(130c) Factors That Affect the Mesoporosity Development in Zsm-12 by Desilication

The development of
mesopores around 15-20nm by alkaline treatment in a unidimensional high silica
content zeolite, namely ZSM-12 was achieved. The factors that affect the generation
of mesopores were thoroughly investigated. For the ZSM-12 with Si/Al ratio of
58, mesopores with volume from 0.25cm³/g to 0.55 cm³/g
were generated without destroying the microporous structure of ZSM-12 by
varying the NaOH solution concentration, operation temperature and time.
Meanwhile, parent ZSM-12s with different Si/Al ratios in the range from 30 to
140 were also treated in order to investigate the influence of Si/Al ratios on
the desilication of ZSM-12. For the ZSM-12 with relatively low Si/Al ratios
ranging from 30 to 58, relatively high temperature or high NaOH concentration
was favorable for the generation of mesopores while preserving the microporous
structure and acidic property of ZSM-12. However, for the samples with higher
Si/Al ratios, lower temperature or lower NaOH concentration were more
appropriate for the creation of mesopores. This behavior indicated the content
of tetrahedrally coordinated aluminum in the structure controls the mesopores
formation by desilication in alkaline medium. For the as synthesized ZSM-12 prior
to the removal of template, Si was more difficult to be extracted than the
calcined samples with comparable Si/Al ratios, which also had an influence on
the desilication process. The adjustable mesopores developed in ZSM-12 by
alkaline treatment opened a new and economic path for the improvement of
diffusion in the zeolite framework.