PRECURSORS OF THE ZEOLITE ZSM-5 IMAGED BY CRYO-TEM AND ANALYZED BY SAXS

被引:73
作者
REGEV, O [1 ]
COHEN, Y [1 ]
KEHAT, E [1 ]
TALMON, Y [1 ]
机构
[1] TECHNION ISRAEL INST TECHNOL,DEPT CHEM ENGN,IL-32000 HAIFA,ISRAEL
来源
ZEOLITES | 1994年 / 14卷 / 05期
关键词
ZEOLITE; ZSM-5; PRECURSOR; NUCLEATION; CLUSTER; TETRAPOD; ELECTRON MICROSCOPY; SMALL-ANGLE X-RAY SCATTERING;
D O I
10.1016/0144-2449(94)90103-1
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The microstructural evolution in the nucleation stage of a synthesis reaction of ZSM-5 zeolite was studied, with particular emphasis on the role of the organic cation, TPA+ (tetrapropylammonium). Direct observation of the microstructure was achieved by cryo-transmission electron microscopy (cryo-TEM). The quanitative evaluation of the structural units was obtained by small-angle X-ray scattering (SAXS) measurements. In the presence of the organic cation TPA+, we found globular structural units 5 nm in diameter that aggregate to elongated bodies 44 nm long. The globular structural units were found in reaction mixtures with or without the organic template TPA-OH, as long as the pH of the initial solution was kept above 11.6. Without TPA+, aggregation to cylindrical particles was not observed after 2 h of heating, and no ZSM-5 crystallinity was attained at the end of the reaction (after 8 d). These results suggest that the zeolite ZSM-5 building blocks are globular structural units, 5 nm in diameter, containing silica, alumina, organic cation, and water, which fuse together to produce elongated aggregates that may compose the final unit cell. It is concluded that the globular structural unit is a cluster of tetrapods similar to those found in the final ZSM-5 crystals.
引用
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页码:314 / 319
页数:6
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