restricted Fe NP growth within zeolite Y. Above all, the successful confinement of small Fe NPs within the microcrystals of zeolite Y enhanced the catalyst activity with 36.2% selectivity for light olefins (C2–C4=) at a CO conversion of 91.2% during evaluation in Fischer–Tropsch synthesis. The techniques presented in this work open up a new avenue worth exploiting for the synthesis of nano/microcrystalline materials and highly active metal–zeolite composites in heterogeneous catalysis.
Graphitic carbon nitride (g-C3N4) has aroused broad interest in the field of photocatalysis and luminescence as a kind of metal-free semiconductor with a suitable band gap of ∼2.7 eV. The properties largely depend on the polymerization degree of g-C3N4. This research exploits the nanocages of zeolite-Y to confine the polymerization of the melamine monomer to form g-C3N4. The composites are achieved via a facile two-step method, i.e., melamine–Na+ ion exchange reaction in the cage of the zeolite and subsequent calcination. BET measurement and transmission electron microscopy (TEM) confirm that the g-C3N4 is encapsulated in zeolite-Y, and the polymerization degree can be controlled by the melamine contents exchanged with Na+ in the cages of zeolite-Y. Photoluminescence and vibration spectroscopy also show the features of g-C3N4 with different polymerization degrees in the zeolite-Y composites. This research gives a perspective of fabricating subnanoscale g-C3N4 in porous zeolite, which may find potential applications in photocatalysis and optoelectronics.
Zeolite Y nanoparticle assemblies (Y-NA) with a mesoporous structure were directly synthesized at 75 °C for 16 h without adding any organic templates. The changes in structure, morphology and textural parameters of the materials obtained after different crystallization times were investigated via powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2-sorption. The results show that Y-NA had a micro–mesoporous structure composed of highly crystalline particle assemblies with sizes of 400–900 nm. The H-form Y-NA (HY-NA) is strongly acidic, and exhibits a good catalytic performance in the Ritter reaction, as compared with the H-form microporous zeolite Y and mesoporous zeolite ZSM-5.
Hierarchical zeolite Y was hydrothermally synthesized using ionic liquid 1-methyl-3-[3′-(trimethoxysilyl)propyl]imidazolium chloride, which was added into the conventional synthesis composition for crystalline microporous aluminosilicate as a mesopore-directing agent. An extremely short diffusion path length and abundant exposed acid sites in the hierarchical zeolite Y made it suitable for the catalytic transformation of bulky molecules. Then the catalytic performance of hierarchical zeolites Y was investigated using the alkylation of o-xylene with styrene. The ionic liquid directed hierarchical zeolite Y exhibited a remarkably high catalytic activity and long catalytic lifetime for the production of 1-phenyl-1-xylylethane via alkylation reaction, as compared with that of solely microporous zeolite Y. The distinct catalytic performances of the novel hierarchical zeolite Y could be attributed to the enhancement of medium strong acid amount and its micro–mesoporous structural properties which are favorable for the fast diffusion of products.
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