Dissolution of high-silica zeolites in alkaline solutions .2. Dissolution of 'activated' silicalite-1 and ZSM-5 with different aluminum content

被引:78
作者
Cizmek, A
Subotic, B
Smit, I
Tonejc, A
Aiello, R
Crea, F
Nastro, A
机构
[1] RUDJER BOSKOVIC INST, ZAGREB 10001, CROATIA
[2] UNIV ZAGREB, FAC SCI, DEPT PHYS, ZAGREB 10000, CROATIA
[3] UNIV CALABRIA, DIPARTIMENTO CHIM, ARCAVACATA, CS, ITALY
来源
MICROPOROUS MATERIALS | 1997年 / 8卷 / 3-4期
关键词
organic-free pentasils; ZSM-5; silicalite-1; dissolution; kinetics; mechanism;
D O I
10.1016/S0927-6513(96)00082-X
中图分类号
O69 [应用化学];
学科分类号
081704 ;
摘要
Dissolution of organic-free ('activated') high-silica pentasils (silicalite-l and ZSM-5 with different Al-content) in 5 M NaOH solution at 60 degrees C was investigated by different methods such as X-ray diffractometry, Fourier transform infrared spectroscopy (FTIR), scanning-electron microscopy (SEM) and measuring the silicon and aluminum concentration in the liquid phase. Analysis of the experimental results showed that the process of dissolution of the 'activated' high-silica pentasils is controlled by two essential reactions; a forward one caused by breaking of the Si-O-Si and/or Si-O-Al bonds owing to the action of OH- ions from solution, and a backward one caused by the reaction between soluble species from the liquid phase or by their reaction on/with the surface of the dissolving solid. The rate of the forward reaction decreased with an increase of the Al-content in the ZSM-5 crystals, whereas the backward reaction resulted in the formation of amorphous SiO2 (ZSM-5) and/or different crystalline modifications of SiO2 or even different hydrates of sodium silicate (silicalite-l). A kinetic equation of the dissolution process was derived on the basis of the proposed mechanism of dissolution.
引用
收藏
页码:159 / 169
页数:11
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