期刊
CRYSTAL GROWTH & DESIGN
卷 13, 期 11, 页码 5025-5035出版社
AMER CHEMICAL SOC
DOI: 10.1021/cg4010483
关键词
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资金
- Swiss National Science Foundation [200021-134572]
The manifestation of zeolite recrystallization and the formation of amorphous aluminosilicate species during desilication are examined to better understand the properties of alkaline-treated hierarchical zeolites and their catalytic performance. This is achieved using a systematic experimental strategy, starting from treating the filtrate of alkaline-treated silicalite-1 in the presence of various external additives. No recrystallization is evidenced upon addition of tetrapropylammonium (TPA(+)) and/or aluminum hydroxide ions [Al(OH)(4)(-)], confirming the low probability of zeolite nucleation and/or growth during desilication. Conversely, ordered mesoporous materials (OMMs) form upon addition of cetyltrimethylammonium (CTA(+)) to the filtrate. By using other silicon sources, i.e., tetramethyl orthosilicate or the organosilane dimethyloctadecyl[3-(trimethoxysilyppropyl] ammonium, we verify the facile formation of amorphous materials during alkaline treatment of USY zeolites in the presence of hydrophobic micelle-forming alkyl moieties. A systematic characterization by X-ray diffraction, transmission electron microscopy, N-2 and Ar adsorption, inductively coupled plasma optical emission spectroscopy, and Fourier transform infrared spectroscopy of pyridine adsorbed, demonstrates that zeolites exposed to base solutions containing CTA(+) display weaker zeolitic properties, compared to those prepared using TPA(+), and should be considered as hierarchical zeolite/OMM composites. Catalytic tests in the alkylation of toluene with isopropyl alcohol or benzyl alcohol evidence that CTA(+)-derived composites do not outperform the conventional USY zeolite. Only the hierarchical USY zeolite prepared by alkaline treatment in the presence of TPA(+) yielded a superior catalytic performance.
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