Design,Synthesis And Application Of MFI Type Hollow Zeolites

Zeolites offer a tunable acidity, shape selectivity and hydrothermal stability, leading to their use in adsorption, separation and catalysis. In the past years, hollow zeolites have attracted considerable interest because of their superior performance in the selectivity of product, anti-leaching of active site and anti-sintering of metal. In this thesis, we design and synthesize a series of hollow zeolite (S-1, ZSM-5) single crystals with metal-encapsulated interior. They showed excellent catalytic performance in the reactions, such as synthesis of ethyl acetate, Suzuki coupling, methane dry reforming, phenol oxidation, alkylation of diphenyl. The results are summarized as follow:A strategy involving desilication and re-crystallization of S-1 in tetrapropylammonium hydroxide (TPAOH) solution was developed to prepare hollow zeolite nanocubes and three-dimensionally macroporous zeolite monoliths. Large hollow cores were introduced to S-1 crystals by controlled silicon leaching and thin intact shells were formed by the re-crystallization of silicon. Different pore sizes of the hollow zeolite can be controlled by varying the amount of competitive Na+ adsorbent added to the TPAOH solution. Furthermore, three-dimensional macroporous zeolite monoliths can be formed when a kind of electrolyte, such as NaCl, was added to the TPAOH solution.We choose hollow S-1 as the shell and use the ship-in-bottle approach to synthesize phosphotungstic acid (HPW) in the large cavity. When HPW@Hollow S-1 was used as a catalyst for esterification of acetic acid with ethanol, it shows high activity and outstanding stability. By TPAOH hydrothermal treatment with an "impregnation-dissolution-recrystallization" process, (1) Pd and Pd-CuO nanoparticles were encapsulated in hollow S-1 single crystals, which displays excellent substrate selectivity for the meta-and para-substituted aryl bromides in the Suzuki-Miyaura reaction. (2) Highly dispersed Ni-Pt bimetallic nanoparticles were encapsulated in hollow S-1 single crystals (Ni-Pt@Hol S-1). Compared with single metal (Ni or Pt), Ni-Pt@Hol S-1 enhances the dispersion of nickel and platinum. In the dry reforming of methane, the Ni-Pt@Hol S-1 catalyst operated stably under high gaseous hourly space velocity (GHSV=72000 mLg-1h-1) without any inert gas. Only 1.0 wt% carbon deposition was observed by thermogravimetric analysis after 6 h the reaction. (3) Highly dispersed Fe-Cu bimetallic oxide nanoparticles were encapsulated in hollow S-1 single crystals (Fe2O3-CuO@Hol S-1). Fe2O3-CuO bimetallic oxide exhibits a higher dispersion with the particle size decreasing from ?11.3 nm to?3.7 nm. For aqueous phenol degradation, the Fe2O3-CuO@Hol S-1 catalyst exhibits high activity attributed to the enhanced transport of reactants/products in the short microporous channels (20 nm) and the small metal oxide particle size, about 4 times higher than that of conventional Fe2O3-CuO@Hol S-1. Preventing the leaching of metal oxide particles, maintains 80% phenol conversion when 5 repeated uses.We designed and synthesized a now hollow nanovesicle assembly with Fe2O3-encapsulated hollow single crystals of ZSM-5 zeolite. This material possesses a microporous (0.4-0.6 nm) wall of hollow crystals, a mesoporous (5-17 nm) shell of nanovesicle with macropores (about 350 nm) in the core. This hierarchical structure facilitates the transport of reactant/products; enables excellent Fe2O3 dispersion (3-4 nm) and resistance to sintering even at 800 ?, as well as superior activity and resistance to leaching in phenol degradation. For aqueous phenol degradation, two orders of magnitude higher than that of conventional Fe2O3/nono-S-1. Preventing the leaching of metal oxide particles, maintains nearly 100% phenol conversion when 5 repeated uses. Hollow nanovesicle assembly of Fe-Pt bimetal-encapsulated hollow ZSM-5 crystals was also prepared.Hollow ZSM-5 single crystals with silicon-rich exterior surface were prepared by a "dissolution-recrystallization" strategy in TPAOH solution. In this strategy, selective dissolution and exterior recrystallization causes the silicon components to migrate from the inside to outside. The as-prepared hollow ZSM-5 exhibits excellent acid catalysis with inhibited isomerization and enhanced shape selectivity, as shown in biphenyl methylation as a probe reaction. Hollow ZSM-5 single crystals with double shells were successfully prepared by layer-by-layer technique followed with dissolution-recrystallization strategy. Furthermore, hollow ZSM-5 encapsulating iron and carbon nanotubes were successfully synthesized. Furthermore, hollow ZSM-5 nano-sized crystals with the interior functionalized as bimetallic (oxide) nanoparticles such as CuO-Pd, CuO-Pt and Fe2O3-Au were also successfully synthesized.